patient monitoring using surface electromyography

1
ACKNOWLEDGEMENT
I express my sincere thanks to my project guide, Prof. Avinash Tandle of DEPT.
of Electronics & Communication for guiding me right from the inception till the
successful completion of the project. I sincerely acknowledge him for extending
their valuable guidance, support for literature, critical review of project and the
report and above all the moral support he had provided to me with all stages of
this project.
My thanks are due to all those who have directly or indirectly helped me in
preparing this project report. However, I accept the sole responsibility for any
possible error of omission and would be extremely grateful to the readers of this
project report if they bring such mistakes to my notice.

2
Index
Index................................................................................................................................... 2
List of figures...................................................................................................................... 4
List of tables........................................................................................................................ 6
Abstract.............................................................................................................................. 7
1. Introduction ................................................................................................................... 8
1.1 Problem statement ................................................................................................ 8
1.2 Project Survey........................................................................................................ 9
1.3 Project Selection.................................................................................................... 9
1.4 Definition of Wireless Biotelemetry..................................................................... 9
1.5 History of Biotelemetry........................................................................................ 11
1.7.1 Obstetrical Telemetry System.................................................................... 14
1.7.2 Telemetry in Operating Rooms.................................................................. 15
1.7.3 Sports Physiology Studies through Telemetry ........................................ 15
1.8 Working Principle................................................................................................. 17
1.8.1 Frequency Modulation................................................................................. 20
1.8.2 Pulse Width Modulation .............................................................................. 20
1.9 Implantable units.................................................................................................. 21
1.10 Advantages ........................................................................................................ 22
1.11 Disadvantages ................................................................................................... 22
2.0 Electromyography.................................................................................................... 23
2.1 Definition of EMG ................................................................................................ 23
2.1.1 Wide spread use of EMG............................................................................ 23
2.2 Signal origin:......................................................................................................... 24
2.3 Excitability of muscle membranes .................................................................... 25
2.4 Generation of EMG signal.................................................................................. 25
2.6 composition of EMG signal ................................................................................ 28
2.7 Nature of the EMG signal................................................................................... 30
2.8 Factors influencing the EMG signal.................................................................. 31
2.9 Physiology of EMG.............................................................................................. 32
2.9.1 Electrodes...................................................................................................... 33
2.9.2 EMG Electrode Placement ......................................................................... 36
2.9.3 Amplifier of EMG signals............................................................................. 38
2.10 Definition of Pulse (Heartbeat) rate:............................................................... 40
2.10.1 Physiology................................................................................................... 41
2.10.2 Normal Pulse Rates:.................................................................................. 42
3.0 Taxonomy of wireless medical systems .............................................................. 43
3.1 Radio Frequency ................................................................................................. 43
4.0 System design.......................................................................................................... 48
4.3 Instrumentation Amplifier.................................................................................... 49
4.3.1 Low pass filter:.............................................................................................. 49
4.3.2 High pass filter:............................................................................................. 51
4.4 Pulse monitoring system .................................................................................... 52
4.5 design description................................................................................................ 52
4.6 Transmitter circuit diagram ........................................................................... 55
4.7 Receiver circuit diagram:............................................................................... 56

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5.0 Programmer description for system...................................................................... 57
5.1 Observed signals................................................................................................. 59
5.2 Flowchart............................................................................................................... 61
5.2.1 TX section flowchart..................................................................................... 61
5.3 Pulse rate result................................................................................................... 63
5.4 Emg result............................................................................................................. 65
5.5 result Suggestions for further advancements ................................................. 68
5.6 Application area of project.................................................................................. 68
Conclusion & Future work............................................................................................. 70
References...................................................................................................................... 71
Appendix.......................................................................................................................... 72

4
List of figures
Figure 1 ECG measurement using immersion electrodes. Original Cambridge
electrocardiograph (1912) built for Sir Thomas Lewis. ............................................ 12
Figure 2: Telemetry receiving system for monitoring foetal heart rate and urine
contractions in use......................................................................................................... 15
Figure 3: A three channel telemetry system to monitor the physiological data of a
sprinter............................................................................................................................. 17
Figure 4: Transmitter circuit.......................................................................................... 18
Figure 5: Receiver Circuit ............................................................................................. 18
Figure 6: Biotelemetry mobile unit............................................................................... 19
Figure 7: Pulse Width Modulation................................................................................ 20
Figure 8: Implantable units ........................................................................................... 21
Figure 9 Basmajian & DeLuca: Definition Muscles Alive Unlike the classical...... 23
Figure 10 : Application areas of kinesiological EMG................................................ 24
Figure 11 Motor unit. Adopted & modified.................................................................. 24
Figure 12 Schematic illustration of depolarization/ Repolarization cycle .............. 25
Figure 13 The Action Potential. Adopted & redrawn ................................................ 26
Figure 14 The depolarization zone on muscle fiber membranes. Adopted &
modified2.5 signal propagation and detection........................................................... 26
Figure 15 The model of a wandering electrical dipole on muscle fiber
membranes. Adopted & modified ................................................................................ 27
Figure 16 Generation of the triphasic motor unit action potential. Adopted &
modified ........................................................................................................................... 28
Figure 17 Superposition of MUAPs to a resulting electromyogram Adopted &
modified ........................................................................................................................... 28
Figure 18 Recruitment and firing frequency of motor units modulates force output
and is reflected in the superposed EMG signal Adopted & modified..................... 29
Figure 19 The raw EMG recording of 3 contractions bursts. .................................. 30
Figure 20 The influence of varying thickness of tissue layers below the
electrodes: Given the same amount of muscle electricity condition 1 produces
more EMG magnitude due to smaller distance between muscle and electrodes 31
Figure 21 Raw EMG recording with heavy ECG....................................................... 32
Figure 22 Frequency Spectrum of the EMG signal ................................................. 33
Figure 23 Surface EMG electrodes............................................................................. 34
Figure 24 Ground electrode for surface EMG .......................................................... 34
Figure 25 The preferred electrode location is between the motor point and the
tedious insertion ............................................................................................................. 36
Figure 26 A schematic of the differential amplifier configuration............................ 39
Figure 27 pulse rate basic ............................................................................................ 42
Figure 28 Bluetooth Protocol Stack............................................................................. 45
Figure 29 ZigBee Protocol Stack................................................................................. 47
Figure 30 Block diagram ............................................................................................... 48
Figure 31 Burr brown amplifier..................................................................................... 48
Figure 32 Burr brown using INA 128........................................................................... 49
Figure 33 2nd order LPF............................................................................................... 49

5
Figure 34 Low pass Filter design................................................................................. 50
Figure 35 Burr brown HPF............................................................................................ 51
Figure 36 High pass filter design ................................................................................. 51
Figure 37 Pulse monitoring system............................................................................. 52
Figure 38 Transmitter circuit diagram .............................................................................. 55
Figure 39 Receiver circuit diagram.............................................................................. 56
Figure 40 keil software .................................................................................................. 57
Figure 41 X-CTU ............................................................................................................ 58
Figure 42 Filter pro......................................................................................................... 58
Figure 43 Put the finger .................................................................................................... 63
Figure 44Observe the TX pulse........................................................................................ 63
Figure 45 Observe the RX pulse....................................................................................... 64
Figure 46 Lcd display ....................................................................................................... 64
Figure 47 Place the electrode............................................................................................ 65
Figure 48 Push the muscle fiber........................................................................................ 65
Figure 49 Observe the RX pulse....................................................................................... 66
Figure 50 Observe the pulse on LCD ............................................................................... 66
Figure 51 Reception of alert message............................................................................... 67
Figure 52 Read the message ............................................................................................. 67

6
List of tables
Table 1 Wireless technologies characteristic graph ................................................. 43
Table 2 ZigBee Uperhand............................................................................................. 47
Table 3 Instrumentation amplifier comparison .......................................................... 52
Table 4 Quad selection comparison............................................................................ 52
Table 5 Wireless device selection ............................................................................... 53
Table 6 Electrode Selection.......................................................................................... 53
Table 7 Microcontroller Selection ................................................................................ 54
Table 8 Comparator Selection ..................................................................................... 54

7
Abstract
With miniaturization and technical advancements in electronics and
communications field, we are now in a position to safely monitor, diagnose and
treat various intricate ailments in patients with relative ease. This has made
complex surgeries simple, easy and efficient.
Wireless communications have enabled development of monitoring devices that
can be made available for general use by individuals/patients and caregivers.
New methods for short-range wireless communications not encumbered by radio
spectrum restrictions (e.g., ultra-wideband) will enable applications of wireless
monitoring without interference in ambulatory subjects, in home care, and in
hospitals.
Wireless biomonitoring, first used in human beings for featal heart-rate
monitoring has now become a technology for remote sensing of patients' activity,
blood pulse pressure, oxygen saturation, internal pressures, orthopedic device
loading, and gastrointestinal endoscopy. Biotelemetry provides a wireless link
between the subject and the remote site where the recording, signal processing,
and displaying functions are performed. Rather than using a traditional radio
transceiver, which can only broadcast over a limited range, now-a-days the
readily available cell phones are used to transmit biological data by creating a
link between the subject and a computer receiving the signal via a landline
phone.
Wireless telemetry of bioelectric signals, specifically neural recordings, is
desirable in many research and clinical applications. These include, but are not
limited to telemetry and recording of neural activity in laboratory animals,
telemetry of EEG, telemetry of short-term implanted electrode arrays for epilepsy
medical diagnosis, functional electrical stimulation (FES) systems, and
implantable neuroprosthetic devices for sensory and command control.
This study will focus on Wireless telemetry in general and also details of Wireless
biotelemetry.

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1. Introduction
1.1 Problem statement
The main goal of this project was to design and implement a wirelessly
transmitted activity monitor. This device was to record heart rate as well as blood
pressure. This data would be used to determine a person’s physical capabilities
using a “job match” method. This method would then analyze a person’s heart
rate and blood pressure during different physical activities to determine whether
or not they are capable of performing the duties required of an occupation. As a
person increases in age, their heart may not be able to support the same
physical activities it could when he or she were younger. The primary users of
this device, occupational therapists, will check the measurements against a
reference to determine the candidate’s suitability for the position. It can also be
used to evaluate recovery from injury, or even the validity of claims of on-site
injuries in the workplace. This method and device would result in an entirely new
approach to workman’s compensation, and drastically cut down on false claims.
Given the wireless nature of the device and its capability to interface with the
majority of PC’s on the market, networking it to a hospital or EMT service for
high-risk patients in the home is also an added benefit. There are many people
who suffer from heart diseases and high blood pressure. There have been
multiple cases where one of these individuals has a heart attack and no one can
get to them fast enough to resuscitate them. The wireless activity monitor, in part,
is designed to give these individuals a better chance of survival by monitoring
their heart rate and blood pressure and transmitting the data wirelessly to a local
computer. If a person’s heart rate or blood pressure shows abnormal activity a
hospital can be notified immediately over the Internet and a paramedic can be
dispatched to the person’s house. Being a light weight package and oriented on
the body in a way as to not interfere with job tasks, daily activities, or test
procedures, this will become a highly valuable evaluation tool when dealing with
physical activity.
The design goals for this project were to acquire heart rate and blood pressure
readings from a wrist mounted cuff, transmit those readings wirelessly to a local
computer, access those readings remotely over a network using a different
computer, and display those readings in an intuitive display.

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1.2 Project Survey
Our academic final sem. Engineering purpose for our project team survey many
different type of unique and intelligent working project survey some industrial
visit, books, and internet Medias. We survey some project as described below.
1. Blood analysis system.
2. Wi-Fi Speech Analyzer.
3. Endoscopy Robot.
4. GSM Security Device.
All above project survey we decide that all are very expensive and some material
are not available in local market and also require lot of time and heavy R & D
hence, we avoid to make it.[1]
1.3 Project Selection
Wireless Biotelemetry system is very useful in medical critical I.C.U.
For patient and doctor also because this project through any time pulse variation
position mobile through under observation continuity between patient and doctor.
This technology GSM based satellite communication link then doctor handling
patient around the world.
Wireless Biotelemetry system project selection for next main advantage all
component available in local market, affordable project cost and technical
support easily available in college books and websites.[1]
1.4 Definition of Wireless Biotelemetry
Biotelemetry is defined as a means of transmitting biomedical or physiological
data from a remote location (e.g., astronauts in space) to a location that has the
capability to interpret the data and affect decision making (e.g. ground controllers
at Mission Control Center). Biotelemetry is a vital constituent in the field of
medical sciences. It entails remote measurement of biological parameters. Mode
of transmission of physiological data from point of generation to the point of
reception can take many forms. Use of wires to transmit data may be eliminated
by wireless technology. Biotelemetry, using wireless diagnosis, can monitor
electronically the symptoms and movements of patients.
This development has opened up avenues for medical diagnosis and treatment.
It enables monitoring of activity levels in patients suffering from heart trouble,
asthma, pain, Alzheimer’s disease, mood disorders, cardiovascular problems,
accidents, etc.

10
A patient’s response and reaction to drugs can be investigated for treatment.
Radio-telemetry transmits biological data using various radio transmission
techniques. No wires are required to be attached to the patient’s body. The
patient just carries a bracelet-sized transmitter that enables monitoring of the
patient’s symptoms. Literally, biotelemetry is the measurement of biological
parameters over a distance. The means of transmitting the data from the point of
generation to the point of reception can take many forms. Perhaps the simplest
application of the principle of biotelemetry is the stethoscope, whereby
heartbeats are amplified acoustically and transmitted through a hollow tube
system to be picked up by the ear of the physician for interpretation. A major
advantage of modern telemetry is the elimination of the use of wires.
The use of telemetry methods for sending signals from a living organism over
some distance to a receiver. Usually, biotelemetry is used for gathering data
about the physiology, behavior, or location of the organism. Generally, the
signals are carried by radio, light, or sound waves. Consequently, biotelemetry
implies the absence of wires between the subject and receiver.
Generally, biotelemetry techniques are necessary in situations when wires
running from a subject to a recorder would inhibit the subject's activity; when the
proximity of an investigator to a subject might alter the subject's behavior; and
when the movements of the subject and the duration of the monitoring make it
impractical for the investigator to remain within sight of the subject. Biotelemetry
is widely used in medical fields to monitor patients and research subjects, and
now even to operate devices such as drug delivery systems and prosthetics.
Sensors and transmitters placed on or implanted in animals are used to study
physiology and behavior in the laboratory and to study the movements, behavior,
and physiology of wildlife species in their natural environments.
Biotelemetry is an important technique for biomedical research and clinical
medicine. Perhaps cardiovascular research and treatment have benefited the
most from biotelemetry. Heart rate, blood flow, and blood pressure can be
measured in ambulatory subjects and transmitted to a remote receiver-recorder.
Telemetry also has been used to obtain data about local oxygen pressure on the
surface of organs (for example, liver and myocardium) and for studies of capillary
exchange (that is, oxygen supply and discharge). Biomedical research with
telemetry includes measuring cardiovascular performance during the
weightlessness of space flight and portable monitoring of radioactive indicators
as they are dispersed through the body by the blood vessels.

11
Telemetry has been applied widely to animal research, for example, to record
electroencephalograms, heart rates, heart muscle contractions, and respiration,
even from sleeping mammals and birds. Telemetry and video recording have
been combined in research of the relationships between neural and cardiac
activity and behavior.
There are usually two concerns associated with the use of biotelemetry: the
distance over which the signal can be received, and the size of the transmitter
package. Often, both of these concerns depend on the power source for the
transmitter. Integrated circuits and surface mount technology allow production of
very small electronic circuitry in transmitters, making batteries the largest part of
the transmitter package.[1]
1.5 History of Biotelemetry[5]
In the early days of human space flight, NASA utilized biotelemetry to provide
biomedical data from orbiting astronauts to medical personnel at the NASA
Johnson Space Center (Manned Space Flight center in the early 1960's).
Biomedical data transmitted to Earth from space included astronaut's heart rate,
body temperature, ECG, oxygen (O2) and carbon dioxide (CO2) concentration.
Further research and technology from NASA was instrumental in driving both
telemetry and telemedicine into civil health care.
Distance medicine has been around for most of this century. In the early days,
doctors treated patients in remote locations via wireless radio and by sending
diagnostic samples through the mail. Today, communication is done digitally, and
it's called biotelemetry. On an extended space flight, the need to consult,
diagnose and deliver effective medical care when the doctor is far away from the
patients is crucial. Scientists are developing hardware and software to facilitate
this process. Whether it's a case of analyzing blood samples for medical
diagnosis when a problem occurs during a three year voyage to Mars or installing
a microchip inside the body to measure vital signs, biotelemetry is revolutionizing
medical care in space.
Historically, Linthoven, the originator of the electrocardiogram, as a means of
analysis of the electrical activity of the heart, transmitted electrocardiograms from
a hospital to his laboratory many miles away as early s 1903. The rather crude
immersion electrodes were connected to a remote galvanometer directly by
telephone lines. The telephone lines in this instance were merely used as
conductors for the current produced by the biopotentials.

12
Figure 1 ECG measurement using immersion electrodes. Original Cambridge electrocardiograph
(1912) built for Sir Thomas Lewis.
1.6 Physiological and Technology Parameters[5]
Any quantity that can be measured in the biomedical field is adaptable to
biotelemetry. The measurements are divided into two categories: bioelectrical
and physiological variables. Bioelectrical variables include measurements like
ECG, EMG, and EEG. Signals are obtained directly in the electric form.
Physiological variables such as temperature, blood pressure, blood flow, etc
require some excitation or external electrical parameters. Transducers are used
for the conversion of physiological parameters into an electrical signal.
Parameters are measured as the variations of resistance, capacitance, or
inductance. Variations can be calibrated to represent pressure, temperature, or
blood flow. Base signal is modulated for transmission. And finally, this signal is
detected (demodulated) and converted back to its original form.
PCM technology offers significant advantages in the application of telemetry to
medical and physiological studies. The requirements for less complicated
handling, standardized system layout, improvement of weight, size and power
supply by commercial battery modules, as well as different wireless data links are
met better by a PCM encoder which was specially developed for physiological
applications. The advantages of PCM are illustrated by relating the experimental
requirements to technical specifications for the elements of a telemetry link.

13
1. Temperature by rectal or oral thermistor.
2. Respiration by impedance pneumograph.
3. Electrocardiograms by surface electrodes.
4. Indirect blood pressure by contact microphone and cuff.
As the technology progressed, it became apparent that literally any quantity that
could be measured was adaptable to biotelemetry. Just as with hardwire
systems, measurements can be applied to two categories:
1. Bioelectrical variables, such as ECG, EMG, and EEG.
2. Physiological variables that require transducers, such as blood
pressure, gastrointestinal pressure, blood flow, and temperatures.
With the first category, a signal is obtained directly in electrical form, whereas the
second category requires a type of excitation, for the physiological parameters
are eventually measured as variations of resistance, inductance, or capacitance.
The differential signals obtained from these variations can be calibrated to
represent pressure, flow, temperature, and so on, since some physical
relationships exist.
In a typical system, the appropriate analog signal (voltage, current, etc.) is
converted into a form or code capable of being transmitted. Currently, the most
widespread use of biotelemetry for bioelectric potential is in the transmission of
the electrocardiogram.
One example of ECG telemetry is the transmission of electrocardiograms from
an ambulance or site of an emergency to a hospital. Telemetry is also being used
for transmission of the electroencephalogram. Most applications have been
involved with experimental animals for research purposes. Telemetry of EEG
signals has also been used in studies of mentally disturbed children. The third
type of bioelectric signal that can be telemetered is the electromyogram.
Telemetry can also be used in transmitting stimulus signals to a patient or
subject. For example, it is well known that an electrical impulse can trigger the
firing of nerves. Another example is the use of telemetry in the treatment of
dropfoot, which is one of the most common disabilities resulting from stroke. A
method for correcting dropfoot by transmitting a signal implanted electronic
stimulator has been used successfully at Rancho Los Amigos Hospital in Los
Angeles.
1.7 Application of the system
There are many instances in which it is necessary to monitor physiological
events from a distance. Typical applications include the following:
1. Radio-frequency transmissions for monitoring astronauts in space.

14
2. Patient monitoring where freedom of movement is desired, such as in
obtaining an exercise electrocardiogram. In this instance, the requirement
of trailing wires is both cumbersome and dangerous.
3. Patient monitoring in an ambulance and in other locations away from the
hospital.
4. Collection of medical data from a home or office.
5. Research on unrestrained, un-anesthetized animals in their natural
habitat.
6. Use of telephone links for transmission of electrocardiograms or other
medical data.
7. Special internal techniques, such as tracing acidity or pressure through
the gastrointestinal tract.
8. Isolation of an electrically susceptible patient from power-line operated
ECG equipment to protect him from accidental shock. These applications have
indicated the need for systems that can adapt existing methods of measuring
physiological variables to a method of transmission of resulting data. This is the
branch of biomedical instrumentation known as biomedical telemetry or
biotelemetry.
1.7.1 Obstetrical Telemetry System
There has been a great deal of interest to provide greater freedom of movement
to patients during labour while the patient is continuously monitored through a
wireless link. Thus, from a central location, it is possible to maintain a continuous
surveillance of cardiotocogram records for several ambulatory patients. In the
delivery room, telemetry reduces the encumbering instrumentation, cables at the
bedside. Moreover, when an emergency occurs, there is no loss of monitoring in
the vital minutes during patient transfer.
The patient carries a small pocket-sized transmitter which is designed to pick up
signals for foetal heart rate and uterine activity. The foetal heart rate is derived
from Foetal ECG which is obtained via a scalp electrode attached to the foetus
after the mother’s membranes are ruptured. Uterine activity is measured via an
intra-uterine pressure transducer. If only foetal ECG is measured, the patient
herself can indicate uterine activity or foetal movement by using a handheld
pushbutton.
The receiver located away from the patient, is connected to a conventional
cardiotocograph. If the patient exceeds the effective transmission range or the
electrode has a poor contact, it is appropriately transmitted for corrective action.

15
Figure 2: Telemetry receiving system for monitoring foetal heart rate and urine contractions in
use.
1.7.2 Telemetry in Operating Rooms
The use of telemetry in operating rooms seems to be particularly attractive as it
offers a means of achieving a high degree of patient safety from electric shock as
well as elimination of the hanging inter-connecting patient leads which are
necessary in direct wired equipment. Normally there are several parameters
which are of interest in surgical patient monitoring, most common being ECG,
blood pressure, peripheral pulse and EEG.
Basically, the signal encoding is based upon frequency modulation of 4
subcarriers centered at 2.2, 3.5, 5.0 and 7.5 kHz, respectively. The system is
designed to give a bandwidth of dc to 100 Hz at the 3 dB point and the
discriminator provides 1.0 V dc output for a 10% shift.. The transmitted signals
are tuned by a FM tuner whose output is fed into a fourth-channel discriminator
which separates the subcarriers through filtering and demodulates each using a
phase-locked loop. The demodulated signals are displayed on an oscilloscope.
1.7.3 Sports Physiology Studies through Telemetry
Monitoring of pulmonary ventilation, heart rate and respiration rate is necessary
for a study of energy expenditure during physical work, particularly for sports
such as squash, handball, tennis and track, etc. The transmitter uses pulse

16
duration modulation, i.e., each channel is sampled sequentially and a pulse is
generated, the width of which is proportional to the amplitude of the
corresponding signal. At the end of a frame, a synchronization gap is inserted to
ensure that the receiving system locks correctly onto the signal. Each channel is
sampled 200 times a second. With each clock pulse, the counter advances one
step, making the gates to open sequentially. At the opening of a particular gate,
the corresponding physiological signal gets through to a comparator where it is
compared with the ramp. As soon as the ramp voltage exceeds the signal
voltage, the comparator changes state. Thus, the time required for the
comparator to change state would depend upon the amplitude of the signal. The
counter and gates serve as multiplexer.[5]

17
Figure 3: A three channel telemetry system to monitor the physiological data of a sprinter.
1.8 Working Principle[5]
To illustrate the basic principles involved in telemetry, a simple system is
described. The stages of a typical biotelemetry system can be broken down into
functional blocks, as shown in the Fig for transmitter and for the receiver.
Physiological signals are obtained from the subject by means of appropriate
transducers. The signal is then passed through a stage of amplification and

18
processing circuits that include generation of a sub carrier and a modulation
stage for transmission.
Figure 4: Transmitter circuit
The receiver consists of a tuner to select the transmitting frequency, a
demodulator to separate the signal from the carrier wave, and a means of
displaying or recording the signal.
Figure 5: Receiver Circuit
It receives the multiplexed RF carrier emitted by the patient’s transmitter, as
shown in Fig. The tuner has a tuning circuit. When the circuit is tuned to receive
signals, the appropriate signal is selected and the unwanted signals are rejected.
The multiplexed RF carrier is demodulated to recover the individual sub-carriers.
Sub-carriers are then demodulated to reproduce original physiological signals

19
emitted by the patient.A recorder records physiological signals for future
reference. Signals can be stored on any secondary media like tape, magnetic
discs etc. Display system used can be CRT or computer monitor, chart etc.
The modulation systems used in wireless telemetry for transmitting biomedical
signals makes use of two modulators .This means that a comparatively lower
freq. subcarrier is employed in addition to the VHF which finally transmits the
signal from the transmitter. The principle of double modulation gives better
interference free performance in transmission and reception of low frequency
biological signals. The sub-modulator can be a FM (freq modulation) system or
PWM (Pulse Width modulation) system, whereas the final modulator is practically
always FM system.
Figure 6: Biotelemetry mobile unit
If several physiological signals are to be transmitted simultaneously, each signal
is placed on a subcarrier of a different frequency and all subcarriers are
combined to simultaneously modulate the RF carrier. This process of transmitting
many channels of data on a single RF carrier, called frequency multiplexing, is
more efficient. The subcarrier is modulated either by AM (amplitude modulation)
or FM (frequency modulation). For reducing noise interference, FM is frequently
used. The method of modulating sub-carrier, followed by modulating the RF
carrier, is termed as AM/FM or FM/FM depending sub-carriers are frequency-

20
modulated and the 1W carrier amplitude modulated, the method is designated as
FM / AM. If both the subcarriers and the RF carrier are frequency-modulated, it is
designated as FM / FM.
1.8.1 Frequency Modulation
In freq modulation, intelligence is transmitted by varying the instantaneous freq in
accordance with the signal to be modulated on the wave, while keeping the
amplitude of the carrier wave constant. The rate at which the instantaneous freq
varies is
the modulating frequency. The magnitude to which the carrier frequency varies
away from the center freq is called .Freq Deviation. and is proportional to the
amplitude of the modulating signal. Usually, an FM signal is produced by
controlling the freq of an oscillator by the Amplitude of the modulating voltage.
For example The frequency of oscillation in most oscillators depends on a
particular value of capacitance. If the modulation signal can be applied in such a
way that it changes value of capacitance, frequency of oscillation will change in
accordance with the amplitude of the modulating signal.
1.8.2 Pulse Width Modulation
Pulse width modulation method offers the advantage that it is less perceptive to
distortion and noise. In practice the negative edge of the square wave is varied in
rhythm with the ECG signal. Therefore, only this edge contains information of
interest. The ratio P : Q represents the momentary amplitude of the ECG. Pulses
generated by astable multivibrator (symmetrical 1000Hz) The amplitude or even
the frequency variation of the the P: Q ratio and consequently on the ECG signal.
The signal output from this modulator is fed to a normal speech transmitter,
usually via an attenuator, to make it suitable to the input level of the transmitter.
Figure 7: Pulse Width Modulation
Modulation schemes are used depending not only on the noise interference, but
also on size of the unit, its complexity, location, and other operational aspects.

21
The receiver circuit uses RF tuner to select the transmitted frequency of the base
station. The signal is demodulated though demodulator and sent to the
processor. The processor enables necessary action depending on the command
given to it from the base station. Both transmitter and receiver circuits function as
a modem. Control feedback incorporates a control system to enable automatic
control of the stimulus, the transducers, or any other part of the instrument
system. Tins system comprises a loop in which output from the signal
conditioning equipment or signal received is used to control the operation of the
system.
1.9 Implantable units
Figure 8: Implantable units
It was mentioned previously that sometimes it is desirable to implant the
telemetry transmitter or receiver subcutaneously. The implanted transmitter is
especially useful in animal studies, where the equipment must be protected from
the animal. The implanted receiver has been used with patients for stimulation of

22
nerves. The life of the unit depends on how long the battery can supply the
necessary current.
A partial implant is a good example of a system used for the monitoring of the
electroencephalogram where the electrodes have been implanted into the brain
and the telemetry unit is implanted within and on top of the skull. This type of unit
needs a protective helmet. The use of implantable units also restricts the
distance of transmission of the signal. The body fluids and the skin greatly
attenuate the signal and because the unit must be small to be implanted,
therefore has little power, the range of signal is quite restricted, often to just a few
feet. This disadvantage has been overcome by picking up the signal with a
nearby antenna and retransmitting it. However, with the plastic potting
compounds and plastic materials available today, encapsulation is easily
possible. Silicon encapsulation is commonly used.
Mercury and silver-oxide primary batteries have been used extensively and,
more recently, lithium batteries have found many applications. For field work with
free roaming animals, the power requirements are quite different from those
needed in a closed laboratory cage. Requirements range from an electrical
capacity of 20 mA-hr to 1000 mA-hr.
1.10 Advantages
1. Reduction of the impediment of the information source (patient, subject or
animal).
2. Reduction of the psychological effects on the information source.
3. Reduction of measuring artifacts,
4. Reduction of the risk for electroshock,
5. Reduction of the complexity of monitoring of physiological variables, as well
as a potential reduction of the total cost of patient care.
6. Totally battery operated instrument so not risk of electrical shutdown.
7. Compact size and light weight.
8. Reliable and repairable product.
1.11 Disadvantages
Limitations the system has inherent limitations. Movement of the patient is
restricted. If the patient goes beyond the range of the system, his ECG cannot be
monitored. Research is in progress for upgrades. Practical systems are being
developed to build on existing technology and public infrastructure.

23
2.0 Electromyography
2.1 Definition of EMG[1]
"Electromyography (EMG) is an experimental technique concerned with the
development, recording and analysis of myoelectric signals. Myoelectric signals
are formed by physiological variations in the state of muscle fiber membranes."
Figure 9 Basmajian & DeLuca: Definition Muscles Alive Unlike the classical
Neurological EMG, where an artificial muscle response due to external electrical
stimulation is analyzed in static conditions, the focus of Kinesiological EMG can
be described as the study of the neuromuscular activation of muscles within
postural tasks, functional movements, work conditions and treatment/training
regimes.
2.1.1 Wide spread use of EMG
Besides basic physiological and biomechanical studies, kinesiological EMG is
established as an evaluation tool for applied research,
physiotherapy/rehabilitation, sports training and interactions of the human body
to industrial products and work conditions:
Typical benefits of EMG
The use of EMG starts with the basic question: “What are the muscles doing?”
Typical benefits are:
1. EMG allows to directly “look” into the muscle
2. It allows measurement of muscular performance
3. Helps in decision making both before/after surgery
4. Documents treatment and training regimes
5. Helps patients to “find” and train their muscles
6. Allows analysis to improve sports activities
7. Detects muscle response in ergonomic studies

24
Figure 10 : Application areas of kinesiological EMG
2.2 Signal origin:
The Motor Unit
The smallest functional unit to describe the neural control of the muscular
contraction process is called a Motor Unit (Figure 11). It is defined as “...the cell
body and dendrites of a motor neuron, the multiple branches of its axon, and the
muscle fibers that innervates it . The term units outlines the behavior, that all
muscle fibers of a given motor unit act “as one” within the innervation process.
Figure 11 Motor unit. Adopted & modified

25
2.3 Excitability of muscle membranes[6]
The excitability of muscle fibers through neural control represents a major factor
in muscle physiology. This phenomenon can be explained by a model of a semi-
permeable membrane describing the electrical properties of the sarcolemna. An
ionic equilibrium between the inner and outer spaces of a muscle cell forms a
resting potential at the muscle fiber membrane (approximately -80 to -90 mV
when not contracted). This difference in potential which is maintained by
physiological processes (ion pump) results in a negative intracellular charge
compared to the external surface. The activation of an alpha-motor anterior horn
cell (induced by the central nervous system or reflex) results in the conduction of
the excitation along the motor nerve. After the release of transmitter substances
at the motor endplates, an endplate potential is formed at the muscle fiber
innervated by this motor unit. The diffusion characteristics of the muscle fiber
membrane are briefly modified and Na+ ions flow in. This causes a membrane
Depolarization which is immediately restored by backward exchange of ions
within the active ion pump mechanism, the Repolarization.
Figure 12 Schematic illustration of depolarization/ Repolarization cycle
2.4 Generation of EMG signal
The Action Potential
If a certain threshold level is exceeded within the Na+ influx, the depolarization of
the membrane causes an Action potential to quickly change from – 80 mV up to
+ 30 mV (Fig. 13). It is a monopolar electrical burst that is immediately restored
by the Repolarization phase and followed by an After Hyperpolarization period
of the membrane. Starting from the motor end plates, the action potential
spreads along the muscle fiber in both directions and inside the muscle fiber
through a tubular system.
This excitation leads to the release of calcium ions in the intra-cellular space.
Linked chemical processes (Electro-mechanical coupling) finally produce a
shortening of the contractile elements of the muscle cell. This model linking

26
excitation and contraction represents a highly correlated relationship (although
weak excitations can exist that do not result in contraction). From a practical
point of view, one can assume that in a healthy muscle any form of muscle
contraction is accompanied by the described mechanisms.
Figure 13 The Action Potential. Adopted & redrawn
The EMG - signal is based upon action potentials at the muscle fiber membrane
resulting from depolarization and repolarization processes as described above.
The extent of this Depolarization zone (Fig. 13) is described in the literature as
approximately 1-3mm² (11). After initial excitation this zone travels along the
muscle fiber at a velocity of 2-6m/s and passes the electrode side.
Figure 14 The depolarization zone on muscle fiber membranes. Adopted & modified2.5 signal
propagation and detection

27
An electrical model for the motor action potential
The depolarization – repolarization cycle forms a depolarization wave or
electrical dipole which travels along the surface of a muscle fiber. Typically
bipolar electrode configurations and a differential amplification are used for
kinesiological EMG measures. For simplicity, in a first step, only the detection of
a single muscle fiber is illustrated in the following scheme. Depending on the
spatial distance between electrodes 1 and 2 the dipole forms a potential
difference between the electrodes.
Figure 15 The model of a wandering electrical dipole on muscle fiber membranes. Adopted &
modified
In the example illustrated in figure 15, at time point T1 the action potential is
generated and travels towards the electrode pair. An increasing potential
difference is measured between the electrodes which is highest at position T2. If
the dipole reaches an equal distance between the electrodes the potential
difference passes the zero line and becomes highest at position T4, which
means the shortest distance to electrode 2.
This model explains why the monopolar action potential creates a bipolar signal
within the differential amplification process. Because a motor unit consists of
many muscle fibers, the electrode pair “sees” the magnitude of all innervated
fibers within this motor unit - depending on their spatial distance and resolution.
Typically, they sum up to a triphasic Motor unit action potential (“MUAP” - 2),
which differs in form and size depending on the geometrical fiber orientation in
ratio to the electrode site (Fig. 16):

28
Figure 16 Generation of the triphasic motor unit action potential. Adopted & modified
2.6 composition of EMG signal
Superposition of MUAPs
Within kinesiological studies the motor unit action potentials of all active motor
units detectable under the electrode site are electrically superposed (Fig. 17)
and observed as a bipolar signal with symmetric distribution of positive and
negative amplitudes (mean value equals to zero). It is called an Interference
pattern.
Figure 17 Superposition of MUAPs to a resulting electromyogram Adopted & modified

29
Recruitment and Firing Frequency
The two most important mechanisms influencing the magnitude and density of
the observed signal are the Recruitment of MUAPs and their Firing Frequency.
These are the main control strategies to adjust the contraction process and
modulate the force output of the involved muscle. Because the human
connective tissue and skin layers have a low pass filter effect on the original
signal, the analyzed firing frequency e.g. of a surface EMG does not present the
original firing and amplitude characteristics. For simplicity, one can say that the
EMG signal directly reflects the recruitment and firing characteristics of the
detected motor units within the measured muscle (Fig. 18):
Figure 18 Recruitment and firing frequency of motor units modulates force output and is reflected
in the superposed EMG signal Adopted & modified

30
2.7 Nature of the EMG signal
The “raw” EMG signal
An unfiltered (exception: amplifier bandpass) and unprocessed signal detecting
the superposed MUAPs is called a raw EMG Signal. In the example given below
(Fig. 19), a raw surface EMG recording (sEMG) was done for three static
contractions of the biceps brachii muscle:
Figure 19 The raw EMG recording of 3 contractions bursts.
When the muscle is relaxed, a more or less noise-free EMG Baseline can be
seen. The raw EMG baseline noise depends on many factors, especially the
quality of the EMG amplifier, the environment noise and the quality of the given
detection condition. Assuming a state-of-the-art amplifier performance and
proper skin preparation (see the following chapters), the averaged baseline noise
should not be higher than 3 – 5 microvolts, 1 to 2 should be the target. The
investigation of the EMG baseline quality is a very important checkpoint of every
EMG measurement. Be careful not to interpret interfering noise or problems
within the detection apparatus as “increased” base activity or muscle (hyper-)
tonus!
The healthy relaxed muscle shows no significant EMG activity due to lack of
depolarization and action potentials! By its nature, raw EMG spikes are of
random shape, which means one raw recording burst cannot be precisely
reproduced in exact shape. This is due to the fact that the actual set of recruited
motor units constantly changes within the matrix/diameter of available motor
units: If occasionally two or more motor units fire at the same time and they are
located near the electrodes, they produce a strong superposition spike! By
applying a smoothing algorithm (e.g. moving average) or selecting a proper
amplitude parameter (e.g. area under the rectified curve), the non- reproducible
contents of the signal is eliminated or at least minimized.

31
Raw sEMG can range between +/- 5000 microvolts (athletes!) and typically the
frequency contents ranges between 6 and 500 Hz, showing most frequency
power between ~ 20 and 150 Hz (see chapter Signal Check Procedures)
2.8 Factors influencing the EMG signal
On its way from the muscle membrane up to the electrodes, the EMG signal can
be influenced by several external factors altering its shape and characteristics.
They can basically be grouped in:
1) Tissue characteristics
The human body is a good electrical conductor, but unfortunately the electrical
conductivity varies with tissue type, thickness (Fig. 20), physiological changes
and temperature. These conditions can greatly vary from subject to subject (and
even within subject) and prohibit a direct quantitative comparison of EMG
amplitude parameters calculated on the unprocessed EMG signal.
Figure 20 The influence of varying thickness of tissue layers below the electrodes: Given the
same amount of muscle electricity condition 1 produces more EMG magnitude due to smaller
distance between muscle and electrodes
2) Physiological cross talk
Neighboring muscles may produce a significant amount of EMG that is detected
by the local electrode site. Typically this “Cross Talk” does not exceed 10%-
15% of the overall signal contents or isn’t available at all. However, care must
been taken for narrow arrangements within muscle groups. ECG spikes can
interfere with the EMG recording, especially when performed on the upper trunk /
shoulder muscles. They are easy to see and new algorithms are developed to
eliminate them (see ECG Reduction).

32
Figure 21 Raw EMG recording with heavy ECG
3) Changes in the geometry between muscle belly and electrode site
Any change of distance between signal origin and detection site will alter the
EMG reading. It is an inherent problem of all dynamic movement studies and can
also be caused by external pressure.
4) External noise
Special care must be taken in very noisy electrical environments. The most
demanding is the direct interference of power hum, typically produced by
incorrect grounding of other external devices.
5) Electrode and amplifiers
The selection/quality of electrodes and internal amplifier noise may add signal
contents to the EMG baseline. Internal amplifier noise should not exceed 5 Vrms
(ISEK Standards, see chapter “Guidelines…”) Most of these factors can be
minimized or controlled by accurate preparation and checking the given
room/laboratory conditions.[6]
2.9 Physiology of EMG[1]
Electromyography, also referred to as myoelectric activity, measures the
electrical impulses of muscles at rest and during contraction. As with other
electrophysiological signals, an EMG signal is small and needs to be amplified
with an amplifier that is specifically designed to measure physiological signals.
This signal can be recorded or measured with an electrode, and is then displayed
on an oscilloscope, which would then provide information about the ability of the
muscle to respond to nerve stimuli based upon the presence, size and shape of
the wave – the resulting action potential. While the electrode could be inserted
invasively into the muscle (needle electrodes), a skin surface electrode is often
the preferred instrument, because it is placed directly on the skin surface above
the muscle without employing the method of pinch insertion into the test subject.
When EMG is measured from electrodes, the electrical signal is composed of all
the action potentials occurring in the muscles underlying the electrode. This
signal could either be of positive or negative voltage since it is generated before
muscle force is produced and occurs at random intervals.
The EMG signal is first picked up by electrode and amplified. Frequently more
than one amplification stages are needed, since before the signal could be
displayed or recorded, it must be processed to eliminate low or high frequency

33
noise, or any other factors that may affect the outcome of the data. The point of
interest of the signal is the amplitude, which can range between 0 to 10 millivolts
(peak-to-peak) or 0 to 1.5 millivolts (rms). The frequency of an EMG signal is
between 0 to 500 Hz. However, the usable energy of EMG signal is dominant
between 50-150 Hz.
Figure 22 Frequency Spectrum of the EMG signal
In order to obtain a signal that yields the maximum information, the
method employed and the implementation device has to be considered. There
are many dependent factors that could affect a surface EMG since the signal is
susceptible to noise interference such as hum, signal acquisition such as clipping
and baseline drift, skin artifacts, processing errors, and interpretation problems.
For example, the contact of electrode to the skin could distort a recording signal.
The inadequate amplification of the signal could cause a recorder detection
problem. A wrong filter could efface some of desirable information of a signal.
Moreover, there are other factors such as the distance between electrodes as
well as the recording times used in the experiment. The device utilized in the
measuring of the signal must also be considered since low-level input into a
recording device could also affect data and yield inaccurate results.
2.9.1 Electrodes
The EMG electrode could be explained by a receiving antenna concept. A
receiving antenna is an electrical device that detects oscillating magnetic fields,
which are generated from various sources. Then the signal is transmitted through
the air from source to the receiving antenna, a concept that is used to engineer
the design of electrode. In terms of recording the EMG signal, the muscle fiber is
a biological signal generator, spreading out over voltage fields to the volume-
conductivity surrounded by fluid. This fluid serves to convey an EMG signal to an
electrode, like air carry signals to an antenna.
The EMG recording starts from the beginning of the bioelectrical events. The
changing conductivities in the membranes will make action currents flow across
the membranes as well as into the extracellular fluids around active cells. The

34
extracellular currents will then generate potential gradients as they flow through
the resistive extracellular fluids. The changing potential gradients, subsequently,
will produce electrical currents in the electrode leads by capacitive conductance
across the metal/electrolyte interface of the electrode contacts. These weak
currents will then flow through the high impedance circuits of the amplifier input
stages, which will then convert these currents into large output voltages.
Figure 23 Surface EMG electrodes
Figure 24 Ground electrode for surface EMG
The EMG electrodes can be classified by using its geometry. There are six
classes of EMG electrodes: monopolar electrode, bipolar electrode, tripolar
electrode, multipolar electrode, barrier or patch electrode, and belly tendon
electrode.
A monopolar electrode takes potential from electrode and ground as the inputs to
the differential amplifier. When measuring, only a bare electrode is placed,
without utilizing other electrical connection. Because the ground yields a negative

35
input to differential amplifier, the potential from electrode is always based on
ground.
A bipolar electrode is used to measure the voltage different between two specific
points. It generally must be used with a differential amplifier. A bipolar electrode
has two contacts that are not connected to each other. Therefore, one node will
be used for positive input, and the other will be used for a negative input for the
differential amplifier. Because the differential amplifier treats both inputs equally,
it will yield an accurate output. However the distance between the electrodes
could affect the measurement result. Placing the electrodes too far from one
another could yield a weak signal. On the other hand, placing them too close
may also result in unusable data, since the amplifier preprocesses each inputs
signal separately before subtracting those signals for output.
A tripolar electrode has three electrodes that are placed at equal intervals along
a straight line. The central electrode is usually connected to the positive input of
a differential amplifier, while the electrodes on the sides are usually connected to
the negative input of a differential amplifier. This configuration also requires
another electrode to serve as a reference. The tripolar electrode is often used to
record nerve potentials, as its configuration holds the advantage of being able to
reject some forms of biological noise.
A multipolar electrode consists of rows of bipolar electrodes where an equal lead
is connected each side of bipolar electrodes to serve as a positive and negative
input for a differential amplifier. Besides, another electrode must be applied as a
reference point. The multipolar electrode is often used to record the activity of
certain motor units based on idiosyncrasies in their fiber locations.
The barrier or patch electrodes are typical bipolar electrodes that are closely
connected to a dielectrical barrier. The dielectrical is a non conductive substance
that is placed between the electrodes. This configuration redirects currents in
extracellular flowing around the tissue nearby. The patch also keeps the currents
that are generated from tissues on each side to prevent them from spreading into
each other. Consequently, the potential gradient of a desired action is larger, and
the potential gradient of an undesired action is smaller.
A belly tendon electrode is one of the fields of interest in the clinical EMG. Its
geometry is an interesting hybrid of the monopolar and bipolar approaches. In
this technique, the first electrode is placed in or over the middle point of the
muscle of the belly, which serves as the positive input to the amplifier. The
second electrode is placed over the tendon of the same muscle, which is usually
about the end of contractile elements, and serves as the negative input to the
amplifier. This arrangement gives a clean leading negative waveform, since there
is no virtual active contribution from tendon electrode. A belly tendon electrode is
employed specifically for tendon applications although it is not used for
measuring a selective muscle EMG recording during physiological activity.

36
All of electrode geometries discussed above could be considered as a dipole
antenna in term of electrical behavior. Monopolar electrodes are used to
measure the EMG signal of very small muscle. This is a good approach for
sampling a signal that occurs near the surface of an active single fiber. On the
other hand, tripolar electrodes and multipolar electrodes are used for sampling
some large muscles.
2.9.2 EMG Electrode Placement
2.9.2.1 Location and Orientation of the electrode
The electrode should be placed between a motor point and the tendon
insertion or between two motor points, and along the longitudinal midline of the
muscle. The longitudinal axis of the electrode (which passes through both
detection surfaces) should be aligned parallel to the length of the muscle fibers.
Figure provides schematic representation of the preferred electrode location.
Figure 25 The preferred electrode location is between the motor point and the
tedious insertion
2.9.2.2 NOT on or near the tendon of the muscle
As the muscle fibers approach the fibers of the tendon, the muscle fibers become
thinner and fewer in number, reducing the amplitude of the EMG signal. Also in
this region the physical dimension of the muscle is considerably reduced
rendering it difficult to properly locate the electrode, and making the detection of
the signal susceptible to crosstalk because of the likely proximity of agonistic
muscles.
2.9.2.3 NOT at the outside edges of the muscle
In this region, the electrode is susceptible to detecting crosstalk signals from
adjacent muscles. It is good practice to avoid this situation. For some
applications, crosstalk signals may be undesirable.
2.9.2.4 Orientation of the electrode with respect to the muscle fibers
The longitudinal axis of the electrode (which passes through both detection
surfaces) should be aligned parallel to the length of the muscle fibers. When so
arranged, both detection surfaces will intersect most of the same muscle fibers.
Hence, the spectral characteristics of the EMG signal will reflect the properties of
fixed set of muscle fibers in the region of the electrode. Also, the frequency

37
spectrums of the EMG signal will be independent of any trigonometric factor that
would provide an erroneous estimate of the conduction velocity. The resultant
value of the conduction velocity affects the EMG signal by altering the temporal
characteristics of the EMG signal, and consequently its frequency spectrum.
2.9.2.5 Reference electrode placement
The reference electrode (at times called the ground electrode) is necessary for
providing a common reference to the differential input of the preamplifier in the
electrode. For this purpose, the reference electrode should be placed as far away
as possible and on electrically neutral tissue (say over a bony prominence).Often
this arrangement is inconvenient because the separation of the detecting
electrode and reference electrode leads requires two wires between the
electrodes and the amplifier. It is imperative that the reference electrode make
very good electrical contact with the skin. For this reason, the electrode should
be large (2 cm x 2 cm). If smaller, the material must be highly conductive and
should have strong adhesive properties that will secure it to the skin with
considerable mechanical stability. Electrically conductive gels are particularly
good for this purpose. Often, power line interference noise may be reduced and
eliminated by judicious placement of the ground electrode.
2.9.2.6 Some Guidelines for use of surface EMG electrodes
Skin Preparation
- Alcohol removal of dirt, oil, and dead skin.
- Shave excess hair if necessary. (Under ideal conditions this should
always be done. However, it is not feasible in many cases.)
- If the skin is dry, some electrode gel rubbed into the skin can help.
- If the person is going to be sweating, spray an antiperspirant on the
skin after cleaning with alcohol.
Placement of Electrodes
- There are specific references for different ways to measure for
placement.
- General guidelines for large muscle groups:
1. Best if over the largest mass of the muscle and align
electrodes with muscle fibers.
2. Use motor point and motor point finder to locate (general
location charts are available)
Cross Talk
- Not a real problem with large muscle groups.
- Can sometimes be avoided my adjusting the electrode size, inter-
electrode distance (if an option on your brand of electrode), or by
use of fine wires.
Application
- Skin placement.

38
- Avoid movement of electrodes by using straps or tape to firmly
secure electrode in place.
- Avoid bending of leads, place leads pointing in the direction that
you want the wire to continue in. (e.g., For electrodes placed on an
extremity, have the lead pointing towards the proximal end of the
extremity so that the wire will not have to be bent in order to go in
the proximal direction.)
- Avoid any stress on the wires by making sure that the wires are
loose underneath the tape or wrap that is holding them in place. Be
sure to check when the wires cross the joint that once the joint is
fully extended the wires are not drawn taunt.
- Avoid placing electrodes over scars.
Testing
- Do manual muscle tests to assure that you are getting a signal and
that you are over the intended muscle.
- Do trial session to check signal and to get subject used to the setup
and how instrumented.
2.9.3 Amplifier of EMG signals[6]
The amplifier is an electronic device that serves to boost low power signal to
higher power signal that is usable to perform work. There are two reasons to
amplify the signal. First, amplification increases the level of signal enough to
protect an electrical interference during transmission. Second, the signal is
amplified so that it could be stored in a storage device, or displayed by a
measurement device like oscilloscope. In case of an EMG signal, an amplifier is
necessary. There are no such devices that can measure EMG signal without
amplification. A differential amplifier is used to amplify an EMG signal, as it has
the ability to eliminate the noise from the signal. As shown in Figure 26 the
differential amplifier takes two inputs, subtracts them and amplifies the different.
In this case, if there is noise interference through the input wires, the noise could
be circuitry canceled out so long the transmission of the two inputs is completely
symmetrical manner. It is difficult to make an amplifier with perfect subtraction.
The Common Mode Rejection Ratio (CMRR) could measure the accuracy of
subtraction in each amplifier. It is suggested to have a CMRR value at 90dB in
order to sufficiently discard a contaminated noise. Yet with modern technology,
the differential amplifier could make a CMRR value of 120dB. However, even
though a differential amplifier has the ability to reduce unwanted noise signals
that occur from both sides of the input wires, contaminated noises could still
exist. This noise could have been injected into the signal by a stray capacitance
that has been amplified, and thus, degrading the signal.

39
Figure 26 A schematic of the differential amplifier configuration
Every electronic component or even an amplifier itself behaves as an effective
filter, since there are no such electronic devices that can transfer all frequency
range. The electrode itself tends to have lower impedance for a higher frequency
and have higher impedance for a lower frequency. The connection of electrode,
cable and amplifier creates an implicit filter effect. The electrode contacts are
connected in series to an amplifier; they function similar to that of a capacitor,
while an impedance of amplifier is similar to that of a resistor. This connection
visualizes a High-Pass filter circuit. The low frequency voltage tends to be
attenuated and drop the highest voltage across the electrode contacts rather
than the amplifier. On the other hand, the cables that connect electrodes to an
amplifier have a stray capacitor behavior. It is considered that this capacitor is
connected to ground, which simulates a Low-Pass filter circuit. The stray
capacitor will provide low impedance, at which the high frequency picked up by
electrodes tend to drop their voltage here. Therefore an amplifier will see an
attenuation of high frequency. The implicit filter could cause signal problems if it
is not considered carefully in the design of an amplifier. The explicit filter with real
components (resistor and capacitor) functions by using the same concept of an
implicit filter, and could help in increasing the signal-to-noise ratio. Since a signal
is desired to be within in some frequency range, it is good idea to have an explicit
filter for that particular band. Therefore, noise with the frequency outside a
desired frequency band will be distorted.
2.9.3.1 Problem with noise and artifacts[1]
In the process of recording an EMG signal, the source of the generated signal is
not only from bioelectrical generator or active cell, but also from any electrical
fields that occur around an electrode and lead cables. These electrical fields
produce some signals that could also be added to an EMG signal, causing a form
of interference that is called noise.
Interference noise can be produced from anything that has an electrical field
such as power lines, computer monitors, transformers, or EMG amplifier itself.
Once noise has occurred, it could cause problem in recording an EMG signal.
Therefore while planning out the design of the amplifier device and recording the

40
EMG signal, noise factors should be taken into consideration, since noise could
come from a variety of sources such as electronic components, recording
devices, ambient noise, motion artifacts, or inherent instability of the signal.
Any electronic devices can produce noise. The noise frequency is range between
0 Hz to a 1000 Hz. This kind of noise cannot be eliminated. Using an intelligent
circuit design and a good quality of electronic components to construct the device
can only reduce the noise.
Ambient noise could be generated from any electronic device that created an
electromagnetic field such as televisions, computer monitors, motors, electrical
power lines, fluorescent lamps or light bulbs. In fact there are radio waves and
magnetic fields floating all over our body. It is virtually impossible to drain these
radiators to ground (earth surface). The ambient noise also cannot be avoided.
The ambient noise frequency occurs primarily within the range 50 Hz or 60 Hz,
while the amplitude of an ambient noise is about one to three times greater than
that of an EMG signal.
Motor artifacts come from two sources; first, from the contact of an electrode to
skin; second, from the connection of cable from electrode to the amplifier. When
performing a grasping experiment, a movement of the wire alone could cause a
noise problem. This electrical noise from both sources has the frequency range
between zeros to twenty hertz. However, a proper design of circuitry with a good
connector and stable electrode contact could reduce this motion artifact problem.
Inherent instability of the signal is caused by a nature of EMG signal. The
amplitude of the EMG signal frequency range between zero hertz to twenty hertz
is particularly unstable due to the quasi-random nature of the firing rate of motor
units. It is suggested to consider an EMG signal frequency in this range as an
unwanted noise signal. There is no boundary in what amplitude of an EMG signal
is good for yielding accurate recordings. While a certain amount of noise could
be tolerated, the question is exactly how much noise could be allowed. In other
words, there is a question about the tolerable levels of the signal-to-noise ratio.
The signal-to-noise ratio is determined by taking the ratio of the amplitude of
desire signal over the amplitude of added noise signal. The main concern now is
in the lever of the signal-to-noise ratio that could degrade an analysis result. If
the noise is produced from thermal motion, then twice of desired signal amplitude
over the noise amplitude is good enough. However, if the noise occurred
periodically and forms a pattern similar to the desired signal, it is suggested that
ten times grater of the desire signal amplitude than the noise amplitude would be
clarified a confusing event. In order to determine signal-to-noise ratio, the study
of noise behavior alone may be required to see how noise could affect the real
signal.
2.10 Definition of Pulse (Heartbeat) rate:[7]
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat
by trained fingertips. The pulse may be palpated in any place that allows an

41
artery to be compressed against a bone, such as at the neck (carotid artery), at
the wrist (radial artery), behind the knee (popliteal artery), on the inside of the
elbow (brachial artery), and near the ankle joint (posterior tibial artery). The pulse
can also be measured by listening to the heart beat directly (auscultation),
traditionally using a stethoscope.
2.10.1 Physiology
The pulse is a decidedly low tech/high yield and antiquated term still useful at the
bedside in an age of computational analysis of cardiac performance. Claudius
Galen was perhaps the first physiologist to describe the pulse. The pulse is an
expedient tactile method of determination of systolic blood pressure to a trained
observer. Diastolic blood pressure is non-palpable and unobservable by tactile
methods, occurring between heartbeats.
Practitioners in Chinese Medicine are trained in Pulse Diagnosis and seek six
different pulses in each wrist, each corresponding to specific organs of the body.
The Chinese practitioner is trained to evaluate the frequency, rhythm and volume
of the pulse and may characterize it as strong, thready, slippery or floating.
Pressure waves generated by cardiac systole move the artery walls, which are
pliable and compliant. These properties form enough to create a palpable
pressure wave.
The Heart Rate may be greater or lesser than the Pulse Rate depending upon
physiologic demand. In this case, the heart rate are determined by auscultation
or audible sounds at the heart apex, in which case it is not the pulse. The pulse
deficit (difference between heart beats and pulsations at the periphery) is
determined by simultaneous palpation at the radial artery and auscultation at the
heart apex.
Pulse velocity, pulse deficits and much more physiologic data is readily and
simplistically visualized by the use of one or more arterial catheters connected to
a transducer and oscilloscope. This invasive technique has been commonly used
in intensive care since the 1970s.
The rate of the pulse is observed and measured by tactile or visual means on the
outside of an artery and is recorded as beats per minute or BPM.
The pulse may be further indirectly observed under Light absorbance’s of varying
wavelengths with assigned and inexpensively reproduced mathematical ratios.
Applied capture of variances of light signal from the Blood component
Hemoglobin under oxygenated vs. deoxygenated conditions allows the
technology of Pulse Oximetry.

42
Figure 27 pulse rate basic
2.10.2 Normal Pulse Rates:
Normal pulse rates in beats per minute (BPM):
Newborn 1 – 12
months
1 – 2
years
2 – 6
years
6 – 12
years
12 years -
adults
adult
athletes
120 - 160 80 - 140 80 – 130 75 – 120 75 – 110 60 - 100 40 - 70

43
3.0 Taxonomy of wireless medical systems
A wireless surface electromyography system is a taxonomy that categories
existing wireless medical system. Multiple wireless sensor applications have
been proposed to help user our society into a wireless future. Examples of such
applications include security, military, medical, environmental, and industrial/
building automation. The medical industry has embraced wireless sensor
networks as more and more innovative developments have evolved and
confirmed that wireless sensor networks are a valuable complement to current
medical system. A methodology for categorizing wireless medical system (WMS)
has been developed based on system function, technology, hardware
components (including sensors) and application.
The second level of the taxonomy categories the wireless technology
implemented within each medical system. Typical wireless medical systems
communicate within unlicensed frequencies. Table 1 shows a characteristic
graph that compares common unlicensed wireless technologies, namely
Bluetooth, ZigBee and Wi-Fi (Wireless Fidelity). This section explains the
characteristics of each of these technologies.
Table 1 Wireless technologies characteristic graph
3.1 Radio Frequency
In the United States the Federal Communication Commission regulates the use
of industrial, scientific and medical (ISM) radio bands. The ISM radio band was
originally reserved internationally for the license-free use of RtaF electromagnetic
fields. In license-free radio bands, users don’t have to purchase a license and the
spectrum is widely available. This allows WMS to wirelessly transmit medical
sensor data on ISM radio bands without having to purchase an expensive
license.
In recent years, the ISM license-free radio frequencies have been used for
communication technologies such as Wi-Fi, Bluetooth and ZigBee. The more

44
commonly used license-free RF bands are 900MHz, 1.8GHz, and 5.8GHz. The
two methods for radio frequency modulation in the unlicensed 2.4GHz ISM band
are frequency-hopping spread spectrum (FHSS) and direct-sequence spread
spectrum (DSSS). FHSS is a spread-spectrum method of transmitting radio
signals by rapidly switching a carrier among many frequency channels, using a
pseudorandom sequence known to both transmitter and receiver. DSSS is a
modulation technique in which the transmitted signal takes up more bandwidth
than the information signal that is being modulated. The 900MHz radio frequency
band is for unlicensed use only in North America, Australia and Israel, while the
2.4 GHz radio frequency band can be used worldwide (including North America,
Australia and Israel).
Wi-Fi is a wireless networking protocol based on the IEEE 802.11 specifications.
The primary motivation for Wi-Fi is data throughput. Wi-Fi is typically used to
connect computers to wireless local area networks (WLAN) and indirectly to the
internet. Wi-Fi devices transmit at frequencies of 2.4 GHz or 5 GHz. Wi-Fi uses
DSSS, with each channel being 22 MHz wide, allowing up to three evenly-
distributed channels to be used simultaneously without overlapping each
other.[5]
3.2 Bluetooth
Many companies such as Sprint, Motorola and Microsoft have incorporated
Bluetooth into mobile phones, portable computers, cars, stereo headsets, MP3
players, etc. Bluetooth is a short range low power, low cost communication
standard that uses radio technology. Originally, in 1984 Bluetooth was
envisioned as a cable-replacement technology. In 1999 seven companies
teamed up and formed a group called the Bluetooth Special Interest Group (SIG).
The SIG developed Bluetooth into an attractive compatible wireless standard.
Three different classes of Bluetooth radios exist, class 1, class 2, class 3. Each
with different operating ranges. A class 1 radio has an operating range of up to
100 meters, class 2 up to 10 meters, class 3 up to 1 meter. There are two core
specification versions of Bluetooth, both with different data rates; Version 2.0 has
an enhanced data rate of 3 Mbps and Version 1.2 has a basic data rate of 1
mbps. Batteries powering a Bluetooth device have a very short life expectancy,
usually a few days.
Bluetooth devices can from a personal are network called a piconet. A piconet is
an ad-hoc computer network of devices using Bluetooth technology protocols to
allow one master device to interconnect with up to seven active slave devices.
Piconets can communicate with each other, thus allowing devices that are out of
range to communicate through several hops from one piconet to the other.[2]

45
Figure 28 Bluetooth Protocol Stack
Bluetooth protocol stack is illustrated in the radio layer is primarily concerned with
the design of the Bluetooth transceivers. The baseband layer defines how
Bluetooth devices search for and connect to other devices. The master and slave
roles are defined her, as are the frequency-hopping sequences used by devices.
The baseband layer supports two types of links: Synchronous Connection
Oriented (SCO) and Asynchronous Connection Less (ACL). SCO links are
characterized by a periodic, single-slot packet assignment, and are primarily
used for voice transmission that requires fast, consistent data transfer.
A device with an ACL link can send variable length packets of 1, 3 or 5 time-slot
lengths. The link manager layer manages the properties of the air interface link
between devices. The logical link control and Adaptation Protocol (L2CAP) layer
provides the interface between the higher-layer protocols and the lower-layer
protocols. L2CAP allows multiple protocols and applications to share the air-
interface. L2CAP is also responsible for packet segmentation and reassembly,
and for maintaining the negotiated service level between devices. The Host
Controller Interface (HCI) layer defines a standard interface for upper level
applications to access the lower layers of the stack.
A Bluetooth transceiver uses frequency hopping-spectrum (FHSS) in the
unlicensed 2.4 GHz ISM frequency band. This data transmission technique
makes signals difficult to intercept because FHSS signals sound like momentary
noise bursts. Typically, 79 channels are available for a Bluetooth device. A
device can only operate on a channel for 0.4 seconds within a 30 second
window, and transmits using pseudorandom hops across all 79 channels at a
rate of 1600 hops per second.
Bluetooth devices use a polling technique to transmit packets. The master device
transmits only in even numbered time slots. The slave devices transmit only in
odd numbered time slots. A different frequency channel is use in each time
slot.[7]
3.3 ZigBee
ZigBee has become attractive wireless standard due to its reliable cost, effective
low power wireless network capabilities. Zigbee is based on an open global
standard and its primarily used for short range wireless application. For this

46
reason many industries has opted to apply the Zigbee standard within their
product monitoring and control application.
ZigBee is wireless standard based technology that addresses the need for
remote monitoring and con troll and censoring network application it enables the
deployment of large cintite of wireless networks with low cost and low power
solutions and provides the ability to operate for years on inexpensive batteries.
zigbee is built on IEEE 802.15.4 wireless, personal area network standard and
uses the unlicensed radio band 2.4GHz, 868MHz and 915 MHz the zigbee
standard uses direct sequence spread system (DSSS) for radio frequency
modulation over 16 channel each channel occupies 3MHz and its centered 5MHz
from adjacent channels, giving a 2 MHz gap between pairs of channels
A zigbee network usually consists of one master device one or more slave device
and operational router. The master device responsible for establishing a network
with a personal area network identifier the slave devices can be programmed to
sleep so that battery power is conserved.
The wireless technology characteristic says that zigbee transmit at a slower data
rate, 250 KBPS than the other wireless standards however this transmission rate
is ideal for system that intermittently transmit small amounts of data. Because
zigbee performs just a few specific, simple task the protocol stack can be as
small as 28KB, therefore the system controller requires less energy and
consumes less power. The small amounts of data that are transmitted also
contribute to systems minimal energy consumption. Bluetooth device consumes
more power because they are typically constant lay on and don’t spend much
time sleeping whereas zigbee slave devices spend a majority of their time
sleeping
Zigbee clearly has advantage over other wireless technique when network size is
considered a zigbee network can deploy over 65500 sensor nodes within
network system this nodes count gains over Bluetooth 7, Wi-Fi 32 by a sizeable
margin on the attractive feature of zigbee is its ability to transmit data up to 300
meter or up to 30 times farther than Bluetooth and 3 times farther than Wi-Fi.

47
Figure 29 ZigBee Protocol Stack
Zigbee network can arrange in three different topology mesh, tree and star. The
mesh topology nodes connect to communicate directly with a coordinator or
router. The Wi-Fi server communicate routes may exists. Only the node that data
is intended for reacts in star topology zigbee network contains one coordinator,
no router and no of devices that are all within range of the coordinator. The third
topology arranges communicate routers so that true exist exactly one route from
one device to another.[4]
Zigbee Bluetooth WiFi
Applications:
Monitoring and
control
Cable replacement Web, video email
Data capacity
(Kbps):
250 1,000 11,000+
Range (meters): 70 10 100
Battery life Years Days Hours
Nodes per
network
255 - 65,000 8 30
Software size
(Kbytes):
4 - 32 250 1,000+
Table 2 ZigBee Uperhand

48
4.0 System design
4.1 Block Diagram:
Figure 30 Block diagram
4.2 EMG amplifier
Figure 31 Burr brown amplifier
As explained earlier, EMG signal is so small that computer could not read it.
While the amplitude of the signal is between 0 to 10 mill volts (peak-to-peak), the
usable frequency of an EMG signal is ranging between 50-150 Hz [1]. At this
state, we need a huge gain (about thousand times) to boost the EMG signal
without changing phase or frequency of the signal. This amplifier uses a typical
differential amplifier circuit, which contains two inputs (positive input and negative
input). The differential amplifier circuit subtracts two inputs and amplifiers the
difference. To get the right level of the input signal, we need a body reference
which works as a feedback from the inputs. Whenever the signal changes due to
noise introduced by the body, this body reference will help maintain the correct
level of signal.
LCD Display
ADC Microcontroller
ZigBee
Transmitter
ZigBee
ReceiverDACMicrocontroller
Pulse
Sensor & EMG
Electrodes
GSM Module

49
4.3 Instrumentation Amplifier
Figure 32 Burr brown using lm 124
A suitable operational amplifier (op-amp) for this type of application is the
Instrumentation Amplifier. Its versatile 3-op amp design and small size make it
ideal for a wide range of applications. This type of op-amp usually provides
excellent accuracy because it provides high bandwidth even at high gain. The
EMG amplifier used a BURR-BROWN, lm124 chip for the amplifier, as suggested
by the application information data sheet of lm 124. The gain of the amplifier can
be adjusted by changing the resistor Rg between pin number 1 and 8.
4.3.1 Low pass filter:
Figure 33 4th order LPF
When handling pulse trains and signal bursts of EMG signals, it might be
favorable to use filters which have negligible over-shoot. When handling pulse
trains and signal bursts, it might be favorable to use filter which have negligible

50
over shoot in the step response. A class of filters particularly suitable for this type
of signals is the Bessel filter. The phase characteristics of this class of filters
exhibit a linear increase with frequency. The group delay, defined as the
derivative of the phase with respect to frequency, is hence extremely flat over a
wide range of frequencies. Frequency range of EMG signal is between 50-150Hz
so 4th order Bessel filter is required for the low pass filtration of 150Hz.
Figure 34 Low pass Filter design

51
4.3.2 High pass filter:
Figure 35 1
st
order HPF
The dominant energy of the EMG signal is located in the 50-150 Hz range, to
eliminate the movement artifacts, inherent instability of the signal which ranges
between 0 to 15 Hz and the ambient noise arises from the 60 Hz 1st order high
pass filtration of 50Hz is required.
Figure 36 High pass filter design

52
4.4 Pulse monitoring system
Figure 37 Pulse monitoring system
4.5 design description
1) Instrumentation amplifier.
IC INA 128 INA 131 INA 217 INA 333
Gain(vv) 1 to 10000 100 1 to 10000 1 to 1000
CMRR(db) 120 110 100 100
Bandwidth(KHz) 200 70 800 800
IP Bias
current(namp)
5 2 12 0.2
Noise(nv) 8 12 1.3 25
Table 3 Instrumentation amplifier comparison
Selection (INA 128): After brief literature survey & discussion I come to know that
INA128 instrumentation amplifier is well suited for our project because its low
offset voltage, low input bias current, low drift and high CMRR.
2) Quadruple Operational Amplifiers.
IC LM 124 LM 224 LM 324 OPA 4131
GBW(MHz) 1.1 1.2 1.2 3
CMRR(db) 70 70 65 50
Noise(nv) - 35 35 42
No. of
Channels
4 4 4 4
Cost us$ 0.29 0.11 0.11 0.40
Table 4 Quad selection comparison

53
Selection (LM 124) : After brief literature survey i have selected LM 124 because
it provides high performance at low cost.
3) Wireless device
Zigbee Bluetooth WiFi
Applications:
Monitoring and
control
Cable
replacement
Web, video
email
Data capacity
(Kbps):
250 1,000 11,000+
Range
(meters):
70 10 100
Battery life Years Days Hours
Nodes per
network
255 - 65,000 8 30
Software size
(Kbytes):
4 - 32 250 1,000+
Table 5 Wireless device selection
4) Electrode selection
Type of Electrodes Selected electrode Reason
Surface Electrodes,
Needle Electrodes
Surface electrode These electrodes are
not very expensive and
easy to use as
compared to needle
electrodes.
Table 6 Electrode Selection

54
5) Microcontroller selection
Type of Microcontroller Selected Reason
AVR, 8051 AT89s52 Easy to use, Availability
cost of the product.
Table 7 Microcontroller Selection
6) Comparator selection
IC LM 158 LM 258 LM 2904 LM 358
GBW(MHz) 0.7 0.7 0.7 0.7
CMRR(db) 70 70 70 70
Noise(nv) - 40 40 40
No. of
channels
2 2 2 2
Cost(US$) 1.62 0.11 0.12 0.10
Table 8 Comparator Selection
Selection (LM 358) : After a brief study I have selected LM 358 because it gives efficient
performance at low cost and easily availability.

55
4.6 Transmitter circuit diagram
Figure 38 Transmitter circuit diagram

56
4.7 Receiver circuit diagram:
Figure 39 Receiver circuit diagram

57
5.0 Programmer description for system
Figure 40 keil software

58
Figure 41 X-CTU
Figure 42 Filter pro

59
5.1 Observed signals
Recorded samples from the digital oscilloscope using the developed EMG
amplifier device. The samples were recorded in real time from real human hand.
The experiment preformed grasping of objects of different sizes and shapes.
1. Vpp = 484mV, Frequency =140.4Hz

60

61
5.2 Flowchart
5.2.1 TX section flowchart

63
5.3 Pulse rate result
Figure 43 Put the finger
Figure 44Observe the TX pulse

64
Figure 45 Observe the RX pulse
Figure 46 Lcd display

65
5.4 Emg result
Figure 47 Place the electrode
Figure 48 Push the muscle fiber

66
Figure 49 Observe the RX pulse
Figure 50 Observe the pulse on LCD

67
Figure 51 Reception of alert message
Figure 52 Read the message

68
5.5 result Suggestions for further advancements
The feasibility of the signals can be improved using suction cup electrodes rather
than the Peel-and-stick surface electrode. The use of surface electrode was
owing to the unavailability of the suction cup electrode and the cost constraints.
Better performance can also be obtained with the help of electrodes with built in
preamplifiers. The signals obtained from the body can be converted into digital
form and can be further processed digitally using digital processors to carry out
various analysis related to the muscular structure as well as their functioning.
The microcontroller incorporated in the project can be used as a base to work
upon and develop various functionalities such as emergency braking, obstacle
detection and many more. The EMG amplifier, the size of the enclosure should
be considered. The electrode extensions should be eliminated. The amplifier
should be able to hold electrodes directly on the unit. The amplifier and electrode
holders could be placed in the same PCB which has a connector to transfer the
output to the microcontroller unit. This amplifier unit would be then placed directly
on the hand.
5.6 Application area of project
Currently there are three common applications of the EMG signal.
1.To determine the activation timing of the muscle; that is, when the excitation to
the muscle begins and ends.
2. To estimate the force produced by the muscle.
3. To obtain an index of the rate at which a muscle fatigues through the analysis
of the frequency spectrum of the signal. To observer the change in patient heart
Rate fluctuation.
In the not so distant future, we can expect applications in the assessment of
neurological diseases which affect the fiber typing or the fiber cross-sectional
area of the muscle. The relationship between the force produced by the muscle
and the amplitude of the EMG signal requires further description. During the past
five decades, the scientific literature has promulgated an apparent controversy
on this issue. Some reports describe a relatively linear relationship, whereas
others describe a relative on-linear relationship, with the amplitude of the EMG
signal increasing greater than the force. Where the firing rate of the motor units
has a greater dynamic range and motor unit recruitment is limited to the lower
end of the force range, the relationship is relatively linear. Whereas, in larger
muscles where motor unit recruitment continues into the upper end of the force
range and the firing rate have a lower dynamic range, the relationship is relatively
non-linear. In the applications discussed herein, data collected via the neural
implant were directly used for control purposes, thereby removing the need for
any other external control devices. To control an electric wheelchair, a sequential
–state machine was implemented, with a command signal decoded in real time

69
from the neural signals being used to halt the cycle at the intended action. In this
way, the overall control of the wheelchair was made to be as simple as possible.
Initial experiments involved selective processing of the signals obtained from
several of the electrodes on the array over time to produce the discrete direction
control outputs.
With a small amount of learning time, the subject was able to control the direction
and velocity of the fully autonomous mobile robot. On board sensors allow the
robot to the override commands from the user to safely navigate local objects in
the environment. The technique was further implemented on an electric
wheelchair.
With the command signal from the implant controller received by the wheelchair’s
driver mechanism via a short-range digital radio link. The command signal
essentially obtained by the user closing his hand, halted the sequential state
machine at the desired output. The action of the sequential state machine was
indicated by a number of light-emitting diodes positioned in front of the user on
the right arm of the chair. These actions corresponded to the wheelchair motions
of forward, backward, left, and right.

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