Wireless power transfer by resonant inductive coupling project proposal
1. BACHELOR'S DEGREE PROGRAMME
Wireless Energy Transfer by Resonant
Pacheco de Oliveira, Felipe
2. EXECUTIVE SUMMARY
Our project addresses the issue of powering and charging electrical devices using
lengthy, inconvenient, non-recyclable wires.
With the rising usage of devices such as mobile phones, laptops, smart watches and
even electric vehicles the accumulation of different wires and charging cables in
everyday life is becoming inconvenient and hindering, with more suitable way of
charging batteries becoming evermore necessary.
In this project we are planning to use inductive resonant coupling technology to
design an apparatus that will allow us to power and charge electrical devices
3. LIST OF ABBREVIATIONS
ICNIRP International Commission on Non-Ionizing Radiation
M Mutual inductance
K Coupling coefficient
MF Magnetic field
WPT Wireless power transmission
RF Radio Frequency
w0 Resonant Frequency
Q- factor is a dimensionless parameter that describes how underdamped
an oscillator or resonator is
Bandwidth distance between lower cut off frequency and upper cut off
The fraction of magnetic flux produced by the current in one
coil that links with the other coil
5. LIST OF EQUATIONS
No. Name Equation
1 Q-Factor Q = P
Q = R
Q = R
K = M
√L L1 2
6. TABLE OF CONTENTS
Executive Summary 1
List of abbreviations 2
List of equations 4
1. Introduction 6
1.1 Background and Motivation 6
1.2 Project Objectives 7
1.3 Constraints 7
1.4 Related Work 8
2. Methods and Techniques 9
2.1 Basic principle of Resonant Wireless charging 9
2.2 Theoretical study 9
2.3 Wireless energy transfer circuit (Resonant inductive coupling) 10
2.4 Key points 10
2.5 Q- factor, Bandwidth and K factor 11
2.6 Mutual inductance and Self inductance 11
2.7 Impacts to the system 12
2.8 Why use resonance inductive coupling over other techniques? 13
2.9 Other techniques 13
3. Project Requirements & Products 15
4. Work Breakdown Structure 16
4.1 Project Schedule 17
5. Resources and Budget 20
6. Risk Management 21
7. References/Bibliography 22
7. 1. INTRODUCTION
1.1 BACKGROUND AND MOTIVATION
Most of the electrical devices in use today require batteries to be powered and are
charged by using lengthy wires. Smartphone usage has increased by 61% since 2014
with estimated 2.53 billion users  worldwide in 2018.
About 3 million fully electric and plug-in hybrid cars have been sold globally since
2011 with 1 million units sold only in 2017 , together with the rising usage of
other electronic devices such as laptops, tablets and even smart watches the
accumulation of different wires and charging cables in everyday life is becoming
inconvenient, hindering and environmentally concerning due to the fact that there’s
estimated 1 million tons of non-recyclable  charging cables produced annually
highlighting the need of more suitable way a of charging batteries that’s compatible
with more devices.
Wireless power transfer can provide convenient, safe, and flexible means to charge
electrical devices under stationary and dynamic conditions.
Using wired technology to charge an electric vehicle is burdened by the need for
cables and plug chargers, galvanic isolation of on-board electronics, bulk and cost of
different chargers. With wireless power transfer the owner will be able to simply park
the car over a charging station and the car begins with the charging process 
therefore eliminating the factor of human error of failing to remember to plug in the
Furthermore, this technology will be significantly beneficial for fully autonomous
vehicles as they will be able to charge themselves  without the need of anyone
having to plug them in.
Moreover, devices like mobile phones, laptops, smart watches, speakers, kitchen
appliances etc. can be charged by being put over a charging station which can be
8. integrated in the furniture  or by being connected to a main transmitter which will
charge all the devices in the room .
In general, Wireless power transfer could reduce demand for power cables while
making gadgets more durable and convenient, eliminate the need for disposable
throwaway batteries and perhaps even accelerate the adoption of electric cars.
1.2 PROJECT OBJECTIVES
The aim of this project is not only to develop our own version of a wireless power
transfer device. The whole project is a part of a learning process, where we strive to
gain technical knowledge along with practical knowledge useful for a career in the
field of an engineer. We wish to end up with a product that the university and future
students can be proud of and benefit from. We want to be able to exhibit our product
to awake an interest in the viewer or the future student.
The aim of the project is not to come up with a flawless innovative product, but we
want to leave space for further research and improvements.
More specifically we are aiming to create a resonant coupling power transferring
device, that can transfer power over a distance of 1 meter to a light source or any
other device in the power range of 60 W. However, we want to accomplish this in
small preliminary steps of 0.25 meters. A model will be created virtually with
Comsol, MultiSim and MATLAB. Later on a physical model will be build based on
the virtual model.
9. 1.3 CONSTRAINTS
There are regulations when it comes to the human exposure to electromagnetic fields
as given by ICNIRP. 
As we will most likely be dealing with frequencies in the range of 3 kHz to 100 kHz
we shouldn’t exceed an electric field strength E of 2,7 , a magnetic field0· 1 −2
strength H of and a magnetic flux density B of 2,7 .12 A
m 0 T· 1 −5
As for contact with currents when we are in range of 2,5kHz to 100 kHz we shouldn’t
exceed a current of 0,2 [mA]· f
1.4 RELATED WORK
There has been a great amount of work done in the field of wireless energy transfer.
Both in academia and in the industry itself.
The City of Rotterdam ran between the June of 2015 and June of 2017 a wireless
charging initiative whose goal was to identify the technical, organizational and
environmental implications of wireless charging in real life and to gain experience
with the implementation and use of wireless charging solutions within public space
. An MIT team demonstrated a highly resonant technique able to transfer energy
wirelessly for gaps of 2 meters, based on that Witricy was founded, a company that
provides wireless charging solutions since 2007 via resonant coupling .
Academia work varies from, developing a unified, design-oriented, scalable model
that can predict accurately the behavior of Resonant Inductive Coupling systems
under different conditions , to demonstrating efficient non-radiative power
transfer over distances up to eight times the radius of the coils . Our project is
therefore vastly benefited from having such a range of literature at our disposal in a
sense that we aim to learn from them while creating and testing our own work to
evaluate previous results and think on other alternatives and possibilities.
10. 2. METHODS AND TECHNIQUES
The Method(s) for achieving the goal is directly linked to what are the specifications
of the goal.
For this project “Resonant inductive coupling” technique will be used, as per our
discussions, a medium sized power transmission/reception. This method makes use of
inductive coupling in harmony with two resonating LC circuits to transfer power over
distances greater than several centimeters.
2.1 BASIC PRINCIPLE OF RESONANT WIRELESS CHARGING
A magnetic loop antenna (copper coil) is used to create an oscillating magnetic field,
which can create a current in one or more receives antennas.
If the appropriate capacitance is added so that the loops resonate at the same
frequency, the amount of induced current in the receivers increases.
This is called resonant inductive charging or magnetic resonance; it enables power
transmission at greater distances between transmitter and receiver and increases
2.2 THEORETICAL STUDY
In order to get a better understanding of the task, we need to familiarize ourselves
with the theoretical background of the system. Because the theory is fairly extensive,
we divided our study research in three parts:
1. Electrical circuit : Basic circuit understanding, size of capacitors.
2. Coil geometries : Self and mutual inductances, Number of coil turns, turn
3. Coil optimization : Magnetic shielding, shielding geometries, coil resistance,
11. 2.3 RESONANT INDUCTIVE COUPLING WPT
Figure 1.0: Capacitor C1 is in series with the primary coil. Voltage UG is applied to
the primary side which induces a voltage UL on the secondary side.
RG is the power generator’s resistance. L1 and L2 are primary coil and secondary coil’s
self inductances. M is the mutual inductance. RL can be described as the battery we
want to charge. C1 and C2 are the capacitors we use to create a resonant circuit and
control the circuit performance.
2.4 KEY POINTS
1. This technique takes advantage of strong coupling that occurs between
resonant coils, even when coil separation is tens of centimeters.
2. The energy “tunnels” from one coil to the other instead of spreading Omni
directionally from the primary coil.
3. The result is that the primary source of attenuation is the Q factor (gain
bandwidth) of the coils and little by distance.
12. 2.5 Q- FACTOR, BANDWIDTH AND K FACTOR
= 2𝜋Q = P
energy dissipated during one period
Stored electrical and magnetic energy
Q = R
series resonance circuit⇒
Q = R
arallel resonance circuit⇒ p
K = M
√L L1 2
oupling coefficient⇒ C
These are the list of formulas which are used to make a resonating system work at
optimal capacity. However, Q-Factor and K cannot be calculated without
simulating/calculating the most important parameters of the system.
2.6 MUTUAL INDUCTANCE AND SELF INDUCTANCE
Mutual Inductance is the basic operating principle of the transformer, motors,
generators and any other electrical component that interacts with another magnetic
field. Then we can define mutual induction as the current flowing in one coil that
induces a voltage in an adjacent coil.
Self inductance of the coil is defined as the property of the coil due to which it
opposes the change of current flowing through it. Inductance is attained by a coil due
to the self-induced emf produced in the coil itself by changing the current flowing
13. As far as we have researched it’s absolutely imperative that we simulate (COMSOL)
different coil geometries with shielding and nearby hindrances to calculate mutual
Self inductances of both coils can be measured by means of an oscilloscope, current
probe and appropriate formulas.
2.7 IMPACTS TO THE SYSTEM
There are several key factors to consider that affect how we are going to achieve this
goal. One of them was discussed earlier in this document which is the Q-factor.
Higher Q-factor is necessary because: As the Q of a resonant circuit increases so the
losses decrease. This means that any oscillation set up within the circuit will take
longer to die away (Ringing)
Oscillator phase noise: Any oscillator generates what is known as phase noise. As
might be expected, this noise is not wanted and therefore needs to be minimized.
The sharper the filter and the higher the level of Q, the better the circuit will be able
to remove the spurious signals.
Basically, a under-damped system is one where the Q factor is greater than a half.
Those systems may oscillate once or twice when a step impulse is applied before the
oscillation falls away. As the quality factor increases, so the damping falls and
oscillations will be sustained for longer.
Distance between the Coils
Coupling coefficient in the resonance state: The degree of coupling is captured by a
parameter called coupling coefficient which can be calculated using formula (2)
Because the Q factor can be very high, only a small percentage of the field must be
coupled from one coil to the other to achieve high efficiency, even though the field
dies quickly with distance from a coil, the primary and secondary can be several
14. Still, a lot of research/knowledge is required to simulate the coil in various situations
to get the best possible result.
Size of coil: As the size of coils and resonators is reduced, the Q-value tends to
decrease. This is because the electromagnetic energy is proportional to volume, the
dissipated power for metallic structures is proportional to surface area, and the ratio
decreases with structure size.
Magnetic shielding: Metal plates around secondary coil can shield the surrounding
from magnetic fields. However, the MF induce eddy currents on the plates and reduce
coupling coefficient. Ferrites, a material with very low eddy currents and high
permeability, can be placed on both primary and secondary coils to “tunnel” energy
from one side to the other and reduce/cancel the effects of metal plates.
2.8 WHY USE RESONANCE INDUCTIVE COUPLING OVER OTHER TECHNIQUES?
1. Over greater distances the non-resonant induction method is highly inefficient
and wastes vast majority of the energy in resistive losses of the primary coil.
2. Significant power may be transmitted between the coils over a range of a few
times the coil diameters at reasonable efficiency
3. Its ability to transfer power between a single primary coil and multiple
4. Power transfer through surfaces
5. Spatial freedom i.e load can move over a certain surface and still get optimal
1. High frequencies can cause electromagnetic interferences
2. Less efficiency compared to tightly coupled technique.
15. 2.9 OTHER TECHNIQUES
1. WPT with inductive coupling: This technique was not favoured over the chosen
technique because it is only efficient when transferring power over some
millimeters of coil distance. As, our main goal is transfer power over several
centimeters, this technique wasn’t chosen.
2. RF wireless charging: RF wireless charging is different in that is uses
electromagnetic waves, rather than induced magnetic fields (induction). This
method is beyond our scope so we choose not to do it.
16. 3. PROJECT REQUIREMENTS & PRODUCTS
1. Access to MATLAB/Simulink for modeling circuits.
2. Access to COMSOL for modeling characteristics of coils with different
3. Access to university resources such as: Laboratories and computer rooms in
order to test and validate our findings
4. Documentation, studies and reports from previous works in the field (both
academic and industry applications).
17. 4. WORK BREAKDOWN STRUCTURE
The overall structure of the project is shown in the mindmap bellow. These represent
important phases of the project. These phases are further divided into work packages,
which will be addressed at 4.1 Project schedule.
18. 4.1 PROJECT SCHEDULE
March April May June
10 17 24 31 7 14 21 28 5 12 19 26 2 9 16 23 30
1. PLAN PROJECT Responsible DEADLINES
Literature Review All 16
Project Goal All 16
WBS Creation All 7
Plan Timelines & Milestones All 16
Create Budget All 16
Risk Management All 16
Assign WPs responsibilities All 9
Present Plan All 14
2. STUDY BACKGROUND Responsible DEADLINES
Context and Potential for
Related Work Felipe 16
Availability of resources Felipe 16
Safety Aspects Mads 16
3. THEORY STUDY AND
Study resonance inductive
Define parameters to be
calculated and their
19. Scope of target devices Mads 16
4. SIMULATE CIRCUIT &
Research benefits of different
geometries and materials
Simulate basic coils Berin 15
Calculate self-inductance and
coefficient (k) for "free air"
Calculate coil resistances Muaaz 5
Simulate basic coils with
Calculate self-inductance and
considering adjacent objects
coefficient (k) with "adjacent
Calculate coil resistances
with "adjacent loads"
Assign values to components
(active & passive elements)
Implement results from
calculations (to multisim
Calculate efficiency Berin 30
Filter based on constraints Felipe 30
5. DOCUMENT PROJECT Responsible DEADLINES
Create project significance
Create project aim and
Define technical background Muaaz 14
20. Link to related work &
Create project reference and
Create presentation for the
17th of April
Create project proposal for
17th of April
End of Summer Semester
presentation - 1st Draft
As it can be noted by looking at our project’s scheduling, we have only provided
timelines for those work packages relevant to the first step of our project “Project 1”.
Even though we have already planned for further phases, we felt that assigning
precise deadlines for the future work of the project would not have a solid
embasement and would be, therefore, pure assumptions. We plan to come back to
these in the beginning of “Project 2” and considering all the learning from the current
phase, plan realistic timelines for the future phases.
21. 5. RESOURCES AND BUDGET
Items Price Realistic Price Optimistic
Wires €18.00 €18.00
Capacitors €20.00 €20.00
Frequency generator €16.00 €80.00
Coil support €15.00 €25.00
Oscilloscope €35.00 €35.00
PCB board €10.00 €10.00
AC/DC rectifier €10.00 €10.00
Microcontroller €12.00 €12.00
Shielding plates €100.00 €100.00
Website domain €14.00 €14.00
Total €250.00 €324.00
As it can be observed in the budget the shielding plates have a significant impact in
the overall budget. As we will be working with high frequencies, ferrite plates are
required and these have shown to be expensive. The other differences lie on different
choices of frequency generators (DIY x Standard model) and materials to build the
coil’s support (Styrofoam x Acrylic).
22. 6. RISK MANAGEMENT
( 1 - 4)
(1 - 4)
Not having enough budget 3 3
Not having access to labs 1 3
Not having access to university resources (3D printer,
Late delivery of components 3 4
Not being able to articulate the project properly 2 1
Technical difficulties that won't allow us to reach the
end goal of the project
Inadequate knowledge (software and theory) 2 2
Obtaining calculated values that do not make sense 2 2
Not enough time 1 4
Not enough components (damage while testing) 1 4
OCCUPATIONAL HEALTH AND HAZARD
Overwhelming university schedule (exam, stress,
Group members getting sick and/or injured 1 2
Being electrocuted in the lab 1 4
Massive short circuit current 2 4
Slippery, wet & dirty environment 1 1
Being deported 1 1
Exposure to high magnetic fields 1 1
Likelihood - Impact: 1 - Lowest, 4 - Highest
23. 7. REFERENCES/BIBLIOGRAPHY
 "Number of smartphone users worldwide ...."
 "Electric and plug-in hybrid cars whiz past 3m mark worldwide ...." 25 Dec. 2017,
 "World e-waste rises 8 percent by weight in 2 years as ... - ScienceDaily." 13 Dec. 2017,
 "How Wireless EV Charging Works for Tesla Model S | Plugless Power."
 "How Will Autonomous Vehicles Charge Themselves? | Plugless Power."
 "Veryday - Wireless Charging Furniture." http://veryday.com/case/ikea-home-smart/.
 "Disney Research Wireless Charging Room - Refinery29." 26 Feb. 2017,
 "ICNIRP guidelines." 15 jun.. 2010,
 "Pilot Wireless Charging - Rotterdam - ElaadNL." 8 Nov. 2016,
 "Highly Resonant Wireless Power Transfer: Safe, Efficient ... - WiTricity." 18 Dec. 2016,
 "Resonant Inductive Coupling Wireless Power Transfer - UPCommons."
 "Power transfer through strongly coupled resonances."