1. Wireless Temperature Measurement in Nuclear Reactor Based on
RFID Technology
Dr. Cheryl Xu, Florida State University, cxu@fsu.edu
1. Motivationand Background
1.1 Significance of the proposedresearch
The purposeof proposedresearchis to develop a wireless thermalsensor,getting
rid of traditional reliance on power circuit, so that temperature sensor can even
transmitsignalsembedding temperatureinformationfromveryharshenvironment.
The proposed wireless sensor is designed to work in high temperature, radiation,
pressure, and erosiveenvironment. Nuclear reactor is its application of interest. As
we know, temperaturesensors working in nuclear reactor are subjectto almost all
environmental challenges mentioned above. Currently, wired thermal sensors are
most widely used in real application, simply because they are easy to be designed
and installed. Meanwhile, wireless temperature sensors also have come into
application. RFID-based temperature sensors and readers are commercially
available in supermarket. But these wireless sensors cannot test temperature in
larger range due to the restriction of material, nor can they be applied to nuclear
reactor where environmental requirement is comparatively high. Thermocouple
measurement is the most common method used in nuclear reactor right now. But
is still has inadequate properties that hurdle accurate measure for long operating
duration. In this proposal, we present a wireless measurement based on RFID
technology. Its advantages over other sensors, especially wired ones, are obvious.
1) Traditional sensors cannot work sustainably without batteries, which may
decay under extreme heat and pressure in nuclear reactor. Even when using a
certain battery survive in such harsh environment, it is still inconvenient to
recharge it periodically. These challenges are posed by the harsh environment
within nuclear reaction facility. To tackle with these problems, our proposed
research applies completely passive (self-powered) sensor-embedded circuit and
insert it into the fuel rod. Passivesensor does not need power supply from circuit.
This facilitates installing and simplifyingsensorsystemto a largeextent. Meanwhile,
the material used as sensor head in our research is a kind of polymer derived

2. ceramics (PDC) which is synthesized in our lab. Ceramic materials are replacing
traditional metallic materials in engineering application due to their excellent
mechanic and thermal properties. Being a member of ceramic materials, PDC
materials are proved to demonstrate even more excellent thermo-mechanical
properties under 1500 Co
[1]. In this way, therewill beno need to open fuel rod and
replace batteries, which may spoiling the operation of nuclear reaction, as well as
consumingmoretime and fundsdoingthat. Moreover,thelife time of sensorusage
extends much longer if the material of sensor is relatively inertia to radiative
environment it is exposed to. This constitutes another reason for choosing PDC as
a replacement for sensor material.
2) Another distinguished advantage of our design is that we get rid of wires for
circuit connection. Having trouble to examine and fix wires triggers our desire to
make sensor transmitthermal signalwirelessly. As a replacement, radio frequency
identification (RFID) method is employed to transfer data between tag (sensor and
antenna included) and R FID reader. This process resembles RFID-based tag
temperature sensor in Walmart Supermarket: sensor tag and target being tested
are separated from each other. Traditionally, as it is shown in figure 1, fuel rods
directly heat coolant, increasing temperature inside the pressurevessel, as well as
pressure caused by accumulating steam. It is researchers’ desire to acquire
accurate temperatureinformation within fuel rod, yet, it is obvious that bold wires
cannotsurviveundersuchharshenvironment.To avoid damagemadefromerosive
gas and irradiation inside pressurevessel, one existing method is to lengthen the
cladding of fuel rod and cover endurable insulation over circuit wires. Special
codding can create insulation for metal wires within. Yet this will add great costto
nuclear reactor apparatus simply because of the high cost of insulation materials
or rectifying structure. Figure 2 illustrates how we rectify the sensor system, thus
achieve radio frequency-based communication by replacing existing sensors with
our RFID-based wireless sensor. Unlikethermocouplewhich is usually protected in
metal tubes and extend outof pressurevesselstartingfrominner fuel rod, wireless
sensor communicates with receiver end using antenna designed by us. The whole
systemfunctions as radio frequency system, with sending signalfrom one end and
receiving from the other end. Wireless sensor facilitates covering a clear distance
while reporting temperature. By doing so, we can still acquire stable, reliable

3. temperature data as well as lower the cost of sensing measurement system in
nuclear reactor. Specifically, our design is to attach the resilient PDCsensor inside
Fig. 1 Schematic diagramof Advanced Test Reactor (ATR) [2]. Fig. 2 Proposedwireless sensor communicationinside reactor
fuel rod. Admittedly, fixture has to be added to fuel rod to stabilize the position of
sensor chip, it will not pose any difficulties achieving that simple adjustment.
To send signal out, receiver is installed to the outlet of pressure vessel. The
function of receiver contains two parts. First function is energizing passivesensor
chip so that sensor translates temperature difference into electromagnetic
difference. The electromagnetic signal will be recycled by receiver circuit with the
help of RFID antenna. Typically, there is a long distance between the ends of fuel
rod to the inner wall of the pressure vessel, as shown in figure 2. We will try to
optimize the gain of antenna so that maximum distance of transmission can be
achieved. In experiment, the wireless transmission distancewill be set as 40cmat
first, and will be extended to a longer value step by step in order of meters. The
purposeofdoing so is to provethe liability of wirelesstransmissionatthe beginning,
and then optimizing the procedurein the following stages.
1.2 Polymer-derivedceramics andtheir unique properties thermal sensor
Following the sensor design section, therecent advancement and our preliminary
resultson processingand propertiesof the polymer-derivedceramicswillbe briefly
described so that solid proof lends supportto the utilization of PDC as our selected
Coolant
Concrete Wall
RFID Reader
Fuel Rods
PDC Sensor
ChipAntenna
Pressure Vessel
40cm
Wireless
Transmission
Distance

4. sensor material. The results have revealed a unique opportunity to develop novel
high temperature sensors for applications in advanced energy generation system,
i.e., passivesensor chip in our case.
PDCsare a new classof high temperature multifunctional ceramicssynthesizedby
thermal decomposition of polymeric precursors [2]. The synthesis processing
includes the following steps, shown in figure 3. 1). Synthesize/modify polymer
precursors,2).Shapeandcross-linktoforminfusiblepolymercomponents/devices,
and 3). Convertthe polymer components/devicesto ceramic ones by pyrolysis.The
materials formed by this process are predominantly amorphous ceramic alloys,
consistingof silicon,oxygen,carbonand nitrogen [2].Otherelements suchasboron
and aluminum can also be incorporated into the network by modifying the
precursors to tailor and improve their properties.
The preliminary research at the University of Central Florida (UCF) (Dr. Linan An,
Co-PI) has demonstrated that PDCs possess a unique combination of high-
temperature capability, microfabricationcapability, and desiredmultifunctionality,
making them very promising for high-temperature micro-sensor applications.
These results includes:
1) PDCs possess a set of excellent high-temperature thermos-mechanical
properties that make them suitable for applications in high pressureenvironment,
such as nuclear reactor and gas turbine.
PDCs arethermally stable and resistlarge-scalecrystallization at temperatures up
to 1500 Co
[1]; and their creep resistance exceeds that of polycrystalline SiC and
Si3N4. Particularly, we demonstrated that AI-doped SiCN ceramics (SiAlCN) exhibit
an anomalously high resistanceto oxidation and hot-corrosion (Figure4), which is
a major limit for SiC and Si3N4 sensors that are currently under investigation for
high-temperature applications.
2) PDCs have excellent microfabrication capability and compatibility with existing
silicon-based microfabrication processing.
Figure 3. Basic processing steps in polymer-derived ceramics
Start
chemicals Precursors
Infusible
component
s
Ceramic
component
s
Synthesize Shape
Cross-link
Pyrolysis

5. Figure 4. Scanningelectronmicroscope (SEM) images ofthe surfaces of (a)typical silicon-basedceramics without Al-doping after
heat-treatment in water vapor and/or NaCl-containing environments, (b) polymer derived SiAlCN ceramics after annealing at
1400oC for 300 hrs in 50%H2O-50%O2, and (c) polymer derived SiAlCN ceramics after annealing at 1200oCfor 50 hrs in a NaCl-
containingenvironment. Clearly, SiAlCN ceramics possess muchbetter corrosion resistance thanthose without Al-doping.
Unlike conventional ceramic materials, PDCmicro-devices can be fabricated using
well-developed microfabrication processingtechnologies.The basic idea is that the
micro-devices are first fabricated in organic form using well-documented
technologies developed for micro-fabricating plastic materials and then converted
to ceramics by pyrolysis. Recently, several microfabrication techniques such as
micro-casting, lithography and polymer-based bonding, have been developed by
Dr. An and his co-workers for the fabrication of PDC-based ceramic MEMS [3].
These works havebeen widely cited in MEMS society. Figure5 shows a few typical
micro-structures and devices made frompolymer-derived ceramics. PDCs can also
be processed in the form of thin/thick films using spin-on coating methods and
patterned into desired thin film or thick film devices. In this process, the precursor
for PDCs, which is either liquid or dissolvableinto organic solvent, can be modified
to be photosensitive and processed similar to photoresist and patterned using
conventional photolithography. Figure6 shows our recent results of SiAlCN film of
800 nm on Si substrate deposited via spin-on coating and SiAlCN structures
patterned on Si substrateby photolithography.
Figure 5. Typical MEMS structures made from SiCN:(a) micro-gear made bymicrocasting, (b)micro-channel heat exchanger made
bylithography(single-layer structure), and (c) atomizer made bylithography(two-layer structure).

6. Figure 6. (a) Cross-sectionand (b)surface SEM images of the SiAlCN film onSi substrate. (c) Optical microscopyimage of SiAlCN
microstructureson Si substrate.
3) PDCs possess tunable semiconducting behavior and extremely high piezo
resistivity.
PDCs are high-temperature amorphous semiconductors, and their electrical
conductivities can be easily tuned in a large range. Figure 7 shows a typical
conductivity vs. temperature curve of a PDC ceramic up to 1000oC. The
temperature coefficient of resistivity of this material is > 10-3
(better than Pt, which
has the highest thermal coefficient of resistivity among current high temperature
sensing materials). The curve exhibits three regions, suggesting that the material
exhibits typical amorphous semiconductor behavior. It is also illustrated that the
conductivity of the material is perfectly repeatable during heating/cooling cycles,
therefore the sensors made from the material can be repeatedly used to high
temperatures when conductivity is used as the sensing mechanism. The resistivity
of PDCs can be easily tailored in a large range by varying the chemistry of the
precursors.
Figure 7. Electrical conductivityof a PDCas a function oftemperature, measuredduring both heatingandcooling.

7. 2. Sensor Deployment andTheory Support
1) Impedance Matching and Design
The purpose of impedance matching design is to maximize the transmission
distance, as we mentioned in our first part. Whenever a source of power with a
fixed output impedance such as an electric signal source, a radio transmitter or a
mechanical sound operates into a load, the maximum possible power is delivered
to the load when the impedance of the load (load impedance or input impedance)
is equal to the complex conjugate of the impedance of the source (that is, its
internal impedance or output impedance). For two impedances to be complex
conjugates their resistances mustbe equal, and their resistances must be equal in
magnitude but of oppositesigns. In low-frequency or DC systems (or systems with
purely resistive sources and loads) the reactance are zero, or small enough to be
ignored. In this case, maximum power transfer occurs when the resistance of the
load is equal to the resistance of the source. For our purpose, we find that the
transmission of radio signal covers a distance that is proportional to the gain of
sensor chip circuit when impedance is matched. We know that transmission outof
range may result in inadequate power received by tag from reader, or failure of
detection from reader end. Figure 8 demonstrates the equivalent circuit of tag.
Based on Friis Transmission Equation for free space, the read range (largest
theoretical distance between reader and tag) is calculated as:
4
t
t r
th
P
r G G
P




Figure 8. RFID Tag Equivalent Circuit
Antenna
PDCSensor Chip
V Zc
Za

8. where tP is the power transmitted by the reader, tG is the gain of the reader
antenna, rG is the gain of the receiving tag antenna,  is the wavelength, thP is the
minimum threshold power necessary to power up the chip, and  is the power
transmission coefficient[5].
The equivalent RFID transponder circuit shown in figure 8 is also a typical back-
scattered RFID transponder (tag) consists of an antenna and an integrated circuit
(chip). The chip is usually placed right at the terminals of the tag antenna, and both
chip and antenna have complex input impedances.
The system operates in the following way. Base station module (RFID reader)
transmits an RF (radio frequency) signal, which is received by an RFID tag antenna.
The voltage developed on antenna terminals powers up the chip, which sends the
information back by varying its input impedance and thus modulating the
backscattered signal.
Proper impedance match between the antenna and the chip is of paramount
importance in RFID [6]. It greatly determines important RFID tag characteristics,
such as tag read range. Impedance match can be characterized by the power
transmission coefficient whose behavior determines tag performanceand can be
analyzed as shown below. A specific RFID tag design example with modeling and
simulation results which agrees with measurement data is also presented as an
illustration of the analysis.
Consider an equivalent lumped circuit of RFID tag shown in figure 8, where
Zc=Rc+jXc is the complex chip impedance and Za=Ra+jXa is the complex antenna
impedance. The voltage sourcerepresentsan open circuit RF voltage developed on
the terminals of the receiving antenna. The chip impedance includes the effects of
chip packageparasitic. Both Za and Zc are frequency dependent. Here it is deserved
to bementioned that ourPDCsensorcan beequivalent to complex chip impedance
virtually. In addition, chip impedance Zc may vary with the power absorbed by the
chip. The antenna is usually matched to the chip at the minimum threshold pwer
level necessary for chip to respond.
The amount of power Pc that can be absorbed by the chip from the antenna is
given by
Pc=Paτ

9. where Pa is the maximum available power from the antenna and τ is the power
transmission coefficient.
The read range, which is concern of interest, can be normalized to the maximum
possible range of the tag when it is perfectly matched to the chip, i.e., when τ=1.
Such normalization allows us to see what improvement in read range can be
obtained by better impedance matching. For example, for the tag in figure 9,
impedance matching with τ=0.5 corresponds to about 70% of the maximum
attainable read range.
2) RFID Tag Design
The communication in passive RFID system, which is employed in our sensor tag
design, is based on backscattering: the reader transmits energy, commands and
data to tag which then responds by backscattering its identification data back to
the reader as depicted in figure10. RFID consistof an antenna and a microchip and
the tags get all the energy for functioning from the electromagnetic radiation
emitted by the reader through a rectifier, a voltage multiplier and a voltage
modulator inside the microchip. The only difference between our sensor tag and
RFID microchip tags in general is that the material used to build chips and tags is
replaced by PDC instead. Combined with PDC’s excellent thermos-mechanical
properties, sensor tag getting rid of the restraintfrompower supply survives much
longer than any existing sensors. To correspond with input command, the tag
sends the information back to the reader by switching between two states: one is
matched to the antenna and another one is strongly mismatched.
For receiver design, we will makeadaption
to well-established RFID receiver [7] and
modulate receiver being used to test so that
it fulfills its function. Shownin figure11is an
example of signals received by the RFID
reader antenna showing both forward and
backward communications. RFID normally
uses simple modulations such as ASK
(Amplitude Shift Keying), PSK (Phase Shift
Keying), and FSK (Frequency Shift Keying).
Figure 9 Tag impedance matching relationship

10. Figure 10 Passive RFIDsystemdiagram
Pulse refers to a single pair of encoded symbols, wherethe RF envelope goes low-
high-low or high-low-high. Burstrefers to contiguous set of encoded symbols from
a single transmitter while CW is the entire signal from where the interrogator
power turns on until it turns off [8]. The RF forward communication can be
represented by one transmitting antenna and one receiving antenna. The power
density at distance fromthe transmitting antenna in the direction , )trans trans  is:
2
, )
W
4
trans trans trans trans
trans
P G
R
 


where Ptrans is the input power of the transmitting antenna, and Gtrans is the gain of
the transmitting reader antenna. The PtransGtrans is called the reader transmitted
equivalent isotropic radiated power (EIRP). The power received by the RFID tag
antenna is related to the wavelength of transmitting wave. So maximizing
transmission power is mostly equivalent to enlarging transmitting length (read
distance) to largestextent.
Figure 11 [7]. Reader receivedsignals from Agilent vector signal analyzer

11. To sumup, our design tries to bridge communication between RFID reader circuit
and tags according to Faraday’s principleof magnetic induction: far field emissions
captureelectromagnetic waves propagating froma dipoleantenna attached to the
reader, and the aroused tag circuit sends electromagnetic waves for RFIDreader to
recognizeshown in figure 12.
More specifically in our design, we will narrow operating frequency band to
approximate 920 925Hz Hz . This ultra-high frequency bandwidth and its high
frequency characteristics help to reducethe difficulty of recognizing informational
signal sending from tags. To realize narrow bandwidth and ultra-high frequency
communication (UHF), we will devote more effort into designing geometry of
antenna and selecting its material discreetly, so that the resonation frequency can
be tuned to the desired range.
3. ResearchTasks andDetails
Task 1. Setting upBasic Experimental Apparatus
To simulate the real nuclear reactor environment and configuration, we will
deploy experimental setup as shown in Figure 12. The steel column container is
used to simulate fuel rod’s cladding, which functions as a metallic cover preventing
inner heat and radiation influencing outside. Within the container, there will be
supporting springs fixing the sensor chip inside it. This correspond to earlier
mentioned category “fixture” in this proposal. Spring fixturehas its own advantage
of damping vibration so that acquired signal has higher quality.
Figure 11. RFIDTag Antenna Configuration
RFID
Reader
RFID Tag
Antenna
Dipole
Electromagnetic
Waves
Near-Field Far-Field

12. The sensorhead is placed in the container,while a short,anti-erosivewirecovered
by protective cover extrudes out of container. The steel container simulates
pressure vessel in Figure 2. Inside the “wall”, cooling fluid submerges the steel
container. The whole design tries to simulate real nuclear reactor as similar as
possible, in order to make sure designed sensor in this proposal has practical
utilization and application.
Task 2. Reference TemperatureMeasurement
In order to provide high temperature environment, we will use a resistance
heater to heat up cooling fluid, which will simultaneously transfer heat to steel
column container and its inside. Actually in
real nuclear reactor, it is fuel rod which
produces increasing heat due to chemical
reaction within it that heats up the cooling
fluid inside pressure vessel. Meanwhile, a
commercial thermocouple will be attached
to steel container so that a reference
temperature can be acquired and compared
with experimental data, consolidating the
viability of this experiment.
Task 3. Circuit DesignandConfiguration
The most significant part of this
experiment is to establish data
communication between sensor chip and
RFID reader. Since no wire will be used to
connectreader circuitoutsidewith tag, radio
frequency identification is employed to
bridge the gap. Also note that
electromagnetic wave will not be disturbed
or corrupted by either extreme heat or
pressure, therefore ensuring accurate
temperature measurement. In design, PDC
sensor will be machined and integrated into
Figure 12 Experiment Setup
V
PDC
Sensor
chip
Supporting
springs
Steel
Container
Oxide
Pellets
Resistance
Heater
RFID
reader
Power
Supply
Steel
Column
Container
Cooling
Fluid
Protective
Cover
Reference
temperature
Measure
Thermocouple
Wireless
transmission
Cable

13. electroplated inductive coil with screen printed (a LC circuit). The geometry of
inductive coil and sensor head depend on frequency-related calculation.
Task 4. RadioFrequency Signal Translation
To identify the radio frequency language and translate it into readable
temperature data, circuit logistic is needed, which involves two operations needed
to be done beforehand: a). Filter ultra-high or ultra-low frequency signals and let
the signalswithin designed rangepass.b). Replace the existence of radio frequency
signal with voltage signal, and then replace voltage with discrete signals, with “0”
representing low voltagelevel and “1” representing high voltage level. Specifically,
the readercircuit containsthreemain componentsto achievethese twooperations:
an envelope detector removing low frequency waves, a peak finder that stores the
peak energy value of RFID signals in its capacitor, and a comparator that outputs a
“1” bit when the received signal energy is larger than threshold value.
Task 5. Analysis and Evaluation of Experimental Results, Rectification and
Improvement
In this task the experimental result will be compared with acquired reference
temperature, and comparative graph will be drawn to show their difference and
evaluate the reliability of our method. Based on these evaluations and analysis, we
will make adjustments or rectifications to improve the experimental results.
4. ResearchSchedule
Task 1: Setting up Basic Experimental Apparatus 1
month
Task 2: Reference Temperature Measurement 2
months
Task 3: Circuit Design and Configuration 3
months
Task 4: Radio Frequency Signal Translation 1
month
Task 5: Analysis and Evaluation of Experimental Results, Rectification and
Improvement
1
month
Report and Documenting ½
month

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Guide
5. K.V.S.Rao,Pavel V.Nikitin,“Impedance MatchingConceptsinRFIDTransponderDesign”,Automatic
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