surface acoustic wave (saw) wireless passive rf sensor systems
DESCRIPTION
How can variables be measured in environments that are too hot, too cold, or moving too fast for traditional circuit-based sensors? A new technology for obtaining multiple, real-time measurements under extreme environmental conditions is being developed under Phase 1 and 2 funding contracts from NASA's Kennedy Space Center’s Small Business Technology Transfer (STTR) program. Opportunities for early deployment licensing and Phase 3 STTR contracts are now being accepted.Passive, remote measuring systems can be created using new Orthogonal Frequency Code (OFC) multiplexing techniques and specially developed, next-generation SAW sensors. As a result, very cost-effective applications such as spaceflight sensing (for instance, temperature, pressure, or acceleration monitoring), remote cryogenic fluid level sensing, or an almost limitless number of other rigorous monitoring applications are possible.TRANSCRIPT
Surface Acoustic Wave (SAW)Wireless Passive RF Sensor
SystemsDonald C. Malocha
School of Electrical Engineering & ComputerScience
University of Central FloridaOrlando, Fl. 32816-2450dcm@[email protected]
Univ. of Central Florida SAW• UCF Center for Acoustoelectronic
Technology (CAAT) has been actively doingSAW and BAW research for over 25 years
• Research includes communication devicesand systems, new piezoelectric materials, &sensors
• Capabilities include SAW/BAW analysis,design, mask generation, device fabrication,RF testing, and RF system development
• Current group has 8 PhDs and 1 MS• Graduated 14 PhDs and 38 MS students 2
UCF SAWCapabilities
• Class 100 & 1000 cleanrooms– Sub micron mask pattern generator– Submicron device capability– Extensive photolithography and thin film
• RF Probe stations• Complete SAW characterization facility• Extensive software for data analysis and parameter
extraction• Extensive RF laboratory for SAW technology 3
Research Areas
Thin Films
Processing
Material Charaterization
Measurement
SensorsDesign & Analysis
Center for
Applied
Acoustoelectronics
Technology
Device/System
Fabrication
Synthesis
Modeling
University of Central FloridaSchool of Electrical Engineering and Computer Science
4
What is a typical SAW Device?• A solid state device
– Converts electrical energy into a mechanical wave ona single crystal substrate
– Provides very complex signal processing in a verysmall volume
• It is estimated that approximately 4 billion SAWdevices are produced each year
Applications:Cellular phones and TV (largestmarket)Military (Radar, filters, advancedsystemsCurrently emerging – sensors,RFID
SAW Sensors
• This is a very new and exciting area• Since SAW devices are sensitive to
temperature, stress, pressure, liquids,viscosity and surface effects, a wide rangeof sensors are possible
Sensor Wish-list– Passive, Wireless, Coded– Small, rugged, cheap– Operate over all temperatures and
environments– Measure physical, chemical and biological
variables– No cross sensitivity– Low loss and variable frequency– Radiation hard for space applications– Large range to 100’s meters or more
• SAW sensors meet many of these criteria
SAW Background• Solid state acoustoelectronic technology• Operates from 10MHz to 3 GHz• Fabricated using IC technology• Manufactured on piezoelectric substrates• Operate from cryogenic to 1000 oC• Small, cheap, rugged, high performance
2mm
10mm
Quartz FilterSAW packaged filtershowing 2 transducers,bus bars, bonding, etc.
Applications of SAW DevicesMilitary (continued)
Military Applications Functions Performed
Radar Pulse Compression Pulse Expansion and CompressionFilters
ECM Jammers Pulse Memory Delay Line
ECCMDirect Sequence Spread Spectrum-
Fast Frequency Hopping-
Pulse Shaping, Matched Filters,Programmable Tapped Delay Lines,Convolvers, Fast Hop Synthesizer
Fast Hop Synthesizer
Ranging Pulse Expansion & CompressionFilters
A Few Examples
SAW 7 Bank Active Channelizer
From Triquint, Inc.
Applications of SAW Devices
Consumer Applications Functions Performed
TV IF Filter
Cellular Telephones RF and IF Filters
VCR IF Filter & Output ModulatorResonators
CATV Converter IF Filter, 2nd LO & OutputModulator Resonators
Satellite TV Receiver IF Filter & Output Modulator
A Few Examples
VSB Filter for CATV - Sawtek
Bidirectional Transducer Technology – IF Filter w/moderate loss; passband shaping and highselectivity.
Basic Wave ParametersWaves may be graphed as a function of time or distance. A single frequencywave will appear as a sine wave in either case. From the distance graph thewavelength may be determined. From the time graph, the period and frequencycan be obtained. From both together, the wave speed can be determined.
Velocity*time=distance
Velocity=distance/time= T/!
The amplitude of the wave can beabsolute, relative or normalized.Often the amplitude is normalizedto the wavelength in a mechanicalwave. A=0.1*wavelength
SAW Advantage
SAW Transducer & ReflectorDegrees of Freedom
• Parameter Degrees of Freedom– Electrode amplitude and/or length– Electrode phase (electrical)– Electrode position (delay)– Instantaneous electrode frequency
• Device Infrastructure Degrees of Freedom– Material Choice– Thin Films on the Substrate– Spatial Diversity on the Substrate– Electrical Networks and Interface
Piezoelectricity(pie-eezo-e-lec-tri-ci-ty)
SAW Transducer
Surface Wave Particle DisplacementSAW is trapped within ~ 1 wavelength of surface
Schematic of Apodized SAW Filter
2mm
10mm
Quartz Filter
SAW Filter Fabrication Process
Trim (if necessary)DiceCleanFinal TrimPackage
Mask Structure DeviceFeatures
2.5mm
10mm
LiNbO3 Filter
Fabrication – Electrode Widths
From: Siemens
RF Probe Station withTemperature Controlled Chuck
for SAW Device Testing
RF Probe and ANATop view of chuckassembly with RFprobes
Response of SAW Reflector Test Structure
Measurement of S21 using a swept frequency provides the required data.
62 64 66 68 70 72 74 76 78 80-90
-80
-70
-60
-50
-40
-30
-20
Frequency (MHz)
dB(S
21)
Transducerresponse
Reflector response isa time echo whichproduces a frequencyripple
20_0 50_0 50_020_0 20_0 50_0 50_020_0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-80
-70
-60
-50
-40
-30
-20
-10
Time (µs)
dB (s
21
)
Direct SAW
response
Reflector
response
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-80
-70
-60
-50
-40
-30
-20
-10
Time (µs)
dB (s
21
)
Direct SAW
response
Reflector
response
SAW OFC Device TestingRF Wafer Probing
Actual device with RFprobe
Why Use SAW Sensors and Tags?• Frequency/time are measured with greatest
accuracy compared to any other physicalmeasurement (10-10 - 10-14).
• External stimuli affects device parameters(frequency, phase, amplitude, delay)
• Operate from cryogenic to >1000oC• Ability to both measure a stimuli and to
wirelessly, passively transmit information• Frequency range ~10 MHz – 3 GHz• Monolithic structure fabricated with current IC
photolithography techniques, small, rugged
Goals• Applications: SAW sensors for NASA
ground, space-flight, and space-exploration
• SAW Wireless, Passive, OrthogonalFrequency Coded (OFC) SpreadSpectrum Sensor System
• Multiple sensors (temperature, gas, liquid,pressure, other) in a single platform
• Operation up to 50 meters at ~ 1 GHz• Ultra-wide band operation
26University of Central Florida School of Electrical Engineering and Computer Science
SAW OFC Properties• Extremely robust
• Operating temperature range: cryogenic to ~1000 oC• Radiation hard, solid state
• Wireless and passive (NO BATTERIES)• Coding and spread spectrum embodiments
• Security in coding; reduced fading effects• Multi-sensors or tags can be interrogated
• Wide range of sensors in a single platform• Temperature, pressure, liquid, gas, etc.
• Integration of external sensor
27University of Central Florida
School of Electrical Engineeringand Computer Science
Basic Passive Wireless SAWSystem
Sensor 3
Sensor 1
Sensor 2
Clock
Interrogator
Post Processor
28University of Central Florida School of Electrical Engineering and Computer Science
Goals:•Interroga-ondistance:1–50meters
•lowlossOFCsensor/tag(<6dB)•#ofdevices:10’s–100’s‐codedanddis-nguishableatTxRx•Spaceapplica-ons–radhard,widetemp.,etc.•SingleplaPormandTxRxfordifferingsensorcombina-ons
•Sensor#1Gas,Sensor#2Temp,Sensor#3Pressure
Multi-Sensor TAG Approaches• Silicon RFID – integrated or external sensors
– Requires battery, energy scavenging, or transmitpower
– Radiation sensitive– Limited operating temperature & environments
• SAW RFID Tags - integrated or external sensors– Passive – powered by interrogation signal– Radiation hard– Operational temperatures ~ 0 - 500+ K
• Single frequency (no coding, low loss, jamming)• CDMA( coding, 40-50 dB loss, code collision)• OFC( coding, 3-20 dB loss, code collision solutions, wideband)
29
University of Central FloridaSchool of Electrical Engineering and Computer Science
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SAW Example: Schematic and ActualNano-film H2 OFC Gas Sensor
•For palladium hydrogen gas sensor, Pd film is in only in one delay path,a change in differential delay senses the gas (τ1 = τ2)
OFC Sensor Schematic
Actual device with RFprobe
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80
0.2
0.4
0.6
0.8
Normalized Frequency
Magnitude (Linear)
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Schematic of OFC SAW ID TagSchematic of OFC SAW ID Tag
0 1 2 3 4 5 6 71
0.5
0
0.5
1
Normalized Time (Chip Lengths)
Piezoelectric Substrate
f1
f4
f6
f0
f2
f5
f3
Example OFCTag
Piezoelectric Substrate
f1
f4
f2
f6
f5
f0
f3
100 150 200 250 300 350 400-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.5
-0.45
-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
100 150 200 250 300 350 400-0.5
-0.45
-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
Frequency (MHz)
S11
(dB)
OFC Sensor Response
S11 of SAW OFC RFID –Target Reflection
S11 w/ absorber and w/o reflectors
32
University of Central Florida School of Electrical Engineering and Computer Science
SAW
absorber
Dual-sided SAW OFC Sensor
2.00 mm
1.25 mm 1.38 mm 1.19 mm2.94 mm
6.75 mm
f3 f
5 f
0 f
6f
2 f
4f
1
Piezoelectric Substrate
!1
f3
f5 f
0f
6f
2f
4f
1f
1f
4 f2
f6
f0
f5
f3
!2
SAW CDMA and OFC Tag Schematics
Piezoelectric Substrate
f1
f4
f6
f0
f2
f5
f3
0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.460
50
40
30
20
Experimental
COM Simulated
Time (us)
Mag
nit
ud
e (d
B)
CDMA Tag
•Single frequency
•Time signal rolloff due to reflectedenergy yielding reduced transmissionenergy
•Short chips, low reflectivity
-(typically 40-50 dB IL)
•OFC Tag
•Multi-frequency (7 shown)
•Long chips, high reflectivity
•Orthogonal frequencyreflectors –low loss (0-7dB IL)
•Time signal non-uniformity dueto transducer design rolloff
34University of Central FloridaSchool of Electrical Engineering and Computer Science
SAW Velocity vs Temperature
University of Central FloridaDepartment of Electrical and ComputerEngineering
36
OFC SAW Dual-Sided TemperatureSensor
Piezoelectric Substrate
f1
f4
f6
f0
f2
f5
f3
f1
f4
f6
f0
f2
f5
f3
!1
!2
0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.460
50
40
30
20
Experimental
COM Simulated
Time (us)
Mag
nit
ud
e (
dB
)
University of CentralFloridaSchool of ElectricalEngineering andComputer Science
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Temperature Sensor using Differential DelayCorrelator Embodiment
Piezoelectric Substrate
f1
f4
f6
f0
f2
f5
f3
f1
f4
f6
f0
f2
f5
f3
!1
!2
Temperature SensorExample
250 MHz LiNbO3, 7 chipreflector, OFC SAW sensortested using temperaturecontrolled RF probe station
OFC Code: Mitigate CodeCollisions
• Multi-layered coding– OFC– PN (pseudo noise)
– TDMA(time division multiple access)
• (-1,0,1 coding)– FDMA
(frequency division multiple access) 32 OFC codes simultaneouslyreceived at antenna:
non-optimized
Noise-like signal
Effect of Code Collisions from Multiple SAWRFID Tags -Simulation
0 1 2 3 4 5 6 7 810
0
10
Optimal Correlation Output
Actual Recevied Correlation Output
3rd Bit
Time Normalized to a Chip Length
Norm
aliz
ed A
mplitu
de
Due to asynchronous nature of passive tags,the random summation of multiple correlatedtags can produce false correlation peaks and
erroneous information
39University of Central Florida School of Electrical Engineering and Computer Science
University of Central FloridaSchool of Electrical Engineering and Computer Science
40
OFC Coding• Time division diversity (TDD): Extend the
possible number of chips and allow +1, 0, -1amplitude– # of codes increases dramatically, M>N chips, >2M*N!– Reduced code collisions in multi-device environment
Sensor #1
0 5 102!
1!
0
1
2
Time Response
Time Normalized to Chip Length
Nor
mal
ized
Am
plitu
de
456 MHZ SAW OFC TDD Coding
University of Central Florida School of Electrical Engineering and Computer Science41
A 456 MHz, dual sided, 5 chip, tag COM-predicted and measured timeresponses illustrating OFC-PN-TDD coding. Chip amplitude variations areprimarily due to polarity weighted transducer effect and fabrication variation.
1.5 2 2.5 3 3.5
-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
-55
Time (µs)
s11
(dB)
Simulation
Experiment
University of Central FloridaSchool of Electrical Engineering and Computer Science
OFC FDM Coding• Frequency division multiplexing: System uses N-frequencies
but any device uses M < N frequencies– System bandwidth is N*Bwchip– OFC Device is M*BWchip
• Narrower fractional bandwidth• Lower transducer loss• Smaller antenna bandwidth
42
Sensor #1
Sensor #2
32 Sensor Code Set - TDD
43
Optimized
NotOptimized
Receiver CorrelationReceiver Antenna Input
University of Central FloridaDepartment of Electrical and Computer Engineering
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Chirp Interrogation SynchronousTransceiver- Software Radio
Approach
SAW
sensor
RF Oscillator
Digital control and analysis circuitry
SAW up-
chirp filter
SAW down-
chirp filter
IF Oscillator
A / D
IF Filter
250 MHz OFC TxRx DemoSystem
Synchronous TxRx SAW OFC correlator prototypesystem RF
clocksection
Digitalsection
45University of Central Florida School ofElectrical Engineering and Computer Science
Wireless 250 MHz SAW OFCtemperature test using a free runninghot plate. The red dashed curve is aTC and the solid blue curve is theSAW extracted temperature.
ADC &Postprocessoroutput
WIRELESS SAWTEMPERATURE SENSOR
DEMONSTRATION
46
25 cm 25 cm
5 cm 5 cm
SAW
Sensor/Tag
Interrogator
(Transmitter)
Receiver
Hot Plate
78°C
Thermal
Controller
Thermal
Couple
Real-time wireless 250 MHz SAW OFC temperaturetest using a free running hot plate. The red dashedcurve is a TC and the solid blue curve is the SAWextracted temperature.
Postprocessoroutput
915 MHz Transceiver System
Packaged 915 MHz SAW OFC temperaturesensor and antenna used on sensors andtransceiver.
• Principle of operation of the adaptive matched OFC ideal filter response tomaximize the correlation waveform and extract the SAW sensortemperature.
An initial OFC SAWtemperature sensor datarun on a free runninghotplate from an initial 250MHz transceiver system.The system used 5 chipsand a fractional bandwidthof approximately 19%. Theupper curve is athermocouple reading andthe jagged curve is theSAW temperature extracted
data.
50 cm 50 cm
30 cm 30 cm
SAW
Sensor /Tag
Interrogator
(Transmitter )
Receiver
Hot Plate
78°C
Thermal
Controller
Thermal Couple
250 MHz Wireless OFC SAW System 1st Pass
250 MHz Wireless OFC SAW System - 2nd Pass
A final OFC SAW temperature sensor datarun on a free running hotplate from animproved 250 MHz transceiver system.The system used 5 chips and afractional bandwidth of approximately19%. The dashed curve is athermocouple reading and the solidcurve is the SAW temperatureextracted data. The SAW sensor istracking the thermocouple very well;the slight offset is probably due to theposition and conductivity of thethermocouple.
50 cm 50 cm
30 cm 30 cm
SAW
Sensor /Tag
Interrogator
(Transmitter )
Receiver
Hot Plate
78°C
Thermal
Controller
Thermal Couple
915 MHz Sensor System - 1st Pass
Initial results of the 915 MHz SAW OFC temperature sensor transceiver system. FourOFC SAW sensors are co-located in close range to each other; two are at roomtemperature and one is at +62◦C and another at -38◦C. Data was takensimultaneously from all four sensors and then temperature extracted in the correlatorreceiver software.
UCF OFC SensorSuccessful Demonstrations
• Temperature sensing– Cryogenic: liquid nitrogen– Room temperature to 250oC– Currently working on sensor for operation to
750oC• Cryogenic liquid level sensor: liquid
nitrogen• Pressure/Strain sensor• Hydrogen gas sensor
University of Central FloridaSchool of Electrical Engineering and Computer Science
54
Temperature Sensor Results
• 250 MHz LiNbO3, 7 chip reflector,OFC SAW sensor tested usingtemperature controlled RF probestation
• Temp range: 25-200oC• Results applied to simulated
transceiver and compared withthermocouple measurements
0 20 40 60 80 100 120 140 160 180 2000
20
40
60
80
100
120
140
160
180
200
Temperature Sensor Results
Time (min)
Temperature (
°C)
LiNbO3 SAW Sensor
Thermocouple
University of Central FloridaSchool of Electrical Engineering and Computer Science 55
OFC Cryogenic Sensor Results
0 5 10 15 20 25-200
-150
-100
-50
0
50
Time (min)
Temperature (
°C)
Thermocouple
LiNbO 3 SAW Sensor
Scale
Vertical: +50 to -200 oC
Horizontal: Relative time (min)
Measurementsystem withliquidnitrogenDewar andvacuumchamber forDUT
OFC SAW temperaturesensor results andcomparison withthermocouplemeasurements at cryogenictemperatures. Temperaturescale is between +50 to -200oC and horizontal scale isrelative time in minutes.
University of Central FloridaSchool of Electrical Engineering and ComputerScience
56
Schematic and Actual OFC Gas Sensor
•For palladium hydrogen gas sensor, Pd film is in only in one delay path, achange in differential delay senses the gas (τ1 = τ2) (in progress)
OFC Sensor Schematic
Actual device with RFprobe
Palladium Background Information• The bulk of PD research has
been performed for Pd in the100-10000 Angstrom thickness
• Morphology of ultra-thin films ofPd are dependent on substrateconditions, deposition and manyother parameters
• Pd absorbs H2 gas which causeslattice expansion of the Pd film –called Hydrogen Induced LatticeExpansion (HILE) – Resistivityreduces
• Pd absorbs H2 gas which causespalladium hydride formation –Resistivity increases
• Examine these effects for ultra-thin films (<5nm) on SAWdevices
HILE - Each small circlerepresents a nano-sized
cluster of Pd atoms
CO
NTA
CT
CO
NTA
CT
Without H2
CO
NTA
CT
CO
NTA
CT
With H2
57
Measured E-Beam Evaporated PalladiumConductivity v Film Thickness
Conductivitymeasurements made in-situunder vacuum
σinf = 9.5·104 S/cm
58
Ultra-thin Pd on SAW Devicesfor Hydrogen Gas Sensing
• Pd is known to be very sensitive to hydrogen gas
•Due to the SAW AE interaction with resistive films andthe potentially large change in Pd resistivity, a sensitiveSAW hydrogen sensor is possible
•Experimental investigation of the SAW-Pd-H2 interaction
59
Pd Films on SAW DevicesSchematic of Test Conditions
• Control: SAW delay line on YZLiNbO3 wafers w/ 2transducers and reflector w/oPd film
• Center frequency 123 MHz
• (A) SAW delay line w/ Pd inpropagation path betweentransducer and reflector
• (B) SAW delay line w/ Pd onreflector only
Pd Film
(A)
(B)
Pd Film1.27 mm
60
Test Conditions and Measurement
• S21 time domainmeasurement of SAWdelay line– Main response– TTE– Reflector return
responsePd Film
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.2580
76
72
68
64
60
56
52
48
44
40
36
32
28
24
20
16
12
8
4
0
DL w/o Pd
Before Exp
During 1st Exp
After 1st Exp
During 2nd Exp
After 2nd Exp
During 3rd Exp
After 3rd Exp
During 4th Exp
After 4th Exp
S21 Time Response
Time (micro-seconds)
Norm
aliz
ed M
agnitude
(dB
)
TTE
SAW MainReflector
61
SAW Propagation Loss and Reflectivity Pd Film ~ 15 Ang. (prior to H2)
• S21 time domain comparison ofdelay line with Pd in propagationpath vs. on the reflector
• Greater loss when Pd is placed inpropagation path than in thereflector– ~7dB loss when Pd is on
reflector• reflector length 1.47 mm
– ~22dB loss when Pd is inpropagation path
• 1.27 mm one-way path length• Propagation loss ~75dB/cm loss
1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 2.2 2.2580
77
74
71
68
65
62
59
56
53
50
47
44
41
38
35
32
29
26
23
20
DL w/o Pd
DL w/ Pd In Delay Path
DL w/ Pd on Reflector Bank
S21 Time Response
Time (micro-seconds)
Norm
aliz
ed M
agnitude
(dB
)
vfs 3488m
s:=
Pd Film
Pd F ilm
NoPd
62
SAW DevicePd in Propagation Path w/ 2% H2 Exposure
• Close-up of reflector bankS21 time domain response.
• A comparison of the traceslabeled “DL w/o Pd” and”Before Exp” shows achange in reflectivity due tothe presence of the Pd film.
• A gradual reduction inpropagation loss withincreased H2 exposure.– Irreversible change– ~ 20 dB reduction in
loss• Minimum propagation
loss ~6.8 dB/cm
1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 2.2 2.2580
77
74
71
68
65
62
59
56
53
50
47
44
41
38
35
32
29
26
23
20
DL w/o Pd
Before Exp
During 1st Exp
After 1st Exp
During 2nd Exp
After 2nd Exp
During 3rd Exp
After 3rd Exp
During 4th Exp
After 4th Exp
S21 Time Response
Time (micro-seconds)N
orm
aliz
ed M
agnitude
(dB
)
63
Pd Film
SAW DevicePd on Reflector w/ 2% H2 Exposure
• Close-up of reflector bankS21 time domain response.
• A comparison of the traceslabeled “DL w/o Pd” and”Before Exp” shows a changein delay as well as reflectivitydue to the presence of thePd film.
• A gradual increase inreflectivity with eachexposure to H2 gas isobserved
– ~ 7 dB change in IL– Irreversible
1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 2.2 2.2580
76
72
68
64
60
56
52
48
44
40
36
32
28
24
20
16
12
8
4
0
DL w/o Pd
Before Exp
During 1st Exp
After 1st Exp
During 2nd Exp
After 2nd Exp
During 3rd Exp
After 3rd Exp
During 4th Exp
After 4th Exp
S21 Time Response
Time (micro-seconds)
Norm
aliz
ed M
agnitude
(dB
)
64
Pd Film
Hydrogen GasSensor Results:
2% H2 gas
65
1.7 1. 8 1.9 2 2.1 2.280
76
72
68
64
60
56
52
48
44
40
36
32
28
24
20
Delay Line w/o Pd
After Pd Film
During 1st H2 Exposure
After 1s t H2 Exposure
During 2nd H2 Exposure
After 2nd H2 Exposure
During 3rd H2 Exposure
After 3rd H2 Exposure
During 4th H2 Exposure
After 4th H2 Exposure
Time (micro-seconds)
Norm
aliz
ed M
agnit
ude
(dB
)
Pd
Film
100 1 .103
1 .104
1 .105
0
40
80
120
160
200
240
3410
3425
3440
3455
3470
3485
3500
Loss/cm @ 123 MHz
Loss/cm due to Pd Film
Loss/cm due to Pd Film After Final H2 Gas Exposure
Loss/cm due to successive H2 exposure
SAW Velocity
SAW Velocity due to Pd Film
SAW Velocity due to Pd Film After Final H2 Gas Exposure
SAW Velocity due to successive H2 exposure
Propagation Loss (dB/cm) and Velocity(m/s) vs. Film Resistivity
Resistivity (ohm-cm)
Loss
(dB
/cm
)
SA
W V
eloci
ty (
m/s
)
Pd Film
Nano-Pd Film – 25 Ang.
•The change in ILindicates >10xchange in Pdresistivity – WOW!
•The large changesuggests anunexpected change inPd film morphology.
OFC Cantilever Strain Sensor
• Measure Delayversus Strain
66
Plot generated by ANSYS demonstrating thestrain distribution along the z-axis of thecrystal.
Test fixture, this shows the surface mountpackage, which contains the cantileverdevice, securely clamped down onto a PCboard which is connected to a NetworkAnalyzer.
OFC Cantilever Strain Sensor
School of Electrical Engineering and Computer Science68
Applications• Current efforts include OFC SAW liquid level,
hydrogen gas, pressure and temperature sensors• Multi-sensor spread spectrum systems• Cryogenic sensing• High temperature sensing• Space applications• Turbine generators• Harsh environments• Ultra Wide band (UWB) Communication
– UWB OFC transducers• Potentially many others
Vision for Future• Multiple access, SAW RFID sensors• SAW RFID sensor loss approaching 0 dB
– Unidirectional transducers– Low loss reflectors
• New and novel coding approaches usingOFC-type transducers and reflectors
• Operation in the 1-3 GHz range for small size• Single platform for various sensors
(temperature, gas, pressure, etc.)• SAW sensors in space flight and support
operations in 2 to 5 yearsUniversity of Central Florida
School of Electrical Engineering and Computer Science
69
NASA Support andCollaborations
• NASA support– KSC
• 4 Phase I STTRs and 4 Phase II STTRs: 2005-2011
• Latest STTR Phase II begins this summer– JSC
• 900 MHz device development in 2008– Langley
• GRA OFC sensor funding: 2008-2010
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Collaborations• Micro System Sensors 2005-2006, STTR
• ASR&D, 2007-present, STTR
• Mnemonics, 2007-present, STTR– United Space Alliance (USA): 2nd order collaboration
• MtronPTI – 1995-present, STTR• Triquint Semiconductor -2009
• Vectron -2009 (SenGenuity 2nd order collaboration)
• Univ. of South Florida 2005-present, SAWsensors
• Univ. of Puerto Rico Mayaguez – initiating SAWsensor activity
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SAW Research at UCF• Approximately 200 publications and 7 patents
+ (5 pending) on SAW technology• Approximately $5M in SAW contracts and
grants• Approximately 50 graduate students• Many international collaborations• Contracts with industry, DOD and NASA• Current efforts on SAW sensors for space
applications funded by NASA
Current Graduate ResearchStudent Contributors
• Brian Fisher• Daniel Gallagher• Mark Gallagher• Nick Kozlovski• Matt Pavlina
• Luis Rodriguez• Mike Roller
• Nancy Saldanha
University of Central FloridaSchool of Electrical Engineering and Computer Science
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Acknowledgment
Thank you for your attention!
•The authors wish to thank continuing support fromNASA, and especially Dr. Robert Youngquist, NASA-KSC.•The foundation of this work was funded throughNASA Graduate Student Research ProgramFellowships, the University of Central Florida - FloridaSolar Energy Center (FSEC), and NASA STTRcontracts.•Continuing research is funded through NASA STTRcontracts and industrial collaboration with AppliedSensor Research and Development Corporation, andMnemonics Corp.
University of Central FloridaSchool of Electrical Engineering and Computer Science
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