surface acoustic wave (saw) wireless passive rf sensor systems

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


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


30

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


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)

University of CentralFloridaSchool of ElectricalEngineering andComputer Science

31

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


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


!1

f3

f5 f

0f

6f

2f

4f

1f

1f

4 f2

f6

f0

f5

f3

!2

SAW CDMA and OFC Tag Schematics


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


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

37

Temperature Sensor using Differential DelayCorrelator Embodiment


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



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


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

44

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


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


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


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


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


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

70

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


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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.


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Doug FosterFuentek, LLC

(919) 249-0327www.fuentek.com/technologies/SAW.htm

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