Surface Acoustic Wave (SAW) Wireless Passive Temperature Sensors VECTRON International - SenGenuity La Jolla, CA June 07 th 2012 Dr. S. SABAH sabah@vectron.com Slide 1
History of Surface Acoustic Wave (SAW) History of Surface Acoustic Wave (SAW) 1880 Piezoelectricity, discovered by Jacques and Pierre Curie in quartz crystals` 1885 Lord Rayleigh characterizes Surface Acoustic Waves (earth quake) 1889 First interdigital electrode design, Electric condenser U.S. patent Nikole Tesla 1965 First Interdigital Transducer (IDT s) on a polished piezoelectric plate (White / Voltmer) 1970 First applications: pulse expansion and compression in radar systems 1985 SAW filters replace LC filter in TVs and VCRs 1990 SAW filters allow for miniaturization of mobile phones Slide 2
Surface Acoustic Wave Technology Electrical power Electric fields lines Wave propagation 3000 [m/s] Rayleigh wave SAW - Rayleigh Wave propagation Piezoelectric substrate Bus bar IDT Surface Acoustic Wave (SAW) Slide 3
SAW Resonator as Temperature Sensor Reflector IDT Reflector First Fact: Surface wave velocities are temperature dependent and are determined by the orientation and type of crystalline material used to fabricate the sensor v SAW f SAW f SAW ( T, Cut,...) Second Fact: Very low power is required to excite the acoustic wave Energy Harvesting (EM-Wave) Slide 4
Frequency in MHz Conductance / S Single SAW Resonator: Absolute measurement EM Wave (power) Antenna SAW SAW Resonator on Piezoelectric substrate 434,5 434,4 434,3 0.04 0.035 434,2 0.03 434,1 434,0 0.025 433,9 433,8 0.02 433,7 433,6 0.015 433,5 433,4 0.01 433,3 433,2-25 -15-5 5 15 25 35 45 55 65 75 85 95 105 115 125 Temperature in C 0.005 0 433.5 433.6 433.7 433.8 433.9 434 434.1 434.2 434.3 434.4 Frequency / MHz Slide 5
Double SAW Resonator: Differential measurement T1 T2 R m1 L m1 C m1 R m2 L m2 C m2 C st = C 01 +C 02 0.07 0.06 0.05 Conductance / S 0.04 0.03 0.02 0.01 0 433 433.5 434 434.5 Frequency / MHz Slide 6
SAW Temperature Sensors: Absolute Measurement 438 437 436 f c / MHz magnitude Six Temperature Sensors TFSS429 TFSS431 TFSS432 TFSS433L TFSS435 TFSS436 428 Frequency [MHz] 439 435 434 433 ISM band 432 431 430 429-20 0 20 40 60 80 100 120 140 160 temperature / C 0.05 Temperature measurement system with 6 / 12 / 36 sensors 0.045 0.04 0.035 Conductance / S 0.03 0.025 0.02 0.015 0.01 0.005 Types of sensor modules 0 428 429 430 431 432 433 434 435 436 437 438 Frequency / MHz Slide 7
SAW Temperature Sensors : Differential Measurement 0.06 0.05 35 C 50 C 65 C 70 C 0.04 85 C 100 C 115 C ORING SEAL CRIMPED HOUSING WELD FITTING Conductance / S 0.03 0.02 130 C 145 C 160 C 180 C 195 C 210 C 225 C 240 C 255 C 275 C 285 C 300 C THERMAL CEMENT SENSOR 0.01 325 C 0 432 432.5 433 433.5 434 434.5 435 435.5 436 436.5 437 Frequency / MHz Types of sensor modules Slide 8
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Support of Absolute and Differential Measurement Absolute Measurement Measurement of absolute frequency of one resonator Advantages: Less consumption of bandwidth Easier frequency trimming of sensors in manufacturing Faster interrogation Slightly higher reading range Differential Measurement Measurement of absolute frequency of two resonances Difference frequency calculated from measured resonances Advantages: Higher stability caused by lower pulling effects during sensor module manufacturing and caused by environment Reduced ageing of difference frequency Slightly cheaper reader architecture Disadvantages: Higher pulling effects Higher ageing of frequency More expensive frequency source for interrogation unit Disadvantages: Higher bandwidth consumption Questionable frequency trimming of difference frequency Slightly slower interrogation Slightly lower reading range Slide 10
Receive Power (RX) - Friis Formula Specification: Maximum possible temperature resolution Storage Maximum Echo or receive signal (Rx) level Friis Formula: 2 2 4 G i GSAW P r Pe 1 4 (4 r) e T e t com Q factor Pr : Receive power Pe : Reader output power Gi : Reader antenna gain Gsaw: SAW sensor antenna gain r : Distance between Interrogator and sensor antennas α : matching/loss between antenna an sensor Τ/ t co : The interval of the transmission / commutation between Tx and RX Slide 11
Sensor Antenna Ansoft Name LLC X Y 0.00 m1 433.0000-3.5230 m3 436.0000-3.4266 Return Loss - NMHA ANSOFT Ansoft Name LLC X Y 600.00 m1 431.0000 9.9021 HFSSDesign1 Curve Info db(s(1,1)) Setup1 : Sw eep1 $f_move='0mm' $rad_off='0.5mm' 500.00 Impedance HFSSDesign1 ANSOFT Curve Info im(z(1,1)) Setup1 : Sw eep1 re(z(1,1)) Setup1 : Sw eep1 400.00-1.25 300.00 db(s(1,1)) Y1 200.00-2.50 100.00 0.00 m1 m1 m3-100.00-3.75-200.00 350.00 375.00 400.00 425.00 450.00 475.00 500.00 350.00 375.00 400.00 425.00 450.00 475.00 500.00 Freq [MHz] Freq [MHz] Slide 12
Reader Antenna Slide 13
Hardware: SAW Wireless Temperature System SAW Sensor Modules Reader Antennas Reader Units Sensor Antenna SAW RS485 or 4/20mA Interface RS232 Interface USB - MINI CAN Interface Slide 14
Software: SAW Wireless Temperature System Temperature RX (Receive signal) TX (Transmit signal) TH (Threshold) Slide 15
Starter Kit: Wireless SAW Temperature Sensors Slide 16
Applications Slide 17
Measurement results 140 120 Wireless SAW & Thermometer Wireless SAW Sensor Wired Thermometer 100 Temperature [C] 80 60 40 20 0 9:06:20 9:07:40 9:09:00 9:10:21 9:11:41 9:13:01 9:14:22 9:15:42 9:17:02 9:18:22 9:19:43 9:21:03 9:22:23 9:23:44 Time 9:25:04 9:26:24 9:27:45 9:29:05 9:30:25 9:31:45 9:33:06 9:34:26 9:35:46 9:37:07 9:38:27 9:39:47 Slide 18
Measured results 0.6 System Accuracy System Accuracy 0.4 0.2 System Accuracy [C] 0-0.2-0.4 17.7 32.7 52.1 70.6 86.7 101 111 116 119 121 122 119 110 100 91.6 84.1 77.4 71.4 66.2 61.5 v 57.3 53.5 50.3 47.3 44.7 42.3 40.2 38.3 36.6 35-0.6-0.8-1 -1.2 Temerature [C] Slide 19
System Accuracy of all Six Sensors System Accuracy of 6 Sensors Accuracy [C] 2 1.5 1 0.5 0-0.5-1 -1.5-2 17.7 32.7 52.1 70.6 86.7 100.9 110.5 115.6 119.2 120.8 121.5 118.5 109.5 100.1 Temperature [C] 91.6 84.1 77.4 71.4 66.2 61.5 57.3 53.5 50.3 47.3 44.7 42.3 40.2 38.3 36.6 S429 S421 S432 S433L S435 S436 Slide 20
Solution and solution differentiator Solution (Advantages) Passive and Wireless, non-invasive and no active electronic circuits It has been estimated that typical wiring cost in industrial installation is US$ 130 650 per meter and adopting wireless technology would eliminate 20% - 80% of this cost Medium & High temperature operating ranges: -20 C to 120 C & up to +260 C Reading Distance: 0.1 to 3 Meters (depend on the antenna and RF environment) System accuracy: ± 2 C (temperature operating range -20 C to 120 C) Robust, reliable, stable and suitable for harsh, hazard and inaccessible hot-spots Multi- Communication Protocol: RS485, RS232, USB, CAN. Analog-Output, MODBU User Friendly, ease of installation, simple to use Interfaces and data logging Real-Time and Continuously Thermal Monitoring 24/7/365 Miniature: small and light, low cost Low Maintenances Low ageing degradations (± 2 C <12 years) Environmental and green technology no recycling of battery Slide 21
Limitations Limitations FCC/EC/EMC Number of Sensors - Interference Slide 22
Questions? Thank You www.sengenuity.com Slide 23