PWST SAW - Sensor System

Transcription

1 PWST SAW - Sensor System Hines, J. H., Solie, L. P., Cote, G. O., Corey, J. D., Tucker, D. Y. G., Hines, A. T., *Borguet, E. U. Applied Sensor Research & Development Corporation, Arnold, MD, USA *Department of Chemistry, Temple University, Philadelphia, PA, USA jhines@asrdcorp.com

2 How do SAW sensors work? Sensing Region RF Signal Features Benefits Operate wirelessly Eliminate wiring harness; Low installation cost Operate on rotating parts RFID capable Individual sensor ID enables multisensor systems Require no batteries No battery changes; Low maintenance cost Sensitive/accurate Comparable to wired sensors measurements Real time measurements Rapid response; Variable sampling rate Last for decades Suitable for embedded use and long-term monitoring Survive & operate in Cryogenic to 1000 C+; Measure where Si fails extreme environments Radiation hard Low cost - based on Existing manufacturing infrastructure established technology Enable low cost distributed sensing

3 Products under development: > Coded sensor-tag wireless interface devices > Humidity sensors > Hydrogen sensors > Temperature sensors > Methane sensors > Hypergol leak detection sensors (MMH, DMH, NTO) > (Cryogenic) liquid (level) sensors > Concrete maturity monitor > Biosensor for infectious agents (CT) Focus on these today & on recent coding advances

4 Coded sensor-tag wireless interface devices: > SAW device acts as wireless interface to existing sensor > SAW coded and individually identifiable > Read SAW code & sensor reading > Read impedance varying & voltage producing sensors > Temperature sensors > Strain gauges > Switch positions > Bus voltages > Acoustic emission sensors > Goal: Elimination of wiring harness to existing sensors

5 Overview Ø SAW humidity sensor system with 16 individually identifiable devices Ø Nanoparticle PVP/LiCl-doped TiO 2 films Ø Rapid responses to humidity variation Ø Used time diversity and code diversity (DFC) Ø Wireless SAW sensor interrogation system utilizing a differential time integrating correlation approach Ø Demonstrated passive wireless measurement of a chemical vapor using film coated SAW sensors Ø Advances in code anti-collision Ø Barker Coding with time, frequency diversity 100 sensor-tags Ø DSSS codes with time, frequency diversity 32 T sensors Ø Conclusions

6 SAW Test Device - Films S21 (db) S21 (db) Time (usec) Time (usec) Simulation Actual Device

7 Nanoparticle PVP-LiCl/TiO 2 (a) SEM image of TiO- 2 /LiCl film; (b) typical AFM 3D-image used to determine film thickness; (c) AFM cross-section showing profile of the film edge Andrii I. Buvailo, Yangjun Xing, Jacqueline Hines, Norman Dollahon, and Eric Borguet, TiO 2 /LiCl based nanostructured thin film for humidity sensor applications. ACS Appl. Mater. Interfaces 2011, 3,

8 LiCl/TiO 2 Response to Full Humidity

9 LiCl/TiO 2 Recovery (100% 20%)

10 LiCl/TiO 2 Response to Humidity -60 Response of sensor vs. time with varying RH exposures ) -75 B (d e s -80 n o p s -85 e R r o -90 s n e S ) (% H R Time (s) 0 Sensor Response 3 hr. 300C Humidity (reference sensor)

11 LiCl/TiO 2 Response to Humidity -50 Response and Recovery Times (dry => 40% RH => dry) -60 ) B -70 (d s o L -80 n rtio e s In Time (s) 24 hr. 500 C 24 hr. 300C 3 hr. 500C 3 hr. 300C

12 Implementation of Multi-Sensors Ø Designed and manufactured 64 coded SAW humidity sensor devices Ø Used time diversity and code diversity Ø Set of 16 delivered to NASA Ø Discrete Frequency Coding (DFC) code diversity Ø Implemented eight good codes Ø Time Diversity Ø Re-used each code at eight distinct time delays

13 Orthogonal Frequency Coding (OFC) Orthogonal chips at specified frequencies are placed at different delays to produce codes Magnitude (Linear) Normalized Frequency 1 f 1 f 4 f 2 f 6 f 0 f 5 f Piezoelectric Substrate Normalized Time (Chip Lengths) Puccio, D.; Malocha, D.C.; Saldhana, N.; Gallagher, D.R.; Hines J.H. SAW Sensors Using Orthogonal Frequency Coding", IEEE Trans UFFC V 53, No. 2, pp Feb. 2006

14 Discrete Frequency Coding (DFC) Similar to OFC, but with code chips in frequency bands that do not overlap U.S. 7,791,249 (2010) "Frequency Coded Sensors Incorporating Tapers", Hines et. al.

15 Coded Chemical Sensor Device Code Chips Sensing Film Delay! Coded Transducer Uncoded Transducer

16 Time & Frequency Coding Amplitude CcorrC 0.8 AcorrC BcorrC 0.6 CcorrD Simulated Code C auto and cross correlations t Time Autocorrelation C Cross correlations A C Cross correlations B C Cross correlations C D Normalized Amplitude Measured Time (usec) CW to AW cross- correlation CW to BW cross- correlation DW to CW cross- correlation CW autocorrelation Sample: Auto- and cross-correlation of 4 codes

17 Simulated System Response System simulation: Matched filter responses (codes A-DD) to sensor with code A!

18 Time & Frequency Coding Sample: Code A only at 8 delays

19 Coded Chemical Sensor Device Upper Half Passband Sensing Path Reference Path Lower Half Passband Division of DFC code into reference and sensor path degrades correlation performance è Used only 2 codes for final sensor set!

20 Wireless system Ø Time integrating correlator-based transceiver Ø Power spectral density of response measured Ø Half-passband integrated energy

21 Wireless system Ø Room temperature measurement of RH Ø 16 individually identifiable sensors Ø Passive wireless measurement of humidity Ø Need to incorporate temperature sensing to provide calibrated RH

22 Wired humidity measurements

23 Wireless humidity measurements Dry Low RH RH~70% Sensor B read alone at a distance of 2.5 ft from reader

24 Wireless humidity measurements Dry Low RH RH~70% Sensor B read with three sensors in the field of view of reader

25 Wireless humidity measurements Sensor A Sensor B Sensor C Sensor A, B, and C together Sensor A, B, and C together Sensor A, B, and C together

26 Autocorrelation for13-bit Barker code Advances in Sensor-tag Coding Ø 13-bit Barker code with time & frequency diversity 100 sensor-tags

27 100 Barker coded sensor-tags Ø Frequency Diversity x 10 Autocorrelation of single sensor Cross-correlation with 9 other sensors at the same delay and at different frequencies

28 Cross-correlation with 9 other sensors at the same frequency and different delays 100 Barker coded sensor-tags Ø Time diversity x 10 Autocorrelation of single sensor DFC

29 100 Barker coded sensor-tags Ø Autocorrelation of 1 sensor (gold) frequency 3, delay 5 Ø Cross-correlation this sensor with the 99 other sensors

30 100 Barker coded sensor-tags Ø Autocorrelation of 1 sensor (green) frequency 3, delay 5 Ø Cross-correlation this sensor with the 99 other sensors Measured data, correlations simulated in MATLAB

31 Advances in Sensor-tag Coding Ø DSSS code generation Correlation behavior for a set of three 31- bit Gold codes Set of three 28-bit codes with improved cross-correlation

32 Advances in Sensor-tag Coding Ø Simulated system response with three 31-bit Gold codes Sensor 1 Sensor 2 Sensor 3 Sensor 1, 2, and 3 together

33 Advances in Sensor-tag Coding Ø Simulated system response with three 28-bit DSSS codes Sensor 1 Sensor 2 Sensor 3 Sensor 1, 2, and 3 together

34 Conclusions Ø Designed and manufactured 16 individually identifiable SAW sensor devices with rapid, reversible, quantitative responses to humidity Ø Developed novel differential time integrating correlation- based wireless SAW sensor interrogation system Ø Delivered 16-sensor system to Kennedy Space Center and demonstrated system operation on Nov. 30, 2011 Ø Demonstrated (we believe for the first time) the passive wireless measurement of humidity using SAW sensors with integrated nanostructured chemically sensitive films Ø Made significant advances in code anti-collision Ø Barker Coding with time, frequency diversity 100 sensor-tags Ø DSSS codes with time, frequency diversity 32 T sensors Ø Sets of 32 or more sensor-tags operating simultaneously are achievable

35 Acknowlegements: This work was supported by NASA STTR Contracts NNX08CD42P and NNX09CB77C ASR&D would like to thank Bob Youngquist, NASA KSC And Temple University colleagues: Eric U. Borguet Andrii Buvailo, Yangjun Xing, Devika Sil, Olivier Katz, Nicole Haloupek, Uduak Udeyo, Aseem Malhotra, and Chigozem Oguh

36 Any questions or comments? Please contact me at: Thank you