Surface acoustic wave (SAW) chemical multi-sensor array

• US 5,325,704 A
• Filed: 11/22/1993
• Issued: 07/05/1994
• Est. Priority Date: 11/22/1993
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Skudera, William J. Jr., Mariani, Elio A.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Wiggins, John David
• Application Number:
  US08/157,847
• Time in Patent Office: 225 Days
• Field of Search: 73/24.06, 73/24.01, 310/313 B, 310/313 D, 310/313 R
• US Class Current: 73/24.06
• CPC Class Codes: G01N 2291/0215 Mixtures of three or more gases, e.g. air
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/106 one or more transducer arrays
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 30/00 Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation G01N3/00, G01N5/00, G01N7/00, G01N9/00, G01N11/00, G01N13/00, G01N15/00, G01N17/00, G01N19/00, G01N21/00, G01N22/00, G01N23/00, G01N24/00, G01N25/00, G01N27/00, G01N29/00 take precedence

Abstract

A sensor for chemical vapor detection using a surface acoustic wave (SAW) ray that provides a means for simultaneously detecting several chemical agents. The sensor has a piezoelectric substrate and a bidirectional surface acoustic wave transducer on the substrate. Also on the substrate are several pairs of identical acoustic sensing and reference channels each on opposite sides of the transducer in a mirror image fashion. Each channel pair has a thin film capable of absorbing a chemical vapor to be monitored and a metallic surface acoustic wave grating reflector capable of receiving and reflecting surface acoustic waves through the thin film and back to the transducer. An acoustic absorber separates each channel. The reference channels are protected from ambient conditions while the sensing channels are exposed to such conditions. An RF signal is applied to the transducer causing the propagation of an acoustic signal into each of the sensing channels and reference channels. Output signals from the transducer are then detected. The array is preferably in a miniature configuration which is suitable for wearing on a person'"'"'s wrist or arm.

Claims

1. A surface acoustic wave, multi-channel sensor which comprises a piezoelectric substrate;

a bidirectional surface acoustic wave transducer disposed on the substrate;

a plurality of pairs of acoustic sensing and reference channels, each pair member being substantially identical to its corresponding other pair member, the sensing channels being sequentially disposed on the substrate in juxtaposition with one side of the transducer and the reference channels being sequentially disposed on the substrate in juxtaposition with the other side of the transducer;

each respective sensing channel and reference channel pair sequentially comprising a thin film whose composition is capable of absorbing a chemical vapor to be monitored, and a metallic surface acoustic wave grating reflector capable of receiving incident surface acoustic waves transmitted by the transducer through the thin film and reflecting them back again into the thin film to the transducer;

for each channel pair, the reflector grating and thin film is spaced equidistantly from the center line of the bidirectional transducer such that each respective sensing channel and reference channel pair is a mirror image of the other;

an acoustic absorber disposed on the substrate between each sensing channel and each reference channel;

means for protecting each of the reference channels from ambient conditions and simultaneously exposing each of the sensing channels to ambient conditions;

means for applying an RF signal to the transducer which causes the propagation of an acoustic signal into each of the sensing channels and reference channels; and

means for detecting output signals from the transducer.

3. The sensor of claim 1 wherein the acoustically absorbing material is selected from the group consisting of rubber, silicone, and room temperature vulcanizable material.

4. The sensor of claim 1 wherein the thin film comprises a material selected from the group consisting of poly(epichlorohydrin), polyisobutylene and fluoropolyols.

5. The sensor of claim 1 wherein the thin film material has a thickness of from about 2,000 to about 6,000 angstroms.

6. The sensor of claim 1 wherein the thin film material has a length and width ranging from about 0.01 to about 1.0 inch.

7. The sensor of claim 1 wherein the surface acoustic wave transducer comprises a layer of a metal having a thickness of from about 500 to about 2,000 angstroms.

8. The sensor of claim 1 wherein the surface acoustic wave transducer comprises aluminum, gold or aluminum alloyed with copper.

9. The sensor of claim 1 wherein the piezoelectric substrate has a length and width ranging from about 0.25 to about 2.0 inches and a thickness of from about 0.01 to about 0.03 inch.

2. The sensor of claim i wherein the piezoelectric substrate comprises a material selected from the group consisting of polished quartz, lithium niobate, and lithium tantalate.

10. A method for detecting chemical contamination comprising the steps of:

A.) providing a surface acoustic wave, multi-channel sensor which comprises

a.) a piezoelectric substrate;

b.) a bidirectional surface acoustic wave transducer disposed on the substrate;

c.) a plurality of pairs of acoustic sensing and reference channels, each pair member being substantially identical to its corresponding other pair member, the sensing channels being sequentially disposed on the substrate in juxtaposition with one side of the transducer and the reference channels being sequentially disposed on the substrate in juxtaposition with the other side of the transducer;

each respective sensing channel and reference channel pair sequentially comprising a thin film whose composition is capable of absorbing a chemical vapor to be monitored, and a metallic surface acoustic wave grating reflector capable of receiving incident surface acoustic waves transmitted by the transducer through the thin film and reflecting them back again into the thin film to the transducer;

for each channel pair, the reflector grating and thin film is spaced equidistantly from the center line of the bidirectional transducer such that each respective sensing channel and reference channel pair is a mirror image of the other;

d.) an acoustic absorber disposed on the substrate between each sensing channel and each reference channel;

e.) means for protecting each of the reference channels from ambient conditions and simultaneously exposing each of the sensing channels to ambient conditions;

f.) means for applying an RF signal to the transducer which causes the propagation of an acoustic signal into each of the sensing channels and reference channels;

g.) means for detecting output signals from the transducer; and

B.) applying an RF signal to the transducer and causing the propagation of an acoustic signal into each of the sensing channels and reference channels; and

C.) detecting output signals from the sensing channels and the reference channels via the transducer.

11. The method of claim 10 wherein the RF signal has a frequency ranging from about 100 to about 1,000 megahertz.

12. The method of claim 10 wherein the output signals from the sensing channels and the reference channels are coherent.

13. The method of claim 10 wherein the output signals from the sensing channels and the reference channels are out of phase.

14. The method of claim 10 wherein the output signals from the sensing channels and the reference channels are 180°

out of phase.

15. The method of claim 10 wherein the piezoelectric substrate comprises a material selected from the group consisting of polished quartz, lithium niobate, and lithium tantalate.

16. The method of claim 10 wherein the acoustically absorbing material is selected from the group consisting of rubber, silicone, and room temperature vulcanizable material.

17. The method of claim 10 wherein the thin film comprises a material selected from the group consisting of poly(epichlorohydrin), polyisobutylene and fluoropolyols.

18. The method of claim 10 wherein the thin film material has a thickness of from about 2,000 to about 6,000 angstroms and a length and width ranging from about 0.01 to about 1.0 inch.

19. The method of claim 10 wherein the surface acoustic wave transducer comprises a layer of a metal having a thickness of from about 500 to about 2,000 angstroms.

20. The method of claim 10 wherein the surface acoustic wave transducer comprises aluminum, gold or aluminum alloyed with copper.