FREQUENCY CODED SENSORS INCORPORATING TAPERS

• US 20070296305A1
• Filed: 06/26/2007
• Published: 12/27/2007
• Est. Priority Date: 06/26/2006
• Status: Active Grant

• Current Assignee: Sensanna Incorporated
• Original Assignee: Applied Sensor Research & Development Corporation (Sensanna Incorporated)
• Inventors: Solie, Leland P., Hines, Jacqueline H.
• Granted Patent: US 7,791,249 B2
• Time in Patent Office: Days
• US Class Current: 310/313.00B
• CPC Class Codes: H03H 2240/00 Indexing scheme relating to filter banks
• CPC Class Codes: H03H 9/14547 Fan shaped; Tilted; Shifted; Slanted; Tapered; Arched; Stepped finger transducers

Abstract

A surface acoustic wave device includes a piezoelectric substrate on which is formed a transducer that generates acoustic waves on the surface of the substrate from electrical waves received by the transducer. The waves are carried along an acoustic track to either a second transducer or a reflector. The transducers or transducer and reflector are formed of subsections that are constructed to operate at mutually different frequencies. The subsections of at least one of the transducers or transducer and reflector are out of alignment with respect to one another relative to the transverse of the propagation direction. The out of aligned subsections provide not only a frequency component but also a time to the signal output signal. Frequency response characteristics are improved. An alternative embodiment provides that the transducers and/or reflectors are continuously tapered instead of having discrete frequency subsections.

Claims

1. A coded surface acoustic wave device, comprising

(a) a piezoelectric substrate;

(b) at least one first transducer arranged on at least a portion of said piezoelectric substrate wherein said first transducer includes at least two sub-transducers located in spatially adjacent acoustic stacks and wherein said at least two sub-transducers are electrically connected in parallel by busbars;

(c) said at least two sub-transducers having electrode structures capable of generating and receiving acoustic waves of different frequencies, wherein a centerline of each of said at least two sub-transducers are coincident;

(d) at least one second surface acoustic wave element formed on said piezoelectric substrate and spaced from said first transducer, said at least one second surface acoustic wave element comprising sub-elements equal in number and operating frequency to corresponding ones of said at least two sub-transducers of said first transducer; and

(e) wherein the at least one second surface acoustic wave element is structured such that said sub-elements of said second surface acoustic wave element are spaced at different relative positions along the acoustic tracks from said first transducer, so as to effect different delays within each of said acoustic tracks, thereby effecting a code.

2. A coded surface acoustic wave device as defined in claim 1, wherein said at least one second surface acoustic wave element comprises a transducer made up of sub-transducers electrically connected in parallel.

3. A coded surface acoustic wave device as defined in claim 1, wherein said at least one second surface acoustic wave element comprises a reflector made up of sub-reflectors.

4. A coded surface acoustic wave device as defined in claim 1, wherein said at least one second surface acoustic wave element is a pair of second surface acoustic wave elements connected with said piezoelectric substrate spaced from said at least one first transducer.

5. A coded surface acoustic wave device as defined in claim 4, wherein the pair of second surface acoustic wave elements are mirror images of one another and are located on opposite sides of said at least one first transducer.

6. A coded surface acoustic wave device as defined in claim 4, wherein the said at least one first transducer comprises a pair of transducers electrically connected in parallel and spaced in different acoustic tracks, and wherein said pair of second surface acoustic wave elements are spaced from and located on a same side of said first transducers.

7. A coded surface acoustic wave device as defined in claim 1, wherein each of said sub-transducers of said first transducer and each of said sub-element of said at least one second surface acoustic wave elements include parallel electrodes.

8. A coded surface acoustic wave device as defined in claim 1, wherein each of said sub-transducers of said first transducer and each of said sub-elements of said at least one second surface acoustic wave elements include continuously tapered electrodes.

9. A coded surface acoustic wave device as defined in claim 2, wherein said at least one second surface acoustic wave element includes busbars, and further comprising:

an external sensing element electrically connected to said busbars of said at least one second surface acoustic wave element.

11. A sensor, comprising:

a coded surface acoustic wave device as defined in claim 9, wherein the parameter to be measured affects the electrical impedance of said external sensing element, thereby altering the performance of said device.

10. A sensor, comprising:

a coded surface acoustic wave device coded surface acoustic wave device, including;

(a) a piezoelectric substrate;

(b) at least one first transducer arranged on at least a portion of said piezoelectric substrate wherein said first transducer includes at least two sub-transducers located in spatially adjacent acoustic stacks and wherein said at least two sub-transducers are electrically connected in parallel by busbars;

(c) said at least two sub-transducers having electrode structures capable of generating and receiving acoustic waves of different frequencies, wherein a centerline of each of said at least two sub-transducers are coincident;

(d) at least one second surface acoustic wave element formed on said piezoelectric substrate and spaced from said first transducer, said at least one second surface acoustic wave element comprising sub-elements equal in number and operating frequency to corresponding ones of said at least two sub-transducers of said first transducer; and

(e) wherein the at least one second surface acoustic wave element is structured such that said sub-elements of said second surface acoustic wave element are spaced at different relative positions along the acoustic tracks from said first transducer, so as to effect different delays within each of said acoustic tracks, thereby effecting a code,

wherein a parameter to be measured affects the acoustic wave propagation within said device.

12. A system for measuring sensed parameters, comprising

(a) a coded surface acoustic wave device, comprising

(i) a piezoelectric substrate;

(ii) at least one first transducer arranged on at least a portion of said piezoelectric substrate wherein said transducer includes at least two sub-transducers located in spatially adjacent acoustic channels and wherein said at least two sub-transducers are electrically connected in parallel by busbars;

(iii) said at least two sub-transducers having electrode structures capable of generating and receiving acoustic waves of different frequencies, wherein centerlines of said at least two sub-transducers are spatially offset from one another so as to effect a code;

(iv) at least one second surface acoustic wave element formed on said piezoelectric substrate and spaced from said first transducer, said at least one second surface acoustic wave element comprising sub-elements equal in number and operating frequency to the corresponding sub-transducers of the first transducer; and

(iv) wherein the at least one second surface acoustic wave element is structured such that the centerlines of the sub-elements of the second surface acoustic wave element are coincident.

(b) an interrogator which transmits an interrogating signal to said sensor and receives the response signal from said sensor, said interrogator including

(1) a voltage source for providing the interrogating signal;

(2) a communicating device for transmitting the interrogating signal to said sensor and for receiving the response signal therefrom; and

(3) a signal processor for converting the response signal into a metric corresponding to the measured parameter.

13. A system as defined in claim 12, wherein said communicating device includes at least one antenna for wireless transmission and reception of signals.