ACOUSTIC DELAY SURFACE WAVE MOTION TRANSDUCERS

• US 3,863,497 A
• Filed: 10/24/1972
• Issued: 02/04/1975
• Est. Priority Date: 10/24/1972
• Status: Expired due to Term

• Current Assignee: Herman Van De Vaart, Hugh B. Matthews, James C. Worley
• Original Assignee: Herman Van De Vaart, Hugh B. Matthews, James C. Worley
• Inventors: Matthews, Hugh B., Worley, James C., van de Vaart, Herman
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Beauchamp, John P.
• Application Number:
  US05/300,034
• Time in Patent Office: 833 Days
• Field of Search: 73/67.5R,67.6,71.2,71.4,517R,408,141A
• US Class Current: 73/654
• CPC Class Codes: G01L 1/165 with acoustic surface waves
• CPC Class Codes: G01P 15/0975 by acoustic surface wave resonators or delay lines

Abstract

Transducer device employing relative changes in the acoustic propagation characteristics of waves of the Rayleigh type flowing at a polished surface of a thin elastic member yield a measure of the degree of flexing of the elastic member, which latter may take the form, for instance, of a cantilever clamped at one end. Applications such as to strain or displacement gages and to accelerometers are provided.

Claims

1. Transducer means comprising:

elongate cantilever flexure means having first and second ends and a flexible surface layer adapted to propagate acoustic waves, exciter means for exciting and propagating said acoustic waves along a predetermined path at said flexible surface layer, receiver means along said path for receiving and converting said acoustic waves into electrical signals, signal generator means for driving said exciter means, and signal processing circuit means responsive to said signal generator means and to said receiver means for deriving a measure of the flexure of said flexure means.

2. Apparatus as described in claim 1 wherein said first end is clamped with respect to base means.

3. Apparatus as described in claim 2 wherein said second end is free to move substantially at right angles to said elongate cantilever means, said end having one degree of freedom of motion.

4. Apparatus as described in claim 3 wherein said second end has seismic mass means affixed thereto.

5. Apparatus as described in claim 2 wherein said exciter means is disposed on said surface layer at said first end adjacent said base means.

6. Apparatus as described in claim 2 wherein said receiver means is disposed on said surface layer means at said second end.

7. Apparatus as described in claim 1 wherein:

said signal generator means comprises periodic wave oscillator means, said signal processing circuit means comprises phase shift circuit means for determining the normal frequency of oscillation of said periodic wave oscillator means, and said phase shift circuit means is responsive to said receiver means for varying the frequency of said periodic wave oscillator means.

8. Apparatus as described in claim 1 wherein:

said signal generator means comprises periodic wave oscillator means, and said signal processing circuit means comprises phase detector means responsive to said periodic wave oscillator means and to said receiver means.

9. Apparatus as described in claim 1 wherein:

said signal generator means comprises pulse generator means, and said signal processing circuit means comprises pulse interval detection means responsive to said pulse generator means and to said receiver means.

10. Apparatus as described in claim 1 wherein:

said exciter means comprises first and second cooperative digital electrode means disposed in interdigital surface wave generating relation at said flexible surface layer, said electrode means having parallel digital fingers disposed in parallel array relation at right angles to said predetermined path.

11. Apparatus as described in claim 1 wherein:

said receiver means comprises first and second cooperative digital electrode means disposed in interdigital surface wave receiving relation at said flexible surface layer, said electrode means having parallel digital fingers disposed in parallel array relation at right angles to said predetermined path.

12. Apparatus as described in claim 1 additionally including:

reflector means at said flexible surface layer at said second end, said exciter means and said receiver means being disposed in side-by-side relation at said flexible surface layer means at said first end, said reflector means causing acoustic waves propagated by said exciter means toward it to be re-directed for conversion within said receiver means.

13. Apparatus as described in claim 12 wherein said reflector means comprises discontinuity means penetrating at least a major fraction of one wave length into said flexible surface layer at the carrier frequency of said acoustic wave.

14. Apparatus as described in claim 12 wherein:

said reflector means comprises vee-shaped discontinuity means having first and second portions, said first portion causing said acoustic waves to be directed toward said second portion, and said second portion causing said acoustic waves to be directed toward said exciter means.

15. Transducer means comprising:

elongate cantilever flexure means having a flexible surface layer adapted to propagate acoustic waves and having first and second ends, exciter means for exciting and propagating said acoustic waves along a predetermined path at said flexible surface layer, receiver means along said path for receiving and converting said acoustic waves into electrical signals, signal generator means for driving said exciter means, and signal processing circuit means responsive to said signal generator means and to said receiver means for deriving a measure of the flexure of said flexure means, said flexure means being composed of quartz so cut as to demonstrate a substantially zero temperature coefficient of surface wave propagation velocity at room temperature.

16. Transducer means comprising:

cantilever flexure means having first and second opposed flexible surface layer means for separately propagating respective acoustic waves along first and second respective predetermined paths therein, first and second exciter means for exciting and propagating said respective acoustic waves along said respective predetermined paths, first and second receiver means along said respective predetermined paths for receiving and converting said acoustic waves into electric signals, signal generator means comprising first and second feed back oscillator means respectively in feed back relation with said respective first and second receiver means for independently driving said respective first and second exciter means, and signal processing circuit means responsive to said signal generator means and to said first and second receiver means for deriving a measure of the flexure of said flexure means.

17. Apparatus as described in claim 16 further including mixer means responsive to said first and second receiver means.

18. Transducer means comprising:

flexure diaphram means forming a wall of a pressure vessel and having a flexible surface layer adapted to propagate acoustic waves, exciter means for exciting and propagating said acoustic waves along a predetermined path at said flexible surface layer, receiver means along said path for receiving and converting said acoustic waves into electrical signals, signal generator means for driving said exciter means, and signal processing circuit means responsive to said signal generator means and to said receiver means for deriving a measure of the flexure of said flexure diaphram means.