Differential surface acoustic wave transducer

• US 4,100,811 A
• Filed: 03/18/1977
• Issued: 07/18/1978
• Est. Priority Date: 03/18/1977
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Cullen, Donald E., Reeder, Thomas M.
• Primary Examiner(s): Myracle, Jerry W.
• Application Number:
  US05/779,106
• Time in Patent Office: 487 Days
• Field of Search: 73/71.2, 73/67.5 R, 73/71.4, 73/398 R, 73/67.6, 73/DIG. 4, 73/88 R, 333/30 R, 310/8.1
• US Class Current: 73/654
• CPC Class Codes: G01L 9/0025 with acoustic surface waves
• CPC Class Codes: Y10S 73/04 Piezoelectric

Abstract

A diaphragm formed in a substrate and having a piezoelectric surface includes a first surface acoustic wave (SAW) delay line disposed on said surface and connected in an oscillator circuit for a significant frequency sensitivity to surface strain of said diaphragm, and a second, similar oscillator with the SAW delay line thereof connected for a significant frequency sensitivity to surface strain of the diaphragm opposite in sense to that of the first oscillator, and a mixer for providing the difference in the frequencies of the two oscillators, whereby the overall sensitivity to strain is enhanced, while at the same time the sensitivity to temperature variations is reduced significantly through subtractive combination.

Claims

1. A differential surface acoustic wave transducer for measuring a parameter, the effects of which induce strain in a piezoelectric diaphragm, the combination with said diaphragm, comprising:

a plurality of surface acoustic wave delay lines disposed on a single surface of said diaphragm at positions thereon which provide substantial control over the wave propagation velocity of the surface acoustic wave in each delay line, the sense of said control in one of said delay lines being opposite to the sense of said control in another of said delay lines;

a plurality of amplifiers, one for each of said delay lines, each having an input and an output, each of said delay lines connected from the output of a corresponding one of said amplifiers to the input thereof in feedback relationship so as to form an oscillator, the output of which is at a natural frequency of the related one of said delay lines and varies as a function of strain in said diaphragm in a manner opposite to another one of said oscillators; and

means for mixing the outputs of said oscillators to provide a difference frequency which is a function of the response of all of said delay lines to the strain in said diaphragm.

2. A differential surface acoustic wave oscillator for measuring a parameter capable of inducing strain, comprising:

a piezoelectric diaphragm having a principal surface;

a pair of oscillators, each of said oscillators including an amplifier and a surface acoustic wave delay line connected in feedback relation with said amplifier, said delay lines formed at respective portions of said surface so that each of said oscillators has a frequence dependent on strain of the related portion of said diaphragm which is opposite in sense to that of the other of said oscillators; and

mixing means for providing as an output of said transducer the frequency difference between said oscillators, whereby the sensitivity of said transducer to strain is greater than that of either of said oscillators and the sensitivity in frequency of each of said oscillators to temperature is substantially canceled by said mixing means.