| 摘要 |
PURPOSE:To digitize variation in measured physical quantity precisely by providing a piezoelectric substrate which is so constituted as to obtain a frequency variation output only at the time of a difference in propagation constant is generated by a thin film, a low-pass filter, an A/D converter, a digital display device, etc. CONSTITUTION:This device is equipped with an exciting oscillator 1, a 180 deg. phase shifter 2, input IDTs 3a and 3b, a physical quantity measuring thin film 5, an output IDT 6, a low-pass filter 7, the A/D converter 8, and the digital display device 9. When the physical quantity measuring thin film 5 is for example a palladium alloy thin film, a gas detector for hydrogen, etc., is formed and when the thin film 5 is a silica gel thin film, etc., a temperature sensor is formed. This device, sends out 180 deg. phase-inverted surface acoustic waves from the input IDTs 3a and 3b and they cancel each other at the output IDT 6, so that no response output signal is generated. If, however, the propagation constant of the thin film 5 varies with the measured physical quantity, an output is obtained in the form of variation in frequency.
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