| 摘要 |
PURPOSE:To enable the measurement of a short distance by providing a circular groove part so that it surrounds the surface of a protecting case whereon a piezoelectric element is joined and by disposing a vibration proof elastic substance in said groove part. CONSTITUTION:A circular groove part 3 is provided so that it surrounds the surface of a protecting case 2 whereon a piezoelectric element 1 is joined, and a vibration proof elastic substance 4 is disposed in said grove part 3. By this constitution, vibrations of the surface of the case 2 whereon the element 1 is joined are absorbed by the groove part 3 surrounding this surface and by the elastic substance 4 disposed in said groove part 3, and consequently they are hardly transmitted to the other part of the case 2. Accordingly, reverberation is reduced and the measurement of a short distance is enabled.
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