| 摘要 |
PURPOSE:To improve a directional characteristic in a wave transmitter and to improve an S/N in a wave receiver in terms of a device provided with a piezoelectric board comprised by forming electrodes its both surfaces by disposing an attenuation member whose attenuation is low in the center and gradually becomes larger in the peripheral direction. CONSTITUTION:The attenuation member 4 of the same wall thickness is stuck to the wave transmitting/receiving surface of the piezoelectric board l. The attenuation member 4 uses an organic base material such as epoxy resin as a carrier 5, and is comprised by mixing a hollow sphere 6 made of fine grains such as a glass ballon and a Silastic ballon. The fine grains increase gradually in the perpheral direction in the hollw sphere 6. Thus an attenuation ratio in the peripheral direction is increased. If the piezoelectric board is used for the wave transmitter, an auxiliary vibration in an auxliary pole drops compared with a main vibration arising in the center in a main pole, and directivity is improved. At the time of receiving an acoustic wave is attenuated on the periphery of the piezoelectric board, and the frequency detection signals from the periphery is reduced, thereby improving the S/N.
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