| 摘要 |
PURPOSE:To improve a directional characteristic in a wave transmitter and to improve an S/N in a wave receiver by making the electric resistasnce value of a piezoelectric board used by a piezoelectric wave transmitter-receiver lower in the center and higher gradually in the peripheral direction and highly polarizing the center compared with the periphery. CONSTITUTION:Resistance electrodes 2 and 3 formed on both surfaces of a piezoelectric substrate are comprised with a disk-like central electrode piece 4 and plural circular electrode pieces 5a-5c sequentailly surrounding the electrode. The resistance is so distributed that the electrical resistance value of the central electrode piece 4 can be minimum and the resistance values of the circular electrode pieces San 5c gradually increase toward their peripheries. Synthetic rubber is used for a base material, and the quantity of silver powder mixed with the rubber is adjusted, whereby the resistance values of the electrode pieces 4 and 5a-5c can be selected. As a result high polarization is made in the center of the substrate l, and its polarization degree sequentially drops in the peripheral direction. Accordingly a signal voltage can be satisfactorily picked up from the center, and a wave transmission and reception ratio in a main pole can be improved compared with an auxiliary pole.
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