| 摘要 |
A piezo-electric element (12) with its electrodes (12a,12b) is firmly fixed to the inner surface of an upper plate (11a) of a cylindrical casing (11). The plate is made of a porous plastic material and has a lateral cylindrical wall (11b). The wall is surrounded by a metallic tube (18) which has a slot parallel to the axial axis. This has an acoustic impedance greater than that of the upper plate, with the assembly ensuring damping of oscillations on the sides of the oscillation chamber. The chamber is enclosed by a cover (13) which itself is covered by an isolating layer (16) through which electrode connections are made by pins (14a,14b) and lead wires.
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