Piezoelectric electroacoustic transducer for telephone instruments - has oscillating diaphragm surface partially covered with piezoelectric material and nodal line thickness depending on resonance point

摘要

The pickup has a diaphragm provided with a layer of piezoelectric material on at least a part of its oscillating surface. Mechanical oscillation conditions determined by its shape and kind of its fastening produce at least one resonant point in the frequency range of interest. The layer of piezoelectric material has nodal lines of different thickness or polarisation, depending on position of the resonance point, or at least one of the resonant points. The degree of polarisation, which varies according to position, is produced by large, and/or variable plus and minus polarisation voltages, which are applied via corresponding selected electrode zones (1-9). The chosen electrode zones (2-9) are electrically interconnected when the transducer is working.