Design of matching networks transducers

Underwater acoustic transducers convert electrical signals into the longitudinal pressure waves constituting acoustic propagation in water. The mechanical construction of most acoustic transducers (excluding those broad-band receiver transducers known as hydrophones) usually results in narrow-band devices. For example, many projector transducers employed in power drive applications are a development of a construction principle known as the Langevin resonator’, in which an active piezoelectric drive crystal is sandwiched between metal end masses. This design method, illustrated in idealized form in Figure I, allows fabrication of relatively cheap and very robust acoustic projectors. A common design ploy is to couple acoustic radiation into the water load through one radiating end face, the other end of the transducer being effectively airbacked and thus unable to radiate significantly. Since there will typically be a considerable mismatch between the acoustic impedance of the radiating end mass ( z 15 x lo6 Rayl*) and that of the water load ( z 1.5 x lo6 Rayl) only a relatively small fraction of the acoustic energy stored per half cycle ‘leaks’ into the water load. The transducer thus rings sustainedly as a bell rings when struck. It follows that the transducer quality factor, Q, is high. Its bandwidth, as a fraction of its fundamental resonance frequency, fO, is small and its transfer function is of simple Lorentzian form, obeying the law