An Experimental Method for Characterizing Ultrasonic Transducers
It is well known that linear systems, when described through convenient variables, exhibit symmetrical properties in their matricial internal relations which may be interpreted in terms of reciprocal physical properties. For example, the efficiency of an emitting transducer may be related to its receiving transfer function. These symmetrical properties are in fact of thermodynamical origin and an in-depth view shows that they are related to Maxwell relations for conservative systems and both to Maxwell and Onsager relations for dissipative systems. We want here to recall briefly the rules for choosing adequate variables, giving the simple example of the unidimensional piston-like transducer. Afterwards, an extension will be given for a complex real transducer and we shall show that through the obtained symmetrical relations, it is possible to elaborate an experimental procedure permitting to obtain the complete description of the transducer as an emitter or as a receiver at any frequency, taking in account both its electrical and mechanical environments. This procedure may be of special interest for the study of the elementary transducer included in a linear or a matricial array used in acoustical imaging. A detailed illustration of the case of the linear array is given here.
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