Anhui Bureau of Tech. Supervision, 30 Ma An Shan Rd., Hefei, Anhui 230001, People's Republic of China
An electromechanical transducer can be regarded as an energy converter, and also as an impedance inverter. It could be significant for understanding the transduction process to introduce a new generalized concept, inversive impedance, which is defined as a ratio of the open-circuited voltage caused by a motion at the mechanical end of a transducer to the exciting current required to produce the same motion, i.e., a ratio of the receiving (voltage) sensitivity of a transducer to its sending (current) sensitivity. Thus the electrical driving-point impedance is composed of an impedance without coupling and a inversive impedance, which is induced by electromechanical coupling, and is constant at a given frequency for a particular transducer. The transduction process or the impedance inversion process can be described by only three independent parameters [L.-F. Ge, J. Acoust. Soc. Am. 91, 2326 (A) (1992)], and determined uniquely by a mapping between the electrical driving-point impedance and its mechanical load impedance. It is an inherent physical property independent of analogy-type chosen and mathematical representation that a piezoelectric-type transducer is reciprocal, and an electrodynamic-type transducer is antireciprocal. Thus there exists, respectively, an optimum way to perform reciprocity calibration for the two types of electromechanical transducers.