### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 4pEA9. Some second thoughts on electromechanical coupling.

**Li-Feng Ge
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*Anhui Bureau of Tech. Supervision, 30 Ma An Shan Rd., Hefei, Anhui 230001,
People's Republic of China
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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.