ANALYSIS OF HARMONIC DISTORTION IN ELECTROACOUSTIC TRANSDUCERS UNDER INDIRECT DRIVE CONDITIONS

Nonlinear transducer equations for the six major types of electroacous tic transducers (electrostatic, variable reluctance, moving coil, piez oelectric, electrostrictive, and magnetostrictive) are formulated in a common way and solved approximately by perturbation analysis for indi rect drive, i.e., current drive of electric field transducers and volt age drive of magnetic field transducers. The direct drive analysis, i. e., voltage drive of electric field transducers and current drive of m agnetic field transducers, was given in J. Acoust. Sec. Am. 98, 1596-1 611 (1995). Expressions and graphs are given for some of the indirect drive harmonics which apply to all six transducer types. The solutions for direct and indirect drive are compared, and some of the differenc es are discussed with emphasis on the question of which drive gives lo wer harmonic distortion. No answer to this question has been found tha t is applicable to all nonlinear mechanisms in all transducers at all frequencies. However, it is shown that for transducers of all types wi th low electrical loss operated near resonance direct drive usually gi ves lower second harmonics. The exceptions occur when mechanical sprin gs are the dominant nonlinearity and the electromechanical coupling is very high; then indirect drive gives lower second harmonics. It is sh own how the results, although based on simple lumped parameter models, can be applied in some cases to more complex transducer structures. ( C) 1997 Acoustical Society of America.