Overview

Electrical and acoustical measurements are made on transducers to determine performance characteristics and parameters for comparison with goals and theoretical models when the latter are available. In this chapter we discuss the procedures and means for making such measurements [1 10]. Admittance or impedance measurements are normally made first under air loading (which simulates a vacuum) and then under water loading, often at various hydrostatic pressures, temperatures, and drive levels. Measurements of the transmitting response, source level, efficiency, receiving response, beam patterns, and harmonic distortion of transducers and transducer arrays are usually made in the far field, where spherical spreading holds. However, in some cases measurements can be made in the near field and projected to the far field through extrapolation formulas. Measurement is the important final step in evaluating the performance of all transducers.

This chapter also discusses means for evaluating the important transducer parameters Q _m, fr, and k _eff and the lumped elements for a simple equivalent circuit representation, including resistances caused by electrical and mechanical dissipation. The tuning of a transducer is an important last step in its implementation, since the tuning element improves the power factor and reduces volt-ampere requirements in service and during high-power testing. The transmitting and receiving responses, as well as the admittance and impedance curves, are discussed for both electric and magnetic field transducers as a guide for evaluating measured results. A development of the reciprocity relation between transmitting and receiving is also presented. Specific projector and hydrophone designs...