Absolute Ultrasonic Measurements with Piezoelectric Transducers

The absolute calibration of a piezoelectric transducer refers to the determination of the relationship between the electrical and acoustical quantities for a transducer coupled to a solid. It is shown how a well-characterized ultrasonic system, consisting of source,structure and receiver can be used to make such measurements for transducers operating as sources or receivers. Results are given, showing the effects of coupling between transducer and solid and the electrical characteristics of the associated source and receiver electronics. This poster paper describes the principles and procedures for making absolute ultra·sonic measurements with a piezoelectric transducer coupled to a solid. Publication of these results will be in the 1979 Ultrasonics Symposium Proceedings [1]. As described in a recent review article [2], the complete characterization of an ultrasonic transducer acting as source or receiver entails two parts. One part deals with the tranduction process in which the relationship between electrical and mechanical quantities is established. The second deals with the characterization of the radiation field of the transducer. This paper concerns itself with measurements which characterize the transduction process of a piezoelectric transducer coupled to a solid. INTRODUCTION As elaborated in the review article by Sachse and Hsu [2], several assumptions need to be made in order to permit a ready characterization of the transduction process. As shown in Figure 1, a transducer operating as a source may involve processes which are not well understood or difficult to describe precisely. The excitation voltaqe and current imposed on a transducer result in a complicated distribution of time-dependent surface tractions and displacements (or velocities) each with longitudinal and shear components, acting over the transducer area on the specimen. Only when one makes the simplifying assumptions of mode uncoupling, field variable independency and linear system response does one find a simple matrix relationship between the electrical excitation parameters and the resulting mechanical excitation. Then, wtien restricted to a fixed specimen and electronics can a relationship between electrical excitation and produced mechanical force be written in terms of a linear transfer function equation in either the timeor frequency-domains,