Transmission circuits for thick-transducer ultrasound transmission test systems

Pulse techniques for the measurement of ultrasonic absorption over a wide frequency bandwidth are limited by the narrow band nature of conventional piezoelectric transducers. This problem can be overcome if the piezoelectric devices are operated as thick elements. In this paper the insertion characteristics of transducers operating in this mode are determined. The compromise between system sensitivity, bandwidth and noise generation in receiving circuits is examined.It is shown that high voltage generators with rise times of a few nanoseconds are required to drive thick transmission transducers. The design of suitable generators, based on avalanche operation of one or more bipolar transistors is described in detail. It is concluded that exciting signals of sufficient amplitude and short enough rise-time could be generated for absorption measurements to be made over at least two decades of frequency with a dynamic range of 100 dB without a change of transducer.