Low noise design of ultrasonic transducers

Several industrial applications of ultrasonic techniques are limited by the signal-to-noise ratio (SNR). Examples include NDE or process monitoring. Transducers in these applications usually operate in the pulse-echo mode. Several transducers, especially those for high temperatures, use buffer rods. Interference of echo signal and noise causes errors of both amplitude and phase measurement of the detected echoes. This work aims to discuss the influence of major noise sources as a function of transducer materials, geometry, construction and operating environment. The effects are studied with the help of both experiments and models. The results are applied to an ultrasonic density sensor operating in the pulse-echo mode, however are applicable to any pulse-echo mode transducer comprising cylindrical buffer rods. The paper shows how the SNR of the density transducer was improved by careful design to 72 dB.