Optimization of buffer rod geometry for ultrasonic sensors with reference path.

Several applications of ultrasonic techniques are limited by the signal-to-noise ratio (SNR). Transducers in these applications usually operate in the pulse-echo mode. Many transducers, especially those for high temperatures, use buffer rods. Often a reference path is used to eliminate electrical and transducer drift. Interference of echo signals and noise causes errors of both amplitude and phase measurement of the detected echoes. In this paper we discuss the influence of major noise sources as a function of geometry and operating environment. The effects are studied using both experimental results and models. Although the results are applied to an ultrasonic density sensor operating in the pulse-echo mode, they are applicable to other pulse-echo mode transducers comprising homogeneous cylindrical buffer rods. This paper will show how the SNR of the density transducer was improved in a special time window from 34 to 72 dB by careful design.