Acoustic Design of a Transducer Array for Ultrasonic Clamp-on Flow Metering

Abstract

Current ultrasonic clamp-on flow meters are based on single-element transducers that require manual calibration by aligning these to a fixed acoustic path. Moreover, the size and operational frequency of the transducers cannot be adapted to the parameters of the pipe and the liquid, which are in practice not precisely known a priory. A set of two transducer arrays could be used to solve these issues. With an array, properties of the pipe and the liquid can be estimated before measuring flow. Furthermore, electronic beam steering can be used for auto-alignment of the acoustic beam, reducing the need for manual calibration. Moreover, an array allows for the use of signal processing to suppress the effects of spurious Lamb waves propagating in the pipe wall. This research work describes the acoustic design process of a transducer array for ultrasonic clamp-on flow measurements for a wide range of conditions. First, performance requirements are defined. Then, the design models are presented, and a step by step process of the acoustic stack design of the transducer array is described. At each design step, material dimensions are optimized to achieve a thickness resonance mode at 1 MHz within a bandwidth of interest between 0.2 MHz and 2 MHz. Finally, the expected performance of the designed array is reported, based on simulation results.