Experimental mapping of the acoustic field generated by ultrasonic transducers

Abstract

In recent years, a laboratory noncontact excitation method based on the focused ultrasound radiation force, generated by an ultrasonic transducer has been exploited to excite vibrations within structures with size ranging from the micro to macro scale. The excitation frequency has a range from a few kHz to 1 MHz and can potentially be used for modal testing. However, the inability to monitor the real time acoustic radiation force prevents this approach from being used as a practical technique for measuring the frequency response functions in modal testing. This work deals with understanding the acoustic field generated from ultrasonic transducers in order to monitor and control the acoustic radiation pressure and force imparted to a structure. In this paper, the acoustic field generated by circular ultrasonic transducers was calculated based on the Rayleigh Integral and a boundary element method. The vibration velocity distribution of the vibration surface of an ultrasonic transducer at certain frequencies was measured, linearly interpolated, and mapped to the radially discretized elements of transducer surface, which was then used to map the acoustic pressure generated. A microphone array was built to measure the frequency response functions (FRFs) of acoustic pressure with respect to the drive voltage at several spatial locations within three vertical and one horizontal planes in front of the transducer. The comparison between the simulation results and experimental results is presented and shows good agreement.