A Study on Propagation of Monopole Ultrasonic Pulse by Simulation and Experiment

Abstract

The shock wave or intense impulsive acoustic wave generated by an explosion, whether in air or in water, can produce unexpected lesions on the human body. Short monopole or impulsive-like ultrasonic pulses have a fast rise and are similar to a shock wave generated by an explosion. Investigation of the propagation of the monopole ultrasonic pulse in a lossy medium would be basic research for clarifing where the problems lie. In this study, we investigate the sound field of the monopole ultrasonic pulse in degassed water and glycerine by simulation and experiment, as well as its mechanism and effect in a lossy medium. The results show that waveform changed from a monopole to a dipole owing to a diffraction loss as the pulse transmitted in the medium, the amplitude of a received pulse was decreased considerably in glycerine by the large absorption, and also the rise of the amplitude was more gradual owing to the reduction of high-frequency components. A short monopole ultrasonic pulse will approach a shock wave if the wave propagates as a plane wave because the pulse remains impulsive. As a monopole ultrasonic pulse radiated from a small source is transmitted, a negative pressure grows, and its action on a medium per unit time will weaken owing to the large absorption of the transmission medium.