Approach to characterize the sound field of pulse-excited ultrasonic sensors using a Laser-Doppler vibrometer

A new efficient approach to make visible sound fields in front of acoustic sensors in liquids will be presented. The goal is to investigate the sound field characteristic of real manufactured acoustic transmitters particularly by discontinuous excitation like pulse, burst, and other. Another point is the analysis of the influence of materials and sensor design on the final acoustic behavior. In comparison to the Schlieren technique it is possible to use moderate excitation of transmitters (only a few volts) and more variable signal shapes too. The experimental setup consists of a Laser Doppler vibrometer and a high-resolution three-dimensional positioning system. The control of the positioning system as well as the data acquisition and processing will be fully automatic realized by a personal computer. A software tool archives the data and calculates the complex sound field characteristic in dependence on time or place. The result is an interesting animation representing the real sound field characteristic of acoustic sensors. The advantages and limits of the approach and developed experimental setup will be described. Some examples will show the sound fields in front of cylindrical focusing transmitters. The influence of different excitation signal shapes on the final sound field will be discussed.