Comparisson of different microphone arrays for signal processing of air-ultrasonic signals in nondestructive testing

Acoustic cameras consist of an array of microphones with well-defined positions, which receive individual sound signals. They provide real-time acoustic images after reconstruction mostly based on beamforming algorithms. In the work presented here, we transfer this technique to the ultrasonic frequency range. In the first step we examine different microphone configurations for localization of air ultrasonic sound sources. Afterwards we use a one-microphone-method to build a synthetic microphone array and reconstruct the source from the ultrasonic signals received by one transducer. With the help of this method, it is possible to evaluate the recorded signals with different microphone arrangements, by just performing one area scan. The spatial resolution and dynamic range of the array are investigated as a function of array-source distance and microphone arrangement. Furthermore, the reconstruction results are compared with simulations.