Comparison of Interferometric Ultrasonic Field Measurements in Fluids to Finite Element Sound Field Simulations

摘要

We presented two methodologies using laser interferometry, where the output is the sound pressure distribution. One measures optical path length changes induced by the sound pressure and computes sound pressure values through computed tomography algorithms. The second one uses finite element sound field calculations with the transducer surface vibration distribution as boundary condition. Both achieve comparable results to hydrophone measurements at the chosen operating frequency. Further research has to be conducted to fully benefit from the generally high sensitivity of laser vibrometers. Only then an advantage to hydrophones can be achieved, especially in the upper MHz-range (>20 MHz). Usually those instruments are optimized for applications in the kHz-range and upper oscillation amplitudes up to cm/s and m/s. Ultrasonic applications are in the MHz-range and velocity amplitudes are in the low mm/s. The wavelength of the Helium-Neon laser installed in laser vibrometers is significantly attenuated in water, hence optical path lengths in water are limited to less than one meter.