Absolute ultrasonic displacement amplitude measurements with a submersible electrostatic acoustic transducer

An experimental technique for absolute measurement of ultrasonic wave particle displacement amplitudes in liquids is reported. The technique is capable of measurements over a frequency range of two decades with a sensitivity less than one angstrom. The technique utilizes a previously reported submersible electrostatic acoustic transducer (ESAT) [Rev. Sci. Instrum. 50, 31 (1979)] featuring a conductive membrane stretched over a recessed electrode. An uncertainty analysis shows that the displacement amplitude of an ultrasonic plane wave incident on the ESAT can be experimentally determined to better than 2.3%–4%, depending on frequency, in the frequency range of 0.5–15 MHz. Membranes with lower and more uniform areal densities can improve the accuracy and extend the operation to higher frequencies.