Customization of the acoustic field produced by a piezoelectric array through interelement delays

Abstract

A method for producing a prescribed acoustic pressure field from a piezoelectric array was investigated. The array consisted of 170 elements placed on the inner surface of a 15 cm radius spherical cap. Each element was independently driven by using individual pulsers each capable of generating 1.2 kV. Acoustic field customization was achieved by independently controlling the time when each element was excited. The set of time delays necessary to produce a particular acoustic field was determined by using an optimization scheme. The acoustic field at the focal plane was simulated by using the angular spectrum method, and the optimization searched for the time delays that minimized the least squared difference between the magnitudes of the simulated and desired pressure fields. The acoustic field was shaped in two different ways: the −6 dB focal width was increased to different desired widths and the ring-shaped pressure distributions of various prescribed diameters were produced. For both cases, the set of delays resulting from the respective optimization schemes were confirmed to yield the desired pressure distributions by using simulations and measurements. The simulations, however, predicted peak positive pressures roughly half those obtained from the measurements, which was attributed to the exclusion of nonlinearity in the simulations.

Linear hydrophone arrays for measurement of shock wave lithotripter acoustic fields

“…5, the initial full-width-half-maximum pressure field beamwidths were in the range of 1.3 mm for the first 500 shots and then increased slowly to around 3 mm towards shot 1,600. The initial lateral beamwidth values agree favorably with previous system measurements [5], but the element spacing (1.25 mm center to center) for HA1 did not provide adequate resolution to fully resolve the beamwidth.…”

“…The waveform displays the characteristic rapid rise and fall in pressure from the PEL shock front with a very slow rise in pressure before the shock front. This slow pressure increase led to a somewhat higher estimate of the 10 to 90% rise time (110 ns) versus that previously measured with a fiber optic hydrophone (30 ns [5]). However, if we look at the 15 to 90% rise time, we obtain a value of 32 ns, which is consistent with the previous measurements.…”

“…The PEL array consisted of 170 elements, each having a surface area of 88 mm 2 , placed on a spherical cap with a radius of curvature of 150 mm and a total aperture of 154 mm (Imasonic S. A., Besancon, France) [5]. The PEL array was driven by a 170-channel high voltage pulser (Gammers Applied Technologies, LLC, Exmore, VA) that permitted each element to be excited individually.…”

Hydrophone arrays for instantaneous measurement of high-pressure acoustic fields

“…Due to the ≈ 1.5 mm lateral beamwidth of the PEL [6], only a few central elements detected a pressure signal. A plot of amplitude versus shock number of the three central elements (10 through 12) is shown in Fig.…”

“…The PEL source was described in [6]. Briefly, the PEL consisted of 170 elements arranged on a spherical cap with a total aperture of 154 mm and a radius of curvature of 150 mm.…”