Linear hydrophone arrays for measurement of shock wave lithotripter acoustic fields

Abstract

Lithotripter acoustic field characterization is based on single-element hydrophone measurements even though many clinical lithotripters do not have highly repeatable sound fields. Here, linear hydrophone arrays composed of 20 elements, each measuring 0.5 by 0.5 mm and spaced 1.25 mm center to center, are described and characterized. The arrays were fabricated by bonding a 9 m piezopolymer film to a flex circuit on which an array pattern had been formed using standard printed circuit board etching techniques. After bonding, the devices were backed with an epoxy plug in order to provide structural support. The sensitivity of each hydrophone element was measured at 41 mm axial distance with a pressure of 4.5 kPa using a 5.25 MHz, 14-cycle tone burst. The resulting sensitivities were normalized across each array. The normalized RMS voltages were quite uniform across each array, and between arrays, with an ≈ 6% variation in voltage. The arrays were also placed in a piezoelectric lithotripter in order to determine the shot-to-shot repeatability for peak positive pressures of 60 MPa. The array elements withstood about 500 shock waves before slowly losing sensitivity.

Single-shot measurements of the acoustic field of an electrohydraulic lithotripter using a hydrophone array

“…Finally, the trace lines on the CCP were covered with a thick layer of adhesive tape to ensure insulation from water and reduce electrical noise. Unlike earlier versions of the hydrophone array, 19 an epoxy backing-plug was not bonded to the CCP behind the array elements. This was done to avoid hard edges that could cause acoustic scattering near hydrophone elements and also simplified the fabrication process.…”

“…Here, we present improvements to a hydrophone array described initially by Kreider et al 18 with further refinements discussed by Ketterling et al 19 The arrays were composed of a piezopolymer film bonded to a copper-clad polyimide substrate. The substrate had the array elements and electrical trace lines etched onto its surface.…”

Multiple-frequency calibration of two-dimensional hydrophone arrays for instantaneous beam width measurements of shock-wave lithotripters

“…The hydrophone arrays were fabricated using a technique similar to that described in [2], [5], [6]. The hydrophones were constructed by bonding a 9 µm polyvinylidene fluoride (PVDF) film to a copper-clad-polyimide (CCP) film with a non-conductive epoxy (Fig.…”