Hydrophone arrays for instantaneous measurement of high-pressure acoustic fields

Electrohydraulic lithotripter acoustic fields are measured with single-element hydrophones even though the acoustic fields are not highly repeatable. The ability to obtain an instantaneous "snapshot" of the sound field would have broad implications for advancing the understanding of how lithotripters fragment stones and damage kidney tissue. To better characterize the acoustic field of lithotripters, linear hydrophone arrays were fabricated by bonding a 9 μm piezopolymer film to a copper-clad polyimide which had an array pattern etched on the copper layer. After bonding, the devices were backed with an epoxy plug in order to provide structural support. The array elements were each 0.5 by 0.5 mm, spaced 1.25 mm center to center, and there were 20 elements. The relative sensitivity of each hydrophone element was measured at 5.25 MHz for an acoustic pressure of 4.5 kPa and the elements were found to vary by ≈ 6%. The arrays were then placed in the focus of a piezoelectric lithotripter and were found to maintain their sensitivity for roughly 500 shock waves before gradually losing sensitivity. © 2010 American Institute of Physics

Linear hydrophone arrays for measurement of shock wave lithotripter acoustic fields

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 μm 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. ©2009 IEEE

Instantaneous beamwidth measurements of an electrohydraulic lithotripter

Acoustic field measurements of electrohydraulic lithotripters (EHL) aretypically conducted with single-element hydrophones and are subject to spatialaveraging errors because the spark source location varies from shock to shock.Linear hydrophone arrays provide a means of obtaining the instantaneous soundfield of EHLs and a more detailed understanding of EHL sound fields. Here,20-element hydrophone arrays were used to study the variability of theinstantaneous acoustic field of an experimental EHL. Calibrated arrays wereplaced at the geometric focus of an EHL and exposed to as many as 1500 shockwaves using excitations of 14, 17 and 20 kV. Instantaneous data were acquiredfrom all 20 hydrophone elements and then were processed for beamwidth, peakpressure location, and peak pressure. Instantaneous beamwidths were found to besmaller than when using a single-element hydrophone approach and peak pressureswere observed to vary more as the excitation voltage increased. © 2010IEEE

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

Piezopolymer-based hydrophone arrays consisting of 20 elements were fabricated and tested for use in measuring the acoustic field from a shock-wave lithotripter. The arrays were fabricated from piezopolymer films and were mounted in a housing to allow submersion into water. The motivation was to use the array to determine how the shot-to-shot variability of the spark discharge in an electrohydraulic lithotripter affects the resulting focused acoustic field. It was found that the dominant effect of shot-to-shot variability was to laterally shift the location of the focus by up to 5 mm from the nominal acoustic axis of the lithotripter. The effect was more pronounced when the spark discharge was initiated with higher voltages. The lateral beamwidth of individual, instantaneous shock waves were observed to range from 1.5 mm to 24 mm. Due to the spatial variation of the acoustic field, the average of instantaneous beamwidths were observed to be 1 to 2 mm narrower than beamwidths determined from traditional single-point measurements that average the pressure measured at each location before computing beamwidth

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

Piezopolymer-based hydrophone arrays consisting of 20 elements were fabricated and tested for use in measuring the acoustic field from a shock-wave lithotripter. The arrays were fabricated from piezopolymer films and were mounted in a housing to allow submersion into water. The motivation was to use the array to determine how the shot-to-shot variability of the spark discharge in an electrohydraulic lithotripter affects the resulting focused acoustic field. It was found that the dominant effect of shot-to-shot variability was to laterally shift the location of the focus by up to 5 mm from the nominal acoustic axis of the lithotripter. The effect was more pronounced when the spark discharge was initiated with higher voltages. The lateral beamwidth of individual, instantaneous shock waves were observed to range from 1.5 mm to 24 mm. Due to the spatial variation of the acoustic field, the average of instantaneous beamwidths were observed to be 1 to 2 mm narrower than beamwidths determined from traditional single-point measurements that average the pressure measured at each location before computing beamwidth

Inside a micro-reactor

Gas bubbles in a liquid can convert sound energy into light. Detailed\ud measurements of a single bubble show that, in fact, most of the sound\ud energy goes into chemical reactions taking place inside this 'micro-reactor'

Circuits and systems for biosensing with microultrasound

Ultrasound imaging is a well-established, noninvasive imaging modality used in many clinical procedures. New developments in high-resolution microultrasound are well suited to biosensing, including applications such as material characterisation, biometrics and chemical sensing. Electronic system design for ultrasound and microultrasound is most commonly associated with the use of piezoelectric transducers to generate and sense the ultrasonic pressure waves. This chapter covers the basics of ultrasound physics and piezoelectric transducers as well as their context within the larger field of biosensing. An example of an ultrasound imaging system is presented, and the availability and suitability of commercial solutions are discussed in comparison to individual approaches seen in the research domain. Finally, possible variations in ultrasound device characteristics are discussed, and the impact of these and overall system concerns on ASIC development is considered