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

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

Fabrication and characterization of annular-array, high-frequency, ultrasonic transducers based on PZT thick film

In this work, low temperature deposition of ceramics, in combination with micromachining techniques have been used to fabricate a kerfed, annular-array, high-frequency, micro ultrasonic transducer (with seven elements). This transducer was based on PZT thick film and operated in thickness mode. The 27 μm thick PZT film was fabricated using a low temperature (720 °C) composite sol-gel ceramic (sol + ceramic powder) deposition technique. Chemical wet etching was used to pattern the PZT thick film to produce the annular array ultrasonic transducer with a kerf of 90 μm between rings. A 67 MHz parallel resonant frequency in air was obtained. Pulse-echo responses were measured in water, showing that this device was able to operate in water medium. The resonance frequency and pulse-echo response have shown the frequency response presented additional resonance mode, which were due to the lateral modes induced by the small width-to-height ratios, especially for peripheral rings. A hybrid finite-difference (FD) and pseudospectral time-domain (PSTD) method (FD-PSTD) was used to simulate the acoustic field characteristics of two types of annular devices. One has no physical separation of the rings while the other has 90 μm kerf between each ring. The results show that the kerfed annular-array device has higher sensitivity than the kerfless one

Lead-free high-frequency linear-array transducer (30 MHz) for in vivo skin imaging

International audience— This work presents the fabrication of a 30 MHz, linear-array transducer based on a KN, 1-3 piezocomposite. Performances of the transducer were characterized and compared to a PZT-based linear array with similar structure. The composites were designed to minimize lateral modes of vibration which can severely degrade imaging performances. Fabrication steps were optimized to achieve a 40 MHz resonant frequency in air with a composite thickness of 69 microns. The measured thickness coupling factor was around 50 %. A 128-element, linear array was then fabricated with 100 m pitch and 1,5 mm elevation aperture. The structure of the transducer (backing, matching layers, and electric components) was optimized to deliver good fractional bandwidth and sensitivity. The final probe was integrated in a prototype, real-time, 128-channel scanner to acquire high-resolution images of the human skin in vivo. Results showed that, compared to PZT ceramics, KN single crystals provide low density and high acoustic velocity, both highly desirable for the manufacturing of HF transducers. The central frequency of the linear-array transducer was 30 MHz despite the KN composite being 20% thicker than equivalent PZT-based composites and the relative bandwidth was about 50%. High-resolution images of the human skin were acquired. A large ultrasound penetration due to good signal sensitivity was obtained and detailed features could be visualized