Jianhua Yin

Performance and Characterization of New Micromachined High-Frequency Linear Arrays

A new approach for fabricating high frequency (>20 MHz) linear array transducers, based on laser micromachining, has been developed. A 30 MHz, 64-element, 74-mum pitch, linear array design is presented. The performance of the device is demonstrated by comparing electrical and acoustic measurements with analytical, equivalent circuit, and finite-element analysis (FEA) simulations. All FEA results for array performance have been generated using one global set of material parameters. Each fabricated array has been integrated onto a flex circuit for case of handling, and the flex has been integrated onto a custom printed circuit board test card for ease of testing. For a fully assembled array, with an acoustic lens, the center frequency was 28.7 MHz with a one-way -3 dB and -6 dB bandwidth of 59% arid 83%, respectively, arid a -20 dB pulse width of -99 ns. The per-element peak acoustic power, for a plusmn30 V single cycle pulse, measured at the 10 mm focal length of the lens was 590 kPa with a -6 dB directivity span of about 30 degrees. The worst-case total cross talk of the combined array and flex assembly is for nearest neighboring elements and was measured to have an average level -40 dB across the -6 dB bandwidth of the device. Any significant deviation from simulation can be explained through limitations in apparatus calibration and in device packaging

2F-1 Fabrication and Performance of a High-Frequency Geometrically Focussed Composite Transducer with Triangular Pillar Geometry

A single-element, 40 MHz, 3 mm diameter transducer was fabricated with a geometric focus at 9 mm. The transducer was based on a piezo-composite substrate with triangular-shaped composite pillars. The transducer produced pulses with a two-way bandwidth of 55 %. The bandwidth and impedance magnitude were in agreement with that predicted using finite element modeling. A one-way radiation pattern was collected using a needle hydrophone. The oneway -3 dB beamwidth at the geometric focus was measured to be 120 mum and the -3 dB depth-of-field was 2.5 mm This is in good agreement to the theoretical predictions of 112.5 mum and 2.4 mm The triangular-pillar composite transducer was then compared to a transducer with square composite pillars. A 12 dB reduction in the amplitude of the secondary resonance was found for the triangular- pillar composite.

Effect of triangular pillar geometry on high- frequency piezocomposite transducers

Piezocomposite materials are used extensively in biomedical transducer array fabrication. However, developing high-frequency piezocomposite materials for imaging systems is still a challenge due to the extremely small pillar dimensions required to avoid the interference from lateral resonances. The use of triangular pillar piezocomposite material has been shown to suppress lateral resonances that appear in square pillar composite designs. To further understand how the geometry of the pillars affects the lateral resonances, piezocomposite materials with triangular pillars of different angles have been simulated and fabricated. Simulations were performed on composite transducers of 70-?m pitch, 18-?m kerf width, and 100-?m thickness with isosceles triangular pillars in which the isosceles angle varied from 30? to 60? using a finite-element analysis. By varying the pillar geometry, the composite transducers show large differences in lateral resonances. The simulation results demonstrate that the composite with 45? angle pillars has the lowest secondary pulse amplitude. The secondary pulse becomes larger when the pillar angle deviates from 45?. To study whether the pillar height (which determines the resonance frequency) and aspect ratio would change the optimum angle, composites with 40-?m pitch, 15-?m kerf width, and 45-?m thickness were also simulated. Finally, the composite with triangle pillars was compared with composites with square and round pillars. The simulation results show that the 45? triangular pillar geometry is, for high-frequency applications, the best configuration among all investigated in this work. Composite samples have also been fabricated to confirm results from finite-element modeling. Acoustical and electrical measurements were carried out to compare with theoretical predictions. Three composite transducers with pillar angles of 30?, 45?, and 60? were fabricated using a dice-and-fill technique. The measured electrical impedances and one-way pulse responses agreed well with the theoretical predictions and confirm the optimal nature of the 45? design.

Design and fabrication of ultrafine piezoelectric composites.

Making fine scale (<20 μm) piezoelectric composites for high frequency (>50 MHz) ultrasound transducers remains challenging. Interdigital phase bonding (IPhB), described in this paper, presents a new technique developed to make piezoelectric composites at the ultrafine scale using a conventional dicing saw. Using the IPhB technique, a composite structure with a pitch that is less than the dicing saw blade thickness can be created. The approach is flexible enough to make composites of different combination of pitch and volume ratio. Using a conventional dicing saw with a 50 μm thick blade, composite with a 25 μm pitch and a volume ratio of 61 percent are fabricated. Such a composite is suitable for fabrication of ultrasonic transducers and arrays with central frequencies of up to 85 MHz. Single element transducers working at central frequencies of 50–60 MHz were made of these composites as a mean to characterize the acoustic performance. Measurement results of the transducers show that the longitudinal electromechanical coupling coefficient is greater than 0.6 and that there are no noticeable lateral resonances in the frequency range of 55-150 MHz. Design criteria for fine scale elements are also discussed based on theoretical results from finite element analysis (FEA).

Dual frequency imaging of microbubbles using 1.7-MHz transmit stacks parallel to a 21-MHz receive array

The concept of contrast imaging using microbubble superharmonic signals was introduced in 2002[1]. A number of implementations with detection above 10 MHz have been reported, in particular by our group using a 25–30 MHz single element receive transducer concentric with a low 2–4 MHz transmit ring[2]. In the present work, the implementation of dual frequency (DF) imaging on a Vevo 2100 (VisualSonics, Toronto) was investigated (Fig.1-A).