High-frequency single-element and annular array transducers incorporating PVDF

Polyvinylidene fluoride (PVDF) transducers have been developed for ultrasonic backscatter microscopy (UBM) applications. Single element devices encompassed the frequency range of 40 to 65 MHz and incorporated a variety of backing materials and tuning circuits. Pulse-echo testing was performed using the 1 (mu) J energy setting on a Panametrics 5900 pulser/receiver, configured with +40dB gain and 20 dB attenuation. A broad spectrum of performance was observed depending on the choice of backing and tuning, with -6dB bandwidths of 55% to 116% and echo amplitudes from 100mVpp to 940mVpp. It was observed that electrical impedance matching increased sensitivity and tuned the center frequency at the expense of reduced bandwidth. For imaging applications the tuned devices provided superior performance. Although single element transducers in this frequency range provide axial resolution on the order of 50 micrometer, a tradeoff exists between the lateral resolution and the depth of field. To obtain high lateral resolution and a long depth of field an annular array design was adopted. Laser dicing was used to fabricate the elements of the array from a sheet of PVDF. Interconnect to each element was achieved using pin contacts molded into the backing. The design incorporated a 5 mm aperture with six equal area elements focused at 10 mm. At a center frequency of 50 MHz this design will achieve a lateral resolution of 58 micrometer, comparable to the axial resolution, over the entire 7.5 mm depth of field.