A Kerfless PVDF Array for Photoacoustic Imaging

Photoacoustic signals can have very large bandwidth and large dynamic range. With appropriate electrical impedance matching, off-resonance PVDF transducers offer the bandwidth and sensitivity to fully capture these signals. Minimizing pitch and kerf in ultrasound transducer to improve lateral resolution is of great importance. Kerfless arrays, where the electrodes are patterned onto the piezoelectric material, fulfill such a demand and are simpler to manufacture. We have manufactured and characterized a kerfless off resonance PVDF array of 10 elements with dimensions of 1 mm×1.5 mm×28 μm (w×h×t) both numerically and experimentally for PA imaging. We matched the high impedance of the PVDF elements with low impedance of acquisition system through an appropriate LNA (26 dB amplification over 10 MHz BW). PA signals from a tungsten wire with a diameter of 35 μm were received with our device, and compared to those recorded with a 0.2 mm needle hydrophone. Based on simulation and measurement results, the phase change in the off-resonance PVDF is negligible. The crosstalk between adjacent elements is -30dB. We measured a sensitivity for our array of about 1.38 μV/Pa at 3 MHz. The RMS output noise level is 240 μV over the entire bandwidth (10Hz - 10 MHz).