Fabrication of Radial Array Transducers Using 1-3 Composite via a Bending and Superposition Technique

Piezoelectric composite materials, combining the advantages of both piezoelectric materials and polymers, have been extensively used in ultrasonic transducers. However, the pitch size of radial array ultrasonic transducers normally exceeds one wavelength, which limits their performance. In order to minimize grating lobes of current radial transducers and then increase their imaging resolution, a 2.5 MHz 1-3 composite radial array transducer with 64 elements and 600 μm pitch was designed and fabricated by combining flexible circuit board and using a bending-and-superposition method. All the array elements were connected and actuated via the customized circuit board which is thin and soft. The kerf size is set to be 1/3 wavelength. PZT-5H/epoxy 1-3 composite was used as an active material because it exhibits an ultrahigh electromechanical coupling coefficient (<i>k_t</i> = 0.74), a very low mechanical quality factor (<i>Q_m</i> = 11), and relatively low acoustic impedance (<i>Z_c</i> = 13.43 MRayls). The developed radial array transducer exhibited a center frequency of 2.72 MHz, an average -6 dB bandwidth of 36%, an insertion loss of 31.86 dB, and a crosstalk of -26.56 dB between the adjacent elements near the center frequency. These results indicate that the bending-and-superposition method is an effective way to fabricate radial array transducers by binding flexible circuit boards. Furthermore, the utilization of tailored flexible circuitry boards presents an effective approach for realizing reductions in crosstalk level (CTL).