Ultrasound-assisted 3D printing of tungsten/photosensitive resin composites for acoustic backing layers applications

Abstract The backing layer is the core component of an ultrasonic transducer, which can absorb the acoustic energy and suppresses excess vibration to obtain a broad bandwidth pulse-echo signal. Ultrasound-assisted 3D printing can control the orientation/alignment and local composition of particles in liquid resin and fabricate materials with periodic complex structures. In this paper, three types of tungsten/photosensitive resin composites (1–3, 2–2, and 3–3) were prepared using ultrasound-assisted stereolithography technique. The acoustic properties of these composites were investigated in relation to the particle arrangement patterns under ultrasonic stimulation at two different frequencies (0.92 MHz and 1.12 MHz). Among the three types, the 3–3 type composite exhibits relatively good acoustic properties with high attenuation coefficients and low acoustic impedance, which is more suitable for backing layer applications. Besides, the composites printed under higher frequency stimulation (1.12 MHz) have higher acoustic velocity and lower acoustic impedance. Finally, the 3–3 type composite stimulated by a frequency of 1.12 MHz was selected as the backing layer for evaluating the transducer performance. Transducers based on PZT ceramics were designed and fabricated with center frequencies of 5 MHz and 20 MHz, respectively. After attaching backing layer, the −6 dB relative bandwidth of 5 MHz transducer increased from 14.76% to 30.48%, and that of the 20 MHz transducer increased from 10.78% to 22.33%. Besides, the trailing of the pulse echo is significantly improved. The results suggest that the ultrasound-assisted 3D printing have good potential applications in backing layers with periodic complex structures.