Focus of ultrasonic underwater sound with 3D printed phononic crystal

Abstract

Ultrasound is widely used in various applications, ranging from ultrasound imaging to particle manipulation. Acoustic materials, such as phononic crystal (PC) and metamaterials, are designed to control the propagation and concentration of ultrasound. While traditional metal-based underwater PCs are usually limited to large 2D structures and used for low-frequency sound wave manipulation, it is difficult to reach the ultrasonic frequency region of the order of 1 MHz with cumbersome metallic structures. Here, in this work, we proposed a 3D printed gradient-index phononic crystal (GRIN PC) lens based on the hyperbolic secant index profile. With a huge impedance difference between air and the 3D printing materials, the GRIN PC lens adhered to the ultrasonic transducers can easily manipulate the propagation of acoustic waves and achieve wave focusing. This transparent and flat lens demonstrates the beam focusing in water even at a high frequency. The integration and miniaturization of transducer and lens make particle capture convenient in relevant medical applications.