Metagel with Broadband Tunable Acoustic Properties Over Air–Water–Solid Ranges

Abstract Materials capable of varying their acoustic impedances to match those of air, water, and solid materials over broadband frequencies will enable new applications in fields as diverse as medical imaging, underwater sonar and communication, and marine biology. However, such tunability has not been achieved with conventional acoustic materials including metals, polymers, ceramics and woods. Here, the invention of metagel, a class of designed hydrogel composites with unprecedented tunable acoustic properties over broadband frequencies, is reported. The metagel consists of patterned channels in a tough hydrogel matrix, where air, water, or liquid metal can be purged through the channels to tune the metagel's acoustic transmission over air–water–solid ranges and broadband frequencies on demand. It is shown that the acoustic properties of the metagel can be tuned by varying the volume ratio of the channels, properties, different filler materials with combined experiments, theory, and simulations. The metagel enables novel functions such as adjustable imaging regions of ultrasound, demonstrating tangible applications in underwater acoustics and medical imaging.