Learn from dolphins! Learn the secrets of sound waves and become more comfortable underwater~

Author: Li Chuanfu

In the depths of the ocean, dolphins demonstrate amazing navigation and detection capabilities with their unique sonar system, echolocation. They detect and analyze their surroundings by emitting high-frequency sound waves and receiving the reflected echoes. Whether in dark or turbid waters, they can accurately locate prey, identify obstacles, and even communicate with their companions. This sonar system relies on the fat pads on the dolphin's forehead to focus and guide the sound waves, and the fat pads on the lower jaw to receive the sound waves and transmit them to the inner ear for processing. This ability of dolphins is not only a miracle in nature, but also inspires human scientists.

Inspired by the dolphin sonar system, Professor Zhang Yu's team at Xiamen University has developed a new acoustic soft bio-metamaterial. This material has high acoustic transparency and gradient refractive index, making it an ideal material for underwater monitoring and medical ultrasound applications. Unlike traditional rigid metamaterials, this acoustic soft bio-metamaterial consists of micron-sized solid particles or droplets embedded in a silicone matrix. This design not only gives the material softness, but also enables it to effectively transmit and manipulate sound waves.

Schematic diagram of a new acoustic soft bio-metamaterial developed inspired by the dolphin sonar system. Image source: Xiamen University

The acoustic refractive index of the acoustic soft bio-metamaterial shows a nonlinear change with the increase of inclusion content, which makes it possible to design functional devices with gradient acoustic properties. In the frequency range of 0.5 to 2 MHz, this material shows a dispersion-free characteristic, and in theory it can even work stably at frequencies up to 20 MHz. This material has high acoustic transparency underwater, and the acoustic transmission coefficient is close to 100%, thanks to the extremely small difference in acoustic impedance between it and water, which reduces the interface reflection loss.

This acoustically soft bio-based metamaterial can undergo significant deformation under tensile loads without becoming overly stiff, making it extremely useful in applications that require flexibility and deformability. Whether it is a solid particle or a liquid microdroplet, its acoustic and mechanical properties can be tuned while maintaining low stiffness of the material.

The acoustic beamformer based on this acoustic soft bio-metamaterial can dynamically change the acoustic beam pattern through mechanical stretching, thereby achieving effective control of the acoustic field. This tunable metamaterial brings new opportunities for acoustic manipulation applications, by introducing microstructures to optimize the ultrasonic properties of soft matter, achieve collimation, focusing and vortex formation, and enhance detection, imaging and communication.

With the continuous progress of materials science, this acoustic soft bio-metamaterial will integrate more intelligent functions, such as magnetic, optical or thermally active particles, to achieve more complex and sophisticated acoustic field control. This will not only promote the development of science and technology, but also provide more powerful tools for humans to explore the unknown world. This new material shows great potential in acoustic monitoring, imaging and communication, indicating that there will be more breakthroughs and innovations in the field of marine acoustics and biomedical ultrasound in the future.