Acoustic metamaterial can send complex signals directly between water and air - Telecom - Hi Tech & Innovation

Schematic of HDM metamaterial for high-speed all-sound communication across the water–air media. Credit: IMDEA Materials Institute

Researchers from IMDEA Materials Institute, in collaboration with China's Nanjing and Huazhong Universities, have developed a new acoustic metamaterial capable of transmitting complex sound signals directly between water and air. The advance, reported in the paper "High-dimensional multiplexed metamaterial for cross-media all-sound communication," introduces a novel approach that could significantly improve underwater communication technologies and enable new applications ranging from ocean monitoring to medical imaging.

Sound travels very differently through water and air because they have drastically different acoustic properties such as density and sound speed. This mismatch means that most sound waves hitting the water-air boundary are reflected rather than transmitted, blocking efficient sound communication.

As a result, modern systems often rely on intermediate devices such as buoys or ships that convert underwater acoustic signals into radio signals before relaying them through the air. This process is not only expensive, but also slow and vulnerable to electromagnetic interference.

A new high-dimensional metamaterial bridge

To overcome this limitation, researchers designed a high-dimensional multiplexed (HDM) acoustic metamaterial that acts as a passive bridge for sound waves between water and air. Unlike conventional materials, which can typically control only one or two aspects of sound, the new structure can simultaneously modulate amplitude, phase, frequency, and orbital angular momentum (OAM), four key dimensions of acoustic waves.

The research is published in Materials Horizons.

"We have demonstrated that the proposed HDM metamaterial is capable of modulating all dimensions of cross-water-air sound waves including amplitude, phase, frequency, and orbital angular momentum in a passive, compact and efficient way," explains Prof. Johan Christensen from IMDEA Materials, one of the authors behind the publication.

"Thanks to this high-dimensional characteristic, this metamaterial enables simultaneously relaying and demodulating the spatial-spectral multiplexed signals from one medium to another, which significantly enhances channel capacity and spectral efficiency."

Real-world tests and performance gains

This multidimensional control dramatically increases the amount of information that can be transmitted, boosting both channel capacity and spectral efficiency. In experiments, the team demonstrated real-time transmission of a complex image from an underwater source to multiple airborne receivers using the metamaterial as a passive "meta-repeater."

The system supported four independent communication channels and achieved a very low bit-error rate, well below one tenth of the forward error correction limit, while remaining robust against background noise and fluctuations at the water surface.

Because the technique uses only sound waves and does not require conversion to radio signals, it could also offer improved security and reliability.

"This HDM metamaterial-based technique opens a new paradigm for controlling sound waves in complex cross-media systems," said Prof. Christensen.

"Beyond underwater communications and air-sea operations, it also has far-reaching implications ranging specific cases such as transcranial ultrasound imaging to next-generation communication systems in the emerging Internet of Everything."

"I would also like to highlight the excellent collaboration behind this work, particularly with Prof. Bin Liang and his team at Nanjing University, who first proposed this research," concluded Prof. Christensen. 

Provided by IMDEA Materials 

by IMDEA Materials

edited by Gaby Clark, reviewed by Robert Egan 

Source: Acoustic metamaterial can send complex signals directly between water and air