Comparison of Acoustic-Laser and Acoustic-Millimeter Wave Cross-Medium Communication Channels

The new cross-medium communication system combining acoustic and electromagnetic waves enables direct information transmission across water and air media without the need for relays. An underwater speaker is used as the transmitter to transmit acoustic signals towards the water surface. A millimeter-Wave (mmWave) radar is used as the receiver to detect vibrations on the water surface. However, the mmWave radar demonstrates high accuracy only for short-distance detection between the water surface and air. To address this limitation, we have explored the feasibility of using laser Doppler vibrometers (LDVs) to replace mmWave radar, which is expected to offer high-precision, long-range detection. In this paper, we analyze the transmission mechanisms and channel models for the two cross-medium systems and explain why both the acoustic-laser channel and the acoustic-mmWave channel have direct paths. The anechoic tank experiments were conducted to confirm the single-path propagation characteristics of both channels and to demonstrate the significantly higher in-band SNR achieved by the acoustic-laser system. This study is believed to lay theoretical and experimental foundations and facilitate real-world deployment of cross-medium communication systems.