Enhanced mmWave Radar Sound Sensing: A Passive Relay for Long-Range, Source-Independent Sound Acquisition

mmWave radar-based sound sensing have attracted extensive attention due to its advantages such as simultaneous measurement of multiple sound sources, and strong noise resistance. However, limited by the mmWave reflection properties of the target sound source, existing methods can only measure targets with strong mmWave reflection characteristics at relatively short distance. This paper proposes a long-distance, source-independent sound sensing (LISS) method with mmWave radar. By designing an mmWave-acoustic passive relay, the incoming sound wave excitation is converted into modulation of the mmWave signal, enabling long-distance sound sensing without being affected by the shape or material of the sound source. Additionally, the unique structure of the relay provides directionality for sound source while maintaining omnidirectionality for incident mmWave. The LISS sensing method, the design principles, and the working mechanism of the relay are detailed in this paper. Experimental validations demonstrate that the proposed method extends sound sensing range by more than 7.5 times compared to exising methods and is not affected by the intrinsic properties of the sound source, providing a promising approach for long-range, source-independent sound sensing.