Audio Recovery by a 120-GHz Superheterodyne Doppler Radar

Mechanical vibrations of sound-producing or resonating objects can be exploited to recover audio signals through non-acoustic methods. In this work, we present a custom-designed 120-GHz continuous-wave Doppler radar sensor capable of detecting micron-scale vibrations on active loudspeaker surfaces. The sensor utilizes two low-cost commercial radar chips with zero-IF architectures. Each chip operates at distinct local oscillator (LO) frequencies to produce an intermediate frequency (IF). This configuration mitigates common zero-IF limitations such as DC offset, flicker noise, and I/Q imbalance. Experimental evaluations demonstrate the sensor’s ability to recover audio signals across a broad frequency range. Notably, the recovered speech audio is compatible with existing speech recognition systems, demonstrating its potential in non-acoustic audio recovery applications.