Methods for Beamforming Using Structural Sensors on an Elastic Panel

The design of an acoustic beamforming microphone is demonstrated using an array of vibration sensors coupled to an elastic plate. The signals recorded by each sensor are mechanically coupled to the bending resonant modes of the plate, which are, in turn, acoustically coupled to the direction and amplitude of the incident pressure wave. A filter is designed for each sensor to tune the magnitude and phase of each recorded signal so that a target directional acoustic response is achieved when the filtered signals are summed. Experimental results demonstrate that a linear array of structural sensors achieve an increased directivity of nearly 6dB at low frequencies compared to a conventional microphone array, while being able to beamform in both elevation and azimuth. Although the resonances of the plate introduce reverberation into the recorded signal that affect speech intelligibility, the surface beamformer reduced the worderror-rate of a transcribed speech signal from 134.8% to 24.7% in the presence of a babble interfering source that was spatially separated from the target speech source by 60°.