Simulation and design of a microphone array for beamforming on a moving acoustic source

Abstract

A microphone array was designed and tested for the purpose of measuring the noise radiated by a moving acoustic source. Beamforming is used to enhance the signal-to-noise-ratio (SNR), with interfering sources moving at the same speed and along the same straight path as the measured source. A method is described for calculating moving source beampatterns that illustrates the SNR enhancement. The beamforming algorithm includes a de-Dopplerisation process to correct for the Doppler shift that occurs in the signals received at the array. This process leads to SNR enhancements that differ depending on whether the interfering source leads or lags the measured source when passing the array. The de-Dopplerisation process also causes grating lobes associated with spatial aliasing to move to lower frequencies when the interfering source leads the measured source. The described effects of the de-Dopplerisation process become more pronounced at higher speeds and when the interfering sources are farther away from the measured source. Hence, when designing a microphone array, it is important to conduct simulations that involve the use of a moving, rather than stationary, acoustic source, especially when the source moves at high speed. The modelling method presented in this paper was used to design an array which was tested in an anechoic chamber. The measured beampatterns for a stationary source are presented.