Acoustical Direction Finding with Time-Modulated Arrays

Time-Modulated Linear Arrays (TMLAs) offer useful efficiency savings over conventional phased arrays when applied in parameter estimation applications. The present paper considers the application of TMLAs to acoustic systems and proposes an algorithm for efficiently deriving the arrival angle of a signal. The proposed technique is applied in the frequency domain, where the signal and harmonic content is captured. Using a weighted average method on harmonic amplitudes and their respective main beam angles, it is possible to determine an estimate for the signal's direction of arrival. The method is demonstrated and evaluated using results from both numerical and practical implementations and performance data is provided. The use of Micro-Electromechanical Systems (MEMS) sensors allows time-modulation techniques to be applied at ultrasonic frequencies. Theoretical predictions for an array of five isotropic elements with half-wavelength spacing and 1000 data samples suggest an accuracy of +/- 1 degrees within an angular range of approximately +/- 50 degrees. In experiments of a 40 kHz five-element microphone array, a Direction of Arrival (DoA) estimation within +/- 2.5 degrees of the target signal is readily achieved inside a +/- 45 degrees range using a single switched input stage and a simple hardware setup.