Circular array based on the tangent line method

The tangent line method (TLM) is an array signal processing for generating curvilinear acoustic beams. The curvilinear beam is generated as an envelope of tangent lines to the curve. The tangent lines are produced as mainlobes of the far-field delay-and-sum beamformer. Because the beam trajectory is specifically determined as the envelope, directivity control and distance discrimination can be performed according to the trajectory. In earlier studies on the TLM, line arrays were investigated. However, a line array induces an undesired beam in back of the array, because of its symmetry at the front and back. In this study, circular arrays are investigated as an example of asymmetric arrays. Array signal processing to produce a circular beam using a circular array is formulated. The developed theory is validated through simulations and experiments. The experiments are conducted by using a circular microphone array.