High-resolution Piezopolymer Acoustic Bearing Estimator

A novel acoustic sensor is described that utilizes two coincident, distributed, shaded PVDF piezopolymer sensors to provide high-resolution acoustic source bearing estimates. Sensor shading is accomplished by shaping the charge collection electrodes deposited on the sensing layer. When these two sensor shadings are matched via a derivative in space, the ratio of their signal outputs is linearly proportional to the direction cosine of an incident acoustic field; this is an extension of the well-known "monopulse" concept in radar. By using derivative-matched aperture shadings, the monopulse ratio is independent of frequency. This, combined with PVDF’s flat frequency response, facilitates wide bandwidth application of the sensor. A hardware realization of the sensor concept is described, and experimental results are presented for an underwater (e.g., sonar) implementation of the sensor. Agreement between theory and experiment for bearing estimation is excellent for source locations within the sum aperture’s main lobe. For SNR greater than 20dB, the ratio of the sum aperture’s 3dB main lobe width to the bearing estimation standard deviation (the “split ratio”) approaches 100. The sensor described here provides a means of obtaining high spatial resolution acoustic bearing estimates for applications such as source tracking for teleconferencing, novel audio/user interfaces, and multimedia applications.