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- Underwater acoustic spiral source: pool tests and calibrationPublication . Viegas, Sergio; Zabel, Friedrich; Silva, AntónioUnderwater acoustic spiral sources are able to generate spiral acoustic fields where the phase depends on the bearing angle. It allows to estimate the bearing angle relatively to a receiver by subtracting the phases of a spiral and a circular wavefront, and can be used to estimate bearing angles with a single hydrophone/projector pair, e.g., for unmanned underwater vehicles localization. The developed spiral source comprises four monopoles/quadrants and it will be shown that the spiral source behavior is linear, which means that the generated acoustic signals are the sum of the four acoustic signals from each separate monopole, for any amplitude value. This work presents two calibration methods for spiral acoustic sources and the linearity evaluation for the used spiral source. Unlike the calibrations performed on signal reception, the two proposed calibration methods adjust the phase of the emitted signals to form the acoustic spiral field. The first calibration method rectifies the phase of one quadrant based on the contribution of the four quadrants. This method was tested and presented a performance lower than the performance of the calibration on the receiving side. After evaluating the linearity, a new calibration approach is suggested. This new approach uses the signals from separate quadrants instead of the contribution of the four quadrants. This method needs to be tested experimentally to check its validity.
- In-Lab demonstration of an underwater acoustic spiral sourcePublication . Viegas, Rúben; Zabel, Friedrich; Silva, AntónioUnderwater acoustic spiral sources can generate spiral acoustic fields where the phase depends on the bearing angle. This allows estimating the bearing angle of a single hydrophone relative to a single source and implementing localization equipment, e.g., for target detection or unmanned underwater vehicle navigation, without requiring an array of hydrophones and/or projectors. A spiral acoustic source prototype made out of a single standard piezoceramic cylinder, which is able to generate both spiral and circular fields, is presented. This paper reports the prototyping process and the multi-frequency acoustic tests performed in a water tank where the spiral source was characterized in terms of the transmitting voltage response, phase, and horizontal and vertical directivity patterns. A receiving calibration method for the spiral source is proposed and showed a maximum angle error of 3° when the calibration and the operation were carried out in the same conditions and a mean angle error of up to 6° for frequencies above 25 kHz when the same conditions were not fulfilled.