Underwater acoustic spiral wavefront transducer with low phase directionality error

The phase and azimuth angle of acoustic spiral wavefronts are linearly related. Based on this phase directionality of spiral wavefronts, the complex azimuth determination of the positioning of unmanned underwater vehicles can be converted into simple phase acquisition processes, where the azimuth determination accuracy is influenced by the phase directionality error of a spiral wavefront transducer. This study proposes a spiral wavefront transducer that improves the underwater positioning accuracy. The transducer can emit low-frequency acoustic spiral wavefronts with low phase directionality error. Moreover, the causes of the phase directionality error of phased-spiral transducers are discussed, and optimization design principles for minimizing the error were presented. Subsequently, a transducer prototype is designed, fabricated, and tested. In the experiment, the transmitting voltage response and phase directionality of the prototype in a water tank are measured, and experimental results well agreed with the simulation results. For the prototype, the resonance frequency is 1312 Hz, the maximum transmitting voltage response is 129.7 dB, and the phase directionality error is 1.45 degrees.