Multi-Axial Transducers for Passive Point Source Localization

Acoustic cavitation is often monitored by single passive cavitation detectors. A single transducer can provide information on the type, intensity, and duration of activity, while being small and relatively inexpensive. However, spatial information about cavitation activity is lacking with these systems. Multi-axial transducers, or transducers with more than one pair of orthogonal electrodes, are hypothesized to provide directivity information about a received signal using a single transducer. Thus, the objective of this study was to demonstrate in-silico that single multi-axial transducers can provide directivity information and two multi-axial transducers can provide accurate source location estimates. Two sets of frequency-domain simulations were performed, one each for two biaxial transducers (two pairs of orthogonal electrodes) and two triaxial transducers (two pairs of orthogonal electrodes). Transducers were placed 2 cm apart along the x axis while acoustic point sources were placed at depths between 10 and 14 cm from the top face of the transducers. Points were a maximum of 4 cm away from the origin in the xy-plane. Signal and amplitude ratio were mapped to source direction using a radial basis function. Trigonometry was then used to calculate two- and three-dimensional positions for biaxial and triaxial cases, respectively. RMS and median localization errors were calculated as a measure of accuracy. Median localization error of less than 1 mm was observer in all cases. Therefore, single multi-axial transducers can estimate the direction of a point source and pairs of multi-axial transducers can estimate the location of a point source.