Simulation of acoustic lens influence on wavefront shaping

The main objective of presented study is to examine the influence of an acoustic lens on shape of the wavefront. To conveniently illustrate the difference between acoustic pressure wave propagation with and without the lens, an isodynamic transducer was chosen as a source. This kind of loudspeaker generates flat wavefront as a result of approximately uniform distribution of speed and phase on the entire diaphragm. The designed lens consisted of a matrix of individual waveguides. Manipulation of size and position of output matrix in relation to input matrix allowed for achieving the desired waveguide length distribution. Differences in lengths of lens’s channels resulted in wavefront delay distribution at the output matrix. A numerical model of transducer and waveguide matrix was created to evaluate the behaviour of acoustic pressure wave propagation trough the designed lens. With stationary study, a spatial pressure distribution was calculated, in the near field and far field, in hemisphere in front of the lens as well as in hemisphere in front of just the transducer. The differences in wavefront shapes between the two cases were clearly visible in comparisons, confirming the expected pressure wave delay distribution of the lens. The resulting wavefront curvature was compared to the assumed one in theoretical design. Results of those comparisons proved the possibility of influencing the wavefront shape, by manipulating the output matrix with some caveats discussed in the paper. The data from numerical calculation of pressure propagation allowed for visualizing calculated sound pressure level distribution, adding the directivity evaluation to the comparisons.