Abstract
A physical boundary mounted with active sources can cancel acoustic waves arriving at the boundary, and emit synthesized waves into the neighboring medium to fully control the acoustic wavefield in an experimental setup such as a water tank or air-filled cavity. Using the same principles, a physical experiment can be artificially immersed within an extended virtual (numerical) domain so that waves propagate seamlessly between the experimental setup and virtual domain. Such an immersive wave control experiment requires physical monopolar sources on the active boundary. However, real physical sources (e.g., piezoelectric transducers) project waves at middle-to-high sonic frequencies (e.g., 1-20 kHz) that do not fully conform to the theoretically required monopolar radiation pattern; if left uncorrected, this causes controlled wavefields to deviate from those desired in immersive experiments. A method is proposed to compensate for the non-monopole-like radiation patterns of the sources, and can be interpreted physically in terms of Huygens principle. The method is implemented as a pre-computation procedure that modifies the extrapolation Green's functions in the Kirchhoff-Helmholtz integral before the actual experiments take place. Two-dimensional finite-difference simulations show that the processing method can effectively suppress the undesired effect caused by non-monopolar active sources in immersive wave control experiments.
Highlights
By emitting carefully chosen signals, acoustic sources can be used as acoustic sinks
II we review the acoustic immersive boundary condition theory and incorporate new wavefield processing methods that compensate for non-monopole-like radiation patterns of physical sources on an active boundary
Such wave control experiments face the challenge of using non-monopolar sources at the active boundary, which do not conform to theoretical boundary conditions
Summary
By emitting carefully chosen signals, acoustic sources (e.g., loudspeakers) can be used as acoustic sinks. In addition to achieving exact wavefield cancellation at the active boundary surrounding a physical domain, van Manen et al (2007) and Vasmel et al (2013) proposed the concept of a (numerical) virtual domain within which the physical experimental setup can be fully immersed such that waves travel seamlessly back and forth. For 2D and 3D immersive wave control experimentation, physical sources mounted on the rigid boundary should be monopoles, as this is required in other types of active boundary designs and sound field control experiments (Berkhout et al, 1993; Ise, 1999; Miller, 2006).
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