Spacetime transformation acoustics

TL;DR

This paper compares the new analogue transformation acoustics (ATA) method with the standard approach, demonstrating ATA's ability to handle full spacetime transformations and designing an acoustic frequency converter.

Contribution

It introduces the ATA method based on the velocity potential equation, enabling full spacetime transformation acoustics beyond the limitations of the standard approach.

Findings

ATA can perform all spacetime transformations, unlike STA.

An acoustic frequency converter was designed and simulated using ATA.

ATA extends transformation acoustics to general spacetime transformations.

Abstract

A recently proposed analogue transformation method has allowed the extension of transformation acoustics to general spacetime transformations. We analyze here in detail the differences between this new analogue transformation acoustics (ATA) method and the standard one (STA). We show explicitly that STA is not suitable for transformations that mix space and time. ATA takes as starting point the acoustic equation for the velocity potential, instead of that for the pressure as in STA. This velocity-potential equation by itself already allows for some transformations mixing space and time, but not all of them. We explicitly obtain the entire set of transformations that do not leave its form invariant. It is in these cases that ATA shows its true potential, allowing for building a transformation acoustics method that enables the full range of spacetime transformations. We provide an example of an important transformation which cannot be achieved with STA. Using this transformation, we design and simulate an acoustic frequency converter via the ATA approach. Furthermore, in those cases in which one can apply both the STA and ATA approaches, we study the different transformational properties of the corresponding physical quantities.