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Deutsche Physikalische Gessellschaft IOP Institute of Physics

Material parameters and vector scaling in transformation acoustics

Focus on Cloaking and Transformation Optics

Steven A Cummer1,3, Marco Rahm1 and David Schurig2

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Part of Focus on Cloaking and Transformation Optics

The degree to which the coordinate transformation concept first demonstrated for electromagnetic waves can be applied to other classes of waves remains an open question. In this work, we thoroughly examine the coordinate transformation invariance of acoustic waves. We employ a purely physical argument to show how the acoustic velocity vector must transform differently than the E and H fields in Maxwell's equations, which explains why acoustic coordinate transformation invariance was not found in some previous analyses. A first principles analysis of the acoustic equations under arbitrary coordinate transformations confirms that the divergence operator is preserved only if velocity transforms in this physically correct way. This analysis also yields closed-form expressions for the bulk modulus and mass density tensor of the material required to realize an arbitrary coordinate transformation on the acoustic fields, which we show are equivalent to forms presented elsewhere. We demonstrate the computation of these material parameters in two specific cases and show that the change in velocity and pressure gradient vectors under a nonorthogonal coordinate transformation is precisely how these vectors must change from purely physical arguments. This analysis confirms that all of the electromagnetic devices and materials that have been conceived using the coordinate transformation approach are also in principle realizable for acoustic waves. Together with previous work, this analysis also shows how the curl, divergence and gradient operators maintain form under arbitrary coordinate transformations, opening the door to analyzing other wave systems built on these three vector operators.


PACS

62.65.+k Acoustical properties of solids

46.25.Cc Theoretical studies

41.20.-q Applied classical electromagnetism

03.50.De Classical electromagnetism, Maxwell equations

Subjects

Accelerators, beams and electromagnetism

Condensed matter: structural, mechanical & thermal

Particle physics and field theory

Dates

Issue 11 (November 2008)

Received 11 June 2008

Published 27 November 2008



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