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Tuesday, July 9 • 12:10 - 12:30

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In 2007 Woon Siong Gan first introduced gauge invariance into acoustic field equations. This is a milestone in the history of gauge invariance in physics. In gauge invariance formulation, the acoustic fields are expressed in terms of the gauge fields of vector potential and scalar potential. Gauge fields are of more fundamental nature than acoustic fields. The gauge invariance approach with symmetry nature will enable the simplification of the complexity encountered. Hence gauge invariance approach is useful in dealing with nonlinear acoustics problem. As an example of the application of gauge invariance to multiple scattering is time reversal acoustics. The forward propagation acoustic waves will undergo multiple scattering in inhomogeneities . On the other hand, the time reversed sound wave will bypass the inhomogeneities. The more inhomogeneous the medium is, the better will be the propagation of the time reversed sound wave. The scattering mechanism is that with the time reversed process, the target will become the virtual source and the scattering points of inhomogeneities will become the secondary sources reflecting the informations from the target back to the sound source. Hence the larger the number of inhomogeneity scattering points the more will be the information back reflected to the source. This is an example of the application of time reversal symmetry, a form of gauge invariance to acoustic multiple scattering. This also illustrates that time reversal symmetry can simplify the complexity of scattering by inhomogeneities. For other cases of multiple scattering, the action principle and path integral will be used. The form of Lie group has to be chosen with symmetry properties helping to reduce the complexity of the problem.


Tuesday July 9, 2019 12:10 - 12:30 EDT
Westmount 1

Attendees (6)