Acoustic Illusion of a Rigid Object for a Moving Emitter via Equivalent Surface Control

Abstract

We report a three-dimensional acoustic illusion of a rigid object illuminated by an emitter moving along an arbitrary trajectory. The object is absent: control sources are arranged around its location, the closed surface they define being termed the equivalent surface. Driven by the field the object would have scattered onto this surface, the sources radiate, by the Kirchhoff--Helmholtz representation, that same field beyond it. The control signals follow in closed form from a time-dependent physical optics formulation that we derive for a moving emitter, in which the motion enters analytically through the acoustic travel times, so that the scattering problem need not be re-solved at each emitter position, nor the propagation domain discretized. For objects too large to enclose, the signals are mapped onto an internal surface, an option whose advantages and penalties are discussed. Numerical simulations validate the method in both configurations.