Abstract
We consider theoretically the scattering of an incident evanescent plane wave by a spherical particle. The scattering problem is treated in a classic way by applying the T-matrix formalism and the resulting field is expressed on the basis of the different vibration modes of the particle. Compared to the case of a homogeneous plane incident wave, additional azimuthal scattered modes are excited and their contribution provokes a symmetry breaking of the field. Importantly, if a mode is preferentially excited by choosing the corresponding reduced frequency, the scattered radiation exhibits a spiral structure. The scattered field has a rotating phase around the scatterer which comes from the formation of spiral scattered waves and this effect is accentuated by increasing the evanescence degree of the incident wave. These results could have important implications for the contactless manipulation of objects with acoustic radiation forces and torques.
Highlights
Evanescent waves are inhomogeneous waves naturally occurring near the surface of objects and their interaction with particles may lead to several functional applications
For exemple they are used in optics or acoustics for sub-wavelength imaging which consists in investigating the near field of objects using a probe to collect the evanescent components of the field spatially richer than those of homogeneous waves [1]
The scattering problem was investigated few decades ago for optical waves and it has been shown that additional mode contributions can be strongly enhanced in the scattering of an evanescent wave compared to a homogeneous wave [8, 9]
Summary
Evanescent waves are inhomogeneous waves naturally occurring near the surface of objects and their interaction with particles may lead to several functional applications For exemple they are used in optics or acoustics for sub-wavelength imaging which consists in investigating the near field of objects using a probe to collect the evanescent components of the field spatially richer than those of homogeneous waves [1]. They are exploited for microfluidics devices [2] or for the search of sediments in the naval sector [3]. Understand the propagation of surface waves in heterogeneous media as in seismology or non destructive testing, and for applications in acoustic imaging or particle manipulation
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