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Sonic field enhancement assisted by coupling to the fundamental mode of a slab waveguide. At the coupler interface (lower part, ) an irradiating oblique sound beam leaks evanescent waves into the surrounding upper medium due to TIR. Calculations have been performed for guides of various values of which correspond to different resonant wavelengths yielding a frustrated TIR which amplifies the decaying field. Inset: Diagram of the guide with index of refraction and height adjacent to the surrounding medium which extends up/down to the coupler interfaces located at and . The mass density is assumed to be uniform in this structure.
Source at and images at ( is the slab height) produced by a slab waveguide for different values of in the slab. With the chosen configurations the images are plotted for the second sonic slab guided mode at a fixed index of refraction corresponding to wavelengths five times larger than the slit width .
Realistic implementation of our schemes for field enhancement (left) and superlensing (right) by means of a planar silicone rubber waveguide. (a) At an air/water interface an incident sound beam undergoes TIR. The decaying wave is significantly amplified when it is coupled to the trapped modes of the silicone rubber slab of index relative to water. (b) Complex subwavelength source (slit width ) placed at . (c) Image plane at with highest field intensity normalized to , as produced by the slab.
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