  Lenses that can collect the perfect image of an object must restore
propagative and evanescent waves. However, for efficient information transfer,
e.g., in compressed sensing, it is often desirable to detect only the fast
spatial variations of the wave field (carried by evanescent waves), as the one
created by edges or small details. Image processing edge detection algorithms
perform such operation but they add time and complexity to the imaging process.
Here, we present a new subwavelength approach that generates an image of only
those components of the acoustic field that are equal to or smaller than the
operating wavelength. The proposed technique converts evanescent waves into
propagative waves exciting trapped resonances in a waveguide, and it uses
periodicity to attenuate the propagative components. This approach achieves
resolutions about an order of magnitude smaller than the operating wavelength
and makes it possible to visualize independently edges aligned along different
directions.
