Evanescent electromagnetic waves
abound in the vicinity of luminous
objects. These waves, consisting
of oscillating electric and magnetic fields in regions of space immediately surrounding an object, do not transfer their stored energy to other regions and, therefore, remain
localized in space. Like all electromagnetic waves, the behavior of evanescent waves is governed by Maxwell's equations, and their presence in the vicinity of an object helps
to satisfy the requirements of field continuity at the object's boundaries. Evanescent fields decay exponentially with distance away from the object's surface, making them exceedingly difficult to detect at distances much greater than a wavelength.
by Masud Mansuripur