Subwavelength Sensing Using Nonlinear Feedback in a Wave-Chaotic Cavity
Seth Cohen
Here, I describe a new sensing technique for resolving the position of
a subwavelength scatterer (< lambda) with vastly subwavelength
resolution (< < lambda). My approach combines two separate fields of
scientific inquiry: time-delayed nonlinear feedback and wave chaos. In
typical time-delayed nonlinear feedback systems, the output of a
nonlinear device is delayed and fed back to its input. In my
experiment, the output of a radio-frequency (lambda~15 cm) nonlinear
circuit is injected into a complex scattering environment known as a
wave-chaotic cavity. Inside the cavity, the field interacts with a
subwavelength dielectric object from all sides, and a portion of the
scattered waves are coupled out of the cavity, amplified, and fed back
to the input of the nonlinear circuit. The resulting closed-feedback
loop generates its own radio-frequency illumination field (> 1 GHz),
which contains multiple wavelengths and is sensitive to location of
the scattering object. Using the dynamical changes in the illumination
field, I demonstrate subwavelength position-sensing of the scatterer’s
location in the cavity with a two-dimensional resolution of
lambda/300.