Cascaded Metasurface Design Using Electromagnetic Inversion with
Gradient-Based Optimization
Abstract
This paper presents an electromagnetic inversion algorithm for the
design of cascaded metasurfaces that enables the design process to begin
from more practical output field specifications such as a desired power
pattern or far-field performance criteria. Thus, this method combines
the greater field transformation support of multiple metasurfaces with
the flexibility of the electromagnetic inverse source framework. To this
end, two optimization problems are formed: one associated with the
interior space between two metasurfaces, and the other for the exterior
space. The cost functionals corresponding to each of these two
optimization problems are minimized using the nonlinear conjugate
gradient algorithm with analytic expressions for the gradient operators.
A total variation regularizer is incorporated into the optimization
procedure to favour smooth field variations from one unit cell to the
next. The numerical implementation of the developed design procedure is
presented in detail along with several two-dimensional (2D) simulated
examples to demonstrate the capabilities of the method.