Theoretical Analysis on the Absorbing Structures Under Open Boundary Condition

In this article, absorbers with open boundary condition are analyzed theoretically. First, a complex analysis method is used to obtain integrations of the reflection and transmission over the whole frequency band for slab with general boundary condition, which can be regarded as a general extension of Rozanov's discussion. Second, integration relations with open boundary condition for single-layer slab and multilayer slab are obtained successively. Third, theoretical limitations for the absorbers with open boundary condition are deduced. As an application, complete analytic limitations between the reflection, transmission, operating band, and thickness are provided for single-layer nonmagnetic absorber with small reflection and transmission required. Finally, after presenting optimal design method for single-layer nonmagnetic slab, several absorbers are designed as examples.