Metamaterial Absorbers for Lining System Shield Box and Packaging: Cavity Analysis and Equivalent Material Design

Metamaterial absorbers have been introduced as custom-designed solutions for mitigating radiated emissions from a system shield box. In this article, the analysis of these system enclosures is generalized by using a cavity analysis approach. Inspecting surface current, frequency, and quality factor of the resonant cavity modes of a shield box with metamaterial lining provides insight into evaluating and quantifying the efficacy of an absorber solution. The increased radiated emission from an enclosed system is traced back to the potential excitation of resonant cavity modes. The cavity modes can be excited when common mode signals are present at proper locations. In a generic high-speed differential signaling system, common mode signals are shown to be created as a result of differential line phase mismatches and demonstrated to yield strong spectral components at twice the harmonics of Nyquist frequency. A second design approach is introduced herein that involves finding the equivalent complex permittivity and permeability, i.e., an equivalent bulk material characteristic for the metamaterial absorber. This approach expedites the design of metamaterial absorbers and evaluation of their effectiveness for emission reduction from few hours to few minutes.