Investigation of a Metamaterial Absorber with a Ground Plane by Impedance Analysis

Abstract

A metamaterial absorber is a fascinating candidate for stealth technology because it can prevent the propagation of reflected electromagnetic waves. Many metamaterial absorbers use a ground plane to yield high absorbance. Two theories are applied to investigate metamaterial absorbers: the matching air impedance and the high imaginary part of the refractive index simultaneously, or destructive interference theory. Destructive interference theory is often used to investigate metamaterial absorbers with a ground plane. In this work, a metamaterial perfect absorber with a ground plane is investigated using impedance analysis. High absorbance is generated while the matching air impedance condition is fulfilled for the metamaterial absorber with a ground plane. The $$ \left| {\left( {z_{\rm{r}} \left( {\hbox{real}} \right) - 1} \right) + iz_{\rm{r}} \left( {\hbox{imaginary}} \right)} \right| $$ is calculated to describe the matching air impedance criteria, where zr (real) and zr (imaginary) are the real and imaginary values of relative impedance, respectively. The absorbance is below 0.1 in the $$ \left| {\left( {z_{\rm{r}} \left( {\hbox{real}} \right) - 1} \right) + iz_{\rm{r}} \left( {\hbox{imaginary}} \right)} \right| > 2 $$ range. The gradient of the graph in the $$ \left| {\left( {z_{\rm{r}} \left( {\hbox{real}} \right) - 1} \right) + iz_{\rm{r}} \left( {\hbox{imaginary}} \right)} \right| > 2 $$ range is close to zero; thus, the absorbance performance gradually changes. A significant change in absorbance is found in the $$ 0 \le \left| {\left( {z_{\rm{r}} \left( {\hbox{real}} \right) - 1} \right) + iz_{\rm{r}} \left( {\hbox{imaginary}} \right)} \right| \le 2 $$ range. The gradient of the graph in the $$ 0 \le \left| {\left( {z\left( {\hbox{real}} \right) - 1} \right) + iz\left( {\hbox{imaginary}} \right)} \right| \le 2 $$ range is around 0.45. Overall, the $$ \left| {\left( {z_{\rm{r}} \left( {\hbox{real}} \right) - 1} \right) + iz_{\rm{r}} \left( {\hbox{imaginary}} \right)} \right| $$ result successfully clarified the absorbance performance for the cross-shaped metamaterial absorber with a ground plane.