Analyzing the absorption peak frequency of metamaterial absorber*

Metamaterial absorbers typically consist of a layer of split ring resonators (SRRs), a dielectric spacer layer, and a metallic ground plane. We have investigated the effect of both the spacer layer thickness and the SRR resonant frequency on the absorption peak frequencies. We find that by neglecting the coupling between the metamaterials and the ground plane, the absorption peak frequencies start at the resonant frequencies of the SRRs in the limit of zero spacer thickness and undergo a red shift as the spacer thickness increases. Furthermore, for a given frequency, absorption peaks can periodically be achieved as the phase delay in the spacer approaches integer multiples of 2 pi. Moreover, we find that the absorption peak frequency shift due to the variation of spacer permittivity originates predominately from the real part rather than the imaginary part. Our findings can be applied to guide metamaterial absorber design and understand the absorption peak frequency shift of sensors based on metamaterial absorbers.