Broadband and ultra-thin terahertz metamaterial absorber based on multi-circular patches

An ultra-thin narrow-band metamaterial absorber (MA) based on a periodic array of circular metal patch is numerically proposed at terahertz frequencies. The MA could exhibit an absorption peak at 5.91 THz with the absorptivity of 99.9%. The surface current distributions and distributions of the z-component electric field indicate that high absorption is due to the strong magnetic resonance between the two metallic layers and prefect impedance-matched to the free space at the resonance frequency. By simply assembling a diagonal arrangement of several circular patches with slightly different geometric parameters into a unit cell, the bandwidth of strong absorption (more than 90%) can be effectively improved. Finally, the bandwidth of strong absorption for the four-patch MA achieves 0.98 THz and the corresponding full width at half maximum (FWHM) increases to 1.49 THz. Moreover, the thickness of the four-patch MA is only about 22 times smaller than the central wavelength and it could operate well at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.