Structural investigation of metamaterial unit-cells: development of incident angle insensitive metamaterial absorbers

Abstract

Initially, the importance of incident angle insensitive property for metamaterial (MTM) absorbers has been discussed in this paper. Later, two different novel approaches to design incident angle insensitive MTM absorbers have been given. Using these two approaches, two incident angle insensitive MTM absorbers have been designed, simulated, fabricated and measured. Additional to incidence angle insensitive property, the two MTM absorbers also exhibits polarization angle insensitive property. Eight-fold and four-fold symmetrical natures of the two MTM absorbers are responsible for the polarization angle insensitive property. Both the absorbers use FR4 substrate having thickness 0.6 mm as a dielectric. One absorber has a resonant frequency of 7.8 GHz and for another one, it is 4.8 GHz. In one absorber, eight smaller radius circles around a basic MTM unit cell provide angle insensitive property. In the second absorber, cross-shaped copper etchings form basic unit cell provide the angle insensitive property. In one case, up to 75° and in another case, up to 70° incident angles, absorptivity of more than 80% has been achieved.