Dual- and Triple-Band Polarization Insensitive Ultrathin Conformal Metamaterial Absorbers With Wide Angular Stability

This paper describes a dual-band electromagnetic (EM) absorber for
C
- and
X
-band applications. The proposed structure consists of two circular ring resonators that are modified to make the absorber compact. The proposed absorber is demonstrated to be conformal, insensitive to polarization and angle of oblique incidence of incoming EM wave. To the authors’ knowledge, it is the thinnest absorber reported with a thickness of
${{\boldsymbol{\lambda }}_0}/142.65$
at lowest frequency of absorption. The absorption bands with absorption peaks of about 97% and 99% are observed at center frequencies of 4.19 and 9.75 GHz, respectively. The absorption frequency bandwidth (more than 90% of peak absorption) at these frequencies is 665 and 860 MHz, respectively. The double-band absorber can be extended to work at three frequencies by simply adding another ring between the two modified circular rings of dual-band absorber. The modified structure has absorption bandwidth of 610, 670, and 570 MHz with absorption peaks of 97.50%, 96.50%, and 98.85% at resonant center frequencies 4.19, 6.64, and 9.95 GHz, respectively. The temperature profile of the proposed absorber is measured by using lock-in infrared thermography and a temperature increase of 1.5 °C is observed at all the absorbing frequencies with transmitted RF power of 10 dBm. The experimental results agree well with the simulation results, and the proposed structure is insensitive for the transverse magnetic/transverse electric field polarization of incident waves and also the angle of incidence. It provides wide angular stability up to 45°. Along with a flat surface, the proposed absorbers are tested on a curved surface to exhibit its conformal nature.