An Investigation on Multiband Ultra-Thin Polarization Insensitive Metamaterial Based Microwave Absorber and Their Application

Abstract

A dual-band ultra-thin compact polarization-independent metamaterial absorber is proposed. The proposed absorber consists of two resonating structures i.e. a swastika-shaped and a square ring-shaped. The swastika-shaped structure is enclosed within a square ring. The size and thickness of the unit cell are 6 × 6 mm2 and 0.015λ (where λ is the lowest resonating frequency), respectively. The combination of two resonating structures provides peak absorbance at 5.65GHz and 10.91GHz with maximum absorptivity 98.8% and 99.5%, respectively. The application platform of the reposed absorber lies in C and X band. A compact ultrathin metamaterial absorber with three resonances in S-band, X-band and Ku-band is proposed. The geometry of the proposed absorber consists of a square ring, a split ring, and a plus-shaped resonating structure. The plus-shaped structure is enclosed within a split-ring resonator and it is further enclosed by an outer square ring. The proposed absorber is fabricated on a low-cost FR4 substrate of thickness 1mm i.e. 0.011 λ (where, λ is the lowest resonating frequency). The size of the unit cell size is 10 × 10 mm2. It exhibits are 99.6%, 99.1%, and 99.1% absorption at 3.4 GHz, 9.6 GHz and 13 GHz, respectively. Further, a wideband metamaterial absorber has been discussed in this thesis. The proposed structure consists of an L-shaped structure and a diagonal rectangular shaped structure. The dimension of the unit cell arrangement is 5 × 5 mm2 and the thickness of the structure is 1.54 mm. The proposed structure provides the wideband absorptivity of 9 GHz from 12 GHz to 21 GHz having absorption of 99.6%, 99.9% and 97.6% at three resonating frequencies i.e. 12 GHz, 17 GHz and 21 GHz respectively. Finally, a multiple-input multiple-output (MIMO) configuration planar inverted-F antenna (PIFA) has been presented for the use in mobile handsets with high isolation between the antenna elements. The isolation is enhanced by using an array of the metamaterial absorber between the antenna elements at a focused frequency of 5.65 GHz. The proposed antenna elements geometry consists of swastika-shaped design on the FR-4 substrate having dimensions of 7 × 7 × 0.8 mm3 at a height of 2.8mm from the ground plane of dimensions 100 × 50 × 0.8 mm3. An array of 4 × 4 unit cells of metamaterial absorber is used to enhance isolation between the antenna elements. Results show that the isolation between the antenna elements has improved from -12dB to -25dB at the operating frequency of 5.65 GHz. Further, S-parameters, radiation characteristics, and diversity parameters are analyzed.