DEVELOPMENT OF A FREQUENCY SELECTIVE SURFACE BASED FLEXIBLE AND WIDEBAND ELECTROMAGNETIC ABSORBER

Abstract

This thesis presents the development of a frequency selective surface based flexible and wideband absorber. A circular ring shaped structure with joined inner concentric rings is proposed to provide a wide-band absorption in the frequency range of 7.8 GHz to 17.7GHz . The structure is designed using RT duroid 5880 dielectric having thin copper layers on both sides of the substrate The thickness of the dielectric is 0.13mm whereas the thickness of copper layer is 0.017mm each. The structure has a multi-layer geometry having two RT duroid substrates. A commercially available foam is placed between the two layers of RT duroid 5880 in order to provide support to the structure. The total thickness of the structure is 3.664mm. Lumped resistors are added in the structure in order to widen absorption bandwidth as well as increase absorption performance of the absorber by increasing ohmic losses. There are total of 8 resistors per unit cell. Resistors also improve impedance matching of the structure and thus improve its overall absorption performance. The structure is simulated in Simulia’s CST software using frequency domain solver The simulated results shows a wideband absorption within the range of 7.8GHz to 17.7 GHz at normal incidence . The structure exhibits an angular stability upto 30° for an absorption of more than 80%. A 14x14 array (185.5mm x 185.5mm) prototype was fabricated in order to experimentally measure the aforesaid calculations. The structure was fabricated using negative photolithography technique and free space method was used to measure the reflection coefficients of the absorber. The measured results of the absorber in planar and Conformal (R=150mm) configurations are reported and the structure provides good absorption for a wideband frequency alongwith being flexible.