Electromagnetic Wave Absorbing Composites with a Square Patterned Conducting Polymer Layer for Wideband Characteristics

The applications of electromagnetic- (EM-) wave-absorbers are being expanded for commercial and military purposes. For military applications in particular, EM-wave-absorbers (EMWAs) could minimize Radar Cross Section (RCS) of structures, which could reduce the possibility of detection by radar. In this study, EMWA composite structure containing a square periodic patterned layer is presented. It was found that control of the pattern geometry and surface resistance induced EMWA characteristics which can create multiresonance for wideband absorption in composite structures. 1. Introduction 1.1. Periodic Patterns for Radar Absorbing Structures (RAS) An electrically conductive medium is used as an EM-wave reflector and shielding structure. When the conductive surface is engraved, DC can always be conducted, but in the case of AC, there is a specific region where the EM wave cannot be transmitted or reflected. In the frequency range of interest, periodic patterns such as EM wave filters are considered frequency selective surfaces. There are various methods and equations to verify the characteristics of the pattern layer; however, a computer simulation using FEM was assumed to be an effective tool to verify the accuracy of the equations. When the square array pattern is located in free space, the approximate equation for the resonance characteristics is as follows [1]: Total transmission occurs at and mean the size of unit cell and is the wavelength. From the Babinet principle, the grid type and patch type have the same resonance point, with opposite filter characteristics. The equation assumes the medium of frequency selective surface (FSS) is a metallic material like perfect electric conductor (PEC) of an infinitely thin film. When we design the periodic pattern for a radome, this equation is useful. but the equation assumes a free-space boundary. When a dielectric slab is added to the FSS layer, the real characteristics of the periodic pattern are changed. In general, the degree of change depends on the dielectric properties and the resonance frequency moves to the low frequency range [2]. The high impedance surface is different from the lossy surface; the periodic pattern is usually made by metal. The pattern controls only the reactive part of the impedance, and the layer is assumed to be thicker than the skin depth. As a result, control of the pattern thickness cannot affect the EM characteristics of the filter. 1.2. Advantage of Periodic-Pattern-Layered RAS (PPRAS) One of the basic models for RAS is the Salisbury absorber, which uses a specific resistive