Abstract
Frequency Tunable Microwave absorbers in desired low thickness is a critical requirement in electronics, radar and military applications where Electro Magnetic Interference has become a major concern. Composite are obvious choice of absorbers in above applications. The aim of this paper is to investigate the use of carbon fiber grid layers as Frequency Selective Surface (FSS) on Carbon Filler based Glass-Epoxy composites. In this work, three key points are highlighted, first is design, modeling of FSS grid, using equivalent circuit model and Transmission Line Theory, second is the use of fillers including Milled Carbon Fibers and Carbon Nano Tubes (CNTs) for microwave absorption, third is to have the desired reflection loss at specified thickness of around 6-7 mm which is low as compared to recent trends. It is found that the factors like the number of grid layers , their unit cell dimensions, type of filler, and the top surface layer, affects the resonance frequency and hence the microwave absorption characteristics of the composite laminates. The results are satisfactory showing minimum of -9.8 Db of Reflection Loss at 6-7 mm thickness laminates, for varied range of frequency.
Highlights
Electro Magnetic Interference has made Microwave absorbers an immediate requirement in various fields of electronic and military equipment [1]
We have investigated two types of filler one is Milled Carbon Fibers and other is Carbon Nano Tubes (CNTs) with high conductivity and high aspect ratio, which is more suitable at high frequency
The physical effects i.e. the losses, reflection can be modelled by equivalent circuit analysis with lumped parameters which can be calculated by characteristic impedance and absorption coefficient of the absorber
Summary
Electro Magnetic Interference has made Microwave absorbers an immediate requirement in various fields of electronic and military equipment [1]. With the grid having more free transparent area, there is formation of capacitive network while more opaque area and transparent lines leads to formation of conducting lines across the composite structure to allow inductive magnetic effects to dominate [10] These distributed capacitance and inductance causes attenuation of the incident Electric and Magnetic field respectively at the resonance range. The conventional designs of microwave absorbers were based on metallic FSS surfaces like Salisbury screens, jaumun absorbers that follow simple design rules of multiple reflection, phase cancellation due to the path difference created by the quarter wave layer These designs were having tunable resonant frequency but due to heavy structures and low mechanical flexibility, became difficult to use in military applications. In this paper we designed a microwave absorber composite with epoxy resin and carbon-based fillers on top of which a carbon Fiber Grid structure was pasted which acts as a FSS layer. The results appreciate their use in applications like EMI shielding where the equipments work in different frequency ranges like 5-6 GHz and for stealth based uses in military applications targeting 8-12 GHz range
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