Thin Electromagnetic Absorber Research Articles

Electromagnetic Absorbing Materials

Electromagnetic absorbing materials can be classified into: conventional absorbers, metamaterial absorbers , and reconfigurable absorbers. This paper includes a short survey on these types and there applications. It also includes the design of a thin electromagnetic absorber. The absorber is based on mushroom-like electromagnetic band gap structure with square patches. A simple procedure is developed to design the absorber. The design is checked by simulation using HFSS package. The effect of changing dimensions of the structure on absorption is evaluated. The results of the parametric study were used to trim the design and get more accurate dimensions of the structure.

Exceptionally porous three-dimensional architectural nanostructure derived from CNTs/graphene aerogel towards the ultra-wideband EM absorption

Till now, development of a thin thickness (<2.0 mm), wideband absorption, ultralow filling ratio and lightweight electromagnetic (EM) that aims to solve the EM wave pollution is highly desirable but is urgent challenging. Herein, we tackle this issue by developing a novel carbon nanotube/reduced graphene oxide aerogel (CNTs/GA) absorber via a facile in-situ hydrothermal and subsequent freeze-drying route. The fabricated CNTs/GA absorber possessed the porous three-dimensional (3D) network structure, which not only greatly enhances the EM absorption capability but also contributes to the ultralow density and conductive percolation threshold. As a consequence, the absorption layer with 4 wt% of absorber (CNTs/GA aerogel) shows exceptionally EM wave absorption ability with the maximum qualified absorption bandwidth (fE) of 8.5 GHz at a thinner thickness of 1.7 mm. These achievements light the way that producing porous 3D network shaped aerogels constructed with light element can be a good candidate for wideband, ultralight, thin EM absorbers.

Metasurface Salisbury screen: achieving ultra-wideband microwave absorption.

The metasurfaces have recently been demonstrated to provide full control of the phase responses of electromagnetic (EM) wave scattering over subwavelength scales, enabling a wide range of practical applications. Here, we propose a comprehensive scheme for the efficient and flexible design of metasurface Salisbury screen (MSS) capable of absorbing the impinging EM wave in an ultra-wide frequency band. We show that properly designed reflective metasurface can be used to substitute the metallic ground of conventional Salisbury screen for generating diverse resonances in a desirable way, thus providing large controllability over the absorption bandwidth. Based on this concept, we establish an equivalent circuit model to qualitatively analysis the resonances in MSS and design algorithms to optimize the overall performance of the MSS. Experiments have been carried out to demonstrate that the absorption bandwidth from 6 GHz to 30 GHz with an efficiency higher than 85% can be achieved by the proposal, which is apparently much larger than that of conventional Salisbury screen (7 GHz - 17 GHz). The proposed concept of MSS could offer opportunities for flexibly designing thin electromagnetic absorbers with simultaneously ultra-wide bandwidth, polarization insensitivity, and wide incident angle, exhibiting promising potentials for many applications such as in EM compatibility, stealth technique, etc.

Polarisation independent resistively loaded frequency selective surface absorber with optimum oblique incidence performance

This study presents the design of a thin electromagnetic absorber which exhibits radar backscatter suppression that is independent of the wave polarisation at large incidence angles. The structure consists of a metal backed printed frequency selective surface (FSS), with resistors placed across narrow gaps inserted in the middle of each of the four sides of the conductor loops. The geometry of the periodic array and the value of the vertical and horizontal resistor pairs are carefully chosen to present a real impedance of 377 Ω at the centre operating frequency for both TE and TM polarised waves. Angular sensitivity and reflectivity bandwidth have been investigated for FSS absorber designs with thicknesses of 1, 2 and 3 mm. Each of the three structures was optimised to work at a centre frequency of 10 GHz and an incident angle of 45°. The design methodology is verified by measuring the radar backscatter suppression from a 3 mm (λ / 10) thick screen in the frequency range 8–12 GHz. The absorber construction was simplified by filling the four metal gaps in each unit cell with shielding paint, and selecting the ink thickness to give the two required surface resistance values.

Analysis of metamaterial absorber in normal and oblique incidence by using interference theory

Metamaterial absorber (MMA), which is a kind of thin electromagnetic absorber consisting of sub-wavelength metamaterial resonators and can exhibit near-perfect absorption characteristics, has been widely investigated in recently years. The impedance matching theory was proposed to analyze the configuration of MMA in most literatures. Such theory, however, may not suitable to analyze the interactions of metamaterial resonators and the ground plane. The interference theory, on another hand, can play effective approach for this kind of problem presented in recent studies, whereas little attention has been paid on the oblique incidence conditions. In this paper, we firstly extend the interference theory model to make it applicable for oblique incident waves and analyze MMA using the extended interference theory model. Secondly, we further explore the sufficient condition for the maximum absorptivity at both normal and oblique incidence cases. Thirdly, with the sufficient condition, we can obtain the absorbing frequency directly if the thickness of MMA is given. These theoretical results have significant effects on the design and analyze of MMA. And lastly, we point out that absorptivity is not absolutely insensitive to the incidence angle in TM mode as what previous study claims, but insensitive when the dielectric slab is high loss, which can also be explained by interference theory.

IN-SITU LARGE AREA FABRICATION OF METAMATERIALS ON ARBITRARY SUBSTRATES USING PAINT PROCESS

This paper proposes a novel method to make large area metamaterials on arbitrary planar hard or ∞exible substrates, in-situ. The method is based on painting the desired substrate with metallic and dielectric paints through a patterned stencil mask. We demonstrate this painting approach to fabricate ultra- thin electromagnetic absorbers based on metamaterials at X-band frequencies (8{12GHz) with paper-based stencils, silver ink and latex paint. Measurement results on absorber samples made with this process show absorption of 95%{99% in close agreement with simulation results. The proposed painting approach is a simple low cost additive manufacturing process that can be used to realize metamaterials, frequency selective surfaces, radar absorbers, camou∞age screens, electromagnetic sensors and EMI protection devices.

Analysis and Design of Ultra Thin Electromagnetic Absorbers Comprising Resistively Loaded High Impedance Surfaces

High-Impedance Surfaces (HIS) comprising lossy Frequency Selective Surfaces (FSS) are employed to design thin electromagnetic absorbers. The structure, despite its typical resonant behavior, is able to perform a very wideband absorption in a reduced thickness. Losses in the frequency selective surface are introduced by printing the periodic pattern through resistive inks and hence avoiding the typical soldering of a large number of lumped resistors. The effect of the surface resistance of the FSS and dielectric substrate characteristics on the input impedance of the absorber is discussed by means of a circuital model. It is shown that the optimum value of surface resistance is affected both by substrate parameters (thickness and permittivity) and by FSS element shape. The equivalent circuit model is then used to introduce the working principles of the narrowband and the wideband absorbing structure and to derive the best-suited element for wideband absorption. Finally, the experimental validation of the presented structures is presented.

Thin absorbers using space‐filling curve artificial magnetic conductors

AbstractFollowing our previous work, here an artificial magnetic conducting (AMC) surface, comprised of Hilbert and/or Peano space‐filling curve inclusions is utilized as a thin electromagnetic absorber. Numerical results are presented to show the effects of the incident angle, conducting strip widths and substrate thicknesses on the absorbing properties of such surfaces. The performance of a fabricated thin absorber in reducing the RCS of a conducting plate is demonstrated through measurement. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 785–790, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24186

A Thin Electromagnetic Absorber for Wide Incidence Angles and Both Polarizations

A design for planar electromagnetic absorbers is presented. The performance of this absorber is maintained over a wide incidence angles and for both TE and TM polarization. The absorber is composed of a high-impedance surface comprising an array of patches over a grounded lossy dielectric slab perforated with metallic vias (wire medium). The main contribution of the paper is to demonstrate and practically use the presence of an additional resonance when the plasma frequency of the wire medium in the dielectric substrate is close to the original resonance of the high-impedance surface. The presence of the vias between FSS and the ground plane is discussed both for the case of a high-permittivity absorber and for a low permittivity one, through the derivation of simple and efficient analytical expressions, specifically derived for the problem at hand. We show that the presence of the vias influences the oblique incidence TM absorption, and when properly designed, the insertion of the vias into the absorber structure results in a bandwidth enlargement and higher absorption performance.

New theoretical concept of thin electromagnetic wave absorber using resonant and scattering effect of dielectric and magnetic materials

Thin electromagnetic absorber such as less than 2/spl sim/3 mm will be required for wireless LAN for domestic and business use together with millimeter wave broadcasting in the future. To make a thin construction, many resonators with lossy material were used. This paper present theoretical results that are useful for absorber designs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wide band electromagnetic wave absorber with thin magnetic layers

This paper presents the design and the trially made examples of the wideband thin electromagnetic absorber with multiple layers of magnetic materials, which will be useful for the walls in houses and office buildings for protection from thee radiated waves from wireless LANs and electronic equipment.. We achieved an absorbing performance of more than 80% at 1.9 GHz, 2.45 GHz and 19 GHz by using a 0.5 mm layer of the epoxy resin containing a carbonyl iron powder and another 2.5 mm layer of epoxy resin containing a ferrite powder.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>