A REVIEW ON THE PURSUIT OF AN OPTIMAL MICROWAVE ABSORBER

Mitigation of the electromagnetic radiations is essential for reliable communication of information. The challenges lie in achieving sufficiently good absorption over a broad range of frequencies. Considering the applications in airborne and handheld devices where light weight, thin, conformable and broadband absorbers are desired, numerous techniques and methods are applied to design broadband absorbers. In this review paper, a detailed analysis on electromagnetic absorbers including evolution, the materials used, and characteristics such as absorption efficiency over the years is presented. Progress on recent research on various polymer- based and metamaterial- based microwave shields are included along with their findings. Several prospects such as broadbanding, flexibility, multibanding are described here. Various material and structural composition offering good absorption performance in different frequency bands are also summarized whose the techniques can be used for suppressing electromagnetic interference and radar signature. The paper specifies the aspects one encounters while designing and realizing a perfect microwave absorber. Explored here are several works of distinguished authors  which are based on various techniques used to achieve good absorption performance with ease of mounting

Ultrabroadband light absorbing Fe/polymer flexible metamaterial for soft opto-mechanical devices

Altres ajuts: ICN2 is funded by the CERCA programme/Generalitat de Catalunya.Ultrabroadband light absorbers are attracting increasing interest for applications in energy harvesting, photodetection, self-regulated devices or soft robotics. However, current absorbers show detrimental insufficient absorption spectral range, or light angle and polarization dependence. Here we show that the unexplored optical properties of highly-damped plasmonic materials combined with the infrared absorption of thin polymer films enable developing ultrabroadband light-absorbing soft metamaterials. The developed metamaterial, composed of a nanostructured Fe layer mechanically coupled to a thin polydimethylsiloxane (PDMS) film, shows unprecedented ultrabroadband and angle-independent optical absorption (averaging 84% within 300-18000 nm). The excellent photothermal efficiency and large thermal-expansion mismatch of the metamaterial is efficiently transformed into large mechanical deflections, which we exploit to show an artificial iris that self-regulates the transmitted light power from the ultraviolet to the long-wave infrared, an untethered light-controlled mechanical gripper and a light-triggered electrical switch

Design and simulation of cross-block structured radar absorbing metamaterial based on carbonyl iron powder composite

This paper reports the design and simulation of a three layered cross-block structured radar absorbing metamaterial (RAMM). The effective electromagnetic parameters of the designed structure are highly dependent on its geometric dimensions, subsequently behaving as a metamaterial. COMSOL Multiphysics simulation software was used to analyze the frequency dependent absorption response of the designed RAMM. The input impedance of multilayered absorber and strong fluctuation theory equations are used to theoretically verify the absorption response of the RAMM. The simulated result showed that the reflectivity of the RAMM is below -10dB from 4.2 – 18.0 GHz frequency band with absorber thickness of 4.2mm. The calculated reflectivity result is in close agreement with the simulated result, thus confirming the validity of the design. The operational bandwidth to thickness ratio of this RAMM was found to be 13.029 making it better than the recently reported one with a value of 9.745 and thus contributing significantly in overcoming the contradicting demand of broadband and thin thickness.Keywords: Bandwidth, COMSOL Multiphysics, Metamaterial, Radar Absorbing Metamaterial, Reflectivit

Theory, design and perspectives of electromagnetic wave absorbers

Electromagnetic absorbers for free space and cavity absorption are discussed. Classical configurations are described as well as more recent designs. The presented layouts are able to provide absorbing behaviors spanning from ultra-narrow band to ultra-wideband. A comparison among various solutions is presented both in terms of achievable bandwidth and in terms of minimum theoretical thickness. The problem of cavity resonances is also addressed. It is shown that resonances can be damped by using alternative solutions with respect to the classic use of lossy magnetic materials

Total absorption of visible light in ultrathin weakly absorbing semiconductor gratings

© 2016 Optical Society of America. The perfect absorption of light in subwavelength thickness layers generally relies on exotic materials, metamaterials or thick metallic gratings. Here we demonstrate that total light absorption can be achieved in ultra-thin gratings composed of conventional materials, including relatively weakly-absorbing semiconductors, which are compatible with optoelectronic applications such as photodetectors and optical modulators. We fabricate a 41 nm thick antimony sulphide grating structure that has a measured absorptance of A = 99.3% at a visible wavelength of 591 nm, in excellent agreement with theory. We infer that the absorption within the grating is A = 98.7%, with only A = 0.6% within the silver mirror. A planar reference sample absorbs A = 7.7% at this wavelength

Pyramidal metamaterial absorber for mode damping in microwave resonant structures

In many resonant structures the damping of parasitic or higher order modes is indispensable to guarantee a correct and stable performance. This is particularly true in the microwave region in case of cavities or other resonant systems operating in accelerating structures, where the mitigation of spurious resonance effects is mandatory to achieve high quality particle beams. We present the results on the mode suppression in a real pillbox cavity by inserting a properly designed pyramidal metamaterial that acts as light, small volume damper for specific resonances in the range 3-4 GHz, only slightly perturbing other intrinsic modes. Measurements of the cavity response without and with the metamaterial absorber are presented and compared with full wave simulations. Field distribution for the pillbox intrinsic modes under scrutiny is also presented, showing that damping induced by the metamaterial critically depends on its relative position inside the cavity