Metamaterials in Electromagnetic Wave Absorbers

Abstract

Stealth technology in terms of absorption of electromagnetic waves is a most valuable research area for military purposes. Development of radar absorbing materials (RAM) had been actively researched for a quite long time. In the RAM design, weight, thickness, absorptivity, environmental resistance and mechanical strength are the key factors and therefore development of RAM with low density and high strength is a challenging task. As an alternative, research interest has shifted towards radar absorbing structures (RAS) and metamaterial is one of the lucrative options for the development of RAS. Metamaterials are a new class of ordered composites that exhibit exceptional electromagnetic properties not readily observed in nature. Built from microstructure that is small compared to wavelength of operation, metamaterials can be designed with effective permittivity and permeability values that can be large or small or even negative at any selected frequency. In this review paper, we first place the stealth technology in brief and then concept of metamaterials in context of conventional materials. We then discuss reflection theory of metamaterials from stealth point of view. Next section deals with recent progress towards its application as electromagnetic absorbers and future prospects especially in higher frequency region.

Microencapsulation of Traditional Chinese Herbs—PentaHerbs extracts and potential application in healthcare textiles

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Role of ammonium chloride in preparing poly(urea‐formaldehyde) microcapsules using one‐step method

“…Microcapsules have been widely used in various fields, such as pharmaceuticals,1, 2 textiles,3, 4 food additives,5, 6 electronic inks,7, 8 pesticides,9 and self‐healing materials10, 11 among others. There are many techniques for fabricating microcapsules, including interfacial polymerization, in situ polymerization, and coacervation 12. Among them, the in situ polymerization process with urea–formaldehyde resins as the capsule wall, has attracted the attention of researchers13–16 due to its simplicity and excellent mechanical strength of the resulting capsules.…”

Encapsulation of lipophilic fragrance by polymerization of the intermediate aqueous phase of an oil-in-water-in-oil (O/W/O) double emulsion

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“…Nowadays, encapsulation is present everywhere as in pharmaceutical 4 , agro-food 5 , phyto-sanitary 6 industries or cosmetics and fragrance applications 7,8 . Two main categories of capsules are described in literature 2 : the core-shell and the matrix capsules. In the latter, the active ingredients are integrated within the matrix capsules.…”