Broadband ultrathin low-profile metamaterial microwave absorber Deepak Sood 1 • Chandra Charu Tripathi 1 Received: 29 July 2015 / Accepted: 17 November 2015 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract In this paper, a single-layer broadband low- profile ultrathin metamaterial microwave absorber is pro- posed for wide angle of incidence. The proposed absorber provides triple-band absorption under normal incidence of electromagnetic wave with two peaks lying in X-band and one in Ku-band. The unit cell is designed by using para- metric optimization in such a way that the three peaks merge together to give broadband absorption. The absorber exhibits full width at half maxima bandwidth (FWHM) of 7.75 GHz from 7.55 to 15.30 GHz for wide angle of incidence up to 60° for both TE and TM polarizations. The mechanism of absorption of the absorber has been analyzed by field and surface current distributions. The proposed absorber has been fabricated and experimentally tested for different angles of incidence and polarization of the inci- dent wave. The absorber is low profile with unit cell dimension of the order of 0.168k 0 , and it is ultrathin with a thickness of *k 0 /17 at the center frequency of 11.43 GHz corresponding to the FWHM absorption bandwidth. This proposed absorber can be used for many potential appli- cations such as stealth technology, cloaking and in antenna systems. 1 Introduction Periodic array of conducting elements, i.e., metamaterials, has been highly investigated due to their unusual and exotic properties not found in nature [1]. They find their appli- cations in cloaking [2], antenna structure [3], lens imaging [4], solar cells [5] and thermal imaging [6], etc. Till date, metamaterials are continually used for improving the per- formance of microwave absorbers [7–9]. A perfect micro- wave absorber can efficiently absorb incident radiations with almost zero reflection and transmission. Metamaterial- based absorbers offer benefits over conventional absorbers such as low profile, nearly perfect absorption, ultrathin thickness and ease of design. In these absorber structures, effective medium properties, viz. permittivity and perme- ability, are modified in such a way that for an incident electromagnetic field the input impedance of the structure becomes equal to the free space impedance, which results in absorption. Although metamaterial absorbers are miniaturized structures and provide nearly perfect absorption, due to their resonant design they suffer from narrow absorption bandwidth [10]. Many, monolayer bandwidth-enhanced, metamaterial microwave absorbers with some increment in bandwidth have been proposed in [11–14]. These resonant structures have complicated design and require concurrent optimization of individual resonant frequencies. Use of multiple layers is another technique for bandwidth enhancement [15–17]. It increases the overall thickness of the absorber and limits its use for conformal planar appli- cations. Based on scaling technique, some absorber designs comprising combinations of more than one resonant structure are proposed in [9, 18–21]. This increases the unit cell dimensions and makes it unsuitable for practical applications. Another approach of bandwidth enhancement Electronic supplementary material The online version of this article (doi:10.1007/s00339-016-9884-2) contains supplementary material, which is available to authorized users. & Deepak Sood deepaksood.uiet@gmail.com 1 University Institute of Engineering & Technology, Kurukshetra University, Kurukshetra, Haryana, India 123 Appl. Phys. A (2016)122:332 DOI 10.1007/s00339-016-9884-2