Wide-band polarization independent perfect metamaterial absorber based on concentric rings topology for solar cells application Patrick Rufangura a , Cumali Sabah b, * a Sustainable Environment and Energy Systems, Middle East Technical University e Northern Cyprus Campus, Kalkanli, Guzelyurt, 99738, TRNC / Mersin 10, Turkey b Department of Electrical and Electronics Engineering, Middle East Technical University e Northern Cyprus Campus, Kalkanli, Guzelyurt, 99738, TRNC / Mersin 10, Turkey article info Article history: Received 25 February 2016 Received in revised form 15 April 2016 Accepted 17 April 2016 Available online 19 April 2016 Keywords: Metamaterial Absorber Solar cell Photovoltaic applications Wide-band abstract Since the discovery of metamaterial absorber to the present days, several designs were proposed which display single-, dual-, and multiple-bands absorption responses in almost all regions of solar spectrum. However, little work has been done for wide-band metamaterial absorber in the visible frequency range. Hence, a novel wide-band metamaterial perfect absorber (MPA) based on concentric Circular Ring Resonator (CRR) topology is proposed for the application to improve the absorbance of solar photovoltaic cells for the visible frequency region. The proposed design consists of three basic components as reso- nators, ground metal, and dielectric spacer. The geometrical parametric study is conducted in order to investigate the flexibility of the proposed MPA structure. The design flexibility also analyzed by the polarization angle insensitivity character, in which the proposed design provides the perfect absorption for different angles of the incident electromagnetic wave as well as for TE and TM polarized waves. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Fossil fuels are still dominating the world energy production regardless of uncertainty on their future availability and their contributions to greenhouse gas emissions which causes global warming and current change in weather patterns. The reduction of CO 2 emissions is on top of the agenda for every nation and inter- national communities, with renewable energy technologies (wind, hydro, solar energy and others) and development of other envi- ronmental friendly energy resources assumed to play a critical role in the near future [1]. Solar energy technologies seem to be one of the best alternatives for fossil fuel based energy production [2], mainly because solar radiations are freely available for every land and they have potential use for both on-grid and off-grid projects. Several technologies for solar energy harvesting have been devel- oped so far and with others still in the pipeline. The very famous one is solar photovoltaic cell (Solar PV cell) which converts solar radiations directly into electricity and solar thermal system which uses solar radiations to generate thermal energy and then elec- tricity [3e6]. However, the development of these technologies has been threatened by the limited efficiency of solar cells which is caused by their inability to absorb solar radiations effectively [7]. Several researchers have been working hard to improve the effi- ciency of solar cells. But, lots of improvement still need to be done in order to harness this resource effectively. The good news is the current emergence of metamaterials research which revealed the ability to produce metamaterial perfect absorber for solar cells and the enhancement of the absorption capability of these devices [8]. Few decades ago, Smith et al. [9] developed the first artificial man-made materials to exhibit exotic properties not easily obtainable or unavailable in nature. These engineered materials also called ‘metamaterials’, which consists of a periodic arrange- ment of sub-wavelength unit cell structures (as metaledielectric layers). By careful tailoring of the shape and size of the meta- materials, unusual electromagnetic ‘EM’ properties (such as nega- tive electric permittivity, negative magnetic permeability, negative index of refraction, and so on) can be realized [9e15]. Owing these exotic EM properties, metamaterial technology has attracted attention of many researchers and has also brought several appli- cations in electromagnetic research field [16e24]. The very prom- inent application is the realization of perfect metamaterial absorber ‘MPA’ which was first proposed by Landy et al., in 2008 [24]. Their proposed metamaterial absorber unit cell consists of two metallic * Corresponding author. E-mail address: sabah@metu.edu.tr (C. Sabah). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2016.04.162 0925-8388/© 2016 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 680 (2016) 473e479