Metasurfaces (MTSs) are planar artificial structures used to control the waves in a desired manner [1–2]. These engineered structures with ultrathin thickness have made it possible to manipulate the electromagnetic (EM) waves in an unprecedented manner, providing various useful functionalities, including anomalous reflection/refraction, polarization conversion, absorption, chemical and bio sensing, dynamic beam steering, vortex, Airy and Bessel beam generations and holographic image projection to name a few [2–4]. Besides the abovementioned, polarization conversion and absorption are the two important functionalities that can be realized from MTSs and is the recent hot topic of research, due to its applications in wireless communications, imaging, holography, stealth technology, sensing and many more [2–9]. Although almost near perfect absorption has been achieved in various frequency regimes using various MTSs [5, 6], however they still lake some features like polarization insensitivity, angular stability and multiband operation, etc. Therefore, there is a strong need to design MTS based absorbers which have the features of high angular stability, polarization independency, wide and multiple band operations and so forth. Similarly, Polarization conversion which have been realized in many frequency regimes using different MTS based structures [7–9]. However, there is still a huge space to make these polarization converters more efficient and with the feature of multi-band which might be more practical. For example, in a real time scenario we need a broad, multi-band and angularly stable polarization converter with high polarization conversion ratio (PCR). Moreover, it is highly demanding to design a MTS which can perform multiple tasks using the same shared aperture. Thus there is a strong desire to design a MTS which can perform polarization conversion in one case accompanied by some other useful functionality in the other case. In this article we present near perfect absorption and polarization conversion in different frequency bands, by designing a novel unit cell and then a MTS with their periodic arrangement in the two-dimensional spatial plane.
In this paper the effect of coupling two kinds of metamaterial cells with a coil to achieve Magnetic Resonance Imaging (MRI) is investigated. Both an array of four spirals and a single spiral-shaped metamaterial are associated to the coil antenna. The goal is to increase the sensitivity of the whole system and to improve the homogeneity of the RF magnetic field pattern. The spiralshaped metamaterials associated to the antenna give very promising numerical results. We are fabricating both structures using microfabrication techniques because of the small size of the structures.
A metamaterial, with an asymmetric geometry, characterized simultaneously by a double negative permittivity and permeability is introduced. We show that tuning a left-handed symmetric bilayer metamaterial recently proposed by Ozbay et al. towards an asymmetric monolayer in the microwave regime does not suppress the left-handed behavior at normal incidence. The bilayer structure is transformed step by step firstly into a monolayer symmetric structure which does not exhibit any left-handed behavior and finally into an asymmetric monolayer material where a left-handed behavior reappears at normal incidence.
In this study, we present the conception, the simulation and the characterization of a controllable left-handed (CLHM) material operating between 7 and 16 GHz. This compact material, composed from metallic wires including p-i-n diodes and split-ring resonators is optimized to have a controllable permittivity and a fixed permeability. Changing the bias current of the p-i-n diodes controls the dielectric permittivity of the material, which is negative. This allows the tuning of the CLHM material from a reflection state to a transmission state. We have measured the transmission of the material between 7 and 16GHz, and its negative refraction index at oblique incidence, demonstrating the switching of the electromagnetic state of the material.
Materials with a periodically structured dielectric constant may exhibit forbidden photonic band gaps (PBG), that is, frequency domains where electromagnetic fields cannot propagate. The position and width of forbidden gaps can be controlled via the geometrical parameters of the structures and the contrast between the different permittivities. PBG materials have potential applications to a variety of devices in the microwave domain such as waveguides, couplers, reflectors and antenna substrate. This work reports on first experimental and theoretical studies of microwave guides and ring couplers based on PBG materials. Experiments are performed in the 27-75 GHz frequency range. Different coupling situations are given in illustration.
Since the event of metamaterials, a considerable effort has been performed to fabricate them in the infrared and optical regimes. However, apart from the experimental demonstration and observation of H. J. Lezec et al based on surface plasma polariton, direct visualisation of negative refraction based on metal-dielectric resonances have not been performed experimentally so far in the infrared or visible regime (photonic crystals with periodicity on the order of the wavelength are not considered here). Very often only simulations have given the needed phase information for the retrieval methods in optical experiments. In this paper, a metamaterial composed of SRR (Split Ring Resonators) and a continuous wire is considered. We extract the phase information from the transmission and the reflection measurements through a diffraction grating made of the metamaterial to be characterized and silicon or gold. This retrieval allows a unambiguous retrieval of the effective parameters under conditions discussed in the paper at IR and visible wavelengths.
