Electromagnetically induced transparency and lattice resonances in metasurfaces composed of silicon nanocylinders

Densely packed metasurfaces composed of cylindrical silicon nano-resonators were found to demonstrate the phenomenon of electromagnetically induced transparency at electric dipolar resonances. It was shown that this phenomenon is not related to overlapping of dipolar resonances or to the Kerker’s effects. The observed transparency appeared to be related to interference between waves scattered by nano-resonators and by additional scattering centers including the electric branch of lattice resonances. Coupled resonance fields were also found to contribute to observed phenomena

Triple-notch UWB monopole antenna with fractal Koch and T-shaped stub

© 2015 Elsevier GmbH. All rights reserved. In this study, a triple-notch ultra-wideband (UWB) monopole antenna with fractal Koch and T-shaped stub is presented. The prototype antenna is based on a circular monopole antenna with a back-plane feed line modified for 2-11 GHz in an omnidirectional pattern. By implementing a combination of fractal Koch and T-shaped stub on the antenna, a triple-notch band occurred at 2, 3.5, and 5.8 GHz for rejecting personal communication services (PCS), worldwide interoperability for microwave access (WiMAX), and wireless local area network (WLAN). In addition to the UWB application frequency range of 3.1-10.6 GHz, the final antenna covers a frequency range of 1.78-1.91 GHz for GSM 1800, 2.28-3.120 GHz for Wi-Fi, and 2.4 GHz for Bluetooth applications with a voltage standing wave ratio (VSWR) \u3c 2. Simulated results of HFSS and CST are compared with experimental results. The dimensions of the antenna are 50 mm × 50 mm × 1.6 mm. The current distribution and efficiency at notch frequency are noted for the whole frequency band, and the maximum antenna gain is between -3.5 and 6.5 dBi. In this study, methods using Koch structure and T-shaped stub to achieve triple-notch antenna are implemented in three steps. In addition, the effects of T-shaped stub and fractal Koch on the magnitude of the antenna (S11) are studied

Investigation and design of an ultra-wideband fractal ring antenna for notch applications

In this article, an ultra wideband ring antenna with a fractal formation for notch application is presented. The antenna was printed on FR-4 substrate, which was a low cost one with the relative permittivity of 4.4 and thickness of 1.6 mm. The total dimension of antenna was 50 mm × 50 mm. It could be applied as a notch antenna for propagation rejection in IEEE 802.11a for instance by covering were as without conflicting with wireless systems. The prototype antenna presented in this article, has a rejection band at 5-6 GHz and covers the frequency range of 2.1-11 GHz with the VSWR of less than 2. For improvement of the notch frequencies and for obtaining dual notch band characteristic some changes in prototype antenna with a slot at fractal structure have been performed. The final antenna had dual notch band at 2.5 and 5.5 GHz. The current distribution in the notch frequency has been provided. The efficiency has also been checked for the entire frequency band. The maximum antenna gain was achieved between 2-8 dBi. All the simulations were done in HFSS and compared with the experimental results

Novel optical polarizer design based on metasurface nano aperture for biological sensing in mid-infrared regime

© 2017, Springer Science+Business Media New York. Since Metasurfaces are playing important roles in optical devices such as optical polarizers and detectors, in this article, we have proposed a novel shape of nano aperture antenna for mid-infrared applications such as bio-sensing and other potential optical applications based on plasmonic characteristic of the gold layer over the SiN substrate. The transmittance tensor is obtained for vertical and horizontal linear polarization and base on boundary condition of the metasurface, the circular polarizations are extracted which are confirmed by the electric field distributions. We have shown by the parametric studies that the phase difference is altered by the gap and slot width and so with the dimension modification, we are able to achieve circular polarizer in the optical range. The biological materials with a thickness of 80 nm have then been placed over the metasurface layer and the figures of merits have been obtained. We have revealed that when the circular polarization is osculated to the metasurface at a special frequency the linear polarization is obtained in the other side of the metasurface. The nano aperture has been modeled and the finite difference time domain calculations are performed in CST Microwave Studio as a commercial full wave simulation software

Superluminal media formed by photonic crystals for transformation optics-based invisibility cloaks

© 2016 IOP Publishing Ltd. We have developed an approach to building superluminal medium for transformation optics-based devices, including invisibility cloaks, from photonic crystals. Analysis of dispersion diagrams of 2D arrays composed from dielectric rods has shown that at frequencies corresponding to the second bands formed due to bandgap opening at increase of rod permittivity, the medium formed by arrays exhibits refractive indices providing for superluminal phase velocities of propagating waves. It is further demonstrated that rod arrays with various lattice constants could be used for realizing a range of superluminal index values prescribed by transformation optics for cylindrical cloaks at arbitrary chosen operating frequency. The performed studies allowed for solving a row of problems with employment rod arrays in the cloak medium: in particular, formulating transformation optics-based prescriptions for refractive index dispersion in the cloaking shell, defining the dimensions of array fragments capable of responding similar to infinite arrays, finding optimal distribution of linear arrays sets at their coiling to form concentric material layers in the cloaking shell, and employing interaction between neighboring array sets with various lattice constants to assist the realization of prescribed index dispersion. The performance of the superluminal medium formed by rod array sets was demonstrated on an example of a cloaking shell developed for microwave frequency range. In contrast to metamaterial-based cloak media, the developed media requires neither material homogenization, nor obtaining the effective parameters with peculiar values and Lorentz\u27s type resonances in rods. Combination of these advantages and low losses makes photonic crystals perspective materials for invisibility cloaks operating in THz and optical ranges

Unconventional designs of RF probes for high-field MRI to enhance magnetic field uniformity

© 2017 USNC-URSI. We present approaches to enhancing magnetic field uniformity produced by RF probes in high-field Magnetic Resonance Imaging (MRI) scanners by introducing compensating non-uniformities in the probe designs. Unconventional designs of RF probes for operating at 600 MHz in 14 T MRI scanners are demonstrated, including a solenoid coil with non-uniform wrapping and dielectric separators, a system of microstrip patch antennas with substrates engineered by using high permittivity inserts, and a system of specifically shaped patch antennas. The advantages of the proposed probe designs are discussed