Gain Enhancement of a Wide Slot Antenna Using a Second-Order Bandpass Frequency Selective Surface

Gain enhancement of a wide slot antenna over a wide frequency band using a low profile, second order bandpass frequency selective surface (FSS) as a superstrate is presented in this paper. The proposed multilayered FSS with non-resonant unit cells in each layer allows in-phase transmission of waves radiated from the antenna over a 3dB bandwidth of about 50%. The design allows an enhancement of upto 4dBi in the antenna gain over the entire frequency band (5-8GHz) of operation. The FSS provides a very low insertion loss between the two transmission poles along with a linearly decreasing transmission phase over the band. The composite structure shows an impedance bandwidth (-10dB) of 65% with an average gain between 6-8dBi over the frequency band with a peak gain of 9dBi. Measurement results of the fabricated prototype matches well with the predicted values

A Dual Layer Frequency Selective Surface Reflector for Wideband Applications

A dual-layer, bandstop frequency selective surface (FSS) is presented in this paper for wideband applications. Each layer uses patch type FSS with slots for miniaturization and are cascaded with an air gap in between. The low-profile FSS with unit cell dimension on the order of 0.2λ0×0.2λ0 provides transmission coefficient below -10dB in the frequency range of 4-7 GHz with 56% bandwidth. The FSS exhibits a nearly linear phase variation with frequency in the operating band and can be used as a substrate below planar wide band antennas with bi-directional radiation for enhancing its gain, directivity in the broadside direction as well as shielding it against nearby conductive surfaces such as metal cases, other printed antennas. Detailed design method, equivalent circuit analysis and measurement results of the FSS are presented in this paper

Deep Shape Matching

We cast shape matching as metric learning with convolutional networks. We break the end-to-end process of image representation into two parts. Firstly, well established efficient methods are chosen to turn the images into edge maps. Secondly, the network is trained with edge maps of landmark images, which are automatically obtained by a structure-from-motion pipeline. The learned representation is evaluated on a range of different tasks, providing improvements on challenging cases of domain generalization, generic sketch-based image retrieval or its fine-grained counterpart. In contrast to other methods that learn a different model per task, object category, or domain, we use the same network throughout all our experiments, achieving state-of-the-art results in multiple benchmarks.Comment: ECCV 201

Filtering DRA Array and Its Applications in MIMO for Sub-6 GHz Band

A dielectric resonator-based filtering array antenna along with multi input - multi output (MIMO) characteristics is represented in this paper. Two rectangular dielectric resonators, together with a filtering power splitter (PS) is used to get a high gain filtering response. The PS, which consists of a simple T-junction 3-dB power splitters and two pairs of band-rejection resonators, provides four transmission zeros outside the passband. Detail study with an equivalent circuit is presented to understand the working principle of the filtering PS. By utilizing this PS, a two element DRA array is designed at sub-6 GHz frequency band (3.20 GHz-3.54 GHz) with an average broadside gain of 7.8 dBi in the passband and four radiation dips outside the passband. The proposed filtering DRA array effectively suppresses the out-of-band signal, delivers sharp selectivity at band edges. Finally, coalescing the two-filtering array, a MIMO antenna system is presented here. The filtering array MIMO antenna gives reasonable port isolation of greater than 20 dB throughout the operating band. All the major diversity parameters to establish MIMO characteristics e.g. envelop correlation coefficient (ECC), diversity gain (DG), channel loss capacity (CCL), and total reflection coefficient (TARC) persists within their tolerable ranges

High-Entropy Alloys as Catalysts for the CO2 and CO Reduction Reactions: Experimental Realization

Conversion of carbon dioxide into selective hydrocarbon using a stable catalyst remains a holy grail in the catalysis community. The high overpotential, stability, and selectivity in the use of a single-metal-based catalyst still remain a challenge. In current work, instead of using pure noble metals (Ag, Au, and Pt) as the catalyst, a nanocrystalline high-entropy alloy (HEA: AuAgPtPdCu) has been used for the conversion of CO2 into gaseous hydrocarbons. Utilizing an approach of multimetallic HEA, a faradic efficiency of about 100% toward gaseous products is obtained at a low applied potential (−0.3 V vs reversible hydrogen electrode). The reason behind the catalytic activity and selectivity of the high-entropy alloy (HEA) toward CO2 electroreduction was established through first-principles-based density functional theory (DFT) by comparing it with the pristine Cu(111) surface. This is attributed to the reversal in adsorption trends for two out of the total eight intermediates—*OCH3 and *O on Cu(111) and HEA surfaces

A High Gain Dual Notch Compact UWB Antenna with Minimal Dispersion for Ground Penetrating Radar Application

A compact (27.5×16.5×0.8 mm3) co-planar waveguide fed printed ultra-wideband antenna operating in the impedance band of 1.75-10.3 GHz with two wide frequency notch bands at 2.2–3.9 GHz and 5.1–6 GHz, is introduced. Dual notch is achieved by inserting U-slot on the radiator and with inverted patch shaped downscaled parasitic load at the opposite end of feed line. Maximum antenna gain augmentation by about 5 dBi is achieved without changing the bandwidth, by incorporating a dual layer reflective frequency selective surface (FSS) of dimension 33×33×1.6 mm3 below the antenna. The antenna-FSS composite structure exhibits maximum radiation in the broadside direction with a peak gain of 9 dBi and an average radiation efficiency of more than 80% in the operating band. Antenna transfer function and group delay are experimentally studied in ground coupling mode of ground penetrating radar (GPR). Linear magnitude response of transfer function and consistent, flat group delay are achieved, that ensure minimal antenna dispersion and its ability for GPR application

A Compact Umbrella-Shaped UWB Antenna with Gain Augmentation Using Frequency Selective Surface

A compact (35 mm × 30 mm × 0.8 mm) co-planar waveguide fed ultra-wideband antenna with bended ground plane suitable for GPR applications is proposed in this article. The umbrella shaped radiating element is constructed using the intersection of two ellipses. The proposed antenna provides a wide impedance bandwidth of 10.35 GHz (3.05–13.4 GHz) covering the unlicensed UWB band. The simply structured antenna is easy to fabricate and to integrate in PCB board. A frequency selective surface (FSS) with two layers, each of 4×4 array, cascaded via air gap, is incorporated in the antenna as a substrate to enhance the gain by 2 to 4 dBi over the entire frequency band. Metamaterial inspired unit cells are chosen for the FSS layers, with unit cell dimension on the order of λ/10 with respect to 3 GHz, much less than λ/4. The spacing between the antenna and FSS is kept so as to enhance the gain value without hampering nearly flat gain response over the band. The gain is maintained between 5.5–8.5 dBi over the band. The antenna was investigated by comparing the simulated and measured fundamental antenna parameters. High radiation efficiency of more than 90% with non-varying group delay and nearly omnidirectional H-plane radiation pattern were achieved. Measurement results validated the antenna performance and gain enhancement due to the addition of FSS layers

Dynamical effects of missed switching in current-mode controlled DC-DC converters

Past investigations on nonlinear phenomena in DC-DC converters assume ideal switching and ignore the practical issue of switching ripples, for which the sampled data models yield piecewise smooth but continuous maps. In this brief, we show that the unavoidable nonidealities in the switching result in discontinuity in the map, which drastically changes the bifurcation structures. We demonstrate these effects experimentally, and develop simple one-dimensional models that account for switching delay and transients, and can predict the bifurcations in such systems with reasonable accuracy. Using the recent developments in bifurcation theory, we derive the limiting conditions for a reliable period-1 operation when these effects are considered