Transmissive 2-bit anisotropic coding metasurface

Coding metasurfaces have attracted tremendous interests due to unique capabilities of manipulating electromagnetic wave. However, archiving transmissive coding metasurface is still challenging. Here we propose a transmissive anisotropic coding metasurface that enables the independent control of two orthogonal polarizations. The polarization beam splitter and the OAM generator have been studied as typical applications of anisotropic 2-bit coding metasurface. The simulated far field patterns illustrate that the x and y polarized electromagnetic waves are deflected into two different directions, respectively. The anisotropic coding metasurface has been experimentally verified to realize an orbital angular momentum (OAM) beam with l = 2 of right-handed polarized wave, resulting from both contributions from linear-to-circular polarization conversion and the phase profile modulation. This work is beneficial to enrich the polarization manipulation field and develop transmissive coding metasurfaces.

Multi-band Antenna with CSRR Loaded Ground Plane and Stubs Incorporated Patch for WiMAX/WLAN Applications

This paper proposes a novel compact, single structure, multi-band antenna along with tested results for wireless local area networks (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) applications. In this work, modified complementary split-ring resonators (CSRR) were incorporated in the ground layer of the patch to achieve permeable bands to accommodate multi-resonance frequencies in a single device. The proposed antenna design supported the upgraded performance and led to desirable size reduction. Open stubs were incorporated at the edges of the triangle batch to get the improved reflection coefficient responses. It resulted in specific band spectra of 2.4 / 3.4 / 5.1 / 5.8GHz for WLAN/WiMAX applications. For constructive antenna design, CST microwave studio simulation software was utilized. S11 parameter was observed as -24dB at 2.4GHZ, -32dB at 3.4GHz. -15dB at 5.1GHz and -22dB at 5.8GHz bands. Field patterns of each band were observed. The parametric study of the arrangement and positioning of the CSRR unit cell was examined. Excellent consistency between the experimental and simulated results revealed the capability of the projected structure to perform with improved gain.

Bimodal Remapping of Visual Grids

Spatially modulated neurons from the rat secondary visual cortex (V2) show grid-like firing patterns during freely foraging in open-field enclosures. However, the remapping of the V2 grid cells is not well understood. Here we report two classes of V2 grid cell populations with distinct remapping properties: one regular class with invariant grid field patterns, and the other bimodal class that has remapping induced by environmental manipulations such as changes in enclosure shape, size, orientation and lighting in a familiar environment. The bimodal V2 grid cell pattern remains stable regardless of the follow-up manipulations, but restores to the original firing pattern upon animal's re-entry into the familiar environment on the next day or from the novel environment. The bimodal V2 grid cells are modulated with theta frequency during the course of remapping and stabilize quickly. We also found conjunctive bistable V2 grid cells with invariant head directional tuning. Overall, our results suggest a new grid cell mechanism in V2 that is different from the medial entorhinal cortex (MEC) grid cells.

Frequency-Diverse Holographic Metasurface Antenna for Near-Field Microwave Computational Imaging

This article presents a holographic metasurface antenna with stochastically distributed surface impedance, which produces randomly frequency-diverse radiation patterns. Low mutual coherence electric field patterns generated by the holographic metasurface antenna can cover the K-band from 18 to 26 GHz with 0.1 GHz intervals. By utilizing the frequency-diverse holographic metasurface (FDHM) antenna, we build a near-field microwave computational imaging system based on reflected signals in the frequency domain. A standard horn antenna is adopted to acquire frequency domain signals radiated from the proposed FDHM antenna. A detail imaging restoration process is presented, and the desired targets are correctly reconstructed using the 81 frequency-diverse patterns through full-wave simulation studies. Compressed sensing technique and iterative shrinkage/thresholding algorithms are applied for the imaging reconstruction. The achieved compressive ratio of this computational imaging system on the physical layer is 30:1.

A Cross-Correlation-Based Approach to Pattern Distortion and Mutual Coupling for Shared-Aperture Antennas

This paper proposes a pattern distortion coefficient as a new figure of merit to quantitatively evaluate both mutual coupling and pattern distortions in multi-antenna systems. The proposed coefficient is defined as a cross correlation between unaffected and affected far-field patterns of antennas under test, and the input patterns are weighted using a Gaussian function to consider the target operation angle. The feasibility of the proposed approach is validated using a two-antenna system composed of an inverted-F antenna and a microstrip patch antenna, and the amount of mutual coupling is adjusted by changing the distance between the two antennas. The evaluation is further extended to a single-antenna system with a conducting wall that produces strong platform effects with serious pattern distortions. The results demonstrate that the proposed figure of merit provides quantitative insight into the amplitude and phase distortions of far-field patterns that can be caused by both mutual coupling and platform effects.

Classroom activities to study Magnetic field patterns due to current configurations

Magnets are widely used in electric devices such as motors, generators, speakers, microphones, scanning devices etc. Magnetic field produced by a current configuration like solenoid, circular coil and straight conductor find applications in engineering. In this article, techniques of visualizing the magnetic field patterns due to the above current configurations is demonstrated. These experiments are beneficial to identify suitable current configurations to produce a specific field pattern for applications in scanning and other applications. These experiments can be easily conducted in classroom. Students acquire practical knowledge on relationship between current and magnetic fields. This enables them to inculcate application skills to design current distributions to obtain a specific magnetic field pattern.

Polarization-independent anapole response of a trimer-based dielectric metasurface

The phenomenon of anapole has attracted considerable attention in the field of metamaterials as a possible realization of radiationless objects. We comprehensively study this phenomenon in the cluster-based systems of dielectric particles by considering conditions of anapole manifestation in both single trimers of disk-shaped particles and metamaterial composed on such trimers. Our analytical approach is based on the multipole decomposition method and the secondary multipole decomposition technique. They allow us to associate the anapole with the multipole moments of the trimer and the separate multipole moments of its constitutive particles. The manifestation of anapole in a two-dimensional metamaterial (metasurface) is confirmed by checking the resonant states in the reflected field as well as from the electromagnetic near-field patterns obtained from the full-wave numerical simulation. It is demonstrated that the anapole excitation in trimers results in the polarization-independent suppression of reflection with the resonant enhancement of local electromagnetic fields in the metasurface. Finally, experimental verification of the theoretical results is presented and discussed.

Bonding of Al6061 by Hot Compression Forming: A Computational and Experimental Study of Interface Conditions at Bonded Surfaces

In recent years, there has been a growing interest in composite components, which may be designed to provide enhanced mechanical and physical effective properties. One of the methods available to produce such components is joining by plastic deformation, which results in metallurgical bonding at the interface. However, the portions of the interface that are bonded and the inhomogeneity in the bonding strength achieved at the interface tend to be overlooked. In the present study, Al6061 beams were bonded, by hot compression (300–500 °C) to different degrees of reduction. The compression was followed by tensile debonding experiments and the revealed interface was microscopically characterized in order to determine the areas that were metallurgically bonded. The SEM characterization revealed that the actual bonded area is much smaller than the interface contact area. Thermo-mechanical finite element models of the compression stage were used to investigate the thermo-mechanical fields, which develop along the interface and influence the resulting bonding strength. The principal strain field patterns across the interface area were shown to be similar to the experimentally observed temperature-dependent bonding patterns. In addition, a quantitative criterion for bonding quality was implemented and shown to correlate with the experimental findings.