A transmission-type cross-polarization converter is designed based on a frequency selective surface (FSS) and is investigated theoretically and experimentally. The FSS structure is built up with rotationally asymmetric fourfold supercell. The subcell of each supercell is a monopole-via-monopole (MVM) module, which consists of a receiving monopole, a transmitting monopole, and a quasi-wave-guiding structure (a through-via hole passing through the perforated shielding ground) to connect the monopole pair. In each supercell, the receiving and transmitting monopoles are orthogonally oriented to form a chiral geometry. The cross-polarization converter allows an incident wave linearly polarized at arbitrary azimuth to pass through and convert it into its cross-polarization state, while it operates as an FSS filter (without polarization state conversion) for the incidence of both circularly polarized waves. It exhibits a 3.0-dB transmission bandwidth ranging from 5.5 to 6.18 GHz (12%) with the peak insertion loss less than 0.16 dB at 5.8 GHz. The novelties of the reported cross-polarization converter lie in the insensitivity to the incident linear polarization azimuth and very low insertion loss within the investigated frequency band. To verify the proposed concept, a prototype is designed, fabricated, and measured, and good agreement between the simulated and experimental results is observed.

Polarization-Insensitive Cross-Polarization Converter

The mitigation of electromagnetic pollution is becoming an increasing issue due to the proliferation and miniaturization of electronic components. Electromagnetic interference (EMI) shields must be considered to bring about electromagnetic compatibility (EMC), where analyzing the shielding effectiveness (SE) is of great importance. Graphene-enhanced polymer composite materials are recently introduced as a replacement for metal-based EMI shielding materials due to their low cost, resistance to corrosion, lightweight, versatile, and straightforward processability, as well as broad bandwidth properties compared to conventional metal-based materials. The SE can be determined from the bulk material properties, including permittivity, permeability, and conductivity, using analytical or numerical solutions to Maxwell's equations. Though, Due to the heterogeneity of graphene-based polymer composites, characterization of these values remains difficult. This article attempts to summarise and critically review the state-of-the-art progress in the fabrication and characterization of these materials. Also, this review elaborates on accurate modelling techniques based on the underlying micromechanics, e.g., percolation, electron tunnelling, agglomeration, imperfect interface, frequency-dependent nanocapacitance and electron hopping. The model is designed to predict the electromagnetic properties of the nanocomposite from the pre-determined properties of the polymer matrix and carbon-based filler. This understanding may ultimately lead to the development of graphene/polymer composites with optimized EMI shielding properties to develop emerging EMI shielding materials. This paper focuses heavily on Graphite Nanoplatelet (GnP)/Epoxy as the choice of graphene/polymer.

Modelling, fabrication and characterization of graphene/polymer nanocomposites for electromagnetic interference shielding applications

A compact and asymmetric multi-band reflective polarization converter metasurface has been offered in this paper. The proposed simple converter can effectively convert an incident linearly polarized EM wave to its orthogonal counterpart and circular polarized waves (RHCP and LHCP) at two frequency bands. The design consists of a square with two curves on the top right and lower left corners and a square Split Ring Resonator (SRR) responsible for linear-to-linear and linear-to-circular polarization conversions, respectively. The simulated results show that the converter successfully transforms a y-polarized incident wave to its orthogonal counterpart in a frequency range of 15.5–16.5 GHz with unity conversion at 16 GHz and circularly-polarized (RHCP) wave at 13 GHz and (LHCP) at 18 GHz, verified through the fabricated and measured sample. Wide angular stability up to 60° oblique incidence along with high efficiency reveals the good applicability of the structure. Moreover, the root cause of the cross-polarization conversion has been analyzed and confirmed through Bi-Mode Foster equivalent circuit and surface current distribution as well. Finally, a fabricated prototype is tested to validate the simulated results through measurement.

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Multiband and multifunctional polarization converter using an asymmetric metasurface.

Core/shell structured SiO2/MIL-100(Fe) fibrous membrane was prepared for photocatalytic degradation of dyes. The metal organic framework shells of MIL-100(Fe) were decorated on electrospun SiO2 nanofiber surface through layer-by-layer assembly. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy tests confirmed the successful synthesis of the MIL-100(Fe) nanoparticles. The formed SiO2/MIL-100(Fe) catalysts exhibited high catalytic activity towards degradation of Rhodamine B under visible light irradiation. The photocatalytic activity remained above 80% within 90 min illumination after three cycles. Due to the easy preparation and high photocatalytic performance, as well as convenient collection for reuse, the obtained SiO2/MIL-100(Fe) membranes are promising catalysts for practical application.

https://link.springer.com/content/pdf/10.1007%2Fs10854-018-0370-9.pdf

Fabrication of flexible MIL-100(Fe) supported SiO 2 nanofibrous membrane for visible light photocatalysis

The Pancharatnam-Berry (PB) phase can be used to control the phase of circularly polarized electromagnetic waves. However, there are few studies on the modulation of dual-circularly polarized multi-beam using the transmissive coding metasurface. A scheme of spin-controlling multi-beam by transmissive coding metasurface is proposed for dual-circular polarization simultaneously. The transmissive coding metasurface (TCMS) can transmit linearly polarized incidence into multi-beam with orthogonally circular polarization. The phase distribution is designed based the convolution theorem, and the elements of metasurface conforming to the PB phase are arranged according to the phase distribution. In order to compensate the emitting spherical waves into plane waves and realize the transmissive waves with dual-circular polarization, an interesting scheme of elements in different regions with different rotating phase are presented based on the principle of phase compensation. TCMS can transmit linearly polarized waves into two left-hand circularly polarized (LHCP) beams and two right-hand circularly polarized (RHCP) beams. The prototype of TCMS is fabricated and measured, and the experimental results agree well with the simulated data. The transmissive metasurface has potential application in holograms and satellite communication. 

Transmissive coding metasurface with dual-circularly polarized multi-beam

In this paper, we present a design of circular-to-linear polarization converter operating in C-band based on a composite frequency selective surface which consists of two types of via-coupled patch modules. The building unit cell is built with four modules, and each one is a truncated patch pair printed on the double-layer substrate and vertically connected by a metal via-hole. A perforated common ground plane is sandwiched between the double layers to support transverse electric and magnetic mode coupling between the front and back patches. The front diagonally truncated patch array responds to the incident right-handed circularly polarized wave, and it is identically converted into general right- and left-handed elliptically or circularly polarized waves with same phase shifts, amplitudes and axial ratio, thus a resultant linear polarized wave is generated in forward transmission mode.

Circular-to-linear polarization converter based on composite via-coupled patch frequency selective surfaces

Conventional piezoelectric cantilever-based vibration energy harvesters have narrow bandwidth. In this article, we develop a dual-beam piezoelectric energy harvester featuring an annular potential energy function that can harvest vibration energy over a wide spectrum under small amplitude excitations. The proposed harvester contains two conventional piezoelectric cantilevers placed orthogonal to each other which are coupled by repulsive magnetic force. We demonstrate analytically and numerically that a new annular potential energy function can be built with proper configuration. In the new annular stable state, the harvester can detour around the potential barrier rather than jump over it, yielding large amplitude voltage outputs throughout a wide spectrum. Case studies were carried out, and it is proved that the proposed annular stable harvester has a bandwidth of 3.9 Hz and a voltage output performance 3.01 times better than that of a conventional bistable one under excitations of 3 m/s2. The nonlinear dynamics of the proposed harvester are analyzed in detail. 

/pdf/modeling-and-analysis-of-magnetically-coupled-piezoelectric-2igz7qm5.pdf

Modeling and analysis of magnetically coupled piezoelectric dual beam with an annular potential energy function for broadband vibration energy harvesting

Nan Shao

Papers

Circular-to-linear polarization converter based on composite via-coupled patch frequency selective surfaces

Modeling and analysis of magnetically coupled piezoelectric dual beam with an annular potential energy function for broadband vibration energy harvesting