1,720,995 research outputs found
Design of WideBand transmission polarization converters
Full text linkA designing tool for wideband transmission polarization converting surfaces is presented. The optimized wideband polarizer comprises several metasurface layers whose unit cell is gradually rotated. The analysis is based on an analytical transmission line model of the multilayer structure with anisotropic elements
Systematic design of transmission-type polarization converters comprising multilayered anisotropic metasurfaces
Full text linkA simple but efficient approach for the synthesis of transmission-type wideband polarization converters is presented. The proposed configuration comprises multilayer metasurfaces including resonant particles that are progressively rotated layer by layer. The progressive rotation of the particles allows for a polarization conversion over a large frequency band. The polarizing structure is efficiently designed and optimized through a transmission-line-model approach handling the cascade of anisotropic impedance layers and dielectrics. An optimized eight-layer design based on gradually rotated dipole resonators is presented as a proof of concept. The results obtained through the efficient transmission-line model are compared with full-wave simulations once the structure is optimized, showing satisfactory agreement. A prototype of the wideband polarization converter is fabricated and measured
Electromagnetic Model of Reflective Intelligent Surfaces
No full textAn accurate and simple analytical model for the computation of the reflection amplitude and phase of Reconfigurable Intelligent Surfaces is presented. The model is based on a transmission-line circuit representation of the RIS which takes into account the physics behind the structure including the effect of all relevant geometrical and electrical parameters. The proposed representation of the RIS allows to take into account the effect of incidence angle, mutual coupling among elements and the effect of the interaction of the periodic surface with the RIS ground plane. It is shown that the proposed approach allows to design a physically realisable RIS without recurring to onerous electromagnetic simulations. The proposed model aims at filling the gap between RIS assisted communications algorithms and physical implementation issues which determine realistic performance of these surfaces
A Simple Equivalent Circuit Approach for Anisotropic Frequency-Selective Surfaces and Metasurfaces
Full text linkAn equivalent circuit (EC) model for the frequency-selective surfaces (FSSs) comprising anisotropic elements is presented. The periodic surface is initially simulated with an arbitrary azimuthal incidence angle, and its surface impedance matrix is derived. The impedance matrix is subsequently rotated by an angle φrot on the crystal axes χ1 and χ2, thus nullifying its extra diagonal terms. The rotation angle φrot is derived according to the spectral theorem by using the terms of the matrix initially extracted. The diagonal terms of the rotated matrix, that is, the impedances Zχ1 and Zχ2, are finally matched with the simple LC networks. The circuit model representation of the anisotropic element can be used to analyze the anisotropic FSSs rotated by a generic azimuth angle. The methodology provides a compact description of the generic FSS elements with only five parameters: The lumped parameters of the LC network Lχ1, Cχ1, Lχ2, Cχ2 and the rotation angle φrot. The circuit model can consider the presence of the dielectric substrates close to the FSS or a variation in the FSS periodicity without additional computational efforts. The EC model is finally applied to the design of the two transmitting polarization converters based on the anisotropic metasurfaces
Circuit Modelling of Reflecting Intelligent Surfaces
No full textWe present an accurate and simple analytical model for the computation of the reflection coefficient amplitude and phase of Reflecting Intelligent Surfaces (RIS). The proposed approach takes into account mutual coupling among cells, the effect of incidence angle and polarization of impinging electro-magnetic waves. The model is based on a transmission-line circuit representation of the RIS unit cells, and it is a physics-based approach which includes the effect of all relevant geometrical and electrical properties of the designed surface. The proposed approach is useful for a quick but physically aware design of RIS-based communications links
An Extended Equivalent Circuit Model for Reconfigurable Intelligent Surfaces
No full textThe circuit model of a dual polarized resonant reconfigurable intelligent surface is discussed. The RIS is characterized by two resonances where the phase response can be controlled. It is shown that the proposed circuit model provides an accurate prediction of the reflection properties not only for the first resonance but also for the second one
Comparative analysis of dual-polarized varactor loaded Reconfigurable Intelligent Surfaces
No full textA comparative analysis of different varactor loaded RIS elements is presented. In particular, three dual polarized element topologies are compared by selecting the same substrate properties and the same tunable lumped elements. It is shown that the elements are characterized by two resonances where the phase response can be controlled. The fundamental resonance is typically characterized by low loss with respect to the second resonance. However, at the first resonance, the unit cell is smaller in terms of wavelength with respect to the second resonance. This implies higher number of varactors diodes are necessary to control the RIS with a consequent increase of the cost
MM-wave and THz design strategies of Reconfigurable Intelligent Surfaces
No full textReflecting Intelligent Surfaces (RISs) have garnered considerable attention as a viable solution for wireless communication systems in recent years1. RISs operate by manipulating the phase and amplitude of incoming signals through precise adjustments in surface impedance2, 3. Moreover, RISs offer real-time dynamic changes in impedance and reflectivity, enabling various advantages for wireless communication systems such as enhanced spectral efficiency, expanded coverage, and reduced interference4. Several techniques are employed to achieve reconfigurability in RISs, including the utilization of Varactor Diodes5-7, PIN Diodes8, 9 and MEMS10
Mesenchymal stem cell-conditioned medium promotes vascularization of nanostructured scaffold transplanted into nude mice: a morphological study
No full textDepolarizing chipless tags with polarization insensitive capabilities
Full text linkA novel depolarizing chipless tag configuration with high angular insensitivity is presented. The basic tag comprises two dipole resonators arranged with a relative rotation of 45°. The proposed configuration improves the depolarization properties performance of a single dipole over the ground plane which provides a peak with perfect polarization conversion only if the electric field impinges at 45° with respect to the dipole resonator. The second dipole arranged at 45° compensates the cross‐polar reduction which is observed when the electric field is not correctly polarized. Indeed, when the field is tilted by 90° with respect to the first dipole, it forms an angle of 45° with the second one. The proposed configuration is also analyzed for providing multiple frequency peaks. A tag with 4 angular independent frequency peaks laying between 2 GHz and 5.5 GHz is designed. Angular frequency maps are used to illustrate the peculiar frequency shifts achieved when the electric fields rotate in the plane of the dipole. Finally, a prototype of the polarization insensitive tags is fabricated and measured to confirm the simulated results
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