Proper Permittivity Research Articles

High Frequency Electromagnetic Shielding by Biochar-Based Composites

We report on the microwave shielding efficiency of non-structural composites, where inclusions of biochar—a cost effective and eco-friendly material—are dispersed in matrices of interest for building construction. We directly measured the complex permittivity of raw materials and composites, in the frequency range 100 MHz–8 GHz. A proper permittivity mixing formula allows obtaining other combinations, to enlarge the case studies. From complex permittivity, finally, we calculated the shielding efficiency, showing that tailoring the content of biochar allows obtaining a desired value of electromagnetic shielding, potentially useful for different applications. This approach represents a quick preliminary evaluation tool to design composites with desired shielding properties starting from physical parameters.

Impacts of Point Cloud Modeling on the Accuracy of Ray-Based Multipath Propagation Simulations

This article reports the comparison of multipath channels of outdoor small cells at 28 GHz simulated by point-cloud-based ray tracer and those from measurements. The comparison shows that the ray tracer is capable of reproducing measured channels with reasonable accuracy, given proper permittivity values set for major building walls. The accuracy, however, depends on the types of point clouds we input to the ray tracer: 1) raw point cloud from laser scanning measurements of the cellular site; 2) flattened point cloud where structural details of the environments are all lost like what we find in publicly available digital maps; and 3) processed point cloud where missing sections are complemented, flat and rough sections of surfaces are identified and wedges are detected. For condensed parameters of channels such as path loss, delay, and angular spreads, ray tracing with the processed and raw point clouds shows equally good accuracy. In contrast, the ray tracing with the processed point cloud shows clear advantage of accuracy over that with the raw point cloud when simulating physical propagation paths. The raw point cloud produces many spurious paths that do not exist in measurements, whereas the processed point cloud reproduces multipath richness in form of many weak diffracted paths that are found in measurements and cannot be reproduced by diffuse scattering. Ray tracing with the flattened point cloud is in least agreement with measurements. Still, first-order specular reflections from large smooth walls are reproduced well by ray tracer with any of the tested point clouds. We thereby demonstrate the superiority of using the processed point cloud as inputs to ray tracer to obtain multipath channels with the highest fidelity to measurements.

Dual-wide band plasmonic filter based on nanocomposite media

A dual, wide band pass metal–insulator–metal plasmonic filter based on nanocomposite media in the near-infrared band, 0.75 to 2.5 μm wavelength range, is proposed. Simulation results show that the pass bands can be adjusted to proper ranges by changing the size of the device and the relative permittivity of the dielectric region. Due to the importance of small structures in optical integration, we focused on tuning the transmitted bands by changing the dielectric relative permittivity. Realization of any desired relative permittivity for the dielectric region may be difficult using general dielectrics. In this way, the dielectric region is designed based on nanocomposite media, which no previous studies have focused on. Dielectric region is realized by a polymeric medium, poly-methyl-methacrylate, that consists of random distribution of guest spherical silver nanoparticles. The proper permittivity and consequently, the desired pass bands are obtained by changing the fill fraction of guest nanoparticles.

Co-Evaluation of Reflection Loss and Surface Wave Attenuation for Magnetic Absorbing Material

Magnetic absorbing material (MAM) sheet was fabricated by calendaring carbonyl iron flakes into acrylonitrile-butadiene rubber. The complex permittivity and permeability of the sample were measured within 0.3–18 GHz. The calculated reflection loss (RL) and surface wave attenuation constants of the MAM are shown to be effectively manipulated by the layer thickness and electromagnetic (EM) parameters, respectively. It is found that the thickness of MAM should be suitable so as to realize good microwave wave absorption and surface wave attenuation performances in wide frequency range. In view of this goal, there also exist consistency requirements in EM parameters of MAM, i.e., a proper permittivity and high permeability. Furthermore, the measured RL and monostatic radar cross section reduction of a slab coated with the fabricated MAM sheet are in good agreement with the theoretical calculation. The present results provide a pathway to the development of MAM with high-efficiency absorption on both incidence EM waves and surface waves in the gigahertz range.

Magnetically tunable Fano resonance with enhanced nonreciprocity in a ferrite-dielectric metamolecule

A magnetic tunable Fano-resonant metamaterial structure with enhanced nonreciprocity at microwave frequencies has been designed and investigated. The metamolecule has been implemented by using a dielectric cube and a magnetically biased ferrite. The Fano resonances originate from mode coupling between two constituents. The structure possesses a nonreciprocal feature since the external field breaks the time-reversal symmetry, and the Fano-type interference further enhances the nonreciprocal nature of biased ferrite. We are able to manipulate the Fano modes by adjusting the applied magnetic field. Simulation results suggest that the proper permittivity of the dielectric cube will optimize the nonreciprocal contrast. The magnetically tunable feature of the proposed metamaterial can potentially be applied to design dynamically controlled switches and isolators.

Perpendicular-Corporate Feed in Three-Layered Parallel-Plate Radiating-Slot Array

We propose a perpendicular-corporate feed in a three-layered parallel-plate radiating-slot array to remove the x-shaped cavity walls completely in the radiating part of the conventional planar corporate-feed waveguide slot array antenna. Coupling apertures on the bottom excite radiating slots spaced with the half of their spacing on the middle in the parallel plates. We place dielectric with proper permittivity in the region between the coupling aperture and the radiating-slot layer to excite a standing wave strongly there for a large number of slots. A parasitic-slot layer is added on the top to improve the bandwidth. A $16 \times 16$ slot array antenna is designed for uniform excitation with the perpendicular and the planar corporate feeds, and fabricated in the 60 GHz band. At the design frequency of 61.5 GHz, the measured directivity is 33.5 dBi with the aperture efficiency of 90.6%.

Proper Permittivity for Depolarization Field in Perfectly Insulating Ferroelectric and Examination of Background Permittivity

Depolarization field Edemerging from spontaneous polarization P Sis considered to play an essential role in the characteristics of ferroelectrics. For the estimation of Ed, correct dc-permittivity ϵ dis necessary but is still a controversial issue such as background permittivity ϵ b. This paper examines the permittivity ϵ din the case of 1-dimensional insulating single-domained ferroelectric, by noting that ϵ ddepends on how P Sis defined. This examination shows that ϵ dshould be unity when experimental P Sor self-consistent P Sis used. Without relying on special theories, a generic consideration based on this results shows that 1-dimensional insulating single-domained ferroelectric having 1st order ferroelectric transition cannot exist thermodynamically.

Proper Permittivity for Depolarization Field and Its Implication to Universal Instability of Insulating Ferroelectric: A Note

Because the permittivity for the depolarization field E d depends on the definition of the spontaneous polarization P S , improper permittivity is often used in the literature. Therefore, we define proper combinations of the permittivity and P S for E d that are consistent with experimental conditions. We show that the permittivity for E d should be unity in most cases , especially for nonideal capacitor structures, which are often discussed on the basis of the Mehta formula. This choice of permittivity is shown to be consistent with the experimental linear permittivity in response to the external field. This permittivity indicates the problem with assuming a ferroelectric as an insulator under E d : A strain-free two-dimensional single-domain ferroelectric phase with a P S ⊥ surface cannot exist regardless of the thickness of the ferroelectric, when at least one of the surfaces is unscreened. Alternatively, the agreement between experimental and theoretical results obtained at a permittivity ≫1 for E d s...

Improvement of open resonator technique for dielectric measurement at millimetre wavelengths

An open resonator system is designed and constructed for the accurate measurement of complex permittivity at Ka band. It is solved successfully for the first time in how to achieve the consistency of cavity lengths corresponding to different resonant frequencies over a broad band and how to determine the proper permittivity from multiple transcendental equation roots of one sample. Many kinds of samples such as fused quartz, Teflon, quartz ceramic, MgF 2 and MgAl 2 O 4 are measured and the results are in good agreement with published data. The systematic error analysis shows that the relative standard deviation of the measurement system is less than 0.172% for permittivity and 18.35% for loss tangent. The software developed to control the system improves the measurement efficiency greatly.

Guided Waves along Lorentz-Resonant Layers

Guided waves in layers of Lorentz-type resonant material are considered. Eigenvalue equations and dispersion curves are evaluated for single- and dual-slab systems. The results show that in the situation of negligible losses, one can obtain rather flat dispersion curves applicable for superlens imaging by properly choosing the material parameters and geometry. Backward-wave propagation in such structures is possible with proper permittivity values and geometry. The effects of losses on propagation are studied. Near the resonant frequency, the imaginary part of the permittivity grows, but at the frequency corresponding to the plasmon mode, the imaginary part is reasonably small. It is shown that even small losses have considerable effects for propagation properties of plasmon guided waves.

Analysis and design of a novel leaky YIG film guided wave optical isolator

A guided wave optical isolator using a four layered leaky yttrium iron garnet (YIG) waveguide with a YIG guiding layer is proposed and analyzed through a transfer matrix formulation. The dependence of isolation characteristics on different waveguide parameters are discussed. It is shown that for four layered structures an isolation ratio of about 24 dB can be achieved with YIG films having large gyrotropy. It is also shown that by replacing the single guiding YIG film with multilayers of YIG with compensated walls and proper permittivity, high isolation ratio can be achieved even with currently available YIG films having low gyrotropy.

Efficiency enhancement in a Cherenkov laser by a proper permittivity variation

With the aid of particle simulation, we discuss efficiency enhancement in a single-pass Cherenkov laser by varying the permittivity of a dielectric sheet loaded on a parallel plate waveguide. For the analysis of the problem, a two-dimensional model for the Cherenkov laser is considered which is composed of a planar relativistic electron beam and a parallel plate waveguide, one plate of which is loaded with a dielectric sheet. In order to maintain the synchronism between an electron beam and an electromagnetic wave, the permittivity of the dielectric is properly varied in accordance with the variation in the average velocity of the electron beam. The result of numerical simulation shows that the efficiency of energy transfer from the electron beam to the electromagnetic wave is greatly enhanced by properly varying the permittivity of the dielectric sheet.