Dielectric Plate Research Articles

Passive Inclination Sensor Based on a Patch Antenna with a Reconfigurable Water Load.

In order to ensure the safety and preserve the value of historical buildings, inclination is an essential parameter during the continuous structural health monitoring process. However, the wire and price of a traditional sensor limit application. This paper proposes a low-cost inclination sensor based on a patch antenna with a reconfigurable water load. Only the water directly on the antenna is considered effective. The different volume of the effective water load, which is determined by the inclination of the attached surface, will affect the effective permittivity of the dielectric plate of the patch antenna, further causing a variation in the resonant frequency. Therefore, the proposed antenna sensor can monitor the inclination of the attached surface by interrogating the resonant frequency. The working mechanism is first clarified by theoretically investigating the relationship between the dielectric properties and the inclination of the covering medium. The antenna sensor is then simulated using High-Frequency Structure Simulator ver.15 (HFSS 15), which helps to determine geometric parameters and confirm accuracy and sensitivity. An experiment has been conducted based on the design verified in the simulation. The inclination detection shows a correlation coefficient of 0.9771 with a sensitivity of 7.92 MHz/°, indicating a potential for real application.

Gain improvement of conformal circularly polarized Fabry-Perot resonator antenna based on metasurface

Conformal antenna can keep consistent with the shape of the carrier perfectly, which greatly saves the space of the carrier, so it is widely used in military, aerospace and other fields. In this paper, a cylindrical conformal circular polarization Fabry-Perot resonator antenna is designed, and the adverse effect of conformal on antenna gain is overcome by transmission phase compensation. Firstly, a linear to circular polarization conversion metasurface with adjustable transmission phase is designed. The main reason for choosing the metasurface here is to take advantage of its excellent electromagnetic control ability. The metal structures of the metasurface are printed on the ultra-thin dielectric plates, and then attached to the support structure machined by 3D printing, so as to achieve the conformal design of the metasurface. Secondly, the proposed metasurface is used as the superstructure and is combined with a conformal feed to form a cylindrical conformal circularly polarized Fabry Perot resonator antenna. The conformal feed is a patch antenna which is conformal designed in the same way as the metasurface. The conformal feeder is placed under the conformal metasurface to ensure that the electromagnetic wave radiated by the feeder can enter the resonant cavity composed of the feeder and the metasurface. The curvature of the cylindrical conformal of feed and metasurface is the same, which can ensure the high unity of the different positions in the resonator. Next, by adjusting the transmission phase of the unit on the metaurface, the phase compensation of the transmitted electromagnetic wave is realized, so that the electromagnetic wave radiated by the conformal antenna still presents the characteristic of plane wave. Finally, the conformal Fabry-Perot resonator antenna obtains the same high-gain radiation characteristics as the planar resonator antenna. The designed antenna achieves a maximum gain of 13.1dBic at 10 GHz. The size of the antenna is 2.9λ × 2.9λ, so the aperture efficiency is about 19.9 %. The antenna proposed in this paper overcomes the influence of conformal design on the gain of the antenna, so that it can be conformal on the surface of a cylindrical object and obtain better gain characteristics.

A method of multi-bit optical coding by constructing Brewster angles to enhance photonic spin Hall effect

The photonic spin Hall effect, characterized by its polarization-driven spin-related displacement, has played an essential role in coding information processing. In this Letter, using a two-period double-layer dielectric plate, the displacement changes within the angle region are first observed, and a two-bit effective coding is achieved through non-uniform quantization of displacement values and coding. Afterward, by constructing Brewster angles (BAs), effective three-bit coding is achieved at the selected BA by dividing the angle domain. By changing the relative refractive index of the constituent materials (nB), effective coding is achieved at corresponding angles (45°–85°). By connecting two-bit and three-bit coding, a five-bit coding is fulfilled. By setting the last six invalid values, effective correspondence of 26 English letters is obtained. At the same time, the largest displacement peak itself is huge and varies accordingly with different values of nB. This work can provide some reference for designing optical coders.

Thermal insulation materials based on eucalyptus bark fibres

The civil construction industry significantly contributes to global energy consumption, prompting a shift towards sustainable practices to mitigate environmental impacts throughout the building lifecycle. Traditional thermal insulation materials, such as polyurethane foam and mineral wool, are cost-effective but fail to meet environmental safety standards. In this context, plant-based materials have emerged as an eco-friendly alternative for thermal insulation, with agroforestry waste offering a sustainable raw material source. This waste is abundant and often improperly disposed of, thus utilizing it can reduce the environmental footprint of the agroforestry sector. This study focuses on developing thermal insulation plates using eucalyptus bark fibres, with some samples incorporating wheat straw. Various methods were employed: sodium silicate as a binder in some samples, while others used a binder-free method involving pulping bark in lye, and some included carbonised eucalyptus bark. The primary goal was to evaluate properties like thermal conductivity and moisture sorption. The electron microscope analysis provided insights into the microstructure of the fibres, explaining their insulation mechanisms. The thermal conductivity of the plates ranged from 0.036 to 0.059 W/(m·K) at a density of 80–220 kg/m3, influenced by the preparation processes (mechanical grinding, lye pulping, carbonization) and binder use. Eucalyptus bark fibre samples demonstrated low moisture sorption for plant-based materials, with 9.4–14.5 % at 60 % relative humidity and 21.6–38.5 % at 97 % relative humidity. Additionally, the samples showed high resistance to fungal growth when wet, suggesting good durability for thermal insulation applications. Overall, the study's results indicate that eucalyptus bark fibres hold significant promise as a sustainable raw material for producing thermal insulation, offering an environmentally friendly alternative to traditional materials while enhancing the durability and effectiveness of insulation in construction.

Presence of asbestos in building materials and soils in postfire areas of Mati, Kineta and Varimbombi in Greece.

The present study was carried out to determine the presence of asbestos in Wildland Urban Interface (WUI) areas of Attica, Greece affected by wildfires between 2018 and 2021. It concerns the first major campaign that took place in Greece. The samples tested in this work were collected from prespecified buildings of the burned area. The samples included different types of building materials such as bricks, wall coatings, insulation plates etc. Soil samples nearby the buildings were also collected to examine dispersion of the fibers. The identification of asbestos was based on the optical properties of the fibrous particles and was performed with stereo microscope and Polarized Light Microscopy according to P401 provided by BOHS (Health and Safety Executive (HSE) 2021). Scanning Electron Microscopy with energy dispersive spectroscopy was also used to validate the presence of asbestos and determine its chemical composition. In this work, 2 different types of asbestos were determined, chrysotile and crocidolite. In some cases, fragments of asbestos containing materials were also detected in the afore-mentioned soil samples indicating dispersion of asbestos containing debris in an area around the burned spots. The presence of asbestos that was identified in this preliminary study could raise concerns to humans in the urban areas. For that reason, a risk assessment for the identified asbestos containing materials (ACMs) was conducted according to the guidelines on management and abatement of ACMs of Health and Safety Authority and the Asbestos: Survey guide, Appendix 4: Material assessment algorithm of Health and Safety Executive (HSE).

Far-field sub-diffraction focusing and controlled focus shaping of circularly polarized light using a dielectric phase plate

In recent years, sub-diffraction focusing has received substantial attention due to its versatility. However, achieving a flexible sub-diffraction focusing in the far field remains stimulating. Existing techniques either require complex fabrication facilities or are limited to the short focal length and high numerical aperture (NA) of the imaging system. Here, we introduce an optimization method for sub-diffraction focusing of a circularly polarized beam in the far field with a lens of large focal length. A cost-effective dielectric phase plate serves the purpose. By employing a phase plate composed of a thin layer of dielectric Si3N4, the phase of the propagating beam is modulated in the beam’s cross-section, which is divided into two regions of the opposite phase by the plate. A sub-diffraction focusing is achieved for a proper tunning between the two regions. In addition to sub-diffraction focusing, the phase plate is also capable of shaping the focus into a doughnut-shaped and a flat-top profile in the far field. This design provides a simple solution for sub-diffraction focusing and focus shaping that will find potential applications in optical imaging, optical trapping, and material processing.

Analysis of heat transfer modes in the cooling of blocks generating different heat quantities

Achieving improved cooling efficiency and control in electronic components with varying heat outputs can be realized through a thorough analysis of different heat transfer modes, focusing on their contributions and interactions within the system. The analysis is conducted within a cavity containing three circular blocks generating varying amounts of heat. The blocks are affixed to an insulated plate, dividing the cavity into two identical sections with different fluids and different cooling mechanisms. In the open portion of the divided cavity, block cooling is achieved through forced convection using a nanofluid, while the closed section dissipates heat through natural convection and surface radiation. The numerical solution of the governing equations is performed using Galerkin's Finite Element Method, with detailed examination of the cooling process considering various parameters, such as block displacement (1.5cm≤y1≤3.25cm) and dimensions (0.25cm≤R≤1.5cm), Reynolds number (10≤Re≤1000), nanoparticles nature and volumetric fraction(0 %–10 %), emissivity (0≤ε≤1), thermal heat ratio(0.125 to 8), and cavity inclination angle(0°–180°). The results show that the combination of natural convection and surface radiation can be highly effective, rivaling forced convection in cooling the blocks. The study shows that an increase in the Reynolds number results in a temperature reduction of up to 6 °C, while increasing the emissivity leads to a more significant drop of around 10 °C. Additionally, miniaturizing the blocks by reducing their radius by a factor of six causes the maximum temperature to rise by over 20 °C.

Empirical comparative study of new field-cast foamed cement insulation systems

In practical building construction, simply judging the insulating performance of the material by its thermal conductivity is not fully comprehensive. Therefore, the study used the “four identical tests” to compare the effects of insulation materials on energy consumption and indoor comfort in actual buildings. New field-cast foamed cement and extruded polystyrene plate insulation materials with lower thermal conductivity are used in Test Houses 1 and 2. The test houses' indoor temperature and energy consumption were monitored. Comparison of two Test Houses shows that, during the heating shutdown, Test House 2 daily temperature dropped 0.5 °C more than Test House 1. Conversely, Test House 2 exhibits a 5.97 % higher temperature fluctuation during heating than Test House 1. Under normal and heating conditions, Test House 2 consumes 2.2 kW h and 1.6 kW h less energy on average than Test House 1, with energy fluctuation rates 13.54 % and 9.33 % higher, respectively. Although the energy consumption of Test House 1 experimental room using the new type of field-cast foamed cement is slightly higher, it exhibits better temperature stability during the heating period, significantly improving indoor comfort. Moreover, it demonstrates good energy-saving potential and durability, making it a better choice for building insulation.

THz Metamaterial Sensitivity Enhancement by Reduction of Substrate's Fabry-Pérot Oscillations Using Back Plates as an Optical De-Coupler.

This work presents a new method for the enhancement of sensitivity in Terahertz (THz) spectroscopy on metamaterial (MM) in terms of its resonance frequency shift (ΔF), by attaching the dielectric back plate to the MM's silicon (Si) wafer. The dielectric back plates are designed to minimize the Fresnel reflections at the backside of the substrate, identical to a broadband antireflective (AR) plate tailored for THz. Utilizing broadband AR technology, we demonstrate the concept of decoupling MM resonance from the substrate's Fabry-Pérot (FP) oscillations. This is done by effectively coupling the THz light out of the high-permittivity substrate, resulting in the improved quality factor of the MM resonance and overall plasmonic enhancement on the metasurface. The back plate acts as a surface plasmonic enhancer to the THz MM by increasing the field intensity on the front metasurface, leading to enhancement of dielectric response (MM's ΔF). This makes the MM resonance ultrasensitive to the minor changes of particle size/concentration under test spread on the metasurface, contributing to enhanced resonance ΔF. The plate also makes the Si substrate optically lossless, enabling the full effect of MM resonance shift and increasing the resonance ΔF by 8-fold compared with MM's fabricated on conventional Si substrates. This research is backed-up with system-level CST simulations and experimental THz impedance spectroscopy of the MM. This method and chip structure is CMOS compatible having potential applications for any resonant MM fabricated on a substrate aimed to maximize dielectric sensitivity for biosensing and nanoparticle THz spectroscopy.

An equivalent circuit model based design method for wideband absorber using resistive FSS

Abstract In this paper, a design method for wideband absorbers based on equivalent circuit model
(ECM) is proposed. Based on the design requirements, a general ECM is established. Then, the optimized circuit parameters can be obtained by using the particle swarm optimization
(PSO) algorithm. Meanwhile, the ECM combined with PSO algorithm can also realize the electromagnetic performance evaluations. Finally, the according mapping unit topologies are designed. Among them, a superior wideband absorber is selected, which consists of two layers of FSS loaded with resistive film, a single dielectric plate, an air layer and a metal layer.
The fractional bandwidth of the absorber is 149.3% (3.09-20.36 GHz), the total thickness is
9.35 mm. The experiment results consistent well with the simulation results, verifying the universality and effectiveness of the proposed design method.

Seismic performance of RC frames with masonry infills retrofitted by precast ultra-lightweight insulated cementitious composites plates

Seismic performance of RC frames with masonry infills retrofitted by precast ultra-lightweight insulated cementitious composites plates

Optical theorem in the 3-D scattering from a locally perturbed lossless or lossy thin dielectric plate: silver disk-sealed hole analysis

This paper is aimed at devising a new optical theorem formulation for the 3-D plane-wave scattering from an infinite resistive plane and, more generally, a thin dielectric plate with a finite-size inhomogeneity shaped as a hollow or sealed hole. This formulation is further modified to cover the case of the plane guided wave scattering from the same inhomogeneity. For the lossless plane, the diffracted field combines a classical outgoing spherical wave, satisfying the Silver-Muller radiation condition, with an outgoing cylindrical guided wave supported by the plane; the power absorbed in the lossy filling is finite. When a lossy plane is involved, a complication appears: the total absorbed power is infinite. However, a change in the inhomogeneity characteristics perturbs the absorbed power density, thus suggesting the perturbative absorption analysis. After developing the analytical procedure for the resistive plane case and the corresponding generalization to the thin dielectric plate case, we illustrate the significance of the new optical theorem by the numerical analysis of the visible-light scattering from a dielectric plate with a circular nanosize hole sealed with a silver disk. Our analysis uses the in-house code having mathematically guaranteed convergence; it reveals the scattering and absorption resonances on the plasmon modes of the silver nanodisk. The derived optical theorem allows us to see that, in the resonances, the power carried by the guided waves can be comparable to the power scattered into the free space.

Does the capacitor analogy model in fracture mechanics of elastic dielectrics constitute an appropriate approximation?

The analytical solution of an elliptic dielectric cavity in an infinite dielectric plate is taken as basis to investigate a Griffith crack problem which is obtained by letting the semi-minor axis tend towards zero. In the course of this, an erroneous conformal mapping, commonly employed in literature and correctly reproducing the electric field only in a part of the physical space, is rectified. Interpreting the elliptic interface as faces of a mechanically opened crack which is exposed to an oblique remote electric field, surface charges and electrostatic tractions are calculated. In contrast to the established capacitor analogy model, approximately yielding electric charge densities and Coulombic tractions from displacements and electric potentials in the undeformed crack configuration, the work at hand provides exact solutions accounting for different implications of the crack curvature and for the inclination of the electric field. Crack weight functions are finally used to calculate stress and electric displacement intensity factors. As turns out, the surface charges of the capacitor analogy represent an excellent substitute for the exact electric boundary conditions within a relevant range of parameters, whereas inaccurate Coulombic tractions in the vicinity of crack tips may lead to a significantly overestimated mode I stress intensity factor.

Evaluating a green liquid phase plasma discharge process and working mechanism for remediating cobalt contamination in water

Cobalt is a toxic heavy metal contaminant in water and wastewater causing health concerns and on the other hand, a valuable element to recycle. In this study, performance of a novel and green continuous liquid phase plasma discharge (CLPD) process was investigated for removal and recovery of cobalt from aqueous solution without use of any catalysts or chemicals. The CLPD reactor design features two conductive channels and stable electric discharge at the orifice of two dielectric plates sandwiched among the electrodes. The effects of operating factors of the CLPD process were evaluated with liquid flow rate (25–100 mg/L) and applied power (200–300 W), and the highest removal efficiency of cobalt (93 %) was obtained within 25 min at a 50 ml/min liquid flow rate and 300 W applied power. The CLPD energy efficiency for cobalt removal under this condition was 27.44 g kW-1h−1. Reaction kinetics with scavenger tests revealed that oxidative reactive species, i.e., hydroxyl radical and superoxide radicals, produced at the discharge zone were responsible for cobalt removal from water by producing cobalt oxide particles and the reaction pathways were proposed. The CLPD process not only allowed for the efficient removal of cobalt (II) from water but also synthesized cobalt oxides particles with averaged size of 2.75 µm, which can be applied as catalyst. The overall results indicated that the novel CLPD is a robust and highly effective process to remove and recover cobalt from water.

The mutagenic effect of cold plasma on Medicago sativa L.

To explore the feasibility of using cold plasma as a mutagenesis breeding technology for forage crops, in this study we used the Medicago sativa L. cultivar, Zhongcao No. 3, as the experimental material. The effects of plasma treatments on Medicago sativa L. were analyzed through the use of plasma and activated water. Treatments with plasma and activated water inhibited plant height but promoted root growth. By creating a closed environment, adding a dielectric barrier plate, and combining these two treatment methods, the greatest impact can be had on the growth of Medicago sativa L. seeds. After treatment, the plant heights were approximately half those of the control group, and the root lengths were approximately 1.6 times those of the control group. Through emission spectroscopy, it was found that active particles such as O, NO2, and N2* were present and could be considered to have produced plasma-activated water through contact with the water surface, thus affecting the survival and growth of the seeds. Whole-genome resequencing (WGRS) was performed on the wild-type and selected mutants after treatment, with an average sequencing depth of 115.93×, an average genome alignment rate of 91.72 %, and an average genome coverage rate of 91.85 %. Various types of mutations were detected and annotated. After filtering, 7,822,324 SNP (single nucleotide polymorphisms) sites, 2,161,917 indel sites, 200,544 SV sites, 238 CNV (copy number variation) sites. The SNPs, indels (insertions/deletions), and SVs (structural variations) were mainly heterozygous, with heterozygosity rates of 87.13 %, 92.16 %, and 83.49 %, respectively. The CNVs were dominated by low copy numbers, accounting for 53.77 %. These results indicate that plasma treatment has significant effects on plant growth and genome of Medicago sativa L.

Effects of Fungicides on Fungal Development, Conidiophore Morphology, and Conidial Releases from Single Strawberry Powdery Mildew Colonies Assessed Using an Electrostatic Technique

We evaluated the effects of fungicides on strawberry powdery mildew (PM) fungus, Podosphaera aphanis, using an electrostatic technique. Thirty-six fungicides were sprayed on single colonies of P. aphanis on leaves of strawberry seedlings (Fragaria × ananassa Duchesne ex Rozier). Colony development varied depending on the tested fungicides. Particularly, pyraziflumid, triflumizole, triforine, polyoxin, sodium hydrogen carbonate + copper wettable powder, and flutianil + mepanipyrim were highly effective for reducing colony development. P. aphanis colonies were histochemically stained to observe the morphological characteristics of fungal cells forming normal and abnormal conidiophores. Abnormal conidiophores were classified into seven types based on their morphological and cytological characteristics. Finally, asexual conidia were collected from single P. aphanis colonies on the leaves spray-treated with fungicides using a dielectrically polarized insulator plate (electrostatic spore collector); conidia attracted to the insulator plates were counted using a high-fidelity digital microscope. Most tested fungicides highly inhibited the production and/or germination of asexual conidia. The germination of asexual conidia was observed only in thiophanate-methyl (methyl benzimidazole carbamates fungicides; MBC fungicides) and azoxystrobin (quinone outside inhibitors; QoI fungicides). Assessing with the electrostatic technique, we clarified that P. aphanis has developed resistance to both thiophanate-methyl and azoxystrobin. Thus, the methodological assessment analyzing the colony development and the number of conidia released from single colonies will be helpful information for screening effective fungicides.

Large size shielded metal-ceramic cathodes

The technology for manufacturing large size shielded metal-ceramic cold cathodes is described. It has been shown that the use of a shielded metal-ceramic cathode allows to significantly increase the impedance of the vacuum diode and to form an electron beam of constant cross-sectional size or of the required size (up to 400 mm wide) with a fairly uniform electron beam current density distribution (≤15%).It has been found that the emission decline of the shielded metal-ceramic cathode, like that of the metal-dielectric cathode operating at a high repetition rate (≥100 pps), is significant at the beginning of the process and then slows down, allowing continuous operation for up to 40 h. Both cathodes require periodic cleaning of the plates, which is more difficult for metal-ceramic plates.At the same time, a metal-ceramic cathode works better at low vacuum, allowing twice as much current to be generated (in the same geometry) as a metal-dielectric cathode, while reducing the accelerating voltage by ∼15%. However, metal-ceramic plates are about 100 times more expensive to manufacture than dielectric plates for a metal-dielectric cathode.Therefore, the choice of cathode type for vacuum diode accelerators is not a trivial problem, but depends on many factors that must be taken into account in each case and for each radiation technology.

Feasibility study of fabricating 20 nm resolution dielectric Fresnel zone plates with ultrahigh aspect ratio for EUV optics

EUV light optics are either reflective or diffractive due to the substantial absorption characteristics by almost all materials. Despite great successes in manufacturing integrated circuit chips, reflective EUV optics are still unfriendly to small-to-medium enterprise (SME) because of the enormous costs. Recently, diffractive EUV optics has come to the light in hopes to be able to establish manufacturing nanoscale products and inspecting nanoscale structures. Diffractive zone plates with high resolution in EUV wavelengths are urgently needed. This paper reports our latest success in developing 20 nm resolution zone plates for focusing and imaging in the EUV and soft X-ray regions. It firstly discusses the diffraction efficiency of FZPs tailored for 13.5 nm wavelength to decide the essential height of the zone plate. Then, Monte Carlo simulation method was used to figure out the achievable zone plate parameters by high-resolution electron beam lithography (EBL). Finally, this work systematically explored the viability of nanofabricating top-tier 20 nm resolution hydrogen silsesquioxane (HSQ) zone plates with the duty cycle ratio nearing 1:1 and the aspect ratio approaching 13:1 on 50 nm thick Si3N4 membranes.

Electrodynamic properties of a rectangular waveguide with a dielectric plate located in the center of its wide wall

A rectangular waveguide with a dielectric plate located in the E-plane is the basic element of devices for microwave heat treatment of sheet materials. In this regard, it is relevant to study the processes of propagation and transformation of electromagnetic waves in such a system. The purpose of the work is to study the influence of the transformation of the electromagnetic field in the air medium of a rectangular waveguide in the zone of propagation of the slow wave H10 on the distribution of electric field energy in the dominant wavelength range and determining the wavelength, at which its maximum value is reached. The range properties of the intrinsic electrodynamic parameters and the field structure of a rectangular waveguide with a dielectric plate located in the E-plane in the middle of its wide wall have been studied. The wavelength at which the maximum energy level of the electric field in the dielectric plate is achieved is determined. The results obtained can be used in the design of microwave heating devices for dielectric materials.

A bifunctional metamaterial with broadband properties of absorption and linear-to-linear polarization conversion

This paper proposes, measures, and investigates a bifunctional metamaterial capable of achieving absorption and reflective linear-to-linear polarization conversion simultaneously, which both exhibit the characteristics of broadband. The unit cell consists of a metal pattern with resistors, a dielectric plate, an air layer, and a metal backplate. The simulation results demonstrate that the designed metamaterial acquires over 90% absorption in the microwave band of 6.5–9.3 GHz. Within the frequency range of 12.7 GHz–17.2 GHz, the polarization conversion rate exceeds 90%, effectively converting y-polarized incident waves into x-polarized reflected waves. The experimental results align with the simulation data. The surface current and electric field distributions are utilized to analyze the absorption and polarization conversion phenomena. This bifunctional metamaterial exhibits potential application in radar imaging, enhancing data transmission rates, and wireless communication.