In this study, we present an analytical model for predicting the magnetic properties and optimization of thermomagnetic devices using mathematical models. The 3D analytical magnetic model is firstly validated by the dipole model and confirmed through experimentation, enabling to accurately estimate the magnetization of the used magnet. The stray field induced by the permanent magnet over the lateral surface of the rotor is computed. Then, the resultant force and torque are derived allowing to estimate the exact number of ferromagnetic active material required and their angular gap.
The Meek-Raether criterion underpins much of the current physical understanding of gas breakdown. The classical kinetic approach estimates the moment of transition from Townsend’s avalanche to streamer discharge, and has very often been used as a means of explaining experimental breakdown results. The Meek-Raether criterion holds great predictive power for the design of gas insulated systems, owing to its reasonable accuracy that has withstood the test of time. However, with the advent of pulsed power technology which often involves fast-rising and non-standard waveshapes applied to complex (nonuniform) electrode topologies, the limitations of the method have been made increasingly apparent. In this work, the avalanche-to-streamer transition criterion has been theoretically revisited for fast-rising pulsed breakdown, particularly for overstressed breakdown occurring on a rising voltage slope. Based on the simplified transport of a Gaussian-distributed electron density, mathematical analyses unveils the time dependent nature of the electron growth rates and their dependence on the voltage slope. Explicit expressions for the breakdown voltage and formative breakdown time as a function of the rate of rise have further been derived for the limiting case of a non-attaching and non-diffusive gas. From this, it is found that electron diffusion may be an important consideration for pulsed breakdown, and an approximate condition separating the diffusion-dominated regime and where diffusion can be neglected is suggested. The novel analytical approach is also shown to be capable of recreating the upward shift of Paschen’s curve with increasing rate of voltage rise, validated against both simulation and experimental data. Furthermore, the predicted field-time breakdown scaling relationship is also shown to describe observed experimental trends well. The results may be significant for the future development of gas insulated power and pulsed power equipment, and advances the fundamental understanding of fast transient breakdown processes.
With the ever-increasing requirements placed on current and future pulsed power systems in terms of voltage, power, and compactness; solid insulation is a strong candidate for the development of novel insulation systems capable of meeting these specifications. However, the issue of solid-solid interfaces under non-standard and fast-rising impulses must firstly be addressed, as the failure to do so may pose significant risk of electrical breakdown due to reduced dielectric strength across interfacial contacts. In this work, the impulsive breakdown characteristics across dry-mate solid interfaces formed between PVC (polyvinylchloride), Torlon (polyamide-imide), Delrin (polyoxymethylene), Perspex (polymethylmethacrylate), and Ultem (polyetherimide) has been investigated in atmospheric air and under two different impulsive waveforms rising at ∼2400 kV/µs and ∼0.35 kV/µs. The statistical treatment of the obtained impulsive breakdown voltages and time to breakdowns are presented, alongside an analysis of the post-breakdown surfaces and discharge channel morphologies. The results indicate that under low mating pressure conditions (10’s of kPa), the interfacial breakdown strength may be below that of only an air gap with no dielectrics. A correlation between the estimated asperity aspect ratio and the interfacial breakdown strength has been observed. This suggests that under the present experimental conditions, field enhancement around surface asperities may be a dominating factor which defines the breakdown strength of the interface, since the surface asperities do not deform sufficiently to form strong interfacial contact spots, and thus reducing the interfacial tracking resistance. This therefore provides little to impede the development of interfacial discharges. The widths of post-breakdown traces left by plasma channels on the contacting surfaces have also been shown to be dependent on the rate of voltage rise, dV/dt, and on the material forming the interface. The results arising from this work may aid in the future development of high voltage solid insulating systems for power and pulsed power systems.
This paper describes the process followed to implement a system to characterize the complex permittivity of materials in the 10-330 GHz frequency band. Firstly, the method used and the system's calibration process are shown, consisting of a double calibration TRL (Thru-Reflect-Line) and GRL (Gated-Reflect-Line). Subsequently, a smoothing technique is used to improve the accuracy of the results. Finally, a test is performed on quartz and glass fiber samples, showing that the results are quite reliable over the entire measured bandwidth.
This work outlines the procedure to establish a system for assessing materials' complex permittivity and permeability within the 110-170 GHz frequency range. We present the employed methodology and the calibration procedure for the system, incorporating a dual approach using TRL (Thru-Reflect-Line) and GRL (Gated-Reflect-Line) methods. Following that, a smoothing technique is used to enhance the accuracy of the results. Tests were conducted on a HIPS sample to validate the system's performance, demonstrating the results' reliability across the entire measured bandwidth.
Before selecting decontaminants for low and high (sterilizing) levels using an indirect Atmospheric Plasma Jet (APJ), also known as Plasma Activated Water or PAW, the decimal reduction time, D-value, and confidence level should be determined for the most common and persistent single microbes and poly-microbe, especially in the wound healing. Decontaminant solutions or PAW were prepared after exposure to APJ at different gas flow rates and different exposure times. The D-value of a decontaminant solution was determined by inoculating it with a bacterial suspension of 104 to 105 colony-forming units (CFU) and then transferring the mixture to 7 mL of growth media. The mixture was then incubated at optimal conditions. The D-values and confidence levels for various bacteria such as Staphylococcus Aureus (SA), Candida Albicans (CA), and Poly-microbe were determined for the following conditions which are different in gas flow rates (0 ml/min, 1000 ml/min, 1500 ml/min and 2000 ml/min) and exposure times (0s, 30s, 60s, 90s, and 120s). Different gas flow rates observed for SA, CA, and Poly-microbe were 4.15 min, 3.54 min, and 2.64 min respectively. It shows that poly-microbe has the best decimal reduction time compared to the other pathogens. The confidence levels for SA, CA, and poly-microbe were 24.90 min, 21.24 min, and 15.84 min for low-level decontaminants respectively while 49.80 min, 31.68 min, and 42.48 min for high-level decontaminants. At different exposure times, D-CA, SA, and poly-microbe D-values re 3.74 min, 3.40 min, and 2.20 min respectively. For this PAW condition, poly-microbe also showed the best D-value compared to the other pathogens. The confidence levels for SA, CA, and poly-microbe were 22.44 min, 22.40 min, and 13.20 min for low-level decontaminants respectively while 44.88 min, 40.80 min, and 36.40 min for high-level decontaminants. This result also showed that after PAW exposure, the expected decimal reduction time for wound pathogens can be achieved which is higher than 2 min and lower than 10 min. In addition, their confidence level also achieves the expected value which is higher than 10 min for the low level of decontamination and lower than 60 min for high-level decontamination This also demonstrated that PAW can be one of the suggested decontamination methods in wound healing or other medical fields. The suspension studies were an indication of the decontaminant efficacy produced by plasma devices on the microbial. For microbial decontamination, PAW can be used. For low-level and high-level decontaminants, PAW was recommended for poly-microbes compared to other microbes. Although PAW is better used for poly-microbe, PAW also can be applied to SA and CA with the same plasma parameters used. The expected effectiveness from the studied formulations showed that the decontaminant solution or PAW can be recommended for microbial decontamination.
This integrated study presents a thorough investigation into a novel class of electrets known as Magneto-Piezoelectret Thermoformed (MPT) devices. The research focuses on evaluating capacitance, quality factor, and the impact of magnetic fields on these devices. Fabricated by fusing fluoroethylene propylene (FEP) films and integrating magnetic strips, the MPT devices exhibit both magnetostrictive and piezoelectric effects in response to external magnetic fields. The study encompasses the latest advancements in material synthesis, fabrication techniques, characterization methods, and potential device applications. Measurements conducted under various electric currents and frequencies revealed that higher capacitance values are associated with increased electric charge storage in MPT devices. The devices demonstrated exceptional quality factors, particularly in the MHz range, suggesting their potential as efficient electric charge storage devices. Further investigation focused on the influence of magnetic fields on the magneto-piezoelectric response of MPTs. Thermoformed piezoelectrets, featuring open tubular channels and an additional magnetic layer, were explored for their potential as sensors for detecting magnetic fields. While the magnetopiezoelectric response exhibited linearity in the presence of magnetic fields, a decrease in charge storage capacity was observed due to mechanical stress on the tubular channels. The MPTs displayed a maximum resistance of approximately 0.75 T against magnetic fields, reaching complete saturation at a magnetic field strength of 0.8 T. Beyond this point, the relationship between variables became nonlinear, resulting in a null magneto-piezoelectric response. This comprehensive study contributes to a deeper understanding of the capacitance, quality factor, and magnetic field influence on Magneto-Piezoelectret sensors. The insights gained from this research have significant implications for potential applications in advanced technologies that demand high-frequency operation and magnetic field detection.
Silicon (Si) has a high theoretical gravimetric capacity and can replace the graphite in the negative electrode of lithium-ion batteries. Among numerous Si electrode geometries, the Si microwire (SiMW) geometry shows a promising performance compared to Si wafers and particles and alleviates the mechanical instability during lithiation/delithiation process due to high volume expansion/contraction. In this paper, a single-wire model (SWM) is proposed for lithium-ion battery half-cell composed of SiMWs as the positive electrode and lithium metal as the negative/reference electrode. In the proposed SWM, an array of SiMWs is modeled by only one equivalent micro-scale wire. The SWM is the simplest model that incorporates the electrochemical behavior with a minimal computational effort suitable for real-time applications. Despite its simplicity, it is equivalent to a one-dimensional (1D) model of conventional graphite-based lithium-ion batteries. Both numerical and experimental results on a 2.5 mA SiMW half-cell sample, are provided to verify of the proposed SWM.
Weber-Maxwell electrodynamics is a modernized, compressed, cleansed and, in many respects, advantageous representation of classical electrodynamics that results from the Liénard-Wiechert potentials. In the non-relativistic domain, it is compatible with both Maxwell's electrodynamics and Weber electrodynamics. It is suitable for all electrical engineering tasks, ranging from electrical machines to radar and high-frequency technologies. Weber-Maxwell electrodynamics also simplifies access to quantum physics and other areas of modern physics, such as optics and atomic physics. Particular advantages of Weber-Maxwell electrodynamics are its simple and fast computability in computer calculations and, as it is based on point charges, in the simulation of plasmas. The latter is particularly important for fusion research. Moreover, Weber-Maxwell electrodynamics is also highly suited to academic and post-primary education, as it allows an easy comprehension of both magnetism and electromagnetic waves. Due to the novelty of Weber-Maxwell electrodynamics, there are currently no articles that summarize its most important aspects. The present article aims to achieve this.
Very high energy electron (VHEE) beams with energies greater than 100 MeV may be promising candidates for FLASH radiotherapy due to their favourable dose distributions and accessibility of ultrahigh dose-rates (UHDR). Combining VHEE with the normal tissue-sparing FLASH effect of UHDR radiotherapy could improve patient outcomes. The standard dosimeters used for conventional radiotherapy, including ionization chambers and film, have limited application to UHDR radiotherapy due to deficits in dose rate independence and temporal resolution. Plastic scintillator detectors (PSDs) are a potential alternative. PSDs connected to a Medscint Hyperscint RP-100 were used to measure the response to 200 MeV electrons produced by the CERN Linear Electron Accelerator for Research (CLEAR). The dose-response linearity and radiation hardness of PSDs under UHDR VHEE conditions was investigated, using dose rates up to 1.21 × 109 Gy/s. Two scintillators were investigated: a polystyrene-based BCF-12 and a proprietary polyvinyltoluene (PVT)-based material. The BCF-12 probe exhibited linear light output with dose per train from 4.9 to 125.2 Gy, and dose rates up to 1.16 × 109 Gy/s within a single pulse. The output of the PVT-based probe was linear from 3.9 to 59.5 Gy per train, and dose rates up to 9.92 × 108 Gy/s. While output linearity was retained (R2 > 0.998) after delivering 26.2 and 13.8 kGy to the BCF-12 and PVT-based probe, respectively, the light output was reduced by < 1.5%/kGy. The performance of PSDs in this work suggest they may be useful real-time dosimeters for applications in UHDR VHEE radiotherapy.
In this paper, we propose two different methods for time-domain finite-difference analysis of uniform temporally and spatially dispersive metasurfaces using their zero thickness sheet representations using the Generalized Sheet Transition Conditions (GSTCs). Metasurfaces are described here using their effective surface susceptibilities which are assumed to exhibit Lorentzian temporal dispersion characteristics. For both methods, the spatial dispersion of the, the surface susceptibilities (i.e., their dependence on angle of incidence) are represented using the extended GSTCs presented in -. However, the first method takes advantage of a polynomial expansion of the angle-dependent surface susceptibilities in terms of the transverse wavevector to implement spatial derivatives of the electric and magnetic polarization as well as the average field on the surface, leading to a coupled set of field equations encompassing the entire surface. Limitations for this method are presented in terms of poor conditioning for a coupled system of equations and an inconvenient extension to the higher-order expansion of the susceptibility terms. The second method lifts these limitations by solving the spatial dispersion problem in the spatial frequency domain at every time step. Both methods are validated for custom Lorentzian models and two canonical physical cells while comparing their transmission and reflection coefficients with analytical results.
A simple waveguide-Floquet mapping is proposed and theoretically investigated that links the scattering response of a sub-wavelength metasurface unit cell under an infinite periodic array configuration and when measured inside a shielded rectangular waveguide environment. This mapping is based on extracting the effective surface susceptibilities as the fundamental constitutive parameters of the cells, via the Generalized Sheet Transition Conditions (GSTCs) of the unit cell using the waveguide measurements, and then reconstructing the unit cell response at an arbitrary incidence angles. Using two examples of a transmissive Huygens' metasurface and a purely reflective metasurface, the proposed waveguide-Floquet mapping is numerically confirmed to determine the complete angular scattering of the unit cells. The proposed waveguide-Floquet mapping thus represents a simple technique to experimentally determine the angular scattering characteristics of the unit cell using a lowcost effective waveguide measurements.
Partial discharges (PDs) on liquid impregnated pressboard insulation have been investigated for sinusoidal and switched voltages for two different liquids-one mineral oil and one synthetic ester. The insulation models used were a rounded electrode resting on a pressboard plate on a plane electrode representing semi-uniform field, and a sharp-edged electrode representing divergent field. The main result shows that the PD inception voltage (PDIV) is considerably lower at switched than at sinusoidal voltage. Similarly, the mineral oil showed a lower inception voltage than the synthetic ester. Finally, a lower PDIV for the sharp conical electrode compared to the spherical electrode was seen. The differences can be explained by formation and transport of space charges. The space charges will shield the high-field regions when having the same polarity as the voltage and then enhance the electric field right after a voltage polarity reversal. There is minimal time available for charge drift at polarity reversal of switched voltage. Contrary, for sinusoidal slowly varying voltage there is plenty of time for the charges to drift before the opposite voltage peak occurs. Thus, less field enhancement from space charges under sinusoidal voltage. The field enhancement due to space charges of opposite polarity is enhanced for liquids with higher injection current, such as mineral oil.
Nearly ideal vertical AlxGa1-xN (\(0.7\ \le x<1.0\)) p-n diodes are fabricated on an AlN substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity doping, to overcome the major bottleneck of AlN-based material: the control of conductivity. Capacitance-voltage measurements revealed that the net charge concentration agreed well with the DPD charge concentration expected from the device layer structure. The fabricated devices exhibited a low turn-on voltage of 6.5 V, a low differential specific ON-resistance of 3 mΩ cm2, electroluminescence (maximum at 5.1 eV), and an ideality factor of 2 for a wide range of temperatures (room temperature-573 K). Moreover, the breakdown electric field was 7.3 MV cm-1, which was almost twice as high as the reported critical electric field of GaN at the same doping concentration. These results clearly demonstrate the usefulness of DPD in the fabrication of high-performance AlN-based power devices.
We propose a method to extract the equivalent material parameters and circuit models for all-metallic tensor metamaterials. The metamaterials consist of an arrangement of sub-wavelength metallic pins affixed to the bottom plate of an air-filled parallel plate waveguide (PPW). Isotropic and anisotropic configurations are studied, which are implemented with cylindrical and elliptical pins, respectively. The effective permittivity and permeability tensor of an equivalent lossless, homogeneous PPW are extracted. An equivalent circuit model consisting of series inductances and a shunt capacitance is also extracted. An analytical procedure to perform the extraction is outlined. The procedure is validated using full-wave simulations and circuit theory. Finally, representative designs are presented to show the effectiveness and potential applications of the proposed homogenization technique. The extraction of effective material parameters enables the control of the properties of all-metal metamaterials, enabling the design of perfectly-matched, anisotropic unit cells. Ultimately, the accurate mapping between all-metal metamaterials and their equivalent circuit networks could be exploited to accelerate the inverse design of multi-functional metastructures.
This paper presents a method for effectively characterizing the dielectric permittivity of nematic liquid crystals across a broad frequency range. These materials show significant potential for reconfigurable devices operating in microwave and millimeter-wave frequencies. To achieve this goal, an additive manufacturing technique is used to create a microstrip line that can be filled with liquid that acts as its substrate. The liquid crystal is then biased to modulate its permittivity. After manufacturing, a time-gating approach is used to extract the permittivity, eliminating the need for TRL calibration. Finally, the approach is validated through simulations and experimental results, which closely align with those reported using other methods in the bibliography.
Love wave (LW) acoustic sensors are promising devices for biochemical detection in the liquid media. However, their application for in-situ biochemical detection especially in the turbid liquid medium is not yet explored. Turbid liquids are complex in nature with both mechanical and electrical characteristics. These characteristics could be reliably estimated with LW acoustic sensor response, where some of the dedicated sensors based on electrochemistry or optical principle show limitations. This paper presents experimental responses of LW acoustic sensor to turbid liquids based on Formazin solutions and its comparison to the spectrophotometer response. Analysis of sensorâ\euro™s electro-acoustic response is used to better characterize the sensor performance with turbid liquids. Further, this paper demonstrates the feasibility of LW acoustic sensor as a multiparameter sensing unit by estimating the influence of electro-mechanical parameters of the turbid liquids on the overall response of the sensor.