Uniform Field Distribution Research Articles

Finite Element Simulation and Experimental Research on Uniformity Regulation of Microwave Heating of Composite Materials.

As an attractive alternative to the traditional autoclave curing process, microwave curing has been widely used for manufacturing high-performance composites. However, the nonuniform temperature distribution during composite curing is the main problem faced by the microwave curing process, which limits its application in the aerospace industry. This paper studied the regulating effects of cavity structure and mechanical optimization methods on the uniformity of the microwave field by numerical analysis and finite element simulation, and an octagonal microwave heating device with multi-microwave generators, mode stirrers and mobile platform was developed independently and the experimental verification were finally carried out. The results showed that compared with the traditional heating device, the T800/602 carbon fiber reinforced composite laminates cured in the regulating device of microwave heating uniformity established in this paper had more uniform temperature field distribution, a more synchronous curing process and lower residual stresses.

A Reticulated Planar Transmitter Using a Three-Dimensional Rotating Magnetic Field for Free-Positioning Omnidirectional Wireless Power Transfer

This article proposes a free-positioning omnidirectional wireless power transfer (WPT) system with a reticulated planar transmitter, which enables multiple receivers to be powered simultaneously in arbitrary positions and orientations. The reticulated planar transmitter is equipped with four interleaved and overlapped meander coils, thus, a three-dimensional (3-D) rotating magnetic field is generated with the designed excitation current. Therefore, only a planar single-coil (such as a loop-type coil) is required to realize free-positioning omnidirectional WPT. According to the theoretical modeling of the magnetic field, the excitation current that can generate a 3-D rotating magnetic field is given. To obtain a uniform and strong magnetic field distribution, the transmitter grid width is optimized. Furthermore, an excitation current modulation strategy based on phase-shift control is presented to regulate the amplitude of the excitation current. The experimental results show that the output power is greater than 13.1 W no matter how the center of the receiver moves or rotates freely within 400 × 400 mm. When five receivers are powered simultaneously in different positions and orientations, 82.5 W total output power and 55.6% efficiency can be achieved. The experimental results demonstrate that free-positioning omnidirectional WPT can be realized with only planar single-coil receivers by using the proposed reticulated planar transmitter and its excitation current modulation strategy.

Hybrid Bulk-Surface Modes Excited by a Sheet Electron Beam in THz Cherenkov Oscillator

It was shown that a spoof surface plasmon polariton (SSPP) with the uniform RF field distribution compatible with a sheet electron beam is resonantly excited by a bulk wave of an open cavity containing a nonuniform (bi-periodic) grating. This provides an efficient interaction of a wide sheet electron beam with a hybrid bulk surface mode (HBSM) in the THz Cherenkov oscillator that has been demonstrated by 3-D PIC simulations. The presented simulation results showed the excitation of oscillations in the range from 0.628 to 0.648 THz with watt level of output power and output efficiency up to 1% for the 100-mA 17.2–23.2-kV electron beam. The conditions for the suppression of the competing modes having variations across a grating width have been discussed.

A Microwave-Based Microfluidic Cell Detecting Biosensor for Biological Quantification Using the Metallic Nanowire-Filled Membrane Technology.

A label-free, sensitive, miniaturized sensing device was developed for detecting living cells in their flow stream. The outstanding performance of this biosensor in distinguishing living cells in cell suspension was achieved by integrating microstrip stub resonator above a microfluidic structure using the metallic nanowire-filled membrane technology. The cell suspension flows in a microfluidic channel placed between the tip of the stub resonator and its ground plane as the substrate to take advantage of the uniform and concentrated field distribution. We studied the changes in relative permittivity due to the presence of a single living cell in the phase of the transmitted signal (S21). An average variation of as much as 22.85 ± 1.65° at ~11.1 GHz is observed for the living cell sensing using this optimized device. This biosensor could detect rapid flowing cells in their biological medium in real-time and hence, can be used as an early diagnosis and monitoring tool for diseases.

Using Overlapped Resonators in Wireless Power Transfer for Uniform Electromagnetic Field and Removing Blank Spots in Free Moving Applications

We propose an induction link based on overlapping arrays to eliminate blank spots on the electromagnetic field for moving object applications. We use two arrays of four aligned coils that have a 50% overlap between the two plates. This mechanism compensates for the internal coil power drop at positions in the boundaries between two adjacent external coils. We showed that if these plates are excited, a uniform electromagnetic field is created in the movement direction of the moving object. This uniform electromagnetic field distribution will result in a constant receiving power at all points in the path of the moving internal coil with the same power consumption of one coil excitation. Power delivery to the moving object tolerance reaches 10% at most, while, in non-overlapped scenarios, it is approximately 50%. In addition, according to the theoretical calculations, printed circuit coils (PCB) for the array are designed for maximum efficiency. We found that the change in distance and dimensions of the receiver coil has a linear effect on power and efficiency. Moreover, a Specific Absorption Rate (SAR) simulation was performed for biocompatibility. In this paper, we investigate and record a 68% electrical power efficiency for the fabricated system. The array consists of eight transmitters coils of the same size and shape and a receiver coil at a distance of 4 cm. Furthermore, the fabricated coil has shown improved efficiency compared to similar studies in the literature and introduces a promising structure for bio-test applications.

NSGA-II-Based Microchannel Structure Optimization Problem Study

A multiobjective genetic algorithm is used to optimize the structure of circular concave cavities and microchannels. The objective functions of thermal resistance and pumping power are constructed by the response plane approximation method according to the simulation results, and then a mathematical model of multiobjective genetic optimization with the structural parameters of microchannels as variables is established. The Pareto optimized solution sets of thermal resistance and pumping power are calculated by the nondominated ranking genetic algorithm NSGA-II, and the comprehensive heat transfer performance is evaluated by the enhanced heat transfer factor. The results show that the multivariate statistical coefficients R 2 of the thermal resistance and pumping power objective functions are 0.932 9 and 0.996 6, respectively, indicating the high accuracy of the fitted functions. The optimized channel structure ( e 1 = 0.036.8 mm , e 2 = 0.019.3 mm ) was used to achieve a more uniform temperature field distribution and better integrated heat transfer performance (enhanced heat transfer factor η = 1.23 ). When the thermal resistance is larger or the pump work is larger, the comprehensive heat transfer effect is not as good as the working condition when the thermal resistance and pump work are more uniform.

Optimization of an Oscillatory Flow Crystallizer Based on Heat Transfer and Supersaturation Distribution

AbstractTaking supersaturation and heat transfer rate as evaluation indexes, two typical internal geometries of an oscillatory flow crystallizer (OFC) with circular‐orifice baffles (OFC‐COB) and smooth periodic constrictions (OFC‐SPC) were studied by numerical simulation. The results indicated that OFC‐SPC could provide a relatively high heat transfer rate, supersaturation, and similar or lower power density consumption, as well as a uniform flow field distribution without vortex dead zone. Further, a method to prejudge the supersaturation in oscillatory flow crystallizer is proposed, which would be good guidance to determining the operating parameters.

Deep regression with ensembles enables fast, first-order shimming in low-field NMR

Shimming in the context of nuclear magnetic resonance aims to achieve a uniform magnetic field distribution, as perfect as possible, and is crucial for useful spectroscopy and imaging. Currently, shimming precedes most acquisition procedures in the laboratory, and this mostly semi-automatic procedure often needs to be repeated, which can be cumbersome and time-consuming. The paper investigates the feasibility of completely automating and accelerating the shimming procedure by applying deep learning (DL). We show that DL can relate measured spectral shape to shim current specifications and thus rapidly predict three shim currents simultaneously, given only four input spectra. Due to the lack of accessible data for developing shimming algorithms, we also introduce a database that served as our DL training set, and allows inference of changes to 1H NMR signals depending on shim offsets. In situ experiments of deep regression with ensembles demonstrate a high success rate in spectral quality improvement for random shim distortions over different neural architectures and chemical substances. This paper presents a proof-of-concept that machine learning can simplify and accelerate the shimming problem, either as a stand-alone method, or in combination with traditional shimming methods. Our database and code are publicly available.

Optical properties and photothermal conversion performances of graphene based nanofluids

• Single-layer graphene and GO nanofluids were designed for solar thermal application. • Uniform temperature distribution is achieved in nanofluids based on the RI-DASC mode. • The photothermal conversion efficiency of SLG is 49.13% at 100 ppm in the RI-DASC mode. • The photothermal conversion efficiency of GO reaches 46.26% at 100 ppm in the RI-DASC mode. Direct absorption solar collectors (DASC) are extremely attractive in solar energy utilization. In this paper, starting from these two aspects, graphene-based nanofluids, including single-layer graphene (SLG) and graphene oxide (GO), are prepared to enhance solar absorption and photothermal conversion performance. The influence of nanofluids' concentration and two different irradiation modes: traditional DASC and reverse radiation DASC (RI-DASC) on the photothermal conversion performance of graphene-based nanofluids has been studied. The addition of a small amount of SLG or GO significantly improves the photothermal conversion efficiency of base fluid, and it increases along with the increase of the concentration. Furthermore, the RI-DASC mode has a more uniform thermal field distribution and the higher photothermal conversion efficiency than the DASC mode. In DASC mode, the photothermal conversion efficiency of pure water is 17.00%. By changing the irradiation mode, the introduction of GO and SLG nanofluids (100 ppm) increased the photothermal conversion efficiency by about 172% and 189%, reaching 46.26% and 49.13%. According to the photothermal-thermoelectric conversion experiment, the positive correlation between the output power of the TE module and the heating state of the nanofluid makes it possible to adjust the nanofluid in real-time. This work presents a feasible way to enhance solar energy absorption and improve the photothermal conversion efficiency of nanofluids for DASC.

Near‐field radio frequency identification leaky‐wave antenna based on artificial transmission line

The artificial transmission line (ATL) has a good characteristic of wavelength shortening, which can effectively cut down the size of microwave devices. In this article, the near-field radio frequency identification antenna based on an ATL was proposed. It mainly includes the radiating unit structure on the upper layer and the feeding structure on the lower layer. The two layers are connected by copper pillars for feeding. The height of the copper pillars is 16 mm (h0), which can obtain the maximum bandwidth. The antenna unit based on ATL consists of three curved microstrip lines, two interdigital microstrip lines, and four open microstrip lines. The interdigital structure on the upper layer of the antenna unit mainly affects the resonant frequency of the antenna unit, and the asymmetric interdigital microstrip lines increase the impedance matching bandwidth of the antenna unit. Compared with previous antennas, the proposed antenna features a low profile, and a good miniaturization based on an ATL by bending inductance and interdigital capacitance. The leaky-wave characteristic makes the energy radiate at a certain angle on the surface of the antenna. The leaky-wave characteristic and circular polarization characteristic of the antenna achieve a uniform field distribution. The simulated and measured bandwidth cover from 0.78 to 1.1 GHz for |S11| less than −10 dB. More importantly, the antenna has a large recognition area. The measured results demonstrate that the proposed reader antenna has a 100% read rate in 400 × 350 × 400 mm3 area in the metal shelf.

Compact Hybrid Metasurface-Inspired Resonator With Uniform Magnetic Field Distribution for Wireless Power Transfer

Compact and safe charging platforms have been one of the main goals in wireless power transfer (WPT) research and development. Here, we propose a compact hybrid metasurface-inspired resonator with a uniform magnetic field distribution for WPT. It consists of two orthogonally oriented layers of parallel printed wires with high-permittivity dielectric pads between them. This design allows us to spatially separate electric and magnetic fields, which provide high WPT efficiency and electromagnetic safety simultaneously. The prototype with 28 cm × 28 cm working area with uniform magnetic field was fabricated and experimentally studied. The measured coefficient of variation of the magnetic field in the working area of the resonator is 6.8%. The maximum achievable WPT efficiency reaches 70% over the working area. The numerically assessed specific absorption rate in human tissues placed on the proposed structure is 11 mW/kg, which is 30 times lower than on a conventional planar spiral coil. Our results pave the way to compact and safe WPT platforms for one-to-many charging.

Research and optimization of acoustic environment in ordinary classrooms of middle school

A good classroom acoustic environment will contribute to teachers’ health and students’ learning. Comfortable acoustic environment requires suitable reverberation time, sufficient loudness, uniform sound field distribution, high language clarity, and no acoustic defects such as echo and acoustic focusing. In this study, the optimization strategy of acoustic environment is proposed through the investigation, field testing and numerical simulation analysis of a middle school classroom in Wenzhou under different ventilation conditions. The results show: the key factors affecting the classroom acoustic environment are outdoor activity noise, corridor noise, and classroom teacher-student activity noise. Through optimization, the quality of classroom acoustic environment is improved significantly. Classroom reverberation time (intermediate frequency) decreased from 1.5s to 0.7s; ALC decreased from 9.65% to 4.75%; STI increased from 0.534 to 0.664. The research results provided reference for acoustic design of secondary school classrooms in the future.

A Uniformed DC Magnetic Generator Using Ferromagnetic Slot Cage by Geomagnetism Distortion Cancellation

A widely uniform and highly ambient robust DC magnetic field generator for precise motion sensors using inertial measurement units (IMUs) is newly proposed in this paper. Chronic problems such as low uniformity of magnetic field and geomagnetic disturbance of conventional Helmholtz, Merritt, Rubens, Lee-Whiting, and Tetra coils can be significantly mitigated by the proposed uniform DC magnetic field generator (UFG). Different from the previous air coils, the proposed UFG adopts a core-cage so that a strong and uniform DC magnetic field distribution can be generated inside the cage and that the UFG may be quite magnetically robust to ambient changes such as geomagnetic field and ferromagnetic objects. A dedicated power supply was developed for providing not only a DC current to generate the required magnetic field but also an exponentially decaying AC current to demagnetize the residual magnetic field in the core-cage. Design procedures for the UFG are fully established, considering the manufacturing cost, performance, and mechanical robustness for commercialization. Detailed designs of the UFG for magnetic field generation, enhancing uniformity, geomagnetic cancellation, and demagnetizing of the UFG are provided. Experimental results verified by a 30 cm × 30 cm × 30 cm prototype UFG showed that the geomagnetic field inside the UFG was significantly attenuated by 22 dB while the DC magnetic field uniformity (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>t</i></sub> < 5.0°) was achieved over 85% of the total volume of 27,000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

A New Wide Band and Compact H-Plane Horn Antenna Based on Groove Gap Waveguide Technology

In this article, a new H-plane horn antenna is designed using gap waveguide (GW) technology. This antenna consists of a semicircular groove GW (GGW) partially filled by a dielectric to provide uniform field distribution across the antenna aperture in a very compact range. In the proposed structure, the antenna aperture is loaded by an elliptical dielectric which collimates the antenna beam in E-plane resulting in gain enhancement. The designed antenna shows proper radiation performance in both E- and H-planes with low sidelobe levels (SLLs). A sample antenna is designed and simulated for Ku band and a prototype is fabricated. For the designed antenna, the impedance bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11} &lt; -10$ </tex-math></inline-formula> dB) of 49% covering the whole Ku-band is obtained. Likewise, the obtained SSL and gain are −10 dB and 14–17 dBi, respectively, over the operating bandwidth. In comparison with state-of-the-art designs, the proposed antenna introduces higher gain with lower size.

Design, experiment, and performance analysis of magnetorheological clutch with uniform magnetic field distribution along the radial direction for tension control.

High-precision tension control is very important for industrial production. Benefit from the unique property of magnetorheological (MR) fluid, a MR clutch is a potential device in a tension control system due to its fast response and large output dynamics. In this paper, based on the detailed analysis of axial magnetic induction intensity generated by the coil along the radial distribution, a shear-mode MR clutch with uniform magnetic field distribution along the radial direction is proposed for the tension control system. A theoretical model of torque transmission and a magnetic circuit were derived, and a magnetostatic simulation was carried out to validate the effectiveness of the proposed circuit design. Experimental evaluation was conducted to investigate the static and dynamic transmission torque property. Finally, a proportional-integral-differential controller was designed to regulate the output torque. Experimental testing demonstrated the effectiveness and practical feasibility of the MR clutch in tension control.

Design and Test of a Jet Remote Control Spraying Machine for Orchards

Aimed at issues associated with the poor air supply and poor automatic targeting accuracy of existing orchard sprayers, this paper designs a jet-type orchard remote control sprayer with automatic targeting which is suitable for standardized orchards in hilly and mountainous areas. By optimizing the structure of the diversion box, the uniformity of deposition and penetration ability of the pesticide droplets to the fruit tree canopy are improved, and a uniform wild field distribution is realized simultaneously. An accurate positioning of the fruit tree canopy space orientation is achieved through automatic targeting and azimuthal adjustment systems. When the target is detected, the solenoid valve is controlled to open, and vice versa, and the distance from the nozzle to the fruit tree canopy is adjusted in real time to improve the utilization rate of pesticides. The test results show that the effective range of the jet-type orchard remote control sprayer is no more than 3.5 m, and the maximum flow rate range is 6~6.5 L/min. Within the effective spraying range, the farther the distance is, the higher the automatic targeting accuracy. The pesticide droplets sprayed by the spraying machine have a certain penetration ability, and the uniformity of the droplets is good, which solves solidification problems caused by the penetration of pesticide into the soil. This research provides a reference for jet spraying operation and automatic targeting spraying structure design.

On the Use of Ridge Gap Waveguide Technology for the Design of Transverse Stub Resonant Antenna Arrays.

This paper presents some considerations on the design of a novel antenna consisting of the combination of a transverse stubs (TS) array excited by Ridge Gap Waveguides (RGWs), as well as a discussion of the experimental results obtained from a prototype that was manufactured and measured. A combination of Continuous Transverse Stubs (CTSs) is used as the starting point. Subsequently, the CTSs are modified to include some metallic blockers that split each CTS into a combination (array) of shorter TSs. This is performed in order to excite each individual TS column using a different RGW; thus, ensuring a close to uniform field distribution in the transverse plane of the TS arrays. Hence, the directivity of the antenna is increased. As a series-feed configuration is considered, the antenna keeps a resonant behaviour, having a narrow-band response. A Corporate Feeding Network (CFN) using the aforementioned RGW technology placed in the same layer as the rest of the antenna is included in the design. The radiating area of the antenna is, finally, with a simulated peak gain of 26.2 dBi and a Side Lobe Level (SLL) below −13 dB. A prototype is manufactured and tested. The simulated and measured radiation patterns maintain similar shapes to those of the simulations, with very similar angular widths in both main planes, although the frequency corresponding to the highest directivity changes to 31.8 GHz. A matching bandwidth of 517 MHz and a gain of 24.5 is, finally, achieved at that frequency.

Robust and Multi-Objective Pareto Design of a Solenoid

The optimization of the design of a practical electromagnetic device involves many challenging tasks for new algorithms, especially those involving numerical modeling codes in which objective function calls must be minimized for practical design processes. The Compumag Society provides openly accessible, challenging benchmark problems (TEAM problems) for testing novel numerical solvers. This paper deals with a novel solution for the multi-objective TEAM benchmark problem. This solenoid design test problem aims to search for the optimal shape of a coil, which ensures a uniform field distribution in the control region, while the sensitivity and the mass/DC loss of the coil are also considered in the context of robust design. The main differences from the previously published solutions are that the proposed methodology optimizes all three objectives together, not only as two independent two-dimensional sub-problems. We considered the asymmetrical cases in the solution and found that the symmetrical solutions always produced better uniformity and sensitivity measures. However, the difference between the symmetrical and asymmetrical solutions is insignificant for these objectives. Despite the fact that the cheapest solutions are symmetrical setups, they perform worse than the cheapest asymmetric ones in these uniformity and sensitivity criteria. Therefore, some asymmetric solutions that were previously neglected from the solution space can be competitive and interesting for practical design.

Двухзеркальная цилиндрическая антенная система с высоким коэффициентом использования поверхности.

A technique for the synthesis of two-mirror cylindrical antenna systems for a given amplitude distribution in the aperture has been developed. At the first stage geometrical-optical synthesis is carried out, at the second stage a refined solution is found using the field of the feed on the secondary mirror found by the numerical method of finite element. As an example, a two-mirror cylindrical antenna system with a horn-lens feed and a uniform field distribution in the main mirror aperture has been synthesized. Using full-wave simulation by the finite element method, the analysis of the radiation characteristics of a synthesized two-mirror antenna system is carried out. The scanning characteristics of the antenna system by turning the main mirror are investigated. The efficiency of a cylindrical two-mirror antenna system with a horn-lens waveguide transition in the E-plane and an H- sectorial horn feed reaches 0.95 i.e. is close to the limiting value. When scanning the main lobe of the pattern in an angular sector of 27 degrees due to the rotation of the main mirror gain exceeds 26 dB, and efficiency exceeds 0.8.

Electrical TCAD Study of the Low-Voltage Avalanche-Mode Superjunction LED

The CMOS silicon avalanche-mode light-emitting diode (AMLED) has emerged as a potential light source for monolithic optical interconnects. Earlier we presented a superjunction light-emitting diode (SJLED) that offers a higher electroluminescent intensity compared to a conventional AMLED because of its more uniform field distribution. However, for reducing power consumption low-voltage ( ≤ 15V) SJLEDs are desired, not explored before. In this work we present a TCAD simulation feasibility study of the low-voltage SJLED for various doping concentrations and device dimensions. The results show that for obtaining a constant field, approximately a tenfold more aggressive charge balance condition in the SJLED is estimated than traditionally reported. This is important for establishing a guideline to realize optimized RESURF and SJLEDs in the ever-shrinking advanced CMOS nodes.