Non-uniform Field Distribution Research Articles

Research on the Non-Uniform Temperature Field Distribution of Q355B Steel for Grain Storage under Fire Conditions

To reveal the distribution characteristics of the non-uniform temperature field of structural steel under fire conditions, Q355B steel for grain storage was taken as the research object. A multi-channel temperature detection instrument was used to monitor the temperature distribution of Q355B test plate in real time under gas fire, and the distribution characteristics of the non-uniform temperature field of the steel were studied under different heat inputs. The results showed that the temperature changes within 600 mm from the flame point were significant, while the temperature changes beyond 600 mm were not sensitive. The peak temperature Tmax and the heating rate vr at the fire source points of each test plate increased linearly with the increase of heat input Q at the fire source. With the increase of distance d, the variation trend of the time tmax for each test plate to reach the peak temperature in the rolling direction, was the same. As d increased, tmax gradually increased and tended to stabilize. The average cooling rates vd1 and vd2 of each test plate decreased with the increase of d. The temperature distribution patterns of each test plate were the same. The Tmax-d curve of each test plate followed the Boltzmann function distribution, the Q-∆T followed a linear relationship, and the Q-d0 followed an exponential function relationship. By combining the three, a non-uniform distribution model of Tmax-Q temperature field under gas fire was obtained.

Spatial-Dependent Spectral Response of Acousto-Optic Tunable Filters with Inhomogeneous Acoustic Distribution.

The spectral response of an acousto-optic tunable filter (AOTF) is crucial for an AOTF based spectral imaging system. The acousto-optic (AO) interaction within the spatial-distributed area of the acoustic field determines the spectral response of the light incidence. Assuming an ideally uniform acoustic field distribution, phase-matching geometries can be applied to calculate the anisotropic Bragg diffraction in AO interactions, determining the wavelength and direction of the diffracted light. In this ideal scenario, the wavelength of the diffracted light depends solely on the direction of the incident light. However, due to the non-ideal nature of the acoustic field, the wavelength of the diffracted light exhibits slight variations with incident position. In this paper, an analytical model is proposed to calculate the spatial-dependent spectral response of the diffracted light under non-uniform acoustic field distribution. The study computes the variation pattern of the diffracted light amplitude caused by the inhomogeneous acoustic distribution. The theoretical considerations and computational model are confirmed by AOTF frequency scanning experiments. The study demonstrates that the distribution of the acoustic field leads to non-uniform spatial-spectral response in the AOTF, and the spatial AO interaction computational model can provide data support for calibrating AOTF systems in imaging applications.

Calculation method of electromagnetic losses and hot-spots temperature of giant magnetostrictive transducer

Due to the complex energy conversion processes and limited avenues for heat dissipation in the giant magnetostrictive transducer (GMT). Large losses and elevated internal temperature rise are inevitable, this would bring into serious reliability problem for GMT. Accurately analyzing its electromagnetic losses and hot-spots temperature are crucial for designing and optimizing the transducer. High-power GMT typically use permanent magnet (PM) to provide a bias magnetic field for enhanced power density. Although, this structure could significantly reduce the volume of driving part, it also caused issues such as non-uniform magnetic field distribution and bias magnetic field, which have great influence on the magnetic energy loss and hot-spots temperature rise. The previous researches seldomly investigate these influences on total loss at GMT system level. Additionally, the differential excitation coil loss caused by AC resistance among multi-layers can’t be neglected, which can lead to variations in coil loss and temperature rise. Therefore, this paper proposed a detailed electromagnetic losses and hot-spots temperature rise calculation model from material level to GMT system level. This method can obtain the distribution of electromagnetic losses within multiple factors, and the hot-spots temperature rise considering the temperature non-uniform distribution. Firstly, we have developed a precise loss calculation model, which takes the influence caused by PM bias and non-uniform magnetic field on magnetic energy loss into account. Additionally, the proposed model could conclude the impact of inter-coil resistance variations on the eddy current loss in excitation coil. Secondly, based on of the non-uniform distribution of losses in driving part, using the divisional thermal modeling approach and a 2-D T-shaped equivalent thermal network, we further constructed a transient temperature calculation model for GMT. This approach can effectively improve the energy conversion efficiency of GMT, so as to enhance the thermal reliability of the transducer. Finally, a testing system for the loss-thermal of GMT was established to validate the effectiveness of proposed model. Results indicate that the average error between our loss calculation model and experimental results is 2.93%, while the corresponding error for without considering the above factors is 15.97%. This confirms the necessity of conducting a detailed electromagnetic losses calculation model. In addition, the average error of the temperature rise calculation model is less than 5%, while the error for without considering the losses distribution and heat dissipation paths difference is exceed 10%. In conclusion, our proposed method accords well with the measured results, and can provide significant fundamental for design and optimization of GMT.

Uniformity enhancement of a microwave surface-wave plasma by a field agitation

Microwave surface-wave plasma (SWP) provides relatively higher ion density and radical species density than RF plasma, making it a promising plasma source for semiconductor fabrication. However, its plasma uniformity is compromised due to the non-uniform field distribution as the microwave wavelength is typically shorter than chamber dimensions. This could be a bottleneck as the practical application of SWP in semiconductor fabrication demands a large-area plasma with a high uniformity. In this work, we propose field agitation by applying the phase difference of 0° and 180° between the two input microwaves in the chamber to enhance the plasma uniformity. The chamber, optimized for the TM130 mode at 2.458 GHz, successfully produces a large-area SWP with a diameter of 450 mm under 800 W absorption power and 200 mTorr argon pressure. The measurement results show that the system is capable of yielding enhanced uniformity of large-area SWP while maintaining high ion density.

Analytical Design Methodology for Wind Power Permanent Magnet Synchronous Generators

In this paper a novel analytical design methodology for wind power permanent magnet synchronous generators is presented. This kind of electric generator plays a major role in small-scale wind energy conversion systems up to 10 kW. The proposed diameter-cubed sizing equation is based both on the generator requirements, imposed by the application, and the design parameters that rely on the designer criteria. The magnetic field waveforms of both the permanent magnets field and the armature field are considered from the first moment through the winding factors, as well as the slots effects given by the Carter factor. The analytical model of the permanent magnet synchronous generator is validated with the finite element method, showing good agreement, both with no load and under load. As the generator is unsaturated, the main source of divergence between the analytical and the finite element model are the iron losses, due to the nonuniform magnetic field distribution.

Plastic flow and interfacial bonding behaviors of embedded linear friction welding process: Numerical simulation combined with thermo-physical experiment

In this study, a new linear friction welding (LFW) process, embedded LFW process, was put forward, which was mainly applied to combination manufacturing of long or overlong load-carrying titanium alloy structural components in aircraft. The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling Eulerian-Lagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen. In addition, the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed. The results reveal that the plastic flow along oscillating direction of this process is even and sufficient. In the direction perpendicular to oscillation, thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure, resulting in the interfacial plastic zone shown as an inverted “V” shape. The upward plastic flow in this direction is relatively weak, and only a small amount of flash is extruded from top of joint. Moreover, the wedge block and welding components at top of joint are always in un-steady friction stage, leading to non-uniform temperature field distribution and un-welded defects. According to the results of numerical simulation, high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects. The results of thermo-physical simulation illustrate that continuous dynamic recrystallization (CDRX) induces the bonding of interface, accompanying by intense dislocation movement and creation of many low-angle grain boundaries. In the interfacial bonding area, grain orientation is random with relatively low texture density (5.0 mud) owing to CDRX.

Design of a volumetric cylindrical coil-tuned at 298 MHz for 7 T imaging

The concept of a 2D cylindrical High Pass Ladder (2D c-HPL) is used in the development of this ultra-high radio frequency (UHRF) volumetric head coil for 7 T tuned at the Larmor frequency of 298 MHz. The architecture of the 2D c-HPL helps to overcome the challenges associated with non-uniform magnetic field distribution. The prototype consists of an individual resonating array of inductance-capacitance (LC) elements and each component is tuned to the precise fo frequency. The tuning of the (i) inductance, (ii) capacitance, (iii) mesh size, and (iv) coupling coefficient play critical roles to attain the desired Larmor frequency. For this proof-of-concept, the prototype of a volumetric head coil consists of a cylindrical array size of 4 × 6, with individual LC components of inductance magnitude, 98 nH and four fixed value capacitors and one tunable capacitor that allowed to achieve the desired precession frequency, fr = 298 MHz. The model was tested for three different fo values of 269, 275, and 286 MHz. The mutual coupling and the eigenfrequencies were compared through bench testing and dispersion equation. The experimental data were in good agreement (<5%) with the theoretical eigenfrequencies from the dispersion relation. The theoretical eigenfrequencies and the experimental eigenfrequencies are in good agreement for eigenmodes (1,2), (1,3), (2,2), (2,3), and (4,3).

Thermal Analysis and In-Field Critical Current Estimation of Conduction-Cooled REBCO Magnet Considering Nonuniform Temperature Distribution

Due to the high upper critical field and transition temperature, REBCO coated conductor show great promise for conduction-cooled magnet applications. The normal zone of high temperature conductor (HTS) spreads slowly, and the conversion of a weak spot into a hot spot is localized and quite fast. Hence, in-field critical current weak spot evaluation under the nonuniform temperature gradient is important for conduction-cooled magnet stability estimation. Cooling path design needs to take the weak spot into account. In this study, a temperature-field-angle dependent critical current estimation neural network was first trained based on a public database of HTS critical current. The equivalent thermal conductivity was applied for the interface contact between the turns. Thermal contact conditions were given to the interface between the coil and bobbin considering actual production situations, such as thermal grease. Combing the non-uniform magnetic field and thermal distribution, the critical current distribution was evaluated to track the weak part. The results of this study will be employed in the design analysis of high magnetic field conduction cooling magnets in the future.

Electroporation from mitochondria to cell clusters: Model development toward analyzing electrically driven bioeffects over a large spatial range

A general, self-consistent scheme for analyzing cellular electroporation for bio-medical applications is developed to probe realistic biological shapes and different length scales ranging from nanometers to hundreds of micrometers. The COMSOL Multiphysics suite is used with suitable embellishments to incorporate the details of the electroporation (EP) process and the inherent internal physics. The results are obtained for the voltage pulse driven electroporation for a Jurkat cell with mitochondria (as an example organelle) where spatial dimensions on the order of a few nanometers become important, to hundreds of cells (with Bacillus as an example) where collective effects and mutual interactions can dominate. Thus, scalable computing to generalized geometries with the ability to include complex organelles is made available. The results obtained for mitochondrial EP in Jurkat cells compare well with available data. In addition, quantitative predictions of field attenuation and shielding in Bacillus clusters are made, which point to highly nonuniform field distributions and a strong need to engineer novel electrode designs.

Design of anti-misalignment PCB coil for wireless power transfer

This paper focuses on the problem of the non-uniform magnetic field distribution in short-distance magnetic coupled wireless power transfer (MC-WPT) systems, which causes the transfer power and power transfer efficiency to decrease when the transmitter and receiver coils are offset. At first, the distribution law of the magnetic field generated by the printed circuit board (PCB) coil is studied. A new method is proposed to design the transmitter coil, which combines a genetic algorithm (GA) with a partial element equivalent circuit (PEEC). The appropriate turn radii are first obtained by the GA, and the quality factor is further evaluated by the PEEC to select the optimal coil turns. Finally, the PCB coils with uneven pitches are fabricated, and experiments are carried out on an MC-WPT system. The effective power transfer area is expanded noticeably and the high efficiency of the system remains stable, which is very useful to provide a wider working space and steady wireless energy supply for mobile objects.

Influence of magnetic field of a radial focusing external magnetically insulated diode on emission behavior of intense pulsed ion beam

We investigated the effect of magnetic field in the anode and cathode gap (A-C gap) of a radial focusing (Br) external magnetically insulated diode on the emission behavior of IPIB. The magnetic field distribution between the A-C gap was analyzed by finite element method. The non-uniform magnetic field distribution induced the stronger ion emission at the outer ring area of the anode. It revealed the reason for the more serious depletion of the anode outer ring. Within the magnetic induction intensity less than 1.37 Bcrit, it was found experimentally that the diode voltage and ion beam density reached a higher value with the increase of magnetic field. A smoother surface of Al2O3 ceramic was observed after the irradiation of IPIB generated by the Br diode. The study provides guidance for optimizing ion emission uniformity and efficiency of Br diode, promoting the effective application of IPIB technology in materials science.

Magnetorheological fluids subjected to non-uniform magnetic fields: experimental characterization

Magnetorheological (MR) fluids are suspensions of fine, low-coercivity, high-magnetizable particles in a continuous liquid phase. When subjected to magnetic field, the material exhibits a rapid change in the apparent viscosity of several orders of magnitude. This unique capability has been successfully exploited in automotive semi-active suspensions systems or systems for manufacturing high quality optics. In a majority of the existing systems, the rheology of MR fluids is controlled by an external uniform field oriented perpendicularly to the fluid flow direction. In general, it is an inherent feature of MR systems operating in flow, shear or squeeze modes, respectively. There is an experimental evidence that the behavior of MR fluids in the so-called pinch-mode (in which the fluid is subjected to non-uniform magnetic field distributions) clearly stands out against the remaining three operating modes. With the predecessors, the flow through the channel occurs once a pressure across it exceeds the field-dependent threshold pressure. For comparison, in pinch mode valves the magnetic flux energizes mostly the layers of the materials near the channel walls. The outcome is a change in the channel’s effective diameter achieved solely via material means without changing its geometry. To study the fluid’s unique behaviour in the pinch mode, the authors designed a prototype valve assembly and examined several fluid formulations of various particle concentration levels across a wide range of external (velocity, magnetic field density) stimuli in an organized effort to further comprehend the phenomenon. The obtained data indicate that the magnitude of the particular effect does not only depend on the magnitudes of the magnetic stimuli but also on the particle concentration; the smaller the concentration of particles the more pronounced the pinch mode like behavior is. In general, the authors believe that the study may provide guidelines as to the selection of fluid formulations for developing novel valveless actuators utilizing MR fluids operating in pinch mode.

Effect of cryogenic thermal cycling on the microstructure and mechanical properties of Zr-based bulk metallic glasses

This article investigates the effects of cryogenic thermal cycling (CTC) on the microstructure and plasticity of Zr60Cu20Al10Ni10 (Zr60) bulk metallic glass (BMG). The microstructure and mechanical properties of Zr60 BMGs at different energy states are assessed through room-temperature compression and nanoindentation tests. The heterogeneity of the internal structure of the CTC-treated samples causes a different response to thermal expansion resulting in a non-uniform local stress field distribution, which increases the energy state of Zr60 BMGs. At the same time, in the CTC-treated Zr60 BMGs, more free volume (or flow defects) is introduced, and the plasticity is increased. It has been found that, after CTC, the room-temperature plasticity of Zr-based BMGs can be significantly improved by 2–3 times compared to that of the as-cast samples. This introduces flow defects and the inhomogeneous distribution of the strain field causes the serration behavior during the deformation of BMGs to occur more frequently and the second peak of the relaxation spectrum to be more pronounced. This phenomenon indicates a more frequent generation of shear transition zones and shear band movement within them.

Performance Simulation of the Active Magnetic Regenerator under a Pulsed Magnetic Field

Magnetic refrigeration is acknowledged as a potential substitute for the conventional vapor-compression refrigeration technology, owing to its high efficiency and environmental friendliness. Existing magnetic refrigeration systems are mostly based on permanent magnets, owing to the characteristics of lower magnetic field intensity, non-uniform magnetic field distribution, and lower operating frequency due to the moving parts, which results in a low cooling capacity and small temperature difference. Thus, this study proposes the application of a pulsed magnetic field, with a high intensity and frequency, to a magnetic refrigeration system to achieve a high performance. A verified numerical model is established to investigate the thermodynamic cycle and cooling performance of an active magnetic regenerator (AMR). The transient and steady-state performances of AMR under pulsed and permanent magnetic fields are compared. The results suggest that an AMR can establish a stable temperature difference under a pulsed magnetic field that is 40 times faster than that under a permanent magnetic field. The maximum steady-state cooling capacity under a pulsed magnetic field is 2.5 times that under a permanent magnetic field when the temperature difference is 20 K. Additionally, the effects of pulsed magnetic field waveforms, frequency, and intensity on the performance of AMR are investigated under various utilization factors. These results can guide the improvement of room-temperature magnetic refrigerators.

Study of Quench Behavior of No-Insulation REBCO Pancake Considering Complex Critical Current Density Distribution

This study analyzes the quench behavior of No-insulation (NI) REBCO pancake. An quench analysis simulation model considering the complex critical current density distribution was developed and validated experimentally. The developed model includes an equivalent circuit model, a thermal model, a magnetic model, and a magnet critical current estimation model. The simulation model is based on a co-simulation using MATLAB and COMSOL, considering the balance of accuracy and computation time. The lumped parameter of the NI magnet was used to solve the governing equations of the equivalent circuit module and thermal module in MATLAB. To accurately calculate the non-uniform electromagnetic field distribution over the coil, a magnetic finite element method was used in COMSOL. A neural network was used to predict the temperature-field-angle dependent magnet critical current. Considering the numerical convergence at different over-current phases, adaptive simulation was used to reduce the total simulation time. The quench behavior was analyzed using the proposed model, and the results were verified experimentally. The simulation results showed that when the azimuthal current is greater than the magnet critical current, it will gradually saturate and approach the magnet critical current, and then decrease at a similar speed. The rate of decrease is equal to the rate of decrease of the magnet critical current. Through the analyses, the corresponding sudden-discharging behavior was simulated and analyzed. The proposed model can be used to perform the post-quench and sudden discharging analyses of pancake coil and has promising applications in multi-pancake post-quench studies.

Quantitative Crack Depth Monitoring Based on Traveling Wave at Millimeter-Wave Frequency

The electromagnetic (EM) resonator-based sensor has a well-known high sensitivity for crack inspection. The nonuniform field distribution inside the resonator, however, causes an associated position-dependent sensitivity phenomenon. This article is intended to address the accurate problem of EM resonator-based sensors. Instead, a methodology based on the traveling wave is first explored. A transmission line-based sensor is implemented for accurate crack depth evaluation. The sensitivity is maintained by tightly bounded the magnetic field in the cross Section of the transmission line through loading the high dielectric material. The accuracy is naturally improved by the uniform field distributed along the propagation direction. An equivalent circuit is modeled based on the transmission line theory to validate the sensing principle. For a wide range of crack width, both simulation and measurement results demonstrate that the detection sensitivity of crack depth is up to 1.893 GHz/mm. The error bar caused by the variation of crack position can be controlled in 0.166 GHz. The performance of multiple crack detection has been verified for the proposed transmission line-based sensor at the same time. This article paves a way to extend the local structural health monitoring based on EM resonators to the large area structural health monitoring.

Plastic wrinkling of thin-walled tubes under axial compression in non-uniform temperature field

The main purpose of this paper is to reveal the wrinkling behavior of thin-walled tubes under axial compression in a non-uniform temperature field formed by induction heating on a local position. The distribution of non-uniform temperature fields induced by induction heating and the wrinkling behavior of tubes under axial compression were studied by combining experiments and simulations. Moreover, the thickness and hardness distribution of the wrinkled tube were analyzed. The results show that the maximum temperature difference along axial direction of 5052 aluminum alloy and AZ31B magnesium alloy tubes can reach 129.1°C and 134.7°C in experiments, respectively. In the non-uniform temperature field with a maximum temperature of 250°C, axisymmetric wrinkles can be formed under axial compression on the tubes. With the increase of axial compression, the wrinkle width gradually decreases and its height gradually increases. The contour shape of wrinkles can be fitted accurately with GaussAmp function. There is an obvious thickening phenomenon on the wrinkles and the thickest point is located on the wrinkle top, where the thickness gradually increases with increasing the axial compression. In addition, the microhardness at the wrinkles is lower than that of the original tubes. It decreases with the increase in axial compression. The maximum reduction of microhardness of 5052 aluminum alloy and AZ31B magnesium alloy tubes at the wrinkles are 41.6% and 17%, respectively. This study not only can provide tube blank with useful wrinkles for hydroforming, but also can provide experimental data for establishing buckling theory of inhomogeneous tube shells.

Size control method for non-uniform electrical field distribution of an insulator string for power transmission lines

As a result of rising consumer demand, transmission lines voltages have increased from 154 kV to 765 kV. For 154 kV, 345 kV, and 765 kV transmission lines, 9–10, 19–23, and 30–40 insulators are employed, respectively. When multiple insulators are stringed, the divided voltage safety issue becomes critical. The first insulator is typically subjected to a voltage that is 20% higher. The high-voltage division applied to the insulator in the first stage is likely to result in arc generation. The dielectric breakdown voltages of insulator used in power transmission lines range from 12.8 to 16.8 kV/mm, and the dielectric constant varies slightly depending on the frequency. Herein, for the alumina insulator, the 4.94 cristobalite insulator value was 4.48, and the tan δ value was in the range 0.003–0.006. Based on actual measurements, the finite-element method was applied to analyze the field distribution. The size of the insulator was changed to lower the voltage burden applied to the first insulator string. The sizes used were 185, 250, 375, and 500 mm. By changing the size of the insulator, the voltage applied to the first stage decreased from 27.44% to 6.07%.

A computational study for the effects of sample movement and cavity geometry in industrial scale continuous microwave systems during heating and thawing processes

Microwave (MW) applications in food processing are used to reduce process time and increase process efficiency. While 915 MHz frequency is dominant for industrial processes, 2450 MHz systems are also observed. Attained temperature uniformity is specific concern with significant effect of the non-uniform electromagnetic field distribution due to the cavity geometry and design. Therefore, the objective of this study was to determine the cavity geometry effect with applied frequency and to present industrial scale continuous process system with a computational approach. A computational model was developed for heating and thawing processes, and experimental validation was completed in a cylindrical MW cavity. Sample rotational movement and cavity geometry effects (conventional rectangular versus cylindrical, ellipsoidal and triangular) were determined, and industrial scale system designs were presented with frequency effect. Temperature change and electromagnetic field distribution were also introduced for improved design. The results demonstrated improved designs for industrial processes.

Characteristics of multi-mode lasing in cesium lead bromide perovskite microwires with an isosceles right triangle cross-section.

The CsPbBr3 microwires with unique isosceles right triangle cross-sections are commonly observed via chemical vapor deposition method. In this work, we study the correlations between measured multi-mode lasing behaviors and the simulation of the mode patterns inside the triangular-rod microcavity. We confirm that lasing action with higher-order transverse modes can well sustain, even when these modes experience large optical loss due to the isosceles triangle cross-section. By comparing the experimental and simulation results, the higher-order transverse modes tend to show up prior to the fundamental transverse modes for wider microwires. We attribute this behavior to the nonuniform field distribution caused by the high absorption efficiency of CsPbBr3. We also elaborate on the difficulties to sustain the whispering gallery mode in the CsPbBr3 triangular-rod microcavity, which implies that the lateral dimension and geometry of the cavity should be considered carefully for the future design of low threshold wire-based laser devices.