Adjustable Air Gap Research Articles

Investigation of the over-load unintentional remagnetization effect in series hybrid magnet variable flux memory machine

Variable flux memory machines (VFMMs) have become a research hotspot due to their adjustable air-gap flux with the employment of low coercive force (LCF) permanent magnets (PMs). Series hybrid magnet VFMMs (SHM-VFMMs) utilizing series-magnetic-circuit high coercive force (HCF) and LCF PMs are extensively investigated due to their excellent unintentional demagnetization (UD) withstand capability. Nevertheless, the existing researches still focus on the UD of LCF PMs under heavy load operation, and the remagnetization issue remains unreported. Therefore, in this paper, the over-load unintentional remagnetization (UR) effect of the a dual-layer-SHM-VFMM (DLSHM-VFMM) is first revealed, and its mechanism is investigated and analyzed in depth based on finite element (FE) analyses. A DLSHM-VFMM prototype is manufactured and tested to verify the effectiveness of the theoretical analyses.

Hyperspectral Channel-Modulated Static Birefringent Fourier Transform Imaging Spectropolarimeter with Zoomable Spectral Resolution

A novel channel-modulated static birefringent Fourier transform imaging spectropolarimeter (CSBFTIS) is introduced, which is based on a double Wollaston prism (DWP). With an adjustable air gap (AG), the spectral resolution can be adjusted by changing the AG. The CSBFTIS combines the channel-modulated imaging spectropolarimeter and the slit-free static birefringent Fourier transform imaging spectrometer technology with adjustable spectral resolution. The device is compact and robust, with a wide spectral range and a large luminous flux. Compared with various previous spectropolarimeters, it can greatly reduce the size of the spectral image data to adapt to different application requirements. A prototype is built, and simulation and experiments are carried out, and the results prove the effectiveness of the method.

Volumic Eddy-Current Losses in Conductive Massive Parts with Experimental Validations

In this paper, the analytical determination of volumic eddy-current losses in rectangular-shaped conductive massive parts is presented with experimental validations. Eddy currents, as well as the resulting volumic losses, are generated by a sinusoidal spatially uniform applied magnetic field. A U-shaped electromagnetic device with a flat mobile armature (or adjustable air gap) is used to measure the eddy-current losses. The experimental device, its instrumentation, and the conductive massive parts are presented in detail in the paper. Thereafter, the magnetic field distribution applied on the conductive massive parts, which is the mean input data for the eddy-current loss model, is studied. A two-dimensional (2D) numerical model, under the FEMM software, for the magnetic field calculation was also developed. A comparative analysis between the experimental measurements and the numerical results allowed the distribution of the applied magnetic field to be accurately validated. In the final phase, the objective was to estimate the volumic eddy-current losses in rectangular-shaped aluminium conductive massive parts generated by the variation of this applied magnetic field. An analytical model, based on the Maxwell–Fourier method, for the accurate prediction of eddy-current losses has also been developed. An electromagnet with and without the conductive massive parts is characterized in terms of power consumption. By using the power conservation method (i.e., Boucherot’s theorem), the eddy-current losses could be quantified experimentally. The influence of segmentation is also studied. The analytical results are compared to the experimental test results.

A New Artificial Neural Network Model for the Output Voltage and Power Predictions of Permanent Magnet Generators with Variable Air Gaps

—An artificial neural network (ANN) model is recommended for the analysis and prediction of the output results of a recently designed and constructed generator known as a permanent magnet generator with axial flux. The generator is considered to generate a power scale of P = 3 kW, especially for off-grid household usage far from the network. This machine has an adjustable air gap mechanism, and P = 3 kW is the maximum power; thus, this power can be decreased comfortably by increasing the air gap further to 7 mm. In this case, the maximum power rate can be decreased to P = 1.5 kW according to the experimental confirmation. As a new technique, an ANN approach is introduced for the predictions of voltage and power obtained output for various electrical loads, rotor speeds, and air gaps because it is difficult to get output values for all those machine parameters. In addition, this ANN technique enables one to find the generated voltage and power for specific extremely low air gap values (i.e., 0.2 mm, 0.4 mm, 0.6 mm), which is hard in experimental work due to construction difficulties. The ANN model is used to predict the output values of the generator before any laboratory practice successfully, and the users can determine the correct air gap ranges to their required power regimes for this generator.

Exact optical path difference and complete performance analysis of a spectral zooming imaging spectrometer.

The optical path difference (OPD) equations of the dual Wollaston prisms (DWP) with an adjustable air gap (AG) are derived by the wave normal tracing method, which is suitable for arbitrary incidence plane and angle. The spatial distribution of the OPD for various AG is presented. The validity of the OPD equation is verified by comparing the calculated interferograms with experimentally observed one. The performance of a novel static birefringent Fourier transform imaging spectrometer (SBFTIS) based on the DWP is investigated. The spectral resolution can be adjusted by changing the AG and the field of view can reach 10.0°, which is much larger than that predicted by our previous work. The results obtained in this article provide a theoretical basis for completely describing the optical transmission characteristic of the DWP and developing the high-performance birefringent spectral zooming imaging spectrometer.

Study on the detonation reliability of explosive trains with a micro-sized air gap

Air gap thickness significantly affects the detonation reliability of explosive trains. This paper mainly studies the detonation reliability of explosive trains with a micro-sized air gap. First, the detonation process of the JO-9C mild detonation cord initiating the 1.7 g/cm3 JO-11C booster is simulated by the AUTODYN software, and the critical air gap thickness is obtained between 0.32 and 0.40 mm. Second, a test device for explosive trains with adjustable air gap thickness is designed based on the numerical simulation results, and the adjustable step length of the air gap thickness is 0.0625 mm. Finally, a small sample evaluation method that does not depend on the standard deviation of the sensitivity distribution is proposed, and only 86 test samples are needed to verify the detonation reliability of 0.9999 at 0.1 mm air gap thickness. The test device designed and the small sample evaluation method proposed can be referred to for the detonation reliability evaluation of explosive trains with a micro-sized air gap.

Design and Simulation Analysis of Wide-range Current Transformer with Adaptively Adjustable Air Gap Length

Abstract This paper proposes a wide-range current transformer structure with adaptively adjustable air gap length. The length of the air gap of the iron core of this structure can be automatically adjusted with the current harmonic ratio of the secondary side of the current transformer, so that the current transformer has good anti-saturation characteristics; on the other hand, the output voltage value of the detection winding can be adjusted after proportional calculation. The secondary side current is compensated to ensure the accuracy of its measurement. At the end of the article, the structure of the current transformer is simulated and analyzed. The calculation results show that the measurement error of the secondary side current after compensation can reach the design requirements of the 0.2-level standard current transformer during the change of the primary current from 100% to 350%. This structure can effectively broaden the range of the current transformer and improve its measurement accuracy.

Design and Analysis of Dual-Rotor Modular-Stator Hybrid-Excited Axial-Flux Permanent Magnet Vernier Machine

This paper proposes a new structure of the dual-rotor hybrid-excited axial-flux permanent magnet vernier machine (DR-HEAFPMVM) with the modular stator and the consequent-pole PM (CPM) rotor for low-speed, high torque density applications such as in-wheel electric vehicles. The tooth-wound non-overlapping armature windings and direct current (DC) excitation windings are, respectively, arranged in stator main-teeth and split-teeth to obtain the modulated and adjustable air-gap flux densities, resulting in high torque density and outstanding flux-weakening capability. First, the design considerations, operation principles, and air-gap flux density distributions of the proposed machine are elaborated based on the air-gap permeance function. Then, the influence of the pole ratios (PRs) and the DC excitation currents on the main electromagnetic performances of the DR-HEAFPMVM, such as the flux-weakening capability and back-electromotive force (back-EMF), on-load electromagnetic torque, loss distribution, and efficiencies, is investigated using the 3-D finite-element method (FEM). Results verify the feasibility of the flux adjustment of the DC excitation windings equipped in the split-tooth, and the design with a pole ratio of 8/1 tends to have higher torque density, higher machine efficiency, and considerable flux-weakening capability compared with the other two PRs.

Development and experimental validation of a fast and accurate field calculation tool for axial flux permanent magnet machines

A fast calculation method of magnetic flux density in axial flux permanent magnet (AFPM) machine is presented. This method is based on an original combination of magnetic charges concept, image theory, and relative permeance functions. Using this combined approach, significant 3D effects, which are present in axial flux machines such as curvature and edge effects as well as slotting effects due to stator slots, are considered. The main electromagnetic specifications of the AFPM machine such as cogging torque, Back Electromotive Force (EMF), and local air-gap flux density are calculated accurately in very short times. To validate this approach, an original prototype of double stator ironless rotor AFPM machine with adjustable air-gap is used. Experimental protocol including measurements of global characteristics (EMF, Torque) and measurements of local field density is presented. The obtained results are in good agreement with the experimental measurements which allows validating the proposed computation method.

Suppression of Cross-Coupling Effect of Hybrid Permanent Magnet Synchronous Motor with Parallel Magnetic Circuit

Hybrid permanent magnet synchronous motor (HPMSM) has attracted increased attention in recent years due to its adjustable air gap flux. However, as a result of the cross-coupling effect of high- and low-coercive permanent magnets, the precise magnetic adjustment of HPMSM has become increasingly difficult. In order to weaken the cross-coupling effect, two methods of adding magnetic barrier and exciting coil are adopted in this paper. First, the equivalent magnetic circuit model is established, and the theoretical rationality of the weakening method is analyzed. Second, the electromagnetic performance of two weakening methods are analyzed based on the finite element analysis. Finally, the rationality of the theoretical analysis is verified, which provides the structure basis for the precise magnetic adjustment of the hybrid permanent magnet motor.

A novel squirrel cage eddy current coupling with adjustable radial air gap and its performance analysis

A novel squirrel cage eddy current coupling with adjustable radial air gap was presented, which can change the output speed by changing the air gap thickness in radial direction between the copper strips and the permanent magnet. It has the advantages of no axial force in speed regulation and less eccentric force in axisymmetric structure. The 2-D electromagnetic torque model of the rotor was established, and the influence of the air gap thickness on the electromagnetic torque was also studied by finite element method. Further, a novel method to solve the dynamic equation of the eddy current coupling was proposed based on the effect of air gap thickness and relative speed on torque characteristics, and was applied to the speed regulation performance analysis. In addition, the influence of the relative magnetic permeability of the permanent magnet back yoke and the internal rotor on the speed regulation performance was studied.

Magnetic measurement and analysis of c-type amorphous by an improved adjustable air gap tester

A novel magnetic properties tester is designed to accurately and conveniently change the air gap of the core, which can fix cores of various types. The dynamic magnetic characteristics of the amorphous core under sinusoidal excitation within 20 kHz is measured with different air gap lengths and magnetic flux density. It is found that in the case of the small air gap, the total loss decreases as the air gap increases. When the frequency is 20 kHz and the flux density is 0.1 T, the loss can even be reduced by 7%. This paper analyzes the experimental data and summarizes the influence of the air gap and magnetic flux density about the core loss. Besides, the influence of air gap on magnetic flux density distribution is illustrated and analyzed by the means of FEM (Finite Element Method). It is valuable for the design of high frequency transformer and inductor.

Development and Test of One Commercial Megawatt Superconducting DC Induction Heater With Extra High Energy Efficiency

Energy conservation and emission reduction is a critical task for China's aluminum industry. During the last decade, the high temperature superconducting (HTS) technology has been successfully demonstrated to have great potential for energy conservation in this field. Different from the present AC induction heater, this HTS direct current (DC) induction heater is expected to significantly improve the energy efficiency of preheating aluminium billets before extrusion process. This paper thoroughly presents the development of the world's first commercial megawatt HTS DC inducting heater based on 2nd generation HTS tapes. Firstly, the commercial design of this 1MW HTS DC induction heater including design specifications, energy efficiency and commercial potential are analyzed carefully. Subsequently, the manufacture and operation of three core parts including HTS magnet with extra-large diameter, iron core structure and electrical driving system, are introduced. A low cost and practical driving system consisting of motors and gearboxes is developed to solve the problem of peak electromagnetic torque at low rotation. Meanwhile, the heating quality of aluminium billets (i.e., temperature distribution along the radial and axial direction) can be accurately controlled by an adjustable air gap structure. Finally, the present technique challenges and corresponding solutions of this commercial HTS DC induction heaters are summarized and proposed. Compared with an energy efficiency of 45-60% in the MW-class conventional heater, the energy efficiency of this HTS DC induction heater can achieve up to 80.6% based on test results. This work can also provide guidance for the design and optimization of HTS DC induction heaters.

Heating Characteristic and Thermal Optimization of Superconducting DC Induction Heater With Adjustable Air Gap Structure

The novel superconducting direct-current (DC) induction heater shows great advantages of high efficiency and heating quality compared to traditional alternating-current (AC) induction heater in aluminum extrusion. The efficiency of the superconducting DC induction heater can be up to 80–90%, which is much higher than the 40–50% efficiency of the AC induction heater. The uniform and gradient temperature distributions of the aluminum billet are the most significant parameters to evaluate the heating quality of this induction heater, which has a strong influence on the product quality of extrusion processing. In this paper, the superconducting magnet with adjustable air gap structure is designed to achieve controllable axial temperature uniformity and axial temperature gradient distribution. Each adjustable air-gap structure consists of 10 identical iron pieces whose position can be changed independently. Therefore, the uniformity and gradient temperature of the aluminum billet in the axial direction are controllable. The thermal optimization of the uniform and gradient temperature distributions for typical aluminum billets (Φ = 446 mm) is measured. A numerical finite-element method (FEM) model is built to analyze the heating behavior of the aluminum billet. The simulation and experimental results match well. The result of uniform and gradient axial temperatures are ±3 °C and the controllable range from 10 °C/m to 40 °C/m, respectively. The result obtained from the temperature-distribution optimization is useful for industrial applications.

On the Improvement of Thermal Protection for Temperature-Responsive Protective Clothing Incorporated with Shape Memory Alloy.

This study explored the application of shape memory alloy (SMA) springs in a multilayer protective fabric assembly for intelligent insulation that responded to thermal environment changes. Once the SMA spring was actuated, clothing layers were separated, creating an adjustable air gap between the adjacent fabric layers. The impacts of six different SMA arrangement modes and two different spring sizes on thermal protection against either a radiant heat exposure (12 kW/m2) or a hot surface exposure (400 °C) were investigated. The findings showed that the incorporation of SMA springs into the fabric assembly improved the thermal protection, but the extent to which the springs provided thermal protection was dependent on the arrangement mode and spring size. The effectiveness of reinforcing the protective performance using SMA springs depended on the ability of clothing layers to expand an air layer. The regression models were established to quantitatively assess the relationship between the air gap formed by SMA spring and the thermal protective performance of clothing. This study demonstrated the potential of SMA spring as a suitable material for the development of intelligent garments to provide additional thermal protection and thus reduce the number of clothing layers for transitional thermal protective clothing.

Complete description of the optical path difference of a novel spectral zooming imaging spectrometer

A complete description of the optical path difference of a novel spectral zooming imaging spectrometer (SZIS) is presented. SZIS is designed based on two identical Wollaston prisms with an adjustable air gap. Thus, interferogram with arbitrary spectral resolution and great reduction of spectral image size can be conveniently formed to adapt to different application requirements. Ray tracing modeling in arbitrary incidence with a quasi-parallel-plate approximation scheme is proposed to analyze the optical path difference of SZIS. In order to know the characteristics of the apparatus, exact calculations of the corresponding spectral resolution and field of view are both derived and analyzed in detail. We also present a comparison of calculation and experiment to prove the validity of the theory.

Output Voltage Control of the SP topology IPT system based on Primary side Controller operating at ZVS

This paper presents a technique to control the output voltage of a series-parallel (SP) topology inductive power transfer (IPT) system using only a controller, located on the primary side. This reduces the cost, size, complexity and loss of the system compared to conventional IPT dual-side controllers. An asymmetrical duty cycle control (ADC) of full-bridge inverters was used to control the DC output voltage to its designed value. Additionally, a zero voltage switching (ZVS) operation can be obtained at all power levels by varying the switching frequency of the inverter. Theoretical analysis was performed through a mutual inductance coupling model and verified by computer simulation. Experimental results of the circular magnetic structure IPT system with an adjustable air-gap confirm the validity of the proposed controller. The system efficiency was improved throughout the operation and the improvement became obvious as the output power was decreased.

Experimental and Numerical Study of a DC Induction Heater Prototype With an Adjustable Air Gap Structure

To improve the poor efficiency of conventional ac induction heaters, which is usually below 50%, a high-temperature superconducting (HTS) dc induction heater has been proposed as a candidate solution. In previous researches, the air gap structure is fixed, which leads to a less controllable magnetic field distribution along the axial direction of billets, hence a less controllable temperature distribution along the same direction. However, an adjustable temperature distribution along the axial direction of billets is required in the aluminum extrusion industry. In order to solve this problem, a novel adjustable air gap structure is proposed and fabricated in our laboratory-scale prototype of the HTS dc induction heater. To validate the method, heating experiments for uniform and gradient temperature distribution were performed with different air gap structures. In addition, a novel adjustment method, i.e., unilateral adjustment, for air gap structure was proposal and tested, which simplified the adjustment method. A finite-element method model of the heater was built to analyze the temperature distribution and the theoretical availability of adjustable air gap structure.

Finite Element Analysis of an Axial Flux Hysteresis Motor Based on Complex Permeability Concept Considering the Saturation of the Hysteresis Loop

Axial structures of the hysteresis motors, similar to the other axial types of electrical machines, have some outstanding characteristics with regard to radial structures, such as higher torque-to-weight ratio, excellent efficiency, adjustable airgap, and balanced rotor–stator attractive forces. Since the accurate measurement of the hysteresis machine characteristics by prototyping and testing is expensive and time consuming, in this paper, the finite-element analysis is adopted for the prediction and analysis of an axial flux hysteresis motor. The analysis is conducted based on the elliptical approximation of the hysteresis loop. Since the elliptical approximation is not able to model the saturation of the hysteresis loop, an iteration-based method is proposed to overcome this problem and increase the analysis accuracy. Finally, in order to investigate the proposed model accuracy, the device is prototyped, whose experimental results agree well with those extracted from the analytical model.

SU‐E‐J‐38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field

Purpose:Integrating a linac with an MRI system would allow for real time tumour tracking however the patient will be irradiated in the presence of a magnetic field. The present study experimentally investigates the magnetic field effects on entrance, exit, and interface dose for both transverse and parallel magnetic fields.Methods:Polystyrene was used to construct a set of phantoms for Gafchromic film measurements. One phantom had an adjustable air gap and four other phantoms had one surface at various angles. The linac‐MR prototype consisting of a biplanar permanent magnet coupled to a linac was used for the transverse magnetic field measurements. A couple of solenoid electromagnets, stacked on top of each other and irradiated along their bore, were used for the parallel field measurements.Results:All doses are relative to no magnetic field. The transverse magnetic field reduced the entrance dose for all surface angles by strongly deflecting the contaminant electrons. The exit dose in a transverse magnetic field was found to be significantly higher. The entrance dose with a parallel magnetic field present is higher due to the contaminant electrons being concentrated within the beam area. The air gap phantom measurements, done in a transverse magnetic field, show a significant increase of the dose at the proximal side of the air gap and a decrease at the distal side. The measurements, done in the parallel magnetic field, show the concentration of secondary electrons in the air gap.Conclusion:The radiation dose measurements of a 6MV beam in a parallel and transverse magnetic field presented here are currently being replicated using Monte Carlo simulations. This verified Monte Carlo system could provide the dose calculation basis for future linac‐MR systems.