Magnetic Air Gap Research Articles

753: MR-guided proton therapy: Influence of magnetic fields and air gaps on TLD response

753: MR-guided proton therapy: Influence of magnetic fields and air gaps on TLD response

A study on maglev force and vibration attenuation characteristics of quasi-zero stiffness cruciform maglev isolator.

This paper aims to study the maglev force and vibration attenuation characteristics of quasi-zero stiffness cruciform maglev isolators (CMIs). The maglev force and stiffness of CMIs were analytically computed based on equivalent charge theory, and the transfer function of the system was conducted. The effects of magnet geometry parameters and air gap on the maglev force, stiffness, and vibration transmission characteristics of the CMI system were revealed through parametric analyses. With the increase in magnet length and width, the maximum value of maglev force increases, but the displacement range of near-zero stiffness, amplitude, and phase of the system gradually decrease. With the increase in magnet height, the displacement range of near-zero stiffness increases, while the variation in the amplitude and phase of the system has minimal impact. Meanwhile, in the Halbach array, the height variation of the magnet at different positions has different impacts on the magnetic force. As the air gap increases, the maximum value of maglev force decreases, but the amplitude and phase gradually increase, and the displacement range of near-zero stiffness first rises and then decreases. Finally, an experimental study was carried out to test the vibration attenuation characteristics of CMIs, in which sinusoidal excitation, hammer strike excitation, and random excitation were applied.

Investigating the impact of magnetic air gap variations on short circuit characteristics of partially high temperature superconducting generator

Partially high-temperature superconducting generators (PHTSGs) feature large magnetic air gaps imposed by using cryostats for HTS field windings. This increased air gap significantly affects end winding inductance and can lead to elevated fault torque levels. This study investigates the influence of magnetic air gap variation on generator design and end winding inductance and its implications for short-circuit faults in PHTSGs. Through a combination of numerical simulations and analytical analysis, the study explores how changes in the magnetic air gap affect end winding inductance and subsequently influence short-circuit fault behavior. The results reveal a direct correlation between magnetic air gap length, end winding inductance, and key short-circuit parameters such as stator current, field currents, and electromagnetic torque. Notably, an increase in the magnetic air gap is observed to elevate stator and field currents and electromagnetic torque during short-circuit events. These insights underscore the importance of considering magnetic air gap variation and its impact on end winding inductance and its relationship with short circuit characteristics in the design and operation of PHTSGs, providing valuable insights for enhancing the resilience and performance of high-temperature superconductor-based generator systems.

Five-phase space vector carrier-based PWM for third harmonic injection

Five-phase AC drives allow a third harmonic voltage to be fed into the stator winding – in addition to the fundamental voltage – to generate a third harmonic magnetic air gap field. This allows the generation of an additional small constant torque. Furthermore, the undesirable saturation harmonics that occur with saturated iron can be compensated. The desired third harmonic voltage is commonly generated via time-consuming space vector PWM algorithms, which are not well-suited for real-time application, or via look-up tables, which require an increased storage capacity. In our case, the desired third harmonic voltage is generated in the five-phase voltages by adding a non-sinusoidal zero-sequence voltage with five times the fundamental frequency to the fundamental voltage reference signals in carrier-based pulse width modulation (PWM) with a constant switching frequency. This is equivalent to a space vector PWM method (SVPWM) and avoids a significantly high calculation effort. The PWM algorithm programmed in MATLAB in real time allows the fast generation of a third harmonic voltage per phase with freely definable amplitude and phase shift without requiring a lot of storage capacity.

In Search of the Proper Dimensions of the Optimum In-Wheel Permanent Magnet Synchronous Motor Design

In this paper, a new approach to the optimized design of outer rotor Permanent Magnet Synchronous Motors (PMSMs) for in-wheel light electric vehicle (LEV) applications is presented. The optimized design study is based on various dimensions such as back iron depth, permanent magnet depth and air gap length. The novel method is developed to reveal the quality factor of design (QFD), which implies the maximum possible performance results, and determine the best possible design for in-wheel PMSMs for direct-drive LEV applications. Therefore, the thickness of the back iron, permanent magnet and air gap dimensions are altered accordingly to obtain an optimized design. This design study is conducted for an in-wheel PMSM that has rated values of 2.5 kW, 150 V, 900 min−1, and 24-slot/20-pole configuration intended for LEV propulsion. These designs are simulated in order to obtain the maximized combination of efficiency, shaft power, shaft torque and a minimized combination of total weight, iron losses, copper losses, input current and cogging torque. The measure of the optimized parameters is named QFD, which indicates the goodness of the design through the use of radar charts. The values of the essential coefficients of QFD may vary for different applications, e.g., the design of PMSMs used in traction applications has some certain criteria that imply high-performance operation. Additionally, the QFD can guide motor manufacturers as a starting point for a design study.

Magnetic Levitation Belt Conveyor Control System Based on Multi-Sensor Fusion

Belt conveyors are critical in coal transportation systems; however, they are supported by rollers, which incur high energy costs. Magnetic levitation support is adopted. The measurement of a magnetic levitation air gap is important, and a displacement sensor is usually used in real-time. To address the problems of poor linearity and low measurement stability of single displacement sensors in magnetic levitation systems, a magnetic levitation support system based on multi-sensor data fusion is proposed. First, an industrial camera sensor is used to collect images, and the suspended air gap is obtained through image processing. Second, using an extended Kalman filter, the photoelectric position sensor and industrial camera sensor are fused to the suspension air gap value in the process of suspension. The electromagnet current is controlled by the PID (proportion integration differentiation) control algorithm, and experiments are carried out. Experimental results showed that, compared with an estimation of the suspension state of two sensors before and after EKF fusion, the root mean square error is reduced by 0.0597 and 0.0081, respectively, compared with the measurement value of a single sensor. Moreover, the fusion data were more robust, thereby meeting the requirements of magnetic levitation control.

Performance enhancement of electromagnetic vibration energy harvesters via bi-stable structure based on MEMS 3D coils

In this study, we conducted a systematic exploration of a micro-electromagnetic vibration energy harvester with a bi-magnet structure and microelectromechanical systems 3D coils. First, we establish a physical model of stiffness and damping characteristics based on the superposition principle for the bi-magnet structure which has also been verified experimentally. Then, we investigate the influence of magnet gap and air gap on the stiffness and the magnetic flux change rate, mainly focusing on the distance and the potential barrier between the two potential wells. Finally, we fabricate and assemble the bi-magnet VEH prototype and tested the output performance under 1 and 6g excitation, which correspond the intra-well vibration and inter-well vibration, respectively. The tested results show that under 1g excitation, the prototype can output 155.38 μW power with 32 Hz half-power bandwidth and 4939.06 μW·Hz integrated power, which are obviously higher than those for mono-magnet under same excitation. When the excitation raises to 6g, the output power is improved to 362.98 μW with the half power bandwidth and integrated power enhanced to 56 Hz and 9289.96 μW·Hz, respectively. The tested results also prove that the structure proposed in this study can significantly enhance the output performance compared with a mono-magnet structure and other published data.

A review on analytical models of brushless permanent magnet machines

AbstractThis study provides an in‐depth investigation of the use of analytical and numerical methods in analyzing electrical machines. Although numerical models such as the finite‐element method (FEM) can handle complex geometries and saturation effects, they have significant computational burdens, are time‐consuming, and are inflexible when it comes to changing machine geometries or input values. Analytical models based on magnetic equivalent circuits (MEC) or solving Maxwell's equations can be faster and more flexible, but less accurate for complex machine structures. The paper focuses on the recent development of analytical models for brushless permanent‐magnet (PM) machines that have become increasingly popular in low and medium‐power applications. The literature review covers the recent developments in analytical models for PM machines with respect to various machine quantities such as magnetic flux density components, induced voltage, inductances, electromagnetic force/torque, efficiency, or unbalanced magnetic force (UMF). It outlines the advantages and disadvantages of different analytical models such as the zero‐dimensional (0‐D), one‐dimensional (1‐D), two‐dimensional (2‐D), and three‐dimensional (3‐D) analytical methods, as well as the Maxwell and basic mathematical analysis. Although the MEC models are faster than the numerical model, they are not as accurate for various structures of electrical machines including a great magnetic air gap. They also note that the analytical models based on the Maxwell equations are faster than the numerical ones and have the potential to obtain acceptable accuracy similar to the numerical models in electrical machines. Overall, this literature review provides valuable insights for researchers and engineers in selecting appropriate analytical models for PM machines. It highlights the trade‐offs between accuracy and computational efficiency when choosing between numerical and analytical models, and the flexibility of analytical models to address changes in machine geometries or input values. Additionally, this helps researchers save time in determining appropriate references regarding the analytical models of brushless PM machines.

Analytical Modeling of Magnetic Air-Gap Field Distribution Due to Armature Reaction

The following paper presents an analytical study of the air-gap magnetic field distribution produced by the armature reaction of a linear machine. Based on the method of images, the magnetic field generated by a current carrying conductor inside the air-gap between two smooth infinitely permeable iron surfaces is modeled as a complex 2D function. The conductor model then becomes a current sheet model and horizontally oriented current sheets are used to model the magnetic field produced by the armature reaction for smooth ferromagnetic surfaces. Focus will be given to the study of the slot opening function in front of energized slots in comparison to the not energized ones of the classical theory pointing out some remarkable differences. Later, the model is extended to slotted geometries using a complex slotting function adapted for energized slots. At last, the Maxwell tensor expressed in complex formulation will be integrated to obtain the force components acting on the machine tooth tips, quantities that will be compared with FEM simulations in order to validate the proposed analytical model.

Research on Air Gap Magnetic Field Characteristics of Trapezoidal Halbach Permanent Magnet Linear Synchronous Motor Based on Improved Equivalent Surface Current Method

Accurate analysis of the air gap magnetic field is the focus of research in the field of precision permanent magnet linear synchronous motors. In this paper, the two-dimensional air gap magnetic field of a secondary trapezoidal Halbach permanent magnet array coreless permanent magnet linear synchronous motor (PMLSM) was taken as our research object. On the basis of the equivalent surface current method, we proposed an improved equivalent analytical algorithm with a trapezoidal side length unit. The equivalent analytical model of the magnetic induction vector of the two-dimensional air gap was established, and the air gap magnetic field of the trapezoidal Halbach array coreless PMLSM was calculated. At the same time, we analyzed the influence of the bottom angle α of a trapezoidal permanent magnet equivalent width coefficient αw, pole height coefficient αh, and air gap height coefficient αg on the amplitude (Bpeak) and total harmonic distortion (THDB) of the central magnetic field in the air gap. The results show that α and αw have a significant influence on the Bpeak and THDB of the central magnetic field air gap. With the synergy of α and αw, we identified the “flux convergence” effect, which makes the maximum range of Bpeak α > 90° and αw < 0.5. We also found the “equilateral” effect, which causes the minimum region of THDB to change linearly. The calculation results of the improved equivalent surface current analytical model established in this paper agree with those verified by the finite element method. The calculation is convenient, and the accuracy of the result is high. This research provides a new method for analyzing the air gap magnetic field of a permanent magnet with a nonrectangular cross-section and lays a theoretical foundation for optimizing the PMLSM pole model.

A compact permanent magnet for microflow NMR relaxometry

We design and demonstrate a compact, robust, and simple to assemble and tune permanent magnet suitable for NMR relaxometry measurements of microfluidic flows. Soft-magnetic stainless-steel plates, incorporated inside the magnet airgap, are key for obtaining substantially improved and tunable field homogeneity. The design is scalable for different NMR probe sizes with the region of suitable field homogeneity, less than 200 ppm, achievable in a capillary length of about 50 % of the total magnet length. The built physical prototype, having 3.5x3.5x8.0 cm3 in size and 5 mm high airgap, provides a field strength of 0.5 T and sufficient field homogeneity for NMR relaxometry measurements in capillaries up to 1.6 mm i.d. and 20 mm long. The magnet was used for test flow rate measurements in a wide range, from 0.001 ml/min to 20 ml/min.

Softening of Groundwater at Samarra City by Electromagnetic Polarization

The purpose of this investigation is to examine the effect of electromagnetic polarization on groundwater softening. Samples of groundwater were delivered from Samarra city, Salah-Aldin government, Iraq. The electromagnetic polarization treatment process was conducted using a locally manufacturing electromagnetic device. This device uses a magnetic circuit, an iron core, which is made from it a magnetic pole, air gap, and coil made of copper wire. Treated groundwater samples are achieved by passing them through the electromagnetic treatment device with a flow rate of (4, 6, 12, 25, and 50) ml/min., Total hardness concentration (800, 1050, 1300, 1550, 1800) mg/l. as CaCo3 and electromagnetic flux intensity (0.5, 0.75, 1 and 1.25) Tesla. The treatment was repeated with all these parameters. The ability to reduce Total Hardness and Total Dissolved Solids (TDS) of groundwater was assessed by measuring influent and effluent. It was concluded that the amount of (TDS) was slightly reduced and hardness-causing ions (Ca2+ and Mg2+) were significantly reduced after electromagnetic treatment for softening groundwater with efficiency removal ranging from (3.25 to 35.2)%.

Influence of end-effect and end-winding on the electromagnetic losses and efficiency in high speed permanent magnet machines

<span>Permanent-magnet excitation machines (SPMMs) having mounted magnet on the outer surface of their rotor are preferred for high speed applications such as turbochargers, mechanical turbo-compounding systems, racing engines and fuel pumps, over other types of machines including induction and switched-reluctance machines, since the SPMMs integrate the features of high torque density, compact rotor structure, high reliability and simple structure. However, in the SPMMs, due to the need for a retaining sleeve for the rotor, a large magnetic airgap results and consequently a large magnet thickness is required, hence the magnetic end-effect is relatively high. On the other hand, the use of an overlapping distributed winding leads to a significantly large end-winding length. Hence, the end-effect and the end-winding influences on the performances of a high-speed SPMM is considered in this paper. With a view to get the impact of the end-effect, a comparison between three-dimensional (3D-FEA) results and counterparts two-dimensional finite element analyses (2D-FEA) have been conducted. Results show that, higher efficiency at low torque and low speed due to the low electromagnetic losses and at high speeds due to the high flux-weakening capability are seen when the influences of end-effect as well as end-winding are taken into account.</span>

Energy storage in magnetic devices air gap and application analysis

With the rapid development of power electronic conversion technology, energy conversion has become more common than ever, and magnetic devices are more widely utilized. In power electronic conversion, magnetic devices are becoming more important and prominent, which puts forward higher requirements for the design and stability of magnetic devices. Many of domestic and foreign studies on magnetic devices pay particular attention to influence of air gap and loose magnetic field on inductance, but there is little analysis on the air gap energy storage of magnetic devices. This paper focuses on the energy storage relationship in magnetic devices under the condition of constant inductance, and finds energy storage and distribution relationship between Magnetic material and gap. The energy distribution ratio between material and gap of Magnetic Devices is verified on the dual-input power supply transformer of the energy storage converter.The innovation point of this paper is to analyze storage energy distribution ratio on the core and gap of magnetic devices from the perspective of energy that the storage energy distribution ratio of magnetic devices is changed after the addition of air gap. In the design of power supply, according to the demand of energy conversion, adjust the size of air gap appropriately, then change the energy storage position of magnetic devices, increase margin of the saturation flux density, improve the linearity of permeability, adjust the stability of switching power supply, provide theoretical reference for the design of magnetic devices of switching power supply.

A Magnetically Capsule Robot for Biomedical Application

Magnetic-driven capsule robot has been widely studied due to its advantages of safety and reliability. However, when doctors carry out clinical examination, the capsule robot cannot achieve the ideal control effect due to the influence of the external magnetic field air gap. This paper is based on the kinetic energy theorem, combined with the principle of spiral mechanism in mechanical design foundation to construct a calculation method of energy utilization and to improve the control effect of capsule robot, suitable for the human gastrointestinal tract precise control of capsule robot to perform a variety of complex tasks. By calculating the energy utilization rate of the capsule robot under the control of external magnetic field, the method can improve the energy utilization rate by improving the equation parameters, so that the capsule robot can run according to the doctor's ideal performance in practical application. Based on the analysis of the magnetic driven screw capsule robot, the model of the utilization rate of the external magnetic field of the capsule robot is established, and the fluid simulation of the capsule robot is carried out by using the method of computational fluid dynamics. The simulation results and experimental results show that the control effect of capsule robot can be improved by calculating the energy utilization rate of the robot, which is of great significance to human clinical examination and treatment.

Study of magnetic force excitations in salient pole synchronous generators considering geometrical modifications by conformal mapping

The simulation of electrical machines at the first design stage requires efficient methods to characterize among other properties its vibrational behavior. Particularly when considering both designed and parasitic geometrical modifications, magnetic circuit calculations of large-dimensioned machines by finite-element methods (FEM) are cumbersome. Semi-analytical approaches by means of conformal mapping are therefore useful to estimate the impact of several effects, such as asymmetric stator laminations, rotor pole shapes and air gap imperfections. No-load operation is studied and the presented approach is validated by FEM simulations. The aim of this work is to study force excitations by the magnetic air gap field in salient multi-pole synchronous generators deviating from ideal and symmetrical geometrical conditions by using conformal maps.

Novel model of rotor design to increase the air gap flux of superconducting generator

PurposeThe purpose of this study is to investigate a novel rotor design model to improve the technical performance of a superconducting synchronous generator.Design/methodology/approachSuperconducting synchronous generators with a modular rotating cryostat for a single coil of the superconducting winding instead of an old-style single cryostat in which all rotor components are cold are briefly discussed. Subsequently, a new method of cryostat arrangement in the magnetic system of a rotor is considered. Different options were compared for the cryostat placement. The advantages of the novel rotor design model are noted.FindingsIn the novel rotor design model, the leakage coefficient of the excitation winding decreases, and the air gap magnetic flux increases, which will save on a superconductor material.Research limitations/implicationsFor the purposes of this investigation, a finite element study of flux distribution in the cross section of a superconducting synchronous generator with a 10 MW rating at 10 rpm was conducted, and the magnetic fluxes and air gap flux densities were obtained for different modes. For direct-drive superconducting synchronous generators with distributed winding and different pole numbers, the calculations of magnetic fluxes were carried out by calculating the magnetic conductivities.Originality/valueA new method of the cryostat arrangement in the magnetic system of a rotor has been classified as an invention and was protected by a patent. This paper is directly applicable to the field of superconducting synchronous generators.

Modeling and Analysis of Dual-Winding Bearingless Flux-Switching Permanent Magnet Motor Considering Magnetic Saturation Based on Subdomain Model

Dual-winding bearingless flux-switching permanent magnet machine (BFSPMM) is composed of power winding and suspension winding. The permanent magnet and the power winding provide a biased air gap magnetic field, and the suspension winding generates an air gap modulation magnetic field. The structure of stator and rotor are double salient poles. This paper proposes a subdomain model for the on-load field prediction in dual-winding BFSPMM. In the developed model, the field domain is divided into seven types of subdomains, viz. rotor slot, internal air gap, stator slot, permanent magnet slot upper layer, permanent magnet slot lower layer, permanent magnet, and external air gap. The electromagnetic parameters of the motor are analyzed, including air gap flux density, flux linkage, back-EMF, suspension forces, and electromagnetic torque. Based on the principle of conservation of magnetomotive force, a distributed equivalent magnetic circuit model is proposed to compensate for the magnetic saturation. Finally, the analytical predictions are verified by finite-element analysis and prototype experiments.

Optimization Study of Electric Regenerative Shock Absorber (ERSA) Using Taguchi Method

Electronic Regenerative Shock Absorber (ERSA) is a vibration energy harvesting mechanism in vehicles in which the relative motion of the vehicle body to the road is transformed into a source of electrical energy using the concept of a linear generator. Additionally, the performance of the previous ERSA mechanism has been still relatively low, and it has been only able to produce electrical energy generation of 0.8 V. This has been affected by the number of coils, the diameter of the wire and the air gap magnet. In this study, the optimization of the three variables above has been carried out using the Taguchi method. Actually, each variable has consisted of three variations. Factor A (number of coils): 1000, 1500, 2000, factor B (wire diameter): 0.2 mm, 0.3 mm, 0.4 mm and factor C (air gap) 2 mm, 4 mm, 6 mm. From all the factors, nine levels of orthogonal arrays have been formed. Based on the stages undergone in the Taguchi method, the best ERSA configuration has been obtained with the configuration of factor A (number of coils): 2000 coils, factor B (wire diameter): 0.3 mm and factor C (air gap): 0.4 mm. Hence, the optimization data obtained can be used as a reference for future ERSA development.

Design and Force Analysis of Salient Single-Sided Linear Induction Motor

The linear induction motors, due to their unique features, utilize in various applications. The most crucial drawback of the linear induction motors is the large air gap between secondary and primary. This problem deteriorates the performance of linear induction motor, increases power loss, and causes to low efficiency. In this paper, a novel structure of single-sided linear induction motor is proposed to reduce the magnetic air gap. This structure consists of ladder-slit sheets and salient back iron for secondary of single-sided linear induction motor. The salient parts of back iron fill the slits of sheet, and therefore, the effective magnetic air gap can be decreased owing to partial form. Also, the electromagnetic aspects of the proposed secondary such as z-component of air gap flux density, y-component of aluminum eddy current density, and three components of Lorentz force are analyzed. Also, the finite element method and the analytical method is used for the 3 D analysis of the edge effects as well as the end effects. To show the advantages of the proposed structure, the results are compared with other secondary structures. The results show that the thrust and efficiency of the salient single-sided linear induction motor increased in comparison with other ones.