Variable Air Gap Research Articles

Characterization of multilayered structures by swept-frequency eddy current testing

The signals of the electromagnetic non-destructive testing of a multilayered structure are functions of the dimension and the electromagnetic properties of each layer in this structure. The signals of the to-be-characterized layer should be ‘extracted’ from the composite signals. This paper proposes of separating signals of different layers by frequency band, and characterizing the layer of interest by using the correspondent signals. An analytical solution derived in terms of transmission and reflection of electromagnetic waves was used to conduct simulation of swept-frequency eddy current testing of a multilayered structure. A couple of characteristic parameters were extracted from the analysis of the signals and the differences of the signal series in the frequency series. It was found that the thicknesses of the top and lower layers can be determined respectively by using high frequency and low frequency signals. The differences of the signal series in the frequency series are insensitive to the variation of air gap between two conductive layers. The maximum difference of resistance in the frequency series can be used to characterize the lower layer regardless the change of conductivity and air gap.

In-vivo EPID dosimetry for IMRT and VMAT based on through-air predicted portal dose algorithm

We have adapted the methodology of Berry et al. (2012) for Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) treatments at a fixed source to imager distance (SID) based on the manufacturer’s through-air portal dose image prediction algorithm. In order to fix the SID a correction factor was introduced to account for the change in air gap between patient and imager. Commissioning data, collected with multiple field sizes, solid water thicknesses and air gaps, were acquired at 150 cm SID on the Varian aS1200 EPID. The method was verified using six IMRT and seven VMAT plans on up to three different phantoms. The method’s sensitivity and accuracy were investigated by introducing errors. A global 3%/3 mm gamma was used to assess the differences between the predicted and measured portal dose images. The effect of a varying air gap on EPID signal was found to be significant – varying by up to 30% with field size, phantom thickness, and air gap. All IMRT plans passed the 3%/3 mm gamma criteria by more than 95% on the three phantoms. 23 of 24 arcs from the VMAT plans passed the 3%/3 mm gamma criteria by more than 95%. This method was found to be sensitive to a range of potential errors. The presented approach provides fast and accurate in-vivo EPID dosimetry for IMRT and VMAT treatments and can potentially replace many pre-treatment verifications.

Validation of Wireless Power Transfer by using 3D Representation of Magnetically Coupled Resonators Considering Peak Efficiency

This paper focuses on wireless power transfer system based on magnetic resonance coupling which involves creating a resonance and transferring the power without radiating electromagnetic wave outwith the critical distance. Modelling with Ansys<SUP>®</SUP> Maxwell 3D software provides the means to observe the main field quantities with its post-processing capability. Therefore mathematical expressions of optimal coupling coefficients are analyzed by considering mutual coupling model which is presented along with a derivation of key system identifiers such as transmission distance, characteristic impedance and resonance frequency. The effectiveness of the system is analyzed by exciting the resonators with sinusoidal voltage source. Ansys<SUP>®</SUP> Maxwell 3D software is utilized to solve equivalent circuit and also to calculate mutual inductance and characteristic impedance according to air gap variations. Resonance frequency is a key parameter in system design whose value can be changed according to distance between resonators. The peak efficiency is analyzed depending on different air gap values for various characteristic impedances at optimum resonance frequency. In this study, modelling resonators in 3D has been constituted correspondingly. The approach demonstrated in this paper allows fixed load receiver to be moved to different orientation within the range of critical coupling distance and approximately efficiency of 70 %.

Challenges in Modeling of Large Synchronous Machines

Machine simulation models allow the use of embedded numerical computation techniques. The finite element model accuracy is usually gauged by comparing its performance with experimental measurements. In this paper, a large hydrogenerator is modeled and the sensitivity of various model parameters is investigated by comparing the simulated results with experimental measurements. Four hydrogenerator units with the same design drawings are considered in the analysis. The effect of the model parameters was studied by considering the response of the open-circuit voltage in comparison with the measured open-circuit voltage, of the different units. Parameters considered included the effective model depth for a two-dimensional simulation, effective air gap, and effective material permeability of the B–H curve. A 20% variation in operational air gap between two machines of the same design resulted in over 18% difference in open-circuit voltage, particularly beyond the knee point. Reduction in permeability of the soft magnetic materials resulted in agreement between the simulation and measured results at saturation. Consequently, for large machines, the B–H curves from the Epstein measurements are insufficient and should be adjusted accordingly.

Analytical Analysis of a Novel Flux Adjustable Permanent Magnet Eddy-Current Coupling With a Movable Stator Ring

This paper proposes a novel flux adjustable permanent magnet eddy-current coupling with a movable stator ring (MSR). The slip speed of the proposed coupling can be adjusted by shifting the MSR along the axial direction. The structural feature and operation principle of the coupling are illustrated. An analytical model based on magnetic equivalent circuit method is built to compute its electromagnetic characteristics efficiently. The dynamic process of the MSR movement is simulated by employing a variable air-gap reluctance model. The eddy-current field under asymmetric magnetic field is calculated by an improved analytical method. The electromagnetic characteristics of the coupling, such as air-gap magnetic field, eddy-current, and torque-slip speed characteristics, are analytically investigated. The analytical results are verified with the results obtained by the 3-D finite-element method.

Design and Analysis of an Electrodynamic Bearing with Magnets Arranged in Halbach Array

This paper illustrates the working principle of an electrodynamic bearing and investigates the effect of variation of rotational speed, magnet width, its orientation and air gap on the bearing forces. In a case study, the radial force has also been checked using finite element methods for the permanent magnets arranged in Halbach array. The focus of the investigation is to compare the two models and show how the resultant bearing force responds to a change in rotational speed for a particular off-centre displacement and the corresponding changes observed in the Halbach array model from the permanent magnet counterpart. Analysis results show that the magnetic forces are depended on rotational speeds, air gap and magnet width as well as its arrangement.

Maintenance of working capacity of movement mechanism of load trolley with linear traction electric drive of bridge type crane.

The article considers the influence of the air gap size between the linear motor elements on the stability of the traction drive of the movement mechanism of the trolley of the bridge type crane. The main factors affecting the air gap size and the causes of their occurrence are described. The technique of calculating the magnitude of air gap variation is described in relation to the general deformation of the crane metal structure. Recommendations on the need for installation of additional equipment for load trolleys of various designs are given. The optimal values of the length of the trolley base are proposed. Observance of these values ensures normal operation of the traction drive.

Modal analysis of probe-fed circular sector microstrip antenna with and without variable air gap: Investigation with modified cavity model

Determination of accurate modal fields is one of the most crucial issues to understand the proper behavior of circular sector microstrip antennas (CSMAs) to achieve the best performance. In this article, dominant and higher order modal characteristics have been rigorously studied which germinate an improved, accurate, and efficient computer-aided design (CAD) formulation to estimate the resonant frequency of CSMA with and without air gap between substrate and ground plane. The proposed formulation can address the wide variety of issues (such as substrate height, substrate permittivity, air gap height, higher order modes, etc.). The computed results were validated against the results obtained from high-frequency structure simulator (HFSS) and our own experiments, while they have been also justified through the results obtained from the available literature.

Actively compensated aerostatic thrust bearing: design, modelling and experimental validation

Active compensation is an effective method for increasing air bearing static and dynamic performance. This paper describes the design, modelling and experimental validation of an actively compensated externally pressurized gas bearing. The active compensation is obtained through the support compensation strategy. With this strategy, the system’s initial working position is restored by compensating for air gap variations through adjustments to the bearing vertical dimension. The described bearing consists in a conventional thrust bearing which is integrated with a multilayer piezoelectric actuator, a compliant mechanism and a digital controller. Nevertheless the non-linear nature of the air system, a simple linear model results to be an effective choice for neighbour of equilibrium conditions. Results demonstrate the good accuracy of the model and the system’s good capacity of rejecting external force disturbances.

Utilization of Finite Elements Programs and Matlab Simulink in the Study of a Special Electrical Motor

This paper presents the study of a single-phase synchronous motor with permanent magnets (PM) using some computer programs. This motor type is used especially in household applications, and it has a low power. It is known that PM synchronous motors have a great advantage consisting in the lack of rotor losses. For this motor the starting problem has been solved performing a variable air gap under polar shoes, what determine the occurrence of the starting torque due to the fact that the axis of the rotor field created by PM in the rest position differs from the axis of the stator. First the parameters of the motor have been determined by tests and finite elements (FE) simulations, without knowing the properties of the PM. At the beginning magnetostatic FE simulations have been performed and then in magnetodynamic regime. The obtained results in the two regimes are closed. Secondly, with the determined parameters, a Matlab Simulink model has been realized (this being the final goal), and the dynamic regime of the motor has been studied. The results regarding the motor speed in starting process, the current variation, are also presented and discussed.

Numerical modeling of heat transfer and fluid motion in air gap between clothing and human body: Effect of air gap orientation and body movement

Air gap available between the clothing and human body provides significant thermal insulation and hence enhances the protective performance of clothing. A numerical model of fluid motion and heat transfer through the air gap is proposed in this work. The most realistic and detailed model considered in this work shows better accuracy than the previous models and brings several new insights to the combined heat transfer phenomena. Effect of horizontal and vertical air gap orientations on sensor temperature rise, heat flux, thermal protection and fluid flow behavior are analyzed. Results shows that thermal protection with the vertical air gap orientation is significantly better than the protection offered by the horizontal air gap orientation and the difference increases as the air gap width increases. Dynamic mesh technique is used in order to investigate the effect of dynamic air gap which results because of the body movement during heat exposure. Body movement is considered to be such that variation of the air gap with time is sinusoidal. Effect of motion frequency and average air gap width are also studied. Significant difference in convective and total heat flux as well as flow pattern is observed for cases with dynamically varying air gap.

Optimization and experimental verification of coplanar interdigital electroadhesives

A simplified and novel theoretical model for coplanar interdigital electroadhesives has been presented in this paper. The model has been verified based on a mechatronic and reconfigurable testing platform, and a repeatable testing procedure. The theoretical results have shown that, for interdigital electroadhesive pads to achieve the maximum electroadhesive forces on non-conductive substrates, there is an optimum electrode width/space between electrodes (width/space) ratio, approximately 1.8. On conductive substrates, however, the width/space ratio should be as large as possible. The 2D electrostatic simulation results have shown that, the optimum ratio is significantly affected by the existence of the air gap and substrate thickness variation. A novel analysis of the force between the electroadhesive pad and the substrate has highlighted the inappropriateness to derive the normal forces by the division of the measured shear forces and the friction coefficients. In addition, the electroadhesive forces obtained in a 5 d period in an ambient environment have highlighted the importance of controlling the environment when testing the pads to validate the models. Based on the confident experimental platform and procedure, the results obtained have validated the theoretical results. The results are useful insights for the investigation into environmentally stable and optimized electroadhesives.

A New Coreless Axial Flux Interior Permanent Magnet Synchronous Motor With Sinusoidal Rotor Segments

Axial flux permanent magnet (AFPM) motors are frequently used in many applications. Axial gap coreless motors with surface-mounted magnets are the most noteworthy ones due to their potentially higher efficiency and smaller axial length. In this paper, a new spoke-type AFPM coreless disk motor with dual rotor and single stator is proposed with sinusoidal rotor segments. This new disk-type motor is an interior PM (IPM) motor with spoke-type rotor and variable air gap to obtain sinusoidal back Electro-Motive Force waveform. It is shown that it is possible to increase the air-gap flux density in the proposed new coreless AF-IPM motor and increase the torque output compared with the conventional surface-mounted AFPM motors.

Preparation and characterization of self-cleaning alumina hollow fiber membrane using the phase inversion and sintering technique

Asymmetric alumina hollow fiber membranes were prepared using the phase inversion technique followed by the sintering process at high temperatures. The ceramic suspensions were formulated by mixing alumina powder with polyethersulfone (PESf), polyethylene glycol-30-dipolyhydroxystearate and N-methyl-2-pyrrolidone (NMP) as the polymer binder, dispersant and solvent, respectively. The objectives of this study were (i) to investigate the effects of spinning parameters, namely, ceramic loading, ceramic to polymer binder ratio, different internal coagulant temperatures and air gap variation on asymmetric structure formation and (ii) to study the self-cleaning properties of alumina hollow fiber membranes. The ceramic hollow fiber membrane was characterized in terms of its viscosity, structural morphology and mechanical strength using a scanning electron microscope (SEM). The results showed that the finger-like structures in alumina hollow fiber membranes could be formed but their patterns were influenced by the ceramic suspension and spinning parameters. Variations in their morphology resulted in significant effects on the mechanical properties and permeability of ceramic hollow fiber membranes. A CuO/CeO2 catalyst was deposited onto the alumina membrane support with the catalyst distribution determined by SEM/EDX. Self-cleaning properties were examined by comparing normal cleaning and self-cleaning properties with irradiation of UV for protein rejection. The result of self-cleaning by UV showed higher bovine serum albumin (BSA) permeation due to super-hydrophilicity of the CuO/CeO2 catalyst.

폭발볼트의 구속환경에 따른 분리메커니즘 연구

폭발볼트는 고폭약를 사용하는 분리장치의 하나로서 폭발볼트의 내부에서 형성되는 폭압 및 충격파에 의해 분리된다. 이러한 메커니즘을 갖는 폭발볼트는 분리시 생성되는 충격파 및 파편형성 최소화되도록 설계되어야 할 것이다. 본 연구에서는 폭발볼트 및 볼트를 구속하는 구속물과의 거리(Air gap)을 변수로 두어 분리시험을 수행하였다. 이때 Air gap 따른 분리유무 및 분리 형상을 확인 하였고, 가속도 센서를 이용하여 구속물의 전달되는 Pyro-shock를 측정하였다. 또한 ANSYS Autodyn 프로그램을 이용하여 폭발볼트의 분리거동을 해석하였다. 실험 및 해석으로부터 폭발볼트와 구속물 사이의 Air gap 크기에 따른 폭발볼트의 분리거동에 미치는 영향을 확인하였고 특정 볼트에 한해서 최적의 폭발볼트의 구속환경을 설정하였다. Explosive bolt is one of separation device that uses high explosive charge, and is separated by pressure formed by an explosion and the resulting shock waves. Explosive bolt having such a mechanism would have to be designed to minimize shock and debris formation generated during separation. In this study, separation tests were carried out with distance as variable for restraining the explosive bolt (Air Gap). Bolt release and its separating shape with variation of air gap is observed, and we used accelerometer to measure the shock wave transmitted through a bound object. In addition, separation behavior of explosive bolt is analyzed using ANSYS AUOTODYN program. By comparing the results of previously performed experiments and analysis, we could confirm the effects of air gap to the release behavior of explosive bolt, and decide optimum constraining environment for specific separation bolts.

Design and Fabrication of a High-Efficiency Magnetostrictive Energy Harvester for High-Impact Vibration Systems

This paper presents the design and fabrication of a vibration energy harvester based on giant magnetostrictive material, which consists of one coil-wound Terfenol-D rod with a permanent magnet (PM) and air gap in each magnetic circuit, and the PM array on the part of a cap amplifier. In this design, cap amplifiers and variable air gap are used to increase the harvesting effect of systems under environmental impact. Modeling and simulation are developed and performed to validate the concept. The relation of magnetic field in Terfenol-D rod is derived, and its uniformity and intensity are analyzed. Then, principal design parameters of the harvester, air gap, and cap amplifiers are determined, and its static analysis of the harvesting effect is performed. In addition, a prototype is fabricated and tested. The magnetostrictive-based vibration energy harvester can generate larger voltage and power than conventional smart harvesters and they can be safely used under the impact up to 20–30 MPa.

Magnetic pulse welding of Al/Al and Al/Cu metal pairs: Consequences of the dissimilar combination on the interfacial behavior during the welding process

This paper presents a comparison between Al/Al and Al/Cu magnetic pulse welded pairs, which highlights the influence of the dissimilar metal combination on the welded interface with respect to the variation in the initial radial air gap between a flyer and a target part. The welding of the Al/Al pair offers good bonding for a gap between 1mm and 4mm with a constant input voltage of 7.5kV. The Al/Al interfaces show a metal continuity that can either be straight or wavy, and become progressively sheared by the welded parts with the increase in initial gap, so that the nearby grains of the interface evolve from an undeformed equiaxed to a flattened and elongated morphology. The welded joint deteriorated by a formation of fracture and voids which occurs as a result of strong interfacial shearing for large initial air gaps, which also leads to an ejection of fragments. In the welding of an Al/Cu combination, the nature of the interface changes. A formation of intermediate phases in the form of layers or pockets which constitute of a third compound becomes obvious at the Al/Cu interfaces, which may trigger various detrimental phenomena of the joints. Depending on the thickness of the intermediate phase, the interface becomes sensitive to several mode of failures such as formation of radial microcracks, fragmentation, axial propagation of macrocracks in tensile opening mode, fracture due to an interfacial ejection or interfacial separation due to a melting of the intermediate phase. These defects degrade the joint which initiate the formation of cracks at the interface for low initial air gap (g=1mm), even with a thin intermediate phase of few micrometers. The interface becomes completely damaged for an initial air gap of beyond 3mm.

Root-soil air gap and resistance to water flow at the soil-root interface of Robinia pseudoacacia.

During periods of water deficit, growing roots may shrink, retaining only partial contact with the soil. In this study, known mathematical models were used to calculate the root-soil air gap and water flow resistance at the soil-root interface, respectively, of Robinia pseudoacacia L. under different water conditions. Using a digital camera, the root-soil air gap of R. pseudoacacia was investigated in a root growth chamber; this root-soil air gap and the model-inferred water flow resistance at the soil-root interface were compared with predictions based on a separate outdoor experiment. The results indicated progressively greater root shrinkage and loss of root-soil contact with decreasing soil water potential. The average widths of the root-soil air gap for R. pseudoacacia in open fields and in the root growth chamber were 0.24 and 0.39 mm, respectively. The resistance to water flow at the soil-root interface in both environments increased with decreasing soil water potential. Stepwise regression analysis demonstrated that soil water potential and soil temperature were the best predictors of variation in the root-soil air gap. A combination of soil water potential, soil temperature, root-air water potential difference and soil-root water potential difference best predicted the resistance to water flow at the soil-root interface.

Novel capacitive displacement sensor based on interlocking stator electrodes with sequential commutating excitation

A novel capacitive displacement sensor is proposed. The stator consists of a pair of interlocking comb-type electrodes, driven by two consistent high frequency voltage sources with opposite phase. The mover consists of double sensing channels with electrical orthogonal relationship. Through capacitive coupling, a relative displacement between the mover and the stator is converted to quasi sine/cosine signals, featured with direction identification and instantaneous displacement interpolation. Theoretical analysis indicates that the physical resolution of the studied sensor is the same as the electrode unit's width. And also, the interchannel's amplitude ratio and phase difference keep stable in a wide range of air gap size. Hence the performance of displacement detection can be enhanced by amplitude normalization and interpolation. Using a Printed Circuit Board (PCB) fabricated prototype, the proposed scheme was experimentally tested. Typical coupling statuses were captured. Main sensing characteristics and performance were investigated, such as the responding of air gap variation, the displacement sensitivity, and the measurement uncertainty.

Modified calculation for input impedance of probe‐fed and inset‐fed rectangular microstrip antennas

ABSTRACTAn approach to the modified calculation for input impedance of inset‐fed rectangular microstrip antenna and probe‐fed rectangular microstrip antenna with variable air gap and varying aspect ratio is presented. To modify the expressions for the input impedances of the antennas, continuous parameter genetic algorithm (CPGA) has been used. The results obtained by CPGA for different antenna dimensions are compared with the experimental and theoretical results given in the literature. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1650–1652, 2015