International Journal of Applied Electromagnetics and Mechanics

Reflectance spectroscopy obtained from thermally treated silicon nitride carbon based ceramic matrix composites is used to quantity the oxidation products SiO_2 and SiN. The data collection is described in detail in order to point out the potential biasing present in the data processing. A probability distribution is imposed on selected model parameters, and then non-parametrically estimated. A non-parametric estimation is chosen since the exact composition of the material is unknown due to the inherent heterogeneity of ceramic composites. The probability distribution is estimated using the Prohorov metric framework in which the infinite dimensional optimization is reduced to a finite dimensional optimization using an approximating space composed of linear splines. A weighted least squares estimation is carried out, and uncertainty quantification is performed on the model parameters, including a piecewise asymptotic confidence band for the estimated probability density. Our estimation results indicate a distinguishable increase in the SiO_2 present in the samples which were heat treated for 100 hours compared to those treated for 10 hours.

In this article, two novel NDT methods for composite structures are presented. First, the laser ultrasonic method for visualization of impact damage is introduced. A laser ultrasonic scanning system was developed, and the anomalous incident wave (AIW) energy was obtained from the wave-field data to image the artificial and impact damages. Next, a mid-frequency ECT (eddy current testing) system with the working frequency up to 250 kHz developed by the authors' lab for CFRP inspection is presented. The main features of the system include the weak-signal extraction method using the lock-in amplifier and the C-scan imaging techniques. The location and size of different damages were visualized in the scan image. With the developed system, the direction of different fiber plies could also be successfully detected.

In this paper we present a method to determine the current density inside an aluminum plate using eddy current testing procedure to determine the existence of surface cracks. The general idea consists in generating eddy currents in the plate, which in the case of flawless material, must be of uniform density pointing along a pre-defined direction inside a given area on the plate surface. These currents are produced using a planar coil. The eddy current density is determined by inversion of the data obtained from the measurement of a single component of the resultant magnetic field. Tikhonov regularization is applied to the inverted data.

The paper proposes an inverse reconstruction method for surface flaws in a 2-D half-space using guided Rayleigh waves. When a guided Rayleigh wave is sent toward the flaw area, the reflected wave signals are observed and recorded at the far field. From wave scattering theory, the displacement field of reflected wave is expressed by an integral over the unknown flaw surface concerning the total wave field. By introduction of Born approximation and far-field expressions of Green's function, it is found that the reflection coefficient in wavenumber domain is related to the unknown shape of the cavity by a spatial Fourier transform relation. Thus, the location and shape of unknown cavity can be established. Numerical examples are illustrated in the paper. The research can act as a basis for quantitative ultrasonic guided wave non-destructive inspection.

This paper is concerned with material interrogation methods for homogeneous dielectric materials using statistical inversion. Frequency dispersions for homogeneous dielectric materials can be described by a classical Lorentz model. Taking into account that the reflection coefficients are indirectly measurable, the signal response model is given by a complex reflectance at the interface between free space and the dielectric medium. The problem considered here is to quantify uncertainties of the estimated dielectric parameters from the measurements obtained by a reflective interferometer. A computational method using Hamiltonian Monte Carlo sampling based on nonlinear hierarchical models is tested.

This paper describes the detection method of the anomalies in signals proposed by Okabe et al. based on their KM_2O-Langevin framework; breakdown points of the stationarity can be detected to give the sign of anomalies. The method was applied to the sound signals to monitor the state of a generator engine and showed its feasibility.

In this paper, we propose to use an avalanche beacon with frequency of 457 kHz to search for a rescuer buried in rubble in a secondary earthquake disaster. In an avalanche rescue, a searcher proceeds along the magnetic force lines generated by the victim's beacon, and always reaches the magnetic field `zero point', which is guaranteed to be in the proximity of the victim. In this paper, we show that ferromagnetic objects in rubble do not substantially affect a zero point search by theoretical analyses, numerical simulations, and experiments.

It is known that Euler's homogeneity equation provides a system of linear equations for localizing a magnetic dipole from measurements of the magnetic field and its gradients. In this paper, we show that a solution of the equations obtained by Truncated Singular Value Decomposition (TSVD) always gives the true position of the dipole regardless of the singularity of the coefficient matrix. Hence, we can localize a magnetic dipole robustly without estimation bias by TSVD.

A method to reconstruct the current dipoles in human brain for magnetoencephalography was examined. In the method, a spatial filter provided the initial guess of the current dipole distribution. Then the current dipoles were localized by minimized the entropy calculated with the current dipole distribution. The reconstructed dipole moments were corrected in a post processing. In the numerical simulations the proposed method was compared with the focal underdetermined system solver (FOCUSS) which reconstructed a sparse distribution of the current dipoles. The proposed method was able to reconstruct the current dipoles more robustly than FOCUSS from the measured magnetic fluxes with low signal-to-noise ratio.

New nondestructive methods of the flood embankment dampness were tested. Electrical impedance tomography was used to determine the moisture of the test flood blank on a specially built model. Numerical methods of the shape and the topology optimization were based on the level set representation and the shape differentiation. They made possible to change topology during the optimization. Level set method and Gauss-Newton method have been applied very successfully in many areas of the scientific modelling. These approaches were based on shape sensitivity include the boundary design of the elastic interface. The finite element method has been used to solve the forward problem. The proposed solution algorithms are initialized by using the topological sensitivity analysis. Shape derivatives and material derivatives have been incorporated with the level set method to investigate the shape optimization problem. The coupled algorithms are a relatively new procedure to overcome this problem. Using the line measurement is very useful to solve the inverse problem in the flood embankment.

This study proposes a simple and cost-effective method to detect bolt loosening on the basis of low-frequency vibration signals as low as several hertz. Laboratory tests were conducted using M16 bolts connecting two SS400 plates. The bolts were vibrated by external impulse using a test hammer, and their vibrations were measured using accelerometers attached to the nuts holding the bolts. The accelerometers had the lowest measuring frequency of 0.5 Hz, and no high-pass filter was used. The results of the tests show that one can confirm whether or not bolts have been tightened to the rated torque quite clearly in time domain signals. Subsequent field tests were conducted to evaluate the M42 anchor bolts in a factory, and the results demonstrate the effectiveness of the method.

This paper employs three neural networks that are BP, RBF and PNN for rolling bearing fault diagnosis and compares their performance. The preprocessed vibration signals of rolling bearing provide fused feature vectors after the process of wavelet package decomposition and feature fusion. Then the fused feature vectors serve as the inputs of networks. The fault diagnostic aims to recognize health condition, fault types and fault severity of rolling bearings. The simulation results demonstrate that BP has the best accuracy and very complex computation efforts, and RBF has the fastest classification with the lowest precision. Meanwhile, PNN achieves perfect accuracy and speed that can be received.

Because excellent properties of the fixed-point iteration algorithm of fast independent component analysis algorithm (FastICA) and better statistical properties of negative entropy and Newton iteration, a FastICA effectively combining negative entropy and Newton iteration for OMA is put forward in this paper. Modal parameter identification results on simulation data of beam show that this method could identify the main modal vibration modes and natural frequencies correctly and efficiently only from measured signals of stationary random vibration response and more robustness than gradient descent and information maximization based ICA for OMA.

Forced convective heat transfer of turbulent magnetic fluid flow is remarkably suppressed by applying magnetic field. Detailed investigation of this suppression of turbulent heat transfer of magnetic fluid was carried out experimentally in this study. The result shows that the suppression of heat transfer becomes strong by applying stronger magnetic field, but is saturated at a certain strength of magnetic field. This suppression depends on not only magnetic field intensity but also flow condition. For generalization of the suppressed heat transfer characteristics of turbulent magnetic fluid flow by applying magnetic field, we proposed Mh number which is defined by Re divided by a root of magnetic field intensity normalized by saturated magnetization of magnetic fluid. It is found that suppressed heat transfer of magnetic fluid almost linearly increases with increasing Mh number.

Magnetorheological fluids containing nanometer size needle-like nonmagnetic particles whose long axis is 194 nm and aspect ratio is 8.3 are prepared as new magnetic functional fluids. Viscous properties of the fluids are investigated experimentally. Shear stress and viscosity coefficient are measured by using the rheometer which has the additional equipment for measurement in the presence of magnetic field. When the total volume fraction of the particles in the fluid is constant (0.30), larger amount of needle-like particles in the fluid gives larger viscosity in the absence of magnetic field. In the contrast, the viscosity and shear stress of the fluid containing 4% needle-like nonmagnetic particles and 26% micrometer sphere magnetic particles take large value than those of other fluids in the presence of magnetic field.

This paper is concerned with the magnetic fluid surface instability produced by the external alternating magnetic field with lower strength amplitude. Periodic disintegration and reconnection of magnetic fluid bridge between two small permanent magnets were studied with a high-speed video camera analysis system. Disintegration and connection of the liquid bridge were generated by the external alternating magnetic field produced by the Helmholtz coil. The surface shape of magnetic fluid bridge was changed by the external field every moment. The details of surface phenomena on magnetic fluid bridge were revealed. The relation between the surface shape variation and the external magnetic field was discussed with the Bond numbers.

Shielding effectiveness measurement, up to the GHz range, of construction materials with different compositions is an important issue. In this paper a coaxial waveguide, originally developed for thin films, is proposed as a simple device able to perform measurements on test samples with a thickness of a few millimetres. A calibration of the test system, with length extended of 5 mm, has been done both with a theoretical evaluation and an experimental measurement. Data obtained with construction materials of current interest for research are presented. With respect to similar systems reported in literature, where data up to 1.5 GHz are shown, this system has proven to be appropriate for measurements up to 3 GHz without too stringent tolerances in the sample geometry and without contact problems. Moreover, with inorganic polymers test samples, a clear relation between shielding effectiveness and heating temperature of the material has been observed.

The parallel permanent magnetic suspension system using flux-path control is composed of a servo motor, a radially magnetized disk magnet, and a pair of magnetizers. Establishing an accurate mathematical model is difficult owing to the system's special structure and nonlinear characteristics. To acquire an accurate mathematical model, an autoregressive exogenous (ARX) model identification method is applied to the system. First, the system input and output data are acquired from the suspension experiment. Then, an ARX model is established utilizing the data from the system identification method. Lastly, the relevant simulations and experiments are carried out to verify the validity of the ARX model. The results show that the simulation data with the ARX model closely agree with the test data obtained from the same controller. This model identification method can provide a better way to acquire a more accurate mathematical model for improving the controller.

In recent years, micro-compact electric vehicles have been developed and actively marketed, and has become popular as a new short-distance transfer mobility tool. While micro-compact electric vehicles do not have generate an engine sound, road and wind noises cause interior noise, and have a large impact on user comfort in the interior space. Recently the use of interior noise reduction by ANC has been used in the automobile industry. In this study, we propose a system whereby a giant magnetostrictive actuator is installed on the front window of a micro-compact electric vehicle to actively cut interface vibration noise, i.e., road noise, transmitted to the interior of the vehicle. In the experiment, we used an enclosure to simulate the interior of a vehicle and investigated the installation position of the giant magnetostrictive actuator to study the vibration characteristics of a window plate.

Authors made a single-point suspended electromagnetic suspension (EMS) system. This EMS system was applied to the carrier of a transport system. The pitching motion of the carrier converges faster than our physical expectation when the carrier is accelerated or decelerated. The eddy current loss in the iron plate and iron cores due to pitching motion was calculated by a 3D magnetic field analysis software. The calculation result and the experimental one made it clear that such swing convergence is caused by eddy current loss.

In general cam mechanisms, mechanical contact between a cam driver and a cam follower causes problems such as frictional wear, needs for lubrication and noise. Accordingly, we proposed a new cam mechanism whose contact parts are replaced by permanent magnets exerting repulsive force on each other. The purpose of this study is to investigate the efficacy of the mechanism which can drive without mechanical contact. To evaluate the effectiveness of the mechanism, we constructed an analytical model, derived an equation of motion of the cam follower and conducted numerical calculation of it. Furthermore, we conducted experiments corresponding to the model. As a result, occurrence of superharmonic resonance and collision of the driver and the follower in the neighborhood of the primary resonance point were observed. However, except in occurrence region of them, the rotating motion of the driver was favorably converted into reciprocating motion of the follower without contact. Thus we concluded that a magnetic cam is useful at appropriate rotational speed of the driver.

The Macro Fiber Composite (MFC) is the leading low-profile actuator or sensor offering high performance, durability and flexibility in a cost competitive device. As an ideal candidate of active-control devices, its application, however, is restricted by the complicated electromechanical characteristics, and also restricted by the unavoidable time delay lying in the MFC's actuated systems. Given this, this paper attempts to design a GA-based controller for mitigating clamped-free beam actuated by the MFC patches, in which these two factors are both considered. Finally numerical examples and corresponding experimental cases are used to testify the proposed approach is effective in mitigating vibration with different time delays. Also recommended are the implications of the current study on vibration control for other smart structures.

Additive rapid prototyping categorized into fused deposition modeling (FDM) and micro-stereolithography has received increasing interest in the past decade. Recent advance in FDM enables multiple materials to be printed in the same layers of a component. However, for micro-stereolithography, it is still a challenge to fabricate complex structure embedded with another material. In this work, a noncontact ultrasonic clamping stage is proposed for micro-stereolithography to hold the material or structure encapsulated by photo-curable polymer which will be solidified after exposure to UV light. In order to achieve this, ultrasound field is generated by three 2 MHz PZT transducers in millimeter sized region of a chamber filled with photosensitive fluid. Theoretical analysis illustrates that acoustic radiation force and torque will drive micro-particles in the sound field to force potential minimum and maintain their own equilibrium posture. Finally, rectangular silica particle with 100 μ m characteristic length is used to perform the controllability of our device.

An axial gap maglev motor with double stators that can control five-degrees of freedom (5-DOF) of rotor postures has been newly developed for pediatric ventricular assist devices (VADs). The motor has two stators that have an identical structure and a levitated rotor. The rotor is levitated magnetically between the stators and is driven by the mechanism of a synchronous permanent magnet motor. A double-stator structure achieves active 5-DOF posture control and enhances torque production. In this paper, a maglev motor as an actuator of pediatric VAD has been designed and miniaturized based on magnetic field FEM analysis. The performance of the maglev motor, the static magnetic suspension force and the torque of the developed motor, is measured experimentally and is sufficient for stable levitation and rotation.

A self-bearing motor that has tilt control function is proposed. The rotor has two permanent magnets on each side (four PMs in total). The two stators have eight poles each with concentrated windings. The operating principle was clarified by theoretical analysis and FEM analysis. Moreover, it was shown that the proposed motor can control the translation motion, inclinational and rotational motion independently. An experimental setup was fabricated and magnetically levitated rotation was achieved. The control performance of the self-bearing motor was also investigated. In addition, the proposed axial self-bearing motor is also designed and fabricated into a prototype maglev pump. Fabricated pump test rig showed sufficient performance for left ventricular assist device (LVAD) application of 4.35 L/min at 100 mm Hg.

This paper presents the design concept of a magnetically levitated linear slider with non-contact energy transfer, and an analysis of the major components of the design. An open-end generator is introduced to achieve non-contact energy transfer to the levitated platform. Utilization of non-contact energy transfer will overcome difficulties related to charging batteries. Furthermore, we have proposed an improvement for a hybrid electromagnet to achieve better passive lateral alignment under zero power control. The results of FEM analysis and practical testing show that the concept is promising for further study with a prototype system.

Nowadays, ultra-compact electric vehicles have been increasingly demanded under the influence of environmental problem and the aged society. The ultra-compact electric vehicles are possible to travel on poor condition roads, such as narrow and unpaved roads. Thus, the ride comfort of the vehicles is expected to deteriorate when the ultra-compact electric vehicles travel on such road. Then it is important to reduce vibration of the vehicle. To solve these problems, we suggest active seat suspension that can be installed in ultra-compact electric vehicles. In this paper, we focused on the electrooculogram when fall from the bump of roadway boundary.

A method of suppressing vibration in lateral directions is investigated based on varying stiffness strategy. A vertically controlled magnetic suspension system is often subjected to vibration in lightly damped lateral directions. In this paper, a novel approach is proposed to detect the lateral displacement of such magnetic suspension system, and how this displacement can be used to reduce vibration by varying stiffness control is presented. The principle of edge effect is applied to detect the lateral displacement in a magnetic suspension system operated in differential mode. A switching stiffness control and a modified control strategies are used to vary the stiffness of the system in order to reduce lateral vibration. Several experiments are carried out to validate the efficiency of the proposed method.

A wind tunnel system for a spinning body has been designed for the measurement of the hydrodynamic forces acting on the body. The body was successfully suspended and rotated by electromagnets. This existing arrangement is required to be enlarged to observe more accurate hydrodynamic forces acting on the body. Therefore, for the further development and control, it is important to understand the exact magnetic flux distribution inside the system as well as the variation of the force with the increase of the current. In this paper, both 2D symmetric model and 3D model of the arrangement are taken in consideration for the analysis. The magnetic flux distributions as well as magnetic force acting on the suspended object are obtained. The magnetic flux densities are analyzed for the variation of current in electromagnets. Actual force acting on the body is also measured. It is observed that the experimental results support the results obtained by numerical analysis.

In this paper, a novel disk type permanent magnetic motor which can actively control five degrees of freedom (5-DOF) of rotor postures without any contact has been proposed. Hence, although it has similar structure with an original Axial-Gap Self-Bearing Motor (ASBM), other radial magnetic bearings and its shaft of the rotor can be removed. Moreover, the number of stator coils is minimized; therefore, the structure and control system of the motor are simplified. This paper illustrates the structure and control principle of the proposed motor, and then the electromagnetic characteristics calculated by three-dimensional magnetic field FEM analyses are shown. An experimental device whose dimensions was determined based on simulation results was manufactured and tests were carried out to demonstrate the feasibility of the proposed motor.

Nonlinear vibration of a beam is active controlled with a fuzzy logic controller designed. The Von Karman's large deflection equation for a generally elastic beam partially covered by a macro fiber composite actuator (MFC) is established. Galerkin method is employed to convert the nonlinear partial differential equation derived into the nonlinear ordinary differential equation of motion, which is of Duffing's type. The method of multiple scales is adopted to figure out the relationship between the vibration amplitude and the nonlinear frequency. The nonlinear characteristics of the system are discussed when proportional and derivative feedback scheme is used. To depress the nonlinear vibration, a fuzzy logic controller is designed and the vibration of the beam is suppressed effectively.

The conventional impact localization strategies often assume that the wave velocity is independent of the propagation angle and obtain the wave velocity through theoretical calculation. These compromises may lead to inaccuracies of impact locations. In this paper, a Bayesian probabilistic methodology for impact localization is proposed. This approach utilizes the time of flight of diagnostic Lamb waves obtained by a piezoelectric sensor network for parameter identification. Bayes' theorem is then used to build the probabilistic relationship between measured time of flight data and unknown parameters. Finally, Markov chain Monte Carlo method is presented to implement the identification of probability distributions of impact location and wave velocity. Experimental studies carried out by dropping a steel ball on a CFRP panel are conducted to validate the proposed Bayesian impact localization strategy.

To meet the demands of high speed and excellent stability in modern oil free turbomachinery, a hybrid foil-magnetic bearing (HFMB) was first designed by Heshmat in 2000 [1]. However, in the HFMB, the journal should be carried out in certain eccentricity and attitude angle to the center of the bearing house due to hydrodynamic force which provided by the GFB. While the magnetic force caused by the AMB would try to force the journal of the reference position which is usually the center of the bearing at all times when using a conventional PD controller. While magnetic forces were commonly linearize at the center position of the bearing with respect to journal displacement and coil current. Therefore, the fully nonlinear force to displacement and the force to current characteristics concerning the journal eccentricity effect should be applied. The main objective of this paper is to represent a kind of theoretical method to calculate the load capacity, dynamic stiffness and damping coefficients of the HFMB under a specified load sharing factor λ with the predetermined operational state.

This paper presented a coupled electromechanical model and numerical method to obtain the torque response in a gas turbine rotor through transient analysis. Firstly, the FE model of the rotor based on beam elements and the electrical model of the generator were established. Then a contact element was introduced in the FE model to consider the contact effect between discs of the gas turbine rotor. The 4th Runge-Kutta method and Newmark method were used to solve the coupled equations iteratively to obtain the numerical solution of the transient response. Finally, a case study was presented and the results show much differences with those obtained through the conventional uncoupled analysis. The method and results of this paper are important to the rotor dynamic analysis and design of the gas turbine rotor in engineering.

Previously, we have proposed an infinity coil as a high sensibility ECT sensor. This paper has evaluated a possibility of the backside defect searching by the low frequency excitation of a modified infinity coil whose exciting coils are the flat/film shape to fit to the curverved test targets.

In the present paper, we have elucidated the lift-off characteristics of the backside defect searching when employing the low frequency excitation to our flat/film shape infinity coil.

In this study, the strategy to simulate a real stress corrosion crack (SCC) with a closed fatigue crack (FC) in view of eddy current testing (ECT) is investigated. An online four-point bending ECT device is designed and fabricated to provide the closure loading for a plate specimen and to enable online ECT measurements. The amplitudes of ECT signals due to FCs closed with different closure loads are measured. The experimental results show that the amplitudes of ECT signals due to closed FCs change regularly with the applied closure loads, and the ECT signal will recover to the initial state once the closure loading is released. The experimental results also reveal that, instead of the residual plastic strain, the online closure loading can make the FC conductive and a larger load leads to bigger crack conductivity. Through inverse analysis of the measured ECT signals, it is found that the conductivity in the crack region can reach to as big as 45% of the base material conductivity due to a large closure load. The results of this work demonstrated the feasibility positively to simulate a SCC with an online closed FC specimen for ECT measurement.

In this study, quantitative evaluation of defects in an outer-square-inner-round (OSIR), aluminum pipe, which is used as the coolant pipe of Tokamak superconducting magnet, is conducted based on the eddy current testing (ECT) technique. First, numerical simulations to predict ECT signal due to defects in OSIR pipes are performed using a code of A_r method; Second, ECT signal is detected using an Eddyfi ECT instrument with an absolute pancake ECT probe; Finally, the defect profile in OSIR pipe is reconstructed from the experimental ECT signals with the help of a fast-forward ECT solver, the developed multiple databases strategy and the deterministic inversion algorithm.

The detection of a crack under fastener heads (CUF) in a multi-layered aircraft structure remains a challenge in non-destructive evaluation (NDE). An EC-GMR system using a linear eddy current (EC) coil with giant magnetoresistive (GMR) sensors located on the axis of symmetry is proposed for detecting discontinuities in conducting materials. The signal received from sensors is greatly influenced by the excitation field. An ideal excitation field is purely tangential and uniform, however this is not achievable with coils of finite dimension. This paper proposed a methodology to optimize the coil design in order to approximate the ideal excitation field to the best extent. In the proposed approach, the coil design is cast as a multi-objective optimization problem. The algorithm for solving this optimization problem is the NSGA II (non-dominated sorting genetic algorithm II). The original version of this algorithm is not efficient in finding the solution, i.e. an evenly-distributed Pareto front. Therefore a problem specific modification is proposed. Numerical simulations showed the effectiveness of the method.

Ultrasonic guided wave tomography provides an imaging potential over a hidden and inaccessible damage zone. The use of shear horizontal guided waves has been proposed as an attractive technique for surface defect characterization. In this paper, imaging of wall thinning defects in plate is investigated by using electromagnetic ultrasonic shear horizontal guided wave tomography. Shear horizontal guided waves are generated and measured by magnetostrictive patch transducers. The quantification via imaging of wall thinning defects is achieved by a modified reconstruction algorithm for the probabilistic inspection of damage tomography algorithm. The location and shape of wall thinning defects are successfully obtained by the electromagnetic ultrasonic wave signals. The present approach provides an alternative alternative, that can be applied for detecting, locating and imaging the wall thinning defects in plate-like structures.

A new magnetostrictive steady-state guided wave technique(MST) based on long time excitation is proposed for Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM) in pipes. Due to the non-contact inspection, it has no need to consider the influence on vibration state while moving sensors along the pipe. Both simulation and experimental results show that the vibration state is associated with specific propagating guided wave mode and the defect causes an obvious change of the steady-state stage vibration amplitude at certain specific positions along the pipe, which can be utilized for defect location. Moreover, the precision of defect location increases with the excitation frequency increasing.

Models of the uniform wall thinning, a cylindrical through-hole for non-magnetic plate and the ferrite cored probes have been solved using the truncated region eigenfunction expansion (TREE) method. However, the solution of Pulsed Eddy Current Testing (PECT) for steel plate with a flat-bottom hole has seldom been given. By constructing the expressions of magnetic vector potential and solving the eigenfunction in the region where the flat-bottom hole placed, the analytical solution of PECT for the ferromagnetic plate with a flat-bottom hole is obtained. The solution is verified by a 2-D Finite Element Modeling (FEM), and the theoretical results obtained with the TREE method are in good agreement with the numerical ones obtained with a 2-D FEM package. The study proposes a theoretical method to analyze the PECT for wall thinning with the size similar to the probe.

Subsurface Corrosion (SSC) has posed a severe threat to the integrity of in-service conductive structures. Although Pulsed Eddy Current technique (PEC) has been proven applicable regarding non-destructive inspection of SSC, it has been found disadvantageous in terms of Signal-to-noise Ratio (SNR) and sensitivity to SSC, etc. In light of this, this paper proposes Pulse-modulation-based Eddy Current technique (PMEC). The advantages of PMEC over PEC have been analyzed via simulations based on analytical modeling and a series of experiments. Through theoretical and experimental investigations, it has been found that PMEC realizes the elaborate inspection of conductive structure, and has higher sensitivity in detection and evaluation of SSC than PEC.

In order to get a thorough comprehension on how the eddy current affects the MFL signal in high speed testing, distribution of eddy current and the magnetic field generated by it are first analysed theoretically. Then, the magnetization statuses of the pipe in static and motional situations are investigated by finite element simulation. Finally the external and internal defect signals are extracted in both static and motional cases. The results show that, in high speed testing, the magnetic field is strengthened at the outer surface and weakened at the inner surface, which increases the external defect signal but decreases internal defect signal.

The objective of this paper is a proof of concept on the possibility to measure the same magnetic fields, by the principle of dilation invariance. According to this principle, dilation of the dimensional and electrical parameters of a probe and a plate with crack reproduces the same magnetic field (measured at every dilated point) which was produced by a probe and a plate with crack, without dilation. This implies that, in order to evaluate the performance of eddy current method in a specific industrial case study, one can carry out tests in a scaled model in the laboratory and then, extend the conclusions to the real situation by using dilation invariance principle. The experimental and simulation results show a good agreement of crack detection by using two eddy current probes of which one is the dilated version of the other.

Ferromagnetic materials are widely used for various artificial products such as cars, trains, ships and so on. Because of its mechanical property, iron steel is most popular in use for the frame materials. Nondestructive testing of iron steel is an extremely important way to maintain their mechanical reliability. It is well known fact that the Barkhausen signals are emitted from only the ferromagnetic materials having magnetic domain structures. Also this signal varies depending upon their past mechanical as well as radioactive stress histories.

In the present paper, we have applied a generalized frequency fluctuation analysis to the Barkhausen signals to detect the various mechanical stresses. Surprisingly, it has been succeeded in clarifying that application of our frequency fluctuation analysis to the Barkhausen signals makes it possible to detect the several kinds of mechanical stress.

In this paper, a new efficient numerical method based on the finite element method (FEM) and the frequency domain summation (FDS) strategy is proposed for the simulation of the pulsed infrared thermography non-destructive testing. With use of the FDS strategy, the temperature distribution due to a pulsed thermal source is simulated based on the thermal response of series of single-frequency sinusoidal heat sources. An interpolation strategy is also adopted to reduce the necessary number of harmonic frequency responses to be calculated, and consequently the simulation time is saved. A comparison of the FDS strategy and the direct time domain integration method is also presented, which indicates that the FDS strategy can simulate pulsed thermography problem with high precision and can promote simulation efficiency.

The short cable is adopted widely in arch bridges and suspension bridges. The tension is an important parameter to guarantee the safety of the bridges in the practical application. Due to the bending stiffness and boundary condition effects, the tension of short cable is difficult to achieve accurate measurement using the flexural vibration method. A feasibility of tension measurement method for the short cable using steady state longitudinal mode guided waves based on the magnetostrictive effect is investigated. The major difference between this method and the magnetostrictive guided wave testing method is that the steady state response of the cable is employed to measure the tension. The cable is established the steady state longitudinal vibration with long time excitation based on the magnetostrictive effect. The longitudinal vibration is induced based on the inverse magnetostrictive effect. The natural frequencies of the cable are extracted from receiving data and employed to estimate the tension. The feasibility experiment results show that the natural frequencies rapidly increase with increasing the tension in low level and slightly increase with increasing the tension in high level, especially in higher modes. The results indicate that the proposed method is able to measure the tension of the short cylinder structure, but the relationship between the tension and the natural frequencies is non-linear.

In order to make the industrial testing and maintenance tasks for the tank floor safer, an automatic navigation magnetic flux leakage testing robot is designed. A fast multi circle detection method is presented for the testing robot with laser ranging location and differential driven technology. The calculation for the orientation deviation angle and the position of the robot is derived. The experimental results demonstrate that the proposed detection method and the incremental PID control algorithm perform the perfect tracking effect with high efficiency.

A new structure damage identification method is proposed based on wavelet packet analysis of the time domain response. It is known that the distribution of the wavelet packet node energy of response varies if the structure is damaged. The presented identification approach considers the variation rate of variance (VRV) of each node energy distribution as the damage detection index. Through decompositions of the time domain responses of intact and damaged structures using the wavelet packet transformation, the location and the degree of damage in the structure can be identified. Both the simulated and experimental studies on damage identifications are carried out for beam structure with crack based on the proposed method. The identification results show that the presented method is able to identify damages more accurately in the case of noise contamination compared with the previous methods.

EC-GMR measurements have been applied for detection of sub-surface corrosion and cracks under fastener (CUF) head. Generally, fastener signal amplitude is larger than the amplitude of the crack signal indication, rendering crack detection a challenging task. Also, another challenge in the analysis of field signals is the stitching problem, commonly present in a raster scan of a row of fasteners. We propose a method based on robust sparse coding (RSC) representation to alleviate the stitching problem and enhance defect detection capability. For the dictionary, we simulate multi-layer geometries using finite element (FE) modeling. Results on simulated and field data demonstrate the feasibility and robustness of the proposed algorithm.

The detection ability of a rotating field transceiver probe designed for axial and circumferential notches for inspecting tubes is studied in this paper. The transceiver probe consists of three identical windings, located 120° apart, on the same physical axis. A three-phase sinusoidal current source is used for exciting the coils. The probe achieves the functionality of a mechanical rotating probe electronically and eliminates the need for mechanical rotation. A three-dimensional finite element model is used to simulate and predict the response of the probe to a variety of machined notches. The feasibility of detecting the axial and circumferential position of a defect by analyzing the amplitude and phase of the transceiver probe signals is studied. A prototype of the probe was built and evaluated using an Inconel tube with axial and circumferential defects.

To alleviate the requirement on excessive computational resources using numerical methods such as finite element analysis in solving large high frequency 3-D eddy current problems, a novel iterative methodology to deal with periodic boundary conditions is proposed. Its implementation in finite element method is also explained in details. Numerical results on the computations of 3-D eddy current fields of a cold crucible are used to demonstrate the robustness and feasibility as well as the advantages of the proposed methodology in solving practical 3-D eddy current field problems.

Eddy current pulsed thermography (ECPT) has been applied for a wide range of conductive materials. The enhancement of thermography to detect the defects is also important. This paper proposes an independent component analysis (ICA) fusion method based fuzzy algorithm to process the thermography images. In ICA, three kinds of contrast function are applied to obtain the different ICs respectively. Then, the corresponding fused ICs are obtained by the fuzzy fusion algorithm. Meanwhile, the kurtosis of each ICs before and after fusion are computed to evaluate the performance of the proposed method. In addition, an experiment is utilized to show the benefits of the proposed ICA fusion method.

Fluxset magnetic sensor based probes with a double exciting coil system have been developed for detecting weakly interacting, low mass and small size magnetic particles for biomedical application. The probe measures the magnetic response of particles to an AC excitation. Measurements were carried out on samples containing 20, 30 and 40 nm size nanoparticles, which were embedded in a cylinder containing aguar-aguar. It was shown that the probe can detect nanoparticles of 20 nm size if their concentration is at least 0.06 mg/mm³ from a distance of 1 mm with reliable signal to noise ratio. The probe detection was found to be improved after magnetization of particles.

In this paper, broadband ultrasonic imaging is presented to check the diameters of tubules. The proposed method applies continuous wavelet transform instead of short-time Fourier transform, and hence overcomes both issues of spatial resolution and frequency resolution. The proposed method can visualize positions of test objects more clearly than the previous work.

Brain micromotion is one of the key factors that influence the longevity of neural probes. In order to improve the long-term stability of brain implanted electrodes, finite element (FE) models, utilizing hyper-viscoelastic constitutive equations, are developed to conduct a series of dynamic analysis of the neural probe-brain model. The influences of neural probe geometry parameters (e.g. tip fillet, wedge angle, wall thickness) on micromotion induced brain injury are investigated. The results show that fillet radius of 20 micrometers keeps both the maximum strain and injury zone in a small region while wedge angle of 70 degree leads to a 10.34% reduction in strain and 34.52% reduction in injury zone. Wall thickness of 15 micrometers generates the minimal injury zone and should be minimized under the condition of probe strength. The results will provide guidance on the development of novel neural probes with long-term stability.

Chronic thromboembolic pulmonary hypertension (CTEPH) is one of the lung diseases caused by thrombi, which occurs in pulmonary arteries. By measuring a size of region dominated by arterial subtree which has thrombi, physicians find a higher treatment effect point. This paper proposes an automated method to extract the lung region dominated by an arterial subtree from MDCT images. The method extracts an arterial subtree associated with a seed point and a region dominated by the extracted arterial subtree. And visualizes them. The results show a clinical ability of visualization and extraction of dominant region from MDCT Images.

This paper first describes the parameters of normal gait from the center of the foot pressure (CoP). In our experimental system, we obtain the foot bottom pressure distribution data by using load distribution sensor. After that, we calculate CoP by image processing and evaluate the movement of CoP by the parameters of normal gait. In this study, we employed 153 healthy subjects and acquired their foot bottom pressure distribution while walking. Next, we applied the normal gait parameters to one Down's syndrome child in 2 cases; with insoles and barefoot. As the results, we confirmed that the parameters of the child was improved by using insoles.

This paper describes an air-coupled ultrasound measurement system to evaluate activities of inner muscle. The system measures inner muscle with lower constrain than conventional method by using MR image, X-ray CT and contacted ultrasound. In generally, sound intensity of air-coupled ultrasound is too small to measure it. To measure the small signal, the system employs a pulsar-receiver with high sensitive pre-amplifier, and wave detection method based on fuzzy inference finds transmitted wave from noisy received wave. The fuzzy inference is derived from characteristics of transmitted wave such as amplitude, frequency, similarity and traveling time. In the experiment, we evaluate the accuracies of wave detection method for human body.

The design and development of coils for paired associative magnetic stimulation are described. The paired associative stimulation technique provides synchronous magnetic stimulation to the brain and peripheral nerves. Because heat is generated in the coil, it is necessary to attain a stronger magnetic field strengths at low discharge voltages. In this study, numerical analyses of coils used to stimulate peripheral nerves are performed to ensure coils can be used continuously and safely without overheating.

Recently, various types of wireless sensor network systems have been developed. Their price has also been reduced, and we can easily use such systems to monitor human states and behaviors in a house. Furthermore, such kind of information is useful for elderly care and nursing care by robot partners. However, we have to integrate different types of data measured by each sensor node to estimate human states and behaviors. If the measurement data are organized and structured, the monitoring system can do flexible monitoring and share the information. Therefore, we have proposed the concept of Informationally Structured Space (ISS). This paper proposes a methodology for human behavior estimation by wireless sensor networks in ISS. Next, we propose a monitoring system for sensor state and human behavior using ISS. Finally, we show several experimental results and discuss the effectiveness of the proposed method.

This paper focuses on the effective reducing of operating costs in the Smart Home Care system. The applied developed system components are designed for seniors auxiliary monitoring of the energy consumption. The paper describes the solution of information processing about quantity of the consumed electric and heat energy, gas and water consumption by using of the advanced system for consumption meters with recognition of video camera signal in the Smart Home Care monitoring system. The concept structure and principles of energy monitoring are designed with developed advanced electronic components, which are realized and verified for industry and commerce sphere.

Left ventricular assist devices (LVADs) have been verified as an effective way for the patients who suffer from the end-stage heart failure. In order to prolong the lifespan of the LVAD, a blood pump with magnetically or hydrodynamically suspended impeller is preferred. Magnetic bearings need active control consuming extra energy and hydrodynamic bearings running at very small clearance gaps can yield increased blood damage. A novel blood pump with a passively injection suspended impeller and a gap between casing and impeller in the large range of 0.6 mm is presented in this paper. This design allows the blood pump to eliminate the sensors for active control and operate at low levels of shearing stress. The computational fluid dynamics (CFD) analysis was conducted to primary verify the effectiveness of injection principle. The hydraulic performance and axial levitation performance test were performed to prove feasibility of the design.

Flexible endoscopes have been widely used for diagnostic and therapeutic interventions in minimally invasive surgeries. The flexible property provides flexible endoscopes the unique ability to reach cavities and viscera. However, in natural orifice transluminal endoscopic surgery(NOTES), during advancing process, a flexible endoscope without shape control is unstable and could lead to cavity buckling. When the end of the endoscope reaches the target, the endoscope should be rigid enough to hold its shape against external forces for better surgery operations. To overcome this problem, a novel variable stiffness over tube based on low melting point alloy (LMPA) was proposed in this paper. It could provide a channel for endoscopic instruments to go through human cavity. The over tube exploits the phase transformation property of LMPA which enable the stiffness change of the over tube. Steel cables were used to control the shape of the over tube. A prototype was built and experiments were carried out to evaluate its shape control effectiveness, variable stiffness property and response characteristics. According to experimental results, it cost 14 s to make the over tube transform from rigid state to flexible state and 15 s to make the over tube transform from flexible state to rigid state. Experimental results also indicated that the over tube is very rigid in rigid state and flexible in compliant state.

The assembled domain structure model (ADSM) is applied to an analysis of thin film magneto impedance (MI) element. The ADSM is a multiscale magnetization model constructed by the assembly of mesoscopic particles called the simplified domain structure models. The ADSM successfully reconstructs the characteristics of the thin film MI element where three stable magnetic domain states coexist. The simulation reveals the influence of longitudinal distribution of magnetic field on the magnetization property that is hardly affected by the perpendicular magnetic field.

This paper deals with the use of a vector Jiles-Atherton hysteresis static model introduced in the solving of a 2D time-domain finite element calculation. To ensure convergence, a Newton-Raphson algorithm is used with a relaxation procedure. The model is applied to simulate the transient operation of a fast-acting electromechanical actuator, accounting for remanence in the ferromagnetic parts. The impact of static hysteresis and eddy currents is investigated.

The high-speed method is proposed for analyzing a shielding current density in a high-temperature superconducting film containing cracks. In the proposed method, the linear-system at each iteration of Newton method is solved by using a GMRES(k) method. Consequently, it is found that the GMRES(k) method is a powerful tool for analyzing the shielding current density in an HTS thin film. In addition, the speed of the GMRES(k) method can be accelerated by a factor of about 2 by using the H-matrix method.

This paper evaluates a permanent magnet variable flux motor that uses centrifugal forces to change its torque constant. As the rotation speed increases, the displacement angle between the separate rotors also automatically increases. The effectiveness of the motor is verified by 3-D finite element analysis and measurements on a prototype. These results show a good agreement with each other. From these, it is verified that the motor can change the characteristics automatically.

This paper presents a helical teethed linear actuator(HTLA) for artificial muscles of human coexistence robots. The HTLA has small number of simple-shaped permanent magnets and coils. The advantages of this actuator are a high force constant and capability of accurate assembly. The performances of the HTLA were investigated by using 3-D finite element method (FEM). As a result, it was found that the maximum thrust force was 23.1 N, and the efficacy of the PID position control for the HTLA was confirmed. In addition, by the force control using encoder signals, the detent force was decreased to 0.56 N and the force constant was 34.9 N/A. Moreover, the control of the stiffness for flexible motions was implemented by using compliance control.

The development of multi degree-of-freedom actuating systems has been required in robotics and industrial machinery fields. In general, however, the actuating system with several degrees of freedom is composed of some single degree-of-freedom motors, which results in large, heavy and complicated structures. Therefore, multi-degree-of-freedom actuators are expected to become a key technology to solve these problems and many types of actuators have been studied. We have been developing a 3-DOF spherical actuator which can rotate around multi axes. In this paper, to improve controllability, a new compensation method which cancels out the cogging torque is proposed and the effectiveness of the control method is verified through 3D-FEM and measurements using a prototype.

This paper proposes a new design of interior permanent magnet (IPM) type brushless DC (BLDC) motor using low-price ferrite magnet which has the similar characteristics as the IPM type BLDC motor that uses expensive NdFeB magnet. In order to replace the NdFeB magnet, the proposed design adopts the structure of the C-shape permanent magnets which are arranged as the flared shape. The characteristics of the proposed IPM motor are compared with the NdFeB IPM motor through the finite element analysis(FEA). It is demonstrated that proposed model satisfied with the characteristics of the NdFeB IPM motor.

This paper proposes a novel dual rotor radial field flux switching permanent magnet machine (FSPMM) with phase-group concentrated-coil (PGCC) windings and two misaligned rotors to obtain high performance, including high torque density and low cogging torque, as well as low torque ripple. The proposed FSPMM features a new combination of stator slots and rotor poles, which is determined by the winding configurations. The PGCC windings are adopted to obtain a unity displacement winding factor, and enhance the flux focusing effects together with the use of spoke-type PM constructions. The unaligned arrangement of two rotors will help to not only achieve further flux magnification by an alternate operating principle for PM flux concentration, but also suppress the cogging torque. To highlight the advantages of the proposed FSPMM, two conventional FSPMMs with typical machine configurations having concentrated windings are adopted for performance comparison based on a finite element method (FEM) using JMAG-Designer.

This paper discusses the shape optimization of chipless radio frequency identification (RFID) tags comprising fractal structures. In the proposed optimization process, scattering electromagnetic waves from a chipless RFID tag are analyzed using a finite-difference time-domain (FDTD) method. The shapes of the chipless RFID tags are optimized by a micro-genetic algorithm (m-GA) to determine the frequencies of the subject scattering waves, as well as to maximize their associated amplitudes and quality factors. As such, a self-similar metal line and metal patch comprising fractal structures are assumed to be a chipless RFID tag. The optimized tags obtained using the FDTD method and m-GA ultimately maintain the selective frequencies, high amplitudes, and quality factors of the scattering electromagnetic waves.

This study proposes an efficient method of local space-time grid refinement and examines the numerical stability and the accuracy of electromagnetic field analysis using the space-time finite-integration technique (FIT). The proposed subgrid method locally refines the space-time grid with three-division or four-division and is stable without inducing numerical instability even after one million time-steps. The grid construction is modified at the corner part of subgrid connection to improve the computational accuracy. The staircase-type grid relaxes the time-step restriction due to the CFL condition.

This paper reports the performance improvement of the planar waveguide slot array antenna by loading the small spherical dielectric lenses. The proposed lens is sphere and small, and can be loaded on each slot independently. To design the antenna with the proposed lenses, other design parameters are fixed, and the optimal slot length is searched by using the finite difference time domain (FDTD) method. From both the calculated and the measured far-field radiation patterns, the optimized antenna with the proposed lenses shows good performance as the resonant uniformly distribution array. By comparing with the conventional antenna, it is found that the gain increase by loading small lens is estimated by 1.07 dB.

This paper presents optimal shape design of planar array antennas for microwave energy harvesters. The topology optimization of the C₄-symmetric array antenna is conducted to maximize their isotropic gain and minimize the return losses in a frequency band ranging from 1.5 to 3.5 GHz. Then, we design the rectifier by varying the circuit parameter based on measurement results to realize the impedance matching between the optimized antenna and rectifier. It is shown by experiment that the harvester composed of the optimized array antenna and rectifier has higher receiving voltage in comparison with the single one. Moreover, the resultant harvester is found to start operating when the arrival electric field is greater than 0.1 V/m.

Resonant Cavity Enhanced (RCE) photodiodes may have advantages over the conventional p-i-n photodiodes due to an enhancement of the quantum efficiency obtained from the constructive interference of the light waves that are made to oscillate in a cavity. In this paper a novel RCE structure, with applications in long wavelength optical communication systems, is proposed and its frequency response is investigated and compared to that obtained for conventional p-i-n devices. An optimization procedure is implemented and the results show that these RCE photodetectors may have bandwidths larger than 80 GHz and a bandwidth-quantum efficiency product above 80%.

It is known that the proper orthogonal decomposition (POD), which is one of the effective approaches for model order reduction (MOR), can effectively reduce computational time for finite element method (FEM). This paper proposes a new method for generation of equivalent circuits based on POD-based FEM. In this method, the circuit parameters are determined by genetic algorithm so that the input impedance of the equivalent circuit is coincident with that computed by POD-based finite element method (FEM). For test of the proposed method, POD-based FEM is applied to analysis of a dipole antenna which is loaded with the Cockcroft Walton circuit. It is shown that this method can reduce the computational time to generate the equivalent circuit without deterioration of accuracy.

The paper presents investigation of dynamical window multi-frequency (DWMF) eddy currents algorithm applied to the helical steam generator tubes of FBR to improve the defect detection when the defect is free of sodium or sodium partially fills the volume of the defect. The task is accomplished using large scale three dimensional (3D) finite element (FE) numerical simulations, based on an in-house developed code massive parallelized, that can take into account full circumferential and partial outer tube defects located near or far from the tube support plate.

A three-degree of freedom (DOF) same-stiffness permanent magnetic spring is proposed, which comprises three groups of permanent annular and cylindrical magnets. The three groups of magnets are symmetrically arranged on a concentric circle. In each group, the permanent cylindrical and annular magnets are coaxial and the same magnetic poles are opposite. The repulsive force in the radial direction is regarded as the magnetic spring force between the permanent cylindrical and annular magnets. The repulsive forces of three groups of magnets can realize the three DOF same-stiffness magnetic spring forces on a plane. In this paper, a mathematical model of the magnetic spring force is established for one group of magnets. The mechanical characteristics of the magnetic spring force are analyzed by calculations with the mathematical model, simulations with the FEM (finite-element method) model, and verifications with the experimental prototype. The results suggest that the force characteristics of the magnetic spring resemble those of a mechanical spring and the different stiffness of the magnetic spring force can be obtained by changing the structural parameters.

In applying eddy current testing to evaluation of fatigue cracks in austenite stainless steels, various influential factors are needed to be considered, such as martensite transformation of austenitic phase, crack closure, and oxide formation between crack faces, and so on. In this study, influential factors of heating of fatigue cracks in type 316 austenitic stainless steels are evaluated through experimental and numerical analysis. Signal phase shift and amplitude decrease by heating is systematically discussed.

An unsuitable value of k may lead to a series of wrong manifolds after dimensionality reduction in local linear embedding (LLE). In order to improve the accuracy of dimensionality reduction in LLE, an improved LLE algorithm (ILLE) is proposed, which determins the optimal number of nearest neighbors k and decreases its sensitivity. In this paper, ILLE is applied to identify the modal shapes of two complex structures and the results show that ILLE identifies the modal shape more accurately than LLE.

Due to the ill-conditioned inverse characteristics of uncorrelated multi-source random dynamic load identification problem, there are large condition number and large identification errors for classic least-squares of generalization method at inherent natural frequencies. In order to avoid its illness and singularity, this multi-objective optimization inverse problem is turned into single-objective optimization forward problem by criterion function of minimization maximum relative errors of all response measuring points, and we adopt genetic algorithm to search this optimal solution then. Results of uncorrelated multi-source vibration load identification on cylindrical shell CAE simulation data set show that this new method is much better in precision and is less sensitive for measurement noise than classic least-squares of generalization method.

Based on the theory of ``time-frozen'', this paper proposes a novel operational modal analysis (OMA) for linear time-varying structure using limited memory principal component analysis (LMPCA). Compared with modal coordinate decomposition of non-stationary response signals for linear time-varying continuous beam structure, it is found that PCA can be decomposed to extract time-varying instantaneous modal parameters, which reveal structure characteristics in limited memory window length L. Numerical simulations results on a cantilever beam with slow time-varying mass are presented to verify the TV instantaneous natural frequencies and modal shapes identification capability of the LMPCA.

In order to separate multiple random fault sources only from mixed vibration measurement response signals of mechanical system, Negentropy and Gradient iteration based fast independent component analysis (FastICA) is applied for blind signal separation (BSS). After finding the association between independent components (ICs) matrix and multiple random fault sources, multiple random fault sources identification problem is turned into ICA of the stationary random vibration response signals of mechanical system. This method uses negative entropy maximization as criterion of independence, Gradient iteration as optimization method to extract random fault sources one by one. Simulation experiment results verified that this method could identify and separate multiple random fault sources only from mixed vibration measurement response signals of mechanical system correctly and effectively.

One buckled simply supported giant magnetostrictive material (GMM) laminated thin film beam model subject to axial colored noise excitations is proposed. Applying the Hamilton principle and Galerkin approach the model is expressed as a one dimensional vibrating model with parametrical random excitation. The stochastic averaging method is used to obtain the probability density function (PDF) of the amplitude when the vibration is around the buckled position and the amplitude of the oscillation is small. The reliability of the system was also studied. The numerical simulation verified the theoretical analysis.

In this paper, a hybrid topology optimization methodology based on ON/OFF method and Genetic Algorithm (GA) is proposed. To cater to the topology optimization, improvements are made on both the ON/OFF method and genetic algorithm. The proposed methodology is applied to the topology optimization of a magnetic actuator to maximize the magnetic force in a specific direction to verify its feasibility and effectiveness. The numerical results have demonstrated that the performance of the proposed methodology is significantly superior to those of available techniques.

This study deals with an experimental methodology developed in order to identify the elastic properties of superconducting ring-shaped windings, constituents of the main coil winding of a magnetic resonance imaging magnet (MRI). Mechanical tensile tests were conducted on real scale specimens associated to an optical full-field displacement measurement technique (stereo image correlation). Strain fields were then obtained from the measured displacement fields by numerical differentiation. Finally, the four in-plane orthotropic stiffnesses of the windings were determined using the Virtual Fields Method (VFM). Experimental set-up also allows detecting a possible occurrence of a delamination thanks to in-plane displacement fields.

For extracting the absorber information in a scattering medium, we investigate the temporal-spatial characteristics of optical intensity distribution ratio by solving the time-dependent photon diffused equation. Numerical results indicated the output power ratio distribution with short accumulated time is effective to obtain the reconstructed absorber with the narrow width. There is no influence of the temporal and spatial widths of the input pulsed light on the reconstructed property. In the numerical conditions used in the paper, the short accumulated time provides 60% of reconstructed absorber size obtained at the saturated time.

This paper proposes a novel permanent magnet synchronous motor with switchable speed-torque (N-T) curves. The structure and operational principle of the proposed motor are described. The proposed motor can be rotated as 3-phase and 6-phase motors. First, the theoretical N-T characteristics using the torque constant and inductance that are computed by 2-D FEM analysis are calculated. Second, the 2 N-T characteristics are verified using FEM analysis under vector control. Finally, the advantages and disadvantages of the proposed motor are described.

This paper proposes new-shaped pole pieces for a low-speed rotor of a magnetic-geared generator, which unify a magnetic gear and a generator and can realize downsizing and maintenance-free operation for large output power machines such as a 2-MW class used for wind power generations. The concept of the new-shaped pole pieces is described, and its effectiveness is verified by finite element analysis and measurements on a prototype downsized in 1-kW class.

This paper presents a novel three-phase U-core stator motor with the modular topology based on the conventional single-phase motor to solve the problems of high torque ripple and non-self-starting ability, which has the similar advanced performance as a two-phase motor. Basic topology and torque analysis are discussed for the proposed three-phase motor in terms of the single-phase modules. Finite-element method (FEM) is carried out to compare and verify the competitive performance of the proposed motor and the practicability of such modular design concept. The dynamic starting performance in the proposed three-phase motor is finally simulated by utilizing the Simulink models and compared to those of the single-phase and two-phase models.

The piezoelectric actuator shows good control of micro linear displacement, but it cannot directly output the angular displacement. In this paper, an angular displacement piezoelectric actuator is proposed, which can amplify the displacement of the piezoelectric stack and realize angular displacement output just through one piezoelectric stack. Finite element modelling (FEM) simulations were used to analyse the angular displacement and the stress conditions. To verify the results of the FEM simulations, a prototype was manufactured and the experiments were performed. The maximum angle displacement was 0.85° when the driven voltage was 120 V.

To develop a fast global optimizer, the whole iterative procedure of a tabu search algorithm is divided into two deliberately designed phases: exploration- and exploitation-phases. Stochastic approximation method is proposed to minimize the computational burdens when computing the gradient information in designing the exploitation phase. Also, some specially oriented mechanisms for enhancing the balance between exploration and exploitation searches are introduced and integrated. Numerical results are reported to showcase the merits of the proposed metaheuristic.

An adaptive quantum-behaved particle swarm optimizer(AQPSO) is proposed to ensure a good balance between exploration and exploitation searches of the algorithm. In the proposed algorithm, some indicators to identify the searching states of a particular particle, the whole swarm, and the iterative process are proposed and used to design an adaptively tuning mechanism for the Contraction-Expansion Coefficient. Moreover, a partially regenerated swarm scheme is designed to select promising particles and to regenerate unpromising ones when the swarm is trapped into a local optimal point. The proposed AQPSO is used to solve the TEAM workshop benchmark problem 22, and compared with existing QPSO. The numerical results have demonstrated that the proposed algorithm outperforms the existing QPSO, especially in view of the global search ability.

The induction motor designed for the variable speed applications are different from those which are designed for constant speed applications. This paper deals with the method for the design of induction motor for variable speed applications starting from the analytical calculation of equivalent circuit parameters. Finally, the main dimensions of the motor geometries are provided by using the relation between the circuit parameters and geometries of a real induction machine. The proposed approach also minimizes the problems caused by the conventional motor design methods for the variable speed application. The effectiveness and accuracy of the proposed design can be verified through Finite Element analysis for practical design.

A new type magnetic harmonic gear is proposed. The new magnetic gear has the stackable structure and is assembled easily. The proposed magnetic gear has stacked ring magnets and thin iron plates for the inner and outer rotors. And the two types of the inner and the outer rotors are compared. The proposed magnetic gears can transmit the maximum transmitted torque over 1 Nm and the input rotational speed exceeding 2000 rpm. Furthermore, the influence of a stack on the maximum transmit torque is revealed through the experiment. Also the maximum transmitted torque is checked through the simulations.

This paper proposes a novel permanent magnet (PM) shape for surface-mounted PM (SPM) machines, with the aim of not only improving the sinusoidal quality of back electromotive force (EMF) and reducing cogging torque as well as torque ripple, but also saving on the magnet material cost. The proposed PM shape is designed to be trapezoidal and symmetrical in the axial direction, and the pieces from breaking the magnets for the trapezoidal shape can be used to create a new pole resulting in a significant reduction of magnet material cost. The design principle of the proposed cost-effective PM shape with two alternatives is illustrated in detail. To highlight the advantages of the proposed PM shape in SPM machines, two conventional rectangular PM shapes and a previously reported sinusoidal PM shape are adopted for performance comparison, based on a 3-D finite element method (FEM) using JMAG-Designer.

One of an electrohydrodynamics (EHD) phenomenon is the induced flow of a functional fluid in the presence of an electric field. In this paper, we describe a small pump in which the flow is generated by such an EHD phenomenon. In the case of pumps based on cylindrical electrodes, which thus far have been the focus of our research on EHD pumps, the total circumference length of the edge of the holes in the electrode that generates the rotational flow is small, leading to a small overall one-directional flow velocity. To increase this area, we produced two different electrode pumps in which the electrode (cylindrical; 6 mm diameter, 1 mm width) contains multiple holes. We measured the pressure-flow rate characteristics of our pumps and compared their performances.

In this paper, an investigative study on the effect of various notch depths and notch location angles in the U-core stator permanent magnet motors is presented, which aims to obtain the proper design combination of notch parameters for the better motor performance. Finite element method is carried out for the motor performance evaluation such as the starting torque, cogging torque as well as the phase back-EMF. The results show that there are certain ranges of the notch depth and the notch location angle to generate the larger back-EMF and starting torque with less cogging torque. Finally, the Simulink models are built and the prototypes are tested for their dynamic performance comparison.

Piezoelectric actuators have been widely applied in micro- and nano-positioning devices, but the hysteresis nonlinear property limits the performance. An adaptive control is designed for hysteresis compensation in piezoelectric actuator. The Prandtl-Ishlinkii model is proposed to describe the inverse of piezoelectric actuator. The weight parameters of Prandtl-Ishlinkii model is updated on real-time control. Experimental results show that the proposed control method can effectively update the weight parameters for real-time control.

A type of giant magnetostrictive-piezoelectric composite vibration energy harvester is proposed in this paper, and its stochastic nonlinear dynamic characteristics are studied. Giant magnetostrictive material is applied to induce the harvester's self-excited vibration to improve its efficiency. Nonlinear differential term is introduced to explain the hysteresis phenomena of a giant magnetostrictive material, and the fitting effect of the constitutive model on experimental data is proved by the partial least-square regression method. The nonlinear dynamic model of a giant magnetostrictive-piezoelectric vibration energy harvester subjected to stochastic foundational excitation is developed, and the stationary probability density function of the system's response is obtained. The transition sets of the system's response are determined, and the conditions of stochastic bifurcation are obtained. Numerical and experimental results show that the stochastic Hopf bifurcation occurs when the parameters varies; the output voltage is quasi-periodic, which means the effective utilization to the environmental stochastic excitation.