International Journal of Applied Electromagnetics and Mechanics - Volume 64, issue 1-4

Authors: Ohji, Takahisa | Kusano, Satoshi | Inoue, Tatsuhiro | Amei, Kenji | Kiyota, Kyohei

Article Type: Research Article

Abstract: Magnetic levitation (maglev) systems for nonmagnetic conductive metals generally generate only repulsive force between the stator and the levitated body. To overturn the conventional common sense, we have fabricated a new maglev device that can generate “attractive force” between the stator consisting of plural ac electromagnets and a nonmagnetic conductive metal ring. In this paper, we elucidate the electromagnetic phenomenon that appropriately arranged seven ac electromagnets continuously pulls up an aluminum (Al) ring, which has 120 mm outer diameter and 5 mm square cross-section, by using finite element analysis. The analysis results reveal the existence of an equilibrium gap where the electromagnetic …pulling force balances with the weight of the Al ring without active control. Besides, the equilibrium gap was measured when different weights were added to Al ring to verify the validity of analysis results. The measured results show that the maglev device has a positive stiffness (i.e., electromagnetic spring) of 50 N/m. Show more

Keywords: Magnetic levitation, ac ampere force, aluminum ring, pull-up force, electromagnetic spring, finite element analysis

DOI: 10.3233/JAE-209320

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 173-180, 2020

Authors: Li, Hao | Geng, Haipeng | Lin, Hao | Feng, Sheng

Article Type: Research Article

Abstract: Gas foil bearings (GFBs) are widely used in synchronous motors for their splendid performance in high speed. However, its working principle can produce unbalanced magnetic pull (UMP) between stator and rotor inevitably. Based on the rotor transverse vibration, this paper analysis the influence of UMP on the dynamic behavior of the rotor system supported by GFBs. The results show that the UMP accounts for a higher proportion of the exciting force acting on the rotor system at lower speed range. And the UMP declines with the decrease of nominal clearance. It is found that UMP will advance the critical speed …of rotor system. According to the simulation results, the rated speed of synchronous motor is set at 90 000 rpm, and the nominal clearance of GFBs is 8 μm. The experimental results show that the rotor system designed in this paper works stably and achieves the predetermined design goal. Show more

Keywords: Synchronous motor, unbalanced magnetic pull, gas foil bearings, critical speed, trajectory calculation

DOI: 10.3233/JAE-209321

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 181-189, 2020

Authors: Song, Haicheng | Yusa, Noritaka

Article Type: Research Article

Abstract: Structural health monitoring (SHM) is a promising method for maintaining the integrity of structures. A reasonable approach is necessary to quantify its detection uncertainty by taking into account the effect of random sensor locations on inspection signals. Recent studies of the authors proposed a model that adopts Monte Carlo simulation to numerically obtain the distribution of inspection signals influenced by random sensor locations. This model can evaluate the effect not only of multiple defect dimensions but also of the placement of sensors on the detection uncertainty. However, its effectiveness has only been confirmed using pseudo-experimental signals generated by artificial pollution. …This study aims to examine the effectiveness of the proposed model in quantifying the detection uncertainty of SHM methods using the experimental signals of low frequency electromagnetic monitoring for inspecting wall thinning in pipes. The results confirm the capability of the proposed model to correctly characterize the distribution of inspection signals affected by random sensor locations and to determine the reasonable probability of detection. Show more

Keywords: Non-normal noise, probabilistic calibration, non-parametric probability density function, finite element simulation

DOI: 10.3233/JAE-209322

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 191-199, 2020

Authors: Tanaka, Yoshikazu | Odake, Satoru | Miyake, Jun | Mutsuda, Hidemi | Popov, Atanas A. | Patel, Rupesh | McWilliam, Stewart

Article Type: Research Article

Abstract: Energy harvesting methods that use functional materials have attracted interest because they can take advantage of an abundant but underutilized energy source. Most vibration energy harvester designs operate most effectively around their resonant frequency. However, in practice, the frequency band for ambient vibrational energy is typically broad. The development of technologies for broadband energy harvesting is therefore desirable. The authors previously proposed an energy harvester, called a flexible piezoelectric device (FPED), that consists of a piezoelectric film (polyvinylidene difluoride) and a soft material, such as silicon rubber or polyethylene terephthalate. The authors also proposed a system based on FPEDs for …broadband energy harvesting. The system consisted of cantilevered FPEDs, with each FPED connected via a spring. Simply supported FPEDs also have potential for broadband energy harvesting, and here, a theoretical evaluation method is proposed for such a system. Experiments are conducted to validate the derived model. Show more

Keywords: Energy harvesting, piezoelectric material, FPED, spring, broad band

DOI: 10.3233/JAE-209323

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 201-210, 2020

Authors: Zhao, Wenliang | Liu, Cong | Li, Yujing | Fan, Xue | Wang, Xiuhe

Article Type: Research Article

Abstract: This paper presents a novel design strategy for surface inset permanent magnet (SIPM) motors to suppress torque pulsations and maintain the high output torque by integrating the magnet skewing and asymmetrical rotor configurations. The magnet skewing is implemented within one magnet pole pitch to reduce cogging torque by avoiding excessive torque degradation, and the asymmetrical rotor is designed to improve the utilization of the torque components, thus to compensate the decreased torque due to the magnet skewing. To highlight the advantages of the proposed motor, a conventional SIPM motor is adopted for performance comparison with the aid of the finite …element method. As a result, the proposed SIPM motor highly reduced the cogging torque (−79.7%) and torque ripple (−54.7%) while maintaining a high average torque when compared to the conventional SIPM motor. Show more

Keywords: Asymmetrical rotor, finite element method, magnet skewing, surface inset permanent magnet motors, torque pulsations

DOI: 10.3233/JAE-209324

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 211-220, 2020

Authors: Zhao, Xianfeng | Zhou, Zhiqi | Liu, Yuan | Yang, Luquan

Article Type: Research Article

Abstract: Magnetic stiffness is one of the important stability parameters of high temperature superconducting levitation systems. Till to now, great efforts have been made to understand levitation properties including flux penetration, magnetization curves, levitation force, ac susceptibilities, etc. In this paper we present a quadratic approximation method for the limit of magnetic stiffness in a high temperature superconducting levitation system based on Kim’s critical state model and Ampère law. The system is composed with a cylindrical permanent magnet (PM) and a coaxial high temperature superconductor (HTS). It is found that the limit of magnetic stiffness depends upon both the penetration history …of shielding currents distribution in HTS and applied magnetic field gradients. Furthermore, the influence of the physical parameters, such as critical current density in HTS and applied magnetic field, on the limits of magnetic stiffness is investigated in detail. The obtained results display that magnetic stiffness decreases with the increasing of critical current density, since shielding currents have not penetrated into the large portion of the HTS. With the increase of applied magnetic field, the magnetic stiffness obtain a larger magnification factor. It is related to the increase of the shielding current penetration volume and the internal magnetic field in HTS. Show more

Keywords: Influence, physical parameters, the limit of magnetic stiffness

DOI: 10.3233/JAE-209325

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 221-227, 2020

Authors: Cai, Yinshan | Dong, Longlei | Zhou, Yanxin

Article Type: Research Article

Abstract: Electrodynamic loudspeakers are the main actuators of the active noise control system, and their harmonic distortion has a detrimental effect on the noise reduction of the system. To improve the performance, this paper proposes a novel narrowband active noise control algorithm with compensating the nonlinearity of the loudspeaker. In the proposed algorithm, the parameters of the controller are obtained by iteration through the filtered-x least mean square algorithm. Meanwhile, they are adjusted in real-time by establishing the online inverse model of the loudspeaker using the Volterra expansion. The simulation experiments for the typical loudspeaker model show that the proposed algorithm …can dramatically improve noise reduction compared to the conventional algorithm. Show more

Keywords: Narrowband active noise control, harmonic distortion, nonlinear compensation

DOI: 10.3233/JAE-209326

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 229-235, 2020

Authors: Ma, Linjie | Dong, Longlei | Han, Yi | Yan, Jian | Zhou, Jiaming

Article Type: Research Article

Abstract: In recent years, the collaborative robots have been widely used in vast fields, like aerospace, industrial, medical and household. Therefore, in robot collision detection, it is more and more important to ensure the safety of robot system. Compared with the traditional methods of installing sensors, a collision detection algorithm based on neural network (NN) is proposed. The current of the joint is estimated by neural network, and the threshold value is set to judge the occurrence of collision. This algorithm does not need to use the dynamic model of the robot, nor the acceleration. Moreover, the algorithm can be easily …applied to existing systems without changing the structure of robots, which reduces the production cost. And a prototype with one degree of freedom (DOF) has been built to verify the validity of the algorithm. Show more

Keywords: Robot manipulator, sensorless, collision detection, motor current, neural network

DOI: 10.3233/JAE-209327

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 237-244, 2020

Authors: Rehman, Abdur | Kim, Byungtaek

Article Type: Research Article

Abstract: This paper deals with the design of SPM vernier machine with high slots/pole/phase q , to get higher torque density as well as improved power factor by applying the concept of series compensation. The torque density of a vernier machine can be enhanced by increasing the number of slots/pole/phase q , but as q increases the drastic increase in the reactance makes the power factor even worse. Therefore, it is general to choose low q , even if higher torque can be obtained with higher q . In this study, the idea of series compensation is applied to get …vernier machine with high q without the low power factor problem. Series compensation is performed by supplying the desired reactive power to the machine from an additional inverter with a floating capacitor. To validate the theoretical analyses, three SPM vernier machines with different q (1 ∼ 3) are designed and then analyzed by using FEM. Show more

Keywords: Floating bridge, maximum torque per ampere (MTPA), open-ended winding vernier motor, dual-inverter drive (DID)

DOI: 10.3233/JAE-209328

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 245-253, 2020

Authors: Sasayama, Teruyoshi | Yoshimura, Wataru | Enpuku, Keiji

Article Type: Research Article

Abstract: Accurate, easy, and fast inspection of defects on the backside of thick steel plates is essential for the maintenance of infrastructures. Low frequency eddy current testing (LF-ECT) is a promising method to detect defects of the backside of steel plates, with a thickness of approximately 10 mm. However, it is possible that the signal from the backside defect is smaller than that from the surface magnetic noise, causing difficulty identifying the backside defect. In this study, we propose a method to reduce the surface noise by employing a square wave inverter to generate a harmonic signal (rectangular wave ECT, …or RECT), and the result demonstrates that the surface noise is successfully reduced using the harmonic signal. Show more

Keywords: Eddy current testing, ferromagnetic material, low frequency, square wave inverter, rectangular wave ECT

DOI: 10.3233/JAE-209329

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 64, no. 1-4, pp. 255-262, 2020