Magnetic Stiffness Research Articles

1216 エレベーター用巻上機の振動による居室騒音の検討(OS0-1 交通・物流システムの解析と開発,OS0 交通・物流一般,オーガナイズド・セッション(OS))

An elevator is an important transportation device. Recently, due to downsizing and weight saving of traction machine, the magnetic flux density increases and stiffness of the structure decreases. Therefore, vibration of traction machine may propagate to near-by room and produce acoustic noise and vibration in the room. If in design phase, whole simulation of vibration and acoustic noise from the motor to the room is performed, reduction measures are provided effectively at noise source, propagation path and noise radiation points. In this paper, the comparison and examination result on the cooperation analysis of the electromagnet, structure and noise for predicting room noise and measurement are reported.

A Study on Mathematical Model of Servo Valve Torque Motor

In this paper, a comprehensive theoretical analysis of servo valve torque motor that includes the ignored magnetic reluctance of magnetic elements is carried out. These analyses are based on fundamental laws of electromagnetism and general mechanics, thus a new mathematical model of servo valve torque motor is derived to improve the accuracy of the model. When using this model structure to fit the simulation data of electromagnetic torque constant and magnetic spring stiffness, the result render closer agreement with than when using existing models.

Non‐invasive assessment of liver fibrosis using magnetic resonance elastography in liver transplant recipients with hepatitis C

Liver biopsy has been the reference standard when evaluating fibrosis due to recurrent hepatitis after liver transplantation. Magnetic resonance elastography estimates liver stiffness, correlating to fibrosis. To investigate the utility of elastography in staging liver fibrosis in transplant recipients with hepatitis C. Fifty-four patients, ≥12 months post-transplant, underwent elastography within three months of biopsy. Discriminatory capability for METAVIR fibrosis stages F0-2 vs. F3-4 and receiver operating characteristic curve (ROC) analysis were determined. On biopsy, 27 patients had METAVIR fibrosis score 0-1; 12 had a 3 or 4. There was significant correlation between histologic fibrosis and shear stiffness (R² = 0.588, p < 0.0001). Using a cutoff value of 3.5 kPa, elastography was 91% sensitive and 72% specific in differentiating fibrosis scores of ≥3 from 0 to 1. The AUC of elastography in predicting a fibrosis score of ≥3 was 0.92. Multivariate analysis revealed no correlation between the grade of histologic inflammation and liver stiffness measured by magnetic resonance elastography (R² = 0.265, p = 0.47). Magnetic resonance elastography is an accurate non-invasive technique for excluding stage ≥3 graft in recipients with hepatitis C.

MR elastography derived shear stiffness-a new imaging biomarker for the assessment of early tumor response to chemotherapy

The overall goal is to develop magnetic resonance elastography derived shear stiffness as a biomarker for the early identification of chemotherapy response, allowing dose, agent type and treatment regimen to be tailored on a per patient basis, improving therapeutic outcome and minimizing normal tissue toxicity. The specific purpose of this study is to test the feasibility of this novel biomarker to measure the treatment response in a well-known chemotherapy model. Tumors were grown in the right flank of genetically modified mice by subcutaneous injection of DoHH2 (non-Hodgkin's lymphoma) cells. Magnetic resonance elastography was used to quantify tumor stiffness before and after injection of a chemotherapeutic agent or saline. Histological tests were also performed on the tumors. A significant decrease (P < 0.0001) in magnetic resonance elastography-derived tumor shear stiffness was observed within 4 days of chemotherapy treatment, while no appreciable change was observed in saline-treated tumors. No significant change in volume occurred at this early stage, but there were decreased levels of cellular proliferation in chemotherapy-treated tumors. These results demonstrate that magnetic resonance elastography-derived estimates of shear stiffness reflect an initial response to cytotoxic therapy and suggest that this metric could be an early and sensitive biomarker of tumor response to chemotherapy.

Eccentricity Related Forces in Two-Pole Induction Motor With Four-Pole Stator Damper Winding Analyzed Using Measured Rotor Orbits

A two-pole induction motor has been fitted with an extra three-phase four-pole stator winding to damp the unbalanced magnetic pull caused by eccentricity. In traditional two-pole induction machines, the interaction of two- and four-pole flux produces most of the magnetic forces. That force is greatly reduced if the four-pole stator winding is used to damp the four-pole flux. This causes some of the other magnetic force components to become more significant. This paper presents an estimate of what components comprise the total force on rotor and how they change when the speed, torque, and two-pole flux density of the machine are changed. The rotor is on a long flexible shaft supported by external bearings allowing the forces to move the rotor. Since the magnetic force depends on rotor eccentricity, the comparisons are done to the magnetic stiffness derived from the force. The radial movement of the rotor is measured as well as the two-, four-, and zero-pole (unipolar, homopolar) air-gap magnetic flux densities. All the results are based on measurements with a prototype test machine.

A negative stiffness vibration isolator using magnetic spring combined with rubber membrane

The most important characteristic of a passive vibration isolator is its natural frequency and load capacity. The vibration isolation performance of a passive vibration isolator in low input frequencies is considerably improved by reducing its natural frequency. This paper presents a negative stiffness magnetic suspension vibration isolator (NSMSVI) using a magnetic spring combined with rubber membranes to obtain lower natural frequency. To study the vibration isolation performance of the NSMSVI, the stretching force of the rubber membrane is measured through experiments. The stiffness of the rubber membrane comes from the derivative of the stretching force. A parametric study of load capacity, axial magnetic stiffness, and natural frequency of the magnetic spring is also performed. Consequently, as a case study, the size dimensions of the magnetic spring are determined. An NSMSVI table is set up for experimental validation, after which the transmissibility curves of the NSMSVI are calculated and tested. Experimental results show that the lowest natural frequency of the NSMSVI reaches 1.5 Hz with a maximum attenuation of -40 dB between 0 Hz and 100 Hz, whereas the NSMSVI has the maximum load capacity at the lowest stiffness. This paper essentially provides an efficient method to construct a negative stiffness vibration isolator for practical applications.

Magnetic properties of (Fe1−xNix)72B20Si4Nb4 (x=0.0–0.5) bulk metallic glasses

The effects of partial substitution of Fe by Ni in (Fe1−xNix)72B20Si4Nb4 (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) bulk metallic glasses (BMGs) on their magnetic properties were studied. It is found that the saturation polarization decreases from 1.15T to 0.69T with increasing Ni content from x=0.0 to x=0.5; the Curie temperature reaches its maximum of 598K for composition x=0.1, and is then followed by a quick decrease with higher Ni content. Moreover, the random anisotropy and mean field theory were developed to investigate the magnetic properties of these BMGs, and the variations of saturation polarization and Curie temperature were well explained by calculating the magnetic exchange stiffness constant A and the nearest neighbor transition-metal-pair exchange interactions J by using the model.

Numerical Analysis on the Magneto-Elastic Stability of Current-Carrying Conductors: Aiming at Applications for the Tokamak System

A novel method for calculating the magnetic stiffness matrix was proposed for the numerical analysis of the magneto-elastic stability of complicated current-carrying structures aiming for application in the magneto-elastic behavior of the tokamak system. A code based on the proposed method was developed and applied to the numerical analysis of two typical current-carrying structures. The good consistency of the numerical and analytical results validated the proposed method and the related numerical code.

The essential role of carefully optimized synthesis for elucidating intrinsic material properties of (Ga,Mn)As

(Ga,Mn)As is at the forefront of spintronics research exploring the synergy of ferromagnetism with the physics and the technology of semiconductors. However, the electronic structure of this model spintronics material has been debated and the systematic and reproducible control of the basic micromagnetic parameters and semiconducting doping trends has not been established. Here we show that seemingly small departures from the individually optimized synthesis protocols yield non-systematic doping trends, extrinsic charge and moment compensation, and inhomogeneities that conceal intrinsic properties of (Ga,Mn)As. On the other hand, we demonstrate reproducible, well controlled and microscopically understood semiconducting doping trends and micromagnetic parameters in our series of carefully optimized epilayers. Hand-in-hand with the optimization of the material synthesis, we have developed experimental capabilities based on the magneto-optical pump-and-probe method that allowed us to simultaneously determine the magnetic anisotropy, Gilbert damping and spin stiffness constants from one consistent set of measured data.

Unbalance vibratory displacement compensation for active magnetic bearings

As the dynamic stiffness of radial magnetic bearings is not big enough, when the rotor spins at high speed, unbalance displacement vibration phenomenon will be produced. The most effective way for reducing the displacement vibration is to enhance the radial magnetic bearing stiffness through increasing the control currents, but the suitable control currents are not easy to be provided, especially, to be provided in real time. To implement real time unbalance displacement vibration compensation, through analyzing active magnetic bearings (AMB) mathematical model, the existence of radial displacement runout is demonstrated. To restrain the runout, a new control scheme-adaptive iterative learning control (AILC) is proposed in view of rotor frequency periodic uncertainties during the startup process. The previous error signal is added into AILC learning law to enhance the convergence speed, and an impacting factor β influenced by the rotor rotating frequency is introduced as learning output coefficient to improve the rotor control effects. As a feed-forward compensation controller, AILC can provide one unknown and perfect compensatory signal to make the rotor rotate around its geometric axis through power amplifier and radial magnetic bearings. To improve AMB closed-loop control system robust stability, one kind of incomplete differential PID feedback controller is adopted. The correctness of the AILC algorithm is validated by the simulation of AMB mathematical model adding AILC compensation algorithm through MATLAB soft. And the compensation for fixed rotational frequency is implemented in the actual AMB system. The simulation and experiment results show that the compensation scheme based on AILC algorithm as feed-forward compensation and PID algorithm as close-loop control can realize AMB system displacement minimum compensation at one fixed frequency, and improve the stability of the control system. The proposed research provides a new adaptive iterative learning control algorithm and control strategy for AMB displacement minimum compensation, and provides some references for time-varied displacement minimum compensation.

Unbalance Compensation Control in Active Magnetic Bearings Using Bias Current Excitation

The model of magnetic bearing and vibration producing mechanism were analyzed. A new adaptive law was developed to eliminate the rotor vibration. The adaptive control system for stabilization of the rotor geometric center to the origin was designed by varying magnetic stiffness through excitation of the bias currents. Finally, the simulation results validated the effectiveness of the proposed algorithm

Experiments on the Vibration Control of Flexible Rotor Using Shear Mode MR Elastomer Damper

A shear mode magnetorheological (MR) elastomer damper is designed and manufactured, in which the MR elastomer is made by mixing RTV silicone, carbonyl iron particles and silicone oil, and solidifying under magnetic field. A flexible cantilever rotor system with single disk is constructed, and the controllability, effectiveness and stability of vibration control for the imbalance response of the rotor system using the MR damper are experimentally studied. From the test, it is found that as the strength of applied magnetic field increases, the damping and stiffness of the damper are increased; the critical speeds of the rotor system supported on the MR damper is increased distinctly, and the vibration at two critical speeds are restrained; the on-off control method may be used to control the rotor vibration while passing through the two critical speeds. The study shows that the shear mode MR elastomer damper is suitable for active vibration control of flexible rotor.

An Investigation Into Using Magnetically Attached Piezoelectric Elements for Vibration Control

A novel vibration control method utilizing magnetically mounted piezoelectric elements is described. Piezoelectric elements are bonded to permanent magnets, termed here as control mounts, which are attached to the surface of a steel beam through their magnetic attraction. The magnetic-piezoelectric control mounts are an alternative to traditional epoxy attachment methods for piezoelectric elements which allows for easy in-the-field reconfiguration. In model and laboratory measurements, the beam is driven through base excitation and the resonant shunt technique is utilized to demonstrate the attenuation characteristics of two magnetic-piezoelectric control mounts. The coupled system is discretized using a Galerkin finite element model that incorporates the tangential and vertical contact stiffnesses of the beam-magnet interface. The vibration reduction provided by the control mounts using a single magnet are compared to those designed with a magnetic array that alternates the magnetic dipoles along the length of the mount. Even though each design uses the same magnet thickness, the alternating magnetic configuration's interfacial contact stiffness is over 1.5 and 4 times larger in the tangential and vertical directions, respectively, than that of the single magnet, resulting in increased vibration reduction. Measured and simulated results show that the magnetic-piezoelectric control mounts reduced the beam's tip velocity by as much as 3.0 dB and 3.1 dB, respectively. The design tradeoffs that occur when replacing the traditional epoxy layer with a magnet are also presented along with some methods that could improve the vibration reduction performance of the control mounts. This analysis shows that the control mounts attenuate significant vibration despite having an imperfect bond with the beam, thus providing a viable and adaptable alternative to traditional piezoelectric attachment methods.

A Design Technique for a Magnetic Bearing-Rotor in a Turbo Blower Considering Critical Speeds

This paper introduces a rotor design technique for a turbo blower supported by magnetic bearings that considers the critical speeds of the rotor. An important factor for rotor critical speeds is the stiffness of its bearings. The magnetic bearing acts as a negative spring, called the position stiffness prior to operation, and rotor systems are initially unstable until the stiffness (current stiffness) and damping in the active control rotating system are determined using closed loop control forces. This paper describes a finite element model for the rotor, derives the stiffness equations for the magnetic bearing, and defines the total magnetic bearing stiffness including the position stiffness and current stiffness. Finally, the magnetic bearing stiffness that avoids the rotor critical speeds is chosen.

Transverse wave propagation in elastically confined single-walled carbon nanotubes subjected to longitudinal magnetic fields using nonlocal elasticity models

Lateral wave propagation in an elastically confined single-walled carbon nanotube (SWCNT) experiences a longitudinal magnetic field is examined using nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The SWCNT is modeled via an equivalent continuum structure (ECS) and its interaction with the surrounding elastic medium is simulated via lateral and rotational continuous springs along its length. For the proposed models, the dimensionless governing equations describing transverse vibration of the SWCNT are constructed. Assuming harmonic solutions for the propagated sound waves, the dispersion equation associated with each model is obtained. Subsequently, the explicit expressions of the frequencies as well as the corresponding phase and group velocities, called characteristics of the waves, are derived for the proposed models. The influences of the slenderness ratio, the mean radius of the ECS, the small-scale parameter, the longitudinal magnetic field, the lateral and rotational stiffness of the surrounding matrix on the characteristics of flexural and shear waves are explored and discussed.

Modeling of Axial Magnetic Force and Stiffness of Ring-Shaped Permanent-Magnet Passive Vibration Isolator and Its Vibration Isolating Experiment

Magnetic suspension vibration isolators have attracted more and more attention in the field of semiconductor industry and high precision equipments. A novel ring-shaped permanent-magnet passive vibration isolator is mainly reported in this paper. An analytical expression of axial magnetic force of the isolator is derived and validated by the finite element analysis and experiment. It proves that the analytical expression is efficient. An analytical expression of the axial stiffness of the isolator is deduced by derivative of the axial magnetic force with respect to the axial relative displacement of the inner ring. Furthermore, the parametric study of the axial magnetic force and stiffness are carried out. As a ring-shaped permanent-magnet passive vibration isolator case study, the isolator was constructed by four couples of the ring-shaped permanent magnets. The vibration isolation performance of the isolator was subsequently calculated and tested. The experimental results have shown a good agreement with the calculated ones. It demonstrates that the proposed isolator can realize low-frequency vibration isolation.

Environmental Vibration Induced Magnetic Field Disturbance in MRI Magnet

Environmental vibrations from building and traffic cause the cryostat to move with respect to the magnet cartridge in MRI magnets. The relative motion will create eddy current in cryostat. The eddy current will disturb the magnet central frequency, which creates ghosting in images. This study is aimed at formulating the methodology for a mechanical and electro-magnetic dynamical coupling system, exploring magnetic stiffness and damping and validating the numerical simulation with experimental tests. It has revealed that the magnetic stiffness and damping have played a unique and important role in MRI magnet designs. The reasonably good correlation between simulation and test was observed after magnetic stiffness and magnetic damping are included.

The frequency, amplitude and magnetic field dependent torsional stiffness of a magneto-sensitive rubber bushing

A dynamic torsional stiffness model of a magneto-sensitive circular annular rubber bushing is presented where influences of frequency, amplitude and magnetic field dependence are included. This is achieved by employing a newly developed non-linear magneto-sensitive audio frequency constitutive equation in an engineering formula for the torsional stiffness of a rubber bushing. The engineering stiffness formula predicts the frequency and amplitude dependent stiffness in a simple way, based on geometric dimensions and the shear modulus. The shear modulus is provided by the rubber model. The results from these calculations predict and clearly display the possibility of controlling the magneto-sensitive rubber bushing stiffness over a large frequency range, through the application of a magnetic field.

On the performance of a dual-mode non-linear vibration energy harvesting device

The research trend for harvesting energy from the ambient vibration sources has moved from using a linear resonant generator to a non-linear generator in order to improve on the performance of a linear generator; for example, the relatively small bandwidth, intolerance to mistune and the suitability of the device for low-frequency applications. This article presents experimental results to illustrate the dynamic behaviour of a dual-mode non-linear energy-harvesting device operating in hardening and bi-stable modes under harmonic excitation. The device is able to change from one mode to another by altering the negative magnetic stiffness by adjusting the separation gap between the magnets and the iron core. Results for the device operating in both modes are presented. They show that there is a larger bandwidth for the device operating in the hardening mode compared to the equivalent linear device. However, the maximum power transfer theory is less applicable for the hardening mode due to occurrence of the maximum power at different frequencies, which depends on the non-linearity and the damping in the system. The results for the bi-stable mode show that the device is insensitive to a range of excitation frequencies depending upon the input level, damping and non-linearity.

MR Elastography in Renal Transplant Patients and Correlation with Renal Allograft Biopsy: A Feasibility Study

Magnetic resonance elastography (MRE) images the propagation of mechanical shear waves in tissue and uses that information to generate quantitative measures of tissue stiffness. Hepatic MRE has been successfully performed in thousands of patients, with good correlation between histologic grade of fibrosis and tissue stiffness. There has been no prior investigation of the utility of MRE for the assessment of kidney transplants. The aims of this study were to prospectively evaluate the feasibility of MRE in a small group of kidney transplant recipients and to correlate the measured magnetic resonance elastographic stiffness values with biopsy-proven histopathologic fibrosis. MRE of renal transplants was performed in 11 patients returning for protocol allograft biopsies. Calculated tissue stiffness values were compared to histologic degree of fibrosis in nine of the 11 patients. The mean stiffness of two patients with moderate interstitial fibrosis was higher than the mean of six patients with mild interstitial fibrosis, but not significantly so (90 Hz, P = .12; 120 Hz, P = .17; 150 Hz, P = .26). The mean stiffness of the two patients with moderate interstitial fibrosis was slightly greater than the mean of one patient with no significant interstitial fibrosis at 90 Hz (P = .78) and slightly less at 120 and 150 Hz (P = .88 and P = .76). The mean stiffness of the six patients with mild interstitial fibrosis did not differ significantly from that of the one patient with no interstitial fibrosis (90 Hz, P = .35; 120 Hz, P = .22; 150 Hz, P = .16). Preliminary results demonstrate feasibility and support known multifactorial influences on renal stiffness.