Magnetizing of permanent magnets using HTS bulk magnets

A demagnetized Nd–Fe–B permanent magnet was scanned just above the magnetic pole which contains the HTS bulk magnet generating a magnetic field of 3.27 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. We examined the magnetic field distributions when the magnetic poles were scanned twice to activate the magnet plate inversely with various overlap distances between the tracks of the bulk magnet. The magnetic field of the “rewritten” magnet reached the values of the magnetically saturated region of the material, showing steep gradients at the border of each magnetic pole. As a replacement for conventional pulse field magnetizing methods, this technique is proposed to expand the degree of freedom in the design of electromagnetic devices, and is proposed as a novel practical method for magnetizing rare-earth magnets, which have excellent magnetic performance and require intense fields of more than 3 T to be activated.     

基于迟滞观测器的压电堆补偿控制

压电堆具有反应速度快、能量密度高等特点被广泛应用于精密仪器的作动装置.然而,压电堆输出位移与驱动电压之间存在的迟滞效应会严重影响控制精度.为了补偿迟滞效应带来的影响,提升控制效果,提出了一种基于滑模变结构理论的类Luenberger迟滞观测器,观测器的设计不仅考虑到了模型中的不确定因素,还可在一定程度上减小外部扰动带来...     

A piezoelectric motor using flexural vibration of a thin piezoelectric membrane

This paper describes a new implementation of a disk-type piezoelectric motor, whose stator is a commercial available piezomembrane composed of a nickel alloy disk to which a piezoceramic disk is bonded. The two disks are concentric, and the total thickness is very small. Ultrasonic motors are based on the concept of driving a rotor by mechanical vibration excited on a stator, via the piezoelectric effect. The rotor is in contact with the stator, and the driving force is the frictional force between rotor and stator. To transform the mechanical vibration of the stator in the rotor rotation, a traveling wave must be excited on the stator surface. The proposed motor can be regarded as a disk-type, single wavelength motor in which the traveling wave is due to the natural flexural vibration of the piezomembrane at low frequency. The behavior of the stator is analyzed both theoretically, by using the theory of isotropic and homogeneous vibrating plates, and by means of a commercial finite element computer code, finding a good agreement with the experimental results. The main features of the motor are very small thickness, appreciable torque, and high speed, obtained with low input power at low voltage; the intended application is to substitute the moving-coil in analogic instrumentation.     

Reducing friction-induced vibration using intelligent active force control (AFC) with piezoelectric actuators

In this paper, a novel approach to reduce the effect of mode coupling that causes friction induced vibration (FIV) is proposed by applying an intelligent active force control (AFC)-based strategy employing piezoelectric actuators with hysteresis effect to a simplified two degree-of-freedom mathematical model of a friction-induced vibration system. At first, the model is simulated and analysed using a closed loop pure Proportional-Integral-Derivative (PID) controller. Later, it is integrated with the intelligent AFC with fuzzy logic (FL) estimator and simulated under similar operating condition. After running several tests with different sets of operating and loading conditions, the results both in time and frequency domains show that the PID controller with the intelligent AFC is much more effective in reducing the vibration, compared to the pure PID controller alone.     

Hydrogen as a working atmosphere for manufacturing permanent magnets based on rare-earth metals

The phase compositions and magnetic properties of permanents magnets of the systems Sm – Co and Nd – Fe – B are analyzed. Features of the hydrogenation–disproportionation–desorption–recombination (HDDR) process in the Nd₂ Fe₁₄ B intermetallic are considered. Using the Dd – Fe – B system as an example, we assess stages of manufacture of commercial permanent magnets and show the prospect of using hydrogen as a working atmosphere for the manufacture of magnetic powder. It is established that the HDDR of Dd – Fe – B alloys leads to their homogenization, grain refinement to a grain size of 0.2 to 0.5 μm, and an increase in the volume content of the main ferromagnetic phase Dd₂ Fe₁₄ B. By optimizing such a treatment, we managed to increase the magnetic energy (by 10%) and the lift force (by 25 – 27%) of Dd – Fe – B commercial permanent magnets.     

利用永磁体的室温磁制冷机性能研究

介绍了利用1.5 T永磁体驱动,氦气作为换热流体,采用主动式磁回热器的室温磁制冷机的实验研究情况.在现有实验装置下,通过调节气体压力与循环频率,高低温端最大达到了10.7K的温差,研究结果为室温磁制冷机的设计以及进一步发展提供了参考.     

Experimental study on the performance of a room temperature magnetic refrigerator using permanent magnets

An investigation of a room temperature active magnetic refrigerator was carried out in this work. An experimental rig was built, in which two reciprocating regenerative beds packed with 1167.4 g of gadolinium were used, helium gas was used as a heat transfer fluid, and an average 1.5 T magnetic field was supplied by permanent magnets. With this apparatus, the influence of the gas pressure, the operating frequency and the temperature range were studied systematically. The lowest no heat load temperature of −2.79 °C at the cold end heat exchanger and a maximum no heat load temperature span of 42.28 °C were obtained. A maximum cooling power of 51.3 W was achieved over a temperature span of 18.16 °C. The results in this study provide useful data for future design and development of room temperature magnetic refrigerators.     

Mechanisms for the longitudinal recoil force in railguns based on the Lorentz force law

In this paper, the electric induction force due to a time-varying current is used to account for the longitudinal recoil force exerted on the rails of railgun accelerators. The analysis is based on the Lorentz force law. The paper shows that the induction force is longitudinal to the rails, and that its magnitude depends on the location, speed, and acceleration of the armature, and can be the strongest at the heads of the rails as observed in experiments.     

Micromachined piezoelectric force sensors based on PZT thin films

A micromachined lead zirconate titanate (PZT) force sensor for scanning force microscope (SFM) is conceptualized by its piezoelectricity. The fabrication procedure is interpreted, and mechanical characteristics of the micromachined PZT force sensors with various lengths are studied in this paper. A compact SFM is constructed by using the piezoelectric PZT sensor. A very clear image is taken by this SFM. The current study of the micromachined PZT force sensor can be considered as a breakthrough of design of SFM as well as a good example of integrated piezoelectric microdevices     

Lorentz force actuation of a heated atomic force microscope cantilever

We report Lorentz force-induced actuation of a silicon microcantilever having an integrated resistive heater. Oscillating current through the cantilever interacts with the magnetic field around a NdFeB permanent magnet and induces a Lorentz force that deflects the cantilever. The same current induces cantilever heating. With AC currents as low as 0.2 mA, the cantilever can be oscillated as much as 80 nm at resonance with a DC temperature rise of less than 5 °C. By comparison, the AC temperature variation leads to a thermomechanical oscillation that is about 1000 times smaller than the Lorentz deflection at the cantilever resonance. The cantilever position in the nonuniform magnetic field affects the Lorentz force-induced deflection, with the magnetic field parallel to the cantilever having the largest effect on cantilever actuation. We demonstrate how the cantilever actuation can be used for imaging, and for measuring the local material softening temperature by sensing the contact resonance shift.     

Nonlinear vibration of the piezoelectric nanobeams based on the nonlocal theory

This paper investigates the nonlinear vibration of the piezoelectric nanobeams based on the nonlocal theory and Timoshenko beam theory. The piezoelectric nanobeam is subjected to an applied voltage and a uniform temperature change. The nonlinear governing equations and boundary conditions are derived by using the Hamilton principle and discretized by using the differential quadrature (DQ) method. A direct iterative method is employed to determine the nonlinear frequencies and mode shapes of the piezoelectric nanobeams. A detailed parametric study is conducted to study the influences of the nonlocal parameter, temperature change and external electric voltage on the size-dependent nonlinear vibration characteristics of the piezoelectric nanobeams.     

基于PVDF压电传感器测量振动结构体积位移

控制振动板结构的体积位移是降低结构总声功率的一种有效策略。本文以工程常见四端位移为零的振动板为例，提出一种新的压电式传感器的设计方法测量体积位移。利用正弦函数展开近似表示固定板振动位移，通过设计特殊形状的PVDF压电薄膜，使PVDF输出信号为所需要的振动结构体积位移。结果表明这种体积位移传感器不仅适用四边简支、四边固定以及介于两者之间的边界条件板结构，而且作为一种误差传感器测量振动结构体积位移是可行的。并对实验数据进行了分析比较。     

Free vibration of laminated piezoelectric composite plates based on an accurate theory

An accurate theory for laminated piezoelectric composite plates in cylindrical bending is developed for free vibration analysis. The displacement and electric potential fields are depicted approximately by the accurate displacement and electric potential distribution functions through thickness, respectively. The two functions are formulated according to particular solutions to the three-dimensional elasticity equilibrium equations and the electrostatics charge equation. The complicated electromechanical coupling relations and the interfacial continuity conditions are enforced. Accordingly the two functions are coupled and make the displacement and potential fields coupled. The governing equations use only four displacement and potential variables, the number of which is independent of the number of layers involved. A corresponding finite element model is also developed. Natural frequencies of piezoelectric laminates subjected to different sets of boundary conditions are given and parameter studies are conducted in numerical examples. The high accuracy of this theory is demonstrated by comparing the present results with the existing exact three-dimensional solutions.     

Nonlinear vibration of piezoelectric nanoplates using nonlocal Mindlin plate theory

ABSTRACT

This article investigates the nonlinear vibration of piezoelectric nanoplate with combined thermo-electric loads under various boundary conditions. The piezoelectric nanoplate model is developed by using the Mindlin plate theory and nonlocal theory. The von Karman type nonlinearity and nonlocal constitutive relationships are employed to derive governing equations through Hamilton's principle. The differential quadrature method is used to discretize the governing equations, which are then solved through a direct iterative method. A detailed parametric study is conducted to examine the effects of the nonlocal parameter, external electric voltage, and temperature rise on the nonlinear vibration characteristics of piezoelectric nanoplates.     

Axisymmetric vibration of infinite piezoelectric cylinders using one-dimensional finite elements

A general finite-element analysis for infinite piezoelectric cylinders has been formulated. The classical three-dimensional elasticity equations of motion are used. The dependence on theta, z, and time are included by assuming appropriate trigonometric functions, and the three-dimensional problem is reduced to a one-dimensional finite element with four degrees of freedom per node. The tabulated results are limited to cylinders with stress-free, shorted electrode (phi=0) boundary conditions at the outside surface of the cylinder. However, solutions for a variety of boundary conditions are possible. Solutions for the piezoelectric cylinder compare favorably with the existing literature. The motion of piezoelectric cylinders with thin coatings is analyzed by modeling the cylinder and thin coating as a layered cylinder.     

Optimizing ultrasonic transducers based on piezoelectric composites using a finite-element method

A novel approach to understanding the vibratory behavior of composite piezoelectric materials is proposed. Elementary ceramic rods, and the effects of their width-to-thickness (W/T) ratio are studied. A model based on the finite-element methods is used. Some experimental results that agree well with the computed data are presented. Plots of resonant frequencies and coupling coefficients versus W/T are given that can be used in transducer design.     

Separation of small nonferrous particles using an inclined drumeddy-current separator with permanent magnets

This paper presents a method for separating small metallic nonferrous particles from two-component nonferrous mixtures using, a new type of dynamic eddy-current separator with permanent magnets. The so-called inclined drum eddy-current separator (IDECS) consists of an inclined vertical rotary drum covered with permanent magnets, alternately N-S and S-N oriented, directly fixed on the axis of an electric engine. The particles to be separated are brought into the field on an oblique trajectory, hit the drum, and are deflected in the variable field under electrodynamic and mechanical interactions. The strongly conducting and poorly conducting particles assume different trajectories depending on their electrical conductivities, which lead to their separation. The paper presents the results of grade and recovery of wastes consisting of small particles (under 5 mm) derived from Cu-Pb and Cu-Al mixtures. The advantages of IDECS are that its efficiency is close to that of the usual dynamic eddy-current separator and its equipment cost is lower. A disadvantage is that the intermediate product must be passed again through a separation process     

Surface effects on free vibration of piezoelectric functionally graded nanobeams using nonlocal elasticity

Free vibration of functionally graded material (FGM) nanobeams is investigated by considering surface effects including surface elasticity, surface stress, and surface density as well as the piezoelectric field using nonlocal elasticity theory. The balance conditions between the nanobeam bulk and its surfaces are satisfied assuming a cubic variation for the normal stress, ${\sigma_{zz}}$ , through the piezoelectric FG nanobeam thickness. Accordingly, the surface density is introduced into the governing equation of the free vibration of nanobeams. The results are obtained for various gradient indices, voltage values of the piezoelectric field, nanobeam lengths, and mode numbers. It is shown that making changes to voltage values and modifying mechanical properties of piezoelectric FGM nanobeams are two main approaches to achieve desired natural frequencies.     

Genetic algorithm based optimal design for vibration control of composite shell structures using piezoelectric sensors and actuators

The present article deals with the design of optimal vibration control of smart fiber reinforced polymer (FRP) composite shell structures using genetic algorithm (GA) based linear quadratic regulator (LQR) and layered shell coupled electro-mechanical finite element analysis. Open loop procedure has been used for optimal placement of actuators considering the control spillover of the higher modes to prevent closed loop instability. An improved real coded GA based LQR control scheme has been developed for designing an optimal controller in order to maximize the closed loop damping ratio while keeping actuators voltages within limit. Results show that increased closed loop-damping has been achieved with a large reduction of control effort considering control spillover.