“电-磁”原理在电梯检验中的应用

在电梯设备的正常运行中,存在着大量基于“电-磁”原理作用的元器件,这些元器件依靠着内部磁能和电能的相互转化,最终可以驱动大量的机械元件,把电源侧的电能转化为电梯可以利用的机械能。文中主要讨论在电梯检验中如何利用该原理对电动机、制动器的一些失效原因进行分析,最后提出建议。

First‑principles study on electronic structure,optical and magnetic properties of rare earth elements X(X=Sc,Y,La,Ce,Eu)doped with two‑dimensional GaSe

The electronic structure,magnetic,and optical properties of two-dimensional(2D)GaSe doped with rare earth elements X(X=Sc,Y,La,Ce,Eu)were calculated using the first-principles plane wave method based on den-sity functional theory.The results show that intrinsic 2D GaSe is a p-type nonmagnetic semiconductor with an indi-rect bandgap of 2.6611 eV.The spin-up and spin-down channels of Sc-,Y-,and La-doped 2D GaSe are symmetric,they are non-magnetic semiconductors.The magnetic moments of Ce-and Eu-doped 2D GaSe are 0.908μ_(B)and 7.163μ_(B),which are magnetic semiconductors.Impurity energy levels appear in both spin-up and spin-down chan-nels of Eu-doped 2D GaSe,which enhances the probability of electron transition.Compared with intrinsic 2D GaSe,the static dielectric constant of the doped 2D GaSe increases,and the polarization ability is strengthened.The ab-sorption spectrum of the doped 2D GaSe shifts in the low-energy direction,and the red-shift phenomenon occurs,which extends the absorption spectral range.The optical reflection coefficient of the doped 2D GaSe is improved in the low energy region,and the improvement of Eu-doped 2D GaSe is the most obvious.

A wireless magnetic sensor for localizing in-vivo medical micro-devices

In order to measure the position and orientation of in-vivo medical micro-devices without the line-of- sight constraints, a wireless magnetic sensor is developed for an electromagnetic localization method. In the electromagnetic localization system, the wireless magnetic sensor is embedded in the micro-devices to measure alternating magnetic signals. The wireless magnetic sensor is composed of an induction coil, a signal processor, a radio frequency （R.F） transmitter, a power manager and batteries. Based on the principle of electromagnetic induction, the induction coil converts the alternating magnetic signals into electrical signals. Via the RF transmitter, the useful data am wirelessly sent outside the body. According to the relation between the magnetic signals and the location, the position and orientation of the micro-devices can be calculated. The experiments demonstrate the feasibility of localizing in-vivo medical micro-devices with the wireless magnetic sensor. The novel localization system is accurate and robust.

Transient Dynamics of Light Propagation in A-Atom EIT Medium

We investigate the transient phenomenon or property of the propagationof an optical probe field in a medium consisting of many A-type three-level atoms coupled to this probe field and a classical driven field. We observe a hidden symmetry and obtain an exact solution for this light propagation problem by means of the spectral generating method. This solution enlightens us to propose a practical protocol implementing the quantum memory robust for quantum decoherence in a crystal. As a transient dynamic process this solution also manifests an exotic result that a wave-packet of light will split into three packets propagating at different group velocities. It is argued that "super-luminal group velocity" and "sub-luminal group velocity" can be observed simultaneously in the same system. This interesting phenomenon is expected to be demonstrated experimentally.

First Principles Study of the Electronic and Magnetic Properties of Ce Doped SrMnO3

The electronic and magnetic properties of Ce doped SrMnO3 have been investigated us- ing the pseudo-potential plane wave method within the generalized gradient approximation method by first principles. The different Mn-O bond lengths indicate that there is a strong Jahn-Teller distortion of the MnO6 octahedron, which associates with a structural phase transition from cubic symmetry （Pm3m） to tetragonal symmetry （I4/mcm）, and the Jahn- Teller ordering stabilizes a chain like （C-type） antiferromagnetie ground state. The electronic structures indicate that SrMnO3 and Sr1-xCexMnO3 （z=0.125 and 0.25） are semiconductor and metallic, respectively. The doping of SrMnO3 with cerium induces simultaneously a decrease in the electrical resistivity, which can be attributed to the formation of Mn3＋ as a result of charge compensation. The density of states and charge density map present that hybridization exists between some of O bands with those of Mn and Ce bands, the bonding between Sr and O is mainly ionic. Density of states and magnetic moment calculations show that the formal valence state of the Ce ion is trivalence.

Fine analysis on advanced detection of transient electromagnetic method

Fault fracture zones and water-bearing bodies in front of the driving head are the main disasters in mine laneways,thus it is important to perform their advanced detection and prediction in advance in order to provide reliable technical support for the excavation.Based on the electromagnetic induction theory,we analyzed the characteristics of primary and secondary fields with a positive and negative wave form of current,proposed the fine processing of the advanced detection with variation rate of apparent resistivity and introduced in detail the computational formulae and procedures.The result of physical simulation experiments illustrate that the tectonic interface of modules can be judged by first-order rate of apparent resistivity with a boundary error of 5%,and the position of water body determined by the fine analysis method agrees well with the result of borehole drilling.This shows that in terms of distinguishing structure and aqueous anomalies,the first-order rate of apparent resistivity is more sensitive than the secondorder rate of apparent resistivity.However,some remaining problems are suggested for future solutions.

Electronic Structure and Magnetic Properties of Cu[C(CN)_3]_2 and Mn[C(CN)_3]_2 Based on First Principles

The electronic structure and the magnetic properties of the molecule-based ferromagnets Cu[C（CN）3]2 and Mn[C（CN）3]2 are studied according to first principles within density-functional theory （DFT） and the full potential linearized augmented plane wave （FP-LAPW） method. The total energy, atomic spin magnetic moments, and density of states （DOS） of Cu[C（CN）3]2 and Mn[C（CN）3]2 are all calculated. The calculations reveal that the compounds have a stable ferromagnetic ground state and half-metallic properties. The total spin magnetic moment is 1.0μB for Cu[C（CN）3]2 and 5.0#B for Mn[C（CN）3]e per molecule, the magnetic moment mainly comes from metal atoms, although there is a slight contribution from N and C atoms.

SIMULATION RESEARCH ON CHARACTERISTICS OFPERMANENT MAGNET LINEAR SYNCHRONOUS MOTOR

In this paper, a simulation model of Permanent Magnet Linear Synchronous Motor (PMLSM) is established by using phase equations method. Special attention is paid to its structure and the influence of longitudinal end effect and the unbalance of current. The analytic method can be used for the analysis of dynamic and static characteristics of PMLSM.

Highly Effective Brushless DC Motor in Which Unidirectional Current Flows in

Authors developed a highly effective brushless DC motor with a simple operation principle. If the operation principle of the motor is simple, a drive circuit will also become simple and its production cost will be lower. From the above fact, Minato motor was noticed. In this motor, a unidirectional current flows in the electromagnets. In other words, unidirectional windings are used. In this motor, only strong repulsive force is utilized when a permanent magnet of a rotor and an electromagnet of a stator are adjacent. Hence, torque constant becomes higher and the efficiency of the motor is high. However, an effective value of the electromagnetic current increases because a large current flows in a short period. Therefore, copper loss increases and the efficiency of the motor decreases. In order to solve above defects, a new motor is proposed. From the experiment, it is clarified that the efficiency of the proposed motor is higher than that of the commercial motors.

First-principles studies of multiferroic and magnetoelectric materials

Multiferroics are materials where two or more ferroic orders coexist owing to the interplay between spin, charge, lattice and orbital degrees of freedom. The explosive expansion of multiferroics literature in recent years demonstrates the fast growing interest in this field. In these studies, the first-principles calculation has played a pioneer role in the experiment explanation, mechanism discovery and prediction of novel multiferroics or magnetoelectric materials. In this review, we discuss, by no means comprehensively, the extensive applications and successful achievements of first-principles approach in the study of multiferroicity, magnetoelectric effect and tunnel junctions. In particular, we introduce some our recently developed methods, e.g., the orbital selective external potential method, which prove to be powerful tools in the finding of mechanisms responsible for the intriguing phenomena occurred in multiferroics or magnetoelectric materials. We also summarize first-principles studies on three types of electric control of magnetism, which is the common goal of both spintronics and multiferroics. Our review offers in depth understanding on the origin of ferroelectricity in transition metal oxides, and the coexistence of ferroelectricity and ordered magnetism, and might be helpful to explore novel multiferroic or magnetoelectric materials in the future.

The form-invariance of wave equations without requiring a priori relations between field variables

According to the principle of relativity,the equations describing the laws of physics should have the same forms in all admissible frames of reference,i.e.,form-invariance is an intrinsic property of correct wave equations.However,so far in the design of metamaterials by transformation methods,the form-invariance is always proved by using certain relations between field variables before and after coordinate transformation.The main contribution of this paper is to give general proofs of form-invariance of electromagnetic,sound and elastic wave equations in the global Cartesian coordinate system without using any assumption of the relation between field variables.The results show that electromagnetic wave equations and sound wave equations are intrinsically form-invariant,but traditional elastodynamic equations are not.As a by-product,one can naturally obtain new elastodynamic equations in the time domain that are locally accurate to describe the elastic wave propagation in inhomogeneous media.The validity of these new equations is demonstrated by some numerical simulations of a perfect elastic wave rotator and an approximate elastic wave cloak.These findings are important for solving inverse scattering problems in many fields such as seismology,nondestructive evaluation and metamaterials.

Principles of electromagnetic waves in metasurfaces

Metasurfaces are artificially structured thin films with unusual properties on demand. Different from metamaterials, the metasurfaces change the electromagnetic waves mainly by exploiting the boundary conditions, rather than the constitutive parameters in three dimensional(3D) spaces. Despite the intrinsic similarities in the operational principles, there is not a universal theory available for the understanding and design of metasurface-based devices. In this article, we propose the concept of metasurface waves(M-waves) and provide a general theory to describe the principles of them. Most importantly, it is shown that the M-waves share some fundamental properties such as extremely short wavelength, abrupt phase change and strong chromatic dispersion, which make them different from traditional bulk waves. It is shown that these properties can enable many important applications such as subwavelength imaging and lithography, planar optical devices, broadband anti-reflection, absorption and polarization conversion. Our results demonstrated unambiguously that traditional laws of diffraction, refraction, reflection and absorption should be revised by using the novel properties of M-waves. The theory provided here may pave the way for the design of new electromagnetic devices and further improvement of metasurfaces. The exotic properties of metasurfaces may also form the foundations for two new sub-disciplines called "subwavelength surface electromagnetics" and "subwavelength electromagnetics".

Numerical Analysis of Electromagnetic Fields in Multiscale Model

Modeling technique for electromagnetic fields excited by antennas is an important topic in computational electromagnetics, which is concerned with the numerical solution of Maxwell's equations. In this paper, a novel hybrid technique that combines method of moments(MoM) with finite-difference time-domain(FDTD) method is presented to handle the problem. This approach employed Huygen's principle to realize the hybridization of the two classical numerical algorithms. For wideband electromagnetic data, the interpolation scheme is used in the MoM based on the dyadic Green's function. On the other hand, with the help of equivalence principle, the scattered electric and magnetic fields on the Huygen's surface calculated by MoM are taken as the sources for FDTD. Therefore, the electromagnetic fields in the environment can be obtained by employing finite-difference time-domain method. Finally, numerical results show the validity of the proposed technique by analyzing two canonical samples.