Bubble domain propagation dynamics in field-access permalloy driving circuits

To improve the understanding of the bubble domain propagation a stroboscopic investigation of bubble displacement with a permalloy T-bar overlay was undertaken at various values of drive field rotation rate. In addition to stepwise change of bubble wall velocity, variation distortion of the bubble shape in the process of propagation and an asynchronous lag of the bubble relative to the drive field vector were also observed, the lag increasing with the rotation rate. To explain these results a simplified method for determining the bubble position in a magnetostatic well was proposed whereby elements of the permalloy overlay was divided into elementary rectangular components. The computed data are in good agreement with the experimental findings and this permits explanation of a number of phenomena observed in bubble circuits.     

On the theory of bubble domain motion in propagation circuits

The stability conditions for a bubble domain in the fields of magnetostatic traps are analyzed. For this purpose the quasi-stationary equations of bubble motion are derived which take into account field nonuniformity across the bubble diameter. The contribution of the Permalloy overlay is considered qualitatively. The conditions of static and dynamic stability of trapped bubbles are studied and the stability role in the operating margin development is analyzed.     

Magnetiostatic interactions in some bubble-domain propagation circuits

Cylindrical magnetic domain (CMD) propagation actually comes to the generation of magnetostatic traps (MST) which successively "capture" the domains on their way along the propagation path. There are three types of MST which correspond to three types of magnetostatic interactions between a domain magnetization and "active" elements of propagation circuits. An interaction of CMD magnetization with ferromagnetic overlay (the third type of an interaction) can generate MST with the maximum depth of approximately 16 Oe. NIST depth in practical propagation circuits is bound to be 6-10 Oe. The data rate upper limit for the techniques using the interaction of CMD and ferromagnetic overlay is determined by the minimum time interval necessary for domain capture by MST and for orthoferrites, which is approximately 1 Mbit/s. The rare-earth orthoferrite single crystals synthesized by the floating zone technique were used throughout the experiments.     

Wave propagation along domain walls in magnetic films

It is shown by theoretical analysis that domain walls can support two different types of waves denoted as "magnetostatic interface waves" and "wall displacement waves". The magnetostatic interface waves are similar in character to magnetostatic surface waves. The wall displacement waves are analogous to displacement waves on strings and to capillary waves on the surface of liquids, Dispersion relations are derived for both types of waves. The displacement waves are approximately dispersion free at high wavenumbers. At low wavenumbers their dispersion diagram reflects the incipient instability of the straight domain wall against sinusoidal displacement, which occurs as the field gradient is reduced.     

Stroboscopic observation of cylindrical domain propagation in a T-bar structure

A technique of stroboscopic observation has been applied to the examination of the dynamic behavior of cylindrical magnetic domains, in a single crystal platelet of Sm0.55Tb0.45FeO3, propagating around a closed path Permalloy film T-bar structured overlay. Domain propagation is achieved by means of the time-varying magnetic pole configuration induced by a rotating magnetic field in the plane of the Permalloy film. Semiquantitative measurements under conditions of continuous propagation show instantaneous wall velocities varying from almost zero to greater than six times the time-averaged domain velocity. The speed of propagation in this T-bar structure is limited by the design of the comer where domains become trapped. The stroboscopic technique used here should find important application in the dynamic evaluation of designs for domain-propagation structures.     

Theory of sound propagation in superfluid 3He-A

The theory of sound propagation in pair-correlated Fermi liquids developed previously by Wölfle is applied to the Anderson-Brinkman-Morel state, believed to describe ³He -A. The effect of quasiparticle collisions is included. Expressions for the anisotropic sound absorption and velocity valid at arbitrary frequency, temperature, and pressure are derived in terms of averages in momentum space of certain simple functions. Numerical results are in good agreement with lower pressure data but deviate by 10–20% at the melting pressure. The discrepancies are attributed to strong coupling effects not included in the theory.     

Time domain analysis of ultrasonic propagation in a five-region layered structure

This paper presents the results of a study of the propagation of ultrasonic waves incident normally on a five-region model consisting of water/ aluminium/adhesive/aluminium/water layers. The ultrasonic signal power reflected from various interfaces in the multi-layered structure was calculated using the energy partition principle; the ultrasonic attenuation in the various media was taken into account in the study. The phase relationship between the incident and reflected portions of each ultrasonic pulse was followed in detailed calculation. Results of the analysis show excellent correlation with experimental results obtained by pulsing ultrasound at a three-layered structure immersed in water.     

流域网格中嵌入式复杂声源的时域传播仿真

针对声学商业软件较难模拟任意形状、时变复杂声源的声辐射问题,使用有限体积法在时域内求解无声源项亥姆霍兹(Helmholtz)方程,将复杂声源嵌入到有限体积单元节点,推导了由给定声源表面声压或振动位移得到速度势公式,提高了声源处理的灵活性和计算效率。该方法允许对初始场问题及复杂时变声源声辐射进行仿真。对常见声源及二阶圆柱体声源声辐射进行了数值模拟,结果与解析解及商业软件结果进行了对比,误差均小于15%。程序具有良好的封装性及通用性,可以灵活地对不同声源进行组合,得出任意复杂声源时域的传播规律,为复杂声源声辐射等线性声学问题的研究提供了一个可靠的平台。     

Theory of the Landau domain structure for thin samples

We present a theory of the Landau domain structure for Type I superconductors which is applicable in the limit of vanishing penetration depth and for slab widths smaller than the coherence length. Results for the perpendicular critical field compare quite satisfactorily with experiments on Al and Cd.Work submitted in partial fulfillment of the Licenciado's Thesis at the Instituto Balseiro.Universidad Nacional de Cuyo.Comisión Nacional de Energía Atómica.     

Theory of partially coherent electromagnetic fields in the space-frequency domain

We construct the coherent-mode representation for fluctuating, statistically stationary electromagnetic fields. The modes are shown to be spatially fully coherent in the sense of a recently introduced spectral degree of electromagnetic coherence. We also prove that the electric cross-spectral density tensor can be rigorously expressed as a correlation tensor averaged over an appropriate ensemble of strictly monochromatic vectorial wave functions. The formalism is demonstrated for partially polarized, partially coherent Gaussian Schell-model beams, but the theory applies to arbitrary random electromagnetic fields and can find applications in radiation and propagation and in inverse problems.     

Theory of domain wall motion induced by microwave magnetic fields

A general theory is developed that applies to arbitrary polarization and takes account of damping and of the dipolar interaction between domains. The effect of the microwave field on the domain structure can be characterized by a pressure on the domain walls and by an alignment energy, both of which are proportional to the square of the rf magnetic field and become large in the vicinity of a resonance. For circular polarization the pressure tends to decrease the Larmor-domains (domains in which the imposed sense of polarization coincides with the sense of the natural spin precession) for frequencies outside the resonance region. Inside the resonance region, however, the pressure tends to increase the Larmor-domains. A linearly polarized field also exerts a pressure on the domain walls, with the polarity dependent upon the orientation of the field to the wall normal. In a linearly polarized magnetic field the domain walls tend to become aligned parallel to the rf field at frequencies ω near the low-frequency resonance (ω =γHa, γ = gyromagnetic ratio, Ha= anisotropy field) and perpendicular to the rf field at frequencies near the high-frequency resonance (ω = γ[Ha(Ha+ 4πM0)]^1/2, M0= saturation magnetization).     

Theory of thermal conduction when the rate of heat propagation is finite

It is assumed that the rate of increase of entropy and of internal energy depend on the temperature and on the first partial derivative of the temperature with respect to the coordinates and time. This assumption enables us to obtain a heatconduction equation of the hyperbolic type from the law of conservation of energy.     

On the propagation of a weak shock front: Theory and application

Summary In this paper the kinematics of a weak shock front governed by a hyperbolic system of conservation laws is studied. This is used to develop a method for solving problems, involving the propagation of nonlinear unimodal waves. It consists of first solving the nonlinear wave problem by moving along the bicharacteristics of the system and then fitting the shock into this solution field, so that it satisfies the necessary jump conditions. The kinematics of the shock leads in a natural way to the definition of shock-rays, which play the same role as the rays in a continuous flow. A special case of a circular cylinder introduced suddenly in a constant streaming flow is studied in detail. The shock fitted in the upstream region propagates with a velocity which is the mean of the velocities of the linear and the nonlinear wave fronts. In the downstream the solution is given by an expansion wave.With 7 Figures     

Application of 3D time domain boundary element formulation to wave propagation in poroelastic solids

The dynamic responses of fluid-saturated semi-infinite porous continua to transient excitations such as seismic waves or ground vibrations are important in the design of soil-structure systems. Biot's theory of porous media governs the wave propagation in a porous elastic solid infiltrated with fluid. The significant difference to an elastic solid is the appearance of the so-called slow compressional wave. The most powerful methodology to tackle wave propagation in a semi-infinite homogeneous poroelastic domain is the boundary element method (BEM). To model the dynamic behavior of a poroelastic material in the time domain, the time domain fundamental solution is needed. Such solution however does not exist in closed form. The recently developed ‘convolution quadrature method’, proposed by Lubich, utilizes the existing Laplace transformed fundamental solution and makes it possible to work in the time domain. Hence, applying this quadrature formula to the time dependent boundary integral equation, a time-stepping procedure is obtained based only on the Laplace domain fundamental solution and a linear multistep method. Finally, two examples show both the accuracy of the proposed time-stepping procedure and the appearance of the slow compressional wave, additionally to the other waves known from elastodynamics.     

Theory of normal-zone propagation along a superconducting wire with allowance for thermal-relaxation processes

For high velocity of a longitudinal propagation of a normal zone along a superconducting wire, one should take into account heat-flux relaxation processes. In such cases these waves are described by a hyperbolic heat-transfer equation, which involves not only the heat-source function but also its derivative. The relaxation effects lead to a limitation of possible values of the normal-zone velocities and to the nonuniqueness of wave solutions. Moreover, the relationships that determine the temperature field in a wire and the propagation speed of the normal zone are obtained. The transient boundary condition between the wire and substrate (e.g., helium bath) is deduced from a heat-flux relaxation theory.     

Plane wave propagation and domain of influence in fractional order thermoelastic materials with three-phase-lag heat transfer

The domain of influence theorem for the fractional order theory of anisotropic thermoelastic materials with three-phase-lag heat transfer is proposed. The fractional order theory of thermoelasticity with three-phase-lag heat transfer has been used to investigate the problem. The plane wave propagation in anisotropic thermoelastic medium having a fractional order derivative in the context of three-phase-lag model of thermoelasticity is studied. The governing equations for a transversely isotropic three-phase-lag model are reduced as a special case. Some wave characteristics are computed numerically and presented graphically.