Reflection of electroacoustic waves from a system of moving domain walls in a ferroelectric

The interaction of electroacoustic waves with a periodic domain structure formed in a tetragonal ferroelectric by a finite number of uniformly moving 180° domain walls is considered in the quasi-static approximation. It is established that the inclusion of the domain-wall motion leads to a significant modification of the reflectance spectra of electroacoustic waves according to the number, intensity, and location of the Bragg reflectance peaks.     

Mode spectrum of noncollinear electroacoustic boundary-guided waves in a ferroelectric with a moving strip domain

The mode spectrum of electroacoustic boundary waves guided by a strip domain uniformly moving in a 4-mm ferroelectric is considered in the quasi-static approximation. The motion of the strip domain is found to cause the wave vector of the electroacoustic wave to be noncollinear with the guiding boundaries. The frequency dependences of the phase velocity are presented for the symmetric and antisymmetric modes of the electroacoustic wave. These dependences are compared in the reference system fixed to the strip domain and in the laboratory reference system. It is shown that, at low and moderate frequencies, the symmetric mode of the electroacoustic wave is more efficiently localized by a moving strip domain than by a single domain wall.     

A trapped wave in a ferroelectric with a moving strip domain

The existence of a shear homogeneous plane wave trapped by a strip domain moving uniformly in a tetragonal ferroelectric crystal is demonstrated. Using the nonrelativistic quasistatic approximation and a change to the moving frame of reference, the solution is obtained and the dispersion relation is derived for the spatial spectrum of the trapped wave. The uniqueness of the solution is established in the case of the multiple degeneracy of the roots of the characteristic equation when the trapped wave contains an attached wave in the strip domain. The trapped wave is shown to correspond to the antisymmetric mode of the electroacoustic wave of the strip domain at the initial point of the spectrum branch. The specific features of the spatial resonance of the trapped wave with a shear wave obliquely incident on the strip domain are considered.     

Interaction of a moving domain wall with surface magnetoelastic waves in yttrium orthoferrite

The amplitude-frequency characteristics of magnetoelastic surface waves excited by moving domain walls in a lamellar yttrium orthoferrite samples are discovered and measured. The results of analysis of the effect of magnetoelastic surface waves on the dynamics of domain walls in this orthoferrite are considered. The nonlinear interaction between magnetoelastic surface waves accompanying a moving domain wall is analyzed.     

Analysis of a turbulent compressed flow by a second-order model

This paper is concerned with the simulation of a turbulent flow submitted to a cyclic one-dimensional compression and expansion between two parallel flat pistons moving with opposite velocities in the direction of their perpendicular axis. The turbulence model used is the second-order model developed at a low Reynolds number by Craft and Launder. Numerical results show that the turbulent field may be considered as homogeneous in an extended part of the domain. The confinement effect appears mainly in the vicinity of the moving walls while the central region is especially influenced by the compression effect. The evolution of the heat flux, transferred from the fluid through the moving walls, tends to a zero limit cycle in the turbulent flow and to a non-zero limit cycle in the laminar flow. The disappearance of the turbulent energy is not predicted by the k-l model.     

Effect of the electron energy on the entry blockage interval during electron scattering by a magnetic film with a strip domain structure

The trajectory of electrons in the stray field of a uniaxial magnetic film containing a strip domain structure (SDS) with a magnetization perpendicular to the sample surface are determined by numerical solution of the equations of motion. The interval of angles between the electron velocity projection onto the film surface and domain walls is determined, in which entry blockage takes place (electron scattering occurs without collisions with the sample surface). It is found that an increase in the electron energy leads to a decrease in this angular interval. The results are analyzed for multiple interactions of an electron moving in the gradient field of an SDS with attracting and repelling domain walls.     

Spectral properties of electroacoustic waves in a ferroelectric with a moving periodic domain structure

The propagation of shear waves in a tetragonal ferroelectric with a moving superlattice of 180° domain walls (DW) is considered in a quasistatic approximation. It is found that the spectrum of shear waves consists of alternating allowed and forbidden bands in both cases of static and moving superlattices. It is shown that, due to the Doppler shift in the wave eigenfrequencies, the motion of the DW superlattice causes the degenerate roots of the dispersion equation to split and the splitting increases with the vibration mode number. The acoustic nonreciprocity induced by the moving DW superlattice in the ferroelectric is discussed.     

Excitation spectrum and thermodynamics of domain walls in the biaxial ferromagnet

The problem on spectrum of linear excitations in the presence of a moving domain wall in 1D Heisenberg ferromagnet with orthorhombic anisotropy is exactly solved. The explicit expressions for spin waves scattering on the domain wall are obtained. The phase shift of a spin wave, as the result of collision of spin wave with a moving wall, is exactly determined. The change in magnon density of states is calculated from this scattering data, and the contribution of domain walls to the classical low-temperature thermodynamics is found.     

Dynamics of Particles Trapped by Dissipative Domain Walls

We study the interactions of the dissipative domain walls with dielectric particles. It is shown that particles can be steadily trapped by the moving domain walls. The influence of the ratchet effect on particle trapping is considered. It is demonstrated, that the ratchet effect allows to obtain high accuracy in particle manipulation.

     

Domain wall structure in BaTiO3 during switching

The increase in the complex permittivity during switching is calculated from a two-dimensional model of residual nuclei, assuming that domain walls possess a pyramidal step structure. The resulting formulae are compared with previous experimental data on BaTiO₃ and with corresponding formulae from the same model with smooth walls. It is shown that the real part of the permittivity during switching is very sensitive to the presence of steps on moving domain walls and that there is an indication that in BaTiO₃ such step structure actually exists.     

DYNAMICS OF PLANAR RELATIVISTIC DOMAIN WALLS

The dynamics of planar relativistic domain walls is investigated with the help of a new method proposed by Arodz and Larsen. Two solutions are found: one is a steady state domain wall, the other is a nonstationary domain wall. They move with the same constant velocity in the laboratory frame coordinates. When the velocity approaches light velocity c, the "width" of the nonstationary wall inflates very slowly. These domain walls can disappear again soon after their creation in the early universe by moving away from our visible universe. So they would not dominate the universe completely, but keep the observed universe approximately isotropic and homogeneous.     

The effect of the parameters of ferrite-garnet films on the generation of microdomains in front of a moving domain wall

The agreement between the spin-wave model of the motion of domain walls and the published results of experimental research relating to the generation of microdomains in front of a moving domain wall in ferrite-garnet films with uniaxial magnetic anisotropy is discussed. Institute of General Physics of the Russian Academy of Sciences at Mordova State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 41, No. 12, pp. 77–84, December, 1998.     

Optimization of electroacoustic absorbers by means of designed experiments

In multivariate systems, when it comes to identifying actual operating conditions ranges, or optimal settings, the use of constrained optimization is often required. Among the different tools for the engineer to perform such optimization, designed experiments offer accurate performances. In this paper, the optimization process of “electroacoustic absorbers” is investigated by means of response surface methodology. A multivariate linear model is established by a series of designed experiments in order to analyze the modification of electroacoustic absorber performances due to the variation of several constitutive parameters (such as the moving mass of the loudspeaker, the enclosure volume, the filling density of mineral fiber within the enclosure, and the electrical load value to which the loudspeaker is connected), that influence their whole absorbing mechanisms. A simple case study is then provided to illustrate the capabilities of the developed optimization procedure, from which general conclusions on such design methodology, as well as on electroacoustic absorbers sensitivity, are drawn.     

Crossed-ratchet effects for magnetic domain wall motion

We study both experimentally and theoretically the driven motion of domain walls in extended amorphous magnetic films patterned with a periodic array of asymmetric holes. We find two crossed-ratchet effects of opposite sign that change the preferred sense for domain wall propagation, depending on whether a flat or a kinked wall is moving. By solving numerically a simple phi(4) model we show that the essential physical ingredients for this effect are quite generic and could be realized in other experimental systems involving elastic interfaces moving in multidimensional ratchet potentials.     

Mechanism of the motion of domain walls with spin wave radiation in uniaxial magnetic films

It is shown, using the example of epitaxial ferrite—garnet films with (111) orientation whose dimensionless damping parameter was varied over a wide range, that for uniaxial magnetic films the mechanism of the motion of the domain walls is universal and includes local rotation of the magnetization ahead of the moving domain wall. The threshold field for the transition to this mechanism of motion of the domain walls is proportional to the uniaxial magnetic anisotropy field. On the curve of the dependence of the domain wall velocity on the acting magnetic field, this mechanism corresponds to the section with increased differential mobility of the domain walls. Magnitooptoelktronika Joint Self-Financing Laboratory, N. R. Ogarev Institute of General Physics, Russian Academy of Sciences, Mordovian State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 9–14, July, 1997.     

Dynamics of antiferromagnetic vortices in yttrium orthoferrite domain walls

The total velocity of solitary flexural waves nonlinearly increases with an increase in the velocity of domain walls and becomes saturated at a level of 20 km s^?1; the smaller the wave amplitude, the more rapidly saturation occurs. Counter collisions of solitary flexural waves lead to the formation of a single wave with a difference amplitude moving in the same direction as the wave with a larger amplitude. The experimental results confirm that solitary flexural waves accompany antiferromagnetic vortices at domain walls in yttrium orthoferrite.     

Magneto-optical study of domain wall dynamics and giant Barkhausen jump in magnetic microwires

Investigation of surface domain walls motion in Co-rich magnetic microwires has been performed in circular and axial magnetic fields. The dc axial magnetic field acceleration of the domain wall motion related to the influence of the axial field on the structure of the moving domain wall has been discovered. Pulsed axial magnetic field induced unidirectional motion of surface domain wall also has been found.     

Dynamics of domain walls in pattern formation with traveling-wave forcing

We study dynamics of domain walls in pattern forming systems that are externally forced by a moving space-periodic modulation close to 2:1 spatial resonance. The motion of the forcing induces nongradient dynamics, while the wave number mismatch breaks explicitly the chiral symmetry of the domain walls. The combination of both effects yields an imperfect nonequilibrium Ising-Bloch bifurcation, where all kinks (including the Ising-like one) drift. Kink velocities and interactions are studied within the generic amplitude equation. For nonzero mismatch, a transition to traveling bound kink-antikink pairs and chaotic wave trains occurs.     

Unidirectional anisotropy of the velocity of domain walls in ferrite-garnet films

A mechanism to explain the gigantic unidirectional anisotropy of the velocity of domain walls, which includes the local rotation of the magnetization in front of a moving domain wall, initiated by radiated spin waves is proposed. Institute of General Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 45–48, September, 1997.     

Adaptive tuning of an electrodynamically driven thermoacoustic cooler

The commercial development of thermoacoustic coolers has been hampered in part by their low efficiencies compared to vapor compression systems. A key component of electrodynamically driven coolers is the electromechanical transducer, or driver. The driver's electroacoustic transduction efficiency, defined as the ratio of the acoustic power delivered to the working gas by the moving piston and the electrical power supplied, must be maintained near its maximum value if a high overall system efficiency is to be achieved. Modeling and experiments have shown that the electroacoustic efficiency peaks sharply near the resonance frequency of the electro-mechano-acoustic system. The optimal operating frequency changes as the loading condition changes, and as the properties of the working gas vary. The driver efficiency may thus drop significantly during continuous operation at a fixed frequency. In this study, an on-line driver efficiency measurement scheme was implemented. It was found that the frequency for maximum electroacoustic efficiency does not precisely match any particular resonance frequency, and that the efficiency at resonance can be significantly lower than the highest achievable efficiency. Therefore, a direct efficiency measurement scheme was implemented and validated using a functional thermoacoustic cooler. An adaptive frequency-tuning scheme was then implemented. Experiments were performed to investigate the effectiveness of the control scheme to maintain the maximum achievable driver efficiency for varying operating conditions.