Development of finite-difference equations for variance of neutron fluxes in reactor

Different sources—methodical, constant, and technological—are discussed for uncertainties in calculation functionals. The basic principles of three methods used in calculations of uncertainties are briefly described.     

Nonlinear magnetoelectric response of a bulk magnetostrictive-piezoelectric composite

Magnetoelectric effect in a bulk composite of nickel ferrite and lead zirconate titanate has been investigated by applying an ac magnetic field with no bias field. The measurements were carried out in the low-frequency region for harmonic magnetic field modulation with amplitude up to 3 kOe. The electric field induced by out-of-plane magnetic field exceeds that induced by in-plane magnetic field by approximately 4 times. Nonlinearity of ferrite magnetostriction of the sample results in a doubling in the frequency and a strong distortion of the ME signals. The magnetically induced voltage can be found by integrating the ordinary ME voltage coefficient over magnetic field.     

Inverse magnetoelectric effect in disk-shaped samples of ferrite piezoelectric composites

A theory of the inverse magnetoelectric effect in the vicinity of electromechanical resonance in disk-shaped samples is presented. An expression for the coefficient of the inverse magnetoelectric transformation has been obtained using the effective parameter method. It has been shown that a sharp increase in the magnitude of the effect occurs at a frequency of electromechanical resonance, and the resonance frequencies for the direct and inverse magnetoelectric effects are different. The dependences of the resonance frequencies on the ferrite percentage in ferrite-nickel spinel samples and lead zirconate titanate samples have been studied experimentally.     

Magnetoelectric Effect in Two-Layer Composites with a Graded Magnetic Phase

Physics of the Solid State - Samples of a homogeneous (x = 0, 0.1, and 0.2) and multilayer ceramics with a gradient composition (x = 0.2 → 0.1 → 0 → 0.1 → 0.2) based on...     

Waves in a superlattice with arbitrary interlayer boundary thickness

The transmittance D(ω), reflectance R(ω), and dispersion ω(k) are investigated for waves of various nature propagating through a one-dimensional superlattice (multilayer structure) with arbitrary thickness of the interlayer boundary. The dependences of the band gap widths δω_m and their positions in the wave spectrum of the superlattice on the interlayer boundary thickness d and the band number m are calculated. Calculations are performed in terms of the modified coupled-mode theory (MCMT) using the frequency dependence of R(ω), as well as in the framework of perturbation theory using the function ω (k), which made it possible to estimate the accuracy of the MCMT method; the MCMT method is found to have a high accuracy in calculating the band gap widths and a much lower accuracy in determining the gap positions. It is shown that the m dependence of δω _m for electromagnetic (or elastic) waves is different from that for spin waves. Furthermore, the widths of the band gaps with m=1 and 2 are practically independent of d, whereas the widths of all gaps for m>2 depend strongly on d. Experimental measurements of these dependences allow one to determine the superlattice interface thicknesses by using spectral methods.     

Calculation of effective diffusion coefficient in even approximations of the surface pseudo source method

The preference of even approximations of the surface pseudo source method for calculation of the diffusion coefficient is substantiated. The homogenization limit for the G ₀ approximation in the case of the cell size tending to zero is analytically proved.     

Structure,Ferroelectric, and Magnetoelectric Properties of Bulk PZT–NiFe<Subscript>1.9</Subscript>Co<Subscript>0.02</Subscript>О<Subscript>4 – δ</Subscript> Composites

The phase composition, microstructure, and dielectric, ferroelectric, magnetic, and magnetoelectric properties of bulk ceramic (1 – x)PZT–xNiFe_1.9Co_0.02О_{4 – δ} composites with 3–0 connectivity have been studied. Using X-ray diffraction and electron microscopy, it has been established that the ferrimagnetic (spinel- like) and ferroelectric (tetragonal perovskite-like) phases separately exist in the composites of all compositions. The simultaneous existence of ferroelectric and ferrimagnetic properties in the composites is confirmed by measuring their P(E) and σ(B) hysteresis loops and studying the temperature dependences of dielectric and magnetic properties. The synthesized composites have high magnetoelectric characteristics: their voltage coefficient at x = 0.4 is 215 mV/A at a frequency of 1 kHz and 130 V/A at an electromechanical resonance frequency of 380 kHz.     

Influence of an interlayer bonding on the magnetoelectric effect in the layered magnetostrictive-piezoelectric structure

The theory of the magnetoelectric effect in magnetostrictive-piezoelectric bilayer structure is presented considering the interlayer bonding material. The expressions for the dispersion relation and the frequency dependence of the magnetoelectric voltage coefficient in the electromechanical resonance region are obtained, using the simultaneous solution of the motion equation and material equations taking into account the interlayer bonding phase. The theoretical and experimental dependence of the magnetoelectric effect on the thickness of the bonding material layer are presented. Results are in good agreement with the theory and experiment.     

Magnetoelectric effect in layered disk-shaped magnetostrictive–piezoelectric structures: Theory and experiment

Theoretical and experimental studies of the magnetoelectric effect in a disk-shaped magnetostrictive–piezoelectric structure in the electromechanical resonance region are presented. An expression for the magnetoelectric voltage coefficient is derived based on the simultaneous solution of elastodynamic and electrostatic equations separately for magnetostrictive and piezoelectric layers. The conditions at the interface were taken into account based on the premise that the interaction between layers is implemented by shear. It is shown that the inhomogeneity of the voltage and strain distribution over the sample thickness, caused by the interface, leads to a significant contribution to the effect in the case of thick layers. The theoretical and experimental dependences of the frequency characteristic of the effect are presented for the permendur–lead zirconate-titanate–permendur structure. The theoretical calculations are in good agreement with experimental data.