Ivan Starkov

Modeling of efficient solid-state cooler on layered multiferroics

We have developed theoretical foundations for the design and optimization of a solid-state cooler working through caloric and multicaloric effects. This approach is based on the careful consideration of the thermodynamics of a layered multiferroic system. The main section of the paper is devoted to the derivation and solution of the heat conduction equation for multiferroic materials. On the basis of the obtained results, we have performed the evaluation of the temperature distribution in the refrigerator under periodic external fields. A few practical examples are considered to illustrate the model. It is demonstrated that a 40-mm structure made of 20 ferroic layers is able to create a temperature difference of 25K. The presented work tries to address the whole hierarchy of physical phenomena to capture all of the essential aspects of solid-state cooling.

Asymptotic Description of the Time and Temperature Hysteresis in the Framework of Landau-Khalatnikov Equation

The main objective of this work is to study and interpret the time dependence of the ferroelectric polarization in the case of a periodic variation of the electric field. It is assumed that the period of oscillations is much longer than the characteristic relaxation time of a ferroelectric. For the process description, we have employed the Landau-Khalatnikov equation for which it is possible to derive an approximate solution. The developed approach has been used for analyzing the influence of the passive layer and presence of the Kittel domain structure on the hysteresis curve.

Temperature Change in the Piezoelectrocaloric Element under Periodic External Fields

The paper presents the analysis of the cooling structure consisted of alternate electro- and piezocaloric layers. The temperature distribution in such a system under periodic electric and elastic fields is investigated. It is demonstrated that the simultaneous application of the external forces allows to increase the temperature difference at the outer surfaces of the system in 2–3 times compared with the operation by a single force. The obtained results can be used for design and optimization of a new generation of cooling devices.

An analytical approach for scanning probe microscope-tip electrostatic field distribution accounting for dead layer and domain wall

We have proposed a new theoretical approach for the determination of the electric field distribution in the ferroelectric/dielectric system with the presence of the SPM tip. The initial statement of the model has only a numerical solution. To find an analytical solution of the problem, some assumptions are introduced: the domain wall thickness can be considered to be much smaller than the domain size, and we use a high ferroelectric dielectric permittivity. The developed approach allows us to obtain explicit formulas for the polarization and electric field intensity. We have calculated and then analyzed the tip capacitance as a function of the distance from the ferroelectric interface. Additionally, different forms of the SPM tip are considered. It is demonstrated that in the presence of charges at the domain, the results differ from those obtained with the widely used dielectric model by 30%.

Diffraction of electromagnetic wave on skin blood vessel: Statement of the problem

A theoretical model for the diffraction of electromagnetic wave on the skin blood vessel is developed. For this purpose, the Greens function formalism is used. The calculations performed in the paper are based on real experimental data, which makes it more compelling. The proposed approach would eliminate fundamental uncertainties in the modeling of biological tissues.

Diffraction of electromagnetic wave on skin capillary

We have formulated and solved the problem of electromagnetic wave diffraction on skin blood vessel. As an important result of our investigation, it is established that the amplitude of the scattered field is proportional to the square of the capillary area. For the case of long waves, the reflected field is linearly dependent on the depth position of the capillary. The proposed approach would eliminate fundamental uncertainties in the modeling of biological tissues.

A Semi-numerical Approach to Radiation Boundary Conditions

The study proposes a new semi-numerical approach to absorbing boundary problem. The developed method relies on the new formulation of generalized impedance boundary conditions. A distinguishing feature of the approach is the possibility to obtain an analytical solution after performing numerical calculations. The accuracy of the presented model was verified by comparing the simulation results with the exact solution for dipole and loop antennas radiation problem. The examples are based on a finite difference scheme but finite element methods can also be used.

Electroelastic field of a sphere located in the vicinity of a plane piezoelectric surface

The electric field generated by a scanning probe microscope is determined. Analytical expressions for the electroelastic field in a piezoelectric sample and the external electric field are derived for a spherical probe. It is demonstrated that the coupling of elastic and electrostatic fields in the piezoelectric material leads to energy redistribution between such fields. This circumstance causes variations in the normal component of the electric field strength at the interface and the capacitance of a probe.

Diffraction of plane wave on a thin/narrow body: Influence of the curvature and torsion

We consider the problem of finding the acoustic field scattered by a thin/narrow body. It is shown that, in the leading approximation, this field is represented by a set of monopole point sources located on the axis of the body L. The amplitude of the sources can be represented as a sum of three terms proportional to the cross-sectional area of the body, and its derivative with respect to the arc length. Moreover, dependence on the curvature and torsion of the curve L affects primarily the curvature of the wavefront of the scattered wave.

Asymptotic solution of the heat conduction equation with weak nonlinearity and rapidly oscillating heat source

The paper examines the temporal and spatial dependence of the temperature field and thermal flows in a layered structure with rapidly oscillating heat source. For the problem solution we derive an analytical approach of the heat conduction equation by means of the generalized two-scale expansion method. A few practical examples are considered to illustrate the model. The computed results confirm the validity of the approximate solution technique.