Three-dimensional data-driven magnetostatic field computation using real-world measurement data

Purpose The purpose of this paper is to present the applicability of data-driven solvers to computationally demanding three-dimensional problems and their practical usability when using real-world measurement data. Design/methodology/approach Instead of using a hard-coded phenomenological material model within the solver, the data-driven computing approach reformulates the boundary value problem such that the field solution is directly computed on raw measurement data. The data-driven formulation results in a double minimization problem based on Lagrange multipliers, where the sought solution must conform to Maxwell’s equations while at the same time being as close as possible to the available measurement data. The data-driven solver is applied to a three-dimensional model of a direct current electromagnet. Findings Numerical results for data sets of increasing cardinality verify that the data-driven solver recovers the conventional solution. Additionally, the practical usability of the solver is shown by using real-world measurement data. This work concludes that the data-driven magnetostatic finite element solver is applicable to computationally demanding three-dimensional problems, as well as in cases where a prescribed material model is not available. Originality/value Although the mathematical derivation of the data-driven problem is well presented in the referenced papers, the application to computationally demanding real-world problems, including real measurement data and its rigorous discussion, is missing. The presented work closes this gap and shows the applicability of data-driven solvers to challenging, real-world test cases.

Easy-cone state in spin-torque diode under combined action of magnetostatics and perpendicular anisotropy

Spin-torque diodes (STDs) with interfacial perpendicular magnetic anisotropy (IPMA) in the free layer have outstanding microwave signal rectification performances. Large sensitivity values in such systems are usually associated with an easy cone (EC) magnetic state, when the magnetization in the free layer is tilted from the normal to the plane of the film. Here we theoretically investigate the phase diagram of the existence of an EC state in an infinite free layer of the magnetic tunnel junction (MTJ) considering both IPMA (first and second order) and magnetostatic interaction. We show that the increase of the magnetostatic field leads to extension of the EC existence region. Then we consider the effect of finite dimensions in case of two differently spatially oriented elliptic nanopillar MTJ on the obtained phase diagrams. And finally, we consider dynamic properties and rectification of two elliptic STD under microwave current injection. These results clarify magnetostatic interaction influence on IPMA based STD rectification and demonstrate possible approach to extend the parameters area of the EC STD highly effective rectification.

Influence of piezoelectricity, doping and magnetostatic field on Brillouin amplification in compound (AIIIBV and AIIBVI) semiconductors

A theoretical formulation followed by numerical analysis describing Brillouin amplification in compound (AIIIBV and AIIBVI) semiconductors is explored. The threshold condition for the onset of Brillouin amplification is determined. Well above the threshold intensity, the influence of piezoelectricity, doping concentration, and external magnetostatic field on the parameters characterizing Brillouin amplification viz. Brillouin amplification coefficient, transmitted intensity of Brillouin-scattered Stokes mode (BSSM), and Brillouin cell efficiency of the Brillouin cell isestimated. Numerical analysis is made for three different Brillouin cells consisting of [Formula: see text]-InSb, [Formula: see text]-GaAs, and [Formula: see text]-CdS, at 77[Formula: see text]K duly irradiated by a pulsed CO2 laser. Efforts are directed towards to determine appropriate values of doping concentration and magnetostatic field to enhance the parameters characterizing Brillouin amplification, at lower excitation intensity, and to establish the suitability of compound semiconductors as hosts for fabrication of efficient Brillouin amplifiers.

Powerful high-orbit gyro-TWT

This paper presents the results of a search for the optimal design of a high-orbit gyro-TWT, which would make it possible to reduce the magnetostatic field when operating at high frequencies close to the millimeter wavelength range, increase the gain and gain bandwidth, and increase the efficiency of the gyro-TWT. To search for the optimal configuration of the high-orbit gyro-TWT, the Gyro-K program was used, in which the equations for the excitation of an irregular waveguide by an electron beam are constructed on the basis of the coordinate transformation method of A.G. Sveshnikov, which is based on replacing the problem of exciting an irregular waveguide with the problem of exciting a regular waveguide with a unit radius. This method allows one to search for the solution of wave equations in the form of expansions in terms of the system of basis functions of a regular cylindrical waveguide. To solve Maxwell's equations, the Galerkin method was used, which is also called the orthogonalization method. The coefficients of the expansion of the field in terms of eigenbasic functions are determined in this method from the condition of the orthogonality of the residuals of the equations for the eigenbasis functions of a regular waveguide. The boundary conditions at the open ends of the waveguide are determined for each mode of the regular waveguide separately, which eliminates the incorrectness of setting the boundary conditions for the full field, as is the case when using the “picˮ technology. As a result, we obtain a system of ordinary differential equations for the expansion coefficients, which now depend only on the longitudinal coordinate. This approach makes it possible to transform the threedimensional problem of excitation of an irregular waveguide into a one-dimensional problem. Ohmic losses in the walls of the waveguide are taken into account on the basis of the Shchukin – Leontovich boundary conditions. For a self-consistent solution of the problem of excitation of an irregular waveguide by an electron beam, the iterative method of sequential lower relaxation was used. An optimized version of a high-orbit gyroTWT has been obtained, which has an electronic efficiency of 28 %, a wave efficiency of 23 %, a gain of 34 dB and a gain band of 11 % at an operating frequency of more than 30 GHz. This was achieved by introducing an additional conducting section of the waveguide into the absorbing part of the waveguide, which led to an improvement in the azimuthal grouping of electrons in the Larmor orbit and, as a consequence, to an increase in the lamp efficiency. A twofold increase in the waveguide length made it possible to increase the lamp gain. Ohmic energy losses in the walls of the waveguide reach 5 % of the power of the electron beam. The implementation of such a powerful gyro-TWT (2 MW) in the millimeter wavelength range will significantly increase the capabilities of radar at long distances and increase the resolution of the radar.

Magnetically Tunable Graphene-Based Terahertz Metasurface

Graphene is a promising platform for configurable terahertz (THz) devices due to its reconfigurability, but most researches focus on its electrical tunability. Here, we propose a graphene-based THz metasurface comprised of graphene cut-wire arrays for magnetic manipulation of the THz wave. With the external magnetostatic field applied, the resonant currents of the graphene cut-wire can be effectively affected by the Lorentz force, leading to an evident tuning of the response of the metasurface. The simulated results fully demonstrate that the resonance frequencies of the graphene THz metasurface can be efficiently modulated under a vertical magnetostatic field bias, resulting in the manipulation of the transmittance and phase of the THz wave. As a new method of the tunable THz metasurface, our structure shows promising applications in the THz regime, including the ultracompact THz modulators and magnetic field sensors.