Spin-torque transfer magnetic random access memory (STT-MRAM) is one potential candidate to replace the dynamic random access memory (DRAM) due to its superior features of nonvolatility, fast read/write speed, and high scalability. The error correction coding methods are applied to improve the reliability of STT-MRAM which is affected by the process variation and thermal fluctuation. In this paper, we investigate, for the first time, the design and optimization of the polarization-adjusted convolutional (PAC) code for the STT-MRAM channel. A crucial problem for the application of PAC codes to the STT-MRAM channel is the optimization of the index set of the non-frozen bits of the PAC codes. Hence, a rate-profile optimization method based on the genetic-algorithm-assisted bit-swapping is proposed. Simulation results show that the PAC code with the optimized rate-profile outperforms both the polar code and the PAC code with existing generic rate-profiles.
Ferrite material has non-negligible permeability, permittivity, and conductivity, so that the magnetic behaviour of ferrite cores is frequency dependent. This article presents a method to predict the complex permeance of ferrite E- and U-cores including electromagnetic resonance. The cores are decomposed into elementary segments, for which the Maxwell equations are solved analytically to obtain a network of frequency-dependent permeances or reluctances.
The eddy current testing (ECT) signals of a crack change with the crack's geometry and electromagnetic properties. The conductivity of the specimen and the conductivity inside or around the crack are generally unknown but play important roles in ECT responses. The objective of this study is to find characteristics features to determine the depth of cracks independently of the material conductivity and the partial conductivity of the cracks. Theoretical and numerical analysis showed that the amplitudes of the intrinsic impedance signal or the magnetic field density signal vary little with frequency. By identifying nearly conductivity-invariant features in the spectra of magnetic flux density signals and constructing a master curve that correlates the characteristic features with crack depth, we will be able to approximately estimate the depth of a crack by referring to the pre-constructed master curve.
Enjoying the merits of compact structure, less noise and high specific power, axial-flux magnetic-geared double-rotor machines (AMGDRMs) have been proved a promising candidate for the electrical-continuously variable transmission (e-CVT) in hybrid electric vehicles (HEVs). However, an additional permanent magnet synchronous machine (PMSM) is needed for torque compensation in the e-CVT system. In this paper, a novel integrated scheme which can realize the functional integration of a PMSM is proposed to improve compactness further. By carefully designing pole-pair number combination, the PMSM torque would be produced by the interaction between the armature fifth-harmonic and PM fundamental magnetic fields when injecting harmonic current. However, such combination would cause significant principled torque ripple. Hence, a suppression method based on the phase-shift structure is proposed to cancel the torque fluctuation out, thus the proposed machine can enable both the MGDRM and PMSM operations without significant torque ripple. Compared with existing dual-winding integrated schemes, an integrated winding configuration where only one set of conventional integral-slot winding is placed into one stator is adopted in the proposed machine, simplifying the manufacture process. First, the machine structure and operation principle are investigated. Second, the torque ripple suppression mechanism is analyzed. Finally, 3-D FEA simulations are carried out to validate the proposed machine and evaluate overall performances.
In this work, ball-milled iron (Fe)-based nanocrystalline alloy sheets and obtaining platelet particles are used to effectively utilize the end material and apply it to a soft magnetic composite. The instrumental analysis results reveal that, although a microstrain is introduced into the nanocrystalline α-Fe grains in the achieved alloy powder, the amorphous part filled among the grains experiences almost no change. The ball-milling treatment greatly increases the coercive force of the pulverized nanocrystalline sheet. Although the coercive force of the alloy powder decreases after the heat treatment, it remained approximately 10 times higher than that of the heat-treated alloy sheet without the ball-milling treatment, even after the heat treatment. The magnetic process of the ball-milled and post-annealed nanocrystalline alloy powder is discussed based on the results of the synchrotron radiation X-ray analysis and transmission electron microscopy with the Lorentz technique.
