Papers by Keyword: Compensation

Abstract: We briefly review backward error analysis as a useful mathematical technique for improving numerical methods used for solving ordinary differential equations describing dynamical systems. Then, we show how backward error analysis-based compensation, an approach recently introduced by the authors, can be applied to the second-order Newmark method for eliminating numerical damping and achieving fourth-order convergence. The presented improvements only require modifying the physical parameters of the system and the excitation, while the Newmark method is left intact. We compare the performance of the resulting improvements with that of several other numerical methods, including a novel partitioned method based on local extrapolation.

Abstract: In this paper, the ferrimagnetic mixed spins (1, 5/2) Blume-Capel model is proposed to investigate the phase diagrams and hysteresis behaviors of a magnetic cylindrical nanotube with a core-shell structure using the mean-field approximation based on the Bogoliubov inequality for the Gibbs free energy. The core sites are occupied by σ= ±1, 0 spins, whereas the shell sites are filled by S= ±5/2, ±3/2, ±1/2 spins. The effects of exchange couplings (J_in, J_S) and single-ion anisotropies (D_C, D_S) on core, shell, and total magnetizations are investigated, as well as hysteresis behaviors. The entropy, free energy, and specific heat are analyzed to establish the stability of the solutions. The presentation and discussion of phase diagrams is detailed. The system shows a first-order and second-order phase transitions, as well as tricritical and critical end- points. In addition, the system shows compensation and reentrant behaviors. Various multiple hysteresis loop behaviors are seen according on the Hamiltonian parameters, such as the presence of triple, quintuple, and septuple hysteresis loops.

Abstract: The magnetic and thermal properties of a ferrimagnetic mixed spin-1 and spin-2 cubic Ising nanowire are studied by using the Monte Carlo simulation. The influences of the nearest (J_AB) and next-nearest neighbor (J_A and J_B) exchange interactions and the single-ion anisotropies (D_A and D_B) on the critical and compensation temperatures are illustrated. Moreover, the phase diagrams on the (temperature, anisotropy) plane are plotted for several values of J_A/|J_AB|. The system shows very rich and interesting behaviors, namely first and second order phase transitions, tricritical points and compensation phenomenon. Finally, the dependence of hysteresis loops on the anisotropies, the exchange interactions and the temperature is also investigated.

Abstract: Aluminum implanted 4H-SiC often shows an unexpected increase of the free hole density at elevated temperatures in Hall Effect measurements. Here we show that this phenomenon cannot solely be traced down to the Hall scattering factor and the presence of excited acceptor states. It is necessary to assume an additional defect center in the lower half of the band gap with ionization energies higher than that of aluminum to explain this behavior. Therefore, we investigated ion-implanted square van-der-Pauw samples with Hall Effect and complementary SIMS measurements. An analysis of the data using the neutrality equation reveals compensation ratios of 20 % to 90 %, depending on the aluminum concentration and the concentration of the deep defect center of up to 50 % of the doping.

Abstract: The prediction of the compensation induced hole concentration reduction in implanted Al regions is a key parameter in developing high power SiC devices. Hall effect measurements are commonly used to determine the compensation ratio of Al implanted regions. Due to the fact that this measurement method is rather complex, an approximate method was developed by using transfer length method structure measurements in combination with a TCAD simulation model. The determined compensation ratios from this work’s simulation and from Hall effect measurements from literature show consistent compensation ratios. Based on this data a fit function was derived which allows for estimating the compensation ratio for a wide Al concentration range.

Abstract: Currently, common inefficient trial-and-error procedures are used in designing bulk forming dies. Numerous iterations, consisting of numerical simulations and subsequent real tests, are needed to achieve accurate parts. During the compensation cycles, manual redesign in CAD environments is necessary to transform discrete data into parametric descriptions causing approximation errors. Automation of these surface reconstruction processes is barely possible. To address these issues, different data-driven numerical strategies have been deduced based on either displacement or force. In this work, a material point tracking method in forming simulation between die and part geometry is presented. Based on this, enhanced displacement-based and stress-based methods for compensation of bulk forming parts are compared. The convergence behavior of both methods is analyzed with respect to the compensation factor. Finally, the material point tracking approach is validated and verified by compensating a two-dimensional bulk-formed component.

Abstract: The machining accuracy of parts depends greatly on the positioning accuracy and repeated positioning accuracy of the machine tools, which can be affected by the transmission backlash. Therefore, it is of great importance to measure and compensate the transmission reverse clearance of NC machine tools at regular intervals. This paper mainly studies how to eliminate the reverse clearance of NC machine tools.

Abstract: In this work, we analyze compensating defects which are formed after implantation of aluminum (Al) into n-type 4H-SiC epitaxial layers and subsequent thermal annealing. These defects reduce the expected free charge carrier density by 84% for a low doped layer with [Al]_impl ≈ 9ž·10¹⁶ cm^-3 and by 27 % for a high doped layer with [Al]_impl ≈ 2·ž10¹⁹ cm^-3. Furthermore, an electrical activation ratio of implanted aluminum ions of 100 % is calculated. The ionization energy of implanted aluminum as measured by Hall effect and admittance spectroscopy ranges from 101 meV to 305 meV depending on the doping concentration.

Abstract: The change in the current-voltage characteristics and in N_d-N_a values in the base of 4H-SiC Schottky diodes and JBS diodes under irradiation with 0.9 MeV electrons and 15 MeV protons has been studied. The carrier removal rate for the diodes irradiated with electrons was 0.07-0.15 cm^-1, and that in the case of protons, 50-70 cm^-1. It was shown that the devices under study retain rectifying current-voltage characteristics up to electron doses of ~10¹⁷ cm^-2. It was found that the radiation resistance of the SiC-based devices significantly exceeds that of silicon p-i-n-diodes with similar breakdown voltages. The simultaneous effect of high temperature and proton irradiation on the characteristics of 4H-SiC pn structures was examined.

Abstract: To suppress the abrupt and unexpected turning velocity fluctuation of the industrial robot under the condition of trajectory tracking, a flexible robotic joint experimental setup with the harmonic drive was established. The measured friction with Stribeck effect and velocity were modeled by a simple polynomial fit method. Two friction compensation control strategies of feedforward and feedback were designed. The friction compensation experiments were carried out on the dSPACE system, the good restraint effect of fluctuation on the turning velocity was verified and the control accuracy of feedback compensation control strategy proved better.