Ripple Distortion Research Articles

Revealing 3D Ripple Structure and Its Dynamics in Freestanding Monolayer MoSe2 by Single-Frame 2D Atomic Image Reconstruction.

An atomic-scale ripple structure has been revealed by electron tomography based on sequential projected atomic-resolution images, but it requires harsh imaging conditions with negligible structure evolution of the imaged samples. Here, we demonstrate that the ripple structure in monolayer MoSe2 can be facilely reconstructed from a single-frame scanning transmission electron microscopy (STEM) image collected at designated collection angles. The intensity and shape of each Se2 atomic column in the single-frame projected STEM image are synergistically combined to precisely map the slight misalignments of two Se atoms induced by rippling, which is then converted to three-dimensional (3D) ripple distortions. The dynamics of 3D ripple deformation can thus be directly visualized at the atomic scale by sequential STEM imaging. In addition, the reconstructed images provide the first opportunity for directly testing the validity of the classical theory of thermal fluctuations. Our method paves the way for a 3D reconstruction of a dynamical process in two-dimensional materials with a reasonable temporal resolution.

Suppressing ripple distortions and spurious pistons in phase-shifting interferometry.

In this paper, we present new phase-shifting algorithms (PSAs) that suppress the ripple distortions and spurious pistons in phase-shifting interferometry. These phase errors arise when non-uniform phase-shifting interferograms are processed with PSAs that assume uniform phase shifts. By modeling the non-uniform phase shifts as a polynomial of the unperturbed phase-shift value $\omega_0$ω0, we show that the conditions for eliminating the ripple distortion and the spurious piston are associated with the $m$mth derivative of the PSA's frequency transfer function (FTF). Thus, we propose an approach to design robust algorithms based on the FTF formalism and we present four ready-to-apply PSAs formulas. Finally, our conclusions are supported by computer simulations.

A Three-Level Universal Electric Vehicle Charger Based on Voltage-Oriented Control and Pulse-Width Modulation

Electric vehicles (EVs) could be used to address the issues of environmental pollution and the depletion of non-renewable energy resources. EVs, which are energized by a battery storage system, are becoming attractive because they keep the environment clean. Furthermore, the cost of EVs is becoming cheaper. Thus, EVs will become a significant load on utility distribution system in the future. EV chargers play a significant role in the expansion of EVs. The input current of an EV charger with a high total harmonic distortion (THD) and a high ripple distortion of the output voltage can impact battery life and battery charging time. Furthermore, the high cost and large size of the chargers are considered other issues in EV development. This work presents the complete design process of a universal EV charger with a special focus on its control algorithms. In this regard, a novel control algorithm based on the integration of voltage-oriented control (VOC) and the sinusoidal pulse-width modulation (SPWM) technique is proposed to ensure effective Levels 1, 2, and 3 battery charging. A simulation of the universal EV charger was conducted and assessed in MATLAB–Simulink. Moreover, a laboratory prototype was constructed with a TMS320F28335 digital signal processor (DSP) programmed as the controller to validate its operation and performance. The findings show that the proposed charger is able to provide a controllable and constant charging voltage for a variety of EVs, with an input current of low total harmonic distortion (THD) and an almost unity power factor.

Modified Rotor Material for Minimization of Torque Ripple for Interior Permanent Magnet BLDC motor

This paper presents a method to minimize the torque ripple of an interior permanent magnet BLDC motor by adopting modified rotor. The analysis method for torque ripple are established using two- dimensional (2 –D) finite-element method (FEM). A cost-effective modified rotor technique is proposed to minimize the torque ripple of the BLDC motor. This proposed method for low torque ripple has an advantage over rotor step skewing method from a manufacturing point of view. The proposed model is compared with the modified rotor method and non-modified rotor method by calculating torque characteristics to determine the effective method to minimize torque ripple distortion. Finally, the finite-element method results have revealed that the rotor angle vs torque. It shows the lower torque ripple but show a maximization of the average torque.

Ultra-low loss dispersion control with chirped transmissive fiber gratings.

Dispersion control is a critical functionality required in systems involving ultra-short (∼100 fs) pulses, and we demonstrate the use of chirped long-period fiber gratings for this purpose. The operation principles of this device share many attributes with the more established fiber Bragg grating technology for dispersion compensation, but with the added benefit of record low loss (0.2dB) and the potential of being free from group-delay ripple distortions. The bandwidth of the transmissive grating device we demonstrate exceeds 12nm, and it provides +52 fs/nm of dispersion in the 1μm wavelength range. This corresponds to the capability of compensating the dispersion of ∼100 fs pulses in approximately meter-long single mode fibers.

Investigation of group delay ripple distorted signals transmitted through all-optical 2R regenerators

We investigate the use of all-optical regenerators to correct pulse distortions introduced by group delay ripple. Group delay ripple creates unwanted satellite pulses and intensity fluctuations. By placing an all-optical regenerator after a device that introduces group delay ripple, we show that the signal distortions can be effectively reduced. This has the benefit of opening the signal eye at the receiver. The performances of both self-phase modulation and four-wave mixing based regenerators in reducing ripple induced system penalties are examined. We find that the regenerator based on four-wave mixing achieves better suppression of group delay ripple distortions than the self-phase modulation based alternative. The eye closure penalty introduced by group delay ripple is reduced by the four-wave mixing based regenerator by 1dB.

Physics of reconstructed silicon surfaces

Low-indexed silicon surfaces are reconstructed, i.e. the surface unit mesh is larger than the unit mesh of an equivalent bulk lattice plane. Up to now, the surface structures observed experimentally could not be predicted from theoretical calculations. However, some of the structural proposals could be sorted out by calculating, e.g. the band structure of the electronic surface states for specific surface atomic arrangements and comparing these results with experimental data. In this paper the results for (100), (110) and (111) silicon surfaces are reviewed. New data are reported on the irreversible structural conversion of the Si(111) −2 × 1 cleavage to the stable 7 × 7 structure and on the Debye temperatures of both structures. A new model combining surface vacancies and ripple distortions is proposed for the Si(111)−7 × 7 structure. Recent cluster calculation have revealed structural parameters lor the Si(111)−2 × 1 structure by minimizing the total energy of the cluster in dependence of the position of the surface atom. These data are in good agreement with experimental values evaluated from LEED studies.