Harmonic

About: Harmonic is a research topic. Over the lifetime, 44833 publications have been published within this topic receiving 495922 citations. The topic is also known as: overtone & partial.

A model for the effect of stress on the low‐frequency harmonic content of the magnetic induction in ferromagnetic materials

Abstract: A simple model used previously by the authors to explain stress variation of magnetic hysteresis is now employed to explain the effect of stress on the amplitudes of the first‐ and third‐order harmonics of the magnetic induction signal resulting from application of an ac magnetic field of low frequency to a steel specimen An improved expression for the effective field contribution Hσ due to stress has been derived from thermodynamic considerations

Ultrasensitive Optical Shape Characterization of Gold Nanoantennas Using Second Harmonic Generation

Abstract: Second harmonic generation from plasmonic nanoantennas is investigated numerically using a surface integral formulation for the calculation of both the fundamental and the second harmonic electric field. The comparison between a realistic and an idealized gold nanoantenna shows that second harmonic generation is extremely sensitive to asymmetry in the nanostructure shape even in cases where the linear response is barely modified. Interestingly, minute geometry asymmetry and surface roughness are clearly revealed by far-field analysis, demonstrating that second harmonic generation is a promising tool for the sensitive optical characterization of plasmonic nanostructures. Furthermore, defects located where the linear field is strong (e.g., in the antenna gap) do not necessarily have the strongest impact on the second harmonic signal.

Atomic-like high-harmonic generation from two-dimensional materials.

Abstract: The generation of high-order harmonics from atomic and molecular gases enables the production of high-energy photons and ultrashort isolated pulses. Obtaining efficiently similar photon energy from solid-state systems could lead, for instance, to more compact extreme ultraviolet and soft x-ray sources. We demonstrate from ab initio simulations that it is possible to generate high-order harmonics from free-standing monolayer materials, with an energy cutoff similar to that of atomic and molecular gases. In the limit in which electrons are driven by the pump laser perpendicularly to the monolayer, they behave qualitatively the same as the electrons responsible for high-harmonic generation (HHG) in atoms, where their trajectories are described by the widely used semiclassical model, and exhibit real-space trajectories similar to those of the atomic case. Despite the similarities, the first and last steps of the well-established three-step model for atomic HHG are remarkably different in the two-dimensional materials from gases. Moreover, we show that the electron-electron interaction plays an important role in harmonic generation from monolayer materials because of strong local-field effects, which modify how the material is ionized. The recombination of the accelerated electron wave packet is also found to be modified because of the infinite extension of the material in the monolayer plane, thus leading to a more favorable wavelength scaling of the harmonic yield than in atomic HHG. Our results establish a novel and efficient way of generating high-order harmonics based on a solid-state device, with an energy cutoff and a more favorable wavelength scaling of the harmonic yield similar to those of atomic and molecular gases. Two-dimensional materials offer a unique platform where both bulk and atomic HHG can be investigated, depending on the angle of incidence. Devices based on two-dimensional materials can extend the limit of existing sources.

Power System Harmonic State Estimation and Observability Analysis via Sparsity Maximization

Abstract: Harmonic state estimation (HSE) is used to locate harmonic sources and estimate harmonic distributions in power transmission networks. When only a limited number of harmonic meters are available, existing HSE methods have limited effectiveness due to observability problems. This paper describes a new system-wide harmonic state estimator that can reliably identify harmonic sources using fewer meters than unknown state variables. Note there are only a small number of simultaneous harmonic sources among the suspicious buses. Traditional observability analysis is extended to general underdetermined estimation when considering the sparsity of state variables. It is shown that the underdetermined HSE can become observable with proper measurement arrangements by applying the sparsity of state variables. The HSE is formulated as a constrained sparsity maximization problem based on L1-norm minimization. It can be solved efficiently by an equivalent linear programming. Numerical experiments are conducted in the IEEE 14-bus power system to test the proposed method. The underdetermined system contains nine meters and 13 suspicious buses. The results show that the proposed sparsity maximization approach can reliably identify harmonic sources in the presence of measurement noises, model parameter deviations, and small nonzero injections

Colonial Competitive Algorithm Development Toward Harmonic Minimization in Multilevel Inverters

Abstract: Selective harmonic elimination pulse width modulation (SHEPWM) is a well-known switching technique applied directly to the output voltage waveform of multilevel inverters which aims to omit low-order harmonics. Related equations for this technique are transcendental, so an objective function should be defined in order to cover all constraints. Evolutionary computation is demonstrated to be a promising tool meeting requirements of such problems. In this paper, the standard colonial competitive algorithm (CCA) is improved to be employed for the mentioned technique in two cases of equal and unequal dc sources. The results are compared with two other successful algorithms namely genetic algorithm (GA) and particle swarm optimization (PSO). Results indicate that this method outperforms other methods in terms of convergence rate and tackling local optima. Experimental results verify the simulation results.