scholarly journals Nonlinear terahertz effects of gold nanofilms

2021 ◽  
Vol 14 (1) ◽  
pp. 20-30
Author(s):  
Peidi Yang ◽  
Baolong Zhang ◽  
Jinglong Ma ◽  
Yutong Li ◽  
Jungang Miao ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
High Speed ◽  
Strong Field ◽  
Nonlinear Behavior ◽  
Nonlinear Effects ◽  
Tunneling Effect ◽  
High Resistivity ◽  
New Paradigm ◽  
Terahertz Waves ◽  
Hybrid Substrates

Nonlinear interaction between strong-field terahertz electromagnetic waves and matters will become one of the next hot research frontiers in nonlinear optics. However, the lack of strong terahertz radiation sources and appropriate nonlinear terahertz materials have impeded its progress. Here we systematically have investigated the strong-field terahertz nonlinear effects of gold (Au) nanofilms on different substrates, including SiO2, high-resistivity Si and SiO2-high-resistivity Si hybrid substrates. The strong-field terahertz waves are emitted from lithium niobate crystals via tilted pulse front technique, and obvious nonlinear transmission responses are observed along with varying the incident field strengths for all the Au samples on the three types of the substrates. The nonlinear behavior is enhanced when the gold nanofilm thickness increases, which can be qualitatively understood by introducing the quantum tunneling effect and carrier multiplication theory generated at the Au nano-slits under the illumination of the strong-field terahertz pulses. Our demonstrations not only open a new paradigm for nonlinear terahertz investigations and future high-speed terahertz devices, but also provide an effective platform for exploring extreme terahertz sciences.

scholarly journals Photonics-Assisted Terahertz-Wave Beam Steering and Its Application in Secured Wireless Communication

Photonics ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 9
Author(s):  
Kazutoshi Kato
Keyword(s):  
Wireless Communication ◽  
Power Efficiency ◽  
Electromagnetic Waves ◽  
High Speed ◽  
Phased Array ◽  
Beam Steering ◽  
Terahertz Wave ◽  
Coherent Detection ◽  
Terahertz Waves ◽  
Optical Domain

Beam forming and beam steering are inevitable technologies for the practical application of high-frequency electromagnetic waves. Specifically, beam control technology using a phased array for terahertz waves above 100 GHz is necessary to realize the future of high-speed wireless communication. By photomixing, which is a promising method for generating terahertz waves, the phase of the generated waves can be tuned in the optical domain, so that the beam from the phased array can be controlled by photonics technologies. Directing the beam of a terahertz wave enables wireless communication to be improved not only via an increase in power efficiency but also in security in the physical layer of the wireless transmission. By utilizing this advantage and using coherent detection at the receiver, a secured wireless communication system is proposed, and the fundamental mechanism is demonstrated in a feasibility experiment.

Theoretical Prediction of Motions of High-Speed Planing Boats in Waves

1978 ◽  
Vol 22 (03) ◽  
pp. 140-169
Author(s):  
Milton Martin
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Nonlinear Effects ◽  
Theoretical Method ◽  
Valuable Insight ◽  
Response Characteristics ◽  
Theoretical Predictions ◽  
Response Amplitude Operators ◽  
Phase Angles ◽  
Good Agreement

A theoretical method is derived for predicting the linearized response characteristics of constant deadrise high-speed planing boats in head and following waves. Comparisons of the theoretical predictions of the pitch and heave response amplitude operators and phase angles with existing experimental data show reasonably good agreement for a wide variety of conditions of interest. It appears that nonlinear effects are more severe at a speed to length ratio of 6 than of, say, 4 or less, principally because of the reduction of the damping ratio of the boat with increasing speed, and the consequent increase in motions in the vicinity of the resonant encounter frequency. However, it is concluded that the linear theory can provide a simple and fast means of determining the effect of various parameters such as trim angle, deadrise, loading, and speed on the damping, natural frequency, and linearized response in waves, and that this can furnish valuable insight into the actual boat dynamics, even though the accurate predictions of large motions and peak accelerations would require a nonlinear analysis.

Novel features of electromagnetic waves in an isotropic degenerate electron-ion plasma

2021 ◽  
Author(s):  
P. Maryam ◽  
Rozina Chaudhary ◽  
Shahid Ali ◽  
Hassan Amir Shah ◽  
Stefaan Poedts
Keyword(s):  
Nonlinear Interaction ◽  
Electromagnetic Waves ◽  
Tunneling Effect ◽  
Fermi Velocity ◽  
Degenerate Electron ◽  
Linear Dispersion ◽  
Direct Function ◽  
Ion Plasma ◽  
Damping Rate ◽  
Electron Quantum

Abstract Within the framework of kinetic theory, the nonlinear interaction of electromagnetic waves (EMWs) with a degenerate electron-ion plasma is studied to account for the electron quantum mechanical effects. For this purpose, a specific quantum regime is considered, for which the degenerate electron Fermi velocity is assumed to be taken of the order of group velocity of EMWs. This eventually leads to the existence of nonlinear Landau damping rate for the EMWs in the presence of electron Ponderomotive force. The electrons-ion density oscillations may be arisen from the nonlinear interaction of EMWs, leading to a new type of nonlinear Schrödinger equation in terms of a complex amplitude for electromagnetic pump wave. The profiles of nonlinear damping rate reveal that EMWs become less damped for increasing the quantum tunnelling effects. The electrostatic response for the linear electrostatic waves is also investigated and derived a linear dispersion for the ion-acoustic damping rate. The latter is a direct function of electron Fermi speed and does not rely on the Bohm tunneling effect. The obtained results are numerically analyzed for the two microwaves of different harmonics in the context of nonrelativistic astrophysical dense plasma environments, e.g., white dwarfs, where the electron quantum corrections cannot be ignored.

A Novel Flux-Weakening Structure of High-Speed Permanent Magnet Motor Based on the Soft Ferrite

2013 ◽  
Vol 694-697 ◽  
pp. 1508-1511
Author(s):  
Xing Hua Wang ◽  
Xue Yuan Lin ◽  
Ming Hui Li ◽  
Yu Chen ◽  
Cheng Hui Zhang
Keyword(s):  
Permanent Magnet ◽  
High Speed ◽  
High Resistivity ◽  
Permanent Magnet Motor ◽  
Soft Magnetic ◽  
Low Loss ◽  
Magnetic Resistance ◽  
The Magnetic Field ◽  
Soft Ferrite ◽  
Flux Weakening

Soft ferrite has the characteristics of high permeability, high resistivity, low loss. Based on this, a new flux-weakening structure of high-speed permanent magnet motor was presented. The structure relies on changing the saturation of soft magnetic ferrite to change the equivalent magnetic resistance of permanent magnet magnetic circuit in the motor, so the main flux of the permanent magnet motor can be reduced. By the 3D Finite Element analyses, the magnetic field distribution characters in the air gap can be pointed out. The analysis results prove the flux-weakening method is presented in this paper is correct and feasible. It can provide a practical flux-weakening method of the high-speed PM motor.

Gravitational waves: Some less discussed intriguing issues

2015 ◽  
Vol 24 (12) ◽  
pp. 1544023 ◽  
Author(s):  
C. Sivaram
Keyword(s):  
Gravitational Waves ◽  
Strong Field ◽  
Direct Detection ◽  
Recent Observation ◽  
High Redshift ◽  
Nonlinear Effects ◽  
Resonant Absorption ◽  
Compact Objects ◽  
The Waves ◽  
Very High

Attempts to detect gravitational waves is actively in progress with sophisticated devices like LIGO setup across continents. Despite being predicted almost 100 years ago, there has so far been no direct detection of these waves. In this work, we draw attention to some of the less discussed but subtle aspects arising, for example, from high orbital eccentricities, where emission near periastron could be millions of times more than that in the distant parts of the orbit. The strong field nonlinear effects close to the compact objects can substantially slow down and deflect the waves in the last (few) orbit(s) where much of the intensity is expected. Spin–orbit and other forces could be significant. There would also be plasma like resonant absorption (of kilohertz radiation) during the collapse. Recent observation of supermassive black holes at high redshift implies cluster collapse, where the gravitational wave intensity depends on very high powers of the mass. Any unambiguous claim of detection should perhaps consider several of these effects.

scholarly journals Low electrical percolation thresholds and nonlinear effects in graphene-reinforced nanocomposites: A numerical analysis

2018 ◽  
Vol 52 (20) ◽  
pp. 2767-2775 ◽  
Author(s):  
Xiaoxin Lu ◽  
Julien Yvonnet ◽  
Fabrice Detrez ◽  
Jinbo Bai
Keyword(s):  
Numerical Model ◽  
Aspect Ratio ◽  
Percolation Threshold ◽  
Barrier Height ◽  
Nonlinear Effects ◽  
Tunneling Effect ◽  
Graphene Sheets ◽  
Microstructural Parameters ◽  
Electric Behavior ◽  
Percolation Thresholds

A numerical model of graphene-reinforced nanocomposites taking into account the electric tunneling effect is employed to analyze the influence of microstructural parameters on the effective electric conductivity and the percolation thresholds of the composite. The generation procedure for the random microstructures of graphene-reinforced nanocomposites is described. Effects of the barrier height, of graphene aspect ratio and alignment of graphene sheets have been quantitatively evaluated. The results show that both higher graphene aspect ratio and lower barrier height can lead to smaller percolation threshold, and the alignment of graphene sheets results in anisotropic electrical behavior without affecting the percolation threshold. The numerical model also shows the importance of the tunneling effect to reproduce the nonlinear electric behavior and the low percolation thresholds reported in the literature. Finally, results are compared with available experimental data.

THz pulse train generation through ultrafast development of surface plasmon-polariton modulation instability

2021 ◽  
Author(s):  
Dmitry A Korobko ◽  
Igor O. Zolotovskii ◽  
Sergey Moiseev ◽  
Alexei S. Kadochkin ◽  
Vyacheslav Svetukhin
Keyword(s):  
Surface Plasmon ◽  
Electromagnetic Waves ◽  
Surface Plasmon Polariton ◽  
Modulation Instability ◽  
Frequency Comb ◽  
Nonlinear Effects ◽  
Wave Dispersion ◽  
Instability Effect ◽  
Plasmon Polariton ◽  
Plasmon Wave

Abstract Propagation of high-intensity electromagnetic waves in a waveguide structure could initiate nonlinear effects resulting in drastic changes of their spatial and temporal characteristics. We study the modulation instability effect induced by propagation of surface plasmon polaritons in a silver thin-film waveguide. The nonlinear Schrodinger equation for propagating surface plasmon wave is obtained. It is shown numerically that the modulation instability effect can give rise to ultrafast spatial redistribution and longitudinal localization of surface plasmon-polariton wave energy in subwavelength scale. The dependence of plasmon wave dispersion and nonlinear characteristics on metal film thickness is considered. We demonstrate that the use of films with the thickness varying along the waveguide length allows reduction of the generated pulse width and increase of frequency comb bandwidth. The proposed technique is promising for design of ultra-compact (tens of nm) optical generators delivering pulse trains with the repetition rate higher than 1THz.

scholarly journals Terahertz Beam Steering Concept Based on a MEMS-Reconfigurable Reflection Grating

Sensors ◽  
2020 ◽  
Vol 20 (10) ◽  
pp. 2874
Author(s):  
Xuan Liu ◽  
Lisa Samfaß ◽  
Kevin Kolpatzeck ◽  
Lars Häring ◽  
Jan C. Balzer ◽  
...  
Keyword(s):  
Diffraction Grating ◽  
High Speed ◽  
Beam Steering ◽  
Vertical Displacement ◽  
Grating Period ◽  
Terahertz Waves ◽  
Large Area ◽  
Electrostatic Actuators ◽  
Reflection Gratings ◽  
Reflection Grating

With an increasing number of applications of terahertz systems in industrial fields and communications, terahertz beamforming and beam steering techniques are required for high-speed, large-area scanning. As a promising means for beam steering, micro-electro-mechanical system (MEMS)-based reflection gratings have been successfully implemented for terahertz beam control. So far, the diffraction grating efficiency is relatively low due to the limited vertical displacement range of the reflectors. In this paper, we propose a design for a reconfigurable MEMS-based reflection grating consisting of multiple subwavelength reflectors which are driven by 5-bit, high-throw electrostatic actuators. We vary the number of the reflectors per grating period and configure the throw of individual reflectors so that the reflection grating is shaped as a blazed grating to steer the terahertz beam with maximum diffraction grating efficiency. Furthermore, we provide a mathematical model for calculating the radiation pattern of the terahertz wave reflected by general reflection gratings consisting of subwavelength reflectors. The calculated and simulated radiation patterns of the designed grating show that we can steer the angle of the terahertz waves in a range of up to ± 56.4 ∘ with a maximum sidelobe level of −10 dB at frequencies from 0.3 THz to 1 THz.

Significance of Considering Nonlinear Effects in Predicting the Dynamic Behavior of Rotating Machinery

1995 ◽  
Vol 1 (4) ◽  
pp. 431-458 ◽  
Author(s):  
Sherif T. Noah ◽  
Padmanabhan Sundararajan
Keyword(s):  
High Performance ◽  
Degrees Of Freedom ◽  
Nonlinear Behavior ◽  
Nonlinear Effects ◽  
Rotating Machinery ◽  
Modeling And Analysis ◽  
Rotor Systems ◽  
Rotor Support ◽  
Complex Phenomena ◽  
New Generation

Limitations of the currently practiced linearized analysis of industrial rotating machinery are dis cussed. An appreciation of these limitations is particularly significant for the development of new generation, high performance machinery in which new materials, rotor supports, coupling components, and sophisticated control systems will be used. In the absence of adequate familiarity and experience with the new systems, vari ous complex phenomena associated with their nonlinearities, which may lead to malfunction or catastrophic failure, could be missed altogether. A uniform approach to accurate modeling and analysis of rotor-support systems will therefore be essential. The present paper provides an exposition of recently published studies in nonlinear rotordynamics and their relevance to the design, analysis, and monitoring of rotating machinery. This includes a brief discussion of available analytical/computational methods and the various techniques proposed, which seek reducing the order of rotor systems with large number of degrees of freedom. In ad dition, new results on the nonlinear behavior of fluid-film bearings are presented herein to further emphasize the importance of nonlinear effects.

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