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Effects of HF frequency on plasma characteristics in dual-frequency helium discharge at atmospheric pressure by fluid modeling

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Plasma Science and Technology 2018年第11期20卷 76-83页

作者： Yinan WANG Shuaixing LI Li WANG Ying JIN Yanhua ZHANG Yue LIU College of Science Liaoning Shihua UniversityFushun 113001People＇s Republic of China Key Laboratory of Materials Modification by Laser Ion and Electron Beams（Ministry of Education）Dalian University of TechnologyDalian 116024People＇s Republic of China

On the basis of the fluid theory and the drift-diffusion approximation, a numerical model for dual-frequency atmospheric pressure helium discharge is established, in order to investigate the effects of the high frequency source （HF） on the characteristics of dual-frequency atmospheric pressure helium discharge. The numerical results showed that the electron heating rate increases with enhancing HF frequency, as well as the particles densities, electron dissipation rate, current density, net electron generation and bulk plasma region. Moreover, it is also observed that the efficient electron heating region moves when the HF frequency has been changed. The plasma parameters are not linear change with the HF frequency linearly increasing.

关键词： dual-frequency numerical study electron energy mechanisms

Simulation of Capacitively Coupled dual-frequency N_2,O_2,N_2/O_2 Discharges:Effects of External Parameters on Plasma Characteristics

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Plasma Science and Technology 2014年第4期16卷 335-343页

作者：尤左伟戴忠玲王友年 School of Physics and Optoelectronic Technology Dalian University of Technology

A one-dimensional fluid model is adopted to simulate the characteristics of N2, O2, and N2/O2 dual-frequency （DF） capacitively coupled plasmas （CCPs） under typical conditions in PECVD technologies. Not only the ground, the excited states but also the vibration levels of the main species are considered. The study focuses on the influence of external parameters such as matching of the high-frequency （HF） and low-frequency （LF）, HF and LF of the voltage sources, as well as discharge pressures, on physical characteristics of discharges. The results show that the decoupling of the two sources is possible by increasing the applied HF, the electron density and ion flux are determined only by the HF of the voltage source, whereas the LF has a little influence on the plasma characteristics. In addition, the matching of frequency affects the characteristics of discharges to some extent. Fhrthermore, the pressure is a main external parameter affecting the characteristics of discharges, and a small amount of oxygen in N2 plasma can efficiently increase N＋ ion flux incident onto the electrode and the density of N atom.

关键词： CCP dual-frequency fluid model N2 discharge O2 discharge

Precision Controlling of frequency Difference for Elastic-Stress Birefringence He-Ne dual-frequency Lasers

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Chinese Physics Letters 2007年第11期24卷 3141-3144页

作者：周鲁飞张书练郭宏任舟 The State Key Laboratory of Precision Measurement Technology and Instruments Department of Precision Instruments Tsinghua University Beijing 100084

Birefringence-Zeeman dual frequency lasers are capable of producing frequency difference from several kilohertz to hundreds of megahertz, but the precision of giving and stabilizing of the beat frequency still needs improvement to the range of ±200 kHz. We design a new elastic force-exerting device comprised of the bottom part, two arms and two pieces of force-exerting sheets. The frequency difference smoothly tuning is realized with this device in a large range of 2 MHz to 20 MHz. Power-balance frequency stabilization system is used to investigate characters of the temperature, frequency difference and laser power. The precision of the frequency difference has reach up to ±100 kHz after system temperature balance. Analyses of the laser frequency difference and power character are carried out.

关键词： Elastic-Stress He-Ne dual-frequency

Analytical Expressions of dual-frequency Plasma Diagnostic Theory

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Plasma Science and Technology 2012年第1期14卷 37-39页

作者：程立时家明许波 Key Laboratory of Pulsed Power Laser Technology Key Lab of Infrared and Low Temperature Plasma of Anhui ProvinceElectronic Engineering Institute

Based on the fundamental ideas concerning microwave attenuation in plasma, we obtain a new expression of transmission attenuation of microwaves as a function of the incident wave frequency. And with reasonable hypothesis, analytical forms of the electron density and the electron-neutral collision frequency are derived from the equations of the transmission attenuation of microwaves at two near frequencies. This method gives an effective and easy approach to diagnose the unmagnetized plasma.

关键词： plasma diagnosis dual-frequency attenuation electron density electron-neutral collision frequency

Optimization of Nonlinear Energy Sink for Vibration Suppression of Systems Under dual-frequency Excitation

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Transactions of Nanjing University of Aeronautics and Astronautics 2018年第6期35卷 986-991页

作者： Sun Bin Wu Zhiqiang School of Mechanical Engineering Tianjin Key Laboratory of Nonlinear Dynamics and Chaos ControlTianjin University School of Aeronautical Engineering Civil Aviation University of China

Aiming to decrease the vibration of wing induced by dual-rotor civil turbofan engines,the dynamic models of a single-degree of freedom (DOF) linear main oscillator coupled with single-DOF and two-DOF nonlinear energy sink (NES) are *** to the related energy criteria for the optimization of the dynamic vibration absorber,focusing on the effects of external excitation on the kinetic energy of the primary mass and total system energy,the vibration suppression effects of single-DOF,two-DOF serial and parallel NES on the main oscillator system are *** the condition that the characteristic parameters of the main oscillator system and additional total mass of the vibration absorber remain unchanged,results show that the two-DOF parallel NES has the best vibration energy suppression effects,which can provide data reference for the optimal design of NES vibration suppression under dual-frequency excitation.

关键词： nonlinear energy sink(NES) civil turbofan engine dual-frequency vibration suppression optimization

The Performance of dual-frequency Polarimetric Scatterometer in Sea Surface Wind Retrieval

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Journal of Ocean University of China 2019年第5期18卷 1051-1060页

作者： LIU Shubo WEI Enbo JIN Xu LV Ailing DANG Hongxing Xi’an Institute of Space Radio Technology China Academy of Space TechnologyXi’an 710100China National Key Laboratory of Science and Technology on Space Microwave Xi’an 710100China Institute of Oceanology and Center for Ocean Mega-Science Chinese Academy of Sciencesand Qingdao National Laboratory for Marine Science and TechnologyQingdao 266071China

The wind retrieval performance of HY-2 A scanning scatterometer operating at Ku-band in HH and VV polarizations has been well evaluated in the wind speed range of 0–25 m s^-*** order to obtain more accurate ocean wind field,a potential extension of dual-frequency(C-band and Ku-band)polarimetric measurements is investigated for both low and very high wind speeds,from 5 to 45 m s^-*** on the geophysical model functions of C-band and Ku-band,the simulation results show that the polarimetric measurements of Ku-band can improve the wind vector retrieval over the entire scatterometer swath,especially in nadir area,with the wind direction root-mean-square error(RMSE)less than 12?in the wind speed range of 5–25 m s^-***,the results also show that C-band cross-polarization plays a very important role in improving the wind speed retrieval,with the wind speed retrieval accuracy better than 2 m s^-1 for all wind conditions(0–45 m s^-1).For extreme winds,the C-band HH backscatter coefficients modeled by CMOD5.N(H)and the ocean co-polarization ratio model at large incidence are used to retrieve sea surface wind *** result reveals that there is a big decrease of wind direction retrieval RMSE for extreme wind fields,and the retrieved result of C-band HH polarization is nearly the same as that of C-band VV polarization for low-to-high wind speed(5–25 m s^-1).Thus,to improve the wind retrieval for all wind conditions,the dual-frequency polarimetric scatterometer with C-band and Ku-band horizontal polarization in inner beam,and C-band horizontal and Ku-band vertical polarization in outer beam,can be used to measure ocean *** study will contribute to the wind retrieval with merged satellites data and the future spaceborne scatterometer.

关键词： dual-frequency polarimetric scatterometer wind vector retrieval

A Physics-Based dual-frequency Approach for Altimeter Wind Speed Retrieval

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Journal of Ocean University of China 2014年第4期13卷 579-583页

作者： LI Shuiqing ZHOU Liangming LI Zhanbin MIAO Qingsheng MOU Lin WANG Aifang Institute of Oceanology Chinese Academy of Sciences Physical Oceanography Laboratory Ocean University of China National Marine Data and Information Service State Oceanic Administration of People’s Republic of China Engineering Reconnaissance and Design Institute Ocean University of China

The altimeter normalized radar cross section(NRCS) has been used to retrieve the sea surface wind speed for decades, and more than a dozen of wind speed retrieval algorithms have been proposed. Despite the continuing efforts to improve the wind speed measurements, a bias dependence on wave state persists in all wind algorithms. On the basis of recent evidence that short waves are essentially modulated by local winds and much less affected by wave state, we proposed a physics-based approach to retrieve the wind speed from the dual-frequency difference in terms of the mean square slope of short waves. A collocated dataset of coincident altimeter/buoy measurements were used to develop and validate the approach. Validation against buoy measurements indicates that the approach is almost unbiased and has an overall root mean square error of 1.24 m s-1, which is 5.3% lower than the single-parameter algorithm in operational use(Witter and Chelton, 1991) and 2.4% lower than another dual-frequency approach(Chen et al., 2002). Furthermore, the results indicate that the new approach significantly improves the wave-dependent bias compared to the single-parameter algorithm. The capacity of altimeter to retrieve sea surface wind speed appears to be limited for the case of winds below 3 m s-1. The validity of the approach at high winds needs to be further examined in the future study.

关键词： altimeter mean square slope dual-frequency wind speed retrieval

dual-frequency Operation of Bow-Tie Microstrip Antenna

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Journal of Shanghai University(English Edition) 2005年第3期9卷 234-236页

作者：钟顺时张需溥 School of Communication and Information Engineering Shanghai University Shanghai 200072 P.R. China

Characteristics of a single-feed dual-frequency bow-tie microstrip antenna are studied. By using the variation method, simple formulas for resonant frequencies of the bow-tie microstrip antenna are derived. It is shown that the dual-frequency ratio can be controlled easily by choosing the parameters of the antenna. This design gives compact antenna size and simple antenna structure. Experimental results are presented, verifying the validity of the design.

关键词： microstrip antennas resonant frequency dual-frequency miniature design.

Three-Dimensional Shape Measuring Method Based on dual-frequency Digital Moiré Fringe

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激光与光电子学进展 2023年第8期60卷 394-401页

作者： Hu Hailing He Renji Chen Yang Zhang Peiqing Shen Xiang Da Shixun Song Baoan Faculty of Electrical Engineering and Computer Science Ningbo UniversityNingbo 315211ZhejiangChina The Research Institute of Advanced Technologies Ningbo UniversityNingbo 315211ZhejiangChina Key Laboratory of Photoelectric Detecting Materials and Devices of Zhejiang Province Ningbo 315211ZhejiangChina Ningbo Institute of Oceanography Ningbo UniversityNingbo 315211ZhejiangChina Engineering Research Center for Advanced Infrared Photoelectric Materials and Devices of Zhejiang Province Ningbo 315211ZhejiangChina

A dual-frequency digital Moiré measurement method(DFDM) is proposed for the three-dimensional(3D) shape measurement of an *** high-and low-frequency fringes are modulated separately along orthogonal direction using different carrier frequencies before being projected onto the measured *** collecting and demodulating the composite fringe,the digital π phase shift is used to remove the DC component of the demodulated fringes,resulting in high-precision Moiré fringes for calculating the wrapped *** unwrapping of the high-frequency wrapped phase is guided by the low-frequency phase to further realistically reconstruct the surface of the measured *** compared with existing single-shot digital Moiré profilometry,DFDM effectively removes the DC component of the fringe and calculates the phase more accurately.

关键词： 3D measurement dual-frequency digital Moiréfringe digitalπphase shift