This work presents a novel radio frequency(RF)narrowband Si micro-electro-mechanical systems(MEMS)filter based on capacitively transduced slotted width extensional mode(WEM)resonators.The flexibility of the plate lead...This work presents a novel radio frequency(RF)narrowband Si micro-electro-mechanical systems(MEMS)filter based on capacitively transduced slotted width extensional mode(WEM)resonators.The flexibility of the plate leads to multiple modes near the target frequency.The high Q-factor resonators of around 100000 enable narrow bandwidth filters with small size and simplified design.The 1-wavelength and 2-wavelength WEMs were first developed as a pair of coupled modes to form a passband.To reduce bandwidth,two plates are coupled with aλ-length coupling beam.The 79.69 MHz coupled plate filter(CPF)achieved a narrow bandwidth of 8.8 kHz,corresponding to a tiny 0.011%.The CPF exhibits an impressive 34.84 dB stopband rejection and 7.82 dB insertion loss with near-zero passband ripple.In summary,the RF MEMS filter presented in this work shows promising potential for application in RF transceiver front-ends.展开更多
This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half...This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half-width of Caussian approximation for the fundamental mode should be defined according to the maximal matching efficiency method. The relationship between the mode-field half-width of the Gaussian approximate field obtained from the maximal matching efficiency and normalized frequency is studied; furthermore, two formulas of mode-field half-widths as a function of normalized frequency are proposed.展开更多
Analytical theories of the geodesic acoustic mode （GAM） are reviewed in the small- and large-orbit drift width limits, respectively. Different physics pictures in these two limits are displayed. As an example, these...Analytical theories of the geodesic acoustic mode （GAM） are reviewed in the small- and large-orbit drift width limits, respectively. Different physics pictures in these two limits are displayed. As an example, these two analytical methods are employed to investigate the plasma shaping effect on the frequency and collisionless damping rate of the GAM.展开更多
在三相两电平逆变器中,虚拟空间矢量调制(virtual space vector modulation,VSVM)因其能降低共模电压的幅值和三次谐波而受到广泛关注,但还存在共模电压的谐波成分丰富,且幅值变化和方向变化的发生率较高的问题,为此提出一种改进型VSVM...在三相两电平逆变器中,虚拟空间矢量调制(virtual space vector modulation,VSVM)因其能降低共模电压的幅值和三次谐波而受到广泛关注,但还存在共模电压的谐波成分丰富,且幅值变化和方向变化的发生率较高的问题,为此提出一种改进型VSVM方法。该方法通过分析经典VSVM的矢量合成和共模电压特点,对虚拟矢量和虚拟零矢量所对应的基本矢量进行优化排序,使每个开关周期的共模电压波形相同,均为单个矩形波。进一步分析了所提方法的共模谐波、死区补偿和开关损耗。在逆变器-永磁同步电机系统中进行仿真和实验。结果表明:与经典VSVM相比,所提方法在保持共模电压低幅值的同时,使幅值变化和方向变化的发生率都降低3倍,完全消除基带谐波和边带谐波分量,并使共模电压的高频段峰值平均减小6 dB,且线电流、线电压、转矩和转速等性能依然良好。该方法在不增加系统体积和成本的情况下,能更有效抑制共模干扰,有利于共模滤波器的设计,并为其他共模抑制脉冲宽度调制(pulse width modulation,PWM)方法的研究提供了借鉴。展开更多
A small-signal model of current programmed mode pulse width modulation converter including the equivalent sampling effect is introduced and analyzed. In this model, an addition pole is brought out by the sampling effe...A small-signal model of current programmed mode pulse width modulation converter including the equivalent sampling effect is introduced and analyzed. In this model, an addition pole is brought out by the sampling effect in the current loop gain, and it affects dynamic bandwidth and stability of the inner current loop. By selecting the appropriate stability parameter which determines the additional pole and describes the degree of peaking in closed loop transfer function, a control model of current programmed full bridge arc welding inverter with maximum frequency bandwidth and stability can be obtained. Small and large amplitude pulse current outputs are employed in simulations and experiments and results validate the design method.展开更多
A study of the evolution of the pulse width in homogeneous dielectric barrier dis- charge at atmospheric pressure with helium as the working gas is reported by using a one- dimensional fluid model. In this paper, a ne...A study of the evolution of the pulse width in homogeneous dielectric barrier dis- charge at atmospheric pressure with helium as the working gas is reported by using a one- dimensional fluid model. In this paper, a new computational method is presented to estimate the pulse width through calculating the time interval between the breakdown voltage and the extinguishing voltage. The effects on the discharge characteristics of the applied voltage and exci- tation frequency are studied based on the computational data. The results of the simulation show that the pulse width is observed to be narrower and the time intervals between two consecutive current pulses decrease with increasing amplitude and excitation frequency, which indicates that the homogeneous discharge is susceptible to the filamentary mode. The simulation results support the conclusion that in order to restrain the transition from the glow mode to filamentary mode, the applied voltage and excitation frequency should be kept within an appropriate range.展开更多
We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wav...We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wavelengths and bandwidths in the tuning range. The wavelength and width of pulse can be tuned in a range of - 20 nm and from - 0.8 ps to 87 ps, respectively. The flexible pulsed fiber laser can be accurately controlled, which is insensitive to environmental disturbance.展开更多
Previous researches on the mixed mode fracture initiation criteria were mostly focused on opening mode fracture. In this study, the authors proposed a new criterion for mixed mode sliding fracture initiation, which is...Previous researches on the mixed mode fracture initiation criteria were mostly focused on opening mode fracture. In this study, the authors proposed a new criterion for mixed mode sliding fracture initiation, which is the maximum twin shear stress factor criterion. The authors studied a finite width plate with central slant crack, subject to a far field uniform uniaxial tensile or compressive stress.展开更多
基金supported by the National Natural Science Foundation of China(61734007)National Key Research and Development Program of China(2022YFF0706100).
文摘This work presents a novel radio frequency(RF)narrowband Si micro-electro-mechanical systems(MEMS)filter based on capacitively transduced slotted width extensional mode(WEM)resonators.The flexibility of the plate leads to multiple modes near the target frequency.The high Q-factor resonators of around 100000 enable narrow bandwidth filters with small size and simplified design.The 1-wavelength and 2-wavelength WEMs were first developed as a pair of coupled modes to form a passband.To reduce bandwidth,two plates are coupled with aλ-length coupling beam.The 79.69 MHz coupled plate filter(CPF)achieved a narrow bandwidth of 8.8 kHz,corresponding to a tiny 0.011%.The CPF exhibits an impressive 34.84 dB stopband rejection and 7.82 dB insertion loss with near-zero passband ripple.In summary,the RF MEMS filter presented in this work shows promising potential for application in RF transceiver front-ends.
基金Project supported by Natural Science Foundation of the Department of Science & Technology of Fujian Province of China (GrantNo 2007F5040)
文摘This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half-width of Caussian approximation for the fundamental mode should be defined according to the maximal matching efficiency method. The relationship between the mode-field half-width of the Gaussian approximate field obtained from the maximal matching efficiency and normalized frequency is studied; furthermore, two formulas of mode-field half-widths as a function of normalized frequency are proposed.
基金supported by National Natural Science Foundation of China (No. 10990214)the Major State Basic Research Development Program of China (Nos. 2009GB105002, 2008GB717804)the JSPS-CAS Core University Program in Plasma and Nuclear Fusion
文摘Analytical theories of the geodesic acoustic mode （GAM） are reviewed in the small- and large-orbit drift width limits, respectively. Different physics pictures in these two limits are displayed. As an example, these two analytical methods are employed to investigate the plasma shaping effect on the frequency and collisionless damping rate of the GAM.
文摘A small-signal model of current programmed mode pulse width modulation converter including the equivalent sampling effect is introduced and analyzed. In this model, an addition pole is brought out by the sampling effect in the current loop gain, and it affects dynamic bandwidth and stability of the inner current loop. By selecting the appropriate stability parameter which determines the additional pole and describes the degree of peaking in closed loop transfer function, a control model of current programmed full bridge arc welding inverter with maximum frequency bandwidth and stability can be obtained. Small and large amplitude pulse current outputs are employed in simulations and experiments and results validate the design method.
基金supported by National Natural Science Foundation of China(No.51077089)
文摘A study of the evolution of the pulse width in homogeneous dielectric barrier dis- charge at atmospheric pressure with helium as the working gas is reported by using a one- dimensional fluid model. In this paper, a new computational method is presented to estimate the pulse width through calculating the time interval between the breakdown voltage and the extinguishing voltage. The effects on the discharge characteristics of the applied voltage and exci- tation frequency are studied based on the computational data. The results of the simulation show that the pulse width is observed to be narrower and the time intervals between two consecutive current pulses decrease with increasing amplitude and excitation frequency, which indicates that the homogeneous discharge is susceptible to the filamentary mode. The simulation results support the conclusion that in order to restrain the transition from the glow mode to filamentary mode, the applied voltage and excitation frequency should be kept within an appropriate range.
基金Project supported by the National Natural Science Foundation of China(Grant No.61575137)the Program on Social Development by Department of Science and Technology of Shanxi Province,China(Grant No.20140313023-3)
文摘We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wavelengths and bandwidths in the tuning range. The wavelength and width of pulse can be tuned in a range of - 20 nm and from - 0.8 ps to 87 ps, respectively. The flexible pulsed fiber laser can be accurately controlled, which is insensitive to environmental disturbance.
文摘Previous researches on the mixed mode fracture initiation criteria were mostly focused on opening mode fracture. In this study, the authors proposed a new criterion for mixed mode sliding fracture initiation, which is the maximum twin shear stress factor criterion. The authors studied a finite width plate with central slant crack, subject to a far field uniform uniaxial tensile or compressive stress.
