Vector control schemes have recently been used to drive linear induction motors(LIM)in high-performance applications.This trend promotes the development of precise and efficient control schemes for individual motors.T...Vector control schemes have recently been used to drive linear induction motors(LIM)in high-performance applications.This trend promotes the development of precise and efficient control schemes for individual motors.This research aims to present a novel framework for speed and thrust force control of LIM using space vector pulse width modulation(SVPWM)inverters.The framework under consideration is developed in four stages.To begin,MATLAB Simulink was used to develop a detailed mathematical and electromechanical dynamicmodel.The research presents a modified SVPWM inverter control scheme.By tuning the proportional-integral(PI)controller with a transfer function,optimized values for the PI controller are derived.All the subsystems mentioned above are integrated to create a robust simulation of the LIM’s precise speed and thrust force control scheme.The reference speed values were chosen to evaluate the performance of the respective system,and the developed system’s response was verified using various data sets.For the low-speed range,a reference value of 10m/s is used,while a reference value of 100 m/s is used for the high-speed range.The speed output response indicates that themotor reached reference speed in amatter of seconds,as the delay time is between 8 and 10 s.The maximum amplitude of thrust achieved is less than 400N,demonstrating the controller’s capability to control a high-speed LIM with minimal thrust ripple.Due to the controlled speed range,the developed system is highly recommended for low-speed and high-speed and heavy-duty traction applications.展开更多
As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is...As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.展开更多
In this paper,the nature and origin of single event effects(SEE) are studied by injecting laser pulses into different circuit blocks,combining with analysis to map pulse width modulators circuitry in the microchip die...In this paper,the nature and origin of single event effects(SEE) are studied by injecting laser pulses into different circuit blocks,combining with analysis to map pulse width modulators circuitry in the microchip die.A time-domain error-identification method is used in the temporal characteristic analysis of SEE.SEE signatures of different injection times are compared.More serious SEE are observed when the laser shot occurs on a rising edge of the device output for blocks of the error amplifier,current sense comparator,and T and SR latches.展开更多
Passive decoy-state quantum key distribution is more desirable than the active one in some scenarios. It is also affected by the imperfections of the devices. In this paper, the influence of modulator attenuation on t...Passive decoy-state quantum key distribution is more desirable than the active one in some scenarios. It is also affected by the imperfections of the devices. In this paper, the influence of modulator attenuation on the passive decoy-state method is considered. We introduce and analyze the unbalanced Mach-Zehnder interferometer, briefly, and combining with the virtual source and imaginary unitary transformation, we characterize the passive decoy-state method using a weak coherent photon source with modulator attenuation. According to the attenuation parameter 6, the pass efficiencies are given. Then, the key generation rate can be acquired. From numerical simulations, it can be seen that modulator attenuation has a non- negligible influence on the performance of passive-state QKD protocol. Based on the research, the analysis method of virtual source and imaginary unitary transformation are preferred in analyzing passive decoy state protocol, and the passive decoy-state method is better than the active one and is close to the active vacuum + weak decoy state under the condition of having the same modulator attenuation.展开更多
This article proposed a new methodology and the principle of sinusoid modulated pulse MIG welding, and systematically established the universal mathematical model of computation of the parameters of the sinusoid modul...This article proposed a new methodology and the principle of sinusoid modulated pulse MIG welding, and systematically established the universal mathematical model of computation of the parameters of the sinusoid modulation pulse, achieving that the welding energy input can be effectively controlled and precisely regulated, the transition of pulse change is smooth and the welding process is stable and reliable. With the characteristics of sinusoidal waveform, such as infinite derivative continuity, eternal periodicity and limited control parameters, this article established the theoretical foundation for choiceness, unification and optimization of the parameters during the new sinusoid modulated pulse MIG welding. Bead-on-plate overlay welding is carried out on the pure aluminum sheet test sample for the test. The result indicated that during the welding process, the real-time current waveform is stable and clear; both the corresponding voltage and the instant welding energy waveform are very stable; the repeatability of the U-I graph plotted is high; its family of lines is clear, neat, and its distribution is concentrated showing that the welding process is stable and the neat and high quality ripple weld seam may be produced.展开更多
High-power intense optical sources in the mid-to-long wavelength infrared region are very attractive for a wide range of fields from fundamental research to materials science and biology applications.However,there are...High-power intense optical sources in the mid-to-long wavelength infrared region are very attractive for a wide range of fields from fundamental research to materials science and biology applications.However,there are still significant challenges in extending long-wavelength infrared pulses into the relativistic regime using conventional optical techniques.Here,based upon a new type of plasma-based optical method,we present an efficient scheme capable of combining several high-power long-wavelength infrared laser pulses into one single,more intense pulse,thus bringing the intensity of the output pulse to the relativistic regime.Such intense infrared pulses will open up new possibilities for strong-field physics and ultrafast applications.Furthermore,this is beneficial to understand the underlying physics and nonlinear processes of modulation,propagation and energy transfer of high-power intense laser pulses in plasmas.展开更多
For improving the energy efficiency of plasma volatile organic compounds( VOCs) decomposition, a pulse modulated power is used to drive the dielectric barrier discharge( DBD) plasma to treat benzene. Through the chang...For improving the energy efficiency of plasma volatile organic compounds( VOCs) decomposition, a pulse modulated power is used to drive the dielectric barrier discharge( DBD) plasma to treat benzene. Through the change of pulse duty cycle,the pulse modulation effect on benzene removal energy efficiency was investigated. The results show that pulse modulation can improve the energy yield and reduce the temperature of the chamber wall. There is an optimal duty cycle for achieving the maximum energy yield at a certain discharge voltage. The effect of initial benzene concentration on the decomposition efficiency and carbon selectivity in pulse modulation plasma were studied. The results indicate that the removal efficiency and carbon balance increase with the specific input energy( SIE) and decrease with the concentration. The energy yield increases with increasing initial concentration and achieves maximum around 180 J / L SIE for all initial concentrations.展开更多
A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation (GPCM), which is suitable for the area where the work conditi...A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation (GPCM), which is suitable for the area where the work condition is poor and a large flow rate is required. It is difficult to control the GPCM system because the system is discrete. With consideration of the stability and speediness of the GPCM position servo control system, a control strategy is developed through the theoretical and ex-perimental analyses. The control strategy integrates the merits of Bang-Bang control, PID control and fuzzy control. With this hybrid control strategy, the electro hydraulic control system has good per-formances, and the servo control is carried out with GPCM through on-off valves.展开更多
The discharge operation regime of pulse modulated atmospheric radio frequency (RF) glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequenc...The discharge operation regime of pulse modulated atmospheric radio frequency (RF) glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha(s)- gamma(γ) mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 kHz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.展开更多
A novel concept of collision avoidance single-photon light detection and ranging(LIDAR) for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for r...A novel concept of collision avoidance single-photon light detection and ranging(LIDAR) for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for robust anti-crosstalk purposes. Besides, single-photon detectors(SPD) and time correlated single photon counting techniques are adapted, to sense the ultra-low power used for the consideration of compact structure and eye safety. Parameters including pulse rate, discrimination threshold, and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite ultra-low transmitting power.展开更多
We experimentally demonstrate ultra-high extinction ratio(ER)optical pulse modulation with an electro-optical modulator(EOM)on thin film lithium niobate(TFLN)and its application for fiber optic distributed acoustic se...We experimentally demonstrate ultra-high extinction ratio(ER)optical pulse modulation with an electro-optical modulator(EOM)on thin film lithium niobate(TFLN)and its application for fiber optic distributed acoustic sensing(DAS).An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered,which can be well addressed by a small compensation component following the main driving signal.An ultrahigh ER>50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer(MZI)structure.The modulated optical_(√)pulses are then utilized as a probe light for a DAS system,showing a sensitivity up to-62.9 dB·rad∕Hz~2(7 pε/Hz)for 2-km single-mode sensing fiber.Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB,clearly revealing its importance to the sensing performance.展开更多
The state space average model and the large signal models of Pulse Skip Modulation (PSM) mode are given in this paper. Farther more, based on these models and simulations of PSM converter circuits, the analysis of t...The state space average model and the large signal models of Pulse Skip Modulation (PSM) mode are given in this paper. Farther more, based on these models and simulations of PSM converter circuits, the analysis of the characteristics of PSM converter is described in this paper, of which include efficiency, frequency spectrum analysis, output voltage ripple, response speed and interference rejection capability. Compared with PWM control mode, PSM converter has high efficiency, especially with fight loads, quick response, good interference rejection and good EMC characteristic. Improved PSM slightly, it could be a kind of good independent regulating mode during the whole operating process for a DC-DC converter. Finally, some experimental results are also presented in this paper.展开更多
This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The propos...This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The proposed SUPWM scheme can achieve an output voltage of(2N+1)(where N is the number of submodules in each arm)levels,which is the same as that of the carrier-phase-shifted PWM(CPSPWM)scheme.Meanwhile,the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC.Moreover,the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers.The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.展开更多
The linear and nonlinear characteristics of time-resolved photoluminescence (PL) of n-type bulk semiconductor GaAs modulated with terahertz (THz) pulse are studied by using an ensemble Monte Carlo (EMC) method. ...The linear and nonlinear characteristics of time-resolved photoluminescence (PL) of n-type bulk semiconductor GaAs modulated with terahertz (THz) pulse are studied by using an ensemble Monte Carlo (EMC) method. In this paper the center energy valley (Г valley) electron concentration changes with the pulse delay time, sampling time and the outfield are mainly discussed. The results show that the sampling time and the THz field should exceed certain thresholds to effectively excite photoluminescence quenching (PLQ). Adopting a direct current (DC) field makes the sampling time threshold shortened and the linear range of THz field-modulation PL expanded. Moreover, controlling the sampling time and the outfield intensity can improve the linear quality: with forward time, the larger outfield is used; with backward time, the smaller outfield is used. This study can provide a theoretical basis of THz field linear modulation in a larger range for new light emitting devices.展开更多
The gas heating mechanism in the pulse-modulated radio-frequency (rf) discharge at atmospheric pressure was inves- tigated with a one-dimensional two-temperature fluid model. Firstly, the spatiotemporal profiles of ...The gas heating mechanism in the pulse-modulated radio-frequency (rf) discharge at atmospheric pressure was inves- tigated with a one-dimensional two-temperature fluid model. Firstly, the spatiotemporal profiles of the gas temperature (Tg) in both consistent rf discharge and pulse-modulated rf discharge were compared. The results indicated that Tg decreases considerably with the pulse-modulated power, and the elastic collision mechanism plays a more important role in the gas heating change. Secondly, the influences of the duty cycle on the discharge parameters, especially on the Tg, were studied. It was found that Tg decreases almost linearly with the reduction of the duty cycle, and there exists one ideal value of the duty cycle, by which both the Tg can be adjusted and the glow mode can be sustained. Thirdly, the discharge mode changing from αto γ mode in the pulse-modulated rf discharge was investigated, the spatial distributions of Tg in the two modes show different features and the ion Joule heating is more important during the mode transition.展开更多
A retarding field energy analyzer(RFEA) is used to measure the time-averaged ion energy distributions(IEDs) on the substrate in both continuous wave(CW) and synchronous pulse modulated radio-frequency(RF) indu...A retarding field energy analyzer(RFEA) is used to measure the time-averaged ion energy distributions(IEDs) on the substrate in both continuous wave(CW) and synchronous pulse modulated radio-frequency(RF) inductively coupled Ar plasmas(ICPs).The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions.It is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes narrower.In order to figure out the physical mechanism,the voltage waveforms on the substrate are also measured.The results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as well.Specifically,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase(i.e.,θ = 0) and a minimum value at the opposite phase(i.e.,θ = π).Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion energy.Besides,as θ increases from π to 2π,the IEDs and their energy widths change reversely.展开更多
基金The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through Large Groups Project under grant number(RGP.2/111/43).
文摘Vector control schemes have recently been used to drive linear induction motors(LIM)in high-performance applications.This trend promotes the development of precise and efficient control schemes for individual motors.This research aims to present a novel framework for speed and thrust force control of LIM using space vector pulse width modulation(SVPWM)inverters.The framework under consideration is developed in four stages.To begin,MATLAB Simulink was used to develop a detailed mathematical and electromechanical dynamicmodel.The research presents a modified SVPWM inverter control scheme.By tuning the proportional-integral(PI)controller with a transfer function,optimized values for the PI controller are derived.All the subsystems mentioned above are integrated to create a robust simulation of the LIM’s precise speed and thrust force control scheme.The reference speed values were chosen to evaluate the performance of the respective system,and the developed system’s response was verified using various data sets.For the low-speed range,a reference value of 10m/s is used,while a reference value of 100 m/s is used for the high-speed range.The speed output response indicates that themotor reached reference speed in amatter of seconds,as the delay time is between 8 and 10 s.The maximum amplitude of thrust achieved is less than 400N,demonstrating the controller’s capability to control a high-speed LIM with minimal thrust ripple.Due to the controlled speed range,the developed system is highly recommended for low-speed and high-speed and heavy-duty traction applications.
基金supported by National Natural Science Foundation of China under Grant Nos.51477177 and 51641707
文摘As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.
基金supported by the National Basic Research Program of China(No.613224)
文摘In this paper,the nature and origin of single event effects(SEE) are studied by injecting laser pulses into different circuit blocks,combining with analysis to map pulse width modulators circuitry in the microchip die.A time-domain error-identification method is used in the temporal characteristic analysis of SEE.SEE signatures of different injection times are compared.More serious SEE are observed when the laser shot occurs on a rising edge of the device output for blocks of the error amplifier,current sense comparator,and T and SR latches.
基金supported by the National Natural Science Foundation of China(Grant No.11304397)
文摘Passive decoy-state quantum key distribution is more desirable than the active one in some scenarios. It is also affected by the imperfections of the devices. In this paper, the influence of modulator attenuation on the passive decoy-state method is considered. We introduce and analyze the unbalanced Mach-Zehnder interferometer, briefly, and combining with the virtual source and imaginary unitary transformation, we characterize the passive decoy-state method using a weak coherent photon source with modulator attenuation. According to the attenuation parameter 6, the pass efficiencies are given. Then, the key generation rate can be acquired. From numerical simulations, it can be seen that modulator attenuation has a non- negligible influence on the performance of passive-state QKD protocol. Based on the research, the analysis method of virtual source and imaginary unitary transformation are preferred in analyzing passive decoy state protocol, and the passive decoy-state method is better than the active one and is close to the active vacuum + weak decoy state under the condition of having the same modulator attenuation.
基金National Natural Science Foundation Project (50875088) Guangdong Province Science and Technology Research Project (2010B010700001)+1 种基金 Huangpu District Science and Technology Research Project (1021) Panyu District Science and Technology Research Project (2010-Z-22-1).
文摘This article proposed a new methodology and the principle of sinusoid modulated pulse MIG welding, and systematically established the universal mathematical model of computation of the parameters of the sinusoid modulation pulse, achieving that the welding energy input can be effectively controlled and precisely regulated, the transition of pulse change is smooth and the welding process is stable and reliable. With the characteristics of sinusoidal waveform, such as infinite derivative continuity, eternal periodicity and limited control parameters, this article established the theoretical foundation for choiceness, unification and optimization of the parameters during the new sinusoid modulated pulse MIG welding. Bead-on-plate overlay welding is carried out on the pure aluminum sheet test sample for the test. The result indicated that during the welding process, the real-time current waveform is stable and clear; both the corresponding voltage and the instant welding energy waveform are very stable; the repeatability of the U-I graph plotted is high; its family of lines is clear, neat, and its distribution is concentrated showing that the welding process is stable and the neat and high quality ripple weld seam may be produced.
基金the National Postdoctoral Program for Innovative Talents of China(No.BX20220206)。
文摘High-power intense optical sources in the mid-to-long wavelength infrared region are very attractive for a wide range of fields from fundamental research to materials science and biology applications.However,there are still significant challenges in extending long-wavelength infrared pulses into the relativistic regime using conventional optical techniques.Here,based upon a new type of plasma-based optical method,we present an efficient scheme capable of combining several high-power long-wavelength infrared laser pulses into one single,more intense pulse,thus bringing the intensity of the output pulse to the relativistic regime.Such intense infrared pulses will open up new possibilities for strong-field physics and ultrafast applications.Furthermore,this is beneficial to understand the underlying physics and nonlinear processes of modulation,propagation and energy transfer of high-power intense laser pulses in plasmas.
文摘For improving the energy efficiency of plasma volatile organic compounds( VOCs) decomposition, a pulse modulated power is used to drive the dielectric barrier discharge( DBD) plasma to treat benzene. Through the change of pulse duty cycle,the pulse modulation effect on benzene removal energy efficiency was investigated. The results show that pulse modulation can improve the energy yield and reduce the temperature of the chamber wall. There is an optimal duty cycle for achieving the maximum energy yield at a certain discharge voltage. The effect of initial benzene concentration on the decomposition efficiency and carbon selectivity in pulse modulation plasma were studied. The results indicate that the removal efficiency and carbon balance increase with the specific input energy( SIE) and decrease with the concentration. The energy yield increases with increasing initial concentration and achieves maximum around 180 J / L SIE for all initial concentrations.
文摘A hybrid control strategy has been designed and developed for the electro-hydraulic posi-tion servo control system with generalized Pulse code modulation (GPCM), which is suitable for the area where the work condition is poor and a large flow rate is required. It is difficult to control the GPCM system because the system is discrete. With consideration of the stability and speediness of the GPCM position servo control system, a control strategy is developed through the theoretical and ex-perimental analyses. The control strategy integrates the merits of Bang-Bang control, PID control and fuzzy control. With this hybrid control strategy, the electro hydraulic control system has good per-formances, and the servo control is carried out with GPCM through on-off valves.
基金supported by National Natural Science Foundation of China(Nos.11475043 and 11375042)
文摘The discharge operation regime of pulse modulated atmospheric radio frequency (RF) glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha(s)- gamma(γ) mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 kHz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.
基金Project supported by Tsinghua University Initiative Scientific Research Program,China(Grant No.2014z21035)
文摘A novel concept of collision avoidance single-photon light detection and ranging(LIDAR) for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for robust anti-crosstalk purposes. Besides, single-photon detectors(SPD) and time correlated single photon counting techniques are adapted, to sense the ultra-low power used for the consideration of compact structure and eye safety. Parameters including pulse rate, discrimination threshold, and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite ultra-low transmitting power.
基金Center-initiated Research Project of Zhejiang Laboratory(K2022ME0AL04)National Key Research and Development Program of China(2021ZD0109904)+1 种基金National Natural Science Foundation of China(62105301)Key Research Project of Zhejiang Laboratory(2020ME0AD02)。
文摘We experimentally demonstrate ultra-high extinction ratio(ER)optical pulse modulation with an electro-optical modulator(EOM)on thin film lithium niobate(TFLN)and its application for fiber optic distributed acoustic sensing(DAS).An interface carrier effect leading to a relaxation-tail response of TFLN EOM is discovered,which can be well addressed by a small compensation component following the main driving signal.An ultrahigh ER>50 dB is achieved by canceling out the tailed response during pulse modulation using the EOM based on a cascaded Mach–Zehnder interferometer(MZI)structure.The modulated optical_(√)pulses are then utilized as a probe light for a DAS system,showing a sensitivity up to-62.9 dB·rad∕Hz~2(7 pε/Hz)for 2-km single-mode sensing fiber.Spatial crosstalk suppression of 24.9 dB along the fiber is also obtained when the ER is improved from 20 dB to 50 dB,clearly revealing its importance to the sensing performance.
基金Supported by the National Natural Science Foundation of China (No.60436030)
文摘The state space average model and the large signal models of Pulse Skip Modulation (PSM) mode are given in this paper. Farther more, based on these models and simulations of PSM converter circuits, the analysis of the characteristics of PSM converter is described in this paper, of which include efficiency, frequency spectrum analysis, output voltage ripple, response speed and interference rejection capability. Compared with PWM control mode, PSM converter has high efficiency, especially with fight loads, quick response, good interference rejection and good EMC characteristic. Improved PSM slightly, it could be a kind of good independent regulating mode during the whole operating process for a DC-DC converter. Finally, some experimental results are also presented in this paper.
基金This work was supported in part by the National Natural Science Foundation of China under Grant 51707088,51607081the 5th-level talent introduction program of Kunming University of Science and Technology.
文摘This paper presents an improved submodule unified pulse width modulation(SUPWM)scheme for a hybrid modular multilevel converter(MMC)composed of half-bridge submodules(HBSMs)and full-bridge submodules(FBSMs).The proposed SUPWM scheme can achieve an output voltage of(2N+1)(where N is the number of submodules in each arm)levels,which is the same as that of the carrier-phase-shifted PWM(CPSPWM)scheme.Meanwhile,the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC.Moreover,the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers.The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.
基金supported by the National Natural Science Foundation of China(Grant Nos.11574105,61475054,61405063,and 61177095)the Hubei Science and Technology Agency Project,China(Grant No.2015BCE052)the Fundamental Research Funds for the Central Universities,China(Grant No.2017KFYXJJ029)
文摘The linear and nonlinear characteristics of time-resolved photoluminescence (PL) of n-type bulk semiconductor GaAs modulated with terahertz (THz) pulse are studied by using an ensemble Monte Carlo (EMC) method. In this paper the center energy valley (Г valley) electron concentration changes with the pulse delay time, sampling time and the outfield are mainly discussed. The results show that the sampling time and the THz field should exceed certain thresholds to effectively excite photoluminescence quenching (PLQ). Adopting a direct current (DC) field makes the sampling time threshold shortened and the linear range of THz field-modulation PL expanded. Moreover, controlling the sampling time and the outfield intensity can improve the linear quality: with forward time, the larger outfield is used; with backward time, the smaller outfield is used. This study can provide a theoretical basis of THz field linear modulation in a larger range for new light emitting devices.
基金Project supported by the National Natural Science Foundation of China(Granted Nos.11405022 and 11475040)Dalian High Level Talent Innovation Support Plan,China(Grant No.2015R050)
文摘The gas heating mechanism in the pulse-modulated radio-frequency (rf) discharge at atmospheric pressure was inves- tigated with a one-dimensional two-temperature fluid model. Firstly, the spatiotemporal profiles of the gas temperature (Tg) in both consistent rf discharge and pulse-modulated rf discharge were compared. The results indicated that Tg decreases considerably with the pulse-modulated power, and the elastic collision mechanism plays a more important role in the gas heating change. Secondly, the influences of the duty cycle on the discharge parameters, especially on the Tg, were studied. It was found that Tg decreases almost linearly with the reduction of the duty cycle, and there exists one ideal value of the duty cycle, by which both the Tg can be adjusted and the glow mode can be sustained. Thirdly, the discharge mode changing from αto γ mode in the pulse-modulated rf discharge was investigated, the spatial distributions of Tg in the two modes show different features and the ion Joule heating is more important during the mode transition.
基金Project supported by the Important National Science and Technology Specific Project,China(Grant No.2011ZX02403-001)the National Natural Science Foundation of China(Grand No.11675039)the Fundamental Research Funds for the Central Universities,China(Grand No.DUT16LK06)
文摘A retarding field energy analyzer(RFEA) is used to measure the time-averaged ion energy distributions(IEDs) on the substrate in both continuous wave(CW) and synchronous pulse modulated radio-frequency(RF) inductively coupled Ar plasmas(ICPs).The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions.It is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes narrower.In order to figure out the physical mechanism,the voltage waveforms on the substrate are also measured.The results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as well.Specifically,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase(i.e.,θ = 0) and a minimum value at the opposite phase(i.e.,θ = π).Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion energy.Besides,as θ increases from π to 2π,the IEDs and their energy widths change reversely.