Lattice-matched In0.5 Ga0.47 As/In0.52 Al 0.48 As high electron mobility transistors （HEMTs） with a cutoff frequency （ft） as high as 218GHz are reported. This fT is the highest value ever reported for HEMTs in Chi...Lattice-matched In0.5 Ga0.47 As/In0.52 Al 0.48 As high electron mobility transistors （HEMTs） with a cutoff frequency （ft） as high as 218GHz are reported. This fT is the highest value ever reported for HEMTs in China. These devices also demonstrate excellent DC characteristics：the extrinsic transconductance is 980mS/mm and the maximum current density is 870mA/mm. The material structure and all the device fabrication technology in this work were developed by our group.展开更多
We theoretically investigate high-order harmonic generation by employing strong-field approximation （SFA） and present a new approach to the extension of the high-order harmonic cutoff frequency via an exploration of...We theoretically investigate high-order harmonic generation by employing strong-field approximation （SFA） and present a new approach to the extension of the high-order harmonic cutoff frequency via an exploration of the dependence of high-order harmonic generation on the waveform of laser fields. The dependence is investigated via detailed analysis of the classical trajectories of the ionized electron moving in the continuum in the velocity-position plane. The classical trajectory consists of three sections （Acceleration Away, Deceleration Away, and Acceleration Back）, and their relationship with the electron recollision energy is investigated. The analysis of classical trajectories indicates that, besides the final （Acceleration Back） section, the electron recollision energy also relies on the previous two sections. We simultaneously optimize the waveform in all three sections to increase the electron recollision energy, and an extension of the cutoff frequency up to Ip ＋ 20.26Up is presented with a theoretically synthesized waveform of the laser field.展开更多
The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors （OTFTs） is studied. The effects of electrode thickness, field-effect mobility, channel length and gate...The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors （OTFTs） is studied. The effects of electrode thickness, field-effect mobility, channel length and gate-source voltage on the contact length （source and drain electrodes＇ length） related contact resistance of bottom-contact OTFTs are performed with a modified transmission line model. It is found that the contact resistance increases dramatically when the contact length is scaled down to 20O nm. With the help of the contact length related contact resistance, contact-size-dependent fT Of bottom-contact OTFTs is studied and it is found that fr increases with the decrease of the contact length in bottom-contact OTFTs.展开更多
Direct current（DC） and radio frequency（RF） performances of InP-based high electron mobility transistors（HEMTs）are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shock...Direct current（DC） and radio frequency（RF） performances of InP-based high electron mobility transistors（HEMTs）are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley–Read–Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover,the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency( f;) of 385 GHz.展开更多
This paper proposed a simple approach to determine noise frequency of boiler drum level in order to improve control performance. Based on analysis of uncertainty of drum level, the redundant oscillation component of s...This paper proposed a simple approach to determine noise frequency of boiler drum level in order to improve control performance. Based on analysis of uncertainty of drum level, the redundant oscillation component of signal, noise is ascribed to the surface wave of drum water. According to the characteristic of surface wave, a new method was proposed to determine noise’s frequency band. By gradually removing the lowest frequency component of signal, the variance of remained component is calculated and observed. An apparent turning point was found and the corresponding critical frequcncy was determined. With this result a low-pass filter was designed to separate noise component. Finally validation is conducted by comparing the proposed method and conventional ones. Results show the accuracy and simpleness of the proposed method.展开更多
Lattice matched InP based InAlAs/InGaAs HEMTs with 120GHz cutoff frequency are reported.These devices demonstrate excellent DC characteristics:the extrinsic transconductance of 600mS/mm,the threshold voltage of -1 ...Lattice matched InP based InAlAs/InGaAs HEMTs with 120GHz cutoff frequency are reported.These devices demonstrate excellent DC characteristics:the extrinsic transconductance of 600mS/mm,the threshold voltage of -1 2V,and the maximum current density of 500mA/mm.展开更多
By epitaxial layer structure design and key fabrication process optimization,a lattice-matched InP-based In0.53Ga0.47 As-In0.52Al0.48As HEMT with an ultra high maximum oscillation frequency （fmax） of 183GHz was fab-...By epitaxial layer structure design and key fabrication process optimization,a lattice-matched InP-based In0.53Ga0.47 As-In0.52Al0.48As HEMT with an ultra high maximum oscillation frequency （fmax） of 183GHz was fab- ricated. The fmax is the highest value for HEMTs in China. Also, the devices are reported, including the device structure, the fabrication process, and the DC and RF performances.展开更多
The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigne...The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigned to particular phonon branches and the points in the Brillouin zone from which the scattering originates.There exists a doublet at 626/636cm -1 with energy difference about 10cm -1 in both n- and p-type 4H-SiC,which is similar to the doublet structure with the same energy difference founded in hexagonal GaN,ZnO, and AlN.The cutoff frequency at 1926cm -1 of the second-order Raman is not the overtone of the A 1(LO) peak of the n-type doping 4H-SiC,but that of the undoping one.The second-order Raman spectrum of 4H-SiC can hardly be affected by doping species or doping density.展开更多
InA1As/InGaAs high electron mobility transistors （HEMTs） on an InP substrate with well-balanced cutoff frequency fT and maximum oscillation frequency frnax are reported. An InA1As/InGaAs HEMT with 100-nm gate length...InA1As/InGaAs high electron mobility transistors （HEMTs） on an InP substrate with well-balanced cutoff frequency fT and maximum oscillation frequency frnax are reported. An InA1As/InGaAs HEMT with 100-nm gate length and gate width of 2 × 50 μm shows excellent DC characteristics, including full channel current of 724 mA/mm, extrinsic maximum transconductance gm.max of 1051 mS/mm, and drain-gate breakdown voltage BVDG of 5.92 V. In addition, this device exhibits fT = 249 GHz and fmax = 415 GHz. These results were obtained by fabricating an asymmetrically recessed gate and minimizing the parasitic resistances. The specific Ohmic contact resistance was reduced to 0.031 0.mm. Moreover, the fT obtained in this work is the highest ever reported in 100-nm gate length InA1As/InGaAs InP-based HEMTs. The outstanding gm.max, fT, fmax, and good BVDG make the device suitable for applications in low noise amplifiers, power amplifiers, and high speed circuits.展开更多
In this paper,under two different electromagnetic modes,the photonic band gaps（PBGs） in the two-dimensional plasma photonic crystals（PPCs） are theoretically investigated based on the plane wave expansion method.Th...In this paper,under two different electromagnetic modes,the photonic band gaps（PBGs） in the two-dimensional plasma photonic crystals（PPCs） are theoretically investigated based on the plane wave expansion method.The proposed PPCs are arranged in rhombus lattices,in which the homogeneous unmagnetized plasma rods are immersed in the isotropic dielectric background.The computed results showed that PBGs can be easily tuned by the angle of rhombus lattices,and a cutoff frequency and a flatbands region can be observed under the TM and TE polarized waves,respectively.The relationships between the relative bandwidths of first PBGs and the parameters of PPCs in two such cases also are discussed.The numerical simulations showed that the PBGs can be manipulated obviously by the parameters as mentioned above.The proposed results can be used to design the waveguide and filter based on the PPCs.展开更多
The filter proposed in this paper is expected to reduce noise whose frequency is lower than higher order harmonics of real signals.It is based on the distributive characteristics of noise,and uses analog circuits to s...The filter proposed in this paper is expected to reduce noise whose frequency is lower than higher order harmonics of real signals.It is based on the distributive characteristics of noise,and uses analog circuits to select the high peak and low peak of the input signal and applies their average in order to reduce random noise.So it has no cutoff frequency and higher order harmonics of real signals are remained.As a result,it gives an instant response to changes in input signals and retains the integrity of real signals.Furthermore,it has only a small phase delay.The simulation results of slew rate,phase delay and spectral analysis under MULTISIM indicate that the quick response noise filter achieves a high slew rate of 472 V/ms and the phase shift is nearly zero.By having it used in a color tester design,it is also demonstrated that the proposed filter effectively reduces noise and remains signal integrity.With the filter 's help,the relative standard deviation of the spectrograph decreases from 1% to 0.22%,indicating better stability.展开更多
High quality speed information is one of the key issues in machine sensorless drives,which often requires proper filtering of the estimated speed.This paper comparatively studies typical low-pass filters(LPF)and phase...High quality speed information is one of the key issues in machine sensorless drives,which often requires proper filtering of the estimated speed.This paper comparatively studies typical low-pass filters(LPF)and phase-locked loop(PLL)type filters with respect to ramp speed reference tracking and steady-state performances,as well as the achievement of adaptive cutoff frequency control.An improved LPF-based filter structure with no ramping and steady-state errors caused by filter parameter quantization effects is proposed,which is suitable for applying LPF for sensorless drives of AC machines,especially when fixed-point digital signal processor is selected e.g.in mass production.Furthermore,the potential of adopting PLL for speed filtering is explored.It is demonstrated that PLL type filters can well maintain the advantages offered by the improved LPF.Moreover,it is found that the PLL type filters exhibit almost linear relationship between the cutoff frequency of the PLL filter and its proportional-integral(PI)gains,which can ease the realization of speed filters with adaptive cutoff frequency for improving the speed transient performance.The proposed filters are verified experimentally.The PLL type filter with adaptive cutoff frequency can provide satisfactory performances under various operating conditions and is therefore recommended.展开更多
In this paper,configuration parameters of the waveguide are altered independently or simultaneously to control the cutoff frequencies of the guided band.The independent control range of the upper and lower cutoff freq...In this paper,configuration parameters of the waveguide are altered independently or simultaneously to control the cutoff frequencies of the guided band.The independent control range of the upper and lower cutoff frequencies is 55.0% and 63.9% of the photonic band gap(PBG),respectively.The regulating range of the simultaneous tuning can be as large as 28.6% in terms of the PBG,or 240% in terms of the bandwidth.This tuning cutoff frequency method provides an efficient way to tailor the guided band and further tune the optical properties of PhCWs.展开更多
The resonant frequencies of the excited surface waves on a metal hole array with respect to the incident angle were studied in the terahertz region.The experimental and theoretical results demonstrate that the resonan...The resonant frequencies of the excited surface waves on a metal hole array with respect to the incident angle were studied in the terahertz region.The experimental and theoretical results demonstrate that the resonant peak of surface wave excitation splits into two when transmitted through a metal hole array off-normally.The high-order mode with resonant frequency above the cutoff frequency fc(plasma frequency effect)has a shorter attenuation length than that of the low-order mode whose resonant frequency is below fc.The reason is that the high-order mode is a coupled mode consisting of surface wave and hole modes,while the low-order mode is just an excited surface wave(which can be considered as the spoof surface plasmons).Our investigation may open a door to distinguish the spoof surface plasmons and the coupled modes of surface waves and hole modes.展开更多
Ultrafast electromagnetic waves radiated from semiconductor material under high electric fields and photoexcited by femtosecond laser pulses have been recorded by using terahertz time domain spectroscopy （THz-TDS）.T...Ultrafast electromagnetic waves radiated from semiconductor material under high electric fields and photoexcited by femtosecond laser pulses have been recorded by using terahertz time domain spectroscopy （THz-TDS）.The waveforms of these electromagnetic waves reflect the dynamics of the photoexcited carriers in the semiconductor material,thus,THz-TDS provides a unique opportunity to observe directly the temporal and spatial evolutions of non-equilibrium transport of carriers within sub-picosecond time scale.We report on the observed THz emission waveforms emitted from GaAs by using a novel technology,the time domain THz electro-optic （EO） sampling,which has a bipolar feature,i.e.,an initial positive peak and a subsequent negative dip that arises from its velocity overshoot.The initial positive peak has been interpreted as electron acceleration in the bottom of Γ valley in GaAs,where electrons have a light effective mass.The subsequent negative dip has been attributed to intervalley transfer from Γ to X and L valleys.Furthermore,the power dissipation spectra of the bulk GaAs in THz range are also investigated by using the Fourier transformation of the time domain THz traces.From the power dissipation spectra,the cutoff frequency for negative power dissipation （i.e.,gain） under step electric field in the bulk GaAs can also be obtained.The cutoff frequency for the gain gradually increases with increasing electric fields up to 50 kV/cm and achieves saturation at approximately 1 THz at 300 K.Furthermore,based on the temperature dependence of the cutoff frequency,we find that this cutoff frequency is governed by the energy relaxation process of electrons from L to Γ valley via successive optical phonon emission.展开更多
Biological processes and behaviors of endothelial cells on the inner surfaces of blood vessels are regulated by the stimulation from biochemical signals contained in the blood.In this paper,the transportation of dynam...Biological processes and behaviors of endothelial cells on the inner surfaces of blood vessels are regulated by the stimulation from biochemical signals contained in the blood.In this paper,the transportation of dynamic biochemical signals in non-reversing oscillatory flows in blood vessels is analyzed by numerically solving a nonlinear governing equation for the time-dependent Taylor-Aris dispersion.Results show that the nonlinear frequency-amplitude modulation of the transportation of biochemical signals is more(less) significant when the frequency of an oscillatory flow is close to(higher than) that of an oscillatory signal.Under steady flow,the transfer function for the signal transmission system is obtained,showing that the system is a low-pass filter.Lower inner radius or higher center-line velocity of a blood vessel increases the cutoff frequency of the transportation system.These results suggest the possibility and condition for the 'remote' transmission of low-frequency dynamic biochemical signals in pulsatile blood flows.展开更多
We demonstrate a photonic band gap（PBG） from one-dimensional（1D） periodic structures created by a double-layer unit cell with an air layer and an anisotropic nonmagnetic left-handed metamaterial（LHM） layer whose...We demonstrate a photonic band gap（PBG） from one-dimensional（1D） periodic structures created by a double-layer unit cell with an air layer and an anisotropic nonmagnetic left-handed metamaterial（LHM） layer whose permittivity elements are partially negative.The requirements imposed on the materials and structures to realize a PBG are derived when the frequency is above or below the cutoff frequency,and the transmission properties of the PBG are discussed by utilizing 4×4 transfer-matrix method with dispersive semiconductor metamaterial.展开更多
The material dispersion of a tapered fiber is described by Sellmeier＇s equation. The dependence of refractive index on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of 632...The material dispersion of a tapered fiber is described by Sellmeier＇s equation. The dependence of refractive index on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of 632.8 nm is used in the experiment. When the cutoff frequency of the fiber is less than the laser frequency, the guiding modes of a singl^-mode fiber （at 1550 am） are investigated. The results show that the original single-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light in the taper region are analyzed. By controlling the taper end size of the fiber, the unique tapered fiber can convert a multi-mode beam into a single-mode one.展开更多
In this manuscript we analyze a unique approach to improve the performance of the bipolar charge plasma transistor(BCPT) by introducing a strained Si/SiGe1-x layer as the active device region. For charge plasma realiz...In this manuscript we analyze a unique approach to improve the performance of the bipolar charge plasma transistor(BCPT) by introducing a strained Si/SiGe1-x layer as the active device region. For charge plasma realization different metal work-function electrodes are used to induce n+ and p+ regions on undoped strained silicon-on-insulator(sSOI or SiGe) to realize emitter, base, and collector regions of the BCPT. Here,by using a calibrated 2-D TCAD simulation the impact of a Si mole fraction x(in SiGe) on device performance metrics is investigated. The analysis demonstrates the band gap lowering with decreasing Si content or effective strain on the Si layer, and its subsequent advantages. This work reports a significant improvement in current gain, cutoff frequency, and lower collector breakdown voltage(BVCEO) for the proposed structure over the conventional device. The effect of varying temperature on the strained Si layer and its implications on the device performance is also investigated. The analysis demonstrates a fair device-level understanding and exhibits the immense potential of the SiGematerial as the device layer. In addition to this, using extensive 2-D mixed-mode TCAD simulation, a considerable improvement in switching transient times are also observed compared to its conventional counterpart.展开更多
A new PMMA/PMGI/ZEP520/PMGI four-layer resistor electron beam lithography technology is successfully developed and used to fabricate a 120 nm gate-length lattice-matched In_（0.53）Ga_（0.47）As/In_（0.52）Al_（0.48）...A new PMMA/PMGI/ZEP520/PMGI four-layer resistor electron beam lithography technology is successfully developed and used to fabricate a 120 nm gate-length lattice-matched In_（0.53）Ga_（0.47）As/In_（0.52）Al_（0.48） As InP-based HEMT,of which the material structure is successfully designed and optimized by our group.A 980 nm ultra-wide T-gate head,which is nearly as wide as 8 times the gatefoot（120 nm）,is successfully obtained,and the excellent T-gate profile greatly reduces the parasitic resistance and capacitance effect and effectively enhances the RF performances. These fabricated devices demonstrate excellent DC and RF performances such as a maximum current gain frequency of 190 GHz and a unilateral power-gain gain frequency of 146 GHz.展开更多
文摘Lattice-matched In0.5 Ga0.47 As/In0.52 Al 0.48 As high electron mobility transistors （HEMTs） with a cutoff frequency （ft） as high as 218GHz are reported. This fT is the highest value ever reported for HEMTs in China. These devices also demonstrate excellent DC characteristics：the extrinsic transconductance is 980mS/mm and the maximum current density is 870mA/mm. The material structure and all the device fabrication technology in this work were developed by our group.
基金supported by the National Basic Research Program of China (Grant No. 2010CB923102)the Special Prophase Project on the National Basic Research Program of China (Grant No. 2011CB311807)the National Natural Science Foundation of China (Grant No. 11074199)
文摘We theoretically investigate high-order harmonic generation by employing strong-field approximation （SFA） and present a new approach to the extension of the high-order harmonic cutoff frequency via an exploration of the dependence of high-order harmonic generation on the waveform of laser fields. The dependence is investigated via detailed analysis of the classical trajectories of the ionized electron moving in the continuum in the velocity-position plane. The classical trajectory consists of three sections （Acceleration Away, Deceleration Away, and Acceleration Back）, and their relationship with the electron recollision energy is investigated. The analysis of classical trajectories indicates that, besides the final （Acceleration Back） section, the electron recollision energy also relies on the previous two sections. We simultaneously optimize the waveform in all three sections to increase the electron recollision energy, and an extension of the cutoff frequency up to Ip ＋ 20.26Up is presented with a theoretically synthesized waveform of the laser field.
基金Supported by the State Key Fundamental Research Project of China under Grant No 2011CBA00606the National Natural Science Foundation of China under Grant Nos 51503167 and 61574107
文摘The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors （OTFTs） is studied. The effects of electrode thickness, field-effect mobility, channel length and gate-source voltage on the contact length （source and drain electrodes＇ length） related contact resistance of bottom-contact OTFTs are performed with a modified transmission line model. It is found that the contact resistance increases dramatically when the contact length is scaled down to 20O nm. With the help of the contact length related contact resistance, contact-size-dependent fT Of bottom-contact OTFTs is studied and it is found that fr increases with the decrease of the contact length in bottom-contact OTFTs.
基金supported by the National Natural Science Foundation of China(Grant Nos.61404115 and 61434006)the Postdoctoral Science Foundation of Henan Province,China(Grant No.2014006)the Development Fund for Outstanding Young Teachers of Zhengzhou University(Grant No.1521317004)
文摘Direct current（DC） and radio frequency（RF） performances of InP-based high electron mobility transistors（HEMTs）are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley–Read–Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover,the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency( f;) of 385 GHz.
文摘This paper proposed a simple approach to determine noise frequency of boiler drum level in order to improve control performance. Based on analysis of uncertainty of drum level, the redundant oscillation component of signal, noise is ascribed to the surface wave of drum water. According to the characteristic of surface wave, a new method was proposed to determine noise’s frequency band. By gradually removing the lowest frequency component of signal, the variance of remained component is calculated and observed. An apparent turning point was found and the corresponding critical frequcncy was determined. With this result a low-pass filter was designed to separate noise component. Finally validation is conducted by comparing the proposed method and conventional ones. Results show the accuracy and simpleness of the proposed method.
文摘Lattice matched InP based InAlAs/InGaAs HEMTs with 120GHz cutoff frequency are reported.These devices demonstrate excellent DC characteristics:the extrinsic transconductance of 600mS/mm,the threshold voltage of -1 2V,and the maximum current density of 500mA/mm.
文摘By epitaxial layer structure design and key fabrication process optimization,a lattice-matched InP-based In0.53Ga0.47 As-In0.52Al0.48As HEMT with an ultra high maximum oscillation frequency （fmax） of 183GHz was fab- ricated. The fmax is the highest value for HEMTs in China. Also, the devices are reported, including the device structure, the fabrication process, and the DC and RF performances.
文摘The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigned to particular phonon branches and the points in the Brillouin zone from which the scattering originates.There exists a doublet at 626/636cm -1 with energy difference about 10cm -1 in both n- and p-type 4H-SiC,which is similar to the doublet structure with the same energy difference founded in hexagonal GaN,ZnO, and AlN.The cutoff frequency at 1926cm -1 of the second-order Raman is not the overtone of the A 1(LO) peak of the n-type doping 4H-SiC,but that of the undoping one.The second-order Raman spectrum of 4H-SiC can hardly be affected by doping species or doping density.
基金Project supported by the National Basic Research Program of China(Grant No.2010CB327502)
文摘InA1As/InGaAs high electron mobility transistors （HEMTs） on an InP substrate with well-balanced cutoff frequency fT and maximum oscillation frequency frnax are reported. An InA1As/InGaAs HEMT with 100-nm gate length and gate width of 2 × 50 μm shows excellent DC characteristics, including full channel current of 724 mA/mm, extrinsic maximum transconductance gm.max of 1051 mS/mm, and drain-gate breakdown voltage BVDG of 5.92 V. In addition, this device exhibits fT = 249 GHz and fmax = 415 GHz. These results were obtained by fabricating an asymmetrically recessed gate and minimizing the parasitic resistances. The specific Ohmic contact resistance was reduced to 0.031 0.mm. Moreover, the fT obtained in this work is the highest ever reported in 100-nm gate length InA1As/InGaAs InP-based HEMTs. The outstanding gm.max, fT, fmax, and good BVDG make the device suitable for applications in low noise amplifiers, power amplifiers, and high speed circuits.
文摘In this paper,under two different electromagnetic modes,the photonic band gaps（PBGs） in the two-dimensional plasma photonic crystals（PPCs） are theoretically investigated based on the plane wave expansion method.The proposed PPCs are arranged in rhombus lattices,in which the homogeneous unmagnetized plasma rods are immersed in the isotropic dielectric background.The computed results showed that PBGs can be easily tuned by the angle of rhombus lattices,and a cutoff frequency and a flatbands region can be observed under the TM and TE polarized waves,respectively.The relationships between the relative bandwidths of first PBGs and the parameters of PPCs in two such cases also are discussed.The numerical simulations showed that the PBGs can be manipulated obviously by the parameters as mentioned above.The proposed results can be used to design the waveguide and filter based on the PPCs.
基金Sponsored by the National High Technology Research and Development Program(Grant No.863-2-5-1-13B)
文摘The filter proposed in this paper is expected to reduce noise whose frequency is lower than higher order harmonics of real signals.It is based on the distributive characteristics of noise,and uses analog circuits to select the high peak and low peak of the input signal and applies their average in order to reduce random noise.So it has no cutoff frequency and higher order harmonics of real signals are remained.As a result,it gives an instant response to changes in input signals and retains the integrity of real signals.Furthermore,it has only a small phase delay.The simulation results of slew rate,phase delay and spectral analysis under MULTISIM indicate that the quick response noise filter achieves a high slew rate of 472 V/ms and the phase shift is nearly zero.By having it used in a color tester design,it is also demonstrated that the proposed filter effectively reduces noise and remains signal integrity.With the filter 's help,the relative standard deviation of the spectrograph decreases from 1% to 0.22%,indicating better stability.
基金This work was supported in part by Lodam A/S and in part by the PSO-ELFORSK Program。
文摘High quality speed information is one of the key issues in machine sensorless drives,which often requires proper filtering of the estimated speed.This paper comparatively studies typical low-pass filters(LPF)and phase-locked loop(PLL)type filters with respect to ramp speed reference tracking and steady-state performances,as well as the achievement of adaptive cutoff frequency control.An improved LPF-based filter structure with no ramping and steady-state errors caused by filter parameter quantization effects is proposed,which is suitable for applying LPF for sensorless drives of AC machines,especially when fixed-point digital signal processor is selected e.g.in mass production.Furthermore,the potential of adopting PLL for speed filtering is explored.It is demonstrated that PLL type filters can well maintain the advantages offered by the improved LPF.Moreover,it is found that the PLL type filters exhibit almost linear relationship between the cutoff frequency of the PLL filter and its proportional-integral(PI)gains,which can ease the realization of speed filters with adaptive cutoff frequency for improving the speed transient performance.The proposed filters are verified experimentally.The PLL type filter with adaptive cutoff frequency can provide satisfactory performances under various operating conditions and is therefore recommended.
基金supported by the Ministry of Science and Technology of China (Grant No. 2007CB936204)the National Natural Science Foundation of China (Grant Nos. 61271050,61076057 and 61171023)
文摘In this paper,configuration parameters of the waveguide are altered independently or simultaneously to control the cutoff frequencies of the guided band.The independent control range of the upper and lower cutoff frequencies is 55.0% and 63.9% of the photonic band gap(PBG),respectively.The regulating range of the simultaneous tuning can be as large as 28.6% in terms of the PBG,or 240% in terms of the bandwidth.This tuning cutoff frequency method provides an efficient way to tailor the guided band and further tune the optical properties of PhCWs.
基金This work is supported by the National Natural Science Foundation of China(11174207,61138001,61007059,61205094)the Key Scientific and Technological Project of Science and Technology Commission of Shanghai Municipality(11DZ1110800)+2 种基金the Major National Development Project of Scientific Instrument and Equipment(2011YQ150021)National Program on Key Basic Research Project of China(2012CB934203)the Leading Academic Discipline Project of Shanghai Municipal Government(S30502).
文摘The resonant frequencies of the excited surface waves on a metal hole array with respect to the incident angle were studied in the terahertz region.The experimental and theoretical results demonstrate that the resonant peak of surface wave excitation splits into two when transmitted through a metal hole array off-normally.The high-order mode with resonant frequency above the cutoff frequency fc(plasma frequency effect)has a shorter attenuation length than that of the low-order mode whose resonant frequency is below fc.The reason is that the high-order mode is a coupled mode consisting of surface wave and hole modes,while the low-order mode is just an excited surface wave(which can be considered as the spoof surface plasmons).Our investigation may open a door to distinguish the spoof surface plasmons and the coupled modes of surface waves and hole modes.
基金supported by the Nanotechnology Special Project of Science and Technology Commission of Shanghai (No. 1052nm07100)the Ministry of Education Doctoral Fund of New Teachers of China (No. 20093120120007)the National Natural Science Foundation of China (No. 61007059)
文摘Ultrafast electromagnetic waves radiated from semiconductor material under high electric fields and photoexcited by femtosecond laser pulses have been recorded by using terahertz time domain spectroscopy （THz-TDS）.The waveforms of these electromagnetic waves reflect the dynamics of the photoexcited carriers in the semiconductor material,thus,THz-TDS provides a unique opportunity to observe directly the temporal and spatial evolutions of non-equilibrium transport of carriers within sub-picosecond time scale.We report on the observed THz emission waveforms emitted from GaAs by using a novel technology,the time domain THz electro-optic （EO） sampling,which has a bipolar feature,i.e.,an initial positive peak and a subsequent negative dip that arises from its velocity overshoot.The initial positive peak has been interpreted as electron acceleration in the bottom of Γ valley in GaAs,where electrons have a light effective mass.The subsequent negative dip has been attributed to intervalley transfer from Γ to X and L valleys.Furthermore,the power dissipation spectra of the bulk GaAs in THz range are also investigated by using the Fourier transformation of the time domain THz traces.From the power dissipation spectra,the cutoff frequency for negative power dissipation （i.e.,gain） under step electric field in the bulk GaAs can also be obtained.The cutoff frequency for the gain gradually increases with increasing electric fields up to 50 kV/cm and achieves saturation at approximately 1 THz at 300 K.Furthermore,based on the temperature dependence of the cutoff frequency,we find that this cutoff frequency is governed by the energy relaxation process of electrons from L to Γ valley via successive optical phonon emission.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11172060 and 10972139)the Fundamental Research Funds for the Central Universities in China (Grant No. DUT12JB11)
文摘Biological processes and behaviors of endothelial cells on the inner surfaces of blood vessels are regulated by the stimulation from biochemical signals contained in the blood.In this paper,the transportation of dynamic biochemical signals in non-reversing oscillatory flows in blood vessels is analyzed by numerically solving a nonlinear governing equation for the time-dependent Taylor-Aris dispersion.Results show that the nonlinear frequency-amplitude modulation of the transportation of biochemical signals is more(less) significant when the frequency of an oscillatory flow is close to(higher than) that of an oscillatory signal.Under steady flow,the transfer function for the signal transmission system is obtained,showing that the system is a low-pass filter.Lower inner radius or higher center-line velocity of a blood vessel increases the cutoff frequency of the transportation system.These results suggest the possibility and condition for the 'remote' transmission of low-frequency dynamic biochemical signals in pulsatile blood flows.
基金supported by the National Natural Science Foundation of China under Grant No.60771045
文摘We demonstrate a photonic band gap（PBG） from one-dimensional（1D） periodic structures created by a double-layer unit cell with an air layer and an anisotropic nonmagnetic left-handed metamaterial（LHM） layer whose permittivity elements are partially negative.The requirements imposed on the materials and structures to realize a PBG are derived when the frequency is above or below the cutoff frequency,and the transmission properties of the PBG are discussed by utilizing 4×4 transfer-matrix method with dispersive semiconductor metamaterial.
文摘The material dispersion of a tapered fiber is described by Sellmeier＇s equation. The dependence of refractive index on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of 632.8 nm is used in the experiment. When the cutoff frequency of the fiber is less than the laser frequency, the guiding modes of a singl^-mode fiber （at 1550 am） are investigated. The results show that the original single-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light in the taper region are analyzed. By controlling the taper end size of the fiber, the unique tapered fiber can convert a multi-mode beam into a single-mode one.
文摘In this manuscript we analyze a unique approach to improve the performance of the bipolar charge plasma transistor(BCPT) by introducing a strained Si/SiGe1-x layer as the active device region. For charge plasma realization different metal work-function electrodes are used to induce n+ and p+ regions on undoped strained silicon-on-insulator(sSOI or SiGe) to realize emitter, base, and collector regions of the BCPT. Here,by using a calibrated 2-D TCAD simulation the impact of a Si mole fraction x(in SiGe) on device performance metrics is investigated. The analysis demonstrates the band gap lowering with decreasing Si content or effective strain on the Si layer, and its subsequent advantages. This work reports a significant improvement in current gain, cutoff frequency, and lower collector breakdown voltage(BVCEO) for the proposed structure over the conventional device. The effect of varying temperature on the strained Si layer and its implications on the device performance is also investigated. The analysis demonstrates a fair device-level understanding and exhibits the immense potential of the SiGematerial as the device layer. In addition to this, using extensive 2-D mixed-mode TCAD simulation, a considerable improvement in switching transient times are also observed compared to its conventional counterpart.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.60806024)the Fundamental Research Funds for Central University,China(No.XDJK2009C020)
文摘A new PMMA/PMGI/ZEP520/PMGI four-layer resistor electron beam lithography technology is successfully developed and used to fabricate a 120 nm gate-length lattice-matched In_（0.53）Ga_（0.47）As/In_（0.52）Al_（0.48） As InP-based HEMT,of which the material structure is successfully designed and optimized by our group.A 980 nm ultra-wide T-gate head,which is nearly as wide as 8 times the gatefoot（120 nm）,is successfully obtained,and the excellent T-gate profile greatly reduces the parasitic resistance and capacitance effect and effectively enhances the RF performances. These fabricated devices demonstrate excellent DC and RF performances such as a maximum current gain frequency of 190 GHz and a unilateral power-gain gain frequency of 146 GHz.
