Active damping(AD)strategy is an economical and efficient method to solve the resonant problem of the permanent magnet synchronous motor(PMSM)drive system with inductor-capacitor(LC)sine wave filter.In this article,th...Active damping(AD)strategy is an economical and efficient method to solve the resonant problem of the permanent magnet synchronous motor(PMSM)drive system with inductor-capacitor(LC)sine wave filter.In this article,the AD methods used in PMSM drive system are classified as inherent damping(ID),state variable feedback,and digital filter.Based on this,the purpose of this article is to provide an overview and analysis of the AD methods on PMSM drive system in recent years,and to comprehensively review,compare,and summarize the stability,dynamic performance,robustness,and algorithm complexity.Furthermore,a new expansion of AD method based on capacitor current feedback with high-pass filter(HPF-CCF)is studied to ensure the effectiveness when the resonant frequency is around sixth of the sampling frequency.The simulation and experimental results validate the effectiveness of theoretical analysis.展开更多
The crystals of quartz,lithium,and piezoelectric ceramics have a piezoelectric effect as their major characteristic.The surface acoustic wave filter(SAWF) was designed by using this property.However,the experimental c...The crystals of quartz,lithium,and piezoelectric ceramics have a piezoelectric effect as their major characteristic.The surface acoustic wave filter(SAWF) was designed by using this property.However,the experimental cost of the fabrication of SAWF is higher than that of mechanical filter or LC filter.Through the RLC(resistor,inductor and capacitor) network equivalent circuit and the interdigital transducer(IDT) equivalent circuit model,the electromotive force,the mechanical impedance of piezoelectric plate,and the wave number of Mason circuit model were researched.The equivalent circuit can be used to reduce product development costs and shorten the development cycle.Comparing simulation result by Pspice software with the theory of SAWF,the simulated waveform is similar to theory measurement,and the equivalent circuit model is verified.展开更多
Research was done to overcome traditional problems associated with automatic steering systems of a ship in a seaway. A ship’s dynamic model with wave disturbances was built and a wave filter was designed by means of ...Research was done to overcome traditional problems associated with automatic steering systems of a ship in a seaway. A ship’s dynamic model with wave disturbances was built and a wave filter was designed by means of an extended states observer (ESO). The model estimated the low frequency motion component from a heading measurement corrupted by colorednoise, so back-and-forth steering caused by high frequency wave disturbances was avoided. At the same time, a robust autopilot system, designed by variable structure control theory, was presented. Simulation results achieved in dangerous sea status show that the wave filter works very well and the autopilot has strong robustness to environmental disturbances and model perturbation, and more importantly, the frequency of rudder adjustments is reduced noticeably.展开更多
Various E-plane strip discontinuities are analyzed by the moment method and gener-alized network analysis technique.By introducing an idea of waveguide in a wide-sense,the effectsof the thickness of the strips are tak...Various E-plane strip discontinuities are analyzed by the moment method and gener-alized network analysis technique.By introducing an idea of waveguide in a wide-sense,the effectsof the thickness of the strips are taken into account and a unified treatment of such problems isrealized.A set of curves of the equivalent circuit parameters for the discontinuities of E-planestrips are given.Two E-plane bandpass filters are designed at W-band.The experimental resultsagree well with theoretical predietions.展开更多
Next-generation communication systems require the mass deployment of ultra-small,high-performance filters that integrate multi-physical domains.However,achieving an optimal balance between miniaturization,low insertio...Next-generation communication systems require the mass deployment of ultra-small,high-performance filters that integrate multi-physical domains.However,achieving an optimal balance between miniaturization,low insertion loss,high selectivity,and low cost of millimeter-wave filters remains a challenge for existing technologies.Herein,we propose and demonstrate ultra-small millimeter-wave filters based on the multifunctional lithium niobate(LN)with outstanding nonlinear optical,electro-optic,piezoelectric,ferroelectric,and thermoelectric characteristics.As a high-K material with low dielectric loss and straightforward fabrication,LN provides an ideal platform for integrating photonic,acoustic,and electromagnetic functionalities.Notably,while LN is already proven for acoustic and optical signal processing,its potential for electromagnetic signal processing remains largely unexplored.In this work,we introduce second-order and fourth-order LN-based millimeter-wave bandpass filters(BPFs)tailored for narrowband and wideband millimeter-wave applications,respectively.Through careful optimization of the LN thickness,we elevate the cutoff frequencies of high-order modes,enhancing frequency selectivity while maintaining compactness.The LN-based BPFs exhibit record-breaking performance metrics,including minimal insertion loss,high selectivity,and compatibility with microfabrication processes.The LN-based BPFs fulfill the critical demands of millimeter-wave wireless communications,sensing,imaging,and emerging quantum information systems,paving the way for scalable,multi-physical integrated circuits.展开更多
The most common typical bulk acoustic wave (BAW) filters are fabricated using bulk micromachining technology, but they have several disadvantages. This paper describes a structure for front end passband BAW filters ma...The most common typical bulk acoustic wave (BAW) filters are fabricated using bulk micromachining technology, but they have several disadvantages. This paper describes a structure for front end passband BAW filters manufactured using surface micromachining. Porous silicon is used as a thick sacrificial layer. The structure reduces the influence of the support film on the filter to improve the VLSI compatibility as well as the filter quality. The cross-talk between resonators with different frequencies can be dramatically reduced by using resonators with a self-supporting structure.展开更多
The way to use the least-mean-square (LMS) arithmetic to cancel the direct wave for a passive radar system is introduced. The model of the direct wave is deduced. By using the LMS adaptive FIR filter, the software sol...The way to use the least-mean-square (LMS) arithmetic to cancel the direct wave for a passive radar system is introduced. The model of the direct wave is deduced. By using the LMS adaptive FIR filter, the software solution for FM passive radar system is developed instead of the hardware consumption of the existent experiment system of passive radar. Further more some simulative results are given. The simulative results indicate that using LMS arithmetic to cancel the direct wave is effective.展开更多
Based on wave digital filter(WDF) principles, this paper presents a digital model of cellular neural networks(CNNs). The model can precisely simulate the dynamic behavior of CNNs.
A binary tree representation is designed in this paper for optimization of wave digital filter（WDF）implementation.To achieve this,an equivalent WDF model of the original circuit is converted into abinary tree repres...A binary tree representation is designed in this paper for optimization of wave digital filter（WDF）implementation.To achieve this,an equivalent WDF model of the original circuit is converted into abinary tree representation at first.This WDF binary tree can then be transformed to several topologies with the same implication,since the WDF adaptors have a symmetrical behavior on their ports.Because the WDF implementation is related to field programmable gate array（FPGA）resource usage and the cycle time of emulation,choosing aproper binary tree topology for WDF implementation can help balance the complexity and performance quality of an emulation system.Both WDF-FPGA emulation and HSpice simulation on the same circuit are tested.There is no significant difference between these two simulations.However,in terms of time consumption,the WDF-FPGA emulation has an advantage over the other.Our experiment also demonstrates that the optimized WDF-FPGA emulation has an acceptable accuracy and feasibility.展开更多
It is well known that IIR digital filters require quite fewer computations,comparedwith FIR filters,in order to meet stringent magnitude specifications when the phase distortioncan be tolerated.An approximately linear...It is well known that IIR digital filters require quite fewer computations,comparedwith FIR filters,in order to meet stringent magnitude specifications when the phase distortioncan be tolerated.An approximately linear phase,however,can be also obtained with the IIRfilter by making use of a technique without increasing the complexity.Based on a certain numberof attenuation zeros in the pass band,a new approach is developed for the design of polyphasewave digital filters with exact magnitude responses and Chebyshev approximation of the desiredphase responses.The minimum number of attenuation zeros is estimated,and some examples areincluded.展开更多
In order to suppress the surface wave in three-component seismic exploration, according to the polarization characteristics of body wave and surface wave, a time-frequency domain polarization filtering method based on...In order to suppress the surface wave in three-component seismic exploration, according to the polarization characteristics of body wave and surface wave, a time-frequency domain polarization filtering method based on wavelet transform was studied. A covariance matrix was constructed in the time-frequency domain for the three-component seismic data, measured the polarization parameters of seismic waves. Combining the corresponding eigenvalues and eigenvectors of the matrix, the elliptic rate and elevation angle were used as constraints, and the polarization filter function was built to separate the surface waves. The separated surface waves were inversely transformed and then were adaptively subtracted from the original records. After the polarization filtering suppressed the surface wave, the signal-to-noise ratio of the converted wave was effectively improved. It laid a good foundation for the next seismic data processing and seismic exploration development. The actual data processing results show that the method can effectively extract surface waves from three-component seismic records and avoid the interference of surface waves on seismic signals.展开更多
In this paper we present a wave active filter based on Voltage Differencing Transconductance Amplifiers (VDTAs). The synthesis of active filters basically based on processing of wave quantities. The wave method is pre...In this paper we present a wave active filter based on Voltage Differencing Transconductance Amplifiers (VDTAs). The synthesis of active filters basically based on processing of wave quantities. The wave method is presented for basic building blocks of active filters i.e. a series inductor and parallel capacitor through which realization of various active circuits is made by appropriate connections. The proposed wave active filter is verified by realizing a 4th order low pass Butterworth filter using SPICE simulation with 0.18 μm TSMC CMOS technology parameters.展开更多
This paper presents a higher order voltage and current mode low pass or high pass filter for wave active filter based on Voltage Differencing Transconductance Amplifiers (VDTAs). The wave equivalent variable technique...This paper presents a higher order voltage and current mode low pass or high pass filter for wave active filter based on Voltage Differencing Transconductance Amplifiers (VDTAs). The wave equivalent variable technique and topological simulation as well as operational realization using wave variables techniques are proposed for basic active building blocks of wave active filters. The proposed wave equivalent technique is employed for wave active filter with the proper selection of the terminal connections. This work presented the basic element for the realizing wave active filter is the series inductor with parallel grounded capacitor. The proposed wave active filter is verified by realizing a 4th order low pass and high pass Butterworth filter with minimum power consumption at ±0.82 V using SPICE simulation with 0.18 μm TSMC CMOS technology parameters.展开更多
Two adaptive friction compensation schemes are developed for a high precision turntable system with nonlinear dynamic friction to handle two types of parametric uncertainties in the friction. Both schemes utilize a no...Two adaptive friction compensation schemes are developed for a high precision turntable system with nonlinear dynamic friction to handle two types of parametric uncertainties in the friction. Both schemes utilize a nonlinear observer/filter structure to compensate for uncertainties in corresponding friction parameters associated with the turntable system. Moreover, in the second scheme, adjustable gains are introduced into the dual nonlin- ear filters and they can be tuned to improve the position tracking performance. In both cases, a Lyapunov-like argument is provided for the global asymptotic stability of the closed-loop system. Simulation results demonstrate the effectiveness of the proposed schemes.展开更多
Gravity waves with periods close to the Brunt-V(a|¨)is(a|¨)l(a|¨) period of the upper troposphere are often observed at mesopause altitudes as short period,quasi-monochromatic waves.The assumption that ...Gravity waves with periods close to the Brunt-V(a|¨)is(a|¨)l(a|¨) period of the upper troposphere are often observed at mesopause altitudes as short period,quasi-monochromatic waves.The assumption that these short period waves originate in the troposphere may be problematic because their upward propagation to the mesosphere and lower thermosphere region could be significantly impeded due to an extended region of strong evanescence above the stratopause.To reconcile this apparent paradox,an alternative explanation is proposed in this paper.The inclusion of mean winds and their vertical shears is sufficient to allow certain short period waves to remain internal above the stratopause and to propagate efficiently to higher altitudes.A time-dependent numerical model is used to demonstrate the feasibility of this and to determine the circumstances under which the mesospheric wind shears play a role in the removal and directional filtering of short period gravity waves. Finally this paper concludes that the combination of the height-dependent mean winds and the mean temperature structure probably explains the existence of short period,quasi-monochromatic structures observed in airglow images of mesopause region.展开更多
T-wave alternans (TWA), consisting in an alternation of the electrocardiographic (ECG) repolarization segment (T-wave), is a promising index of the risk of sudden cardiac death. By definition, it is characterized by a...T-wave alternans (TWA), consisting in an alternation of the electrocardiographic (ECG) repolarization segment (T-wave), is a promising index of the risk of sudden cardiac death. By definition, it is characterized by a frequency component, termed fTWA, that matches half heart rate. The heart-rate adaptive match filter (AMF) based method is a technique for automatic TWA identification from the digital ECG. Aim of the present study was to provide a complete technical description of the filter able to explain its methodological principles. The AMF is usually realized as a 6th order Butterworth filter with a narrow (0.12 Hz) passing band centered in fTWA. It is applied in a bidirectional fashion, so that final filtering order is 12. While extracting the TWA component, the AMF simultaneously filters out every ECG component including noise and artefacts, and thus results are very robust. Goodness of the technique was tested using 8 synthetic ECG tracings corrupted by typical noisy factors, such as white random noise, baseline wanderings, heart-rate variability, and others. Six ECG tracings were affected by 100 μV TWA, whereas two were not. Results indicate that the AMF-based method is able to prevent false-positive and false-negative detections and, thus, represents a useful tool for a reliable TWA identification.展开更多
A microwave photonic notch filter with a complex coefficient is proposed and demonstrated based on four wave mixing(FWM). FWM effect of two single-frequency laser beams occurs in a highly nonlinear fiber(HNLF), and mu...A microwave photonic notch filter with a complex coefficient is proposed and demonstrated based on four wave mixing(FWM). FWM effect of two single-frequency laser beams occurs in a highly nonlinear fiber(HNLF), and multi-wavelength optical signals are generated and used to generate the multi-tap of microwave photonic filter(MPF). The complex coefficient is generated by using a Fourier-domain optical processor(FD-OP) to control the amplitude and phase of the optical carrier and phase modulation sidebands. The results show that this filter can be changed from bandpass filter to notch filter by controlling the FD-OP. The center frequency of the notch filter can be continuously tuned from 5.853 GHz to 29.311 GHz with free spectral range(FSR) of 11.729 GHz. The shape of the frequency response keeps unchanged when the phase is tuned.展开更多
The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formul...The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formula based on continuous wavelet transform. For an arbitrary given square-integrable function f(t),g(t) = f(t/λ) is derived by continuous wavelet transform and its inverse transform. The result shows that time-scale transformation may be obtained through the modification of the time-scale of wavelet function filter using equivalent substitution. The paper demonstrates the result by theoretic derivations and experimental simulation.展开更多
Great interest in surface acoustic wave device based on diamond is attracted because diamond has the highest surface acoustic wave velocity of all substrates.In this paper,400 nm ZnO film was deposited on polycrystall...Great interest in surface acoustic wave device based on diamond is attracted because diamond has the highest surface acoustic wave velocity of all substrates.In this paper,400 nm ZnO film was deposited on polycrystalline diamond wafer by magnetron sputtering.The experimental results indicate that highly c-axis oriented and fine-grain polycrystalline ZnO films have been obtained.100 nm Al thin film was deposited on ZnO/diamond by electron evaporation.Standard interdigital-transducers with the electrodes of 1.0μm width were fabricated on the Al film using photolithography and reactive ion etching (RIE) processes.A 2.48 GHz longitudinally-coupled double-mode surface acoustic wave filter has been successfully fabricated using the Al/ZnO/diamond structure.展开更多
基金supported in part by the National Natural Science Foundational of China under Grants 62373363 and 52007190
文摘Active damping(AD)strategy is an economical and efficient method to solve the resonant problem of the permanent magnet synchronous motor(PMSM)drive system with inductor-capacitor(LC)sine wave filter.In this article,the AD methods used in PMSM drive system are classified as inherent damping(ID),state variable feedback,and digital filter.Based on this,the purpose of this article is to provide an overview and analysis of the AD methods on PMSM drive system in recent years,and to comprehensively review,compare,and summarize the stability,dynamic performance,robustness,and algorithm complexity.Furthermore,a new expansion of AD method based on capacitor current feedback with high-pass filter(HPF-CCF)is studied to ensure the effectiveness when the resonant frequency is around sixth of the sampling frequency.The simulation and experimental results validate the effectiveness of theoretical analysis.
基金National Natural Science Foundation of China (No.60976058)
文摘The crystals of quartz,lithium,and piezoelectric ceramics have a piezoelectric effect as their major characteristic.The surface acoustic wave filter(SAWF) was designed by using this property.However,the experimental cost of the fabrication of SAWF is higher than that of mechanical filter or LC filter.Through the RLC(resistor,inductor and capacitor) network equivalent circuit and the interdigital transducer(IDT) equivalent circuit model,the electromotive force,the mechanical impedance of piezoelectric plate,and the wave number of Mason circuit model were researched.The equivalent circuit can be used to reduce product development costs and shorten the development cycle.Comparing simulation result by Pspice software with the theory of SAWF,the simulated waveform is similar to theory measurement,and the equivalent circuit model is verified.
文摘Research was done to overcome traditional problems associated with automatic steering systems of a ship in a seaway. A ship’s dynamic model with wave disturbances was built and a wave filter was designed by means of an extended states observer (ESO). The model estimated the low frequency motion component from a heading measurement corrupted by colorednoise, so back-and-forth steering caused by high frequency wave disturbances was avoided. At the same time, a robust autopilot system, designed by variable structure control theory, was presented. Simulation results achieved in dangerous sea status show that the wave filter works very well and the autopilot has strong robustness to environmental disturbances and model perturbation, and more importantly, the frequency of rudder adjustments is reduced noticeably.
文摘Various E-plane strip discontinuities are analyzed by the moment method and gener-alized network analysis technique.By introducing an idea of waveguide in a wide-sense,the effectsof the thickness of the strips are taken into account and a unified treatment of such problems isrealized.A set of curves of the equivalent circuit parameters for the discontinuities of E-planestrips are given.Two E-plane bandpass filters are designed at W-band.The experimental resultsagree well with theoretical predietions.
基金supported in part by the Hong Kong Research Grants Council under Grant 26202122in part by the National Natural Science Foundation of China under Grant 62304193+2 种基金in part by the Hong Kong Innovation and Technology Commission under Grant ITS/144/23in part by Hong Kong RGC Strategic Topics Grant STG3/E-602/23 Nin part by HKUST Bridge Gap Fund under Grant BGF.030.2024.
文摘Next-generation communication systems require the mass deployment of ultra-small,high-performance filters that integrate multi-physical domains.However,achieving an optimal balance between miniaturization,low insertion loss,high selectivity,and low cost of millimeter-wave filters remains a challenge for existing technologies.Herein,we propose and demonstrate ultra-small millimeter-wave filters based on the multifunctional lithium niobate(LN)with outstanding nonlinear optical,electro-optic,piezoelectric,ferroelectric,and thermoelectric characteristics.As a high-K material with low dielectric loss and straightforward fabrication,LN provides an ideal platform for integrating photonic,acoustic,and electromagnetic functionalities.Notably,while LN is already proven for acoustic and optical signal processing,its potential for electromagnetic signal processing remains largely unexplored.In this work,we introduce second-order and fourth-order LN-based millimeter-wave bandpass filters(BPFs)tailored for narrowband and wideband millimeter-wave applications,respectively.Through careful optimization of the LN thickness,we elevate the cutoff frequencies of high-order modes,enhancing frequency selectivity while maintaining compactness.The LN-based BPFs exhibit record-breaking performance metrics,including minimal insertion loss,high selectivity,and compatibility with microfabrication processes.The LN-based BPFs fulfill the critical demands of millimeter-wave wireless communications,sensing,imaging,and emerging quantum information systems,paving the way for scalable,multi-physical integrated circuits.
基金Supported by the National High-Technology Development Program of China(No.G1999033105)the National Natural Science Foundation of China (No.69806007)
文摘The most common typical bulk acoustic wave (BAW) filters are fabricated using bulk micromachining technology, but they have several disadvantages. This paper describes a structure for front end passband BAW filters manufactured using surface micromachining. Porous silicon is used as a thick sacrificial layer. The structure reduces the influence of the support film on the filter to improve the VLSI compatibility as well as the filter quality. The cross-talk between resonators with different frequencies can be dramatically reduced by using resonators with a self-supporting structure.
文摘The way to use the least-mean-square (LMS) arithmetic to cancel the direct wave for a passive radar system is introduced. The model of the direct wave is deduced. By using the LMS adaptive FIR filter, the software solution for FM passive radar system is developed instead of the hardware consumption of the existent experiment system of passive radar. Further more some simulative results are given. The simulative results indicate that using LMS arithmetic to cancel the direct wave is effective.
文摘Based on wave digital filter(WDF) principles, this paper presents a digital model of cellular neural networks(CNNs). The model can precisely simulate the dynamic behavior of CNNs.
基金Supported by the National Natural Science Foundation of China(61271113)
文摘A binary tree representation is designed in this paper for optimization of wave digital filter（WDF）implementation.To achieve this,an equivalent WDF model of the original circuit is converted into abinary tree representation at first.This WDF binary tree can then be transformed to several topologies with the same implication,since the WDF adaptors have a symmetrical behavior on their ports.Because the WDF implementation is related to field programmable gate array（FPGA）resource usage and the cycle time of emulation,choosing aproper binary tree topology for WDF implementation can help balance the complexity and performance quality of an emulation system.Both WDF-FPGA emulation and HSpice simulation on the same circuit are tested.There is no significant difference between these two simulations.However,in terms of time consumption,the WDF-FPGA emulation has an advantage over the other.Our experiment also demonstrates that the optimized WDF-FPGA emulation has an acceptable accuracy and feasibility.
文摘It is well known that IIR digital filters require quite fewer computations,comparedwith FIR filters,in order to meet stringent magnitude specifications when the phase distortioncan be tolerated.An approximately linear phase,however,can be also obtained with the IIRfilter by making use of a technique without increasing the complexity.Based on a certain numberof attenuation zeros in the pass band,a new approach is developed for the design of polyphasewave digital filters with exact magnitude responses and Chebyshev approximation of the desiredphase responses.The minimum number of attenuation zeros is estimated,and some examples areincluded.
文摘In order to suppress the surface wave in three-component seismic exploration, according to the polarization characteristics of body wave and surface wave, a time-frequency domain polarization filtering method based on wavelet transform was studied. A covariance matrix was constructed in the time-frequency domain for the three-component seismic data, measured the polarization parameters of seismic waves. Combining the corresponding eigenvalues and eigenvectors of the matrix, the elliptic rate and elevation angle were used as constraints, and the polarization filter function was built to separate the surface waves. The separated surface waves were inversely transformed and then were adaptively subtracted from the original records. After the polarization filtering suppressed the surface wave, the signal-to-noise ratio of the converted wave was effectively improved. It laid a good foundation for the next seismic data processing and seismic exploration development. The actual data processing results show that the method can effectively extract surface waves from three-component seismic records and avoid the interference of surface waves on seismic signals.
文摘In this paper we present a wave active filter based on Voltage Differencing Transconductance Amplifiers (VDTAs). The synthesis of active filters basically based on processing of wave quantities. The wave method is presented for basic building blocks of active filters i.e. a series inductor and parallel capacitor through which realization of various active circuits is made by appropriate connections. The proposed wave active filter is verified by realizing a 4th order low pass Butterworth filter using SPICE simulation with 0.18 μm TSMC CMOS technology parameters.
文摘This paper presents a higher order voltage and current mode low pass or high pass filter for wave active filter based on Voltage Differencing Transconductance Amplifiers (VDTAs). The wave equivalent variable technique and topological simulation as well as operational realization using wave variables techniques are proposed for basic active building blocks of wave active filters. The proposed wave equivalent technique is employed for wave active filter with the proper selection of the terminal connections. This work presented the basic element for the realizing wave active filter is the series inductor with parallel grounded capacitor. The proposed wave active filter is verified by realizing a 4th order low pass and high pass Butterworth filter with minimum power consumption at ±0.82 V using SPICE simulation with 0.18 μm TSMC CMOS technology parameters.
文摘Two adaptive friction compensation schemes are developed for a high precision turntable system with nonlinear dynamic friction to handle two types of parametric uncertainties in the friction. Both schemes utilize a nonlinear observer/filter structure to compensate for uncertainties in corresponding friction parameters associated with the turntable system. Moreover, in the second scheme, adjustable gains are introduced into the dual nonlin- ear filters and they can be tuned to improve the position tracking performance. In both cases, a Lyapunov-like argument is provided for the global asymptotic stability of the closed-loop system. Simulation results demonstrate the effectiveness of the proposed schemes.
基金Supported by the National Natural Science Foundation of China(40874100,41174128)
文摘Gravity waves with periods close to the Brunt-V(a|¨)is(a|¨)l(a|¨) period of the upper troposphere are often observed at mesopause altitudes as short period,quasi-monochromatic waves.The assumption that these short period waves originate in the troposphere may be problematic because their upward propagation to the mesosphere and lower thermosphere region could be significantly impeded due to an extended region of strong evanescence above the stratopause.To reconcile this apparent paradox,an alternative explanation is proposed in this paper.The inclusion of mean winds and their vertical shears is sufficient to allow certain short period waves to remain internal above the stratopause and to propagate efficiently to higher altitudes.A time-dependent numerical model is used to demonstrate the feasibility of this and to determine the circumstances under which the mesospheric wind shears play a role in the removal and directional filtering of short period gravity waves. Finally this paper concludes that the combination of the height-dependent mean winds and the mean temperature structure probably explains the existence of short period,quasi-monochromatic structures observed in airglow images of mesopause region.
文摘T-wave alternans (TWA), consisting in an alternation of the electrocardiographic (ECG) repolarization segment (T-wave), is a promising index of the risk of sudden cardiac death. By definition, it is characterized by a frequency component, termed fTWA, that matches half heart rate. The heart-rate adaptive match filter (AMF) based method is a technique for automatic TWA identification from the digital ECG. Aim of the present study was to provide a complete technical description of the filter able to explain its methodological principles. The AMF is usually realized as a 6th order Butterworth filter with a narrow (0.12 Hz) passing band centered in fTWA. It is applied in a bidirectional fashion, so that final filtering order is 12. While extracting the TWA component, the AMF simultaneously filters out every ECG component including noise and artefacts, and thus results are very robust. Goodness of the technique was tested using 8 synthetic ECG tracings corrupted by typical noisy factors, such as white random noise, baseline wanderings, heart-rate variability, and others. Six ECG tracings were affected by 100 μV TWA, whereas two were not. Results indicate that the AMF-based method is able to prevent false-positive and false-negative detections and, thus, represents a useful tool for a reliable TWA identification.
基金supported by the National High Technology Research and Development Program of China(863 Program)(No.2013AA014200)the National Natural Science Foundation of China(No.11444001)the Municipal Natural Science Foundation of Tianjin(No.14JCYBJC16500)
文摘A microwave photonic notch filter with a complex coefficient is proposed and demonstrated based on four wave mixing(FWM). FWM effect of two single-frequency laser beams occurs in a highly nonlinear fiber(HNLF), and multi-wavelength optical signals are generated and used to generate the multi-tap of microwave photonic filter(MPF). The complex coefficient is generated by using a Fourier-domain optical processor(FD-OP) to control the amplitude and phase of the optical carrier and phase modulation sidebands. The results show that this filter can be changed from bandpass filter to notch filter by controlling the FD-OP. The center frequency of the notch filter can be continuously tuned from 5.853 GHz to 29.311 GHz with free spectral range(FSR) of 11.729 GHz. The shape of the frequency response keeps unchanged when the phase is tuned.
文摘The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formula based on continuous wavelet transform. For an arbitrary given square-integrable function f(t),g(t) = f(t/λ) is derived by continuous wavelet transform and its inverse transform. The result shows that time-scale transformation may be obtained through the modification of the time-scale of wavelet function filter using equivalent substitution. The paper demonstrates the result by theoretic derivations and experimental simulation.
文摘Great interest in surface acoustic wave device based on diamond is attracted because diamond has the highest surface acoustic wave velocity of all substrates.In this paper,400 nm ZnO film was deposited on polycrystalline diamond wafer by magnetron sputtering.The experimental results indicate that highly c-axis oriented and fine-grain polycrystalline ZnO films have been obtained.100 nm Al thin film was deposited on ZnO/diamond by electron evaporation.Standard interdigital-transducers with the electrodes of 1.0μm width were fabricated on the Al film using photolithography and reactive ion etching (RIE) processes.A 2.48 GHz longitudinally-coupled double-mode surface acoustic wave filter has been successfully fabricated using the Al/ZnO/diamond structure.
