Time domain reflectometry（TDR） is a measurement technique based upon transmission line theory. The solutions of transmission line equations are reformulated in terms of independent physical properties, instead of co...Time domain reflectometry（TDR） is a measurement technique based upon transmission line theory. The solutions of transmission line equations are reformulated in terms of independent physical properties, instead of coupled per-unit-length circuit parameters. The complete TDR response is effectively modeled by a non-uniform transmission line using the non-recursive ABCD matrix approach. Approaches to calibrate line parameters and perform TDR measurements based upon such model are introduced with an example on dielectric spectroscopy. TDR modeling in terms of decoupled physical parameters and non-recursive algorithm allows more convenient calibration of line parameters and facilitates interpretation of TDR measurements.展开更多
A measurement system for high power electrical variables with ultrasonic frequency was established. It can measure the effective values of the voltage and the current, the active power, the phase difference of voltage...A measurement system for high power electrical variables with ultrasonic frequency was established. It can measure the effective values of the voltage and the current, the active power, the phase difference of voltage and current, the frequency of the transducer during ultrasonic welding and cutting. In sampling circuits of the system, the measured current is sensed by using a no capacitance and no inductance precision resistor and is treated with a difference amplifier, the measured voltage is processed by using a proportional amplifier. For achieving good amplitude frequency characteristics and rapid measurement of high frequency signals, the resistors, capacitors and amplifiers used in the system are rationally selected. Calibrating experiments show that relative errors are less than 1% for voltage and current effective values and less than 2.5% for active power, and absolute errors are ±1 Hz for frequency and ±1.7° for phase difference of voltage and current in the range of 17～23 kHz .展开更多
The research of unmanned aerial vehicles＇（UAVs＇）autonomy navigation and landing guidance with computer vision has important signifcance.However,because of the image blurring,the position of the cooperative points ...The research of unmanned aerial vehicles＇（UAVs＇）autonomy navigation and landing guidance with computer vision has important signifcance.However,because of the image blurring,the position of the cooperative points cannot be obtained accurately,and the pose estimation algorithms based on the feature points have low precision.In this research,the pose estimation algorithm of UAV is proposed based on feature lines of the cooperative object for autonomous landing.This method uses the actual shape of the cooperative-target on ground and the principle of vanishing line.Roll angle is calculated from the vanishing line.Yaw angle is calculated from the location of the target in the image.Finally,the remaining extrinsic parameters are calculated by the coordinates transformation.Experimental results show that the pose estimation algorithm based on line feature has a higher precision and is more reliable than the pose estimation algorithm based on points feature.Moreover,the error of the algorithm we proposed is small enough when the UAV is near to the landing strip,and it can meet the basic requirements of UAV＇s autonomous landing.展开更多
Using the method of line structure light produced by a laser diode,three dimensional profile measurement is deeply researched.A hardware circuit developed is used to get the center position of light section for the im...Using the method of line structure light produced by a laser diode,three dimensional profile measurement is deeply researched.A hardware circuit developed is used to get the center position of light section for the improvement of the measurement speed.A double CCD compensation technology is used to improve the measurement precision. An easy and effective calibration method of the least squares to fit the parameter of system structure is used to get the relative coordinate relationship of objects and images of light section in the directions of height and axis. Sensor scanning segment by segment and layer by layer makes the measurement range expand greatly.展开更多
Smart grids are increasingly dependent on data with the rapid development of communication and measurement.As one of the important data sources of smart grids,phasor measurement unit(PMU)is facing the high risk from a...Smart grids are increasingly dependent on data with the rapid development of communication and measurement.As one of the important data sources of smart grids,phasor measurement unit(PMU)is facing the high risk from attacks.Compared with cyber attacks,global position system(GPS)spoofing attacks(GSAs)are easier to implement because they can be exploited by portable devices,without the need to access the physical system.Therefore,this paper proposes a novel method for pattern recognition of GSA and an additional function of the proposed method is the data correction to the phase angle difference(PAD)deviation.Specifically,this paper analyzes the effect of GSA on PMU measurement and gives two common patterns of GSA,i.e.,the step attack and the ramp attack.Then,the method of estimating the PAD deviation across a transmission line introduced by GSA is proposed,which does not require the line parameters.After obtaining the estimated PAD deviations,the pattern of GSA can be recognized by hypothesis tests and correlation coefficients according to the statistical characteristics of the estimated PAD deviations.Finally,with the case studies,the effectiveness of the proposed method is demonstrated,and the success rate of the pattern recognition and the online performance of the proposed method are analyzed.展开更多
Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration,enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range....Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration,enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range.By comparing a star's spectrum to the astrocomb spectrum,minute radial velocity shifts indicative of an exoplanet's presence can be detected.The highest precision and accuracy astrocombs are generated by laser frequency combs.However,in the visible band,frequency comb calibrators have stringent operational lifetime limitations due to degradation of the supercontinuum-generating medium,and are thus typically used to calibrate FabryPérot etalons,which are then used for simultaneous observations with target stars.This work demonstrates a specially designed crystalline whispering-gallery-mode resonator(WGMR)that serves as an astrocomb etalon,featuring a coupling wavelength span of two octaves and a quasi-single-mode family.Several innovations have been incorporated into the system's compact design to achieve frequency stability,in addition to wide-range wavelength coupling.These include dual-mode thermometric frequency stabilization,in addition to vacuum packaging,effectively minimizing thermal and pressure-induced frequency drift.Long-term frequency stability,measured via a heterodyne RF beat note,exceeds 2×10^(-12),with a projected long-term modal frequency stability of≤10^(-10)(equivalently 3 cm/s in Doppler velocity).This level of stability obviates the need for frequent cross-calibration with a laser reference,as was required with other astrocomb etalons.Overall,the architecture of the WGMR etalon provides a new and powerful capability,beyond what has previously been achieved by microresonator-based etalons,as a compact,ultra-wideband spectral reference for detecting small planets in long-period orbits around nearby stars.It also offers a path forward for a low size,weight,and power(SWaP)spectral reference appropriate for spaceflight.展开更多
基金partly provided by the Environmental Protection Administration, Taiwan
文摘Time domain reflectometry（TDR） is a measurement technique based upon transmission line theory. The solutions of transmission line equations are reformulated in terms of independent physical properties, instead of coupled per-unit-length circuit parameters. The complete TDR response is effectively modeled by a non-uniform transmission line using the non-recursive ABCD matrix approach. Approaches to calibrate line parameters and perform TDR measurements based upon such model are introduced with an example on dielectric spectroscopy. TDR modeling in terms of decoupled physical parameters and non-recursive algorithm allows more convenient calibration of line parameters and facilitates interpretation of TDR measurements.
基金This work has been carried out with the support of National Natural Science Foundation(No.59675054)
文摘A measurement system for high power electrical variables with ultrasonic frequency was established. It can measure the effective values of the voltage and the current, the active power, the phase difference of voltage and current, the frequency of the transducer during ultrasonic welding and cutting. In sampling circuits of the system, the measured current is sensed by using a no capacitance and no inductance precision resistor and is treated with a difference amplifier, the measured voltage is processed by using a proportional amplifier. For achieving good amplitude frequency characteristics and rapid measurement of high frequency signals, the resistors, capacitors and amplifiers used in the system are rationally selected. Calibrating experiments show that relative errors are less than 1% for voltage and current effective values and less than 2.5% for active power, and absolute errors are ±1 Hz for frequency and ±1.7° for phase difference of voltage and current in the range of 17～23 kHz .
基金supported by the NUAA Fundamental Research Funds(No.NS2013034)
文摘The research of unmanned aerial vehicles＇（UAVs＇）autonomy navigation and landing guidance with computer vision has important signifcance.However,because of the image blurring,the position of the cooperative points cannot be obtained accurately,and the pose estimation algorithms based on the feature points have low precision.In this research,the pose estimation algorithm of UAV is proposed based on feature lines of the cooperative object for autonomous landing.This method uses the actual shape of the cooperative-target on ground and the principle of vanishing line.Roll angle is calculated from the vanishing line.Yaw angle is calculated from the location of the target in the image.Finally,the remaining extrinsic parameters are calculated by the coordinates transformation.Experimental results show that the pose estimation algorithm based on line feature has a higher precision and is more reliable than the pose estimation algorithm based on points feature.Moreover,the error of the algorithm we proposed is small enough when the UAV is near to the landing strip,and it can meet the basic requirements of UAV＇s autonomous landing.
文摘Using the method of line structure light produced by a laser diode,three dimensional profile measurement is deeply researched.A hardware circuit developed is used to get the center position of light section for the improvement of the measurement speed.A double CCD compensation technology is used to improve the measurement precision. An easy and effective calibration method of the least squares to fit the parameter of system structure is used to get the relative coordinate relationship of objects and images of light section in the directions of height and axis. Sensor scanning segment by segment and layer by layer makes the measurement range expand greatly.
基金supported by the National Key Research and Development Program of China(No.2017YFB0902900,No.2017YFB0902901)National Natural Science Foundation of China(No.51627811,No.51725702)the Fundamental Research Funds for the Central Universities(No.2018ZD01)
文摘Smart grids are increasingly dependent on data with the rapid development of communication and measurement.As one of the important data sources of smart grids,phasor measurement unit(PMU)is facing the high risk from attacks.Compared with cyber attacks,global position system(GPS)spoofing attacks(GSAs)are easier to implement because they can be exploited by portable devices,without the need to access the physical system.Therefore,this paper proposes a novel method for pattern recognition of GSA and an additional function of the proposed method is the data correction to the phase angle difference(PAD)deviation.Specifically,this paper analyzes the effect of GSA on PMU measurement and gives two common patterns of GSA,i.e.,the step attack and the ramp attack.Then,the method of estimating the PAD deviation across a transmission line introduced by GSA is proposed,which does not require the line parameters.After obtaining the estimated PAD deviations,the pattern of GSA can be recognized by hypothesis tests and correlation coefficients according to the statistical characteristics of the estimated PAD deviations.Finally,with the case studies,the effectiveness of the proposed method is demonstrated,and the success rate of the pattern recognition and the online performance of the proposed method are analyzed.
基金Jet Propulsion Laboratory(80NM0018D0004,1654212,165880)National Aeronautics and Space Administration(NNH18ZDA001N-SAT,80NM0018D0004)。
文摘Astrocombs are highly precise optical reference systems used for astronomical spectrograph calibration,enabling accurate and consistent measurement of stellar absorption line frequencies across a broad spectral range.By comparing a star's spectrum to the astrocomb spectrum,minute radial velocity shifts indicative of an exoplanet's presence can be detected.The highest precision and accuracy astrocombs are generated by laser frequency combs.However,in the visible band,frequency comb calibrators have stringent operational lifetime limitations due to degradation of the supercontinuum-generating medium,and are thus typically used to calibrate FabryPérot etalons,which are then used for simultaneous observations with target stars.This work demonstrates a specially designed crystalline whispering-gallery-mode resonator(WGMR)that serves as an astrocomb etalon,featuring a coupling wavelength span of two octaves and a quasi-single-mode family.Several innovations have been incorporated into the system's compact design to achieve frequency stability,in addition to wide-range wavelength coupling.These include dual-mode thermometric frequency stabilization,in addition to vacuum packaging,effectively minimizing thermal and pressure-induced frequency drift.Long-term frequency stability,measured via a heterodyne RF beat note,exceeds 2×10^(-12),with a projected long-term modal frequency stability of≤10^(-10)(equivalently 3 cm/s in Doppler velocity).This level of stability obviates the need for frequent cross-calibration with a laser reference,as was required with other astrocomb etalons.Overall,the architecture of the WGMR etalon provides a new and powerful capability,beyond what has previously been achieved by microresonator-based etalons,as a compact,ultra-wideband spectral reference for detecting small planets in long-period orbits around nearby stars.It also offers a path forward for a low size,weight,and power(SWaP)spectral reference appropriate for spaceflight.
