This paper puts forward a novel method of measuring the thin period-structure-film thickness based on the Bloch surface wave(BSW) enhanced Goos–Hanchen(GH) shift in one-dimensional photonic crystal(1DPC). The BSW phe...This paper puts forward a novel method of measuring the thin period-structure-film thickness based on the Bloch surface wave(BSW) enhanced Goos–Hanchen(GH) shift in one-dimensional photonic crystal(1DPC). The BSW phenomenon appearing in 1DPC enhances the GH shift generated in the attenuated total internal reflection structure. The GH shift is closely related to the thickness of the film which is composed of layer-structure of 1DPC. The GH shifts under multiple different incident light conditions will be obtained by varying the wavelength and angle of the measured light, and the thickness distribution of the entire structure of 1DPC is calculated by the particle swarm optimization(PSO) algorithm.The relationship between the structure of a 1DPC film composed of TiO_(2) and SiO_(2) layers and the GH shift, is investigated.Under the specific photonic crystal structure and incident conditions, a giant GH shift, 5.1 × 10^(3) times the wavelength of incidence, can be obtained theoretically. Simulation and calculation results show that the thickness of termination layer and periodic structure bilayer of 1DPC film with 0.1-nm resolution can be obtained by measuring the GH shifts. The exact structure of a 1DPC film is innovatively measured by the BSW-enhanced GH shift.展开更多
Using hexagonal boron nitride(h-BN)to prepare resistive switching devices is a promising strategy.Various doping methods have aroused great interest in the semiconductor field in recent years,but many researchers have...Using hexagonal boron nitride(h-BN)to prepare resistive switching devices is a promising strategy.Various doping methods have aroused great interest in the semiconductor field in recent years,but many researchers have overlooked the various repetitive anomalies that occur during the testing process.In this study,the basic electrical properties and additive protrusion behavior of Ga-ion-doped h-BN memristors at micro–nanoscale during the voltage scanning process are investigated via atomic force microscopy(AFM)and energy dispersive spectroscopy.The additive protrusion behavior is subjected to exploratory research,and it is concluded that it is caused by anodic oxidation.An approach is proposed that involves filling the AFM chamber with nitrogen gas to improve the stability of memristor testing,and this method provides a solution for enhanced testing stability of memristors.展开更多
Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 &#...Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 × 1080- LCDs and a half-transmission and half- reflection prisms was proposed in this paper.The physical principal and error model due to the splicing structure has been discussed and analyzed in detail.Based on the Tsinghua Micro star tracker,the error effect and system accuracy has been carefully tested and calibrated.The result showed that this simulator can get the accuracy of 10.4 "(3sigma) within a field of view of,which can meet the simulating requirement of modern star tracker,whose accuracy can reach 3"(3sigma) 。展开更多
DNA methylation has been extensively investigated in recent years,not least because of its known relationship with various diseases.Progress in analytical methods can greatly increase the relevance of DNA methylation ...DNA methylation has been extensively investigated in recent years,not least because of its known relationship with various diseases.Progress in analytical methods can greatly increase the relevance of DNA methylation studies to both clinical medicine and scientific research.Microflu-idic chips are excellent carriers for molecular analysis,and their use can provide improvements from multiple aspects.On-chip molecular analysis has received extensive attention owing to its advantages of portability,high throughput,low cost,and high efficiency.In recent years,the use of novel microfluidic chips for DNA methylation analysis has been widely reported and has shown obvious superiority to conventional methods.In this review,wefirst focus on DNA methylation and its applications.Then,we discuss advanced microfluidic-based methods for DNA methylation analysis and describe the great progress that has been made in recent years.Finally,we summarize the advantages that microfluidic technology brings to DNA methylation analysis and describe several challenges and perspectives for on-chip DNA methylation analysis.This review should help researchers improve their understanding and make progress in developing microfluidic-based methods for DNA methylation analysis.展开更多
This paper presents the design,fabrication,and characterization of cantilever-type resonators with a novel stacked structure.Aluminum nitride is adopted as the material for both the structural layer and the piezoelect...This paper presents the design,fabrication,and characterization of cantilever-type resonators with a novel stacked structure.Aluminum nitride is adopted as the material for both the structural layer and the piezoelectric layer;this simplifies the fabrication process and improves the quality factor of the resonator.Both in-plane and out-of-planeflexural modes were investigated.The effect of the structural dimensions and electrode patterns on the resonator’s performance were also studied.Finite-element simulations and experiments examining anchor loss and thermoelastic damping,which are the main loss mechanisms affecting the quality factor of these resonators,were carried out.The optimal structural dimensions and electrode patterns of the cantilever-type resonators are presented.A quality factor of 7922 with a motional impedance of 88.52 kΩand a quality factor of 8851 with a motional impedance of 67.03 kΩwere achieved for the in-plane and out-of-planeflexural-mode resonators,respectively.The proposed resonator design will contribute to the development of high-performance devices such as accelerometers,gyroscopes,and pressure sensors.展开更多
The ultraviolet(UV) photoresponses of ZnO nanorods directly grown on and between two micro Au-electrodes by using electric-field-assisted wet chemical method are measured comprehensively under different conditions, in...The ultraviolet(UV) photoresponses of ZnO nanorods directly grown on and between two micro Au-electrodes by using electric-field-assisted wet chemical method are measured comprehensively under different conditions, including ambient environment, applied bias voltage, gate voltage and temperature. Experimental results indicate that the photoresponses of the ZnO nanorods can be modulated by surface oxygen adsorptions, applied voltages, as well as temperatures. A model taking into account both surface adsorbed oxygen and electron-hole activities inside ZnO nanorods is proposed. The enhancement effect of the bias voltage on photoresponse is also analyzed. Experimental results shows that the UV response time(to 63%) of ZnO nanorods in air and at 59°C could be shortened from 34.8 s to 0.24 s with a bias of 4 V applied between anode and cathode.展开更多
This paper has developed and characterized a method to produce a velocity-tunable 87 Rb cold atomic source for atomic interferometry application.Using a high speed fluorescence imaging technology,it reports that the d...This paper has developed and characterized a method to produce a velocity-tunable 87 Rb cold atomic source for atomic interferometry application.Using a high speed fluorescence imaging technology,it reports that the dynamic process of the atomic source formation is observed and the source performances including the flux and the initial velocity are characterized.A tunable atomic source with the initial velocity of 1.4～2.6 m/s and the atomic source flux of 2 × 10 8 ～ 6 × 10 9 atoms/s has been obtained with the built experimental setup.展开更多
Fatigue behaviour has important implications for engineering composite structures in sectors ranging from automotive to aerospace. Optical sensing technology displays excellent performance in these fields for monitori...Fatigue behaviour has important implications for engineering composite structures in sectors ranging from automotive to aerospace. Optical sensing technology displays excellent performance in these fields for monitoring. In this paper, temperature and residual strain during fatigue of a carbon fiber reinforced polymer(CFRP) are investigated. Four autoclaved CFRP beam specimens, with fiber Bragg grating(FBG) sensors and thermocouples embedded at selected locations, are subjected to three-point bending cyclic loading on the BOSE testing machine for fatigue testing. Thermocouples are used to measure the temperature while FBGs can sense the temperature and strain as well. Seven tests in total are conducted at different frequencies, and each test lasts for several days. From the experimental results, transient steep peaks of temperature increases (up to 2.3 ℃) are discovered at the beginning of the load. The following constant temperature increments are around 1.0 ℃, which is not relevant to frequencies from 0.1 Hz to 20 Hz and suspected due to fatigue. Residual strains of 1×10?5-2×10?5 during fatigue, fading away rapidly when unloading, are also reported. Embedded FBGs here are validated to sense temperature and strains in composite structures, which demonstrates promising potentials in structure monitoring fields. CFRP are verified to have an excellent performance during fatigue with low temperature increase and residual strain.展开更多
The 3D characteristic diagram of acoustically induced surface vibration was employed to study the influence of different buried landmines on the acoustic detection signal. By using the vehicular experimental system fo...The 3D characteristic diagram of acoustically induced surface vibration was employed to study the influence of different buried landmines on the acoustic detection signal. By using the vehicular experimental system for acoustic landmine detection and the method of scanning detection, the 3D characteristic diagrams of surface vibration were measured when different objects were buried underground, including big plastic landmine, small plastic landmine, big metal landmine and bricks. The results show that, under the given conditions, the surface vibration amplitudes of big plastic landmine, big metal landmine, small plastic landmine and bricks decrease in turn. The 3D characteristic diagrams of surface vibration can be used to further identify the locations of buried landmines.展开更多
External-cavity birefringence feedback effects of the microchip Nd:YAG laser are presented.When a birefringence element is placed in the external feedback cavity of the laser,two orthogonally polarized laser beams wit...External-cavity birefringence feedback effects of the microchip Nd:YAG laser are presented.When a birefringence element is placed in the external feedback cavity of the laser,two orthogonally polarized laser beams with a phase difference are output.The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions.The variable extra-cavity birefringence,caused by rotation of the external-cavity birefringence element,results in tunable phase difference between the two orthogonally polarized beams.This means that the roll angle information has been translated to phase difference of two output laser beams.A theoretical analysis based on the Fabry-Perot cavity equivalent model and refractive index ellipsoid is presented,which is in good agreement with the experimental results.This phenomenon has potential applications for roll angle measurement.展开更多
We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source(LVIS) of atomic beam on light parameters, especially the polarization of cooling laser al...We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source(LVIS) of atomic beam on light parameters, especially the polarization of cooling laser along the atomic beam axis(pushing beam). By changing the polarization of the pushing beam, the longitudinal mean velocity of a rubidium atomic beam can be tuned continuously from 10 to 20 m/s and the flux can range from 3 × 10~8 to 1 × 10~9 atoms/s, corresponding to the maximum sensitivity of the velocity with respect to the polarization angle of 20(m/s)/rad and the mean sensitivity of flux of 1.2 × 10~9(atoms/s)/rad. The mechanism is explained with a Monte-Carlo based numerical simulation method, which shows a qualitative agreement with the experimental result. This is also a demonstration of a method enabling the fast and continuous modulation of a low-velocity intense source of cold atomic beam on the velocity or flux,which can be used in many fields, like the development of a cold atomic beam interferometer and atom lithography.展开更多
To compare mid-infrared(MIR)and near-infrared(NIR)spectroscopies for the determination of the fat and protein contents in milk,the same sample sets with varying concentrations of fat and protein were measured in the M...To compare mid-infrared(MIR)and near-infrared(NIR)spectroscopies for the determination of the fat and protein contents in milk,the same sample sets with varying concentrations of fat and protein were measured in the MIR range of 3 200-700 cm-1 and NIR range of 9 000-4 000 cm-1.The spectral features in the two regions were analyzed.The MIR spectra of milk were characteristic due to the MIR inherent molecular specificity,whereas the NIR spectra were relatively characterless due to the NIR low selectivity.Partial least squares(PLS)regression models for fat and protein were developed by using both MIR and NIR spectra.MIR data with no pretreatment gave better results than NIR data.The square correlation coefficient(R2)and the root mean square error of prediction(RMSEP)were 0.98 and 0.10 g/dL for fat and 0.97 and 0.11 g/dL for protein.With NIR techniques,satisfactory results were not obtained with raw data.However,NIR data after pretreatment gave similarly good results to the ones using MIR method.This paper indicates that either of the MIR and NIR spectral methods is reliable for the determination of the fat and protein contents.展开更多
As actuator of the force-rebalanced servo loop, the electrostatic force generator of the micro-accelerometer shows high nonlinearity while the interpole of the micro-electro-mechanical system(MEMS) sensor is far away ...As actuator of the force-rebalanced servo loop, the electrostatic force generator of the micro-accelerometer shows high nonlinearity while the interpole of the micro-electro-mechanical system(MEMS) sensor is far away from its balance position. The control system cannot rebalance itself with the limited bandwidth after an external long overload, because the characteristics of the force generator differ from normal case. Although for similar problems, solutions with cascading lead-lag blocks, with the anti-windup(AW) technology, or with the sliding-mode control, are widely reported, the problems such as performance loss or difficulty to synthesize a digital controller still remain. Based on existing researches, remedies are developed by analyzing the characteristic of the system not only near the balance position, but also corresponding to the whole moveable range of the interpole, and a new controller is proposed. The solution is compared with the common solutions of cascading lead-lag blocks method, AW methods, and sliding mode methods. Comparison results show that the proposed solution avoid performance loss, compared to cascading lead-lag blocks solution; the proposed solution is easily synthesized and implemented in the analog servo loop of the micro-accelerometer, compared to digital AW methods; at the same time, the proposed solution avoids suffering the chattering effect problem but just utilize it, compared to the sliding-mode control solution. Nevertheless, comparison results show the solution is lack of commonality, since the solution is only more suitable to micro electrostatic force-rebalance system. The SIMULINK models with and without the proposed solution, taking typical micro-accelerometer parameters, have been set up for simulation; corresponding experiments utilizing electrometric method are also conducted after the successful simulations. Simulation and experiment results verify that the micro-accelerometer will reliably return to normal operation after external long overload with the proposed solution. Therefore, it is expected to design the analog servo loop of high performance micro electrostatic force-rebalance system so as to ensure the rebalance after long overload without performance loss.展开更多
Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in...Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in 1016, and the best optical clock has reached a type B uncertainty below 10-18. Besides applications in the metrology, navigation, etc.,ultra-stable and ultra-accurate atomic clocks have also become powerful tools in the basic scientific investigations. In this paper, we focus on the recent developments in the high-performance cold atomic clocks which can be used as frequency standards to calibrate atomic time scales. The basic principles, performances, and limitations of fountain clocks and optical clocks based on signal trapped ion or neutral atoms are summarized. Their applications in metrology and other areas are briefly introduced.展开更多
Laser tracking system(LTS)is an advanced device for large size 3D coordinates measuring with the advantages of broad range, high speed and high accuracy. However, its measuring accuracy is highly dominated by the geom...Laser tracking system(LTS)is an advanced device for large size 3D coordinates measuring with the advantages of broad range, high speed and high accuracy. However, its measuring accuracy is highly dominated by the geometric errors of the tracking mirror mechanism. Proper calibration of LTS is essential prior to the use of it for metrology. A kinematics model that describes not only the motion but also the geometric variations of LTS is developed. Through error analysis of the proposed model, it is claimed that gimbals axis misalignments and tracking mirror center off-set are the key contributors to measuring errors of LTS. A self-calibration method is presented of calibrating LTS with planar constraints. Various calibration strategies utilizing single-plane and multiple-plane constraints are proposed for different situations. For each calibration strategy, issues about the error parameter estimation of LTS are exploded to fred out in which conditions these parameters can be uniquely estimated. Moreover, these conditions reveal the applicability of the planar constraints to LTS self-calibration. Intensive studies have been made to check validity of the theoretical results. The results show that the measuring accuracy of LTS has increased by 5 times since this technique for calibration is used.展开更多
Based on a comprehensive study of various algorithms, the automatic recognition of traditional ocular optical measuring instruments is realized. Taking a universal tools microscope(UTM) lens view image as an example, ...Based on a comprehensive study of various algorithms, the automatic recognition of traditional ocular optical measuring instruments is realized. Taking a universal tools microscope(UTM) lens view image as an example, a 2-layer automatic recognition model for data reading is established after adopting a series of pre-processing algorithms. This model is an optimal combination of the correlation-based template matching method and a concurrent back propagation(BP) neural network. Multiple complementary feature extraction is used in generating the eigenvectors of the concurrent network. In order to improve fault-tolerance capacity, rotation invariant features based on Zernike moments are extracted from digit characters and a 4-dimensional group of the outline features is also obtained. Moreover, the operating time and reading accuracy can be adjusted dy-namically by setting the threshold value. The experimental result indicates that the newly developed algorithm has optimal recognition precision and working speed. The average reading ratio can achieve 97.23%. The recognition method can automatically obtain the results of optical measuring instruments rapidly and stably without modifying their original structure, which meets the application requirements.展开更多
The surface acoustic wave (SAW) propagating in a sample of steel is simulated by using finite element method (FEM). The waves are excited by a load function with propagation properties such as phase velocity dispersio...The surface acoustic wave (SAW) propagating in a sample of steel is simulated by using finite element method (FEM). The waves are excited by a load function with propagation properties such as phase velocity dispersion and wide bandwidth. A two-dimensional model consisting of surface defects loaded with a wideband 50-200 MHz and short time 0.1 μs displacement function is investigated in the time and frequency domains. By transient dynamic analysis, Fourier transform and dispersion calculation, snapshots of propagating wave and responses from sensing points are presented. It is indicated that this supervision approach is sensitive to the surface cracks and reflections.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.51575387 and 51827812)。
文摘This paper puts forward a novel method of measuring the thin period-structure-film thickness based on the Bloch surface wave(BSW) enhanced Goos–Hanchen(GH) shift in one-dimensional photonic crystal(1DPC). The BSW phenomenon appearing in 1DPC enhances the GH shift generated in the attenuated total internal reflection structure. The GH shift is closely related to the thickness of the film which is composed of layer-structure of 1DPC. The GH shifts under multiple different incident light conditions will be obtained by varying the wavelength and angle of the measured light, and the thickness distribution of the entire structure of 1DPC is calculated by the particle swarm optimization(PSO) algorithm.The relationship between the structure of a 1DPC film composed of TiO_(2) and SiO_(2) layers and the GH shift, is investigated.Under the specific photonic crystal structure and incident conditions, a giant GH shift, 5.1 × 10^(3) times the wavelength of incidence, can be obtained theoretically. Simulation and calculation results show that the thickness of termination layer and periodic structure bilayer of 1DPC film with 0.1-nm resolution can be obtained by measuring the GH shifts. The exact structure of a 1DPC film is innovatively measured by the BSW-enhanced GH shift.
基金supported by the Youth Fund of the National Natural Science Foundation of China(Grant No.622041701004267).
文摘Using hexagonal boron nitride(h-BN)to prepare resistive switching devices is a promising strategy.Various doping methods have aroused great interest in the semiconductor field in recent years,but many researchers have overlooked the various repetitive anomalies that occur during the testing process.In this study,the basic electrical properties and additive protrusion behavior of Ga-ion-doped h-BN memristors at micro–nanoscale during the voltage scanning process are investigated via atomic force microscopy(AFM)and energy dispersive spectroscopy.The additive protrusion behavior is subjected to exploratory research,and it is concluded that it is caused by anodic oxidation.An approach is proposed that involves filling the AFM chamber with nitrogen gas to improve the stability of memristor testing,and this method provides a solution for enhanced testing stability of memristors.
文摘Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 × 1080- LCDs and a half-transmission and half- reflection prisms was proposed in this paper.The physical principal and error model due to the splicing structure has been discussed and analyzed in detail.Based on the Tsinghua Micro star tracker,the error effect and system accuracy has been carefully tested and calibrated.The result showed that this simulator can get the accuracy of 10.4 "(3sigma) within a field of view of,which can meet the simulating requirement of modern star tracker,whose accuracy can reach 3"(3sigma) 。
基金support from the National Key R&D Program of China(Grant No.2018YFE0118700)the National Natural Science Foundation of China(NSFC Grant No.62174119)+1 种基金the 111 Project(Grant No.B07014)the Foundation for Talent Scientists of Nanchang Institute for Microtechnology of Tianjin University.
文摘DNA methylation has been extensively investigated in recent years,not least because of its known relationship with various diseases.Progress in analytical methods can greatly increase the relevance of DNA methylation studies to both clinical medicine and scientific research.Microflu-idic chips are excellent carriers for molecular analysis,and their use can provide improvements from multiple aspects.On-chip molecular analysis has received extensive attention owing to its advantages of portability,high throughput,low cost,and high efficiency.In recent years,the use of novel microfluidic chips for DNA methylation analysis has been widely reported and has shown obvious superiority to conventional methods.In this review,wefirst focus on DNA methylation and its applications.Then,we discuss advanced microfluidic-based methods for DNA methylation analysis and describe the great progress that has been made in recent years.Finally,we summarize the advantages that microfluidic technology brings to DNA methylation analysis and describe several challenges and perspectives for on-chip DNA methylation analysis.This review should help researchers improve their understanding and make progress in developing microfluidic-based methods for DNA methylation analysis.
基金supported in part by the National Key Research and Development Program of China(Grant No.2020YFB2008800)in part by the Nanchang Institute for Microtechnology of Tianjin University.
文摘This paper presents the design,fabrication,and characterization of cantilever-type resonators with a novel stacked structure.Aluminum nitride is adopted as the material for both the structural layer and the piezoelectric layer;this simplifies the fabrication process and improves the quality factor of the resonator.Both in-plane and out-of-planeflexural modes were investigated.The effect of the structural dimensions and electrode patterns on the resonator’s performance were also studied.Finite-element simulations and experiments examining anchor loss and thermoelastic damping,which are the main loss mechanisms affecting the quality factor of these resonators,were carried out.The optimal structural dimensions and electrode patterns of the cantilever-type resonators are presented.A quality factor of 7922 with a motional impedance of 88.52 kΩand a quality factor of 8851 with a motional impedance of 67.03 kΩwere achieved for the in-plane and out-of-planeflexural-mode resonators,respectively.The proposed resonator design will contribute to the development of high-performance devices such as accelerometers,gyroscopes,and pressure sensors.
基金Project supported by the National Natural Science Foundation of China(Grant No.91123017)
文摘The ultraviolet(UV) photoresponses of ZnO nanorods directly grown on and between two micro Au-electrodes by using electric-field-assisted wet chemical method are measured comprehensively under different conditions, including ambient environment, applied bias voltage, gate voltage and temperature. Experimental results indicate that the photoresponses of the ZnO nanorods can be modulated by surface oxygen adsorptions, applied voltages, as well as temperatures. A model taking into account both surface adsorbed oxygen and electron-hole activities inside ZnO nanorods is proposed. The enhancement effect of the bias voltage on photoresponse is also analyzed. Experimental results shows that the UV response time(to 63%) of ZnO nanorods in air and at 59°C could be shortened from 34.8 s to 0.24 s with a bias of 4 V applied between anode and cathode.
基金supported in part by National Natural Science Foundation of China (Grant No 50775127/E0525)National Basic Research Specialized Program of China (Grant No 2007CB306504)
文摘This paper has developed and characterized a method to produce a velocity-tunable 87 Rb cold atomic source for atomic interferometry application.Using a high speed fluorescence imaging technology,it reports that the dynamic process of the atomic source formation is observed and the source performances including the flux and the initial velocity are characterized.A tunable atomic source with the initial velocity of 1.4～2.6 m/s and the atomic source flux of 2 × 10 8 ～ 6 × 10 9 atoms/s has been obtained with the built experimental setup.
文摘Fatigue behaviour has important implications for engineering composite structures in sectors ranging from automotive to aerospace. Optical sensing technology displays excellent performance in these fields for monitoring. In this paper, temperature and residual strain during fatigue of a carbon fiber reinforced polymer(CFRP) are investigated. Four autoclaved CFRP beam specimens, with fiber Bragg grating(FBG) sensors and thermocouples embedded at selected locations, are subjected to three-point bending cyclic loading on the BOSE testing machine for fatigue testing. Thermocouples are used to measure the temperature while FBGs can sense the temperature and strain as well. Seven tests in total are conducted at different frequencies, and each test lasts for several days. From the experimental results, transient steep peaks of temperature increases (up to 2.3 ℃) are discovered at the beginning of the load. The following constant temperature increments are around 1.0 ℃, which is not relevant to frequencies from 0.1 Hz to 20 Hz and suspected due to fatigue. Residual strains of 1×10?5-2×10?5 during fatigue, fading away rapidly when unloading, are also reported. Embedded FBGs here are validated to sense temperature and strains in composite structures, which demonstrates promising potentials in structure monitoring fields. CFRP are verified to have an excellent performance during fatigue with low temperature increase and residual strain.
基金Supported by the National Natural Science Foundation of China(No.61575119)Science and Technology on Near-Surface Detection Laboratory(No.TCGZ2015A005)State Key Laboratory of Precision Measuring Technology and Instruments(PIL1402)
文摘The 3D characteristic diagram of acoustically induced surface vibration was employed to study the influence of different buried landmines on the acoustic detection signal. By using the vehicular experimental system for acoustic landmine detection and the method of scanning detection, the 3D characteristic diagrams of surface vibration were measured when different objects were buried underground, including big plastic landmine, small plastic landmine, big metal landmine and bricks. The results show that, under the given conditions, the surface vibration amplitudes of big plastic landmine, big metal landmine, small plastic landmine and bricks decrease in turn. The 3D characteristic diagrams of surface vibration can be used to further identify the locations of buried landmines.
基金supported by the National Natural Science Foundation of China (Grant No 50575110)
文摘External-cavity birefringence feedback effects of the microchip Nd:YAG laser are presented.When a birefringence element is placed in the external feedback cavity of the laser,two orthogonally polarized laser beams with a phase difference are output.The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions.The variable extra-cavity birefringence,caused by rotation of the external-cavity birefringence element,results in tunable phase difference between the two orthogonally polarized beams.This means that the roll angle information has been translated to phase difference of two output laser beams.A theoretical analysis based on the Fabry-Perot cavity equivalent model and refractive index ellipsoid is presented,which is in good agreement with the experimental results.This phenomenon has potential applications for roll angle measurement.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61473166 and 41404146)
文摘We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source(LVIS) of atomic beam on light parameters, especially the polarization of cooling laser along the atomic beam axis(pushing beam). By changing the polarization of the pushing beam, the longitudinal mean velocity of a rubidium atomic beam can be tuned continuously from 10 to 20 m/s and the flux can range from 3 × 10~8 to 1 × 10~9 atoms/s, corresponding to the maximum sensitivity of the velocity with respect to the polarization angle of 20(m/s)/rad and the mean sensitivity of flux of 1.2 × 10~9(atoms/s)/rad. The mechanism is explained with a Monte-Carlo based numerical simulation method, which shows a qualitative agreement with the experimental result. This is also a demonstration of a method enabling the fast and continuous modulation of a low-velocity intense source of cold atomic beam on the velocity or flux,which can be used in many fields, like the development of a cold atomic beam interferometer and atom lithography.
基金Supported by National Natural Science Foundation of China(No.30170261)the 10th Five-Year Plan of China(No.2004BA706B12).
文摘To compare mid-infrared(MIR)and near-infrared(NIR)spectroscopies for the determination of the fat and protein contents in milk,the same sample sets with varying concentrations of fat and protein were measured in the MIR range of 3 200-700 cm-1 and NIR range of 9 000-4 000 cm-1.The spectral features in the two regions were analyzed.The MIR spectra of milk were characteristic due to the MIR inherent molecular specificity,whereas the NIR spectra were relatively characterless due to the NIR low selectivity.Partial least squares(PLS)regression models for fat and protein were developed by using both MIR and NIR spectra.MIR data with no pretreatment gave better results than NIR data.The square correlation coefficient(R2)and the root mean square error of prediction(RMSEP)were 0.98 and 0.10 g/dL for fat and 0.97 and 0.11 g/dL for protein.With NIR techniques,satisfactory results were not obtained with raw data.However,NIR data after pretreatment gave similarly good results to the ones using MIR method.This paper indicates that either of the MIR and NIR spectral methods is reliable for the determination of the fat and protein contents.
基金supported by National Key Technologies R&D Program of China during the 11th Five-Year Plan (Grant No. 51309050208)
文摘As actuator of the force-rebalanced servo loop, the electrostatic force generator of the micro-accelerometer shows high nonlinearity while the interpole of the micro-electro-mechanical system(MEMS) sensor is far away from its balance position. The control system cannot rebalance itself with the limited bandwidth after an external long overload, because the characteristics of the force generator differ from normal case. Although for similar problems, solutions with cascading lead-lag blocks, with the anti-windup(AW) technology, or with the sliding-mode control, are widely reported, the problems such as performance loss or difficulty to synthesize a digital controller still remain. Based on existing researches, remedies are developed by analyzing the characteristic of the system not only near the balance position, but also corresponding to the whole moveable range of the interpole, and a new controller is proposed. The solution is compared with the common solutions of cascading lead-lag blocks method, AW methods, and sliding mode methods. Comparison results show that the proposed solution avoid performance loss, compared to cascading lead-lag blocks solution; the proposed solution is easily synthesized and implemented in the analog servo loop of the micro-accelerometer, compared to digital AW methods; at the same time, the proposed solution avoids suffering the chattering effect problem but just utilize it, compared to the sliding-mode control solution. Nevertheless, comparison results show the solution is lack of commonality, since the solution is only more suitable to micro electrostatic force-rebalance system. The SIMULINK models with and without the proposed solution, taking typical micro-accelerometer parameters, have been set up for simulation; corresponding experiments utilizing electrometric method are also conducted after the successful simulations. Simulation and experiment results verify that the micro-accelerometer will reliably return to normal operation after external long overload with the proposed solution. Therefore, it is expected to design the analog servo loop of high performance micro electrostatic force-rebalance system so as to ensure the rebalance after long overload without performance loss.
基金Project supported by the National Natural Science Foundation of China(Grant No.11873044)the National Key Research and Development Project of China(Grant No.2016YFF0200202)Consulting Research Project of Chinese Academy of Engineering(Grant No.2018-ZCQ-03)。
文摘Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in 1016, and the best optical clock has reached a type B uncertainty below 10-18. Besides applications in the metrology, navigation, etc.,ultra-stable and ultra-accurate atomic clocks have also become powerful tools in the basic scientific investigations. In this paper, we focus on the recent developments in the high-performance cold atomic clocks which can be used as frequency standards to calibrate atomic time scales. The basic principles, performances, and limitations of fountain clocks and optical clocks based on signal trapped ion or neutral atoms are summarized. Their applications in metrology and other areas are briefly introduced.
基金National Natural Science Foundation of China (No. 50475038).
文摘Laser tracking system(LTS)is an advanced device for large size 3D coordinates measuring with the advantages of broad range, high speed and high accuracy. However, its measuring accuracy is highly dominated by the geometric errors of the tracking mirror mechanism. Proper calibration of LTS is essential prior to the use of it for metrology. A kinematics model that describes not only the motion but also the geometric variations of LTS is developed. Through error analysis of the proposed model, it is claimed that gimbals axis misalignments and tracking mirror center off-set are the key contributors to measuring errors of LTS. A self-calibration method is presented of calibrating LTS with planar constraints. Various calibration strategies utilizing single-plane and multiple-plane constraints are proposed for different situations. For each calibration strategy, issues about the error parameter estimation of LTS are exploded to fred out in which conditions these parameters can be uniquely estimated. Moreover, these conditions reveal the applicability of the planar constraints to LTS self-calibration. Intensive studies have been made to check validity of the theoretical results. The results show that the measuring accuracy of LTS has increased by 5 times since this technique for calibration is used.
文摘Based on a comprehensive study of various algorithms, the automatic recognition of traditional ocular optical measuring instruments is realized. Taking a universal tools microscope(UTM) lens view image as an example, a 2-layer automatic recognition model for data reading is established after adopting a series of pre-processing algorithms. This model is an optimal combination of the correlation-based template matching method and a concurrent back propagation(BP) neural network. Multiple complementary feature extraction is used in generating the eigenvectors of the concurrent network. In order to improve fault-tolerance capacity, rotation invariant features based on Zernike moments are extracted from digit characters and a 4-dimensional group of the outline features is also obtained. Moreover, the operating time and reading accuracy can be adjusted dy-namically by setting the threshold value. The experimental result indicates that the newly developed algorithm has optimal recognition precision and working speed. The average reading ratio can achieve 97.23%. The recognition method can automatically obtain the results of optical measuring instruments rapidly and stably without modifying their original structure, which meets the application requirements.
基金Supported by National Natural Science Foundation of China (No. 51075296)Sate Key Laboratory of Precision Measuring Technology and Instruments Project (No. PILT1106)
文摘The surface acoustic wave (SAW) propagating in a sample of steel is simulated by using finite element method (FEM). The waves are excited by a load function with propagation properties such as phase velocity dispersion and wide bandwidth. A two-dimensional model consisting of surface defects loaded with a wideband 50-200 MHz and short time 0.1 μs displacement function is investigated in the time and frequency domains. By transient dynamic analysis, Fourier transform and dispersion calculation, snapshots of propagating wave and responses from sensing points are presented. It is indicated that this supervision approach is sensitive to the surface cracks and reflections.
