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RSS2019 Vol. 43, No. 4
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2019, 43(4): 437-441.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.001
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Abstract:
In order to precisely control the temperature and current of distributed feedback lasers, the drive device of distributed feedback laser was designed by using digital signal processing chip.The device was used to set the reference voltage of the current and the temperature of the laser. After digital-to-analog conversion, through the temperature and current driving module, the reference voltage and the temperature were fed into the distributed feedback laser. And then, the device was used to drive distributed feedback lasers and experiments were carried out to verify the results. The results show that, within 40min, the temperature variation range and the standard difference are no more than 5mK and 0.7mK, respectively. The current variation range and the standard deviation are not more than 40μA and 6μA. When driving the semiconductor optical amplifier, the turn-off time is less than 1μs. The device has good instantaneous response characteristics and high temperature and current stability. The flow control module has good transient characteristics and can precisely control the temperature and current of distributed feedback lasers. The control device can be used to study optical cavity ring-down spectroscopy. It can controll distributed feedback lasers and drive the optical amplifiers to turn off the lasers.
In order to precisely control the temperature and current of distributed feedback lasers, the drive device of distributed feedback laser was designed by using digital signal processing chip.The device was used to set the reference voltage of the current and the temperature of the laser. After digital-to-analog conversion, through the temperature and current driving module, the reference voltage and the temperature were fed into the distributed feedback laser. And then, the device was used to drive distributed feedback lasers and experiments were carried out to verify the results. The results show that, within 40min, the temperature variation range and the standard difference are no more than 5mK and 0.7mK, respectively. The current variation range and the standard deviation are not more than 40μA and 6μA. When driving the semiconductor optical amplifier, the turn-off time is less than 1μs. The device has good instantaneous response characteristics and high temperature and current stability. The flow control module has good transient characteristics and can precisely control the temperature and current of distributed feedback lasers. The control device can be used to study optical cavity ring-down spectroscopy. It can controll distributed feedback lasers and drive the optical amplifiers to turn off the lasers.
2019, 43(4): 442-447.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.002
Abstract:
In order to solve the problems of poor repeatability, cumbersome methods and aperture limitation in the preparation of liquid crystal q-wave-plates, a preparation method of liquid crystal q-wave-plates was adopted based on ultraviolet mask exposure and liquid crystal out-of-plane orientation technology. Theoretical analysis and experimental verification were carried out. The ultraviolet exposure system was built. Large aperture liquid crystal q-wave-plates were prepared with diameter of 2.54cm, topological charges q of 1 and initial angle of 0.The results show that the conversion efficiency of spin angular momentum to orbital angular momentum of the large aperture liquid crystal q-wave-plates constructed by ultraviolet mask method can reach 85%. By using the wave plate, the generation and conversion of vortices and vector vortices are realized. The method of constructing large aperture liquid crystal q-wave-plates based on ultraviolet mask has advantages of low cost, simple preparation process and fast speed. It can realize batch fabrication of liquid crystal q-wave-plates. It is conducive to the commercialization of liquid crystal q-wave-plates.
In order to solve the problems of poor repeatability, cumbersome methods and aperture limitation in the preparation of liquid crystal q-wave-plates, a preparation method of liquid crystal q-wave-plates was adopted based on ultraviolet mask exposure and liquid crystal out-of-plane orientation technology. Theoretical analysis and experimental verification were carried out. The ultraviolet exposure system was built. Large aperture liquid crystal q-wave-plates were prepared with diameter of 2.54cm, topological charges q of 1 and initial angle of 0.The results show that the conversion efficiency of spin angular momentum to orbital angular momentum of the large aperture liquid crystal q-wave-plates constructed by ultraviolet mask method can reach 85%. By using the wave plate, the generation and conversion of vortices and vector vortices are realized. The method of constructing large aperture liquid crystal q-wave-plates based on ultraviolet mask has advantages of low cost, simple preparation process and fast speed. It can realize batch fabrication of liquid crystal q-wave-plates. It is conducive to the commercialization of liquid crystal q-wave-plates.
2019, 43(4): 448-452.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.003
Abstract:
In order to improve classification accuracy of hyperspectral remote sensing images, a classification method based on spatial information and spectral information was proposed by combining pixel neighborhood spectrum with probability co-representation method. Firstly, the neighborhood spectrum of pixels was generated by interpolation method. Then, the probability cooperative representation method was used to classify the samples to be tested. By using the proposed method, classification experiments were carried out on AVIRIS Indian Pines and Salinas scene hyperspectral remote sensing databases, compared with principal component analysis, support vector machine, sparse representation classifier and cooperative representation classifier. The results show that, the recognition accuracy of the proposed method on AVIRIS Indian Pines database is about 17% higher than that of the principal component analysis method. Its recognition accuracy and kappa coefficient are better than those of the other four methods. This method is a good classification method for hyperspectral remote sensing images.
In order to improve classification accuracy of hyperspectral remote sensing images, a classification method based on spatial information and spectral information was proposed by combining pixel neighborhood spectrum with probability co-representation method. Firstly, the neighborhood spectrum of pixels was generated by interpolation method. Then, the probability cooperative representation method was used to classify the samples to be tested. By using the proposed method, classification experiments were carried out on AVIRIS Indian Pines and Salinas scene hyperspectral remote sensing databases, compared with principal component analysis, support vector machine, sparse representation classifier and cooperative representation classifier. The results show that, the recognition accuracy of the proposed method on AVIRIS Indian Pines database is about 17% higher than that of the principal component analysis method. Its recognition accuracy and kappa coefficient are better than those of the other four methods. This method is a good classification method for hyperspectral remote sensing images.
2019, 43(4): 453-459.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.004
Abstract:
In order to explore the feasibility of ultrasonic detection of concrete cracks by laser scanning, sound field was excited by laser scanning concrete surfaces and ultrasonic signal was received with a surface wave probe. The corresponding experimental verification was carried out. The peak value and bipolarity of the experimental signal were analyzed. The location of concrete surface cracks was realized. At the same time, the finite element method was used to simulate the process of scanning laser exciting sound field on the material surface. Ultrasound signal was analyzed in time domain and frequency domain. The results show that, when the distance between laser and crack edge is 1mm, the received signals have typical bipolarity and the peak value reaches the maximum value. When the distance between laser and crack edge continues to decrease, the peak value decreases rapidly. Using the stimulated ultrasound by laser scanning, a 2-D image represented by the peak value of the signal is formed in the dot range. The characteristics of peak-peak mutation and signal bipolarity can locate the defect edge of concrete surfaces.
In order to explore the feasibility of ultrasonic detection of concrete cracks by laser scanning, sound field was excited by laser scanning concrete surfaces and ultrasonic signal was received with a surface wave probe. The corresponding experimental verification was carried out. The peak value and bipolarity of the experimental signal were analyzed. The location of concrete surface cracks was realized. At the same time, the finite element method was used to simulate the process of scanning laser exciting sound field on the material surface. Ultrasound signal was analyzed in time domain and frequency domain. The results show that, when the distance between laser and crack edge is 1mm, the received signals have typical bipolarity and the peak value reaches the maximum value. When the distance between laser and crack edge continues to decrease, the peak value decreases rapidly. Using the stimulated ultrasound by laser scanning, a 2-D image represented by the peak value of the signal is formed in the dot range. The characteristics of peak-peak mutation and signal bipolarity can locate the defect edge of concrete surfaces.
2019, 43(4): 460-463.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.005
Abstract:
In order to explore the formation mechanism and the changing trend of recast layer and heat affected zone (HAZ) of cardiovascular stents induced by key technological parameters in optical fiber microsecond laser processing, experimental method of cutting 316L medical stainless steel by optical fiber microsecond laser based on different single factor parameters was adopted. Through theoretical analysis and experimental verification, the physical model of 316L cardiovascular stent and the detection data of HAZ and recast layer were obtained under single factor parameters. The results show that the thickness of recast layer is mainly affected by pulse width and laser power. It increases with the increase of pulse width and power. The minimum thickness of recast layer is 3.0μm when the pulse width is 20μs. The thickness of HAZ is related to pulse width, pulse frequency, laser power and cutting rate. It increases with the increase of pulse width and frequency. With the increase of power, it increases first and then decreases. With the increase of cutting rate, it decreases first and then increases. When pulse frequency is 5000Hz, the minimum HAZ thickness is 0.2μm. The study of the formation mechanism and trend of recast layer and HAZ of 316L cardiovascular stents gives a foundation for subsequent orthogonal and polishing experiments.
In order to explore the formation mechanism and the changing trend of recast layer and heat affected zone (HAZ) of cardiovascular stents induced by key technological parameters in optical fiber microsecond laser processing, experimental method of cutting 316L medical stainless steel by optical fiber microsecond laser based on different single factor parameters was adopted. Through theoretical analysis and experimental verification, the physical model of 316L cardiovascular stent and the detection data of HAZ and recast layer were obtained under single factor parameters. The results show that the thickness of recast layer is mainly affected by pulse width and laser power. It increases with the increase of pulse width and power. The minimum thickness of recast layer is 3.0μm when the pulse width is 20μs. The thickness of HAZ is related to pulse width, pulse frequency, laser power and cutting rate. It increases with the increase of pulse width and frequency. With the increase of power, it increases first and then decreases. With the increase of cutting rate, it decreases first and then increases. When pulse frequency is 5000Hz, the minimum HAZ thickness is 0.2μm. The study of the formation mechanism and trend of recast layer and HAZ of 316L cardiovascular stents gives a foundation for subsequent orthogonal and polishing experiments.
2019, 43(4): 464-470.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.006
Abstract:
In order to realize one-time accurate measurement of position coordinates of cylindrical object locating points in vertical height direction and horizontal and transverse direction, the linear laser triangulation method was used. Linear laser triangulation positioning measurement model was established. The theoretical analysis was carried out. Based on this method, a set of positioning measurement experimental system was designed. Linear laser spot images reflected by a cylindrical surface were captured by an industrial camera. Blob algorithm was used to extract the vertex pixel coordinates of the laser spot according to the geometrical characteristics of the image. The position coordinates of the cylindrical object positioning points were calculated by combining with the system calibration parameters. The results show that the maximum relative measurement errors in vertical and horizontal directions are 0.14% and 0.89%, respectively. The research results can be used to grasp and locate cylindrical objects in different sizes by manipulators in industrial production.
In order to realize one-time accurate measurement of position coordinates of cylindrical object locating points in vertical height direction and horizontal and transverse direction, the linear laser triangulation method was used. Linear laser triangulation positioning measurement model was established. The theoretical analysis was carried out. Based on this method, a set of positioning measurement experimental system was designed. Linear laser spot images reflected by a cylindrical surface were captured by an industrial camera. Blob algorithm was used to extract the vertex pixel coordinates of the laser spot according to the geometrical characteristics of the image. The position coordinates of the cylindrical object positioning points were calculated by combining with the system calibration parameters. The results show that the maximum relative measurement errors in vertical and horizontal directions are 0.14% and 0.89%, respectively. The research results can be used to grasp and locate cylindrical objects in different sizes by manipulators in industrial production.
2019, 43(4): 471-475.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.007
Abstract:
In order to study effect of atmospheric turbulence and avalanche photodiode (APD) noise when an APD receiving laser transmitted in turbulent atmosphere, both processes, i.e., laser propagation in turbulent atmosphere and laser detection by APD were analyzed. Then, combined with the detection principle of APD, the exponential Weibull-Gauss dual stochastic process model was established. The probability density of APD output current under different signal-to-noise ratios and atmospheric turbulence was measured. Different detection distances and receiving apertures were simulated. The results show that, when the received signal-to-noise ratio is 2, 5 and 10, the variances of light intensity distribution are 0.5354, 0.3565 and 0.2781, respectively and the offsets are 0.05, 0.0109 and 0.0029, respectively. When the structure constants of atmospheric refractive index are 2.5×10-15, 3×10-14, 4.9×10-14, the variances are 0.1198, 0.2781 and 0.4035, respectively and the offsets are 0.0002, 0.0029 and 0.0039, respectively. The dual stochastic process model can accurately describe the process for APD detecting laser transmitting in turbulent atmosphere. The change of detector aperture has little effect on the probability density of APD output current. With the increase of the received signal-to-noise ratio, detection distance and atmospheric refractive index structure constant, the average output current of APD is larger than that of signal current. And the degree of dispersion is aggravated. The establishment of this model has a certain reference value for the research of laser detection technology.
In order to study effect of atmospheric turbulence and avalanche photodiode (APD) noise when an APD receiving laser transmitted in turbulent atmosphere, both processes, i.e., laser propagation in turbulent atmosphere and laser detection by APD were analyzed. Then, combined with the detection principle of APD, the exponential Weibull-Gauss dual stochastic process model was established. The probability density of APD output current under different signal-to-noise ratios and atmospheric turbulence was measured. Different detection distances and receiving apertures were simulated. The results show that, when the received signal-to-noise ratio is 2, 5 and 10, the variances of light intensity distribution are 0.5354, 0.3565 and 0.2781, respectively and the offsets are 0.05, 0.0109 and 0.0029, respectively. When the structure constants of atmospheric refractive index are 2.5×10-15, 3×10-14, 4.9×10-14, the variances are 0.1198, 0.2781 and 0.4035, respectively and the offsets are 0.0002, 0.0029 and 0.0039, respectively. The dual stochastic process model can accurately describe the process for APD detecting laser transmitting in turbulent atmosphere. The change of detector aperture has little effect on the probability density of APD output current. With the increase of the received signal-to-noise ratio, detection distance and atmospheric refractive index structure constant, the average output current of APD is larger than that of signal current. And the degree of dispersion is aggravated. The establishment of this model has a certain reference value for the research of laser detection technology.
2019, 43(4): 476-481.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.008
Abstract:
To avoid the interference of depth of field and occlusion and improve the accuracy of crowd counting, three models of LeNet-5, AlexNet and VGG-16 were adopted and the characteristics of objects with different depth of field in the image were extracted. After adjusting the convolution core size and network structure of the above model, model fusion was carried out. A deep convolution neural network structure based on multi-model fusion was constructed. In the last two layers of the network, the convolution layer with convolution core size of 1×1 was used to replace the traditional full connection layer. The extracted feature maps were integrated with information and the density maps were output. The network parameters were greatly reduced and some improved data was obtained. The efficiency and accuracy of the algorithm were taken into account. The theoretical analysis and experimental verification were carried out. The results show that, in public population counting data set of two subsets of shanghaitech and UCF_CC_50, the mean absolute error and mean square error of this method are 97.99 and 158.02, 23.36 and 41.86, 354.27 and 491.68, respectively. It achieves better performance than the existing traditional crowd counting methods. At the same time, migration experiments are carried out. It proves that the population counting model proposed in this paper has good generalization ability. This study is helpful to improve the accuracy of population counting.
To avoid the interference of depth of field and occlusion and improve the accuracy of crowd counting, three models of LeNet-5, AlexNet and VGG-16 were adopted and the characteristics of objects with different depth of field in the image were extracted. After adjusting the convolution core size and network structure of the above model, model fusion was carried out. A deep convolution neural network structure based on multi-model fusion was constructed. In the last two layers of the network, the convolution layer with convolution core size of 1×1 was used to replace the traditional full connection layer. The extracted feature maps were integrated with information and the density maps were output. The network parameters were greatly reduced and some improved data was obtained. The efficiency and accuracy of the algorithm were taken into account. The theoretical analysis and experimental verification were carried out. The results show that, in public population counting data set of two subsets of shanghaitech and UCF_CC_50, the mean absolute error and mean square error of this method are 97.99 and 158.02, 23.36 and 41.86, 354.27 and 491.68, respectively. It achieves better performance than the existing traditional crowd counting methods. At the same time, migration experiments are carried out. It proves that the population counting model proposed in this paper has good generalization ability. This study is helpful to improve the accuracy of population counting.
2019, 43(4): 482-487.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.009
Abstract:
In order to mark the target image on an arbitrary curved surface with high quality, it is necessary to convert the typesetted 2-D data into 3-D data so that the processing trajectory data of the specific galvanometer can be formed. On the basis of a large number of experimental measurements and calculations of laser scaling, the field-prioria least square conformal map (FPLSCM) algorithm was proposed to minimize distortion of arbitrary free-form surfaces. The practical software design of laser processing system based on a 3-D galvanometer was completed. The theoretical analysis and experimental verification were carried out. A large number of calibration measurement data were obtained. The results show that, in the range of 300mm above and below the z axis, this algorithm can effectively control the calibration distortion caused by the difference between the height and the shape of the surface to be machined at about 1%. And good processing results have been obtained on all kinds of 3-D curved surfaces. This research successfully accomplishes various surface processing tasks on free 3-D curved surface by using dynamic focusing technology. The distortion is effectively reduced by optimization algorithm.
In order to mark the target image on an arbitrary curved surface with high quality, it is necessary to convert the typesetted 2-D data into 3-D data so that the processing trajectory data of the specific galvanometer can be formed. On the basis of a large number of experimental measurements and calculations of laser scaling, the field-prioria least square conformal map (FPLSCM) algorithm was proposed to minimize distortion of arbitrary free-form surfaces. The practical software design of laser processing system based on a 3-D galvanometer was completed. The theoretical analysis and experimental verification were carried out. A large number of calibration measurement data were obtained. The results show that, in the range of 300mm above and below the z axis, this algorithm can effectively control the calibration distortion caused by the difference between the height and the shape of the surface to be machined at about 1%. And good processing results have been obtained on all kinds of 3-D curved surfaces. This research successfully accomplishes various surface processing tasks on free 3-D curved surface by using dynamic focusing technology. The distortion is effectively reduced by optimization algorithm.
2019, 43(4): 488-492.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.010
Abstract:
In order to measure the absorption spectrum accurately and reduce the influence of temperature and turbulence fluctuation on spectral measurement, the method of spectrum simulation and 20kHz high frequency scanning was adopted. The low temperature sensitivity line P(10) in mid-infrared fundamental frequency transition band was selected. The data of absorption spectra and volume fraction of engine CO with the change of time were obtained. The theoretical analysis and experimental verification were carried out. The results show that, the influence of target gas temperature change on volume fraction can be reduced by 48.28% within the scanning range of P branch line. The range of variation is (153±123)×10-6. The scheme can provide a high-speed, accurate and real-time monitoring scheme for CO laser remote sensing measurement of engine exhaust.
In order to measure the absorption spectrum accurately and reduce the influence of temperature and turbulence fluctuation on spectral measurement, the method of spectrum simulation and 20kHz high frequency scanning was adopted. The low temperature sensitivity line P(10) in mid-infrared fundamental frequency transition band was selected. The data of absorption spectra and volume fraction of engine CO with the change of time were obtained. The theoretical analysis and experimental verification were carried out. The results show that, the influence of target gas temperature change on volume fraction can be reduced by 48.28% within the scanning range of P branch line. The range of variation is (153±123)×10-6. The scheme can provide a high-speed, accurate and real-time monitoring scheme for CO laser remote sensing measurement of engine exhaust.
2019, 43(4): 493-499.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.011
Abstract:
Superhydrophobic surfaces have gained wide attention due to their good properties such as slip resistance, corrosion resistance, and anti-friction. Superhydrophobic surfaces etched by laser have advantages of controllability, simplicity, stability, environmental protection, etc. It is expected to achieve industrial production. Firstly, theoretical models and influencing factors of superhydrophobic surfaces are reviewed. Also, the methods of laser etching superhydrophobic surfaces at home and abroad are summarized. The advantages and disadvantages of femtosecond, picosecond and nanosecond lasers for superhydrophobic surfaces are discussed. Finally, the prospect of laser etching superhydrophobic surface technology is put forward. Future research should insist on reducing the production cost, reducing the process steps, improving production efficiency, saving energy and keeping environmental protection, etc. It is important to improve the stability and durability of surface microstructure. Superhydrophobic surfaces will move towards multi-functionality and intelligence.
Superhydrophobic surfaces have gained wide attention due to their good properties such as slip resistance, corrosion resistance, and anti-friction. Superhydrophobic surfaces etched by laser have advantages of controllability, simplicity, stability, environmental protection, etc. It is expected to achieve industrial production. Firstly, theoretical models and influencing factors of superhydrophobic surfaces are reviewed. Also, the methods of laser etching superhydrophobic surfaces at home and abroad are summarized. The advantages and disadvantages of femtosecond, picosecond and nanosecond lasers for superhydrophobic surfaces are discussed. Finally, the prospect of laser etching superhydrophobic surface technology is put forward. Future research should insist on reducing the production cost, reducing the process steps, improving production efficiency, saving energy and keeping environmental protection, etc. It is important to improve the stability and durability of surface microstructure. Superhydrophobic surfaces will move towards multi-functionality and intelligence.
2019, 43(4): 500-505.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.012
Abstract:
In order to achieve effective supervision of transmission line corridors, a method of power line extraction and reconstruction was proposed based on airborne laser radar(LiDAR) point cloud. Firstly, echo information of point clouds was used to filter out the most of ground objects and keep all information about power line. And then, most non-power line point clouds were removed based on grid height elevation and elevation threshold. The initial extraction of power line was realized. For the preliminary extracted point cloud of power line, a single transmission line point was separated by Hough transform. In order to improve the accuracy of power line point extraction, the extraction result of Hough transform was improved. Then the location of the tower was determined by means of local extreme point detection. Finally, a polynomial model with constraints was used to segment each power line and realize 3-D reconstruction of power line model. The results show that, 424 power line points are extracted by this algorithm and the total extraction accuracy is 87.603%. The fitted power line model has a good effect. The algorithm can automatically and accurately extract and reconstruct power lines from LiDAR point cloud data. It has a good practical value for the inspection of transmission line corridors.
In order to achieve effective supervision of transmission line corridors, a method of power line extraction and reconstruction was proposed based on airborne laser radar(LiDAR) point cloud. Firstly, echo information of point clouds was used to filter out the most of ground objects and keep all information about power line. And then, most non-power line point clouds were removed based on grid height elevation and elevation threshold. The initial extraction of power line was realized. For the preliminary extracted point cloud of power line, a single transmission line point was separated by Hough transform. In order to improve the accuracy of power line point extraction, the extraction result of Hough transform was improved. Then the location of the tower was determined by means of local extreme point detection. Finally, a polynomial model with constraints was used to segment each power line and realize 3-D reconstruction of power line model. The results show that, 424 power line points are extracted by this algorithm and the total extraction accuracy is 87.603%. The fitted power line model has a good effect. The algorithm can automatically and accurately extract and reconstruct power lines from LiDAR point cloud data. It has a good practical value for the inspection of transmission line corridors.
2019, 43(4): 506-510.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.013
Abstract:
In order to solve the problems of color approximation and uneven brightness between white blood cells and other cells in blood cell images, a white blood cell segmentation method based on C - Y color space was adopted. The original RGB image was transformed into C - Y image. C - Y image was separated to obtain B - Y color component image with all information. Secondly, a complete white blood cell image is obtained by screening the area of the connected region, opening operation and pixel operation. The contrast stretched G image was extracted. The approximate position of nucleus was obtained by threshold segmentation. And then, the complete nuclear image was segmented by area screening and open operation of connected domain. The results show that the algorithm in this paper has good segmentation accuracy for eosinophils, lymphocytes, monocytes and neutrophils, i.e., 94.33%, 91.60%, 97.72% and 98.66% respectively. The algorithm in this paper can segment white blood cells more completely. It lays a foundation for the follow-up classification research.
In order to solve the problems of color approximation and uneven brightness between white blood cells and other cells in blood cell images, a white blood cell segmentation method based on C - Y color space was adopted. The original RGB image was transformed into C - Y image. C - Y image was separated to obtain B - Y color component image with all information. Secondly, a complete white blood cell image is obtained by screening the area of the connected region, opening operation and pixel operation. The contrast stretched G image was extracted. The approximate position of nucleus was obtained by threshold segmentation. And then, the complete nuclear image was segmented by area screening and open operation of connected domain. The results show that the algorithm in this paper has good segmentation accuracy for eosinophils, lymphocytes, monocytes and neutrophils, i.e., 94.33%, 91.60%, 97.72% and 98.66% respectively. The algorithm in this paper can segment white blood cells more completely. It lays a foundation for the follow-up classification research.
2019, 43(4): 511-516.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.014
Abstract:
In order to improve the sensitivity of a pressure sensor, a novel pressure sensing structure of photonic crystal fiber with side hole and high birefringence was designed, based on the theory of photonic crystal fiber and its high birefringence and flexible design structure. The force and mode field distribution of sensing structure were simulated and analyzed by using full vector finite element method and COMSOL software. The dependence of pressure sensing characteristics on geometrical structure and free space wavelength was obtained. The optimum structural parameters were obtained by optimum design. The high pressure sensitivity was further obtained. The results show that, under the optimal structure, when free space wavelength is 1.55μm and pressure is 200MPa, polarization phase sensitivity is 166.2rad/(MPa·m) and maximum pressure that can be applied is 720MPa. The sensitivity of phase mode birefringence is maintained at about 4.1×10-5MPa-1. The research is helpful to improve the sensitivity of pressure sensors.
In order to improve the sensitivity of a pressure sensor, a novel pressure sensing structure of photonic crystal fiber with side hole and high birefringence was designed, based on the theory of photonic crystal fiber and its high birefringence and flexible design structure. The force and mode field distribution of sensing structure were simulated and analyzed by using full vector finite element method and COMSOL software. The dependence of pressure sensing characteristics on geometrical structure and free space wavelength was obtained. The optimum structural parameters were obtained by optimum design. The high pressure sensitivity was further obtained. The results show that, under the optimal structure, when free space wavelength is 1.55μm and pressure is 200MPa, polarization phase sensitivity is 166.2rad/(MPa·m) and maximum pressure that can be applied is 720MPa. The sensitivity of phase mode birefringence is maintained at about 4.1×10-5MPa-1. The research is helpful to improve the sensitivity of pressure sensors.
2019, 43(4): 517-526.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.015
Abstract:
Lean combustion can improve the thermal efficiency of an engine and reduce the emission of pollutants. But lean combustion is challenged by the low flame propagation and the possible local quenching of the initial flame kernel near the lean limit at high pressures. Laser-induced spark ignition can effectively solve these problems residing in the combustion process of the fuel at low equivalence ratio and high pressures. In addition, the laser-induced spark ignition can achieve multi-point ignition easily and can reduce the combustion time and increase the combustion pressure significantly. Therefore, laser induced spark ignition has many advantages over the traditional electric spark plug ignition technique. Conical cavity, diffractive lens, spatial light modulator and Dammam grating have been used to achieve the multi-point laser-induced spark ignition. Several technical approaches of multi-point laser induced spark ignition are summarized. The research status and the latest achievements of multi-point laser induced spark ignition for internal combustion engines are discussed. Several methods to achieve multi-point ignition of laser-induced spark are evaluated. Furthermore, the advantages and problems to be solved for each method in the multi-point ignition of laser induced spark are pointed out. On the basis of the above examinations, some suggestions on the future work are also proposed.
Lean combustion can improve the thermal efficiency of an engine and reduce the emission of pollutants. But lean combustion is challenged by the low flame propagation and the possible local quenching of the initial flame kernel near the lean limit at high pressures. Laser-induced spark ignition can effectively solve these problems residing in the combustion process of the fuel at low equivalence ratio and high pressures. In addition, the laser-induced spark ignition can achieve multi-point ignition easily and can reduce the combustion time and increase the combustion pressure significantly. Therefore, laser induced spark ignition has many advantages over the traditional electric spark plug ignition technique. Conical cavity, diffractive lens, spatial light modulator and Dammam grating have been used to achieve the multi-point laser-induced spark ignition. Several technical approaches of multi-point laser induced spark ignition are summarized. The research status and the latest achievements of multi-point laser induced spark ignition for internal combustion engines are discussed. Several methods to achieve multi-point ignition of laser-induced spark are evaluated. Furthermore, the advantages and problems to be solved for each method in the multi-point ignition of laser induced spark are pointed out. On the basis of the above examinations, some suggestions on the future work are also proposed.
2019, 43(4): 527-531.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.016
Abstract:
In order to meet the test and calibration requirements of 100m~3km extra-long focal length, a set of long focal length measurement instrument was designed based on Talbot-Moiré fringes. Aiming at the system parameters affecting the measurement uncertainty, different calibration methods were designed respectively. Experiments were carried out to verify the results. The results show that, after calibration, the measurement uncertainty is 6.4%. Measurement results of the long focal length measurement instrument after calibration, and knife-edge instrument meet the measurement uncertainty formula. The maximum comparison result is 0.64, less than 1. Uncertainty evaluation of the long focal length measurement instrument is reasonable. The research validates the feasibility of calibration methods for system parameters of a long focal length measurement instrument.
In order to meet the test and calibration requirements of 100m~3km extra-long focal length, a set of long focal length measurement instrument was designed based on Talbot-Moiré fringes. Aiming at the system parameters affecting the measurement uncertainty, different calibration methods were designed respectively. Experiments were carried out to verify the results. The results show that, after calibration, the measurement uncertainty is 6.4%. Measurement results of the long focal length measurement instrument after calibration, and knife-edge instrument meet the measurement uncertainty formula. The maximum comparison result is 0.64, less than 1. Uncertainty evaluation of the long focal length measurement instrument is reasonable. The research validates the feasibility of calibration methods for system parameters of a long focal length measurement instrument.
2019, 43(4): 532-538.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.017
Abstract:
In order to improve the security of multi-image encryption and solve the problem of large amount of data in multi-image encryption system, the encryption method based on block compressed sensing and improved magic square transform was adopted. During the encryption process, the sensitivity of chaotic sequence to initial value was fully utilized and the periodicity of encryption algorithm based on traditional magic square transformation was solved. Combining the block compression sensing method, the amount of data in the encryption system was reduced. Four 256×256 gray-scale images were encrypted and tested. The results show that the encryption time of the system is only 0.98s. The quality of the reconstructed image is high. The correlation coefficients were higher than 0.99. Peak signal-to-noise ratio (PSNR) values are greater than 35dB. This algorithm reduces the amount of data in the encryption system and further improves the security of the system. The algorithm is easy to implement and can complete multi-image encryption efficiently and safely.
In order to improve the security of multi-image encryption and solve the problem of large amount of data in multi-image encryption system, the encryption method based on block compressed sensing and improved magic square transform was adopted. During the encryption process, the sensitivity of chaotic sequence to initial value was fully utilized and the periodicity of encryption algorithm based on traditional magic square transformation was solved. Combining the block compression sensing method, the amount of data in the encryption system was reduced. Four 256×256 gray-scale images were encrypted and tested. The results show that the encryption time of the system is only 0.98s. The quality of the reconstructed image is high. The correlation coefficients were higher than 0.99. Peak signal-to-noise ratio (PSNR) values are greater than 35dB. This algorithm reduces the amount of data in the encryption system and further improves the security of the system. The algorithm is easy to implement and can complete multi-image encryption efficiently and safely.
2019, 43(4): 539-545.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.018
Abstract:
In order to improve the performance of an outdoor light emitting diode(LED) visible light communication system and solve the interference problems caused by turbulence, such as phase change, beam drift and beam spread, etc., a LED visible light communication system based on multiple-input multiple-output(MIMO) technology was proposed. Firstly, the atmospheric turbulence channel model was constructed. Secondly, the model of LED visible light communication system was built based on MIMO technology. Finally, the original signal was recovered by maximum ratio merging method and bit error rate was calculated. The results show that, at the same turbulence intensity, the greater the diversity of the system, the lower the bit error rate. In the strong turbulent channel environment, the M=3, N=4 communication system achieves a bit error rate of 10-7. Compared with the M=1, N=1 communication system, the bit error rate is reduced by five orders of magnitude. This study verifies the feasibility and effectiveness of MIMO technology in suppressing turbulence effect.
In order to improve the performance of an outdoor light emitting diode(LED) visible light communication system and solve the interference problems caused by turbulence, such as phase change, beam drift and beam spread, etc., a LED visible light communication system based on multiple-input multiple-output(MIMO) technology was proposed. Firstly, the atmospheric turbulence channel model was constructed. Secondly, the model of LED visible light communication system was built based on MIMO technology. Finally, the original signal was recovered by maximum ratio merging method and bit error rate was calculated. The results show that, at the same turbulence intensity, the greater the diversity of the system, the lower the bit error rate. In the strong turbulent channel environment, the M=3, N=4 communication system achieves a bit error rate of 10-7. Compared with the M=1, N=1 communication system, the bit error rate is reduced by five orders of magnitude. This study verifies the feasibility and effectiveness of MIMO technology in suppressing turbulence effect.
2019, 43(4): 546-550.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.019
Abstract:
In order to evaluate surface breaking cracks, laser ultrasonic diffraction shear wave method was used to measure its parameters. Laser-induced shear wave propagating to the crack tip produced a diffraction signal and then the signal was received by the sensors on the other side of the crack. According to the transit time of diffracted shear waves at different receiving points, the formulas for calculating crack parameters were derived. The propagation process of the shear wave in the workpiece was simulated and analyzed. The experimental system of laser-ultrasonic crack measurement was established. The diffraction shear wave data were also collected. The experimental results show that, within the effective detection range, the error between the measured value and the actual value is within 5%. The results can promote the application of laser ultrasound in surface crack detection.
In order to evaluate surface breaking cracks, laser ultrasonic diffraction shear wave method was used to measure its parameters. Laser-induced shear wave propagating to the crack tip produced a diffraction signal and then the signal was received by the sensors on the other side of the crack. According to the transit time of diffracted shear waves at different receiving points, the formulas for calculating crack parameters were derived. The propagation process of the shear wave in the workpiece was simulated and analyzed. The experimental system of laser-ultrasonic crack measurement was established. The diffraction shear wave data were also collected. The experimental results show that, within the effective detection range, the error between the measured value and the actual value is within 5%. The results can promote the application of laser ultrasound in surface crack detection.
2019, 43(4): 551-556.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.020
Abstract:
In order to explore the strong correlation between virtual rendering viewpoints and improve the compression efficiency of optical field image, an optical field image compression algorithm based on viewpoint correlation was proposed. The algorithm was based on high efficiency video coding (HEVC) and screen content coding expansion platform. Linear weighting algorithm and intra-block copy hybrid prediction algorithm were used to improve the prediction accuracy of coded blocks. Distortion optimization process was used to adaptively select the optimal block size and prediction mode. The experimental results show that, the average BJONTEGAARD delta peak signal-to-noise ratio(BD-PSNR) coding gain of the proposed algorithm is 2.55dB compared with that of HEVC standard. At the same time, better quality of virtual view rendering can be gotten. The algorithm makes full use of the strong correlation between virtual rendering viewpoints and improves the coding efficiency of optical field images.
In order to explore the strong correlation between virtual rendering viewpoints and improve the compression efficiency of optical field image, an optical field image compression algorithm based on viewpoint correlation was proposed. The algorithm was based on high efficiency video coding (HEVC) and screen content coding expansion platform. Linear weighting algorithm and intra-block copy hybrid prediction algorithm were used to improve the prediction accuracy of coded blocks. Distortion optimization process was used to adaptively select the optimal block size and prediction mode. The experimental results show that, the average BJONTEGAARD delta peak signal-to-noise ratio(BD-PSNR) coding gain of the proposed algorithm is 2.55dB compared with that of HEVC standard. At the same time, better quality of virtual view rendering can be gotten. The algorithm makes full use of the strong correlation between virtual rendering viewpoints and improves the coding efficiency of optical field images.
2019, 43(4): 557-562.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.021
Abstract:
In order to obtain the tunable absorption spectrum of TE wave in THz band, a tunable THz absorber based on vanadium dioxide was designed by full-wave simulation. Absorption spectrum, electric field, surface current and energy loss of the absorber were analyzed. The effects of structural parameters h4, k and incident angle θ on absorption frequency domain and absorption bandwidth were discussed. The simulation results show that, tunable absorption spectrum can be obtained and absorption performance of the microwave absorber can be improved by changing the physical characteristics of vanadium dioxide resonator unit through external temperature control. When T≥68℃, broadband absorption of microwave absorber can be achieved in 2.70THz~3.36THz band. Absorption rate is above 90% and relative bandwidth can reach 21.8%. When T < 68℃, multiple single frequency points can be absorbed. The position of absorption frequency point and absorption bandwidth can be changed by changing the structural parameters h4 and k. The absorption effect can be affected by changing incident angle θ. This study is helpful for further research of tunable terahertz devices.
In order to obtain the tunable absorption spectrum of TE wave in THz band, a tunable THz absorber based on vanadium dioxide was designed by full-wave simulation. Absorption spectrum, electric field, surface current and energy loss of the absorber were analyzed. The effects of structural parameters h4, k and incident angle θ on absorption frequency domain and absorption bandwidth were discussed. The simulation results show that, tunable absorption spectrum can be obtained and absorption performance of the microwave absorber can be improved by changing the physical characteristics of vanadium dioxide resonator unit through external temperature control. When T≥68℃, broadband absorption of microwave absorber can be achieved in 2.70THz~3.36THz band. Absorption rate is above 90% and relative bandwidth can reach 21.8%. When T < 68℃, multiple single frequency points can be absorbed. The position of absorption frequency point and absorption bandwidth can be changed by changing the structural parameters h4 and k. The absorption effect can be affected by changing incident angle θ. This study is helpful for further research of tunable terahertz devices.
2019, 43(4): 563-568.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.022
Abstract:
In order to make the received two signals orthogonal to each other and correctly demodulate the signal, Schmitt orthogonalization algorithm was used to theoretically analyze and experimentally verify the two signals. The performance of constellation was improved after orthogonal imbalance compensation. The carrier frequency was tracked and captured by the loose tail ring to achieve carrier recovery, and the baseband signal was demodulated correctly. The experimental results show that, after compensation by Schmidt orthogonalization algorithm, the rotated constellation is corrected and the problem of unequal Euclidean distance between constellation points is improved. The baseband signal distortion becomes corrected. When the frequency offset is in the range of -300kHz~300kHz, the loose tail loop can track and capture carrier frequency and baseband signal can be correctly demodulated. The scheme is low complexity and practical, and is suitable for the study of coherent optical communication systems.
In order to make the received two signals orthogonal to each other and correctly demodulate the signal, Schmitt orthogonalization algorithm was used to theoretically analyze and experimentally verify the two signals. The performance of constellation was improved after orthogonal imbalance compensation. The carrier frequency was tracked and captured by the loose tail ring to achieve carrier recovery, and the baseband signal was demodulated correctly. The experimental results show that, after compensation by Schmidt orthogonalization algorithm, the rotated constellation is corrected and the problem of unequal Euclidean distance between constellation points is improved. The baseband signal distortion becomes corrected. When the frequency offset is in the range of -300kHz~300kHz, the loose tail loop can track and capture carrier frequency and baseband signal can be correctly demodulated. The scheme is low complexity and practical, and is suitable for the study of coherent optical communication systems.
2019, 43(4): 569-573.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.023
Abstract:
In order to solve the problem of occlusion or loss of targets caused by drastic change in gray distribution of image pixels by using traditional target tracking algorithms under high-energy laser reflection in the sky background, a correlation tracking algorithm based on local feature segmentation was adopted. The tracking template was divided into blocks according to local features. The block templates with high feature stability were calculated and selected. Template matching was performed for each block in the tracking area. The theoretical analysis and experimental verification were carried out. The results show that the algorithm can track the target stably in real time under strong light interference. And the image processing delay time is less than 2ms. This research is helpful to ensure the performance of ultra-high precision tracking system based on high-energy laser emission.
In order to solve the problem of occlusion or loss of targets caused by drastic change in gray distribution of image pixels by using traditional target tracking algorithms under high-energy laser reflection in the sky background, a correlation tracking algorithm based on local feature segmentation was adopted. The tracking template was divided into blocks according to local features. The block templates with high feature stability were calculated and selected. Template matching was performed for each block in the tracking area. The theoretical analysis and experimental verification were carried out. The results show that the algorithm can track the target stably in real time under strong light interference. And the image processing delay time is less than 2ms. This research is helpful to ensure the performance of ultra-high precision tracking system based on high-energy laser emission.
2019, 43(4): 574-578.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.024
Abstract:
In order to solve the problem of destroying the physical meaning of spectral curve of pixels in dimension reduction of traditional N-FINDR algorithm, the best exponential method of band selection was used instead of feature extraction. The dimension reduction method of N-FINDR algorithm was improved. Experiments were carried out using the simulated and real hyperspectral data. The improved N-FINDR algorithm and other two algorithms were used to extract the terminal elements respectively. Full constrained least squares method was used to solve the mixing problem. The results show that the improved N-FINDR algorithm has higher precision and uses less time. It is feasible to use band selection instead of feature extraction to improve the dimension reduction method and retain the physical meaning of spectral curve in N-FINDR algorithm.
In order to solve the problem of destroying the physical meaning of spectral curve of pixels in dimension reduction of traditional N-FINDR algorithm, the best exponential method of band selection was used instead of feature extraction. The dimension reduction method of N-FINDR algorithm was improved. Experiments were carried out using the simulated and real hyperspectral data. The improved N-FINDR algorithm and other two algorithms were used to extract the terminal elements respectively. Full constrained least squares method was used to solve the mixing problem. The results show that the improved N-FINDR algorithm has higher precision and uses less time. It is feasible to use band selection instead of feature extraction to improve the dimension reduction method and retain the physical meaning of spectral curve in N-FINDR algorithm.
2019, 43(4): 579-584.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.025
Abstract:
In order to investigate the evolution of beam wander of partially coherent crescent beams in non-Kolmogorov turbulence, the extended Huygens-Fresnel principle was used and the corresponding analytical expressions were obtained. Numerical simulation was carried out by using MATLAB. The results show that, in the non-Kolmogorov turbulence, beam wander of partially coherent crescent-like beams decreases with the increase of anisotropic parameters, the increase of turbulent inner scale, the decrease of turbulent outer scale and the decrease of structural constants respectively. Compared with isotropic turbulence, anisotropic turbulence has little effect on beam wander. Off-axis distance of the maximum intensity position of crescent-like beam increases with the increase of wavelength and beam order respectively. It decreases with the increase of coherence length. Off-axis characteristic at the position of the maximum intensity is beneficial for crescent-like beams to transmit around obstacles. The obtained conclusions have some reference value for practical optical communication.
In order to investigate the evolution of beam wander of partially coherent crescent beams in non-Kolmogorov turbulence, the extended Huygens-Fresnel principle was used and the corresponding analytical expressions were obtained. Numerical simulation was carried out by using MATLAB. The results show that, in the non-Kolmogorov turbulence, beam wander of partially coherent crescent-like beams decreases with the increase of anisotropic parameters, the increase of turbulent inner scale, the decrease of turbulent outer scale and the decrease of structural constants respectively. Compared with isotropic turbulence, anisotropic turbulence has little effect on beam wander. Off-axis distance of the maximum intensity position of crescent-like beam increases with the increase of wavelength and beam order respectively. It decreases with the increase of coherence length. Off-axis characteristic at the position of the maximum intensity is beneficial for crescent-like beams to transmit around obstacles. The obtained conclusions have some reference value for practical optical communication.
2019, 43(4): 585-590.
doi: 10.7510/jgjs.issn.1001-3806.2019.04.026
Abstract:
In order to monitor the film thickness of polyethylene terephthalate (PET) composite substrate on 3-D glass, modeling analysis method of PET composite substrates equivalent to single-layer substrates was adopted. The thickness measurement of titanium dioxide gradient refractive index material thin films on complex substrates was realized by ellipsometry. The result show that, the thickness of titanium dioxide gradient refractive index films on PET composite substrates is 212.48nm by this method. The results of scanning electron microscopy is 211nm. The result is very accurate. The equivalent substrate method is validated by taking titanium dioxide as an example. The method is also applicable to other dielectric films. This method can measure and characterize the thickness of titanium dioxide thin films on PET composite substrates with high accuracy, and is of great significance for monitoring the coating process.
In order to monitor the film thickness of polyethylene terephthalate (PET) composite substrate on 3-D glass, modeling analysis method of PET composite substrates equivalent to single-layer substrates was adopted. The thickness measurement of titanium dioxide gradient refractive index material thin films on complex substrates was realized by ellipsometry. The result show that, the thickness of titanium dioxide gradient refractive index films on PET composite substrates is 212.48nm by this method. The results of scanning electron microscopy is 211nm. The result is very accurate. The equivalent substrate method is validated by taking titanium dioxide as an example. The method is also applicable to other dielectric films. This method can measure and characterize the thickness of titanium dioxide thin films on PET composite substrates with high accuracy, and is of great significance for monitoring the coating process.
