Map
WeChat
Email alert
RSS2021 Vol. 45, No. 3
column
Display Method:
[Abstract]
[PDF 269KB]
2021, 45(3): 271-279.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.001
[FullText HTML]
Abstract:
High repetition rate mid-infrared lasers with the wavelength of 3μm~5μm play important roles in the field of photoelectric countermeasures, which are mainly classified into three types: direct pumped high repetition-rate mid-infrared solid-state lasers, high repetition-rate mid-infrared fiber lasers, and high repetition-rate mid-infrared optical parametric oscillators (OPOs). The main technical solutions of generating high repetition-rate mid-infrared lasers have been introduced first, and the related research progress of three types of lasers mentioned above have been discussed in this report. Finally, we also analyze the relative problems and point out some development directions of various technologies in the near future.
High repetition rate mid-infrared lasers with the wavelength of 3μm~5μm play important roles in the field of photoelectric countermeasures, which are mainly classified into three types: direct pumped high repetition-rate mid-infrared solid-state lasers, high repetition-rate mid-infrared fiber lasers, and high repetition-rate mid-infrared optical parametric oscillators (OPOs). The main technical solutions of generating high repetition-rate mid-infrared lasers have been introduced first, and the related research progress of three types of lasers mentioned above have been discussed in this report. Finally, we also analyze the relative problems and point out some development directions of various technologies in the near future.
2021, 45(3): 280-285.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.002
Abstract:
In order to study the influence of laminated structures of carbon fiber reinforced polymer (CFRP) on the temperature under continuous wave (CW) laser irradiation, the ablation processes of five typical laminated CFRPs irradiated by CW laser were simulated by using finite element software COMSOL. The temperature distribution and evolution of five typical laminated composites were obtained by the temperature deviation of the material surface. Meanwhile, based on analyzing the overall temperature distribution of the materials statistically, the variations of the temperature uniformity of the materials with the laser irradiation time were obtained. The results show that the surface temperature near the edge of the spot is most sensitive to the laminated structure in unidirectional ply CFRPs and the temperature curve is non-monotonic. Moreover, the temperature uniformity of CFRP with 45° angle laminated structure is the best in the five types. The results of this work can be referenced for the study of thermomechanics damage of CFRP induced by laser.
In order to study the influence of laminated structures of carbon fiber reinforced polymer (CFRP) on the temperature under continuous wave (CW) laser irradiation, the ablation processes of five typical laminated CFRPs irradiated by CW laser were simulated by using finite element software COMSOL. The temperature distribution and evolution of five typical laminated composites were obtained by the temperature deviation of the material surface. Meanwhile, based on analyzing the overall temperature distribution of the materials statistically, the variations of the temperature uniformity of the materials with the laser irradiation time were obtained. The results show that the surface temperature near the edge of the spot is most sensitive to the laminated structure in unidirectional ply CFRPs and the temperature curve is non-monotonic. Moreover, the temperature uniformity of CFRP with 45° angle laminated structure is the best in the five types. The results of this work can be referenced for the study of thermomechanics damage of CFRP induced by laser.
2021, 45(3): 286-291.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.003
Abstract:
In order to obtain the glass welding seam with good shape and few pores, the method of adding opaque glass frit to the middle layer was used to study the porosity problem in the laser welding of glass. A complete set of welding equipment for laser welding of glass and glass was built with semiconductor laser as the heat source. By analyzing the characteristics of porosity distribution, counting the porosity of weld, measuring the size of porosity, comparing the difference between the front and backside of the weld, the influence of laser average power, welding speed and other process parameters on the formation of porosity and the surface morphology of weld was studied. The results show that when the laser power is too small and the welding speed is too slow, it is not conducive to inhibit the generation of pores in the weld, and the glass plate may not be welded. With the increase of laser power and welding speed, the porosity in the weld increases significantly. When the laser power P, the welding rate v, and the defocusing amount d is respectively set to beequals 35W, 0.1m/min, and -15mm, a well-formed weld with a pore diameter of less than 3.696μm and a uniform distribution can be obtained, and the connection strength is high. This research can provide a theoretical basis for laser sealing of glass, and has a wide industrial application prospect.
In order to obtain the glass welding seam with good shape and few pores, the method of adding opaque glass frit to the middle layer was used to study the porosity problem in the laser welding of glass. A complete set of welding equipment for laser welding of glass and glass was built with semiconductor laser as the heat source. By analyzing the characteristics of porosity distribution, counting the porosity of weld, measuring the size of porosity, comparing the difference between the front and backside of the weld, the influence of laser average power, welding speed and other process parameters on the formation of porosity and the surface morphology of weld was studied. The results show that when the laser power is too small and the welding speed is too slow, it is not conducive to inhibit the generation of pores in the weld, and the glass plate may not be welded. With the increase of laser power and welding speed, the porosity in the weld increases significantly. When the laser power P, the welding rate v, and the defocusing amount d is respectively set to beequals 35W, 0.1m/min, and -15mm, a well-formed weld with a pore diameter of less than 3.696μm and a uniform distribution can be obtained, and the connection strength is high. This research can provide a theoretical basis for laser sealing of glass, and has a wide industrial application prospect.
2021, 45(3): 292-297.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.004
Abstract:
In order to solve the problem of low positioning accuracy of the weld seam center based on line laser vision sensing, a seam tracking method based on an improved tracking-learning-detection (TLD) algorithm was adopted. The weld images were acquired in real time during the weld seam tracking. The TLD algorithm combining the tracker (tracking) and the detector (detection) was adopted to track weld feature points in real time and the online learning mechanism (learning) was adopted to update the classifier parameters, so as to improve the accuracy of seam tracking. On this basis, the region of interest (ROI) was intercepted from the laser stripe images, which greatly reduced the detector's search area. The effective feature points of the tracker were selected to improve the efficiency of the algorithm according to the characteristics of the light intensity distribution of the laser stripe in combination with the rectifying direction. The V-shaped weld and the lapped weld of the stainless steel plate were tracked. The results indicate that the location of the seam center can be achieved by tracking and detecting and the fusion weld tracking method can accurately extract weld feature points. The mean absolute tracking errors of both weld seams were 0.062mm and 0.052mm. This method provides the basis for improving the accuracy of weld seam tracking.
In order to solve the problem of low positioning accuracy of the weld seam center based on line laser vision sensing, a seam tracking method based on an improved tracking-learning-detection (TLD) algorithm was adopted. The weld images were acquired in real time during the weld seam tracking. The TLD algorithm combining the tracker (tracking) and the detector (detection) was adopted to track weld feature points in real time and the online learning mechanism (learning) was adopted to update the classifier parameters, so as to improve the accuracy of seam tracking. On this basis, the region of interest (ROI) was intercepted from the laser stripe images, which greatly reduced the detector's search area. The effective feature points of the tracker were selected to improve the efficiency of the algorithm according to the characteristics of the light intensity distribution of the laser stripe in combination with the rectifying direction. The V-shaped weld and the lapped weld of the stainless steel plate were tracked. The results indicate that the location of the seam center can be achieved by tracking and detecting and the fusion weld tracking method can accurately extract weld feature points. The mean absolute tracking errors of both weld seams were 0.062mm and 0.052mm. This method provides the basis for improving the accuracy of weld seam tracking.
2021, 45(3): 298-302.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.005
Abstract:
To study the influence of radio frequency (RF) power of LD pumped Nd: YVO4 acousto-optic Q-switch on diffraction efficiency, by adjusting the RF power applied on the Q-switch, the changing trend of the light leakage and the rise time of the laser pulse was obtained and analyzed. The results show that the leakage light completely disappears when the RF power increases to 4.4W, and the leakage power is less than 500mW when the RF power is between 2W~3W. And the rise time of laser pulse is 60%~70% of the time to reach the first threshold. In summary, not only the rise time of the outputted laser pulse train is considered after the door signal is turned on, but also the light leakage power of the laser is kept as low as possible when the Q-switch is set at the so-called hold-off status. The research results have good reference value for the construction of an acousto-optic Q-switched solid-state laser that can be turned on quickly and have a serious thermal effect.
To study the influence of radio frequency (RF) power of LD pumped Nd: YVO4 acousto-optic Q-switch on diffraction efficiency, by adjusting the RF power applied on the Q-switch, the changing trend of the light leakage and the rise time of the laser pulse was obtained and analyzed. The results show that the leakage light completely disappears when the RF power increases to 4.4W, and the leakage power is less than 500mW when the RF power is between 2W~3W. And the rise time of laser pulse is 60%~70% of the time to reach the first threshold. In summary, not only the rise time of the outputted laser pulse train is considered after the door signal is turned on, but also the light leakage power of the laser is kept as low as possible when the Q-switch is set at the so-called hold-off status. The research results have good reference value for the construction of an acousto-optic Q-switched solid-state laser that can be turned on quickly and have a serious thermal effect.
2021, 45(3): 303-306.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.006
Abstract:
In order to prove the effectiveness of 3-D fluorescence spectroscopy in the rapid classification of milk beverages on the market, the 3-D fluorescence spectra of 12 different brands of milk beverages which were brought from the market were collected and the spectral data were pretreated. The spectral data after pretreatment were classified by principal component analysis (PCA), factor analysis, and cluster analysis. Through factor analysis, 8 factors representing 3-D fluorescence spectrum data were extracted, and the data after dimension reduction were analyzed by clustering. The results showed that the cumulative contribution rate of the first two principal components in PCA was 95.15%, which could reduce the dimension of spectral data well, but the classification threshold was not easy to be determined. And by selecting 2.5 as a threshold distance, these milk beverages could be divided into formulated milk beverages, fermented milk beverages and lactobacillus beverages and the classified accuracy can reach above 83%. This study verified the feasibility of 3-D fluorescence spectrum binding factor analysis for classification of milk beverages.
In order to prove the effectiveness of 3-D fluorescence spectroscopy in the rapid classification of milk beverages on the market, the 3-D fluorescence spectra of 12 different brands of milk beverages which were brought from the market were collected and the spectral data were pretreated. The spectral data after pretreatment were classified by principal component analysis (PCA), factor analysis, and cluster analysis. Through factor analysis, 8 factors representing 3-D fluorescence spectrum data were extracted, and the data after dimension reduction were analyzed by clustering. The results showed that the cumulative contribution rate of the first two principal components in PCA was 95.15%, which could reduce the dimension of spectral data well, but the classification threshold was not easy to be determined. And by selecting 2.5 as a threshold distance, these milk beverages could be divided into formulated milk beverages, fermented milk beverages and lactobacillus beverages and the classified accuracy can reach above 83%. This study verified the feasibility of 3-D fluorescence spectrum binding factor analysis for classification of milk beverages.
2021, 45(3): 307-312.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.007
Abstract:
To study the relationship between the region range and the parameters of hollow beam in the non-Kolmogorov turbulence propagation path and the beam expansion in different regions, the expressions for the mean-squared width, Rayleigh range, and turbulence distance of hollow beams propagating through non-Kolmogorov turbulence were given by using the extended Huygens-Fresnel principle, and the propagation path was divided into three regions by using the turbulence distance for numerical analysis. The results show that the length of region Ⅰ and region Ⅱ and the starting point of region Ⅲ decrease first and then increase with the increasing of the turbulence generalized exponent parameter α (There is a minimal value, when α=3.11), and increase with the increasing of obscure ratio η and beam orders M(and N). When the value of M(and N)is small(M(and N) < 3), the effect of turbulence on beam spread in Rayleigh range can not be ignored. The larger M(and N)and η is, the easier it is to ignore the effect of turbulence on beam spread in Rayleigh range. In the transmission path, the beam enters area Ⅰ, area Ⅱ and area Ⅲ in turn, and then expands more and more violently. With the increasing of M(and N)and η, the length of region Ⅱ and the starting point of region Ⅲ increase more significantly than the length of region Ⅰ. The results provide a reference for the application of hollow beam propagation in turbulence.
To study the relationship between the region range and the parameters of hollow beam in the non-Kolmogorov turbulence propagation path and the beam expansion in different regions, the expressions for the mean-squared width, Rayleigh range, and turbulence distance of hollow beams propagating through non-Kolmogorov turbulence were given by using the extended Huygens-Fresnel principle, and the propagation path was divided into three regions by using the turbulence distance for numerical analysis. The results show that the length of region Ⅰ and region Ⅱ and the starting point of region Ⅲ decrease first and then increase with the increasing of the turbulence generalized exponent parameter α (There is a minimal value, when α=3.11), and increase with the increasing of obscure ratio η and beam orders M(and N). When the value of M(and N)is small(M(and N) < 3), the effect of turbulence on beam spread in Rayleigh range can not be ignored. The larger M(and N)and η is, the easier it is to ignore the effect of turbulence on beam spread in Rayleigh range. In the transmission path, the beam enters area Ⅰ, area Ⅱ and area Ⅲ in turn, and then expands more and more violently. With the increasing of M(and N)and η, the length of region Ⅱ and the starting point of region Ⅲ increase more significantly than the length of region Ⅰ. The results provide a reference for the application of hollow beam propagation in turbulence.
2021, 45(3): 313-317.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.008
Abstract:
In order to discuss the essence of 1-D photonic crystal band gap, the reflectivity of 1-D photonic crystal consisting of two elements was analyzed, and the expression of the real part of the equivalent refractive index was derived by using the transmission characteristic matrix method. Taking the 1-D photonic crystal composed of magnesium fluoride (MgF2) and zinc sulfide (ZnS) as an example, the analytical numerical calculations of the reflectivity and the real part of the equivalent refractive index were done and the corresponding curves were drawn. It was the conclusion that, wavelength range with reflectivity of 1.0 is the same as that with real part of equivalent refractive index of zero. For the light waves in the band gap, the real part of the equivalent refractive index of 1-D photonic crystal is equal to or close to zero, namely, 1-D photonic crystal is virtual equivalent index material in the extent of band gap. In other words, the optical essence of photonic crystal band gap is that photonic crystal becomes virtual equivalent index material. This study is helpful for the study of 1-D photonic crystal with multi periods consisting of two elements.
In order to discuss the essence of 1-D photonic crystal band gap, the reflectivity of 1-D photonic crystal consisting of two elements was analyzed, and the expression of the real part of the equivalent refractive index was derived by using the transmission characteristic matrix method. Taking the 1-D photonic crystal composed of magnesium fluoride (MgF2) and zinc sulfide (ZnS) as an example, the analytical numerical calculations of the reflectivity and the real part of the equivalent refractive index were done and the corresponding curves were drawn. It was the conclusion that, wavelength range with reflectivity of 1.0 is the same as that with real part of equivalent refractive index of zero. For the light waves in the band gap, the real part of the equivalent refractive index of 1-D photonic crystal is equal to or close to zero, namely, 1-D photonic crystal is virtual equivalent index material in the extent of band gap. In other words, the optical essence of photonic crystal band gap is that photonic crystal becomes virtual equivalent index material. This study is helpful for the study of 1-D photonic crystal with multi periods consisting of two elements.
2021, 45(3): 318-321.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.009
Abstract:
In order to quickly and accurately test and identify the residual paper ashes on the scene of the case, 32 paper ashes from different sources and uses were determined by X-ray fluorescence spectrometry combined with system clustering and principal component analysis of multivariate statistics. Theoretical analysis and experimental verification were then carried out. The results show that the samples can be distinguished accurately according to the types and contents of the elements in the samples. At the same time, 32 samples are divided into five categories, and the classification results of the two methods are basically the same. The cumulative variance contribution rate of PC2 is as high as 99.86%. This research method does not destroy the sample, has good reproducibility, and the results are scientific and ideal, which provides a theoretical basis for the examination of trace evidence.
In order to quickly and accurately test and identify the residual paper ashes on the scene of the case, 32 paper ashes from different sources and uses were determined by X-ray fluorescence spectrometry combined with system clustering and principal component analysis of multivariate statistics. Theoretical analysis and experimental verification were then carried out. The results show that the samples can be distinguished accurately according to the types and contents of the elements in the samples. At the same time, 32 samples are divided into five categories, and the classification results of the two methods are basically the same. The cumulative variance contribution rate of PC2 is as high as 99.86%. This research method does not destroy the sample, has good reproducibility, and the results are scientific and ideal, which provides a theoretical basis for the examination of trace evidence.
2021, 45(3): 322-325.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.010
Abstract:
In order to obtain accurate parameters of the downhole environment in a large range and effectively suppress the noise, an optical fiber sensing internet of things system based on a new fiber Bragg grating(FBG) package was studied. A sensor module that can test strain and temperature simultaneously was designed. The new FBG package structure was trial-produced. An optical fiber stress monitoring distribution network conforming to the tunnel structure was built. A method based on cross-correlation difference calculation was used to eliminate vibration noise. The experiment continuously monitored the stress and temperature of the underground tunnel. The results show that the FBG at 45° and 60° in the arch can accurately record the stress and temperature change data. It can be seen that the system has higher stability and better adaptability in large-scale downhole environmental parameter monitoring.
In order to obtain accurate parameters of the downhole environment in a large range and effectively suppress the noise, an optical fiber sensing internet of things system based on a new fiber Bragg grating(FBG) package was studied. A sensor module that can test strain and temperature simultaneously was designed. The new FBG package structure was trial-produced. An optical fiber stress monitoring distribution network conforming to the tunnel structure was built. A method based on cross-correlation difference calculation was used to eliminate vibration noise. The experiment continuously monitored the stress and temperature of the underground tunnel. The results show that the FBG at 45° and 60° in the arch can accurately record the stress and temperature change data. It can be seen that the system has higher stability and better adaptability in large-scale downhole environmental parameter monitoring.
2021, 45(3): 326-330.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.011
Abstract:
In order to achieve the purpose of high-precision temperature sensing, a novel dual-core photonic crystal fiber coupled perturbation structure was designed. The finite-difference beam propagation method was used to analyze the sensing characteristics of the structure. The Beampronp module of RSOFT software was used to simulate the characteristics of the sensor. The results show that the refractive index sensitivity can reach 7000nm/RUI under the condition of dual core coupling (RUI is the refractive index unit), the coupling spacing sensitivity can reach 2. When the liquid is filled with ethanol, the sensing structure can realize the detection in the temperature range of 278K~338K, and the sensitivity in this range can be up to 4nm/K. The sensor has the characteristics of high linearity and simple process, and the structure is helpful and meaningful to the research of other related sensors.
In order to achieve the purpose of high-precision temperature sensing, a novel dual-core photonic crystal fiber coupled perturbation structure was designed. The finite-difference beam propagation method was used to analyze the sensing characteristics of the structure. The Beampronp module of RSOFT software was used to simulate the characteristics of the sensor. The results show that the refractive index sensitivity can reach 7000nm/RUI under the condition of dual core coupling (RUI is the refractive index unit), the coupling spacing sensitivity can reach 2. When the liquid is filled with ethanol, the sensing structure can realize the detection in the temperature range of 278K~338K, and the sensitivity in this range can be up to 4nm/K. The sensor has the characteristics of high linearity and simple process, and the structure is helpful and meaningful to the research of other related sensors.
2021, 45(3): 331-335.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.012
Abstract:
Using laser-induced breakdown spectroscopy(LIBS) combined with internal standard method to achieve the aim of analyzing the information of uranium concentration in samples fast and quantitatively, the 300nm~800nm spectra of 7ns, 20mJ nanosecond laser pulse induced graphite sheet coated with uranyl nitrate were detected by echelle spectrometer and ICCD, quantitative analysis of uranium samples coated with different concentrations was done. Theoretical analysis and experimental verifications were made to obtain the spectra data of UⅡ 409.01nm, UⅡ 367.01nm, CⅠ 373.72nm, CⅡ 383.57nm and CⅢ 378.94nm. The results show that there is a good linear relationship between normalized uranium intensity and uranium concentration when the sample concentration is lower than 5.0×10-3mol/m2(surface density was studied in this paper), the combination of LIBS and internal standard method could realize the rapid quantitative analysis of uranium concentration in the samples, this study provides reference for the rapid detection and analysis of trace uranium element in nuclear contamination and uranium ore.
Using laser-induced breakdown spectroscopy(LIBS) combined with internal standard method to achieve the aim of analyzing the information of uranium concentration in samples fast and quantitatively, the 300nm~800nm spectra of 7ns, 20mJ nanosecond laser pulse induced graphite sheet coated with uranyl nitrate were detected by echelle spectrometer and ICCD, quantitative analysis of uranium samples coated with different concentrations was done. Theoretical analysis and experimental verifications were made to obtain the spectra data of UⅡ 409.01nm, UⅡ 367.01nm, CⅠ 373.72nm, CⅡ 383.57nm and CⅢ 378.94nm. The results show that there is a good linear relationship between normalized uranium intensity and uranium concentration when the sample concentration is lower than 5.0×10-3mol/m2(surface density was studied in this paper), the combination of LIBS and internal standard method could realize the rapid quantitative analysis of uranium concentration in the samples, this study provides reference for the rapid detection and analysis of trace uranium element in nuclear contamination and uranium ore.
2021, 45(3): 336-343.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.013
Abstract:
In order to study the effect of laser modulation parameters on the peak, signal-to-noise ratio, peak width, symmetry, and signal integrity of second harmonic signals, the analysis based on the hardware system and the Simulink analogue model were verified that the theoretical simulation results were consistent with the signal variation trend of the hardware system, and at the same time the optimal modulation parameters of the CO2 detection system were determined. Through the experimental system, the absorption spectra of different volume fraction of CO2 at 1432.04nm were measured, the inversion model of the signal intensity at the main absorption peak and CO2 volume fraction was established, and the system performance and measurement accuracy were analyzed. The results show that the linear fitting coefficient R2 is 0.9998, the maximum relative error of gas volume fraction inversion is 0.7333%, and the detection limit of the system is 0.0074%. The ideal second harmonic signal can be obtained through the optimal selection of modulation parameters, so as to achieve accurate inversion of the gas volume fraction to be measured. The study provides an important reference for the optimization of modulation parameters in the detection system and provides guidance for the improvement of the measurement accuracy of the system.
In order to study the effect of laser modulation parameters on the peak, signal-to-noise ratio, peak width, symmetry, and signal integrity of second harmonic signals, the analysis based on the hardware system and the Simulink analogue model were verified that the theoretical simulation results were consistent with the signal variation trend of the hardware system, and at the same time the optimal modulation parameters of the CO2 detection system were determined. Through the experimental system, the absorption spectra of different volume fraction of CO2 at 1432.04nm were measured, the inversion model of the signal intensity at the main absorption peak and CO2 volume fraction was established, and the system performance and measurement accuracy were analyzed. The results show that the linear fitting coefficient R2 is 0.9998, the maximum relative error of gas volume fraction inversion is 0.7333%, and the detection limit of the system is 0.0074%. The ideal second harmonic signal can be obtained through the optimal selection of modulation parameters, so as to achieve accurate inversion of the gas volume fraction to be measured. The study provides an important reference for the optimization of modulation parameters in the detection system and provides guidance for the improvement of the measurement accuracy of the system.
2021, 45(3): 344-349.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.014
Abstract:
In order to identify cement road surface with different roughness by laser scattering characteristic, a road surface roughness measurement system was designed. The height distribution of cement road surface was measured by micrometer, and the root mean square of height and relevant length were calculated. According to the above parameters, the random rough surface was generated by power spectral frequency domain filtering to simulate cement road surface, and the rough surface was dispersed into a large number of surface elements by tangential plane approximation. The local field was calculated by Fresnel formula, and the Monte Carlo method was used to obtain the statistical mean values of bidirectional and the back scattered light intensity on rough surface under different polarized light incident conditions. Based on the virtual instrument technology, the high precision automatic laser scattering measurement was carried out, and then the theoretical model was verified according to the experimental data. The results show that the scattered light intensity of bidirectional scattered cement road surface with small roughness has a peak value of 90lx near the scattering angle of 40° in the mirror direction, and decreases gradually on both sides of the mirror direction. The optical characteristics of cement road surface with large roughness are approximate to Lambert body, and the scattered light intensity has little change in each scattering angle direction. The back scattered light intensity peak of small roughness cement road surface is 103lx when the back scattering is perpendicular to the incidence, which decreases gradually with the increase of scattering angle. The large roughness cement road surface has Lambert scattering characteristics. The above conclusions could provide reference for road information perception of autonomous driving schemes.
In order to identify cement road surface with different roughness by laser scattering characteristic, a road surface roughness measurement system was designed. The height distribution of cement road surface was measured by micrometer, and the root mean square of height and relevant length were calculated. According to the above parameters, the random rough surface was generated by power spectral frequency domain filtering to simulate cement road surface, and the rough surface was dispersed into a large number of surface elements by tangential plane approximation. The local field was calculated by Fresnel formula, and the Monte Carlo method was used to obtain the statistical mean values of bidirectional and the back scattered light intensity on rough surface under different polarized light incident conditions. Based on the virtual instrument technology, the high precision automatic laser scattering measurement was carried out, and then the theoretical model was verified according to the experimental data. The results show that the scattered light intensity of bidirectional scattered cement road surface with small roughness has a peak value of 90lx near the scattering angle of 40° in the mirror direction, and decreases gradually on both sides of the mirror direction. The optical characteristics of cement road surface with large roughness are approximate to Lambert body, and the scattered light intensity has little change in each scattering angle direction. The back scattered light intensity peak of small roughness cement road surface is 103lx when the back scattering is perpendicular to the incidence, which decreases gradually with the increase of scattering angle. The large roughness cement road surface has Lambert scattering characteristics. The above conclusions could provide reference for road information perception of autonomous driving schemes.
2021, 45(3): 350-356.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.015
Abstract:
In order to solve the problem that the traditional stripe center extraction algorithm is sensitive to material and noise, an adaptive structured light stripe center extraction algorithm was used to extract the fringe sub-pixel coordinates. The algorithm first preprocesses the image, extracts the region of interest of the stripe image by using the image mask operation, eliminates noise interference through the adaptive convolution template, and obtains the pixel sets of the stripe area cross-sectional width and center coordinates. Secondly, according to the pixel set of the central coordinates, the initial coordinate value of the stripe center was calculated by the quadratic weighted gray centroid method, which will be used as the seed point for regional growth operation, then combined with principal component analysis to decompose the characteristic matrix, and finally the sub-pixel coordinate point of the center of the linear structured light was obtained. The results show that the center sub-pixel coordinates of the structured light stripe can be effectively and quickly obtained by this algorithm. Compared with the gray-scale barycenter method, the extraction results of the algorithm in this paper are less volatile and have a relatively small standard error. The extraction speed is nearly 4 times higher than that of the Steger method based on Hessian matrix, which meets the real-time requirements of the industrial measurement system. The proposed algorithm in this paper has high extraction accuracy, good robustness, low computational complexity, and high real-time performance, which provides nice accuracy guarantee for the subsequent 3-D vision measurement system.
In order to solve the problem that the traditional stripe center extraction algorithm is sensitive to material and noise, an adaptive structured light stripe center extraction algorithm was used to extract the fringe sub-pixel coordinates. The algorithm first preprocesses the image, extracts the region of interest of the stripe image by using the image mask operation, eliminates noise interference through the adaptive convolution template, and obtains the pixel sets of the stripe area cross-sectional width and center coordinates. Secondly, according to the pixel set of the central coordinates, the initial coordinate value of the stripe center was calculated by the quadratic weighted gray centroid method, which will be used as the seed point for regional growth operation, then combined with principal component analysis to decompose the characteristic matrix, and finally the sub-pixel coordinate point of the center of the linear structured light was obtained. The results show that the center sub-pixel coordinates of the structured light stripe can be effectively and quickly obtained by this algorithm. Compared with the gray-scale barycenter method, the extraction results of the algorithm in this paper are less volatile and have a relatively small standard error. The extraction speed is nearly 4 times higher than that of the Steger method based on Hessian matrix, which meets the real-time requirements of the industrial measurement system. The proposed algorithm in this paper has high extraction accuracy, good robustness, low computational complexity, and high real-time performance, which provides nice accuracy guarantee for the subsequent 3-D vision measurement system.
2021, 45(3): 357-361.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.016
Abstract:
In order to obtain white light-emitting diode(LED) beams with high uniformity, symmetry and some special shape and intensity distribution to meet certain specific needs, based on the characteristics of white LED light source as lambert light source, the LED beam was shaped by using free-form curved lens method. Two different shaping structures were respectively adopted: Single free-form curved lens and total internal reflection (TIR) lens and microlens array. The processing technology and theoretical analysis were carried out followed by further experiments. The circular uniform spot and rectangular uniform spot were obtained by the experiment. The total light utilization rate of the circular uniform spot is as high as 96%, and the effective light utilization rate of the effective area is 88.4%. The total utilization rate of the rectangular uniform spot is 91%, the effective light utilization rate of the effective area is 78.7%, and the uniformity of the beam is above 60%, respectively. The results show that the method of free surface lens is very effective in shaping the white LED beam. This method provides important guidance for the further wide application of white LED light source.
In order to obtain white light-emitting diode(LED) beams with high uniformity, symmetry and some special shape and intensity distribution to meet certain specific needs, based on the characteristics of white LED light source as lambert light source, the LED beam was shaped by using free-form curved lens method. Two different shaping structures were respectively adopted: Single free-form curved lens and total internal reflection (TIR) lens and microlens array. The processing technology and theoretical analysis were carried out followed by further experiments. The circular uniform spot and rectangular uniform spot were obtained by the experiment. The total light utilization rate of the circular uniform spot is as high as 96%, and the effective light utilization rate of the effective area is 88.4%. The total utilization rate of the rectangular uniform spot is 91%, the effective light utilization rate of the effective area is 78.7%, and the uniformity of the beam is above 60%, respectively. The results show that the method of free surface lens is very effective in shaping the white LED beam. This method provides important guidance for the further wide application of white LED light source.
2021, 45(3): 362-366.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.017
Abstract:
In order to solve the problem of low accuracy of power line extraction of transmission lines with complex terrain and trending, and uneven point cloud density, an efficient method for automatic extraction and reconstruction of power lines was proposed. Firstly, through the space segmentation and point cloud density analysis method, the improved elevation filtering algorithm was used to achieve the rough extraction of power lines; the filtering algorithm based on the average value of the inclination angle between the point clouds was used to extract the power lines precisely; the statistical filtering algorithm was used to complete the extraction of the whole point cloud of the power lines. Then the power lines were separated by the random sample consensus(RANSAC)-based power line striping extraction algorithm, and finally the power line reconstruction was completed by using a model combining straight lines and paraboloids. The results show that the total power line extraction accuracy of this method is 99.342%, and the minimum reconstruction accuracy of a single power line is 0.042m, which is robust to terrain, line direction, point cloud density and other factors. This research provides a reference for power line extraction and 3-D reconstruction of large-scale transmission lines in complex scenarios.
In order to solve the problem of low accuracy of power line extraction of transmission lines with complex terrain and trending, and uneven point cloud density, an efficient method for automatic extraction and reconstruction of power lines was proposed. Firstly, through the space segmentation and point cloud density analysis method, the improved elevation filtering algorithm was used to achieve the rough extraction of power lines; the filtering algorithm based on the average value of the inclination angle between the point clouds was used to extract the power lines precisely; the statistical filtering algorithm was used to complete the extraction of the whole point cloud of the power lines. Then the power lines were separated by the random sample consensus(RANSAC)-based power line striping extraction algorithm, and finally the power line reconstruction was completed by using a model combining straight lines and paraboloids. The results show that the total power line extraction accuracy of this method is 99.342%, and the minimum reconstruction accuracy of a single power line is 0.042m, which is robust to terrain, line direction, point cloud density and other factors. This research provides a reference for power line extraction and 3-D reconstruction of large-scale transmission lines in complex scenarios.
2021, 45(3): 367-372.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.018
Abstract:
For the problem that the traditional algorithm for the extraction of power tower is sensitive to ground fluctuations, and some points of ground are hard to exclude from the extraction result, a lightweight neural network was proposed with a direct input of the original point cloud data to implement the extraction of power tower. By dividing the original point cloud data into a number of voxel grids of equal size, the feature learning network and a convolutional neural network were used to extract the spatial and structural information in the voxel grid. Then the characteristics of relative height and point density which can be found in traditional algorithms were added to the feature to determine whether the voxel is a type of tower point cloud or not. Finally, clustering was used to eliminate isolated voxels to improve the accuracy and obtain the laser point cloud data of power towers. The experimental results show that the algorithm has an accuracy of about 95% for different terrains and interferences in the extraction of power towers. The algorithm can effectively extract the point cloud of power towers, and has a certain improvement in stability and accuracy compared with the method using grid or other methods, and also has a good anti-interference effect on other factors such as the existence of tall trees or vertical occlusion.
For the problem that the traditional algorithm for the extraction of power tower is sensitive to ground fluctuations, and some points of ground are hard to exclude from the extraction result, a lightweight neural network was proposed with a direct input of the original point cloud data to implement the extraction of power tower. By dividing the original point cloud data into a number of voxel grids of equal size, the feature learning network and a convolutional neural network were used to extract the spatial and structural information in the voxel grid. Then the characteristics of relative height and point density which can be found in traditional algorithms were added to the feature to determine whether the voxel is a type of tower point cloud or not. Finally, clustering was used to eliminate isolated voxels to improve the accuracy and obtain the laser point cloud data of power towers. The experimental results show that the algorithm has an accuracy of about 95% for different terrains and interferences in the extraction of power towers. The algorithm can effectively extract the point cloud of power towers, and has a certain improvement in stability and accuracy compared with the method using grid or other methods, and also has a good anti-interference effect on other factors such as the existence of tall trees or vertical occlusion.
2021, 45(3): 373-377.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.019
Abstract:
In order to improve the efficiency of leather defect detection, a leather defect detection algorithm based on improved bilateral filtering was proposed. Through constructing machine vision detection platform, different kinds of defects in the finished leather sample image were obtained, sample images were processed with improved bilateral filtering algorithms to make the leather background texture fuzzy and keep its defect edge profile. Then, various kinds of defects of four characteristic parameters were calculated as the input vector, and the automatic identification of least squares support vector machine (SVM) mode was constructed. The results showed that compared with cluster analysis algorithm, threshold segmentation algorithm and wavelet analysis algorithm, the algorithm adopted in this paper could detect various defects of leather more efficiently. The average detection time was 0.83s, and the accuracy of defect detection was 93.3%. The results provide an effective way for real-time leather detection.
In order to improve the efficiency of leather defect detection, a leather defect detection algorithm based on improved bilateral filtering was proposed. Through constructing machine vision detection platform, different kinds of defects in the finished leather sample image were obtained, sample images were processed with improved bilateral filtering algorithms to make the leather background texture fuzzy and keep its defect edge profile. Then, various kinds of defects of four characteristic parameters were calculated as the input vector, and the automatic identification of least squares support vector machine (SVM) mode was constructed. The results showed that compared with cluster analysis algorithm, threshold segmentation algorithm and wavelet analysis algorithm, the algorithm adopted in this paper could detect various defects of leather more efficiently. The average detection time was 0.83s, and the accuracy of defect detection was 93.3%. The results provide an effective way for real-time leather detection.
2021, 45(3): 378-385.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.020
Abstract:
In order to avoid the early convergence of the original whale optimization algorithm and easily fall into the local optimum, firstly, the cat mapping generation chaotic sequence combined with the reverse solution method was used to replace the randomly generated initial population in the process of initializing the original whale optimization algorithm. Secondly, the crazy operator and the golden sine algorithm were used in the position updating mechanism. Finally, the improved whale optimization algorithm was used to find the maximum entropy of 2-D image to determine the optimal threshold of image segmentation. The simulation results of 10 classical benchmark functions show that the original whale optimization algorithm can increase the initial population diversity and search ergodicity, and improve the global search ability and get rid of the local optimum. The results show that the optimal value of the function is 0, 0.00030, -3.32.The improved algorithm can achieve accurate segmentation of target image and less time consuming. This study provides a reference for the application of group intelligence algorithms to image segmentation.
In order to avoid the early convergence of the original whale optimization algorithm and easily fall into the local optimum, firstly, the cat mapping generation chaotic sequence combined with the reverse solution method was used to replace the randomly generated initial population in the process of initializing the original whale optimization algorithm. Secondly, the crazy operator and the golden sine algorithm were used in the position updating mechanism. Finally, the improved whale optimization algorithm was used to find the maximum entropy of 2-D image to determine the optimal threshold of image segmentation. The simulation results of 10 classical benchmark functions show that the original whale optimization algorithm can increase the initial population diversity and search ergodicity, and improve the global search ability and get rid of the local optimum. The results show that the optimal value of the function is 0, 0.00030, -3.32.The improved algorithm can achieve accurate segmentation of target image and less time consuming. This study provides a reference for the application of group intelligence algorithms to image segmentation.
2021, 45(3): 386-389.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.021
Abstract:
In order to know micron focal switch of polychromatic TEM22 mode Hermite-Gaussian (HG) beams passing through an apertured dispersion lens system, numerical calculation examples were used to study the beam's intensity distributions. The data of the axial intensity distributions were achieved. It is found that variation of the bandwidth results in change of two maximal intensities of TEM22 mode (HG) beams and thus position of the principle maximal intensity shifts rapidly. When relative bandwidth γ is 0.231 and Fresnel number Fw is 100, the position varies 2.5μm and the phenomenon of micron focal switch presents. The bandwidth and Fresnel number are important factors that induce the micron focal switch. A narrow bandwidth is enough to induce the focal switch of TEM22 mode (HG) beams in the system with large Fresnel number whereas a broad bandwidth is required in the system with small Fresnel number. Results in this paper help the design and manufacture of micro and nano optical devices in optical communication technique.
In order to know micron focal switch of polychromatic TEM22 mode Hermite-Gaussian (HG) beams passing through an apertured dispersion lens system, numerical calculation examples were used to study the beam's intensity distributions. The data of the axial intensity distributions were achieved. It is found that variation of the bandwidth results in change of two maximal intensities of TEM22 mode (HG) beams and thus position of the principle maximal intensity shifts rapidly. When relative bandwidth γ is 0.231 and Fresnel number Fw is 100, the position varies 2.5μm and the phenomenon of micron focal switch presents. The bandwidth and Fresnel number are important factors that induce the micron focal switch. A narrow bandwidth is enough to induce the focal switch of TEM22 mode (HG) beams in the system with large Fresnel number whereas a broad bandwidth is required in the system with small Fresnel number. Results in this paper help the design and manufacture of micro and nano optical devices in optical communication technique.
2021, 45(3): 390-395.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.022
Abstract:
To study the tight focusing characteristics of azimuthally polarized Airy beams, the Richards-Wolf vector diffraction theory was adopt. The influences of the exponential attenuation factor, the radius of the main ring, and the proportional factor of the airy beams on the incident field patterns were respectively studied. The focal field distributions of the azimuthally polarized airy beams and the azimuthally polarized airy beams modulated by a vortex phase filter were studied, from which a sub-wavelength azimuthally polarized doughnut field and a transversally polarized bright field were garnered. The experimental results are basically consistent with the theoretical simulations. Furthermore, the multi-ring vortex phase filter was designed to modulate the azimuthally polarized airy beams according to the particle swarm algorithm, and an ultra-long and non-diffracting super-resolution transversally polarized light needle was produced on tight focusing. It turns out that the full width at half maximum and the depth of focus of the light needle are 0.395λ and 37.432λ respectively, which corresponds to an aspect ratio of 94.788. The polarization patterns of the focal fields are analyzed by calculating the Stokes polarization parameters. It is found that the focal field alternates between the radial polarization and azimuthal polarization and the singularity at the center of the beam disappears, which testify that the transversally polarized bright field distribution is realized. The research holds broad applications in high-density magneto-optical storage, super-resolution optical imaging, nanolithography and particle manipulation.
To study the tight focusing characteristics of azimuthally polarized Airy beams, the Richards-Wolf vector diffraction theory was adopt. The influences of the exponential attenuation factor, the radius of the main ring, and the proportional factor of the airy beams on the incident field patterns were respectively studied. The focal field distributions of the azimuthally polarized airy beams and the azimuthally polarized airy beams modulated by a vortex phase filter were studied, from which a sub-wavelength azimuthally polarized doughnut field and a transversally polarized bright field were garnered. The experimental results are basically consistent with the theoretical simulations. Furthermore, the multi-ring vortex phase filter was designed to modulate the azimuthally polarized airy beams according to the particle swarm algorithm, and an ultra-long and non-diffracting super-resolution transversally polarized light needle was produced on tight focusing. It turns out that the full width at half maximum and the depth of focus of the light needle are 0.395λ and 37.432λ respectively, which corresponds to an aspect ratio of 94.788. The polarization patterns of the focal fields are analyzed by calculating the Stokes polarization parameters. It is found that the focal field alternates between the radial polarization and azimuthal polarization and the singularity at the center of the beam disappears, which testify that the transversally polarized bright field distribution is realized. The research holds broad applications in high-density magneto-optical storage, super-resolution optical imaging, nanolithography and particle manipulation.
2021, 45(3): 396-404.
doi: 10.7510/jgjs.issn.1001-3806.2021.03.023
Abstract:
In order to effectively solve the problem of insufficient training data base on studying the characteristics of infrared dim dots, an improved algorithm for tracking infrared dim dots build upon meta-learning was adopted. Firstly, the pre-training tracking model was used to apply the meta-learning to the convolutional neural network. The general representation of the target were obtained through the offline training on the static infrared image data set, accordingly to obtain the specific representation of the infrared point-like target by using the initial frame target position.The target motion model was predicted by kalman filter algorithm and the optimal search area was obtained. In addition, in order to solve the problem of target loss caused by occlusion, the re-detection mechanism was studied. Theoretical analysis and experimental verification were carried out, with tracking accuracy up to 90%. Concluded that this approach is capable of tracking the infrared dim dots more accurately than other tracking algorithms in the same data set. This research provides a reference for the application of machine learning algorithms in the tracking of infrared dim and small targets.
In order to effectively solve the problem of insufficient training data base on studying the characteristics of infrared dim dots, an improved algorithm for tracking infrared dim dots build upon meta-learning was adopted. Firstly, the pre-training tracking model was used to apply the meta-learning to the convolutional neural network. The general representation of the target were obtained through the offline training on the static infrared image data set, accordingly to obtain the specific representation of the infrared point-like target by using the initial frame target position.The target motion model was predicted by kalman filter algorithm and the optimal search area was obtained. In addition, in order to solve the problem of target loss caused by occlusion, the re-detection mechanism was studied. Theoretical analysis and experimental verification were carried out, with tracking accuracy up to 90%. Concluded that this approach is capable of tracking the infrared dim dots more accurately than other tracking algorithms in the same data set. This research provides a reference for the application of machine learning algorithms in the tracking of infrared dim and small targets.
