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2024, 48(5): 613-619.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.001
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Abstract:
In order to solve the polarization mismatch between echo and local oscillator caused by the atmospheric depolarization effect leading to a decrease in heterodyne efficiency of coherent wind light detection and ranging (LiDAR), the influence of echo polarization on signal-to-noise ratio and ranges and radial wind speed error was simulated using mathematical modeling method, based on the system composition and working principle of coherent Doppler wind LiDAR. By proposing a polarization state correction approach and using Jones matrix, a model was built to discuss the correction accuracy. According to the comparative test of radial wind speed, the influence of different echo polarization on radial wind speed accuracy was verified. The results show that for the same system and weather, if the echo is elliptical polarization, the maximum range will decrease by 46.7% and the radial wind speed accuracy will decrease by 63% compared to the circular polarization. This study provides theoretical support for the optimization of echo receiving module of coherent Doppler wind LiDAR.
In order to solve the polarization mismatch between echo and local oscillator caused by the atmospheric depolarization effect leading to a decrease in heterodyne efficiency of coherent wind light detection and ranging (LiDAR), the influence of echo polarization on signal-to-noise ratio and ranges and radial wind speed error was simulated using mathematical modeling method, based on the system composition and working principle of coherent Doppler wind LiDAR. By proposing a polarization state correction approach and using Jones matrix, a model was built to discuss the correction accuracy. According to the comparative test of radial wind speed, the influence of different echo polarization on radial wind speed accuracy was verified. The results show that for the same system and weather, if the echo is elliptical polarization, the maximum range will decrease by 46.7% and the radial wind speed accuracy will decrease by 63% compared to the circular polarization. This study provides theoretical support for the optimization of echo receiving module of coherent Doppler wind LiDAR.
2024, 48(5): 620-627.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.002
Abstract:
Laser cleaning technology is a new cleaning technology that utilizes the interaction between laser and matter, with the advantages of simple operation, high accuracy, low damage, low emission, and environmental protection. It has been widely studied and investigated by researchers, and many important research results has been proposed, making it very promising for application. Firstly, a brief overview of the development, classification (dry laser cleaning, wet laser cleaning, and laser-induced plasma cleaning), and mechanisms of the laser cleaning technology was presented. A comparative analysis of different cleaning methods was conducted, including the respective strengths and weaknesses, which is helpful for researchers to understand and select this technology for actual situation. In addition, the research progress of the laser cleaning technology in equipment maintenance and support was extensively reviewed according to the literature. Among these, paint removal with the laser has practical applications in foreign aircraft equipment maintenance and support. Rust removal with the laser has been reliably validated on the surface of domestic and foreign naval equipment materials, has an exploration into practical applications abroad. Oil contamination and carbon removal with the laser have been subject to exploratory experimental research both domestically and internationally, but there remains a considerable gap before achieving mature applications. Furthermore, the removal of other contaminants from equipment surfaces, including marine biofouling, mold, and damaged functional coatings, are also discussed. Finally, the research and development of laser cleaning technology are summarized, and prospected.
Laser cleaning technology is a new cleaning technology that utilizes the interaction between laser and matter, with the advantages of simple operation, high accuracy, low damage, low emission, and environmental protection. It has been widely studied and investigated by researchers, and many important research results has been proposed, making it very promising for application. Firstly, a brief overview of the development, classification (dry laser cleaning, wet laser cleaning, and laser-induced plasma cleaning), and mechanisms of the laser cleaning technology was presented. A comparative analysis of different cleaning methods was conducted, including the respective strengths and weaknesses, which is helpful for researchers to understand and select this technology for actual situation. In addition, the research progress of the laser cleaning technology in equipment maintenance and support was extensively reviewed according to the literature. Among these, paint removal with the laser has practical applications in foreign aircraft equipment maintenance and support. Rust removal with the laser has been reliably validated on the surface of domestic and foreign naval equipment materials, has an exploration into practical applications abroad. Oil contamination and carbon removal with the laser have been subject to exploratory experimental research both domestically and internationally, but there remains a considerable gap before achieving mature applications. Furthermore, the removal of other contaminants from equipment surfaces, including marine biofouling, mold, and damaged functional coatings, are also discussed. Finally, the research and development of laser cleaning technology are summarized, and prospected.
2024, 48(5): 628-636.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.003
Abstract:
In order to accurately extract the individual planes from various types of building roof point clouds, metric learning was used to learn separate high-dimensional depth features for the points on each plane, and each plane was considered as a separate instance. Then the extracted high-dimensional depth features were used to perform preliminary clustering of the plane points. The unclustered points were assigned to each plane by a combined metric of simple Euclidean distance and feature space distance. The proposed method was trained and tested on a synthetic dataset and the publicly available airborne point cloud building roof dataset RoofN3D, respectively. The results show that on the synthetic dataset, the accuracy, recall, and F1 scores of the extracted building planes are 0.990, 0.998, and 0.994, respectively. On the airborne point cloud dataset RoofN3D, the accuracy, recall, and F1 scores of the extracted building planes are 0.945, 0.971, and 0.957, respectively. The proposed method not only can accurately and effectively extract different building roof planes, but also the extracted plane edges are very accurate. In addition, the method can also accurately distinguish between the planar and non-planar contents of building roofs, which provides important help for further 3-D modeling of buildings.
In order to accurately extract the individual planes from various types of building roof point clouds, metric learning was used to learn separate high-dimensional depth features for the points on each plane, and each plane was considered as a separate instance. Then the extracted high-dimensional depth features were used to perform preliminary clustering of the plane points. The unclustered points were assigned to each plane by a combined metric of simple Euclidean distance and feature space distance. The proposed method was trained and tested on a synthetic dataset and the publicly available airborne point cloud building roof dataset RoofN3D, respectively. The results show that on the synthetic dataset, the accuracy, recall, and F1 scores of the extracted building planes are 0.990, 0.998, and 0.994, respectively. On the airborne point cloud dataset RoofN3D, the accuracy, recall, and F1 scores of the extracted building planes are 0.945, 0.971, and 0.957, respectively. The proposed method not only can accurately and effectively extract different building roof planes, but also the extracted plane edges are very accurate. In addition, the method can also accurately distinguish between the planar and non-planar contents of building roofs, which provides important help for further 3-D modeling of buildings.
2024, 48(5): 637-642.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.004
Abstract:
To reduce false alarm rate in foggy conditions for wind turbine blade signals, a method was adopted to accurately extract blades signals by using the raw signal data obtained from laser clearance light detection and ranging(LiDAR)as the primary data source, and incorporating spatiotemporal constraints in signal preprocessing. The laser clearance LiDAR integrated with blade signal extraction method was tested in areas with year-round fog. The experimental results show that blade signal extraction method proposed in this paper has achieved good results, with a false alarm rate of less than 2%, which improves the reliability and environmental adaptability of laser clearance LiDAR ranging data. This study provides a reference for the application of laser clearance LiDAR in wind turbine clearance monitoring.
To reduce false alarm rate in foggy conditions for wind turbine blade signals, a method was adopted to accurately extract blades signals by using the raw signal data obtained from laser clearance light detection and ranging(LiDAR)as the primary data source, and incorporating spatiotemporal constraints in signal preprocessing. The laser clearance LiDAR integrated with blade signal extraction method was tested in areas with year-round fog. The experimental results show that blade signal extraction method proposed in this paper has achieved good results, with a false alarm rate of less than 2%, which improves the reliability and environmental adaptability of laser clearance LiDAR ranging data. This study provides a reference for the application of laser clearance LiDAR in wind turbine clearance monitoring.
2024, 48(5): 643-650.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.005
Abstract:
In order to reveal the wind field structure and cause of the downdraft generated by a mesoscale isolated thunderstorm in the central γ region, a method of combining multi-source data was adopted, with a focus on the analysis of the light detection and ranging (LiDAR). A structural field analysis of a wet downdraft that occurred at the entrance end of the runway at Urumqi Airport on 2022-06-25 was carried out, and data that can characterize the development process of the downdraft were obtained. The results showe that under the background of northwest airflow convergence and cold air accumulation, the mid-low level shear line and the ground mesoscale convergence line were the triggering mechanisms for this process. Two Doppler radar volume scans present the process of the initial development and mature stages of the isolated thunderstorm, with the the process of moist downbursts caused by echo center descending and strong echoes reaching the ground. Strong unstable energy was the key factor causing this severe weather process. The unstable energy accumulated to its maximum 6 min before the occurrence of heavy precipitation, and then rapidly released, accompanied by short-term intense precipitation and triggered the wet downdraf. The center position and anticyclonic characteristics of the thunderstorm high pressure initiation were observed through the wind LiDAR, the area of strong winds and the outer boundary of outflow were then estimated, the size and intensity changes of the high-pressure area were clarified. It provided clear indications for the timing and intensity of the outbreak of the downdraft, and provided strong support for the analysis of the structure of thunderstorm-induced downdrafts, as well as fine warning for flight safety.
In order to reveal the wind field structure and cause of the downdraft generated by a mesoscale isolated thunderstorm in the central γ region, a method of combining multi-source data was adopted, with a focus on the analysis of the light detection and ranging (LiDAR). A structural field analysis of a wet downdraft that occurred at the entrance end of the runway at Urumqi Airport on 2022-06-25 was carried out, and data that can characterize the development process of the downdraft were obtained. The results showe that under the background of northwest airflow convergence and cold air accumulation, the mid-low level shear line and the ground mesoscale convergence line were the triggering mechanisms for this process. Two Doppler radar volume scans present the process of the initial development and mature stages of the isolated thunderstorm, with the the process of moist downbursts caused by echo center descending and strong echoes reaching the ground. Strong unstable energy was the key factor causing this severe weather process. The unstable energy accumulated to its maximum 6 min before the occurrence of heavy precipitation, and then rapidly released, accompanied by short-term intense precipitation and triggered the wet downdraf. The center position and anticyclonic characteristics of the thunderstorm high pressure initiation were observed through the wind LiDAR, the area of strong winds and the outer boundary of outflow were then estimated, the size and intensity changes of the high-pressure area were clarified. It provided clear indications for the timing and intensity of the outbreak of the downdraft, and provided strong support for the analysis of the structure of thunderstorm-induced downdrafts, as well as fine warning for flight safety.
2024, 48(5): 651-656.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.006
Abstract:
In order to improve the energy of the pulsed laser passing through the hysteroscope, three lens coupling scheme was adopted was adopted to improve the coupling efficiency. The theoretical analysis and experimental validation were carried out. The results show that the coupling efficiency is increased by about 14%. The experimental data, which indicates that the pulsed laser is more powerful than the pulsed laser, is more efficient than the pulsed laser. A better photoacoustic imaging effect is obtained after passing through our proposed coupling module. The study is expected to improve the effect of photoacoustic imaging technology in endometrial application, and will be able to be applied as an auxiliary tool for the detection of endometrial and other diseases in the clinic.
In order to improve the energy of the pulsed laser passing through the hysteroscope, three lens coupling scheme was adopted was adopted to improve the coupling efficiency. The theoretical analysis and experimental validation were carried out. The results show that the coupling efficiency is increased by about 14%. The experimental data, which indicates that the pulsed laser is more powerful than the pulsed laser, is more efficient than the pulsed laser. A better photoacoustic imaging effect is obtained after passing through our proposed coupling module. The study is expected to improve the effect of photoacoustic imaging technology in endometrial application, and will be able to be applied as an auxiliary tool for the detection of endometrial and other diseases in the clinic.
2024, 48(5): 657-664.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.007
Abstract:
In order to solve the problems of peak shift, weak feature spectrum misjudgment, and artificial spectral line recognition in the wavelength calibration process of visible light spectroradiometers, the adaptive threshold method and the differential method were used to detect and recognize the feature spectrum. Meanwhile, the relationship between wavelength and pixel was determined using the method of least squares and Lagrange interpolation. Theoretical analysis and experimental verification were carried out and the optimum wavelength calibration equation was obtained. The results show that the feature spectrum is detected and recognized sequentially based on the intensity of the spectral lines. The optimal equation was obtained by the Lagrange interpolation method based on 404.6565 nm, 435.8335 nm, 546.0750 nm, and 579.0670 nm, with a residual standard deviation of only 3.2747×10-13nm, the wavelength calibration error distribution is within the range of ±0.2 nm. Therefore, this method improves the efficiency of wavelength calibration. It also avoids noise misjudgment and spectral line recognition error and provides reference for wavelength calibration of other spectral instruments.
In order to solve the problems of peak shift, weak feature spectrum misjudgment, and artificial spectral line recognition in the wavelength calibration process of visible light spectroradiometers, the adaptive threshold method and the differential method were used to detect and recognize the feature spectrum. Meanwhile, the relationship between wavelength and pixel was determined using the method of least squares and Lagrange interpolation. Theoretical analysis and experimental verification were carried out and the optimum wavelength calibration equation was obtained. The results show that the feature spectrum is detected and recognized sequentially based on the intensity of the spectral lines. The optimal equation was obtained by the Lagrange interpolation method based on 404.6565 nm, 435.8335 nm, 546.0750 nm, and 579.0670 nm, with a residual standard deviation of only 3.2747×10-13nm, the wavelength calibration error distribution is within the range of ±0.2 nm. Therefore, this method improves the efficiency of wavelength calibration. It also avoids noise misjudgment and spectral line recognition error and provides reference for wavelength calibration of other spectral instruments.
2024, 48(5): 665-670.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.008
Abstract:
A 32×32 Geiger-mode silicon laser focal plane array detector was developed for the long-distance or weak-laser detection of the 3-D imaging system using the wavelength in range of 350 nm~1100 nm. This detector is mainly composed of silicon avalanche photodiode array, readout circuit chips, microlens arrays, semiconductor refrigerators, and pin-grid array shells. The silicon avalanche photodiode focal plane arrays, adopts the structure of pull through N+-Π1-P--Π2-P+ and works at the Geiger mode. The processing of thin photosensitive areas has been achieved through Si wafer back polishing and blind hole etching technology. An active-quenching-mode design was adopted to control the dead time of the circuit unit within 50 ns. An optimized time-to-digital converter circuit scheme with phase shift technology was used to achieve a time resolution within 2 ns while reducing the power consumption of the readout circuit chip. The results show that under the conditions of reverse bias voltage of 14 V and operating temperature of -40 ℃, the detector can achieve an average photon detection efficiency of 20.7% and an average dark counting rate of 0.59 kHz at the target wavelength of 850 nm, with a time resolution of 1 ns and an effective pixel rate better than 97%. This study provides a reference for the development of thin-type back-illuminated silicon-based laser focal plane detectors.
A 32×32 Geiger-mode silicon laser focal plane array detector was developed for the long-distance or weak-laser detection of the 3-D imaging system using the wavelength in range of 350 nm~1100 nm. This detector is mainly composed of silicon avalanche photodiode array, readout circuit chips, microlens arrays, semiconductor refrigerators, and pin-grid array shells. The silicon avalanche photodiode focal plane arrays, adopts the structure of pull through N+-Π1-P--Π2-P+ and works at the Geiger mode. The processing of thin photosensitive areas has been achieved through Si wafer back polishing and blind hole etching technology. An active-quenching-mode design was adopted to control the dead time of the circuit unit within 50 ns. An optimized time-to-digital converter circuit scheme with phase shift technology was used to achieve a time resolution within 2 ns while reducing the power consumption of the readout circuit chip. The results show that under the conditions of reverse bias voltage of 14 V and operating temperature of -40 ℃, the detector can achieve an average photon detection efficiency of 20.7% and an average dark counting rate of 0.59 kHz at the target wavelength of 850 nm, with a time resolution of 1 ns and an effective pixel rate better than 97%. This study provides a reference for the development of thin-type back-illuminated silicon-based laser focal plane detectors.
2024, 48(5): 671-676.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.009
Abstract:
To address the issue of baseline interference in the subsequent processing of spectral signals, a spectral signal region baseline fitting algorithm was proposed in this study. A certain number of smaller data points were extracted from the original spectrum, and an initial baseline was obtained through linear interpolation. In cases where there were overlapping peaks in the spectrum, the selected smaller data points may contain non-baseline outliers. Smoothing iterations were introduced, and a method for baseline determination based on the rate of change of the slope was proposed. This algorithm was compared with different baseline fitting methods on simulated and actual spectra. The results show that, in the process of fitting simulated baselines, a relative standard deviation of 8.25% is obtained with this algorithm, which is the lowest compared to that obtained with other methods. The correlation of the calibration curve based on this algorithm is the highest at 99.85%, and the smallest root mean square error in prediction is 0.5912. The baseline fitting algorithm proposed in this study demonstrates high accuracy and stability in various types of atomic emission spectra and can effectively estimate the continuous background of atomic emission spectra.
To address the issue of baseline interference in the subsequent processing of spectral signals, a spectral signal region baseline fitting algorithm was proposed in this study. A certain number of smaller data points were extracted from the original spectrum, and an initial baseline was obtained through linear interpolation. In cases where there were overlapping peaks in the spectrum, the selected smaller data points may contain non-baseline outliers. Smoothing iterations were introduced, and a method for baseline determination based on the rate of change of the slope was proposed. This algorithm was compared with different baseline fitting methods on simulated and actual spectra. The results show that, in the process of fitting simulated baselines, a relative standard deviation of 8.25% is obtained with this algorithm, which is the lowest compared to that obtained with other methods. The correlation of the calibration curve based on this algorithm is the highest at 99.85%, and the smallest root mean square error in prediction is 0.5912. The baseline fitting algorithm proposed in this study demonstrates high accuracy and stability in various types of atomic emission spectra and can effectively estimate the continuous background of atomic emission spectra.
2024, 48(5): 677-683.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.010
Abstract:
In order to improve the corrosion resistance of 316L stainless steel and prolong its service life in the marine environment, this paper discusses the method and effect of laser cladding technology on the surface of 316L substrate by cladding pure Ni60 coating and WC+Ni60 composite coating. The WC+Ni60 composite coating combines the hardness of WC particles and the toughness of Ni60 matrix, which has better comprehensive performance and is suitable for higher strength protection of the substrate surface. The coatings were retrieved and tested by hardness tester, X-ray diffractometer and electrochemical workstation, respectively. The results show that the average cross-sectional hardness of the WC+Ni60 composite coating is 719 HV, but the fluctuation in each region is large. At the same time, the surface of the cladding layer is more resistant to corrosion than the pure Ni60 coating. The self-corrosion potential is increased by 0.12 V, and the self-corrosion current density is reduced by 2.49 × 10-6 A/cm2. This study provides a reference for the later preparation of seawater corrosion resistant composite coatings.
In order to improve the corrosion resistance of 316L stainless steel and prolong its service life in the marine environment, this paper discusses the method and effect of laser cladding technology on the surface of 316L substrate by cladding pure Ni60 coating and WC+Ni60 composite coating. The WC+Ni60 composite coating combines the hardness of WC particles and the toughness of Ni60 matrix, which has better comprehensive performance and is suitable for higher strength protection of the substrate surface. The coatings were retrieved and tested by hardness tester, X-ray diffractometer and electrochemical workstation, respectively. The results show that the average cross-sectional hardness of the WC+Ni60 composite coating is 719 HV, but the fluctuation in each region is large. At the same time, the surface of the cladding layer is more resistant to corrosion than the pure Ni60 coating. The self-corrosion potential is increased by 0.12 V, and the self-corrosion current density is reduced by 2.49 × 10-6 A/cm2. This study provides a reference for the later preparation of seawater corrosion resistant composite coatings.
2024, 48(5): 684-690.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.011
Abstract:
In order to process high-quality microstructures on the surface of titanium alloys and to investigate the influence of different factors on the surface quality, the nanosecond laser was used in the experimental research on the processing of titanium alloy Ti6Al4V. The surface morphology of titanium alloy workpieces processed under different parameters was measured by three-dimensional microscope and confocal microscope. Further, orthogonal experiments and one-way analysis of factors were used to investigate the effects of scanning speed, laser power and scanning line spacing on the processing morphology and roughness values. The results show that under the conditions of low power, high speed, and large line spacing, the material removal is discontinuous and the processed surface shows intermittent pit structure; with the increase of power, the decrease of processing speed and the reduction of line spacing, the material removal is gradually continuous and the processed surface quality is improved. The parameters of laser power 24 W, scanning speed 2000 mm/s, and line spacing 0.01 mm were selected to successfully process the array microgroove structure with a width of 500 μm and a depth of 140 μm on the surface of titanium alloy. This study has good practical value for laser processing of the surface microstructure of titanium alloys.
In order to process high-quality microstructures on the surface of titanium alloys and to investigate the influence of different factors on the surface quality, the nanosecond laser was used in the experimental research on the processing of titanium alloy Ti6Al4V. The surface morphology of titanium alloy workpieces processed under different parameters was measured by three-dimensional microscope and confocal microscope. Further, orthogonal experiments and one-way analysis of factors were used to investigate the effects of scanning speed, laser power and scanning line spacing on the processing morphology and roughness values. The results show that under the conditions of low power, high speed, and large line spacing, the material removal is discontinuous and the processed surface shows intermittent pit structure; with the increase of power, the decrease of processing speed and the reduction of line spacing, the material removal is gradually continuous and the processed surface quality is improved. The parameters of laser power 24 W, scanning speed 2000 mm/s, and line spacing 0.01 mm were selected to successfully process the array microgroove structure with a width of 500 μm and a depth of 140 μm on the surface of titanium alloy. This study has good practical value for laser processing of the surface microstructure of titanium alloys.
2024, 48(5): 691-697.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.012
Abstract:
In order to improve the processing quality of ultraviolet (UV) nanosecond solid-state laser cutting polydimethylsiloxane (PDMS), a new method of mask-assisted laser cutting PDMS was proposed in this paper. Using polyimide film as the mask material, the process experiments of cutting PDMS with UV nanosecond solid-state laser without mask and with different thickness masks were carried out. The formation mechanism of microcracks on the surface of PDMS material was analyzed, and the influence of main laser process parameters on the groove depth, groove width, and processing quality of microgrooves was obtained. The results show that the surface quality of laser cutting PDMS under mask condition is good, no microcrack is generated and the glass transition is less. The groove depth and width increase with the increase of laser pulse energy and scanning speed. When the mask thickness is 15 μm and 50 μm, the scanning speed is 40 μm/s and 50 μm/s, and the pulse energy is higher than 0.40 mJ, respectively, and the heat-affected zone of the microgroove surface is small. This study provides a new method for improving the processing quality of UV nanosecond solid-state laser cutting PDMS.
In order to improve the processing quality of ultraviolet (UV) nanosecond solid-state laser cutting polydimethylsiloxane (PDMS), a new method of mask-assisted laser cutting PDMS was proposed in this paper. Using polyimide film as the mask material, the process experiments of cutting PDMS with UV nanosecond solid-state laser without mask and with different thickness masks were carried out. The formation mechanism of microcracks on the surface of PDMS material was analyzed, and the influence of main laser process parameters on the groove depth, groove width, and processing quality of microgrooves was obtained. The results show that the surface quality of laser cutting PDMS under mask condition is good, no microcrack is generated and the glass transition is less. The groove depth and width increase with the increase of laser pulse energy and scanning speed. When the mask thickness is 15 μm and 50 μm, the scanning speed is 40 μm/s and 50 μm/s, and the pulse energy is higher than 0.40 mJ, respectively, and the heat-affected zone of the microgroove surface is small. This study provides a new method for improving the processing quality of UV nanosecond solid-state laser cutting PDMS.
2024, 48(5): 698-704.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.013
Abstract:
To investigate the capture characteristics of Rayleigh particles by partially coherent crescent like beam (PCCL). The generalized Huygens Fresnel principle was adopted to derive the expression of the cross spectral density and the force on Rayleigh particles of PCCL beams transmitted through an ABCD optical system. Software simulation and theoretical analysis were conducted on the normalized intensity and force distribution on Rayleigh particles of a focused PCCL beam in the focal plane, and the patterns of the intensity and capture force of the focused PCCL beam changing with the beam parameters and focal length were obtained. The results show that when the beam order n=3, the initial waist width w0=0.1 mm, and the coherence length d0=6 mm, the PCCL beam focused by the lens with a focal length of f=12 mm, both high and low refractive index particles can be captured. Since the PCCL beam presents an off-axis light intensity distribution in the focal plane, and the peak light intensity is not at the coordinate origin, the focused PCCL light intensity and the force of Rayleigh particles can be controlled by adjusting the beam order, initial waist width, coherence length and focal length, so as to realize the flexible capture of Rayleigh particles at different positions by focusing the PCCL beam. The results of this study provide a theoretical basis for the stable capture of particles by focusing PCCL beams.
To investigate the capture characteristics of Rayleigh particles by partially coherent crescent like beam (PCCL). The generalized Huygens Fresnel principle was adopted to derive the expression of the cross spectral density and the force on Rayleigh particles of PCCL beams transmitted through an ABCD optical system. Software simulation and theoretical analysis were conducted on the normalized intensity and force distribution on Rayleigh particles of a focused PCCL beam in the focal plane, and the patterns of the intensity and capture force of the focused PCCL beam changing with the beam parameters and focal length were obtained. The results show that when the beam order n=3, the initial waist width w0=0.1 mm, and the coherence length d0=6 mm, the PCCL beam focused by the lens with a focal length of f=12 mm, both high and low refractive index particles can be captured. Since the PCCL beam presents an off-axis light intensity distribution in the focal plane, and the peak light intensity is not at the coordinate origin, the focused PCCL light intensity and the force of Rayleigh particles can be controlled by adjusting the beam order, initial waist width, coherence length and focal length, so as to realize the flexible capture of Rayleigh particles at different positions by focusing the PCCL beam. The results of this study provide a theoretical basis for the stable capture of particles by focusing PCCL beams.
2024, 48(5): 705-710.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.014
Abstract:
Aiming at improving the effect of infrared image, increasing its contrast and clarity and enriching its edge and detail information, an infrared image enhancement method by fusion of linear transformation and local equalization was proposed. According to the intensity distribution of image, adaptive piecewise linear transformation on the intensity of pixel was performed, and local histogram equalization on the image was carried out. Then, the contrast weight, saliency weight and brightness weight of the two enhanced images were calculated, respectively. Finally, multi-scale Laplace pyramid decomposition and Gaussian pyramid decomposition were performed on the enhanced images and the corresponding weights, respectively, and multi-scale linear fusion with the decomposed images and the corresponding weights were performed to obtain the final enhanced image. According to the experimental results, it is confirmed that the effectiveness of proposed method compared to existing methods, the enhanced images go with better visual effect, and the information entropy, average gradient and coefficient of variation are higher than existing methods by more than 9.03%, 23.87% and 9.97%, respectively. This study could improve infrared image enhancement performance more effectively.
Aiming at improving the effect of infrared image, increasing its contrast and clarity and enriching its edge and detail information, an infrared image enhancement method by fusion of linear transformation and local equalization was proposed. According to the intensity distribution of image, adaptive piecewise linear transformation on the intensity of pixel was performed, and local histogram equalization on the image was carried out. Then, the contrast weight, saliency weight and brightness weight of the two enhanced images were calculated, respectively. Finally, multi-scale Laplace pyramid decomposition and Gaussian pyramid decomposition were performed on the enhanced images and the corresponding weights, respectively, and multi-scale linear fusion with the decomposed images and the corresponding weights were performed to obtain the final enhanced image. According to the experimental results, it is confirmed that the effectiveness of proposed method compared to existing methods, the enhanced images go with better visual effect, and the information entropy, average gradient and coefficient of variation are higher than existing methods by more than 9.03%, 23.87% and 9.97%, respectively. This study could improve infrared image enhancement performance more effectively.
2024, 48(5): 711-718.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.015
Abstract:
To solve the problem of insufficient flexibility of the traditional counterfeit digital camouflage generation algorithm development platform, a counterfeit digital camouflage generation algorithm based on field-programmable gate array (FPGA) was proposed. The histogram statistics was used to extract main color information, the background image was mosaicked to obtain color distribution information, and the main colors based on color difference was replaced to obtain a method of imitating digital camouflage. Data were obtained with different main color numbers, color difference calculation weights, and color determination numbers. The results show that after determining 3600 colors, 4 main colors are extracted as the main colors of the fake digital camouflage. When the main colors are replaced according to the color difference, the color weight is 3 ∶6 ∶1, the generated fake digital camouflage has a good encryption effect, and is based on FPGA implements this algorithm, the system occupies few resources. The time required to process a single frame color image with a resolution of 800 pixels×480 pixels is approximately 22.21 ms, which meets the real-time requirements for generating fake digital camouflage in dynamic scenes. This research provides a reference for active camouflage technology.
To solve the problem of insufficient flexibility of the traditional counterfeit digital camouflage generation algorithm development platform, a counterfeit digital camouflage generation algorithm based on field-programmable gate array (FPGA) was proposed. The histogram statistics was used to extract main color information, the background image was mosaicked to obtain color distribution information, and the main colors based on color difference was replaced to obtain a method of imitating digital camouflage. Data were obtained with different main color numbers, color difference calculation weights, and color determination numbers. The results show that after determining 3600 colors, 4 main colors are extracted as the main colors of the fake digital camouflage. When the main colors are replaced according to the color difference, the color weight is 3 ∶6 ∶1, the generated fake digital camouflage has a good encryption effect, and is based on FPGA implements this algorithm, the system occupies few resources. The time required to process a single frame color image with a resolution of 800 pixels×480 pixels is approximately 22.21 ms, which meets the real-time requirements for generating fake digital camouflage in dynamic scenes. This research provides a reference for active camouflage technology.
2024, 48(5): 719-725.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.016
Abstract:
A reconfigurable multi-beamforming technology scheme based on optical true time delay and optical switch array was proposed to achieve the reconfiguration between multiple radio frequency (RF) signals and multiple beams in the microwave photonic multi-beamforming system. The scheme includes electro-optical conversion, optical switch array, multibeam splitter array, fixed optical true time delay array, and photoelectric conversion. The working principle and reconfiguration mechanism of the proposed scheme were theoretically analyzed. A simulation system was established to evaluate the performance of reconfiguration between four RF signals and fixed four beams based on the 4-port Benes network and to obtain the beam pattern under various configured states. The results indicate that the proposed scheme reduces the number of optical switches required by about 2 orders of magnitude compared to the scheme based on variable optical true time delay. The cost can be decreased, and complexity of the system can be controlled at the same time. The reconfiguration between four RF signals and four beams is realized, and a new approach for the application of multi-beamforming technology is provided.
A reconfigurable multi-beamforming technology scheme based on optical true time delay and optical switch array was proposed to achieve the reconfiguration between multiple radio frequency (RF) signals and multiple beams in the microwave photonic multi-beamforming system. The scheme includes electro-optical conversion, optical switch array, multibeam splitter array, fixed optical true time delay array, and photoelectric conversion. The working principle and reconfiguration mechanism of the proposed scheme were theoretically analyzed. A simulation system was established to evaluate the performance of reconfiguration between four RF signals and fixed four beams based on the 4-port Benes network and to obtain the beam pattern under various configured states. The results indicate that the proposed scheme reduces the number of optical switches required by about 2 orders of magnitude compared to the scheme based on variable optical true time delay. The cost can be decreased, and complexity of the system can be controlled at the same time. The reconfiguration between four RF signals and four beams is realized, and a new approach for the application of multi-beamforming technology is provided.
2024, 48(5): 726-733.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.017
Abstract:
Laser focal plane detector is a new type of optoelectronic imaging device, which utilizes the avalanche multiplication effect of carriers inside the semiconductor to achieve high-speed, high-sensitivity, nanosecond time-resolved detection for gaze-type laser 3-D imaging system. It is mainly divided into two categories, linear and Geiger, in which the linear-mode detectors have the advantages of fast response speed, no dead time and post-pulse, and can realize single-pulse instantaneous imaging. Firstly, two architectures of linear-mode focal plane readout circuitswere introduced and their principles were briefly described in different application scenarios, then the key circuit modules of pixel units were elaborated and their advantages and disadvantages were compared, and finally two double-threshold moment identification methods to reduce walking errors were analyzed, which were intended to provide some useful references for the researchers in the related fields.
Laser focal plane detector is a new type of optoelectronic imaging device, which utilizes the avalanche multiplication effect of carriers inside the semiconductor to achieve high-speed, high-sensitivity, nanosecond time-resolved detection for gaze-type laser 3-D imaging system. It is mainly divided into two categories, linear and Geiger, in which the linear-mode detectors have the advantages of fast response speed, no dead time and post-pulse, and can realize single-pulse instantaneous imaging. Firstly, two architectures of linear-mode focal plane readout circuitswere introduced and their principles were briefly described in different application scenarios, then the key circuit modules of pixel units were elaborated and their advantages and disadvantages were compared, and finally two double-threshold moment identification methods to reduce walking errors were analyzed, which were intended to provide some useful references for the researchers in the related fields.
2024, 48(5): 734-738.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.018
Abstract:
In order to improve the effect of automatic detection of isolation switch's closing state, a non-contact automatic detection method based on laser displacement sensor was adopted. The resolution of the laser displacement sensor was maximized, the optical parameters of the laser displacement sensor was optimized, and its displacement measurement accuracy was improved; Through the laser displacement sensor with optimized optical parameters, the isolation switch contour curve was collected, and the isolation switch contour curve sampling point set was obtained. Using the least square method, the elliptic equation of the sampling point of the isolation switch contour curve was fitted, and the angle between the conductive arm and the horizontal direction was calculated. When the angle of the conductive arm was within the specified interval, the reasonable switch closing was determined to be in place, and the non-contact automatic detection of the isolation switch closing state was completed. The experimental results show that the angle of the front and back conductive arms calculated by this method is about 0.4° and 0.5° respectively, which is lower than the specified interval of the angle. The results indicate that this result is helpful to realize the non-contact automatic detection of the isolation switch.
In order to improve the effect of automatic detection of isolation switch's closing state, a non-contact automatic detection method based on laser displacement sensor was adopted. The resolution of the laser displacement sensor was maximized, the optical parameters of the laser displacement sensor was optimized, and its displacement measurement accuracy was improved; Through the laser displacement sensor with optimized optical parameters, the isolation switch contour curve was collected, and the isolation switch contour curve sampling point set was obtained. Using the least square method, the elliptic equation of the sampling point of the isolation switch contour curve was fitted, and the angle between the conductive arm and the horizontal direction was calculated. When the angle of the conductive arm was within the specified interval, the reasonable switch closing was determined to be in place, and the non-contact automatic detection of the isolation switch closing state was completed. The experimental results show that the angle of the front and back conductive arms calculated by this method is about 0.4° and 0.5° respectively, which is lower than the specified interval of the angle. The results indicate that this result is helpful to realize the non-contact automatic detection of the isolation switch.
2024, 48(5): 739-745.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.019
Abstract:
The measurement of traditional laser biospeckle is significantly affected by experimental parameters. To address this problem, dynamic light scattering and fluorescence correlation spectroscopy were used to characterize the biospeckle activity. An experimental setup was built and tested with traditional Chinese medicine syrup, yogurt, old yogurt, tomatoes, and apples. The results show that the constructed metric based on the correlation coefficient with a clear physical meaning is mainly determined by the speed of particle movement in the sample, which has an average error less than 5%. As the metric is almost independent of the exposure time of camera and region of interest, it is beneficial for the biospeckle technology to be used in practical applications. Since various characteristics of biological samples in the agricultural and pharmaceutical fields are related to the speed of particle movement, this method is expected to provide a new non-destructive testing tool for food and pharmaceutical industries.
The measurement of traditional laser biospeckle is significantly affected by experimental parameters. To address this problem, dynamic light scattering and fluorescence correlation spectroscopy were used to characterize the biospeckle activity. An experimental setup was built and tested with traditional Chinese medicine syrup, yogurt, old yogurt, tomatoes, and apples. The results show that the constructed metric based on the correlation coefficient with a clear physical meaning is mainly determined by the speed of particle movement in the sample, which has an average error less than 5%. As the metric is almost independent of the exposure time of camera and region of interest, it is beneficial for the biospeckle technology to be used in practical applications. Since various characteristics of biological samples in the agricultural and pharmaceutical fields are related to the speed of particle movement, this method is expected to provide a new non-destructive testing tool for food and pharmaceutical industries.
2024, 48(5): 746-751.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.020
Abstract:
In order to meet the requirements of large field of view, large exit pupil, high imaging quality and light and small structure of virtual reality head-mounted display, a reverse optical path design method was adopted to study pancake structure of a folding optical path. Two lenses were designed for theoretical analysis and software simulation, and the tolerance analysis of the designed optical system was carried out. The results show that the full field Angle is 96°, the exit pupil diameter is 10 mm, the exit pupil distance is 14.94 mm, the modulation transfer function (MTF) is greater than 0.2 at Nyquist frequency (20.83 lp/mm), the maximum distortion is -26.5%, and the maximum vertical color difference is 13.84 μm, respectively. This structure has higher MTF value, smaller vertical color difference and root mean square radius of dispersion class, and reasonable aberration balance. This study provides a reference for the folding optical path structure of the head-mounted display.
In order to meet the requirements of large field of view, large exit pupil, high imaging quality and light and small structure of virtual reality head-mounted display, a reverse optical path design method was adopted to study pancake structure of a folding optical path. Two lenses were designed for theoretical analysis and software simulation, and the tolerance analysis of the designed optical system was carried out. The results show that the full field Angle is 96°, the exit pupil diameter is 10 mm, the exit pupil distance is 14.94 mm, the modulation transfer function (MTF) is greater than 0.2 at Nyquist frequency (20.83 lp/mm), the maximum distortion is -26.5%, and the maximum vertical color difference is 13.84 μm, respectively. This structure has higher MTF value, smaller vertical color difference and root mean square radius of dispersion class, and reasonable aberration balance. This study provides a reference for the folding optical path structure of the head-mounted display.
2024, 48(5): 752-758.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.021
Abstract:
Phase unwrapping plays an important role in many applications, but it is always affected by noise, especially speckle noise. In order to remove the effect of speckle noise on the wrapping phase diagram, the actual phase value was recovered from it. The two-step method was used to make theoretical analysis and experimental demonstration, and the absolute phase was recovered from the phase covered by speckle noise in different degrees. In the first step, based on the swin-UNet-denoise network, the normalized layer in swin block was set back, and the attention value was calculated by cosine similarity. Then, the relative displacement offset was replaced by logarithmic position offset, and the deconvolution layer was fused in the upsampling module to improve the denoising ability of the network. In the second step, the denoising result was unwrapped by least square method, and then the absolute phase was obtained by median filtering. The results show that the structural similarity is 99.77%, the peak signal-to-noise ratio is 39.98, the root-mean-square error is 0.4864, and the average absolute error is 0.4302, respectively. In addition, all the networks are only trained and verified on 300 simulation data sets, which proves that the research can provide a reference for faster, more efficient and accurate phase unwrapping with speckle noise even under the condition of small samples.
Phase unwrapping plays an important role in many applications, but it is always affected by noise, especially speckle noise. In order to remove the effect of speckle noise on the wrapping phase diagram, the actual phase value was recovered from it. The two-step method was used to make theoretical analysis and experimental demonstration, and the absolute phase was recovered from the phase covered by speckle noise in different degrees. In the first step, based on the swin-UNet-denoise network, the normalized layer in swin block was set back, and the attention value was calculated by cosine similarity. Then, the relative displacement offset was replaced by logarithmic position offset, and the deconvolution layer was fused in the upsampling module to improve the denoising ability of the network. In the second step, the denoising result was unwrapped by least square method, and then the absolute phase was obtained by median filtering. The results show that the structural similarity is 99.77%, the peak signal-to-noise ratio is 39.98, the root-mean-square error is 0.4864, and the average absolute error is 0.4302, respectively. In addition, all the networks are only trained and verified on 300 simulation data sets, which proves that the research can provide a reference for faster, more efficient and accurate phase unwrapping with speckle noise even under the condition of small samples.
2024, 48(5): 759-764.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.022
Abstract:
In order to improve the comprehensive performance of HT250 gray cast iron material, a genetic algorithm(GA) multi-objective process parameter optimization method was used to obtain the corresponding empirical parameter group. In the laser cladding 316L alloy experiment on the surface of gray cast iron material, a digital detection instrument was used to comprehensively analyze the changes in macroscopic morphology, Rockwell hardness, geometric shape, and other characteristics of the sample, and the optimal process parameter combination was analyzed and optimized. The results show that when the process parameters are respectively set to powder feeding speed of 0.25 g/s, scanning speed of 10 mm/s, and laser power of 2800 W, the surface geometry of the 316L cladding layer is the best, the macroscopic morphology is good, and the maximum Rockwell hardness reaches 37.6 HRC. The sample cladding performance is good. The comprehensive improvement of various properties of gray cast iron provides practical reference for the repair and reuse of worn gray cast iron products.
In order to improve the comprehensive performance of HT250 gray cast iron material, a genetic algorithm(GA) multi-objective process parameter optimization method was used to obtain the corresponding empirical parameter group. In the laser cladding 316L alloy experiment on the surface of gray cast iron material, a digital detection instrument was used to comprehensively analyze the changes in macroscopic morphology, Rockwell hardness, geometric shape, and other characteristics of the sample, and the optimal process parameter combination was analyzed and optimized. The results show that when the process parameters are respectively set to powder feeding speed of 0.25 g/s, scanning speed of 10 mm/s, and laser power of 2800 W, the surface geometry of the 316L cladding layer is the best, the macroscopic morphology is good, and the maximum Rockwell hardness reaches 37.6 HRC. The sample cladding performance is good. The comprehensive improvement of various properties of gray cast iron provides practical reference for the repair and reuse of worn gray cast iron products.
2024, 48(5): 765-770.
doi: 10.7510/jgjs.issn.1001-3806.2024.05.023
Abstract:
In order to improve the safety of the remote laser wireless charging system used in smart homes, a laser wireless charging protection system based on deep learning was adopted. Meanwhile, in response to the small target of photovoltaic cells attached to the surface of smart homes, which were difficult to identify, a YOLOv7-NH network model was improved to establish a protection monitoring area and incorporate inter frame difference method for real-time monitoring of charging areas. A protection algorithm for image monitoring of the area where the charging target was located was written through the steps of creating a principle analysis algorithm framework building environment debugging, and a testing system was built. The test results show that when the distance between the laser emitting end and the charging target is within 10 m, the response start time of the protection system built based on this algorithm is less than 1ms. That is, when a moving foreign object enters the protection monitoring area with a size of 40 mm×40 mm at a speed of 1.5 m/s below the normal speed, the protection system can stop laser emission before it moves to the optical path where the laser beam is located. This result is helpful for the development of indoor laser remote wireless charging protection technology.
In order to improve the safety of the remote laser wireless charging system used in smart homes, a laser wireless charging protection system based on deep learning was adopted. Meanwhile, in response to the small target of photovoltaic cells attached to the surface of smart homes, which were difficult to identify, a YOLOv7-NH network model was improved to establish a protection monitoring area and incorporate inter frame difference method for real-time monitoring of charging areas. A protection algorithm for image monitoring of the area where the charging target was located was written through the steps of creating a principle analysis algorithm framework building environment debugging, and a testing system was built. The test results show that when the distance between the laser emitting end and the charging target is within 10 m, the response start time of the protection system built based on this algorithm is less than 1ms. That is, when a moving foreign object enters the protection monitoring area with a size of 40 mm×40 mm at a speed of 1.5 m/s below the normal speed, the protection system can stop laser emission before it moves to the optical path where the laser beam is located. This result is helpful for the development of indoor laser remote wireless charging protection technology.
