Map
WeChat
Email alert
RSS2024 Vol. 48, No. 1
Display Method:
[Abstract]
[PDF 253KB]
2024, 48(1): 1-7.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.001
[FullText HTML]
Abstract:
Aiming at the problem of urgent space debris removal for orbiting spacecraft, a simulation model was established, and the simulation results of two typical space-based laser debris removal methods were compared and analyzed. At the same time, the design concept of using solar panels and a large aperture foldable transmitting telescope was put forward so as to reduce the transmitting cost and increase the efficiency ratio. The results show that 10 cm space debris can be used in ablative backflow mode, while 1 cm space debris is more advantageous in direct ablative mode. This study provides a technical reference for the subsequent space-based laser system to clear space debris.
Aiming at the problem of urgent space debris removal for orbiting spacecraft, a simulation model was established, and the simulation results of two typical space-based laser debris removal methods were compared and analyzed. At the same time, the design concept of using solar panels and a large aperture foldable transmitting telescope was put forward so as to reduce the transmitting cost and increase the efficiency ratio. The results show that 10 cm space debris can be used in ablative backflow mode, while 1 cm space debris is more advantageous in direct ablative mode. This study provides a technical reference for the subsequent space-based laser system to clear space debris.
2024, 48(1): 8-13.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.002
Abstract:
In order to improve the laser acoustic communication technology between air platforms and underwater objects, the n-multifrequency shift keying (n-MFSK) modulation method was proposed to further enhance the laser acoustic air-water cross-media communication rate. Based on the thermal expansion effect of laser acoustic, the modulation methods of the long-pulse-duration laser method and the high repetitive rate method were defined and simulated. The result was obtained that 2-MFSK modulation doubles the communication rate on top of 2-FSK modulation for a modulation frequency number of 2. The n-MFSK modulation was achieved by the long-pulse-duration laser method, mainly through the laser array by means of frequency superposition, and the high repetitive rate method by controlling the allocation of time periods on the time domain of the laser frequency change. The results show that as the number of modulation frequencies increases, n-MFSK modulation can increase the communication rate and improve the band utilization relative to n-frequency shift keying (n-FSK) modulation at the cost of loss of the sound pressure level (SPL) and in-water-range. This study provides a reference for the practical application of laser acoustic air-water cross-media communication in the future.
In order to improve the laser acoustic communication technology between air platforms and underwater objects, the n-multifrequency shift keying (n-MFSK) modulation method was proposed to further enhance the laser acoustic air-water cross-media communication rate. Based on the thermal expansion effect of laser acoustic, the modulation methods of the long-pulse-duration laser method and the high repetitive rate method were defined and simulated. The result was obtained that 2-MFSK modulation doubles the communication rate on top of 2-FSK modulation for a modulation frequency number of 2. The n-MFSK modulation was achieved by the long-pulse-duration laser method, mainly through the laser array by means of frequency superposition, and the high repetitive rate method by controlling the allocation of time periods on the time domain of the laser frequency change. The results show that as the number of modulation frequencies increases, n-MFSK modulation can increase the communication rate and improve the band utilization relative to n-frequency shift keying (n-FSK) modulation at the cost of loss of the sound pressure level (SPL) and in-water-range. This study provides a reference for the practical application of laser acoustic air-water cross-media communication in the future.
2024, 48(1): 14-19.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.003
Abstract:
In order to solve the problem of rapid plasma expansion and small fringe offset caused by peripheral plumes in the high vacuum environment, it was difficult to detect a single interference fringe pattern. The electron density distributions of the laser-induced aluminum plasma under 1.333×10-4 Pa and 1.333×10-3 Pa pressure were obtained by using simultaneous phase-shifting interference. At the same time, the expansion process of laser-induced plasma under a high vacuum environment was simulated numerically by using a 2-D axis ymmetric fluid dynamics model, and the two-dimensional distribution of electron density was obtained and analyzed for the reasons for the deviation of numerical simulation results and the improvement methods. The results show that the central electron density of plasma decreases to 1.4×1020 cm-3 at 50 ns. The numerical simulation results are in good agreement with the experimental results, which verifies the reliability of the model. This research provides some reference for the study of laser plasma under high vacuum.
In order to solve the problem of rapid plasma expansion and small fringe offset caused by peripheral plumes in the high vacuum environment, it was difficult to detect a single interference fringe pattern. The electron density distributions of the laser-induced aluminum plasma under 1.333×10-4 Pa and 1.333×10-3 Pa pressure were obtained by using simultaneous phase-shifting interference. At the same time, the expansion process of laser-induced plasma under a high vacuum environment was simulated numerically by using a 2-D axis ymmetric fluid dynamics model, and the two-dimensional distribution of electron density was obtained and analyzed for the reasons for the deviation of numerical simulation results and the improvement methods. The results show that the central electron density of plasma decreases to 1.4×1020 cm-3 at 50 ns. The numerical simulation results are in good agreement with the experimental results, which verifies the reliability of the model. This research provides some reference for the study of laser plasma under high vacuum.
2024, 48(1): 20-26.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.004
Abstract:
In order to further improve the color display capability of the display system and solve the problem of model incompatibility between the three-primary display system and the multi-primary display system, the method of parameter inequality was adopted for theoretical analysis. Based on the difference between the multi-primary display system and the three-primary display system, the solution space corresponding to the peak luminances of the multi-primary display system was solved. The peak luminances of primaries in a multi-primary display system were deduced theoretically, and the equivalence and completeness of solution space were verified by simulation experiments. The results show that the theoretical maximum gamut volumes corresponding to the simulated four-primary, five-primary, and six-primary laser display systems are 2185100, 2258400, and 2395800, respectively. This scheme has important guiding significance to the theoretical simulation of a multi-primary display system.
In order to further improve the color display capability of the display system and solve the problem of model incompatibility between the three-primary display system and the multi-primary display system, the method of parameter inequality was adopted for theoretical analysis. Based on the difference between the multi-primary display system and the three-primary display system, the solution space corresponding to the peak luminances of the multi-primary display system was solved. The peak luminances of primaries in a multi-primary display system were deduced theoretically, and the equivalence and completeness of solution space were verified by simulation experiments. The results show that the theoretical maximum gamut volumes corresponding to the simulated four-primary, five-primary, and six-primary laser display systems are 2185100, 2258400, and 2395800, respectively. This scheme has important guiding significance to the theoretical simulation of a multi-primary display system.
2024, 48(1): 27-33.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.005
Abstract:
In order to solve the problem of the low value of road marking line extraction integrity and accuracy based on vehicle-mounted light detection and ranging(LiDAR) point cloud data, a fast road marking line extraction method based on multiple features of the point cloud was proposed. Based on the strength information, geometric information, and semantic information of urban road marking lines, combined with the strength feature, elevation feature, and point density feature of the road surface point cloud, multiple geographic reference images were generated, and the feature extraction and filling of the multiple feature images were carried out, and then the Ostu algorithm and Alpha shapes algorithm were used to achieve the precise extraction of the road marking line point cloud. According to the geometric and semantic information of the marking line and the model matching scheme, the fine classification of the marking line was realized. The theoretical analysis and experimental verification were carried out, and the point cloud data of a city road in Australia was obtained. The results show that the accuracy of the extracted short dotted line, zebra line, one-way steering arrow and, the long dotted line is higher than 96%, the recall rate is 91% and above, and the comprehensive evaluation index is 94% and above. The study has contributed to the research in the field of driverless driving and also provided certain reference values for the construction of urban digital.
In order to solve the problem of the low value of road marking line extraction integrity and accuracy based on vehicle-mounted light detection and ranging(LiDAR) point cloud data, a fast road marking line extraction method based on multiple features of the point cloud was proposed. Based on the strength information, geometric information, and semantic information of urban road marking lines, combined with the strength feature, elevation feature, and point density feature of the road surface point cloud, multiple geographic reference images were generated, and the feature extraction and filling of the multiple feature images were carried out, and then the Ostu algorithm and Alpha shapes algorithm were used to achieve the precise extraction of the road marking line point cloud. According to the geometric and semantic information of the marking line and the model matching scheme, the fine classification of the marking line was realized. The theoretical analysis and experimental verification were carried out, and the point cloud data of a city road in Australia was obtained. The results show that the accuracy of the extracted short dotted line, zebra line, one-way steering arrow and, the long dotted line is higher than 96%, the recall rate is 91% and above, and the comprehensive evaluation index is 94% and above. The study has contributed to the research in the field of driverless driving and also provided certain reference values for the construction of urban digital.
2024, 48(1): 34-39.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.006
Abstract:
In order to develop a polarization-maintaining fiber with a working wavelength of 1310 nm, the prepare preform and stress rod of polarization-maintaining(PM) fiber were prepared by a modified chemical vapor deposition process. The high-quality PM fiber with precise geometric size was produced after processing, splicing, cleaning, and drawing. At the same time, an efficient test system was set up to measure the refractive index and geometry of preform, mode-field diameter (MFD), and numerical aperture(NA), and geometry of PM fiber by technologies such as the refractive near-field method, far-field scanning and, video gray scale technology (transmission near field). The results show that the standardized test system has simple operation and accurate results, and MFD is 6.26 μm, NA is 0.23, and cladding and coating diameter is 80 μm/135 μm/165 μm (accuracy ±0.7 μm). After the final test, 16.25% of the qualified fiber products are sampled randomly for high and low temperature aging, and the beat length and crosstalk change little after the experiment. The PM fiber developed in this design has stable performance, precise geometric size, uniform structure, low loss, and excellent polarization maintaining performance, which has been widely used in practical production.
In order to develop a polarization-maintaining fiber with a working wavelength of 1310 nm, the prepare preform and stress rod of polarization-maintaining(PM) fiber were prepared by a modified chemical vapor deposition process. The high-quality PM fiber with precise geometric size was produced after processing, splicing, cleaning, and drawing. At the same time, an efficient test system was set up to measure the refractive index and geometry of preform, mode-field diameter (MFD), and numerical aperture(NA), and geometry of PM fiber by technologies such as the refractive near-field method, far-field scanning and, video gray scale technology (transmission near field). The results show that the standardized test system has simple operation and accurate results, and MFD is 6.26 μm, NA is 0.23, and cladding and coating diameter is 80 μm/135 μm/165 μm (accuracy ±0.7 μm). After the final test, 16.25% of the qualified fiber products are sampled randomly for high and low temperature aging, and the beat length and crosstalk change little after the experiment. The PM fiber developed in this design has stable performance, precise geometric size, uniform structure, low loss, and excellent polarization maintaining performance, which has been widely used in practical production.
2024, 48(1): 40-47.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.007
Abstract:
In order to analyze the atmospheric Rayleigh-Brillouin scattering spectrum and obtain the vertical temperature profile of the atmosphere from 0 km to 16 km, a high spectral resolution temperature LiDAR (HSRL) based on a Fizeau interferometer combined with a photomultiplier tube array was used. The temperature retrieval ability and system error under different seasonal environments were analyzed theoretically. The results of the influence of different atmospheric models on temperature profile fitting was obtained by using atmospheric Rayleigh-Brillouin scattering spectra combined with Tenti S6 model for fitting. The results indicate that, using the US76 atmospheric model combined with the Tenti S6 model, after 10000 pulse integrations, the maximum random error within the range of 0 km to 16 km is 1.1 K. Using the temperature and pressure field provided by weather research & forecast (WRF) model to replace the temperature and pressure field of US76 model for simulation, the random error varies slightly with seasons, not exceeding 0.65 K in spring, 0.98 K in summer, 0.59 K in autumn, and 0.63 K in winter. The evaluation results of detection capability of HSRL system by using WRF mode are better than the evaluation results by using US76. If different weather types are selected, this method can also be extended to evaluate the random error of HSRL in different seasons. The advantages of using the WRF model for HSRL evaluation are reflected. This study provides a reference for evaluating the working ability of the HSRL temperature measurement system in different seasons.
In order to analyze the atmospheric Rayleigh-Brillouin scattering spectrum and obtain the vertical temperature profile of the atmosphere from 0 km to 16 km, a high spectral resolution temperature LiDAR (HSRL) based on a Fizeau interferometer combined with a photomultiplier tube array was used. The temperature retrieval ability and system error under different seasonal environments were analyzed theoretically. The results of the influence of different atmospheric models on temperature profile fitting was obtained by using atmospheric Rayleigh-Brillouin scattering spectra combined with Tenti S6 model for fitting. The results indicate that, using the US76 atmospheric model combined with the Tenti S6 model, after 10000 pulse integrations, the maximum random error within the range of 0 km to 16 km is 1.1 K. Using the temperature and pressure field provided by weather research & forecast (WRF) model to replace the temperature and pressure field of US76 model for simulation, the random error varies slightly with seasons, not exceeding 0.65 K in spring, 0.98 K in summer, 0.59 K in autumn, and 0.63 K in winter. The evaluation results of detection capability of HSRL system by using WRF mode are better than the evaluation results by using US76. If different weather types are selected, this method can also be extended to evaluate the random error of HSRL in different seasons. The advantages of using the WRF model for HSRL evaluation are reflected. This study provides a reference for evaluating the working ability of the HSRL temperature measurement system in different seasons.
2024, 48(1): 48-53.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.008
Abstract:
The constant modulus algorithm (CMA) is a popular algorithm for mode-division multiplexing systems to equalize and compensate for impairments such as mode coupling, differential mode group delay, and dispersion in the system to obtain the desired signal. In order to study the equalization performance of the CMA in the strong coupling mode-division multiplexing system, the power coupling theory was used to build a 6×6 mode-division multiplexing system model and use the CMA and modified constant modulus algorithm (MCMA) at the receiving end to equalize the system output signal and obtain the constellation diagrams, root mean square error (RMSE) values and bit error rate (BER). The results show that in terms of the constellation diagram, MCMA can reduce scatter points and make constellation points more compact; in terms of RMSE, the RMSE value of the signal after MCMA equalization is smaller than the RMSE obtained after CMA equalization, indicating that the data dispersion level after MCMA equalization is low; in terms of BER, when BER is 10-3, the optical signal-to-noise ratio required by MCMA is 1.0 dB lower than that of CMA, therefore, MCMA equalization outperforms CMA. The results of this study provide some references for the equalization algorithm in the strong coupling mode-division multiplexing system.
The constant modulus algorithm (CMA) is a popular algorithm for mode-division multiplexing systems to equalize and compensate for impairments such as mode coupling, differential mode group delay, and dispersion in the system to obtain the desired signal. In order to study the equalization performance of the CMA in the strong coupling mode-division multiplexing system, the power coupling theory was used to build a 6×6 mode-division multiplexing system model and use the CMA and modified constant modulus algorithm (MCMA) at the receiving end to equalize the system output signal and obtain the constellation diagrams, root mean square error (RMSE) values and bit error rate (BER). The results show that in terms of the constellation diagram, MCMA can reduce scatter points and make constellation points more compact; in terms of RMSE, the RMSE value of the signal after MCMA equalization is smaller than the RMSE obtained after CMA equalization, indicating that the data dispersion level after MCMA equalization is low; in terms of BER, when BER is 10-3, the optical signal-to-noise ratio required by MCMA is 1.0 dB lower than that of CMA, therefore, MCMA equalization outperforms CMA. The results of this study provide some references for the equalization algorithm in the strong coupling mode-division multiplexing system.
2024, 48(1): 54-59.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.009
Abstract:
In order to improve the low mechanical properties and cracking of the welded joint between ductile iron and low carbon steel, laser welding was used to weld ductile iron and low carbon steel, and the effects of process parameters on the microstructure and properties of the welded joint were studied. The results show that with the increase of laser power or the gradual slowing of welding speed, the tensile strength of the test piece shows a trend of first increasing and then decreasing. When the welding process parameters are at 4250 W welding power and 2.4 m/min welding speed, the strength of the welded joint of the specimen is at the extreme value of 400 MPa.Three kinds of shell structures (double shell structure, single shell structure, and coreless structure) are formed in the heat-affected zone at the side of nodular cast iron. The microstructure in the weld zone is mainly composed of dendrite, a small amount of martensite, and ledeburite. There are microcracks in the weld zone. The crack-free weld can be obtained by adding nickel-based materials, and the tensile strength can be improved by about 40 MPa, reaching 95% of the base metal. This research is helpful in the optimization of the high-power laser welding process between nodular cast iron and low carbon steel.
In order to improve the low mechanical properties and cracking of the welded joint between ductile iron and low carbon steel, laser welding was used to weld ductile iron and low carbon steel, and the effects of process parameters on the microstructure and properties of the welded joint were studied. The results show that with the increase of laser power or the gradual slowing of welding speed, the tensile strength of the test piece shows a trend of first increasing and then decreasing. When the welding process parameters are at 4250 W welding power and 2.4 m/min welding speed, the strength of the welded joint of the specimen is at the extreme value of 400 MPa.Three kinds of shell structures (double shell structure, single shell structure, and coreless structure) are formed in the heat-affected zone at the side of nodular cast iron. The microstructure in the weld zone is mainly composed of dendrite, a small amount of martensite, and ledeburite. There are microcracks in the weld zone. The crack-free weld can be obtained by adding nickel-based materials, and the tensile strength can be improved by about 40 MPa, reaching 95% of the base metal. This research is helpful in the optimization of the high-power laser welding process between nodular cast iron and low carbon steel.
Analysis of the stimulated Brillouin scattering threshold of coupling ring-assisted multi-mode fiber
2024, 48(1): 60-64.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.010
Abstract:
In order to reduce inter-mode crosstalk, a coupling ring-assisted multi-mode fiber structure was proposed, and the mathematical model of its excited Brillouin scattering gain spectrum was established. Theoretically, the excited Brillouin scattering threshold of the coupling ring-assisted multi-mode fiber was analyzed, as well as the effects of fiber parameters and modes on the excited Brillouin scattering spectral threshold. The results show that the coupling ring-assisted structure increases the effective refractive index difference to 1.75 times that of the conventional type step-index multi-mode fiber. The threshold of the excited Brillouin scattering spectrum in coupling ring-assisted multi-mode fiber follows the increase of the fiber length from a sharp decrease to a slow one and finally converges to a constant value of 30 dBm at 18 km, which is higher than that of the conventional step refractive index multi-mode fiber. Other things being equal, the threshold increases linearly with the attenuation coefficient, the effective cross-sectional area of the fiber core, and the mode order of the fiber; it increases exponentially with the increase of the core radius. This study provides a theoretical reference for enhancing the transmission distance and channel capacity of fiber optic communication systems.
In order to reduce inter-mode crosstalk, a coupling ring-assisted multi-mode fiber structure was proposed, and the mathematical model of its excited Brillouin scattering gain spectrum was established. Theoretically, the excited Brillouin scattering threshold of the coupling ring-assisted multi-mode fiber was analyzed, as well as the effects of fiber parameters and modes on the excited Brillouin scattering spectral threshold. The results show that the coupling ring-assisted structure increases the effective refractive index difference to 1.75 times that of the conventional type step-index multi-mode fiber. The threshold of the excited Brillouin scattering spectrum in coupling ring-assisted multi-mode fiber follows the increase of the fiber length from a sharp decrease to a slow one and finally converges to a constant value of 30 dBm at 18 km, which is higher than that of the conventional step refractive index multi-mode fiber. Other things being equal, the threshold increases linearly with the attenuation coefficient, the effective cross-sectional area of the fiber core, and the mode order of the fiber; it increases exponentially with the increase of the core radius. This study provides a theoretical reference for enhancing the transmission distance and channel capacity of fiber optic communication systems.
2024, 48(1): 65-70.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.011
Abstract:
In order to make the fiber grating sensor have the functions of temperature/strain dual-parameter sensing and communication transmission in the application of fiber sensing system, a new flat-top fiber grating sensor structure composed of the chirped long period grating(CLPG) and chirped fiber Bragg grating(CFBG) was proposed. The sensitivity coefficient matrix of temperature and strain of the sensor was established by measuring the displacement of the center wavelength, and the theoretical analysis and simulation were carried out. The results show that, the temperature and strain sensitivities of CLPG were 2660 pm/℃ and 132 pm/με, respectively. CFBG sensitivities were 12.6 pm/℃ for temperature and 0.8 pm/με for strain. Both CLPG and CFBG had flat-top output spectra at the same time, and the flat-top spectral bandwidths reached 13.8 nm and 5.6 nm, respectively. The sensor can realize the simultaneous sensing of both parameters of temperature/strain and has a stable communication transmission band. This study serves as a reference for the application of fiber grating sensors in fiber sensing systems.
In order to make the fiber grating sensor have the functions of temperature/strain dual-parameter sensing and communication transmission in the application of fiber sensing system, a new flat-top fiber grating sensor structure composed of the chirped long period grating(CLPG) and chirped fiber Bragg grating(CFBG) was proposed. The sensitivity coefficient matrix of temperature and strain of the sensor was established by measuring the displacement of the center wavelength, and the theoretical analysis and simulation were carried out. The results show that, the temperature and strain sensitivities of CLPG were 2660 pm/℃ and 132 pm/με, respectively. CFBG sensitivities were 12.6 pm/℃ for temperature and 0.8 pm/με for strain. Both CLPG and CFBG had flat-top output spectra at the same time, and the flat-top spectral bandwidths reached 13.8 nm and 5.6 nm, respectively. The sensor can realize the simultaneous sensing of both parameters of temperature/strain and has a stable communication transmission band. This study serves as a reference for the application of fiber grating sensors in fiber sensing systems.
2024, 48(1): 71-76.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.012
Abstract:
In order to overcome the deficiency that the measurement function of the existing spectral Mueller matrix ellipsometer had been fixed and could not measure more physical quantities according to the experimental requirements, a new scheme was proposed to measure more physical parameters by combining multi-physical field optical simulation and wide-spectrum Mueller matrix ellipsometry measurement data. Taking film thickness measurement as an example, by comparing the matching degree of Mueller matrix obtained by the measured values of an ellipsometer and the simulated values of silicon dioxide films with different thicknesses and at different incident angles on a silicon substrate, the thickness value of the silica film with the smallest relative mean square error was obtained. The results show that the thickness of the film is in good agreement with the measured values. This study validates the feasibility and effectiveness of the combined method of spectral Muller matrix ellipsometry measurement and simulation.
In order to overcome the deficiency that the measurement function of the existing spectral Mueller matrix ellipsometer had been fixed and could not measure more physical quantities according to the experimental requirements, a new scheme was proposed to measure more physical parameters by combining multi-physical field optical simulation and wide-spectrum Mueller matrix ellipsometry measurement data. Taking film thickness measurement as an example, by comparing the matching degree of Mueller matrix obtained by the measured values of an ellipsometer and the simulated values of silicon dioxide films with different thicknesses and at different incident angles on a silicon substrate, the thickness value of the silica film with the smallest relative mean square error was obtained. The results show that the thickness of the film is in good agreement with the measured values. This study validates the feasibility and effectiveness of the combined method of spectral Muller matrix ellipsometry measurement and simulation.
2024, 48(1): 77-82.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.013
Abstract:
In order to solve the problem of poor target localization accuracy in a large field of view fisheye imaging system, a research method based on camera movement to calibrate the imaging model of the fisheye imaging system was adopted. The calibration object was a single fixed point light source, and the fisheye imaging system was driven to move by a motorized high-precision 2-D turntable to record the orientation angle of the point light source in the fisheye imaging system and the pixel position of the light point in the image, respectively, to construct a calibration model of the fisheye imaging system so that the point light source was imaged at each position in the image; the optical center was calculated by using the edge-fitting circle of the effective area of the image, and the aberration parameters were calculated by using the sub-regional calibration method to reduce the calibration error. The results show that when divided into three regions for calibration, the calibration error of the method in the central imaging region is 0.06°. This method has a high accuracy and can be applied to the calibration of large field-of-view fisheye imaging systems such as infrared earth sensors and wide-angle imaging reconnaissance systems.
In order to solve the problem of poor target localization accuracy in a large field of view fisheye imaging system, a research method based on camera movement to calibrate the imaging model of the fisheye imaging system was adopted. The calibration object was a single fixed point light source, and the fisheye imaging system was driven to move by a motorized high-precision 2-D turntable to record the orientation angle of the point light source in the fisheye imaging system and the pixel position of the light point in the image, respectively, to construct a calibration model of the fisheye imaging system so that the point light source was imaged at each position in the image; the optical center was calculated by using the edge-fitting circle of the effective area of the image, and the aberration parameters were calculated by using the sub-regional calibration method to reduce the calibration error. The results show that when divided into three regions for calibration, the calibration error of the method in the central imaging region is 0.06°. This method has a high accuracy and can be applied to the calibration of large field-of-view fisheye imaging systems such as infrared earth sensors and wide-angle imaging reconnaissance systems.
2024, 48(1): 83-91.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.014
Abstract:
In order to study the ablation quality process of carbon fiber reinforced plastics(CFRP) with 20 W nanosecond laser, theoretical analysis and experimental verification were carried out by the single-factor experimental method and photo-section method. Effects of scanning speed, peak power, and defocus amount on the surface processing quality of the material were studied. A piece of 0.5 mm thick CFRP was ablated in experiments. The results show that adjusting the defocusing amount made the focus of the laser and the material plane at the same horizontal height, which could minimize the scanning line width, reduce the heat-affected zone and improve the laser energy utilization. When the laser scanning speed is 220 mm/s and, the peak laser power is 10 W, the average surface roughness of CFRP composite is the smallest. About 3.50 μm, and the roughness data stability sample difference is the best, about 0.133 μm2; the laser process parameter combination method ablation CFRP composite materials can obtain ideal processing performance. The above research for pulsed laser processing CFRP material process research provides some references and lays a certain practical foundation for the application of pulsed laser processing composite material process.
In order to study the ablation quality process of carbon fiber reinforced plastics(CFRP) with 20 W nanosecond laser, theoretical analysis and experimental verification were carried out by the single-factor experimental method and photo-section method. Effects of scanning speed, peak power, and defocus amount on the surface processing quality of the material were studied. A piece of 0.5 mm thick CFRP was ablated in experiments. The results show that adjusting the defocusing amount made the focus of the laser and the material plane at the same horizontal height, which could minimize the scanning line width, reduce the heat-affected zone and improve the laser energy utilization. When the laser scanning speed is 220 mm/s and, the peak laser power is 10 W, the average surface roughness of CFRP composite is the smallest. About 3.50 μm, and the roughness data stability sample difference is the best, about 0.133 μm2; the laser process parameter combination method ablation CFRP composite materials can obtain ideal processing performance. The above research for pulsed laser processing CFRP material process research provides some references and lays a certain practical foundation for the application of pulsed laser processing composite material process.
2024, 48(1): 92-96.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.015
Abstract:
In order to obtain the visualization and scenarioization effect of laser interference on an infrared imaging system, a simulation system of infrared imaging laser countermeasure was built by using unreal engine. Firstly, the model and scene editing function of unreal engine was used to construct the antagonistic scene and simulate infrared imaging. The mathematical model of laser interference was built to generate the simulation of laser interference spot, and the simulation of different distances, different infrared imaging fields of view, and different laser incident angles were realized. The images before and after the interference were compared and analyzed. The results show that when the infrared imaging field of view remains unchanged, the interference distance decreases from 3.7 km to 2.9 km and 2 km, and the interference distance remains unchanged, the infrared imaging field of view decreases from 8° to 6° and 4°. In both cases, the proportion of interference spot area in imaging gradually increases; When the infrared imaging field of view and interference distance remains unchanged, and the laser incidence angle is adjusted within the range of ±4°, the interference spot area remains almost unchanged. This system can simulate the effect of infrared imaging and laser countermeasures and can be used as a basic tool to evaluate the effectiveness of infrared imaging laser countermeasures.
In order to obtain the visualization and scenarioization effect of laser interference on an infrared imaging system, a simulation system of infrared imaging laser countermeasure was built by using unreal engine. Firstly, the model and scene editing function of unreal engine was used to construct the antagonistic scene and simulate infrared imaging. The mathematical model of laser interference was built to generate the simulation of laser interference spot, and the simulation of different distances, different infrared imaging fields of view, and different laser incident angles were realized. The images before and after the interference were compared and analyzed. The results show that when the infrared imaging field of view remains unchanged, the interference distance decreases from 3.7 km to 2.9 km and 2 km, and the interference distance remains unchanged, the infrared imaging field of view decreases from 8° to 6° and 4°. In both cases, the proportion of interference spot area in imaging gradually increases; When the infrared imaging field of view and interference distance remains unchanged, and the laser incidence angle is adjusted within the range of ±4°, the interference spot area remains almost unchanged. This system can simulate the effect of infrared imaging and laser countermeasures and can be used as a basic tool to evaluate the effectiveness of infrared imaging laser countermeasures.
2024, 48(1): 97-104.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.016
Abstract:
In order to control the intensity of the 2-D Airy beam array at the focal point, a simulation study was conducted using the principle of modulation of the Gaussian beam moving in the frequency domain. The results show that the intensity enhancement from 0.85 to 1.1 at the focal point of the 2-D Airy beam array is achieved by shifting the Gaussian beam in the frequency domain, and the operation is flexible and convenient without increasing the number of beams by repeatedly encoding the phase diaphragm to enhance the intensity of the beam at the focal point, and its effect in atmospheric turbulence is simulated, beam intensity enhancement from 0.85 to 1.03 at moderate turbulence intensity. The modulation is of research significance for the laser to resist atmospheric turbulence in the atmosphere and improve the quality of laser communication.
In order to control the intensity of the 2-D Airy beam array at the focal point, a simulation study was conducted using the principle of modulation of the Gaussian beam moving in the frequency domain. The results show that the intensity enhancement from 0.85 to 1.1 at the focal point of the 2-D Airy beam array is achieved by shifting the Gaussian beam in the frequency domain, and the operation is flexible and convenient without increasing the number of beams by repeatedly encoding the phase diaphragm to enhance the intensity of the beam at the focal point, and its effect in atmospheric turbulence is simulated, beam intensity enhancement from 0.85 to 1.03 at moderate turbulence intensity. The modulation is of research significance for the laser to resist atmospheric turbulence in the atmosphere and improve the quality of laser communication.
2024, 48(1): 105-113.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.017
Abstract:
In recent years, non-destructive detection technology based on deep learning has developed rapidly, but traditional neural network technology relies too much on data resources and cannot use the physical prior knowledge implied in the data, which has many limitations. In order to solve this problem, physical-informed neural networks (PINN) were used in this paper. Based on the wave equation of ultrasonic propagation, the forward PINN model of laser ultrasonic single-mode (surface wave) wave field was trained by using the data of numerical calculation, and the inverse PINN model for solving laser ultrasonic single-mode wave field parameters was further established; therefore, the forward imaging and inverse parameter deduction of laser ultrasonic field were carried out. The results show that when detection points do not contain the excitation point, the forward PINN can obtain a high-precision wave field image when the data volume is only 10%, which is an order of magnitude lower than the original wave field; even when the excitation point is included, the reverse PINN can not only reconstruct the wave field by using 25% of the wave field data, but also solve the parameters of the control equation without artificial analysis, and the error of the parameters with the original wave field data is within 5%. Compared with the traditional laser ultrasonic field modeling, the physical model built by PINN is simpler, which can automatically obtain the parameters of the control equation and has better robustness. This research can provide a reference for wave field reconstruction and parameter inversion laser ultrasonic nondestructive testing technology, so PINN has broad application prospects in the field of laser ultrasonic.
In recent years, non-destructive detection technology based on deep learning has developed rapidly, but traditional neural network technology relies too much on data resources and cannot use the physical prior knowledge implied in the data, which has many limitations. In order to solve this problem, physical-informed neural networks (PINN) were used in this paper. Based on the wave equation of ultrasonic propagation, the forward PINN model of laser ultrasonic single-mode (surface wave) wave field was trained by using the data of numerical calculation, and the inverse PINN model for solving laser ultrasonic single-mode wave field parameters was further established; therefore, the forward imaging and inverse parameter deduction of laser ultrasonic field were carried out. The results show that when detection points do not contain the excitation point, the forward PINN can obtain a high-precision wave field image when the data volume is only 10%, which is an order of magnitude lower than the original wave field; even when the excitation point is included, the reverse PINN can not only reconstruct the wave field by using 25% of the wave field data, but also solve the parameters of the control equation without artificial analysis, and the error of the parameters with the original wave field data is within 5%. Compared with the traditional laser ultrasonic field modeling, the physical model built by PINN is simpler, which can automatically obtain the parameters of the control equation and has better robustness. This research can provide a reference for wave field reconstruction and parameter inversion laser ultrasonic nondestructive testing technology, so PINN has broad application prospects in the field of laser ultrasonic.
2024, 48(1): 114-120.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.018
Abstract:
In order to solve the problem of poor applicability and high false alarm rate of target detection algorithm in unmanned aerial vehicle (UAV) detection systems in different scenarios, a UAV detection system based on a field-programmable gate array(FPGA) and digital signal processor architecture was designed by using infrared small target detection algorithm which could be applied to different complex backgrounds. Firstly, a bilateral filter algorithm was used to smooth the background and preserve the edge of the target region. Then, an improved multi-scale top-hat algorithm was adopted to enhance the target and suppress the background to improve the contrast difference between the target and the surrounding area. Finally, the adaptive threshold segmentation method based on maximum and average values was used to extract the target. The experimental results show that the detection rate of the system is 98.15%, and the overall delay is 33.33 ms. Compared with the existing typical infrared small target detection algorithms, the signal-to-noise ratio gain and background suppression factor of this proposed algorithm are increased by 6.8 times and 7.44 times on average, respectively, which effectively suppresses the background and enhances the target. The algorithm can effectively solve the problem of infrared small target detection in complex backgrounds, and it is helpful to improve the applicable ability and detection ability of the UAV detection system in different scenarios.
In order to solve the problem of poor applicability and high false alarm rate of target detection algorithm in unmanned aerial vehicle (UAV) detection systems in different scenarios, a UAV detection system based on a field-programmable gate array(FPGA) and digital signal processor architecture was designed by using infrared small target detection algorithm which could be applied to different complex backgrounds. Firstly, a bilateral filter algorithm was used to smooth the background and preserve the edge of the target region. Then, an improved multi-scale top-hat algorithm was adopted to enhance the target and suppress the background to improve the contrast difference between the target and the surrounding area. Finally, the adaptive threshold segmentation method based on maximum and average values was used to extract the target. The experimental results show that the detection rate of the system is 98.15%, and the overall delay is 33.33 ms. Compared with the existing typical infrared small target detection algorithms, the signal-to-noise ratio gain and background suppression factor of this proposed algorithm are increased by 6.8 times and 7.44 times on average, respectively, which effectively suppresses the background and enhances the target. The algorithm can effectively solve the problem of infrared small target detection in complex backgrounds, and it is helpful to improve the applicable ability and detection ability of the UAV detection system in different scenarios.
2024, 48(1): 121-126.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.019
Abstract:
In order to solve the problem of online assessment of image degradation in retrace compensation infrared imaging system, a quality evaluation method based on the gradient similarity of infrared images was adopted. Based on the idea of a structural similarity algorithm, according to the characteristics of a flyback compensation infrared imaging system, the gradient feature that could effectively measure the degree of image distortion change was extracted, and the average value of the gradient similarity of each sub-image block was calculated, thereby the gradient of the entire image similarity was obtained. The results show that for images with the same degree of degradation, the measured assessment value of the structural similarity algorithm drops from 0.772 to 0.705, and the assessment value of the gradient similarity algorithm drops from 0.700 to 0.543; the gradient similarity algorithm is more sensitive to the quality changes of infrared scan images with different degrees of degradation than the commonly used structural similarity algorithm and does not require external test equipment such as collimators. This study provides a new method for online image quality assessment and optimization of infrared retrace compensation system.
In order to solve the problem of online assessment of image degradation in retrace compensation infrared imaging system, a quality evaluation method based on the gradient similarity of infrared images was adopted. Based on the idea of a structural similarity algorithm, according to the characteristics of a flyback compensation infrared imaging system, the gradient feature that could effectively measure the degree of image distortion change was extracted, and the average value of the gradient similarity of each sub-image block was calculated, thereby the gradient of the entire image similarity was obtained. The results show that for images with the same degree of degradation, the measured assessment value of the structural similarity algorithm drops from 0.772 to 0.705, and the assessment value of the gradient similarity algorithm drops from 0.700 to 0.543; the gradient similarity algorithm is more sensitive to the quality changes of infrared scan images with different degrees of degradation than the commonly used structural similarity algorithm and does not require external test equipment such as collimators. This study provides a new method for online image quality assessment and optimization of infrared retrace compensation system.
2024, 48(1): 127-134.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.020
Abstract:
In order to reduce the computational complexity of the infrared small targets detection algorithm based on tensor low-rank sparse decomposition and improve the detection performance of infrared dim targets, an infrared small target detection algorithm based on the randomized tensor algorithm was proposed. The algorithm combines the spatial-temporal tensor of the image with the randomized algorithm. Firstly, the infrared image sequence was constructed into spatial-temporal tensors as the input of the tensor optimization model, and then the randomized tensor algorithm was applied to solve the tensor optimization problem. Finally, the target image was obtained by restoring the calculated sparse tensor to the image. The results demonstrate that compared with the traditional algorithm based on low-rank sparse decomposition, the proposed algorithm is faster and also has good detection performance. This study provides a reference for the algorithm acceleration of infrared small target detection based on tensor low-rank sparse decomposition.
In order to reduce the computational complexity of the infrared small targets detection algorithm based on tensor low-rank sparse decomposition and improve the detection performance of infrared dim targets, an infrared small target detection algorithm based on the randomized tensor algorithm was proposed. The algorithm combines the spatial-temporal tensor of the image with the randomized algorithm. Firstly, the infrared image sequence was constructed into spatial-temporal tensors as the input of the tensor optimization model, and then the randomized tensor algorithm was applied to solve the tensor optimization problem. Finally, the target image was obtained by restoring the calculated sparse tensor to the image. The results demonstrate that compared with the traditional algorithm based on low-rank sparse decomposition, the proposed algorithm is faster and also has good detection performance. This study provides a reference for the algorithm acceleration of infrared small target detection based on tensor low-rank sparse decomposition.
2024, 48(1): 135-139.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.021
Abstract:
Aiming at the problem of accurate extraction of circle center and ring radius in non-localization interference concentric ring image, taking point light source non-localization interference concentric rings as the object, an algorithm based on image inversion for simultaneous caring of both dark and bright rings was proposed. The reference center was obtained using the Hough circle transformation after the pre-processing of smooth noise reduction. Then intensity outlines with an interval of 5 pixels in the range of [-50, 50] pixels in its x-direction and y-direction, respectively, were taken. With the inversion of each intensity contour line, accurate identification of dark and bright ring peak coordinates, respectively, was achieved. Finally, the accurate extraction of the circle center and radius of the image was achieved by averaging multiple circle parameters after circle regression fitting of obtained series circle center and radius. The results show that the center coordinates of the three bright rings and the three dark rings are very close to each other and have good reproducibility with the maximum deviation of -3.7 pixels to the mean value, i.e., a maximum relative deviation from the mean is -0.15%. The relative error of the radius-square ratio of two adjacent rings to the actual ratio varies between -4.18% and 0.36%, verifying the feasibility of the algorithm. This research is helpful in realizing automatic detection and improving measurement accuracy.
Aiming at the problem of accurate extraction of circle center and ring radius in non-localization interference concentric ring image, taking point light source non-localization interference concentric rings as the object, an algorithm based on image inversion for simultaneous caring of both dark and bright rings was proposed. The reference center was obtained using the Hough circle transformation after the pre-processing of smooth noise reduction. Then intensity outlines with an interval of 5 pixels in the range of [-50, 50] pixels in its x-direction and y-direction, respectively, were taken. With the inversion of each intensity contour line, accurate identification of dark and bright ring peak coordinates, respectively, was achieved. Finally, the accurate extraction of the circle center and radius of the image was achieved by averaging multiple circle parameters after circle regression fitting of obtained series circle center and radius. The results show that the center coordinates of the three bright rings and the three dark rings are very close to each other and have good reproducibility with the maximum deviation of -3.7 pixels to the mean value, i.e., a maximum relative deviation from the mean is -0.15%. The relative error of the radius-square ratio of two adjacent rings to the actual ratio varies between -4.18% and 0.36%, verifying the feasibility of the algorithm. This research is helpful in realizing automatic detection and improving measurement accuracy.
2024, 48(1): 140-144.
doi: 10.7510/jgjs.issn.1001-3806.2024.01.022
Abstract:
In order to realize the rapid and non-destructive automatic recognition of corn plants in farmland, an automatic recognition method of corn plants using the simultaneous localization and mapping(SLAM) point cloud was proposed. The Pegasus SLAM100 hand-held scanner was used to collect the point cloud data of the corn field, making full use of the verticality characteristics of corn plants in the SLAM point cloud and the prior texture characteristics of plants in the scanning process, the top of corn plants were automatically extracted, then the density clustering algorithm was used to distinguish corn plants and automatically identify corn plants. The experimental results show that the method can realize the automatic recognition of corn plants, and the recognition rate is 92.53%. The research has good engineering application reference value in the fields of automatic corn plant identification, crop yield estimation, and intelligent agriculture research.
In order to realize the rapid and non-destructive automatic recognition of corn plants in farmland, an automatic recognition method of corn plants using the simultaneous localization and mapping(SLAM) point cloud was proposed. The Pegasus SLAM100 hand-held scanner was used to collect the point cloud data of the corn field, making full use of the verticality characteristics of corn plants in the SLAM point cloud and the prior texture characteristics of plants in the scanning process, the top of corn plants were automatically extracted, then the density clustering algorithm was used to distinguish corn plants and automatically identify corn plants. The experimental results show that the method can realize the automatic recognition of corn plants, and the recognition rate is 92.53%. The research has good engineering application reference value in the fields of automatic corn plant identification, crop yield estimation, and intelligent agriculture research.
