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RSS2022 Vol. 46, No. 4
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2022, 46(4): 435-443.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.001
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Abstract:
In order to ensure the accuracy of the radar observation data, the first calibration experiment of networked aerosol light detection and ranging (LiDAR) was carried out by Meteorological Observation Center of China Meteorological Administration in september 2017. By adopting the method of single radar's photoelectric system calibration and multi-radar comparison observation calibration based on statistical analysis strategies, the 532nm scattering channel shared by the networked experiment radars was checked and calibrated. After calibration, the relative standard deviation of backscattering coefficient in 532nm channel was reduced from 90.8% to 20.4% in height range of 1km~2km, and from 244.3% to 35.9% in height range of 2km~5km. And the data quality has been greatly improved. In the aerosol lidar calibration experiment, the radar backscattering coefficient difference was significantly reduced, and the consistency of data observation was greatly improved.This work will provide good hardware quality control assurance for aerosol lidar networking applications.
In order to ensure the accuracy of the radar observation data, the first calibration experiment of networked aerosol light detection and ranging (LiDAR) was carried out by Meteorological Observation Center of China Meteorological Administration in september 2017. By adopting the method of single radar's photoelectric system calibration and multi-radar comparison observation calibration based on statistical analysis strategies, the 532nm scattering channel shared by the networked experiment radars was checked and calibrated. After calibration, the relative standard deviation of backscattering coefficient in 532nm channel was reduced from 90.8% to 20.4% in height range of 1km~2km, and from 244.3% to 35.9% in height range of 2km~5km. And the data quality has been greatly improved. In the aerosol lidar calibration experiment, the radar backscattering coefficient difference was significantly reduced, and the consistency of data observation was greatly improved.This work will provide good hardware quality control assurance for aerosol lidar networking applications.
2022, 46(4): 444-453.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.002
Abstract:
Particle size measurement technology is widely used in many fields such as energy, materials, medicine, chemical industry, metallurgy, electronics, machinery, light industry, construction, etc., and has a very important meaning for improving product quality, increasing production efficiency, reducing energy consumption, realizing precision medicine, monitoring environmental pollution, etc. The particle size measurement method based on the optical principle has the advantages of fast response speed, and the particle size measurement range can reach nanometer level. However, there are still some problems in practical applications and need to be continuously improved. Three types of particle size measurement methods based on optical principles: Microscopy, light scattering, and laser imaging were summarized in this paper, including the measurement principles, measurement ranges, advantages and disadvantages, and application areas of various methods. On this basis, the prospects for the research of particle size measurement were prospected
Particle size measurement technology is widely used in many fields such as energy, materials, medicine, chemical industry, metallurgy, electronics, machinery, light industry, construction, etc., and has a very important meaning for improving product quality, increasing production efficiency, reducing energy consumption, realizing precision medicine, monitoring environmental pollution, etc. The particle size measurement method based on the optical principle has the advantages of fast response speed, and the particle size measurement range can reach nanometer level. However, there are still some problems in practical applications and need to be continuously improved. Three types of particle size measurement methods based on optical principles: Microscopy, light scattering, and laser imaging were summarized in this paper, including the measurement principles, measurement ranges, advantages and disadvantages, and application areas of various methods. On this basis, the prospects for the research of particle size measurement were prospected
2022, 46(4): 454-459.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.003
Abstract:
In order to study the influence of electrically controlled phase delay on the polarization state of vector vortices, a full Stokes polarization measurement for electrically controlled polarization vortexing was built by using a liquid crystal variable retarder and a liquid crystal q wave-plate. Muller matrix analysis and experimental verification of Stokes parameter transmission characteristics of electronically controlled vector vortices were presented. By continuous phase control of the input polarized light, the polarization regulation evolution of the output light beam was obtained after it passes through the tuned q wave-plate. The results show that the electrically controlled phase delay can change the ellipsicity of the local polarization of the angular and radial polarized light, and the change of the polarization state can affect the output intensity of the vector vortex light. The research is of great significance to the exploration of polarization conversion of electrically controlled vector vortices.
In order to study the influence of electrically controlled phase delay on the polarization state of vector vortices, a full Stokes polarization measurement for electrically controlled polarization vortexing was built by using a liquid crystal variable retarder and a liquid crystal q wave-plate. Muller matrix analysis and experimental verification of Stokes parameter transmission characteristics of electronically controlled vector vortices were presented. By continuous phase control of the input polarized light, the polarization regulation evolution of the output light beam was obtained after it passes through the tuned q wave-plate. The results show that the electrically controlled phase delay can change the ellipsicity of the local polarization of the angular and radial polarized light, and the change of the polarization state can affect the output intensity of the vector vortex light. The research is of great significance to the exploration of polarization conversion of electrically controlled vector vortices.
2022, 46(4): 460-465.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.004
Abstract:
In order to reduce the wake separation between a ARJ21 aircraft and its front aircraft and to improve the airspace capacity and airport operation efficiency, theoretical analysis and experimental verification were carried out based on the actual detection of aircraft wake vortex data by airport wind lidar combined with the domestic aircraft ARJ21 aerodynamic response model. The aerodynamic force and moment of a ARJ21 aircraft under the action of different front aircraft wake were obtained. The results show that the ARJ21 is in no bump state when follows a B747 with an interval of 9.3km, and the rolling moment coefficient is less than the limit range. When follows a A320 or B737 with an interval of 6km, the ARJ21 is in the state of no turbulence, and the rolling moment coefficient is less than the limit range. The results show that the wake separation of a ARJ21 aircraft has a certain reduction space.
In order to reduce the wake separation between a ARJ21 aircraft and its front aircraft and to improve the airspace capacity and airport operation efficiency, theoretical analysis and experimental verification were carried out based on the actual detection of aircraft wake vortex data by airport wind lidar combined with the domestic aircraft ARJ21 aerodynamic response model. The aerodynamic force and moment of a ARJ21 aircraft under the action of different front aircraft wake were obtained. The results show that the ARJ21 is in no bump state when follows a B747 with an interval of 9.3km, and the rolling moment coefficient is less than the limit range. When follows a A320 or B737 with an interval of 6km, the ARJ21 is in the state of no turbulence, and the rolling moment coefficient is less than the limit range. The results show that the wake separation of a ARJ21 aircraft has a certain reduction space.
2022, 46(4): 466-473.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.005
Abstract:
In order to solve the problems of difficulty in setting multiple feature thresholds and low generality in road extraction based on airborne light detection and ranging (LiDAR) point cloud, a random forest classification model was used to extract road point cloud and then obtain road center line. Firstly, the ground point cloud was obtained by progressive cryptography triangulation filtering. According to the characteristics of mountain roads, the slope, roughness, height difference variance, point density and reflection intensity of each point in the neighborhood of the ground point cloud were calculated, and the classification characteristics of the component points were calculated. Then, positive and negative samples were collected manually to train the random forest classification model of point cloud. The ground point cloud was classified by the model to get the initial road point cloud. And then, the road point cloud was rifined through the algorithm of density-based spatial clustering of application with noise (DBSCAN). Finally, the road point cloud was vectored to obtain the road center line. The results show that the accuracy of road point cloud extraction is 95.29%, the integrity rate is 92.96%, and the extraction quality is 88.88%, respectively. This method can solve the problem of difficult to determine multiple thresholds, and can extract the mountain road point cloud with high precision, and then obtain the effective road center line, which has certain reference value for the study of mountain road information.
In order to solve the problems of difficulty in setting multiple feature thresholds and low generality in road extraction based on airborne light detection and ranging (LiDAR) point cloud, a random forest classification model was used to extract road point cloud and then obtain road center line. Firstly, the ground point cloud was obtained by progressive cryptography triangulation filtering. According to the characteristics of mountain roads, the slope, roughness, height difference variance, point density and reflection intensity of each point in the neighborhood of the ground point cloud were calculated, and the classification characteristics of the component points were calculated. Then, positive and negative samples were collected manually to train the random forest classification model of point cloud. The ground point cloud was classified by the model to get the initial road point cloud. And then, the road point cloud was rifined through the algorithm of density-based spatial clustering of application with noise (DBSCAN). Finally, the road point cloud was vectored to obtain the road center line. The results show that the accuracy of road point cloud extraction is 95.29%, the integrity rate is 92.96%, and the extraction quality is 88.88%, respectively. This method can solve the problem of difficult to determine multiple thresholds, and can extract the mountain road point cloud with high precision, and then obtain the effective road center line, which has certain reference value for the study of mountain road information.
2022, 46(4): 474-480.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.006
Abstract:
In order to obtain welds with low porosity, complete melting of the glass frit, and good morphology, a mathematical model was established according to the Box-Behnken design principle in the response surface method to study the proportion of weld defects in the glass laser welding and the process parameters including pre-sintering peak temperature, laser power, welding speed, and defocus. Based on this model, the interactive influence trend of each process parameter on the proportion of weld defect area was analyzed, and then the process parameters were optimized. The experimental verification was carried out under the optimized conditions of pre-sintering peak temperature 440℃, laser power 37W, welding speed 0.1m/min, and defocusing distance 14.4mm.The results show that the sum of the pore area and the incomplete melting area of the frit accounts for only 0.512% of the total weld area under the optimized process parameters. The experimental results are consistent with the model predictions. The weld surface morphology is good, and the weld shear strength is 17.765MPa, which is higher than the standard value, indicating that the optimized process parameters under the model are reasonable.
In order to obtain welds with low porosity, complete melting of the glass frit, and good morphology, a mathematical model was established according to the Box-Behnken design principle in the response surface method to study the proportion of weld defects in the glass laser welding and the process parameters including pre-sintering peak temperature, laser power, welding speed, and defocus. Based on this model, the interactive influence trend of each process parameter on the proportion of weld defect area was analyzed, and then the process parameters were optimized. The experimental verification was carried out under the optimized conditions of pre-sintering peak temperature 440℃, laser power 37W, welding speed 0.1m/min, and defocusing distance 14.4mm.The results show that the sum of the pore area and the incomplete melting area of the frit accounts for only 0.512% of the total weld area under the optimized process parameters. The experimental results are consistent with the model predictions. The weld surface morphology is good, and the weld shear strength is 17.765MPa, which is higher than the standard value, indicating that the optimized process parameters under the model are reasonable.
2022, 46(4): 481-485.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.007
Abstract:
In order to clarify the influence of the distance between laser and wire on the process of laser welding with filler wire, theoretical analysis and experimental verification on the relationship between surfacing tests and different distances of laser and wire in three laser mode have been carried out by using high-speed camera, appearance inspection, and macroscopic metallography. The data about the influence of the distance between laser and wire on the stability of welding wire melting, droplet transfer, molten pool fluctuation, and weld solidification during filler wire welding was obtained. The results show that: When the distance changes from -5mm to +5mm, the droplet transition goes through the stages of "droplet→droplet+liquid bridge→liquid bridge→droplet+liquid bridge". With the same distance, the penetration depth of the laser mode from the largest to the smallest is respectively single-beam laser mode, dual-beam laser serial mode, and dual-beam parallel mode, and even the weld offset and no penetration appears at the same time. In addition, the single-beam mode and the dual-beam serial mode have similar effects on the wire and the molten pool, while the dual-beam parallel mode with different energy distributions has the different effect. With the increase of the defocus, the penetration depth of the weld is rapidly reduced from the maximum value of 409.8μm to 282.6μm during the single-beam laser welding. While the maximum penetration depth of the weld is only 328.4μm in the dual-beam laser serial mode, which decreases as the defocusing amount decreases, but the weld cross-section is asymmetrical at positive defocusing amount. In the dual-beam laser parallel welding mode, the weld has no penetration when the welding wire is biased to the low-power laser beam; but a small penetration weld of only 226.5μm is formed as the welding wire moves to the high-power laser beam. This research provides a reference for laser additive manufacturing and welding of aluminum alloy.
In order to clarify the influence of the distance between laser and wire on the process of laser welding with filler wire, theoretical analysis and experimental verification on the relationship between surfacing tests and different distances of laser and wire in three laser mode have been carried out by using high-speed camera, appearance inspection, and macroscopic metallography. The data about the influence of the distance between laser and wire on the stability of welding wire melting, droplet transfer, molten pool fluctuation, and weld solidification during filler wire welding was obtained. The results show that: When the distance changes from -5mm to +5mm, the droplet transition goes through the stages of "droplet→droplet+liquid bridge→liquid bridge→droplet+liquid bridge". With the same distance, the penetration depth of the laser mode from the largest to the smallest is respectively single-beam laser mode, dual-beam laser serial mode, and dual-beam parallel mode, and even the weld offset and no penetration appears at the same time. In addition, the single-beam mode and the dual-beam serial mode have similar effects on the wire and the molten pool, while the dual-beam parallel mode with different energy distributions has the different effect. With the increase of the defocus, the penetration depth of the weld is rapidly reduced from the maximum value of 409.8μm to 282.6μm during the single-beam laser welding. While the maximum penetration depth of the weld is only 328.4μm in the dual-beam laser serial mode, which decreases as the defocusing amount decreases, but the weld cross-section is asymmetrical at positive defocusing amount. In the dual-beam laser parallel welding mode, the weld has no penetration when the welding wire is biased to the low-power laser beam; but a small penetration weld of only 226.5μm is formed as the welding wire moves to the high-power laser beam. This research provides a reference for laser additive manufacturing and welding of aluminum alloy.
2022, 46(4): 486-491.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.008
Abstract:
In order to meet the needs of users for large-field of view angle and high resolution of virtual reality head-mounted displays, the initial structure of the optical system was calculated by using reverse design method, and the optical design software was used for simulation analysis optical structure of coaxial large field of view virtual reality head-mounted display. The results show that three aspheric lenses are used in each channel, and the full field angle is 90°, the exit pupil diameter is 8mm, the exit pupil distance is 13mm, the modulation transfer function is greater than 0.3 at Nyquist frequency of 10.58lp/mm, and the maximum distortion is 6.1%, respectively. Compared with the reference, the resolution is higher, the distortion is reduced and aberration balance is reasonable. The design provides a reference for optimizing the optical structure of large field of view head-mounted display.
In order to meet the needs of users for large-field of view angle and high resolution of virtual reality head-mounted displays, the initial structure of the optical system was calculated by using reverse design method, and the optical design software was used for simulation analysis optical structure of coaxial large field of view virtual reality head-mounted display. The results show that three aspheric lenses are used in each channel, and the full field angle is 90°, the exit pupil diameter is 8mm, the exit pupil distance is 13mm, the modulation transfer function is greater than 0.3 at Nyquist frequency of 10.58lp/mm, and the maximum distortion is 6.1%, respectively. Compared with the reference, the resolution is higher, the distortion is reduced and aberration balance is reasonable. The design provides a reference for optimizing the optical structure of large field of view head-mounted display.
2022, 46(4): 492-498.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.009
Abstract:
In order to obtain the gradient material composition of parts easily in the part forming process, a selective laser melting additive manufacturing system for gradient materials was developed by using the real-time powder mixing method which integrates multiple powder mixing actions such as impact mixing after synchronous discharge powders, converging mixing through a conical cavity, and air flow mixing. With this system, the experimental verification of gradient material forming was carried out, and the forming effect was analyzed combined with the sample photos, microscopic images, and energy spectrometer detection. The result shows that the gradient materials can be freely added in the horizontal and vertical directions to produce gradient material parts with complex shape and structure in the system. The micro areas composition analysis of the gradient material zones of the gradient material part shows that the dispersion degree of the average mass content of elements in each micro zone is small. The variability coefficient of the main elements in each micro zone is not more than 0.59 when the average powder mixing time of each layer is 10s~15s during selective laser melting process, achieving good mixing uniformity.This research provides a new way for free manufacturing of gradient material parts.
In order to obtain the gradient material composition of parts easily in the part forming process, a selective laser melting additive manufacturing system for gradient materials was developed by using the real-time powder mixing method which integrates multiple powder mixing actions such as impact mixing after synchronous discharge powders, converging mixing through a conical cavity, and air flow mixing. With this system, the experimental verification of gradient material forming was carried out, and the forming effect was analyzed combined with the sample photos, microscopic images, and energy spectrometer detection. The result shows that the gradient materials can be freely added in the horizontal and vertical directions to produce gradient material parts with complex shape and structure in the system. The micro areas composition analysis of the gradient material zones of the gradient material part shows that the dispersion degree of the average mass content of elements in each micro zone is small. The variability coefficient of the main elements in each micro zone is not more than 0.59 when the average powder mixing time of each layer is 10s~15s during selective laser melting process, achieving good mixing uniformity.This research provides a new way for free manufacturing of gradient material parts.
2022, 46(4): 499-510.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.010
Abstract:
As a radiation source with the wide spectrum, laser-induced plasma can produce X-ray, ultraviolet, visible, infrared, terahertz, and microwave radiation. It has high practical value and can be used in astrophysics, inertial confinement fusion, biomedicine, materials science, spectral analyses, environmental engineering, information technology, ultrafast technology, lithography technology, imaging technology, radar technology, and semiconductor technology, etc. Up to now, most of the literatures about the radiation characteristics of laser-induced plasma concentrate on the interaction between lasers and matter in a certain wave band, while the mechanism of radiation production is not fully understood, and there is still a lack of comprehensive introductions of the researches on a wide spectrum. The radiation characteristics of laser-induced plasma are systematically classified from the point of view of both electromagnetic radiation spectra and radiation mechanisms in this review. The research results of relevant teams at home and abroad are summarized and analyzed, especially the physical relationship between plasma and spectral radiation is explored from different perspectives. The radiation characteristics of laser-induced plasma in various bands are introduced, and the related factors affecting the radiation are discussed. Finally, the research prospect of infrared band and terahertz band are prospected.
As a radiation source with the wide spectrum, laser-induced plasma can produce X-ray, ultraviolet, visible, infrared, terahertz, and microwave radiation. It has high practical value and can be used in astrophysics, inertial confinement fusion, biomedicine, materials science, spectral analyses, environmental engineering, information technology, ultrafast technology, lithography technology, imaging technology, radar technology, and semiconductor technology, etc. Up to now, most of the literatures about the radiation characteristics of laser-induced plasma concentrate on the interaction between lasers and matter in a certain wave band, while the mechanism of radiation production is not fully understood, and there is still a lack of comprehensive introductions of the researches on a wide spectrum. The radiation characteristics of laser-induced plasma are systematically classified from the point of view of both electromagnetic radiation spectra and radiation mechanisms in this review. The research results of relevant teams at home and abroad are summarized and analyzed, especially the physical relationship between plasma and spectral radiation is explored from different perspectives. The radiation characteristics of laser-induced plasma in various bands are introduced, and the related factors affecting the radiation are discussed. Finally, the research prospect of infrared band and terahertz band are prospected.
2022, 46(4): 511-515.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.011
Abstract:
In order to improve capability of a fiber coherent light detection and ranging (LiDAR), antenna characters were analyzed with modeling method. Based on the principle of backward propagating local light, the influence of antenna aperture on signal-to-noise ratio was discussed, and the influence of pupil truncation ratio on antenna efficiency was analyzed. The definition of coupling efficiency was proposed, and the influence of atmospheric refractive constant on d coupling efficiency and range was researched. By building experimental platform to obtain signal to noise ratio and frequency spectrum intensity in different distance gates, the simulation results were verified. The results show that when the range changes from 7km to 10km, the optimal antenna aperture and pupil truncation ratio were 100mm and 0.8, respectively. Moreover, compared with weak turbulence, strong turbulence makes range decrease by 30% for the same system. The research has important theoretical significance and practical value for optimized design of antenna.
In order to improve capability of a fiber coherent light detection and ranging (LiDAR), antenna characters were analyzed with modeling method. Based on the principle of backward propagating local light, the influence of antenna aperture on signal-to-noise ratio was discussed, and the influence of pupil truncation ratio on antenna efficiency was analyzed. The definition of coupling efficiency was proposed, and the influence of atmospheric refractive constant on d coupling efficiency and range was researched. By building experimental platform to obtain signal to noise ratio and frequency spectrum intensity in different distance gates, the simulation results were verified. The results show that when the range changes from 7km to 10km, the optimal antenna aperture and pupil truncation ratio were 100mm and 0.8, respectively. Moreover, compared with weak turbulence, strong turbulence makes range decrease by 30% for the same system. The research has important theoretical significance and practical value for optimized design of antenna.
Scaled experiments on thermal blooming of shortwave infrared laser propagation through water surface
2022, 46(4): 516-518.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.012
Abstract:
To verify the thermal blooming effect while high energy laser propagates through the atmosphere above the water surface, an innovative method of scaled experiment was applied to overcome the difficult of complexity and expensiveness of high energy laser system with big aperture. One effective experimental method of laser propagation through water surface was designed based on theoretical analysis. The wavelength of laser is about 1000nm. The experimental results show that: The thermal blooming could be ignored while choosing suitable laser power and beam diameter. And the results are also helpful for the design of high energy laser system with big aperture.
To verify the thermal blooming effect while high energy laser propagates through the atmosphere above the water surface, an innovative method of scaled experiment was applied to overcome the difficult of complexity and expensiveness of high energy laser system with big aperture. One effective experimental method of laser propagation through water surface was designed based on theoretical analysis. The wavelength of laser is about 1000nm. The experimental results show that: The thermal blooming could be ignored while choosing suitable laser power and beam diameter. And the results are also helpful for the design of high energy laser system with big aperture.
2022, 46(4): 519-524.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.013
Abstract:
To improve the accuracy of indoor visible light positioning, the received signal strength indication visible light positioning method based on Levy flight mutation mechanism combined with adaptive movement factor improved golden sine algorithm was adopted. The light-emithing diode lights on the indoor roof were arranged in a 3×3 grid, and the distance d between the unknown node and the reference node was obtained through the Lambertian model after receiving the light intensity signal. The Levy flight mutation mechanism was used to increase the diversity of the algorithm's search space, and the adaptive movement factor is used to increase the algorithm's convergence speed, so that individual updates were less restricted by local extreme values. The simulation shows that the average positioning error of the improved algorithm is 1cm, and the average number of iterations is 40~80. Therefore, the speed and precise positioning of the improved golden sine algorithm are improved, which is helpful for real-time and rapid positioning of large indoor places.
To improve the accuracy of indoor visible light positioning, the received signal strength indication visible light positioning method based on Levy flight mutation mechanism combined with adaptive movement factor improved golden sine algorithm was adopted. The light-emithing diode lights on the indoor roof were arranged in a 3×3 grid, and the distance d between the unknown node and the reference node was obtained through the Lambertian model after receiving the light intensity signal. The Levy flight mutation mechanism was used to increase the diversity of the algorithm's search space, and the adaptive movement factor is used to increase the algorithm's convergence speed, so that individual updates were less restricted by local extreme values. The simulation shows that the average positioning error of the improved algorithm is 1cm, and the average number of iterations is 40~80. Therefore, the speed and precise positioning of the improved golden sine algorithm are improved, which is helpful for real-time and rapid positioning of large indoor places.
2022, 46(4): 525-531.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.014
Abstract:
In order to solve the peak-to-average power ratio (PAPR) problem in the direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) underwater visible light communication system, a joint PAPR suppression algorithm based on Vandermonde-like matrix (VLM) precoding and improved adaptive scaling was adopted. Firstly, the frequency domain signal was preceded by VLM to reduce the autocorrelation of the signal, and then the time domain signal was adaptively scaled to reduce the nonlinear distortion caused by light-emitting diode (LED). Finally, the PAPR suppression effect of the system was realized. The results show that when the complementary commulative distribution function was 10-3, the PAPR of the joint algorithm was reduced by 3.2dB compared with the original system. Therefore, this research is helpful to suppress the PAPR of DCO-OFDM underwater visible light communication system.
In order to solve the peak-to-average power ratio (PAPR) problem in the direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) underwater visible light communication system, a joint PAPR suppression algorithm based on Vandermonde-like matrix (VLM) precoding and improved adaptive scaling was adopted. Firstly, the frequency domain signal was preceded by VLM to reduce the autocorrelation of the signal, and then the time domain signal was adaptively scaled to reduce the nonlinear distortion caused by light-emitting diode (LED). Finally, the PAPR suppression effect of the system was realized. The results show that when the complementary commulative distribution function was 10-3, the PAPR of the joint algorithm was reduced by 3.2dB compared with the original system. Therefore, this research is helpful to suppress the PAPR of DCO-OFDM underwater visible light communication system.
2022, 46(4): 532-537.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.015
Abstract:
In order to study the classification method of incomplete eggshells and the food safety problems in some egg products, laser-induced breakdown spectroscopy(LIBS) and back propagation neural network(BPNN) were combined to explore the elements of eggshells, to distinguish different types of eggshells, and to detect pollution elements in eggshells, respectively. The results show that the duck eggshell contains Si, Cu, Ca, Mg, C, Na, Al and other elements. LIBS was applied to measure and calibrate the element composition in contaminated preserved eggshells, and the obvious lead characteristic peaks were successfully detected. LIBS and BPNN were combined to quickly distinguish eggshell, duck eggshell, and quail eggshell, and an accuracy rate of 94.167% was obtained. The same method was employed to study on duck eggshell and preserved eggshell to explore the classification of eggshells with different production methods, and an accuracy rate of 97.5% was obtained. The combination of LIBS and BPNN provides a new research method for egg classification and distinguishing.
In order to study the classification method of incomplete eggshells and the food safety problems in some egg products, laser-induced breakdown spectroscopy(LIBS) and back propagation neural network(BPNN) were combined to explore the elements of eggshells, to distinguish different types of eggshells, and to detect pollution elements in eggshells, respectively. The results show that the duck eggshell contains Si, Cu, Ca, Mg, C, Na, Al and other elements. LIBS was applied to measure and calibrate the element composition in contaminated preserved eggshells, and the obvious lead characteristic peaks were successfully detected. LIBS and BPNN were combined to quickly distinguish eggshell, duck eggshell, and quail eggshell, and an accuracy rate of 94.167% was obtained. The same method was employed to study on duck eggshell and preserved eggshell to explore the classification of eggshells with different production methods, and an accuracy rate of 97.5% was obtained. The combination of LIBS and BPNN provides a new research method for egg classification and distinguishing.
2022, 46(4): 538-544.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.016
Abstract:
In order to obtain a stable laser double arc hybrid welding process, the space reconstruction technique was used to calculate the largest Lyapunov exponent(LLE) of the characteristic current in the welding process with different wire spacing. The theoretical analysis and experimental verification experiments were carried out. LLE and its standard deviation data of the welding current with different wire spacing were obtained, When the laser was located in the center of two arcs, LLE was less than 0.61 and the distance was 3mm~9mm, the heat source coupling was good and the welding process was stable. When the welding wire spacing was 7mm, the weld surface was smooth and the penetration was the largest. LLE can be used as the criterion of welding stability, and it was in good agreement with the observation results of electric signal, arc shape and droplet transfer. This result was helpful to ensure the stability and safety of welding process.
In order to obtain a stable laser double arc hybrid welding process, the space reconstruction technique was used to calculate the largest Lyapunov exponent(LLE) of the characteristic current in the welding process with different wire spacing. The theoretical analysis and experimental verification experiments were carried out. LLE and its standard deviation data of the welding current with different wire spacing were obtained, When the laser was located in the center of two arcs, LLE was less than 0.61 and the distance was 3mm~9mm, the heat source coupling was good and the welding process was stable. When the welding wire spacing was 7mm, the weld surface was smooth and the penetration was the largest. LLE can be used as the criterion of welding stability, and it was in good agreement with the observation results of electric signal, arc shape and droplet transfer. This result was helpful to ensure the stability and safety of welding process.
2022, 46(4): 545-550.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.017
Abstract:
In order to solve the demodulation distortion caused by light intensity disturbance and modulation depth drift in traditional phase generated carrier (PGC) demodulation algorithm, an improved PGC demodulation algorithm based on fundamental wave mixing and differential self multiplication was adopted. And relevant theoretical analysis and simulation verification were carried out. The results show that the distortion caused by light intensity disturbance can be suppressed, and the demodulation efficiency can be improved at the same timeby using this algorithm. When the light intensity disturbance of 1.5rad~3.5rad was introduced, the signal-to-noise and distortion ratio of nearly 30dB was obtained, which was 15dB higher than the traditional discrete cosine transform (PGC-DCM) algorithm. In addition, the dependence on modulation depth C can be eliminated, and the total harmonic distortion of less than 0.1% and the signal-to-noise ratio of 30dB can be achieved, which was nearly 10dB higher than the traditional algorithm, and the corresponding linearity was up to 99.99%. It provides a new scheme for the demodulation of optical fiber interferometric sensor.
In order to solve the demodulation distortion caused by light intensity disturbance and modulation depth drift in traditional phase generated carrier (PGC) demodulation algorithm, an improved PGC demodulation algorithm based on fundamental wave mixing and differential self multiplication was adopted. And relevant theoretical analysis and simulation verification were carried out. The results show that the distortion caused by light intensity disturbance can be suppressed, and the demodulation efficiency can be improved at the same timeby using this algorithm. When the light intensity disturbance of 1.5rad~3.5rad was introduced, the signal-to-noise and distortion ratio of nearly 30dB was obtained, which was 15dB higher than the traditional discrete cosine transform (PGC-DCM) algorithm. In addition, the dependence on modulation depth C can be eliminated, and the total harmonic distortion of less than 0.1% and the signal-to-noise ratio of 30dB can be achieved, which was nearly 10dB higher than the traditional algorithm, and the corresponding linearity was up to 99.99%. It provides a new scheme for the demodulation of optical fiber interferometric sensor.
2022, 46(4): 551-555.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.018
Abstract:
In order to improve the surface hardness and wear reduction of TC4 alloy, Fe60-TiO2 composite coatings with different proportions were prepared on the surface of TC4 plate by using several groups of process parameters (different power and different TiO2 powder content). The macroscopic morphology, surface Vickers hardness, and wear reduction property of the cladding layer were analyzed. The results show that when the laser power is 500W and the mass fraction of TiO2 is 0.10, the surface of the cladding layer is smooth. According to the X-ray diffraction analysis, many Ti compounds are formed in the cladding layer, which is very beneficial to improve the hardness and wear reduction of the cladding layer. The hardness of the cladding layer is about 2.5 times higher than that of the substrate. The average friction coefficient of the cladding layer is about 0.46. The results have a certain guiding effect on the hardness and wear reduction process parameters of Fe based composite coating on TC4 titanium alloy surface.
In order to improve the surface hardness and wear reduction of TC4 alloy, Fe60-TiO2 composite coatings with different proportions were prepared on the surface of TC4 plate by using several groups of process parameters (different power and different TiO2 powder content). The macroscopic morphology, surface Vickers hardness, and wear reduction property of the cladding layer were analyzed. The results show that when the laser power is 500W and the mass fraction of TiO2 is 0.10, the surface of the cladding layer is smooth. According to the X-ray diffraction analysis, many Ti compounds are formed in the cladding layer, which is very beneficial to improve the hardness and wear reduction of the cladding layer. The hardness of the cladding layer is about 2.5 times higher than that of the substrate. The average friction coefficient of the cladding layer is about 0.46. The results have a certain guiding effect on the hardness and wear reduction process parameters of Fe based composite coating on TC4 titanium alloy surface.
2022, 46(4): 556-560.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.019
Abstract:
In order to study the relationship between the radiation of high-energy electrons and the electron's initial position, a scattering model of a single high-energy electron interacting with a Gaussian laser pulse was constructed according to the Lagrange's equation. And the method of numerical simulation was adopted to obtain the trajectory of the electron and the spatial radiation characteristics of the scattered light by MATLAB. The influence of the initial position of the electron on the space energy radiation was discussed in detail. The results show that the initially static high-energy electron first oscillates in the +z direction in a plane, and then travels along a straight line after interacting with the linearly polarized tightly focused intense laser. Both the maximum radiated energy and its corresponding radiation direction are greatly affected by the electron's initial position, while a peak value of the former exists as the initial position of the electron moves to the positive direction of z axis, and the azimuth angle of the latter stays unchanged while the polar angle gradually decreasing but finally stabilizing. The maximum radiation energy in the whole space is obtained when the electron is initially set at (0, 0, -7λ0) (λ0 is the wavelength of the laser) with the polar angle and the azimuth angle being 23.5° and 180°, respectively. The research indicates that the highest possible intensity of radiation can be obtained by setting the electron's initial location reasonably.
In order to study the relationship between the radiation of high-energy electrons and the electron's initial position, a scattering model of a single high-energy electron interacting with a Gaussian laser pulse was constructed according to the Lagrange's equation. And the method of numerical simulation was adopted to obtain the trajectory of the electron and the spatial radiation characteristics of the scattered light by MATLAB. The influence of the initial position of the electron on the space energy radiation was discussed in detail. The results show that the initially static high-energy electron first oscillates in the +z direction in a plane, and then travels along a straight line after interacting with the linearly polarized tightly focused intense laser. Both the maximum radiated energy and its corresponding radiation direction are greatly affected by the electron's initial position, while a peak value of the former exists as the initial position of the electron moves to the positive direction of z axis, and the azimuth angle of the latter stays unchanged while the polar angle gradually decreasing but finally stabilizing. The maximum radiation energy in the whole space is obtained when the electron is initially set at (0, 0, -7λ0) (λ0 is the wavelength of the laser) with the polar angle and the azimuth angle being 23.5° and 180°, respectively. The research indicates that the highest possible intensity of radiation can be obtained by setting the electron's initial location reasonably.
2022, 46(4): 561-566.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.020
Abstract:
In order to study the radiation energy distribution of laser pulse width after impact electron, the method of simulation calculation was adopted. Based on Lorentz equation and electron radiation equation, a single electron model of compact focusing laser acting on static single electron was established. The distribution of electron radiation energy produced by laser pulse and electron action under different pulse width was simulated by MATLAB software. The pulse width of femtosecond compact focusing elliptic polarization laser pulse and the peak radiation power between electrons were studied. The simulation results show that when the compact focused laser pulse encounters a stationary single electron, the electron radiates while the laser pulse hits the electron. The scattering radiation accumulates in a sharp cone at the center of the scattering direction. With the increase of laser pulse width, the distribution of radiation power gradually presents a double peak. The wider the pulse width, the smaller the peak value of electron radiation power. When the pulse width is 10λ0, the peak power is only 1% of that when the pulse width is 0.1λ0, and the initial pulse width is λ0=3.33fs. At the same time, the wider the pulse width, the smaller the peak value of the electronic radiation power, the longer the required realization of the peak radiation power, the longer the duration of the peak, the lower the cut-off frequency of the spectrum function, the less high frequency components, and the increase of the harmonic frequency. The results are of great significance to the diagnosis of laser air plasma.
In order to study the radiation energy distribution of laser pulse width after impact electron, the method of simulation calculation was adopted. Based on Lorentz equation and electron radiation equation, a single electron model of compact focusing laser acting on static single electron was established. The distribution of electron radiation energy produced by laser pulse and electron action under different pulse width was simulated by MATLAB software. The pulse width of femtosecond compact focusing elliptic polarization laser pulse and the peak radiation power between electrons were studied. The simulation results show that when the compact focused laser pulse encounters a stationary single electron, the electron radiates while the laser pulse hits the electron. The scattering radiation accumulates in a sharp cone at the center of the scattering direction. With the increase of laser pulse width, the distribution of radiation power gradually presents a double peak. The wider the pulse width, the smaller the peak value of electron radiation power. When the pulse width is 10λ0, the peak power is only 1% of that when the pulse width is 0.1λ0, and the initial pulse width is λ0=3.33fs. At the same time, the wider the pulse width, the smaller the peak value of the electronic radiation power, the longer the required realization of the peak radiation power, the longer the duration of the peak, the lower the cut-off frequency of the spectrum function, the less high frequency components, and the increase of the harmonic frequency. The results are of great significance to the diagnosis of laser air plasma.
2022, 46(4): 567-572.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.021
Abstract:
To solve the surface wear problem of 40Cr steel parts, incorporated with the theory of surface texture, laser phase transformation hardening technology was applied to preparate various shapes (spot and striation) of hard-soft coupling surfaces with regular distribution. Scanning electron microscopy, X-ray diffraction, friction and wear machine and ultra-depth of field microscopy were adopted to analyze the microstructure, physical phase, anti-wear performance, and wear surface morphology of the phase transformation zone. the results show that the cross-section hardness of the spot phase transformation zone is higher than the striation, with the average of (720±3) HV0.1, and the hardening layer is deeper. Martensite, Cr7C3, and Fe7C3 are generated after phase transformation. By comparing the friction coefficient between the untreated surface and the hard-soft coupling surface of 40Cr steel, the friction coefficient of the hard-soft coupling surface is inferior to 0.5 and its fluctuation is smaller which demonstrates great friction stability. In addition, the wear surface damage of the hard-soft coupling surface is small, and the reason of this is that the hard phase could resist the deformation while the soft phase could release the stress concentration and the accumulation of plastic deformations. The soft phase field is mainly pear peeling and adhesion damage, and the hard phase area is mainly small pitting pits. The 900W spot soft-hard coupling surface with the first-rate anti-wear performance. Above all, the conclusion is that the hardening phase with great plastic toughness and a certain proportion (50%) of inerratic surface distribution can markedly increase and promote the anti-wear performance of the material working surface, improve the contact surface of the fraction pair as well as stabilize the friction coefficient, this study can provide a reference for improving the surface wear of 40Cr parts.
To solve the surface wear problem of 40Cr steel parts, incorporated with the theory of surface texture, laser phase transformation hardening technology was applied to preparate various shapes (spot and striation) of hard-soft coupling surfaces with regular distribution. Scanning electron microscopy, X-ray diffraction, friction and wear machine and ultra-depth of field microscopy were adopted to analyze the microstructure, physical phase, anti-wear performance, and wear surface morphology of the phase transformation zone. the results show that the cross-section hardness of the spot phase transformation zone is higher than the striation, with the average of (720±3) HV0.1, and the hardening layer is deeper. Martensite, Cr7C3, and Fe7C3 are generated after phase transformation. By comparing the friction coefficient between the untreated surface and the hard-soft coupling surface of 40Cr steel, the friction coefficient of the hard-soft coupling surface is inferior to 0.5 and its fluctuation is smaller which demonstrates great friction stability. In addition, the wear surface damage of the hard-soft coupling surface is small, and the reason of this is that the hard phase could resist the deformation while the soft phase could release the stress concentration and the accumulation of plastic deformations. The soft phase field is mainly pear peeling and adhesion damage, and the hard phase area is mainly small pitting pits. The 900W spot soft-hard coupling surface with the first-rate anti-wear performance. Above all, the conclusion is that the hardening phase with great plastic toughness and a certain proportion (50%) of inerratic surface distribution can markedly increase and promote the anti-wear performance of the material working surface, improve the contact surface of the fraction pair as well as stabilize the friction coefficient, this study can provide a reference for improving the surface wear of 40Cr parts.
2022, 46(4): 573-578.
doi: 10.7510/jgjs.issn.1001-3806.2022.04.022
Abstract:
In order to study the performance of the photonic microwave signal generated by a semiconductor laser (SL) under optical injection, based on the rate equation of SL and the fiber Bragg grating (FBG) filter theory, the optical spectra, power spectra, and linewidth under different injection parameters were obtained by numerical simulation and theoretical analysis, and the effect of the feedback parameters on the microwave linewidth was also studied. Considering that the generated microwave signal has wide linewidth, a FBG optical feedback was further introduced to narrow the microwave linewidth. The results show that, for the SL subject to optical injection only, the microwave frequency can be continuously tuned and the microwave intensity can be maximized by changing the injection parameters; the microwave linewidth gradually decreases with the increase of feedback strength. Through properly adjusting the feedback parameters, the microwave linewidth can be compressed below 10kHz. The results can provide a theoretical reference for the application of semiconductor laser in the photonic microwave signals generation.
In order to study the performance of the photonic microwave signal generated by a semiconductor laser (SL) under optical injection, based on the rate equation of SL and the fiber Bragg grating (FBG) filter theory, the optical spectra, power spectra, and linewidth under different injection parameters were obtained by numerical simulation and theoretical analysis, and the effect of the feedback parameters on the microwave linewidth was also studied. Considering that the generated microwave signal has wide linewidth, a FBG optical feedback was further introduced to narrow the microwave linewidth. The results show that, for the SL subject to optical injection only, the microwave frequency can be continuously tuned and the microwave intensity can be maximized by changing the injection parameters; the microwave linewidth gradually decreases with the increase of feedback strength. Through properly adjusting the feedback parameters, the microwave linewidth can be compressed below 10kHz. The results can provide a theoretical reference for the application of semiconductor laser in the photonic microwave signals generation.
