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RSS2018 Vol. 42, No. 3
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2018, 42(3): 289-294.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.001
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Abstract:
In recent years, electromagnetic metamaterial has attracted wide attention in many fields since it has special characteristics that natural medium does not possess. Zero refractive index metamaterial(ZRIM) is a material with zero permittivity and zero permeability. It has many unique features in the field of optics, such as wavelength stretching, phase consistency and tunnel effect. Several typical ZRIM structures and the properties implemented in the ZRIM structure were introduced, such as infinite wavelength, uniform field distribution, and so on. The important applications of ZRIM structure in physical optics were discussed, for example, directional emission, emission enhancement, boundary state analysis and light capture. The study on the properties and characteristics of ZRIM provides reference and guidance for the development of new devices and the basic research of new optical elements.
In recent years, electromagnetic metamaterial has attracted wide attention in many fields since it has special characteristics that natural medium does not possess. Zero refractive index metamaterial(ZRIM) is a material with zero permittivity and zero permeability. It has many unique features in the field of optics, such as wavelength stretching, phase consistency and tunnel effect. Several typical ZRIM structures and the properties implemented in the ZRIM structure were introduced, such as infinite wavelength, uniform field distribution, and so on. The important applications of ZRIM structure in physical optics were discussed, for example, directional emission, emission enhancement, boundary state analysis and light capture. The study on the properties and characteristics of ZRIM provides reference and guidance for the development of new devices and the basic research of new optical elements.
2018, 42(3): 295-299.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.002
Abstract:
3-D space position of ground feature points can be quickly obtained by full-waveform airborne laser radars. Compared to other surveying and mapping methods, a full-waveform airborne laser radar has better performance to a certain extent. Firstly, the laser ranging principle of a full-waveform airborne laser radar is introduced. Then the general method of data processing for full-waveform airborne lidar is discussed. The main progress and the research status of data processing technology at home and abroad are summarized. Finally, the key problems in the research of full-waveform lidar data processing are summarized. On this basis, the research prospect of data processing is prospected.
3-D space position of ground feature points can be quickly obtained by full-waveform airborne laser radars. Compared to other surveying and mapping methods, a full-waveform airborne laser radar has better performance to a certain extent. Firstly, the laser ranging principle of a full-waveform airborne laser radar is introduced. Then the general method of data processing for full-waveform airborne lidar is discussed. The main progress and the research status of data processing technology at home and abroad are summarized. Finally, the key problems in the research of full-waveform lidar data processing are summarized. On this basis, the research prospect of data processing is prospected.
2018, 42(3): 300-305.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.003
Abstract:
In order to improve the link gain and transmission distance of radio-over-fiber (RoF) frequency transmission link, ultra-long distributed second-order Raman amplifier structure in L band was used to amplify the light signal. The principle of the distributed 2-order Raman amplifier and the RoF transmission link were explained theoretically. The relationships among them were analyzed by using the coupling equations between signal light, 1-order pumping light, 2-order pumping light and noise. The 1-order radio frequency (RF) signal gain of a RoF transmission system based on ultra-long distributed 2-order Raman amplifier was also obtained. Through numerical simulation and system experiment, the effect of pumping power on on-off gain of ultra-long distributed 2-order Raman amplifier, frequency response and RF gain of RoF transmission system in the range of 0GHz~7GHz, and phase noise of RoF transmission link after the application of ultra-long distributed 2-order Raman amplifier were obtained. The results show that the link gain of 28.1dB is obtained by RoF transmission after the application of an ultra-long distributed 2-order Raman amplifier. Approximate lossless transmission is achieved in optical link with a distance of 80.94km. The on-off gain of RF signal is independent of the frequency of RF signal. The study has important application value in long distance transmission of optical radio frequency links.
In order to improve the link gain and transmission distance of radio-over-fiber (RoF) frequency transmission link, ultra-long distributed second-order Raman amplifier structure in L band was used to amplify the light signal. The principle of the distributed 2-order Raman amplifier and the RoF transmission link were explained theoretically. The relationships among them were analyzed by using the coupling equations between signal light, 1-order pumping light, 2-order pumping light and noise. The 1-order radio frequency (RF) signal gain of a RoF transmission system based on ultra-long distributed 2-order Raman amplifier was also obtained. Through numerical simulation and system experiment, the effect of pumping power on on-off gain of ultra-long distributed 2-order Raman amplifier, frequency response and RF gain of RoF transmission system in the range of 0GHz~7GHz, and phase noise of RoF transmission link after the application of ultra-long distributed 2-order Raman amplifier were obtained. The results show that the link gain of 28.1dB is obtained by RoF transmission after the application of an ultra-long distributed 2-order Raman amplifier. Approximate lossless transmission is achieved in optical link with a distance of 80.94km. The on-off gain of RF signal is independent of the frequency of RF signal. The study has important application value in long distance transmission of optical radio frequency links.
2018, 42(3): 306-310.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.004
Abstract:
In order to solve the problem of short working time and poor endurance of unmanned aerial vehicles (UAV), laser wireless power supply was used in UAV. A set of laser wireless energy supply system based on tracking, capturing and aiming was proposed and designed. After theoretical analysis, the experiment of UAV laser wireless power supply was carried out in the outfield of 200m. The results show that, the overall photoelectric conversion efficiency of the system is about 12%, and the tracking accuracy is better than 500μrad. The study provides a reference for the use of laser tracking and wireless energy supply technology for small space spacecrafts.
In order to solve the problem of short working time and poor endurance of unmanned aerial vehicles (UAV), laser wireless power supply was used in UAV. A set of laser wireless energy supply system based on tracking, capturing and aiming was proposed and designed. After theoretical analysis, the experiment of UAV laser wireless power supply was carried out in the outfield of 200m. The results show that, the overall photoelectric conversion efficiency of the system is about 12%, and the tracking accuracy is better than 500μrad. The study provides a reference for the use of laser tracking and wireless energy supply technology for small space spacecrafts.
2018, 42(3): 311-317.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.005
Abstract:
In order to study overlap ratio and overlap characteristics during pulse laser selective melting forming process, the overlap theoretical models of bow and parabola were adopted, and the forming experiments of single melting point, single cladding and multi-layer block were designed under different conditions to obtain the optimal overlap ratio. The results show that the width of single melting point increases with the increase of exposure time. The optimal overlap ratio between two melting tracks is 30% in the single cladding experiment when exposure time is 40μs~60μs. The overlap ratio is 50% when exposure time is 80μs. The overlap ratio is 60%, when exposure time is 100μs~120μs. The surface morphology of block is slat in the multi-layer block experiment when overlap ratio between two melting tracks is 50%. After the analysis of block density, defect, microstructure and tensile properties, sample density is up to 99.99%, when laser power is 200W, layer thickness is 50μm, exposure time is 100μs, point distance is 65μm and line spacing is 77μm. The research is helpful for understanding overlap characteristics and overlap ratio selection in pulse laser selective melting.
In order to study overlap ratio and overlap characteristics during pulse laser selective melting forming process, the overlap theoretical models of bow and parabola were adopted, and the forming experiments of single melting point, single cladding and multi-layer block were designed under different conditions to obtain the optimal overlap ratio. The results show that the width of single melting point increases with the increase of exposure time. The optimal overlap ratio between two melting tracks is 30% in the single cladding experiment when exposure time is 40μs~60μs. The overlap ratio is 50% when exposure time is 80μs. The overlap ratio is 60%, when exposure time is 100μs~120μs. The surface morphology of block is slat in the multi-layer block experiment when overlap ratio between two melting tracks is 50%. After the analysis of block density, defect, microstructure and tensile properties, sample density is up to 99.99%, when laser power is 200W, layer thickness is 50μm, exposure time is 100μs, point distance is 65μm and line spacing is 77μm. The research is helpful for understanding overlap characteristics and overlap ratio selection in pulse laser selective melting.
2018, 42(3): 318-324.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.006
Abstract:
In order to study photonic band gap of 3-D functional photonic crystal, dispersion curve was calculated by using plane wave expansion method. Correlation calculation formula of plane wave expansion method and function relation of dielectric constant of dielectric sphere were derived. The effects of the adjustable parameter I and dielectric sphere radius R1 on photonic band gap were discussed. The result shows that, 3-D function photonic crystal is cube lattice distribution and air background is filled with medium ball. Compared with conventional 3-D dielectric photonic crystals, 3-D function photonic crystal can obtain the tunable photonic band gap, expand the bandwidth of forbidden band, and increase the number of photonic band gaps. The number, position and bandwidth of photonic band gaps can be tuned by changing the size of tunable parameter I. At the same time, the bandwidth and position of photonic band gaps can be tuned by changing the sphere radius R1 of the medium. The study is helpful for the design of new tunable devices.
In order to study photonic band gap of 3-D functional photonic crystal, dispersion curve was calculated by using plane wave expansion method. Correlation calculation formula of plane wave expansion method and function relation of dielectric constant of dielectric sphere were derived. The effects of the adjustable parameter I and dielectric sphere radius R1 on photonic band gap were discussed. The result shows that, 3-D function photonic crystal is cube lattice distribution and air background is filled with medium ball. Compared with conventional 3-D dielectric photonic crystals, 3-D function photonic crystal can obtain the tunable photonic band gap, expand the bandwidth of forbidden band, and increase the number of photonic band gaps. The number, position and bandwidth of photonic band gaps can be tuned by changing the size of tunable parameter I. At the same time, the bandwidth and position of photonic band gaps can be tuned by changing the sphere radius R1 of the medium. The study is helpful for the design of new tunable devices.
2018, 42(3): 325-330.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.007
Abstract:
In order to study amplification characteristics of a multi-wavelength erbium-doped fiber amplifier (EDFA), steady rate equation for a multi-wavelength Er-doped double cladding fiber amplifier was deduced based on a single frequency amplifier and ignoring the amplified spontaneous emission (ASE). A theoretical model of EDFA was set up. The amplification characteristics of single wavelength amplification, dual wavelength amplification and four-wavelength amplification were numerically simulated and analyzed theoretically by using this model. The results indicate that, the optimum fiber length of the doped fiber amplifier is 8m in case of single wavelength injection. Unlike small signal amplification, the gain spectrum of a high-power EDFA tends to be flat in the range of 1530nm~1560nm. The difference of output power increases linearly with the increase of wavelength interval when double-wavelength signal laser is amplified by EDFA. While wavelength interval is 20nm, the maximum power difference of power balance compensation is 6.855W by adjusting the input signal power ratio. The minimum deviation of output power is 0.28W by adjusting the wavelength interval and power ratio parameter when four-wavelength signal laser is amplified by EDFA. And the gain equalization can be easily achieved within a certain range. The study will be helpful for multi-wavelength Er-doped fiber lasers and their application in laser Doppler radars.
In order to study amplification characteristics of a multi-wavelength erbium-doped fiber amplifier (EDFA), steady rate equation for a multi-wavelength Er-doped double cladding fiber amplifier was deduced based on a single frequency amplifier and ignoring the amplified spontaneous emission (ASE). A theoretical model of EDFA was set up. The amplification characteristics of single wavelength amplification, dual wavelength amplification and four-wavelength amplification were numerically simulated and analyzed theoretically by using this model. The results indicate that, the optimum fiber length of the doped fiber amplifier is 8m in case of single wavelength injection. Unlike small signal amplification, the gain spectrum of a high-power EDFA tends to be flat in the range of 1530nm~1560nm. The difference of output power increases linearly with the increase of wavelength interval when double-wavelength signal laser is amplified by EDFA. While wavelength interval is 20nm, the maximum power difference of power balance compensation is 6.855W by adjusting the input signal power ratio. The minimum deviation of output power is 0.28W by adjusting the wavelength interval and power ratio parameter when four-wavelength signal laser is amplified by EDFA. And the gain equalization can be easily achieved within a certain range. The study will be helpful for multi-wavelength Er-doped fiber lasers and their application in laser Doppler radars.
2018, 42(3): 331-335.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.008
Abstract:
In order to study effect of femtosecond laser pulse energy on the periodic structure of stainless steel surface, the femtosecond laser with pulse width of 50fs and central wavelength of 800nm was used to radiate 304 stainless steel surfaces. Scanning electron microscopy was used to observe the micromorphology and the generation mechanism of different kinds of ripples was analyzed. The results show that with pulse energy from 0.1mJ to 0.3mJ, nanoscale periodic ripple perpendicular to the direction of laser polarization is formed on the surface. With pulse energy from 0.4mJ to 0.7mJ, there is a tendency to produce periodic ripples parallel to the direction of laser polarization. With pulse energy from 0.8mJ to 1.0mJ, obvious micron-scale periodic corrugation parallel to the polarization direction of laser appears on the surface, and the corrugation surface is covered with short periodic corrugation perpendicular to its direction. The study lays the foundation for the subsequent preparation of controllable micromorphology on the surface of stainless steel.
In order to study effect of femtosecond laser pulse energy on the periodic structure of stainless steel surface, the femtosecond laser with pulse width of 50fs and central wavelength of 800nm was used to radiate 304 stainless steel surfaces. Scanning electron microscopy was used to observe the micromorphology and the generation mechanism of different kinds of ripples was analyzed. The results show that with pulse energy from 0.1mJ to 0.3mJ, nanoscale periodic ripple perpendicular to the direction of laser polarization is formed on the surface. With pulse energy from 0.4mJ to 0.7mJ, there is a tendency to produce periodic ripples parallel to the direction of laser polarization. With pulse energy from 0.8mJ to 1.0mJ, obvious micron-scale periodic corrugation parallel to the polarization direction of laser appears on the surface, and the corrugation surface is covered with short periodic corrugation perpendicular to its direction. The study lays the foundation for the subsequent preparation of controllable micromorphology on the surface of stainless steel.
2018, 42(3): 336-340.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.009
Abstract:
In order to improve the stability and accuracy of a fiber Bragg grating(FBG) demodulation system and avoid the problem of nonlinearity of driving voltage and transmission wavelength of a Fabry-Perot(F-P) filter caused by hysteresis, vermicular and temperature changes of the piezoelectric ceramic, a FBG demodulation method was introduced combining with F-P etalon, temperature-compensated reference grating and sensing grating in three separate channels with a tunable ring cavity laser as scanning light source. The method of median filtering and moving average filtering was selected to filter the noise. A spectral correlation peak-seeking algorithm based on intensity threshold was used to find the location of peak value of reflection spectrum more accurately. Through theoretical analysis and experimental verification, the results show that wavelength long-term stability of demodulation scheme with each separated channel can reach 0.4pm and the linearity between temperature and wavelength is higher than 99.90%. The system can measure the stability of the parameters such as temperature and strain.
In order to improve the stability and accuracy of a fiber Bragg grating(FBG) demodulation system and avoid the problem of nonlinearity of driving voltage and transmission wavelength of a Fabry-Perot(F-P) filter caused by hysteresis, vermicular and temperature changes of the piezoelectric ceramic, a FBG demodulation method was introduced combining with F-P etalon, temperature-compensated reference grating and sensing grating in three separate channels with a tunable ring cavity laser as scanning light source. The method of median filtering and moving average filtering was selected to filter the noise. A spectral correlation peak-seeking algorithm based on intensity threshold was used to find the location of peak value of reflection spectrum more accurately. Through theoretical analysis and experimental verification, the results show that wavelength long-term stability of demodulation scheme with each separated channel can reach 0.4pm and the linearity between temperature and wavelength is higher than 99.90%. The system can measure the stability of the parameters such as temperature and strain.
2018, 42(3): 341-345.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.010
Abstract:
In order to study microstructure and microhardness distributions of welded joint of high nitrogen steel at different heat inputs, high nitrogen austenitic stainless steel was welded by Nd:YAG-MAG hybrid welding technology. After theoretical analysis and experimental verification, microstructures and microhardness data of the welded joint were obtained under different heat inputs. The results show that, hybrid welding joint of high nitrogen steel cross-sectional is "goblet" shape. The upper is arc action area, and the lower is laser action area. The microstructure consists of austenite and a small amount of ferrite. With the increasing of heat input, the ferrite fraction increases, the ferrite branch crystal trunk grows longer and thicker, and the secondary dendrites is distributed on both sides of the branch crystal trunk. The microhardness distribution of welded joint is not uniform. The hardness of base metal zone is the highest and the value is between 330HV~370HV. The hardness of welding is the lowest, and the value is between 260HV~300HV. The hardness of welded joint decreases with the increasing of heat input. There is no soft zone in welded joint. The study provides a theoretical basis for the welding of high nitrogen steel under the certain heat input parameters.
In order to study microstructure and microhardness distributions of welded joint of high nitrogen steel at different heat inputs, high nitrogen austenitic stainless steel was welded by Nd:YAG-MAG hybrid welding technology. After theoretical analysis and experimental verification, microstructures and microhardness data of the welded joint were obtained under different heat inputs. The results show that, hybrid welding joint of high nitrogen steel cross-sectional is "goblet" shape. The upper is arc action area, and the lower is laser action area. The microstructure consists of austenite and a small amount of ferrite. With the increasing of heat input, the ferrite fraction increases, the ferrite branch crystal trunk grows longer and thicker, and the secondary dendrites is distributed on both sides of the branch crystal trunk. The microhardness distribution of welded joint is not uniform. The hardness of base metal zone is the highest and the value is between 330HV~370HV. The hardness of welding is the lowest, and the value is between 260HV~300HV. The hardness of welded joint decreases with the increasing of heat input. There is no soft zone in welded joint. The study provides a theoretical basis for the welding of high nitrogen steel under the certain heat input parameters.
2018, 42(3): 346-350.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.011
Abstract:
In order to solve the problem that the sensor signal is seriously disturbed by noise in a Brillouin optical time domain analysis (BOTDA) system based on Rayleigh scattering, the 2-D lifting wavelet transform algorithm was used to convert the measured signal from 1-D space to 2-D space, and the noise was reduced by threshold. Through the theoretical analysis and experimental verification, the traditional wavelet and 2-D lifting wavelet denoised data were obtained. The results show that the signal-to-noise ratio of the 2-D lifting wavelet transform is about 10dB higher than that of the traditional wavelet transform, and the computation amount is reduced by 1/3. The 2-D lifting wavelet makes full use of the time correlation of the measured signal, the transformation structure is simple, the operation speed is quick and the noise reduction effect is superior to the traditional wavelet. It is suitable for noise reduction in a Rayleigh BOTDA system. The results of this paper are of great reference to the research of signal denoising in optical fiber sensing systems.
In order to solve the problem that the sensor signal is seriously disturbed by noise in a Brillouin optical time domain analysis (BOTDA) system based on Rayleigh scattering, the 2-D lifting wavelet transform algorithm was used to convert the measured signal from 1-D space to 2-D space, and the noise was reduced by threshold. Through the theoretical analysis and experimental verification, the traditional wavelet and 2-D lifting wavelet denoised data were obtained. The results show that the signal-to-noise ratio of the 2-D lifting wavelet transform is about 10dB higher than that of the traditional wavelet transform, and the computation amount is reduced by 1/3. The 2-D lifting wavelet makes full use of the time correlation of the measured signal, the transformation structure is simple, the operation speed is quick and the noise reduction effect is superior to the traditional wavelet. It is suitable for noise reduction in a Rayleigh BOTDA system. The results of this paper are of great reference to the research of signal denoising in optical fiber sensing systems.
2018, 42(3): 351-356.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.012
Abstract:
In order to improve the absorption efficiency of ordinary pulsed infrared laser for fused silica, a new method for 1064nm infrared laser etching fused silica assisted by barium compound powder coating was proposed. The etching products adhering to the surface of the groove etched by laser assisted by BaCrO4, BaCl2, and Ba(OH)2 powder coating were tested and analyzed by means of energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) respectively. The results show that the etching mechanisms of BaCrO4 and Ba(OH)2 powder have the chemical reaction to remove quartz glass and the corrosion rates are high. The etching mechanism of BaCl2 powder has no chemical reaction to remove quartz glass and the corrosion rate is low. The study provides the technical basis for the industrial application of laser processing fused silica.
In order to improve the absorption efficiency of ordinary pulsed infrared laser for fused silica, a new method for 1064nm infrared laser etching fused silica assisted by barium compound powder coating was proposed. The etching products adhering to the surface of the groove etched by laser assisted by BaCrO4, BaCl2, and Ba(OH)2 powder coating were tested and analyzed by means of energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) respectively. The results show that the etching mechanisms of BaCrO4 and Ba(OH)2 powder have the chemical reaction to remove quartz glass and the corrosion rates are high. The etching mechanism of BaCl2 powder has no chemical reaction to remove quartz glass and the corrosion rate is low. The study provides the technical basis for the industrial application of laser processing fused silica.
2018, 42(3): 357-361.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.013
Abstract:
In order to measure refractive index of liquid more accurately, one method based on surface plasma resonance wavelength was proposed. The model was built by using Kretschman structure and software simulation was carried out. The experimental platform was set up and the experimental research was carried out. The error between experimental and theoretical results was analyzed. The results show that, when the refractive index changes within the range of 1.33RIU~1.36RIU, the absorption peak of surface plasma resonance produces a frequency shift with the change of refractive index of liquid sample. And its sensitivity is up to 4808.94nm/RIU. Refractive index of liquid can be measured accurately with the method and the system has simple structure and high sensitivity.
In order to measure refractive index of liquid more accurately, one method based on surface plasma resonance wavelength was proposed. The model was built by using Kretschman structure and software simulation was carried out. The experimental platform was set up and the experimental research was carried out. The error between experimental and theoretical results was analyzed. The results show that, when the refractive index changes within the range of 1.33RIU~1.36RIU, the absorption peak of surface plasma resonance produces a frequency shift with the change of refractive index of liquid sample. And its sensitivity is up to 4808.94nm/RIU. Refractive index of liquid can be measured accurately with the method and the system has simple structure and high sensitivity.
2018, 42(3): 362-368.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.014
Abstract:
In order to design a coaxial powder feeding nozzle for high power broad laser cladding, powder convergence property and concentration distribution for broad laser coaxial powder feeding nozzles were analyzed at different inclination angles and exit gap of the powder feeding channel by using the discrete phase model in FLUENT software. And when other conditions were fixed, the effect of outer protective gas velocity on powder convergence was analyzed and the better structure size was obtained. The experiments of powder feeding and cladding were carried out by using the designed and developed broad coaxial powder feeding nozzle. The experimental results show that, the focal point concentration of the coaxial powder nozzle is approximately obeyed by Gaussian distribution in radial direction and axial direction. With the increase of feeding angle, the effect of exit gap on focal length becomes more and more important.The smaller the exit gap, the greater the focal length. When feeding angle is 70° and exit gap is 3.5mm, powder convergence is better and utilization ratio of powder is high.When the other conditions are constant, the fact that outer protective gas velocity is too fast or too slow is not beneficial to powder convergence. When outer protective gas velocity is slightly less than carrying gas velocity, the characteristics of powder convergence of powder feeding nozzle is the best. The quality of surface cladding reaches the expected requirement, and the rationality of the structure is verified. The designed nozzle has a great significance for the research and application of subsequent broad laser cladding.
In order to design a coaxial powder feeding nozzle for high power broad laser cladding, powder convergence property and concentration distribution for broad laser coaxial powder feeding nozzles were analyzed at different inclination angles and exit gap of the powder feeding channel by using the discrete phase model in FLUENT software. And when other conditions were fixed, the effect of outer protective gas velocity on powder convergence was analyzed and the better structure size was obtained. The experiments of powder feeding and cladding were carried out by using the designed and developed broad coaxial powder feeding nozzle. The experimental results show that, the focal point concentration of the coaxial powder nozzle is approximately obeyed by Gaussian distribution in radial direction and axial direction. With the increase of feeding angle, the effect of exit gap on focal length becomes more and more important.The smaller the exit gap, the greater the focal length. When feeding angle is 70° and exit gap is 3.5mm, powder convergence is better and utilization ratio of powder is high.When the other conditions are constant, the fact that outer protective gas velocity is too fast or too slow is not beneficial to powder convergence. When outer protective gas velocity is slightly less than carrying gas velocity, the characteristics of powder convergence of powder feeding nozzle is the best. The quality of surface cladding reaches the expected requirement, and the rationality of the structure is verified. The designed nozzle has a great significance for the research and application of subsequent broad laser cladding.
2018, 42(3): 369-373.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.015
Abstract:
In order to study effect of laser shock processing(LSP) on the fatigue life of fillet structures under different stress levels (the maximum stress during fatigue test), TC4-DT titanium alloy samples were subjected to laser shock processing, and then tensile stress test was carried out. The stress levels were 385MPa and 423MPa respectively, and the stress ratio r was 0.1. The fatigue fracture was analyzed by means of a scanning electron microscope (SEM). The results show that after laser shock processing, the fatigue crack initiation is moved from the fillet surface to the inside, the width of fatigue striation decreases, and the fatigue life of fillet structure is improved. With the increase of stress level, the gain of the fatigue life of the fillet treated by laser shock processing is reduced. When the stress level increases from 385MPa to 423MPa, the fatigue life gain of fillet structure decreases from 246.2% to 111.8%. After LSP, the surface of the fillet has a certain degree of compressive stress, and the fatigue life is improved. However, with the increase of the stress level, thefatigue life gain of the fillet structure is reduced.This result has guiding significance for the study on suppressing fatigue crack initiation by strengthening weak region.
In order to study effect of laser shock processing(LSP) on the fatigue life of fillet structures under different stress levels (the maximum stress during fatigue test), TC4-DT titanium alloy samples were subjected to laser shock processing, and then tensile stress test was carried out. The stress levels were 385MPa and 423MPa respectively, and the stress ratio r was 0.1. The fatigue fracture was analyzed by means of a scanning electron microscope (SEM). The results show that after laser shock processing, the fatigue crack initiation is moved from the fillet surface to the inside, the width of fatigue striation decreases, and the fatigue life of fillet structure is improved. With the increase of stress level, the gain of the fatigue life of the fillet treated by laser shock processing is reduced. When the stress level increases from 385MPa to 423MPa, the fatigue life gain of fillet structure decreases from 246.2% to 111.8%. After LSP, the surface of the fillet has a certain degree of compressive stress, and the fatigue life is improved. However, with the increase of the stress level, thefatigue life gain of the fillet structure is reduced.This result has guiding significance for the study on suppressing fatigue crack initiation by strengthening weak region.
2018, 42(3): 374-378.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.016
Abstract:
In order to further enhance the environmental adaptability of an airborne laser rangefinder in the full temperature range, the relationship between temperature and output power signal-to-noise ratio of a detector module was analyzed. The equation for the optimum multiplier factor and temperature was derived. The reasons for the deviation of the best avalanche multiplier factor caused by temperature change were expounded. According to linear temperature characteristics of the breakdown voltage of an avalanche detector, based on natural logarithm method, a linear temperature controlled circuit of the avalanche bias voltage was designed to compensate the multiplication factor due to temperature in the range of -55℃~70℃. Good test results were obtained with this method used in new airborne laser rangefinders.The experimental results show the measured temperature control coefficient of the avalanche bias voltage is 2.29V/℃ with an error of less than 4% relative to the theoretical coefficient. This method meets the special requirement for airborne environment.
In order to further enhance the environmental adaptability of an airborne laser rangefinder in the full temperature range, the relationship between temperature and output power signal-to-noise ratio of a detector module was analyzed. The equation for the optimum multiplier factor and temperature was derived. The reasons for the deviation of the best avalanche multiplier factor caused by temperature change were expounded. According to linear temperature characteristics of the breakdown voltage of an avalanche detector, based on natural logarithm method, a linear temperature controlled circuit of the avalanche bias voltage was designed to compensate the multiplication factor due to temperature in the range of -55℃~70℃. Good test results were obtained with this method used in new airborne laser rangefinders.The experimental results show the measured temperature control coefficient of the avalanche bias voltage is 2.29V/℃ with an error of less than 4% relative to the theoretical coefficient. This method meets the special requirement for airborne environment.
2018, 42(3): 379-384.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.017
Abstract:
In order to reduce the computational complexity of ship target detection methods for sea surface remote sensing images of traditional high resolution and improve the speed of detection, combined with visual salience algorithm based on histogram contrast and spatial dimension reduction algorithm, a new ship target fast detection algorithm for sea surface remote sensing images of high resolution was proposed.Firstly, spatial dimension reduction of high resolution remote sensing images was carried out. The saliency map was calculated and the interest area of the target area was highlighted. At last, the visual salient image was segmented by the method of maximum inter class variance to obtain the candidate region of the ship target. The results show that the time consumed by the target detection is reduced to 10%~12% of the original.The influence of complex sea surface texture background on target detection is weakened.The research improves ship target detection efficiency for high resolution remote sensing images.
In order to reduce the computational complexity of ship target detection methods for sea surface remote sensing images of traditional high resolution and improve the speed of detection, combined with visual salience algorithm based on histogram contrast and spatial dimension reduction algorithm, a new ship target fast detection algorithm for sea surface remote sensing images of high resolution was proposed.Firstly, spatial dimension reduction of high resolution remote sensing images was carried out. The saliency map was calculated and the interest area of the target area was highlighted. At last, the visual salient image was segmented by the method of maximum inter class variance to obtain the candidate region of the ship target. The results show that the time consumed by the target detection is reduced to 10%~12% of the original.The influence of complex sea surface texture background on target detection is weakened.The research improves ship target detection efficiency for high resolution remote sensing images.
2018, 42(3): 385-389.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.018
Abstract:
In order to improve the problems of traditional digital light processing (DLP) projection system, such as, large volume, complex structure, high cost, and low utilization efficiency of light source, using single three-color light emitting diode as light source and using a novel DLP projection optical structure of forming parallel light by a single lens, the traditional optical path was improved and optimized. Without colorwheel in the traditional optical path, the complex structures of light gathering and light distribution in the traditional projection light path were realized by lens directly.After using TRACEPRO software to model, the projection light path was analyzed by ray tracing. The results show that, the volume of whole optical system is controlled at 76.8mm×32.2mm×25mm, utilization rate of light energy reaches 60.1%, spot uniformity reaches 96.6%, and luminous flux on screen surface is 21.7lm. The research reduces the volume of projection light path, simplifies the optical structure and improves the utilization ratio of light energy.
In order to improve the problems of traditional digital light processing (DLP) projection system, such as, large volume, complex structure, high cost, and low utilization efficiency of light source, using single three-color light emitting diode as light source and using a novel DLP projection optical structure of forming parallel light by a single lens, the traditional optical path was improved and optimized. Without colorwheel in the traditional optical path, the complex structures of light gathering and light distribution in the traditional projection light path were realized by lens directly.After using TRACEPRO software to model, the projection light path was analyzed by ray tracing. The results show that, the volume of whole optical system is controlled at 76.8mm×32.2mm×25mm, utilization rate of light energy reaches 60.1%, spot uniformity reaches 96.6%, and luminous flux on screen surface is 21.7lm. The research reduces the volume of projection light path, simplifies the optical structure and improves the utilization ratio of light energy.
2018, 42(3): 390-394.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.019
Abstract:
In order to study effect of protective gas flow on morphology and droplet transition of hybrid welding joint, theoretical analysis and experimental verification of laser arc hybrid welding test were carried out by using 5mm thick high strength steel sheet. The morphology of welding seam under different gas flow, arc and droplet image during the welding process were obtained. The results show that the welding depth first increases and then decreases with the increase of shelding gas flow. The welding depth reaches the maximum with shelding gas flow of 25L/min. The welding seams have good spreading and less splash. Shelding gas flow affects droplet transition frequency by affecting droplet transition form. Droplet transition frequency reduces with the increase of shelding gas flow. Droplet transition frequency is stable with shelding gas flow of 25L/min. FLUENT software was used to simulate gas flow. The larger the gas flow, the greater the shelding gas flow rate, the smaller the action area on the workpiece surface. The results lay the foundation for the preparation of high quality welding seam with shelding gas flow in practical engineering.
In order to study effect of protective gas flow on morphology and droplet transition of hybrid welding joint, theoretical analysis and experimental verification of laser arc hybrid welding test were carried out by using 5mm thick high strength steel sheet. The morphology of welding seam under different gas flow, arc and droplet image during the welding process were obtained. The results show that the welding depth first increases and then decreases with the increase of shelding gas flow. The welding depth reaches the maximum with shelding gas flow of 25L/min. The welding seams have good spreading and less splash. Shelding gas flow affects droplet transition frequency by affecting droplet transition form. Droplet transition frequency reduces with the increase of shelding gas flow. Droplet transition frequency is stable with shelding gas flow of 25L/min. FLUENT software was used to simulate gas flow. The larger the gas flow, the greater the shelding gas flow rate, the smaller the action area on the workpiece surface. The results lay the foundation for the preparation of high quality welding seam with shelding gas flow in practical engineering.
2018, 42(3): 395-399.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.020
Abstract:
The approximate point-in-triangulation (APIT) localization algorithm was prone to in-to-out and out-to-in errors during the measurement using the optimal point-in-triangulation method, and it would has bad effect on positioning accuracy. In order to solve the problem, an improved APIT localization algorithm based on same side technique of vector product was proposed. A received signal strength indicator localization algorithm was used to realize the initial positioning of the node. And the same side technique of vector product was used to replace the inner point test method. Both of them improved the positioning efficiency. After the simulation on MATLAB, the positioning error data of APIT localization algorithm and the improved APIT localization algorithm were gotten. The results demonstrate that, on positioning accuracy, the improved APIT localization algorithm performs better than APIT algorithm.
The approximate point-in-triangulation (APIT) localization algorithm was prone to in-to-out and out-to-in errors during the measurement using the optimal point-in-triangulation method, and it would has bad effect on positioning accuracy. In order to solve the problem, an improved APIT localization algorithm based on same side technique of vector product was proposed. A received signal strength indicator localization algorithm was used to realize the initial positioning of the node. And the same side technique of vector product was used to replace the inner point test method. Both of them improved the positioning efficiency. After the simulation on MATLAB, the positioning error data of APIT localization algorithm and the improved APIT localization algorithm were gotten. The results demonstrate that, on positioning accuracy, the improved APIT localization algorithm performs better than APIT algorithm.
2018, 42(3): 400-403.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.021
Abstract:
In order to achieve laser output with high quality beam, one new method to simplify the calculation of diffraction loss of different order transverse modes was used by theoretical analysis and numerical calculation. The results show that, when Fresnel number of different transverse modes N>0.7, the relative error between simplified calculation and accurate calculation is less than 0.2%. The diffraction loss of different order transverse modes calculated by the new algorithm can meet the sufficient accuracy. The new algorithm is reasonable and feasible. The sorting of diffraction loss of laser transverse modes carried out by the simplified algorithm rapidly can provide theoretical guidance for the design of high beam quality lasers.
In order to achieve laser output with high quality beam, one new method to simplify the calculation of diffraction loss of different order transverse modes was used by theoretical analysis and numerical calculation. The results show that, when Fresnel number of different transverse modes N>0.7, the relative error between simplified calculation and accurate calculation is less than 0.2%. The diffraction loss of different order transverse modes calculated by the new algorithm can meet the sufficient accuracy. The new algorithm is reasonable and feasible. The sorting of diffraction loss of laser transverse modes carried out by the simplified algorithm rapidly can provide theoretical guidance for the design of high beam quality lasers.
2018, 42(3): 404-409.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.022
Abstract:
Microwave frequency measurement is an important part of electronic reconnaissance. With the development of radar electronic warfare, the operating frequency of microwave increases rapidly. Conventional electronic frequency measurement schemes cannot meet the development of electronic reconnaissance due to their limitation in measurement bandwidth. Approaches of microwave frequency measurement based on photonics have the characteristics of large instantaneous bandwidth, low loss and immunity to electro-magnetic interference. According to the current frequency measurement schemes of microwave signal based on photonics, five technical approaches are introduced and discussed, including instantaneous frequency measurement, photonic-assisted microwave channelization, multi-frequency measurement, microwave frequency measurement based on photonic analog-to-digital conversion, photonic compressive sensing. Moreover, the potential of integrated optics for photonics-based microwave frequency measurement is briefly discussed. In the development of microwave frequency measurement, the photonics-based method has a broad prospect of application.
Microwave frequency measurement is an important part of electronic reconnaissance. With the development of radar electronic warfare, the operating frequency of microwave increases rapidly. Conventional electronic frequency measurement schemes cannot meet the development of electronic reconnaissance due to their limitation in measurement bandwidth. Approaches of microwave frequency measurement based on photonics have the characteristics of large instantaneous bandwidth, low loss and immunity to electro-magnetic interference. According to the current frequency measurement schemes of microwave signal based on photonics, five technical approaches are introduced and discussed, including instantaneous frequency measurement, photonic-assisted microwave channelization, multi-frequency measurement, microwave frequency measurement based on photonic analog-to-digital conversion, photonic compressive sensing. Moreover, the potential of integrated optics for photonics-based microwave frequency measurement is briefly discussed. In the development of microwave frequency measurement, the photonics-based method has a broad prospect of application.
2018, 42(3): 410-416.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.023
Abstract:
In order to solve the problems in the existing point cloud filtering algorithm, such as too many parameters, without ideal filtering effect and inconvenient operation, the cloth simulation filtering (CSF) algorithm was chosen to construct virtual grid to simulate terrain surface. The algorithm was verified using the qualitative and quantitative experiment and analysis in complex terrain point cloud data. The results show that type Ⅰ error is less than 5.7%, type Ⅱ error less than 3.4%, but for the local area with some mixed flat and steep slope the filtering effect is not ideal; The algorithm can achieve the filtering of millions of points in 30s while satisfying the filtering precision, and even hundreds of thousands of points in several seconds. The algorithm requires few parameters and is very efficient. It can satisfy the filtering requirements of most complex terrain data.
In order to solve the problems in the existing point cloud filtering algorithm, such as too many parameters, without ideal filtering effect and inconvenient operation, the cloth simulation filtering (CSF) algorithm was chosen to construct virtual grid to simulate terrain surface. The algorithm was verified using the qualitative and quantitative experiment and analysis in complex terrain point cloud data. The results show that type Ⅰ error is less than 5.7%, type Ⅱ error less than 3.4%, but for the local area with some mixed flat and steep slope the filtering effect is not ideal; The algorithm can achieve the filtering of millions of points in 30s while satisfying the filtering precision, and even hundreds of thousands of points in several seconds. The algorithm requires few parameters and is very efficient. It can satisfy the filtering requirements of most complex terrain data.
2018, 42(3): 417-421.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.024
Abstract:
Band selection is an important method of dimensionality reduction of hyperspectral images. In order to reduce the dimensionality, an unsupervised band selection algorithm combining K-L divergence and mutual information was proposed. And theoretical analysis and experimental verification were carried out. Firstly, the band with the largest information entropy was selected as the initial band. Then, the ratio of divergence to mutual information was defined as the criterion of joint K-L divergence mutual information (KLMI). The band which has large KLMI and information entropy was selected to band subset. Then bands with large information and low similarity were obtained. Finally, the real hyperspectral data classification experiments based maximum-variance principle component analysis (MVPCA), affinity propagation (AP), mutual information (MI) and the proposed method were realized by using k-nearest neighbor classifier. Experimental results show that, the accuracy of the proposed algorithm is higher than that of other algorithms. The overall classification accuracy and kappa coefficient κ are over 0.8. Classification accuracy of the most objects is improved. The proposed method has outstanding performance on classification and is a practical dimensionality reduction algorithm of hyperspectral image.
Band selection is an important method of dimensionality reduction of hyperspectral images. In order to reduce the dimensionality, an unsupervised band selection algorithm combining K-L divergence and mutual information was proposed. And theoretical analysis and experimental verification were carried out. Firstly, the band with the largest information entropy was selected as the initial band. Then, the ratio of divergence to mutual information was defined as the criterion of joint K-L divergence mutual information (KLMI). The band which has large KLMI and information entropy was selected to band subset. Then bands with large information and low similarity were obtained. Finally, the real hyperspectral data classification experiments based maximum-variance principle component analysis (MVPCA), affinity propagation (AP), mutual information (MI) and the proposed method were realized by using k-nearest neighbor classifier. Experimental results show that, the accuracy of the proposed algorithm is higher than that of other algorithms. The overall classification accuracy and kappa coefficient κ are over 0.8. Classification accuracy of the most objects is improved. The proposed method has outstanding performance on classification and is a practical dimensionality reduction algorithm of hyperspectral image.
2018, 42(3): 422-426.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.025
Abstract:
In order to obtain the optimal cutting quality of fracture splitting groove on connecting rod made of new material 36MnVS4, experimental study and theoretical analysis of crack groove fabricated by laser cutting were investigated through orthogonal experimental method. Geometric dimensions such as depth, width, opening angle and curvature radius of fracture splitting groove produced by laser cutting were measured and calculated by laser confocal microscope, respectively. In addition, microstructure and thickness of heat affected zone on the bottom of crack groove were observed and measured by adopting scanning electron microscope. The effects of laser peak power, pulse width, cutting speed and pulse frequency on geometric dimensions of fracture splitting groove were analyzed by using range analysis method. As a result, the optimal parameter combination of cutting fracture splitting groove were found out. The results show that, the depth of heat affected zone on the bottom of crack groove is less than 100μm and there exist micro cracks and pores. The investigated parameters have less impact on the width, opening angle and curvature radius of fracture splitting groove, but have large effect on depth. Moreover, laser peak power and pulse width exert great influence on depth of crack groove, while cutting speed and pulse frequency have little effect on it. The optimal parameters exist with cutting speed of 1.0m/min, laser peak power of 700W, pulse frequency of 1000Hz and pulse width of 50μs. The study is of great importance for actual production.
In order to obtain the optimal cutting quality of fracture splitting groove on connecting rod made of new material 36MnVS4, experimental study and theoretical analysis of crack groove fabricated by laser cutting were investigated through orthogonal experimental method. Geometric dimensions such as depth, width, opening angle and curvature radius of fracture splitting groove produced by laser cutting were measured and calculated by laser confocal microscope, respectively. In addition, microstructure and thickness of heat affected zone on the bottom of crack groove were observed and measured by adopting scanning electron microscope. The effects of laser peak power, pulse width, cutting speed and pulse frequency on geometric dimensions of fracture splitting groove were analyzed by using range analysis method. As a result, the optimal parameter combination of cutting fracture splitting groove were found out. The results show that, the depth of heat affected zone on the bottom of crack groove is less than 100μm and there exist micro cracks and pores. The investigated parameters have less impact on the width, opening angle and curvature radius of fracture splitting groove, but have large effect on depth. Moreover, laser peak power and pulse width exert great influence on depth of crack groove, while cutting speed and pulse frequency have little effect on it. The optimal parameters exist with cutting speed of 1.0m/min, laser peak power of 700W, pulse frequency of 1000Hz and pulse width of 50μs. The study is of great importance for actual production.
2018, 42(3): 427-432.
doi: 10.7510/jgjs.issn.1001-3806.2018.03.026
Abstract:
In order to study the propagation properties of the disturbed Bessel-Gaussian beam in turbulent atmosphere, based on the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function, the formulas of M2 factor for the disturbed Bessel-Gaussian beam were derived by theoretical calculation analysis, and the corresponding numerical calculation was carried out. The results show that, when the size of obstruction is not more than 0.4 times of beam width, the propagation factor of Bessel-Gaussian beam in turbulent atmosphere would increase with the increasing of the propagation distance and atmospheric structure constant, and decrease with the increasing of the inner scale of turbulence and topological charge indexes. Under the same condition, the propagation factor of Bessel-Gaussian beam in turbulent atmosphere increases with the increase of the size of obstruction. These results have certain reference value in free space optical communication and actual laser transmission.
In order to study the propagation properties of the disturbed Bessel-Gaussian beam in turbulent atmosphere, based on the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function, the formulas of M2 factor for the disturbed Bessel-Gaussian beam were derived by theoretical calculation analysis, and the corresponding numerical calculation was carried out. The results show that, when the size of obstruction is not more than 0.4 times of beam width, the propagation factor of Bessel-Gaussian beam in turbulent atmosphere would increase with the increasing of the propagation distance and atmospheric structure constant, and decrease with the increasing of the inner scale of turbulence and topological charge indexes. Under the same condition, the propagation factor of Bessel-Gaussian beam in turbulent atmosphere increases with the increase of the size of obstruction. These results have certain reference value in free space optical communication and actual laser transmission.
