2019 Vol. 48, No. S2
2019, 48(S2): 1-6.
doi: 10.3788/IRLA201948.S205001
The high spectral resolution lidar has the inherent characteristics of separating atmospheric molecular scattering from aerosol scattering signals, and can measure the aerosol backscattering coefficient and extinction coefficient profiles without assuming lidar ratio. However, due to the variable distribution of atmospheric aerosols in the world, the signal -to -noise ratio of the echo signals of the molecular channels and the aerosol channels is inconsistent, and eventually the inversion error becomes larger. Therefore, the transmission energy distribution of the two channels must be considered to reduce the inversion error. Based on the correlation mechanism between echo signals and aerosols distribution, the global aerosol distribution was divided into three types. The signal-to-noise ratio and the inversion error of the molecular channel and the parallel reference channel were analyzed and compared with the splitting ratio, and the optimized splitting ratio in each atmospheric mode was obtained.
2019, 48(S2): 7-15.
doi: 10.3788/IRLA201948.S205002
Laser addictive manufacturing(AM) of titanium alloys have great potential in aerospace field, as its unique advantages in small complex structure fabricaton and large components near-net shape forming. In order to achieve the fabrication of large components with complex structure just in one piece, the laser deposition manufacturing(LDM) was carried out with Ti6Al4V alloy as the basis by selective laser manufacturing(SLM). The attained samples which had two distinguishing AM processes, was conducted annealing treatment at different temperatures to explore the evolution of microstructure and mechanical properties. The result shows that the microstructures of Ti6Al4V alloy structure prepared by the LDM-SLM processes consists of three zones:LDM zone mainly composing laths, SLM zone dominated by slender acicular ' martensite and heat affected zone (HAZ) formed by remelting which is mainly composed of lath and ' martensite. In mechanical properties, the as-built component has the characters of high strength with low plastic, and significant anisotropy; samples annealing at 850℃ exhibit the best comprehensive mechanical properties because of the reasonable balance between the strength and the plastics. Work hardening in the tensile process leads to double necking of the tensile bar after 850℃ annealing.
Laser micro-thruster has become one of the affordable power system options for micro-nano-satellites due to its high specific impulse, low thrust level, small size, low power consumption and high reliability. In view of the influence of laser ignition position and ignition sequence on the attitude of nano-satellite platform during the thrust output of solid fuel tape laser micro-thruster, the attitude dynamics equation based on laser ablation moment was established, and the relationship between attitude angle and its angular velocity with time was simulated and analyzed. The simulation results show that,the laser ignition sequence of micro thruster can be divided into two kinds:symmetrical on both sides and continuous output and symmetrical on both sides and spacing output, the effects of the two modes on the attitude of the nano-satellite are different. However, whether the laser ablation moment was from large to small or from small to large, the moment symmetrical and continuous output has the least impact on the attitude. This lays the foundation for the application of attitude stability control of micro-nano-satellite.
2019, 48(S2): 23-30.
doi: 10.3788/IRLA201948.S213002
In order to reduce the influence of seeker's disturbance rejection rate (DRR) on the output line-of-sight(LOS) angular rate, an online inhibition method for DRR was proposed. Firstly, the transfer functions of different guidance signal extraction points were established based on the platform seeker. Subsequently, the disturbance torque was regarded as the interference angular acceleration and the finite-time sliding mode disturbance observer (SMDOB) was used to estimate it and compensate it into the control loop in real time, so that the additional LOS angular rate caused by the DRR was greatly reduced. The simulation results show that the designed SMDOB could quickly track the disturbance, which is convenient for online compensation and inhibition for LOS deviation caused by DRR. Adopting the proposed strategy, the LOS angular rate error caused by the interference is substantially eliminated, and the accuracy of the output LOS angular rate is improved, which is beneficial for precise guidance.
2019, 48(S2): 31-37.
doi: 10.3788/IRLA201948.S213003
The laser seeker, which is the main dependent object of the missile to achieve reliable target attack, provides the position information of the target for the laser-guided weapon. During the missile flight, the missile's disturbance was coupled to the servo stabilization system of the seeker in various ways. This will affect the stability of the visual axis as well as reducing the accuracy of the seeker in locating the target. The basic structure of the seeker servo system and the basic principle of achieving the stability of the visual axis were analyzed in this paper. In order to solve the disturbance problem of the seeker, a Fuzzy Sliding Mode Control(FSMC) method was proposed. The Sliding Mode Control(SMC) has the advantage of fully adaptive to the disturbances. Besides, it was combined with fuzzy control, which can reduce chattering of SMC. In this way, the robustness of the seeker servo system was improved by FSMC, so did the isolation of the seeker. The simulation results show that compared with PID control, fuzzy sliding mode control can improve the control quality of the system and achieve better control accuracy and response speed.
2019, 48(S2): 38-46.
doi: 10.3788/IRLA201948.S213004
Food is the paramount necessity of the people, safety is the first concern for the food, under the background of widespread application of various pesticides and food additives, illegal food additives have a serious impact on the food safety situation, and the qualitative detection of trace amounts of illegal food additives is of great significance. In order to achieve qualitative detection of pyridine, a sensing system based on HCPCF (Hollow Core Photonic Crystal Fiber) SERS was proposed. Silver nanoparticles were used to make SERS substrate, and SERS signal devices were designed to collect SERS in the same direction. By means of cone pulling on HCPCF to achieve selective filling, the detection scheme of collecting output signals by spectrometer was implemented. After the liquid pyridine sample with the concentration of 0.004 975% was detected, the obvious SERS characteristic spectrum could be observed. The experimental results show that the sensing system can achieve qualitative trace detection of pyridine in the liquid sample.
Passive gas infrared imaging detection technology has become an important method for oil and natural gas leakage detection due to its high detection efficiency, intuitive visualization and no need for laser illumination. Based on the infrared imaging detection principle of alkane gas leakage such as oil and natural gas. The representative detectors and gas leakage infrared imaging detection systems at foreign and domestic were focused, and its technical characteristics and some key technologies in the imaging system were analyzed. The development status of gas detection system performance evaluation technology was comprehensively summarized, which played an important role in promoting the application of gas detection technology and improving system performance. Finally, the development direction and existing problems of infrared gas imaging detection technology for alkane gas leakage were analyzed.
2019, 48(S2): 60-67.
doi: 10.3788/IRLA201948.S204002
In order to improve the defect recognition ability and accuracy of the lock-in thermal wave detection technology, a temperature sequence processing method based on phase-shifting technology was proposed. A step-plate model of carbon fiber composite material with gradual thickness was established to study the relationship between thickness and phase under different modulation periods, effects of non-phase-shifting and phase-shift of temperature series in different modulation periods were numerically analyzed, the results show that the sensitivity of the phase to thickness is increased by three times after phase-shifting by 180, and the phase difference between different thicknesses is increased, which enhances the ability to identify defects. The carbon fiber plate with flat hole defects was used to verify the numerical calculation and the phase diagram obtained by non-phase-shifting and phase-shifting by 180 was compared, the results show that smaller defects can be identified after phase-shifting and the contrast near the defect was enhanced, which proved the effectiveness of phase-shifting technology to improve the ability of lock-in thermal wave for detecting defects.
2019, 48(S2): 68-74.
doi: 10.3788/IRLA201948.S217001
As an alternative to 3He neutron detectors, boron-coated neutron detectors have been a current focus for researchers worldwide. For the boron-coated neutron detectors, a B4C film with low stress and good adhesion to the Al substrate is required. To enhance adhesion of the B4C films on Al substrates, a B4C film with low stress was fabricated by direct current sputtering technique without substrate-heating. The Mg-Al alloy thin film was introduced between the B4C film and its substrate for enhancing the adhesion. The effect of sputtering pressure on the stress of B4C films during deposition was studied. Additionally, the adhesion of B4C films using Mg-Al films as adhesive layers and effects of sputtering pressure and alloy film thickness on adhesion were studied. Scanning and transmission electron microscopies were used to characterize the microstructure. Experimental results show that the stress of B4C films decreases and stabilizes when sputtering pressure increases during deposition. Thin and porous Mg-Al films react well with both B4C films and Al2O3 on Al substrates to enhance adhesion of the B4C films, without substrate-heating.
2019, 48(S2): 75-80.
doi: 10.3788/IRLA201948.S217002
A thorough research of the optical properties of structural color generation based on grating/colloidal crystal was reported in terms of structural design, experimental preparation and spectral color rendering performance testing. Around realizing wide color gamut, narrow band gap, high brightness and anisotropic structure photonic crystal color control problems, the color mechanism of grating/colloidal crystal microsphere composite photonic crystals was explored by gravity deposition and vertical deposition.Taking the gravity sedimentation method, when the concentration of the dispersion was 1%, the colloidal microspheres were uniformly attached to the grating. When the concentration of the solution was 5%, the PS beads can be closely arranged, but cannot form a single layer or double. The layer structure would precipitate multiple layers and the grating structure was not observed. With the vertical settlement assembly method, when the concentration of the dispersion liquid was 1%, the assembly effect was not good and a dense structure couldn't be formed. When the solution concentration was 5%, the composite structure was assembled well, and the colloidal crystal was assembled in the grating groove. The spectral performance was tested and its color properties were evaluated, which laid a theoretical and practical foundation for its effective application in the field of anti-counterfeiting printing.
2019, 48(S2): 81-89.
doi: 10.3788/IRLA201948.S209001
Due to the difference of wavelength in emitting laser and photoelectric tracking for high energy laser system, atmospheric turbulence becomes one of the factors affecting the pointing accuracy. Therefore, the purpose of this paper is to study the influence of atmospheric turbulence on pointing accuracy, and the angular deviation of axis between emitting laser and photoelectric aiming of the system was used to characterize the influence of pointing accuracy. First, atmospheric turbulence phase screen was constructed by Zernike polynomial method, and the model of laser propagation was established by using the theory of angle spectrum diffraction. Next, based on above two methods, the variations of angular deviation in distinct atmospheric turbulence and different tracking wavelength were simulated and analyzed. In the end, some related experiments were carried out to verify the results. It is shown that various tracking imaging wavelengths lead to different angular deviations under the equivalent turbulence conditions. For example, the closer the tracking imaging wavelength to the emitting laser wavelength is, the smaller the angular deviation is. Under the circumstance of the same tracking wavelength, angular deviation adds with an increase of turbulence intensity. The above results can provide important reference for improving the ability of damage of high energy laser system in engineering application.
2019, 48(S2): 90-97.
doi: 10.3788/IRLA201948.S209002
It is important to obtain the real-time atmospheric transmittance of laser waveband with the application of laser technology in numerous scientific fields. Based on measurements and researches of analysis on analogy calculation, a methodology making use of the measurements of sun-photometer to obtain the atmospheric transmittance of infrared laser was proposed. The method was low-cost, high effective, and simultaneous for multiple laser wavebands. Compared with the measurements by 532 nm lidar, the transmittance error is less than 5%. The statistical errors of two infrared laser wavebands are less than 8.5% and 8% respectively, compared with the calculated results by use of the laser transmittance evaluation software based on the real-time measurements of the atmospheric parameters. This method is valuable for the applications of laser engineering in the real atmosphere.
2019, 48(S2): 98-102.
doi: 10.3788/IRLA201948.S219001
Terahertz(THz) imaging technology provides perspective applications in non-destructive inspection, medical diagnostic and national defense. An integrated terahertz confocal imaging system based on THz waveguides was reported in this paper. Firstly, a reflective THz imaging of a metal razor blade with lateral resolution close to wavelength (3 mm) was acquired. Then, a reinforcing metallic bar in concrete was detected effectively, which provided a feasible method to ensure the quality of construction. Further, by introducing a pinhole before the THz detector, a THz confocal imaging system was set up and depth information(24 mm) between two nails inserted in different depths in insulating foam could be extracted, which was three-dimensional information. The results show that the proposed terahertz confocal imaging system based on waveguides structure has the advantages of compact structure and portable integration, which is especially suitable for practical engineering applications.
2019, 48(S2): 103-108.
doi: 10.3788/IRLA201948.S218001
As the focus of current research on hollow core photonic bandgap fiber, reducing fiber loss is of great importance. In the view of fiber design, taking the 19 cell hollow core photonic bandgap fiber for example, the relationship between structure parameters and loss characteristic was investigated using the finite element method. Simulation results indicate that the confinement loss can be effectively reduced by adjusting the cladding parameters. With the increase of the layer of air holes, the air filling fraction and the fillet diameter at the corners, the confinement loss can be reduced below 10-4 dB/km. While the surface scattering loss, which depends on the coupling between the core mode and the surface mode, increases with the thickness of the core wall as well as the core expansion factor. In addition, the appearance of surface mode also leads to a sacrifice of transmission bandwidth. Limited by the fiber structure, the transmission loss of 19 cell hollow core photonic bandgap fiber is difficult to be reduced to less than 1 dB/km. Further reducing fiber loss can only be achieved by removing more air holes to form a larger hollow core structure. The research achievement provides theoretical basis for the realization of low loss hollow core photonic bandgap fibers.
The inherent advantages of superimposed training method are restricted by superposition data information, power allocation, and direct current bias in channel estimation of atmospheric optical communications under sand-dust weather. A novel scheme was proposed to perform these issues, especially for the channel with sand-dust particles. In the proposal, the data-dependent superimposed training algorithm was utilized to mitigate the influence of data information, the correlation matching algorithm was utilized for direct current bias elimination, and the maximum output signal-to-noise ratio was utilized to perform the optimal power allocation factor. The performance of mean square error, power allocation factor, bit error rate and algorithm complexity were numerically evaluated. The results demonstrate that the proposed method has a better performance than conventional methods with a slightly increased computational complexity.
2019, 48(S2): 117-124.
doi: 10.3788/IRLA201948.S218003
It is important to establish the system that is used to evaluate the performance of the inter-satellite laser communication terminals(LCT) under the laboratory conditions before being sent to space. For this reason, beam transmission process of communication was analyzed, and the link simulation based on optical system was also developed in this paper. The relationship between beam transmission and optical magnification with center sampling was studied firstly. Using physical optics principle, the relationship between magnification and transmission distance was established in the next, and on the basis, a system that can be used to test different transmission wavelength and variable transmission distance LCT was designed. Then, the device was tested and calibrated, besides, the relationship between zoom magnification and geometric attenuation was also analyzed. Finally, the precision of transmission distance simulation was discussed. The results indicate that the apparatus can meet less than 100 000 km LCT's simulation with 4% precision of distance simulation and less than 2% stability, which can satisfy the most LCT's testing requirements.
2019, 48(S2): 125-133.
doi: 10.3788/IRLA201948.S226001
In order to solve the problem of small target recognition caused by small size, less edge and texture information in the field of view for UAV in complex battlefield environment, a new model based on deep learning for small target recognition Deep Residual and Feature Pyramid (DRFP) was proposed in this paper. Firstly, the residual structure was used as the skeleton of the model, and the feature pyramid structure was used to achieve feature fusion. Secondly, the cross-entropy function with adjusting factor was used in the loss function to realize the focus of attention on difficult samples. Finally, a non-maximum Gaussian suppression algorithm was used to improve the detection rate of target-intensive areas. The experimental results show that the accuracy(mAP) of proposed single stage model is 83.16% using UAV-images towards vehicle recognition, which achieves the level of two stage network model. At the same time, the recognition speed meets real-time requirements.
2019, 48(S2): 134-141.
doi: 10.3788/IRLA201948.S226002
Aiming at the weak generalization of single-frame image depth estimation, a depth estimation technique based on deep learning was proposed, which used deep convolutional neural network as the basic framework and combined the epipolar geometry constraints to construct the end-to-end mapping from sequence images to the depth information, enabling unsupervised depth estimation that only relied on sequence image information. At the same time, a kind of loss function based on three-dimensional geometric information of the scene was constructed, and the original loss function based on the re-projection error between images was discarded to improve the robustness of the algorithm. Finally, the accuracy and precision of the algorithm were verified by the open source database. At the same time, the generalization of the algorithm was verified by the infrared image dataset, which laid a foundation for the military application.
2019, 48(S2): 142-148.
doi: 10.3788/IRLA201948.S226003
In order to improve the accuracy of the multi-sensor automatic target recognition algorithm,based on line group matching, an image matching algorithm using linear group geometric primitives was proposed. Line group was used to represent the target. Every three lines in line group can compose a triangle. An affine invariant, which consisted of the ratio of these triangles' area, was considered as a distinct feature to describe the line group. The best matching line group was found among the candidate line groups in real-time infrared image. The corresponding points between target and real-time image can be obtained through the matching lines. Then the location of the target can be computed through affine transformation. Finally, the position of the target in the real-time map was detected by the same-named point; in addition, a method of linear purification in the real-time infrared image was proposed. The extracted primary lines provided a condition which ensured the effectiveness and efficiency of the proposed recognition algorithm. Experimental result shows that the proposed algorithm has a high matching accuracy in multi-sensor target recognition.
2019, 48(S2): 149-155.
doi: 10.3788/IRLA201948.S226004
An improved Harris corner detection algorithm was proposed to solve the problem that the number of detection corners was too few and the accuracy was low when detecting infrared images. Firstly, the Canny operator was used to detect the target edge to determine the target region, and then the cubic B-spline gradient operator was used to filter the target area to obtain the M matrix. Then the convolution of the cubic B-spline function and the Gaussian window function was used to replace the original Gaussian window function for data filtering, and extract the corner points of the target area. Finally, the adaptive threshold was used for non-maximum suppression to remove false corners. The experimental results show that compared with the Harris algorithm, the proposed algorithm not only increases the number of corners points extracted, but also reduces the running time of the algorithm by 3/4.
2019, 48(S2): 156-163.
doi: 10.3788/IRLA201948.S216001
Two microwave resonant cavity with different structures for preparing optical diamond film materials were designed. The Hill shape reentrant cavity can provide enough space for microwave to resonate inside, helping to excite high-density plasma. The improved structure with tilted up substrate holde can obtain high quality film with less impurity. In the optimization process of the second design, it was found that the transition structure with cone can obtain stronger electric field intensity and higher deposition rate than the direct connection style. Gas supply ways and flow rate were optimized, two kinds of gas supply modes were proposed. Mode I was that gas enter from one center hole on the top of the cavity, and mode Ⅱ was a circular path on the top. The results show that the air inlet way with mode I is favorable for the deposition of uniform film, and the optimal gas flow rate range is 5-10 m/s. The designed microwave cavity can be applied to the preparation of high quality optical diamond film.
