Chinese Version Light学术出版中心
Latest Issue
Issue 3 ， 2020
-
Design of high spatiotemporal resolution dynamic star simulator
Abstract：Aiming at the problem of image stabilization precision testing of large-aperture space telescopes being developed in China, this paper proposes a high spatiotemporal resolution motion guide star simulation scheme. Firstly, the silicon-based liquid crystal is used as the motion guide star simulation source, and the beam alignment system is combined to provide the infinite motion guide star for the space telescope. The objective lens is added to the light path to improve the motion resolution of the simulated guide star. Then, owing to the special distribution of the telescopic mirror surface structure, a method for simulating the multichannel optical path is proposed to provide real-time moving guide stars for the precision guide sensor on both sides of the telescope and the survey image surface. Finally, the error sources that affect the simulation accuracy of the moving guide star are analyzed, and the error model is established. The simulation results show that under the assumption that the simulation accuracy of the moving guide star is better than 0.5″, with probability of 95% and time-resolution of 3 ms, the precision simulation of the interstar angular distance error of the dynamic star map is less than 0.04″ and the angle is the single star of less than 0.02″. The simulation model was verified by experiments and meets the requirements of high spatiotemporal resolution of moving guide star targets for image stabilization accuracy testing of space telescopes.Keywords：space telescope;moving guide star;image stability accuracy;liquid crystal on silicon;objective lens;error model- 28
- |
- 3
- |
- 1
Published：2023-04-18 -
Detection of surface plasmons based on periodic grating structure
Abstract：Owing to the ability of surface plasmons to circumvent the optical diffraction limit and ultra-fast transmission speed, they are expected to replace electrons and photons as signal carriers in the construction of next-generation high-speed, highly integrated optoelectronic integrated circuits. They can integrate the high bandwidth characteristics of the optical system with the compactness of the electronic system. However, the detection of surface plasmons is difficult. In this study, a simulation model that includes a grating coupler, strip waveguide, and detecting grating was established based on the finite-difference time-domain method for detection surface plasmons both in the visible and optical-communication bands. We first analyzed the operation principle of the proposed detection structure and established three simulation models operating at 670, 1310, and 1 550 nm. Next, the relationship between the coupling efficiency and polarization angle of the incident light was analyzed along with that between the absorption efficiency and waveguide length. Finally, the detection structure was experimentally prepared according to the simulation models. The results reveal that the coupling efficiency exhibits a cosine squared relation with the polarization angle. In the case of a 5-μm waveguide, the absorption efficiency is 4.3% at 670 nm and its attenuation length is calculated as 17.1 μm, which is consistent with the theoretical value of the propagation length (17.5 μm). Furthermore, the variation trend of the photocurrent with polarization angle obtained through experiments matched with the absorption efficiency in simulations. The detection structure is proved to effectively detect the surface plasmons. The proposed models for detecting surface plasmons provide theoretical and experimental bases for future high-speed and integrated plasmonic interconnect circuits.Keywords：photoelectric devices;surface plasmons;periodic gratings;optoelectronic integrated circuits- 27
- |
- 4
- |
- 3
Published：2023-04-18 -
Large dynamic range silicon photomultiplier with epitaxial quenching resistor
Abstract：Silicon photomultipliers with epitaxial quenching resistors(EQR SiPM) are the bulk resistors under each microcell in the epitaxial layer that are used as the quenching resistors. To enhance the photon detection efficiency and solve the problems of lower fill factor and smaller gain for the large dynamic range of EQR SiPM, Novel Device Laboratory (NDL) has changed the size of microcells and newly developed SiPMs with microcell sizes of 15μm and 7 μm and an active area of 1 mm×1 mm based on its previous work. By changing the size of the microcell, the filling factor of the device is effectively increased, thus, improving the photon detection and gain efficiency. The microcell densities of the 15 μm and 7 μm devices are 4 400/mm2 and 23 200/mm2, respectively, which still maintain a large dynamic range. EQR SiPMs can distinguish at least 13 p.e. and the gain values are 5.1×105 and 1.1×105 under 5 V overvoltage. Moreover, the peak photon detection efficiencies at a 400 nm wavelength can reach 40% and 34%.Keywords：Silicon Photomultiplier (SiPM);Epitaxial Quenching Resistance (EQR);single photon detection;high detection efficiency;high gain;large dynamic range- 21
- |
- 4
- |
- 2
Published：2023-04-18 -
Quantitative evaluation of spatial resolution of photovoltaic electroluminescence defect detector
Abstract：To overcome poor accuracy, quantification difficulty, and repeatability of visual judgment of the spatial resolution of a photovoltaic electroluminescent defect detector, different image capturing conditions were adopted based on standards JJF(Min)1088-2018. Further, the images of the spatial resolution line pairs were cut and classified. The convolution neural network employed included a convolution layer, a pooling layer, and a full connection layer. The classified spatial resolution line pairs were used to train the model and were evaluated with test samples. The results show that the discriminant accuracy of the model reaches 99.2% for the test samples. This method satisfies the application requirements and can replace visual discrimination that provides a new solution for quantifying the spatial resolution of photovoltaic electroluminescent defect detector. Given that photoluminescence defect detectors for solar cells have similar imaging mode to electroluminescence defect detectors, this method can be compatible with the performance evaluation of the photoluminescence defect detectors for solar cells.Keywords：photovoltaic;electroluminescent;defect detection;spatial resolution;convolutional neural network;photoluminescence- 14
- |
- 2
- |
- 3
Published：2023-04-18 -
Extraction of heart rate parameters from video of human face
Abstract：To detect the heart rates of subjects in a comfortable non-contact environment, this study designs a signal processing system that can detect heart rate parameters using an ordinary camera. First, the face image captured by the Kanade-Lucas-Tomasi algorithm is converted into the YCbCr color space for skin detection. Simultaneously, the face image is converted to theCg color channel to extract a high-quality photoplethysmography (PPG) signal. Then, Complex Morlet is used as the master wave to draw the wavelet energy spectrum of the PPG signal. Finally, according to the physiological characteristics of the heart rate signal, the pseudo-point noise is removed and the time-varying curve of heart rate parameters is extracted. Compared with the measurement results of the standard instrument, the mean absolute error (|Me|) of all the testers is less than 2 bpm (beats per minute), the standard deviation of error (SDe) is less than 2.5 bpm, and the root mean square error (RMSE) is less than 2.6 bpm in the resting state. The |Me| of all the testers is less than 2.3 bpm, while the SDe is less than 2.9 bpm, and the RMSE is less than 2.9 bpm in the head moving state. A Bland-Altman consistency analysis is performed for the two measurement methods. The results show that the mean of the difference (d) is 0.295 7 bpm and the 95% confidence interval is from -3.340 1 bpm to 3.931 4 bpm in the resting state; d is 0.383 2 bpm and the 95% confidence interval is from -3.677 1 bpm to 4.443 5 bpm in the head moving state. Thus, it is confirmed that the measurement results of the non-contact method proposed in this paper are highly consistent with the measurement results of the standard instrument.Keywords：photoplethysmography;non-contact;heart rate detection;CMOR wavelet;energy spectra image- 24
- |
- 6
- |
- 4
Published：2023-04-18 -
VCSEL end-pumped high-energy
Q -switched Nd:YAG laserAbstract：A high-energy Q-switched 1 064 nm laser output is obtained using a vertical cavity surface emitting laser (VCSEL) with end pumping-Nd:YAG. Compared with the edge emitting diode laser, the VCSEL is a more suitable generator for high efficiency and compact lasers because its pump source has the advantages of equal divergence angles in each direction and exhibits small wavelength shifts with temperature. The 1 064-nm laser with a maximum output of 45 mJ is generated with a pump energy of 200 mJ, corresponding to an optical conversion efficiency of 22.5%. The laser pulse width is 8 ns, and its divergence angle is 1.2 mrad. The doping concentration of Nd3+ is optimized based on simulations and calculations. Furthermore, self-excited oscillation, which affects the enhancement of Q-switched laser energy, is effectively suppressed by reducing the gain of the pump end by using a Nd:YAG crystal with low doping concentration. This provides an effective technical method for obtaining high energy end-pumped Q-switched lasers.Keywords：Vertical Cavity Surface Emitting Laser(VCSEL);end pump;Q-switched laser;self-excited oscillation- 6
- |
- 3
- |
- 4
Published：2023-04-18 -
Double spatial modulation suitable for atmospheric laser communication
Abstract：Compared with traditional optical spatial modulation, optical generalized spatial modulation has a significant improvement in transmission rate and spectral efficiency. However, its bit error rate (BER) is not ideal. In this paper, a double spatial modulation (DSM) is proposed to simultaneously activate two lasers, using pulse position modulation (PPM) and pulse amplitude modulation (PAM). The theoretical upper bound of the bit error rate of DSM is then derived using union bound technology. Furthermore, the effect factors of spectral efficiency, transmission rate, and complexity are analyzed. The performance of DSM is compared with that of the proposed optical spatial modulation. The simulation results show that the DSM improves the spectrum efficiency and transmission rate of the system, and efficiently reduces its BER. When the transmission rate is the same and the bit error rate is 1×10－3, the signal-to-noise ratio of (3, 4)-8PPM-2PAM DSM is improved by approximately 2.5 and 6 dB compared with (4, 4)-8PPM SPPM and (3, 4)-4PPM GSPPM, respectively. Further, its spectral efficiency is increased by 2.335 and 0.375 bits/(s·Hz), respectively. Therefore, DSM scheme can effectively improve the transmission rate of atmospheric laser communication in the future.Keywords：laser communication;double spatial modulation;pulse amplitude modulation;pulse position modulation;transmission rate;spectral efficiency- 25
- |
- 3
- |
- 3
Published：2023-04-18 -
Analysis of earth surface pressure sensitivity on inversion of greenhouse gases columns and observation of greenhouse gases columns in Dunhuang in China
Abstract：Surface pressure has a significant impact on the inversion of greenhouse gas concentrations. Observations of the column-averaged dry air mole fractions of water vapor, carbon dioxide, carbon monoxide, and methane in Dunhuang are presented based on ground-based Fourier transform infrared spectrometer (EM27/SUN). The time series of XH2O, XCO2, XCH4, and XCO from June 27 to July 21 (2018) in Dunhuang were obtained, and the sensitivity of surface pressure to the column-averaged dry air mole fractions retrieval was analyzed. The main results are as follows: The surface pressure has a significant influence on the inversion results, and the underestimated surface pressure results in low inversion results. XH2O, XCO2, XCH4, and XCO are sensitive to changes in surface pressure, and their correlation coefficients with surface pressure are higher than 0.99. The change in the total column volume with surface pressure determines the trend of column-average mole fraction with surface pressure. Compared with CO2, CH4, and CO molecules, XH2O is less sensitive to surface pressure. When the local pressure is changed by 1 hPa, ΔXH2O, ΔXCO2, ΔXCH4 and ΔXCO are 0.027 8%, 0.065 9%, 0.068 6%, and 0.062%, respectively. The daily averages variation range of XH2O and XCO2 are 2 000×10-6—6 000×10-6 and 407.27×10-6—417.60×10-6, respectively. The measurement accuracies of XH2O, XCO2, XCH4, and XCO at Dunhuang site are 2.3%, 0.14%, 0.12%, and 1.7%, respectively. The measurement accuracies of XCO2 and XCH4 are within the requirement of TCCON. Comparing daily averaged XCO2 and XCH4 based on EM27/SUN with GOSAT, the results show that the value of XCO2 and XCH4 based on GOSAT satellite data are lower than our observations, and deviations of 7.07 (XCO2) and 0.025×10-6 (XCH4). The value of XCO2 based on WACCM data are lower than our observations with a deviation of 8×10-6 while the value of XCH4 based on WACCM data are higher than our observations with a deviation of 0.032×10-6, indicating that WACCM data does not reflect the invasion of foreign sources. These results provide a theoretical basis and first-hand observation data to understand the space-time distribution and changes of greenhouse gases in Dunhuang, China.Keywords：Fourier transform infrared spectroscopy;greenhouse gases;Dry air Mole Fractions(DMFs);satellite data;surface pressure- 32
- |
- 4
- |
- 1
Published：2023-04-18
Modern Applied Optics
-
Fabrication and rotation driving of movable microstructures based on femtosecond laser
Abstract：In recent years, microdriven technology has attracted increasing attention because of the diversity of driving methods and their extensive applications. This paper proposes a technique of microstructure processing and rotation driving with the use of a femtosecond laser. Microrotor structures with diameters of 20—30 μm were prepared through two-photon polymerization, and then an optical field with an optical orbital angular momentum was modulated using a spatial light modulator to realize the rotation driving of the microrotor structure at a speed of 40 r/s. In addition, the paper presents the detailed experimental process and optimization parameters of the microrotor structure fabricated using the femtosecond-laser direct writing technology. Moreover, the propagation and focusing characteristics of a vortex beam with different topological charges generated through a spatial light modulator are studied and used to drive the clockwise and counterclockwise rotations of the rotor. This controllable light-driven technology has promising applications in the fields of microfluidics, optical tweezers, targeted drug delivery, and cell dynamics.Keywords：femtosecond laser;spatial light modulation;vortex beam;light-driven- 13
- |
- 4
- |
- 4
Published：2023-04-18 -
Control system of 4 meters telescope based on segmented permanent magnet arc synchronous motor
Abstract：To satisfy the requirement of the drive and tracking accuracy of a 4-m telescope, this paper proposes a design method of a segmented permanent-magnet arc synchronous motor based on the telescope control system. The paper first introduces the construction of the control system and the method for identifying the control model. Next, the position command shaper, which is based on the speed and acceleration information, is designed to rapidly realize the smaller and larger step responses without overshoot. Finally, the position and speed control strategies are designed and experiments are conducted. The experimental results show that when the telescope control system steps 10° and 0.2° signals, the system could reach the command rapidly without overshoot. In the case of a speed of 10 (°)/s and acceleration of 3(°)/s2, the telescope could track an equivalent sine curve, with the maximum tracking error and root mean square error of 2.636″ and 0.673″, respectively. The results demonstrate that the 4-m telescope control system could meet the design requirement, and provides a reference method for the next-generation telescope control system design.Keywords：large-aperture telescope;segmented permanent magnet arc synchronous motor;control model;command shaper- 24
- |
- 2
- |
- 3
Published：2023-04-18 -
Thermal characteristics analysis and test of spindle-column system for CNC machine tool
Abstract：Given that the spindle-column system of a CNC machine tool is affected by thermal deformation, a coupling analysis model of the spindle-column system is established based on the law of energy conservation to obtain its thermal characteristics. In this model, the heat source calculation, heat transfer coefficient calculation, structure constraint, and heat dissipation surface placement are considered comprehensively, and a wind speed method is adopted to obtain the heat transfer coefficient between the spindle and air. In this study, a platform for the CNC machine tool thermal characteristics was designed and set up to verify the validity of the spindle-column system coupling analysis model. Further, one CNC machine tool was used as the research object in the research application to obtain the thermal characteristics of the spindle-column system, such as the temperature field distribution, thermal deformation, and thermal equilibrium time. The experimental results show that the maximum absolute and relative errors of the temperature in the measuring point data are 0.71 ℃ and 2.94%, respectively, which appear at the measuring point of spindle. And the absolute and relative errors of the thermal deformation are 1.49μm and 8.71%, respectively. The thermal characteristics obtained by the coupling analysis model of spindle-column system based on the wind speed method are consistent with the experimental results. The results of this study provide a reference for CNC machine tools to reduce thermal error and improve accuracy retention.Keywords：CNC machine tool;spindle-column system;wind speed method;coupling analysis;thermal characteristics;accuracy retention- 26
- |
- 5
- |
- 5
Published：2023-04-18 -
Precise localization of rotary symmetrical aspheric workpiece in magnetorheological polishing
Abstract：To enhance the precise localization of rotary symmetric aspheric workpiece in magnetorheological polishing, an improved two-level positioning method (ITLICP) based on iterative closest point (ICP) was proposed in this study. The magnetorheological polishing characteristics and requirements revealed that the constant immersion depth control determines the principle of workpiece non-leveling positioning. The classical ICP algorithm was applied to overcome the drawbacks of rotationally symmetric aspheric workpiece positioning of non-uniqueness and low computational efficiency. In this study, an initial iterative matrix was constructed to realize the unique specified matching of the workpiece position and a vertical mapping method was proposed to reduce the matching point cloud size, thus improving the computational efficiency. Then, an improved two-level ICP precise positioning method was proposed. The positioning and verification experiments use a Φ100 mm concave parabolic fused silica workpiece. The results show that the precise positioning method ITLICP satisfied the requirements of magnetorheological polishing positioning. The positioning error is less than 9 μm and the average positioning time is 7.3 min. This demonstrates that both the positioning accuracy and efficiency are improved.Keywords：magnetorheological polishing;rotary symmetrical aspheric workpiece;Iterative Closest Point(ICP);specified match;vertical mapping- 23
- |
- 5
- |
- 4
Published：2023-04-18 -
Rolling bearing fault diagnosis by improved multiscale amplitude-aware permutation entropy and random forest
Abstract：Aiming at the problem of low fault identification accuracy of rolling bearing, a novel fault diagnosis method of rolling bearing was proposed. This method can identify fault types of rolling bearing accurately and analyze the fault severity. Firstly, the optimum proper rotation (PR) component of rolling bearing vibration signal was extracted by intrinsic time-scale decomposition (ITD) to highlight the impact characteristics of fault signal. Then, using the characteristic that improved multi-scale amplitude-aware permutation entropy (IMAAPE) was sensitive to signal amplitude and frequency changes, the AAPE values in different time scales were calculated as the fault feature vector, which improved the coarse-grained process in multi-scale analysis and increased the stability of fault feature extraction. Finally, the random forest multi-classifier was constructed by using the fault feature set to realize the fault type identification and severity analysis of rolling bearing, which had a strong generalization ability. Experimental results show that compared with the existing fault diagnosis methods of rolling bearing, average fault identification accuracy is 99.25%. This method can extract the fault characteristics of rolling bearing stably and effectively with good real-time performance.Keywords：rolling bearing;fault diagnosis;intrinsic time-scale decomposition;amplitude-aware permutation entropy;random forest- 7
- |
- 3
- |
- 4
Published：2023-04-18 -
Optimization of development process for fabrication of high aspect ratio gratings
Abstract：In the development process of high aspect ratio microstructures, the convective mass transfer of the developer is severely limited in the very thick photoresist layer. To improve the uniformity of the development, we have developed a rocker-type shaker-assisted development method that uses the up and down swing of the rocker-type shaker to achieve a uniform flow of the developer. Finite element method is used to simulate the flow field distribution on the surface of the substrate and the different aspect ratios of the microstructure gratings. The simulation results show that the up and down swing of the rocker-bed can achieve a uniform flow in the developer. Furthermore, we propose a rapid development parameter determination method to efficiently define suitable development parameters. The experiments show the relationship between the aspect ratios of the trenches and the development rates, and provide suitable development process parameters. The experimental results verified the rationality of the process parameters. When the development time is 10—12 min and the development rate is 0.21—0.23 m/s, the development uniformity of the grating having a photoresist thickness of 200 μm can be 96% when the aspect ratio of the trenches is 2.5. The simulations and experimental results show that this development method can achieve uniform development of high aspect ratio microstructures and meet the requirements of fabricating high-quality gratings with high aspect ratios.Keywords：high aspect ratio grating;shaker-assisted development process;the aspect ratio of trench;uniform flow- 13
- |
- 2
- |
- 0
Published：2023-04-18 -
Optimization of infrared fresnel lens by injection molding assisted with ultrasonic
Abstract：In order to improve the optical properties of a polymer infrared Fresnel lens, an efficient injection method assisted by ultrasonic was proposed to improve the quality of microgrooves on the surface of polymer infrared Fresnel lens, and optimize the process parameters comprehensively. First, the effect of ultrasonic vibration on the heating and pressurizing of polymers was analyzed, and a comparative test mold with two cavities was designed. Then, the modulation transfer function (MTF) and average heighth of the infrared Fresnel lens were used as quality objectives. A four-step multi-objective optimization process was considered. The comprehensive optimization of process parameters was carried out through experimental design of the relationship between quality objectives and injection process parameters based on a back propagation neural network, and multi-objective optimization based on NSGA-Ⅱ and experimental verification. The experimental results show that the multi-objective optimization process has high accuracy, and the average prediction errors of MTF and h are 4.16% and 3.32% respectively. The Fresnel lens grooves produced by injection molding assisted by ultrasonic have higher reproduction quality. The average groove height h increased by 15.6%, and the fluctuation of h values increased with increasing h value. The MTF value is more affected by h uniformity than by h.Keywords：injection assisted with ultrasonic;infrared fresnel lens;multi-objective optimization;NSGA-Ⅱ algorithm;Back Propagation(BP) neural network- 16
- |
- 3
- |
- 0
Published：2023-04-18 -
Research on interface mechanism of back-end module for on-orbit maintenance
Abstract：On-orbit maintenance can significantly extend the service life of space science instruments, thus reducing economic costs. In order to realize on-orbit operation and replace the back-end module of a space telescope, a set of corresponding interface mechanisms was designed, which can solve the problem of on-orbit rapid positioning and installation. According to the 321 kinematic positioning criteria, the internal composition and working principle of the interface mechanism were introduced in detail. Then, the interface mechanism and back-end module were simulated at the component level. The simulation results show that the first-order mode is much higher than the fundamental frequency of the whole machine, which can prevent resonance when launching. A set of in-plane tooling was designed to simulate the back-end module, and the gravity unloading of the whole mechanism was carried out using the equivalent mass method. A laser tracker was used to measure the repetitive positioning accuracy of the whole back-end module. The experimental data show that the repetitive translation positioning errors ofX, Y, Z in three directions are ±5.58 μm, ±3.24 μm and ±3.63 μm respectively, which are higher than the overall index of ±10 μm. The thermal experimental results show that the whole mechanism can completely release the deformation caused by temperature change, and has high thermal stability. The relative position of the incident light and target surface is stable, and the imaging quality is high, which provides a strong reference value for on-orbit maintenance devices in outer space.Keywords：on-orbit maintenance;interface mechanism;kinematic installation;repeated positioning accuracy;heat release- 19
- |
- 2
- |
- 1
Published：2023-04-18 -
High-precision position control for MSCMG's high-speed rotor
Abstract：Nonlinear problems of magnetic force under the influence of the gyro effect and moving-gimbal effect were the main factors that decrease the position precision for the high-speed rotor of magnetically suspended control moment gyros. Therefore, the characteristics of the magnetic force of the rotor are analyzed, and a nonlinear dynamic model of the rotor system was established. A sliding mode control method based on neural network was proposed to address the problem and to improve the position precision of the rotor. A sliding mode control law was designed. The radial basis function neural network was adopted to approximate the nonlinear model, while the adaptive algorithm adopt the weights of the network according to the error as well as guarantees the stability of the system. The simulation and experimental results indicate that the proposed method improves the position precision of the rotor to 99%, and the static error is 0.000 2 mm. The sliding mode control based on neural network can achieve the high-precision position control of the rotor system.Keywords：Magnetically Suspended Control Moment Gyroscope (MSCMG);magnetically suspended rotor;high-precision position control;sliding mode control;neural network- 24
- |
- 4
- |
- 0
Published：2023-04-18
Micro/Nano Technology and Fine Mechanics
-
Search area and target scale adaptive sea surface object tracking for unmanned surface vessel
Abstract：Sea target tracking is important in the autonomous navigation and intelligent operation of unmanned surface vessels. Compared to target tracking in common scenes, sea surface target tracking faces unique challenges, such as intense dithering of the target and considerable changes in its scale. Aiming at the problem of intense dithering of sea surface targets, an adaptive search area algorithm was present in this paper. The proposed method extracts the position of the sea-sky-line by segmenting sea surface scenes, and it adaptively determined the target's search area in each frame using the motion model of sea-sky-line. To solve the problem of considerable changes in the scale of sea surface targets, this study achieved an adaptive tracking of the targets' scale by segmenting the search area. Based on the correlation filtering tracking framework, combined with the two improves strategies above, the proposed algorithm improved tracking precision by at least 26% compared to the traditional correlation filtering algorithm. Therefore, the proposed algorithm effectively solves the problem of intense object jitter and scale adaptation and improves the accuracy of sea object tracking.Keywords：search area adaptive;target scale adaptive;image segmentation;sea surface target tracking- 21
- |
- 4
- |
- 1
Published：2023-04-18 -
Sum-rate maximization of user-centric visible light communication cells with zero forcing precoding
Abstract：In this paper, the Zero-Forcing (ZF) precoding optimization of a visible light communication (VLC) system was studied in detail. We first derive sum-rate expression via information theory tool. Then, by considering that the optical power restriction of light-emitting diodes and VLC signals was inherently non-negative, the rate maximization problem was given in the form of mathematical optimization. Based on the derived bounds, optimal beamformer designs for max-min fairness sum-rate and maximum sum-rate problems were formulated as convex optimization problems, which then can be efficiently solved using standard optimization packages. Comparison with existing network-centric cooperative and noncooperative schemes in a VLC system show that the user-centric approach performs better, and ZF precoding can effectively improve the sum-rate of the system by approximately 2 nats/s/Hz, as is validated by simulations.Keywords：visible light communication;user-centric;precoding;Zero Forcing(ZF);convex optimization- 16
- |
- 3
- |
- 1
Published：2023-04-18 -
Multi-label classification of traditional national costume pattern image semantic understanding
Abstract：Since current image multi-label classification methods only focus on the category information of image ontology (ontology) and ignore the deep semantic information of the image (implicit), this study proposed an image multi-label classification model of "ontology-implicit" fusion learning. The model first used the middle and higher layers of CNN to learn the image ontology information and implicit information, respectively, and then it used the dependency relationship between the ontology information and implicit information to design the fusion learning model. Meanwhile, the different characteristics of the middle layer and different structures of the model were studied in-depth, to realize the classification of implicit information contained in multiple image categories. Experiments conducted on the traditional national costume pattern image datasets show that the mAP of image ontology multi-label classification and implicit multi-label classification are 0.88 and 0.82, respectively. Comparative experiments conducted on the Scene dataset show that the model is superior to other methods in Hamming loss, one error, and average precision indices, with values of 0.103, 0.091, and 0.083, respectively. Therefore, the experimental results prove the effectiveness and superiority of this method.Keywords：multi-label classification;fusion learning;traditional national costumes;semantic understanding- 20
- |
- 3
- |
- 4
Published：2023-04-18 -
Recognition and multiscale equivalent morphological features extraction of flotation bubbles in NSCT domain
Abstract：To solve the problem of cohesion and background-free and uneven illumination, which makes it difficult to extract direct morphological features from flotation bubble images, a multi-scale equivalent morphological feature extraction and recognition method for flotation bubbles was proposed in a nonsubsampled contourlet transform (NSCT) domain. Firstly, the flotation bubble image was decomposed via NSCT to obtain a low frequency subband and multi-scale and multi-directional high frequency subbands. The fuzzy set method was used for the binarization of the low frequency subband image to obtain the bubble bright spot image, and the number of bright spots, average area, standard deviation, and ellipticity were extracted as the equivalent morphological size features. Thereafter, the directional modulus maxima and differential box-counting method were used to calculate the fractal dimensions of the high frequency subband directions. Finally, by using the multi-scale and multi-directional equivalent morphological size features as the input, the state recognition and classification of three types of flotation bubble images were carried out via a quantum gate node neural network. The experimental results show that the extracted equivalent morphological size features are highly correlated with the classification and it can be effectively used to recognize the state of three types of flotation bubble images. The average recognition accuracy is 95.1%, which is higher than that of several common algorithms, and it is suitable for dynamic flotation conditions.Keywords：flotation bubble image;multi-scale equivalent morphological features;Nonsubsampled Contourlet Transform(NSCT);binarization of fuzzy sets;modulus maxima fractal dimension;quantum gate node neural network- 13
- |
- 3
- |
- 4
Published：2023-04-18 -
Passivity-based neural network H∞ avoidance compliant control of space robot capturing spacecraft
Abstract：The collision avoidance compliant control for space robot on-orbit capture of noncooperative spacecraft was studied. A compliant mechanism, i.e., Rotary Series Elastic Actuator (RSEA), was mounted between the joint motor and manipulator. Its functions were as follows: first, the deformation of its internal spring could absorb the impact energy of the captured spacecraft on the joints of the space robot; second, the joint impact torque could be limited to a safe range by combining with the collision avoidance compliant control scheme. The dynamic models of the space robot and target spacecraft before capture were obtained with the Lagrange approach and Newton-Euler method. Then, based on the impulse theorem, kinematic constraints, and the law of force transfer, the dynamic model of the composite system was derived. Finally, a passivity-based neural network robust H-infinity compliant control was proposed for the post-capture composite system. The simulation results show that the space robot system with RSEA can reduce the collision impact torque of the joint during capture phase by as much as 61.9%, or by at least 47.8%. During the motion stabilization control phase, the joint impact torque is limited to a safe range to realize the effective protection of joints.Keywords：compliant mechanism;space robot;capture spacecraft operation;passivity theory;collision avoidance compliant control;neural network robust H-infinity control- 14
- |
- 2
- |
- 3
Published：2023-04-18 -
SAR ATR based on disentangled representation learning generative adversarial networks and support vector machine
Abstract：To solve the problem of insufficient training samples and sensitivity of the target's aspect angle for Synthetic Aperture Radar (SAR) Automatic Target Recognition (ATR), a target recognition algorithm for SAR images based on a DRGAN and Support Vector Machine (SVM) was proposed in this paper. First, a multiscale fractal feature was used to enhance the input SAR image, and the target binary image was obtained through threshold segmentation. Hu second moments were used to estimate the aspect angle of the target. Second, the estimated angle was quantized into a vector, and the parameters of the designed DRGAN model were trained and optimized using these vectors and original images. Because the deep generative model in DRGAN was designed by disentangling the target's pose from its representation, the aspect angles of SAR image samples could be transformed into the same interval through this model. Normalized gray features were extracted from these transformed training samples, and an SVM classifier was trained using these features. MSTAR database was used to test the performance of the proposed algorithm under different operating conditions. The experimental results demonstrate that the classification accuracy reached 97.97% under standard operating conditions with variants, which is superior to some methods based on a convolutional neural network. The proposed algorithm can achieve classification accuracies of 97.83%, 91.77%, 97.11% and 97.04% under four extended operating conditions, respectively, which are better than traditional methods. Despite some errors during the estimation of the aspect angle of the object in the SAR image, the trained GAN model acting as rotation estimator of SAR objects still achieves better SAR object recognition performance under the condition in which no complex data preprocessing methods are used.Keywords：Synthetic Aperture Radar(SAR) image;target recognition;generative adversarial networks;aspect angle estimation;Support Vector Machine(SVM)- 21
- |
- 3
- |
- 5
Published：2023-04-18 -
Multi images fusion Retinex for low light image enhancement
Abstract：In this paper, a multiple-image fusion enhancement algorithm based on Retinex was proposed to solve the problem of contrast enhancement and naturalness preservation under low-light conditions. First, the maximum value was found in the R, G, and B channels to estimate the brightness of each pixel of the image as an initial illumination estimation. Based on the Retinex theory, the reflection image was generated and adjusted by morphological closing. Furthermore, the global contrast enhancement map and local natural degree keeping illumination map based on the initial illumination map were generated using a gamma transform and a double logarithmic transform, respectively. Subsequently, an adaptive weighted least square filtering fusion strategy was designed to fuse the three illumination images into the final illumination estimation image. Finally, the final illumination image was synthesized, and the reflection image was adjusted to obtain the image after the low-light enhancement. The experimental results indicate that the proposed algorithm has a lower lightness-order-error and natural image quality evaluator value compared to conventional enhancement algorithms. Moreover, the lightness-order-error and natural image quality evaluator values of real natural scenes can be reduced to 4.12 and 3.25, respectively, which yields better enhancement effects than conventional methods. Therefore, the proposed Retinex-based multiple-image algorithm using adaptive weighted least square filtering can effectively enhance the contrast and retain the natural degree of low-light images.Keywords：low light enhancement;retinex;weighted least square filtering;morphological closing;image naturalness saving- 19
- |
- 3
- |
- 11
Published：2023-04-18 -
Scenemigration of indoor flame image based on Cycle-Consistent adversarial networks
Abstract：The training of video fire detection models based on deep learning relies on a large number of positive and negative samples, namely, fire videos and scenario videos involving other disturbances similar to fires. In some instances, the fire video sampled from a scene is insufficient owing to the prohibition of ignition. In this thesis, it was proposed that the flames recorded in other similar scenarios be migrated into the specified scene to increase the data of the fire video in such restricted situations. To complete the content information, a flame kernel was previously implanted into the specified scene, and then style information, such as smoke and ground reflection, were added to fuse the scene and the flame. Our method eliminated the background distortion caused by the loss of information during image translation via the existing multimodal image translation. In addition, Cycle-Consistent adversarial networks were adopted to decrease the dataset quantity and remove the restriction of strict matching of the training images. Compared with other multimodal image-to-image translations, our method ensured that the fire in a scene was diverse, and the migration scene was more visually realistic. The minimum values of FID and LPIPS are achieved, which are 119.6 and 0.134 2, respectively.Keywords：image translation;generative adversarial network;fire image synthesis;Cycle Generative Adversarial Network(CycleGAN)- 26
- |
- 2
- |
- 1
Published：2023-04-18
Information Sciences
Loading...
0