Abstract:The emergence of meta-surface holography is greatly promoted to the development of holographic imaging technology and the application range of electromagnetic meta-surfaces. In order to further clarify the development trajectory of meta-surface holography, this paper systematically reviews the development process of meta-surface technology and the progress of holographic imaging modes benefited from meta-surface technology. With the advancement of technology, the meta-surface holography gradually evolves as the microwave frequency band from the visible light frequency band, and as dynamic holography from static reproduction. Therefore, the discussion of this paper centers on the introduction of meta-surface holography - reconfigurable meta-surfaces and their dynamic holographic technology to the future direction. For the above-mentioned reasons, this paper prospectively discusses the development of reconfigurable meta-surface holography,high-performance innovation technology of meta-surface element,holographic modes of meta-surface, and meta-surface holographic system research.

Abstract:Aimed at the problems that existing discrete-time prescribed performance control (PPC) methodology is high in dependence on sliding mode reaching laws and obvious in chattering defects, a new discrete time PPC approach is proposed for a seeker's stability platform by constructing a new design framework without using sliding mode control. Firstly, the discrete time performance functions are developed to impose envelope constraints on tracking errors. And then, a discrete time transformed error is defined to construct a novel feedback function. Furthermore, discrete time PPC protocols are explored to stabilize the newly developed feedback function instead of the transformed error, guaranteeing not only all the tracking errors with desired prescribed performance, and remedying the defects of control chattering caused by the dependence of control algorithms on sliding mode reaching laws. Finally, by comparing the simulation results and verifying, the method is valid and superior.

Abstract:In view of the issue of transition thrust pinch during power transitions in hybrid propulsion aircraft, a switching control method is proposed for hybrid propulsion aircraft considering thrust pinch.Firstly, for the normal flight control requirements of hybrid propulsion aircraft, a normal flight controller is designed by using a sliding mode control approach based on the super-twisting algorithm, enabling the aircraft to achieve finite-time stable tracking of reference commands in the presence of disturbances. Secondly, in consideration of the control constraints imposed by thrust losses during power transitions, an input-constrained controller is designed to facilitate limited-time convergence of tracking errors during the mode transition phase while reducing the demand for thrust. Furthermore, in combination with the controllers for a normal flight or on a mode transition phase, a soft switching control strategy for combined engine transitions is designed. Finally, the simulation experiments show that the designed controller can not only effectively avoid thrust loss phenomenon, and effectively ensure the stability and the robustness in the switching control system.

Abstract:The maneuver mode recognition problem of reentry gliding vehicle (RGV) is the key to the interceptors in achieving its trajectory prediction. In view of this issue, this paper proposes a set of feature parameters fitted to the maneuver characteristics of vehicle trajectories. Based on the constructed RGV maneuvering mode trajectory library, an LSTM deep learning neural network is built, training the extracted new feature parameters. Compared with the traditional modes recognition method and other typical feature parameters in network training, the results show that the set of the proposed feature parameters is fast at convergence speed, high in recognition accuracy, and good in robustness in LSTM maneuver mode recognition network training.

Abstract:In view of tracking control problem of input-constrained waverider vehicles,an estimation-free prescribed performance control scheme is proposed. Firstly, a new anti-saturation compensation system is designed to address the possible problem of actuator saturation. Then, the states of the compensation system are used to construct new prescribed performance transformed errors, and the controller is designed directly using the constructed new prescribed performance transformed errors based on the prescribed performance control and backstepping control methods. Then, a new prescribed performance transition error is constructed using the compensated system state, and low-complexity controllers without estimation are designed for the velocity subsystem and the altitude subsystem based on the method of prescribed performance control and backstepping control. The superiority of this method is that it eliminates the need for state estimation and neural approximation, which significantly reduces the complexity and computation of the control. Based on Lyapunov stability theory,it was proved that all transformed errors and tracking errors of the system are ultimately uniformly bounded. Finally,the effectiveness of the provided method are validated via numerical simulation.

Abstract:Aimed at the problems that the results of current adaptive control for Flexible Air-breathing Hypersonic Vehicle (FAHV) are capable of only achieving asymptotic error convergence to the preset envelope, and the problems of computational explosion and excessive occupancy of airborne resources remain due to online updating of neural weights, an adaptive control method is proposed for FAHV specified time convergence based on event triggering mechanism and minimum learning parameters. Firstly, an improved preset performance control mechanism is proposed which does not depend on the exact initial error value and can ensure the convergence of the specified error time. Secondly, a relative threshold event-triggered neural network for FAHV interference identification is constructed. Finally, a control algorithm of relative threshold event triggering is designed, which is capable of effectively reducing the consumption of communication resources of the closed-loop controller, and achieving good control accuracy on the basis of nonisoperiodic signal transmission. The simulation results show that the proposed method can track the height/speed reference signal on a specified time under conditions of low computing and transmission resource consumption.

Abstract:In order to meet the needs of flight performance, a tandem drive variable camber wing is designed with NACA4412 airfoil. Wing structure is divided into five sections along chordwise, and leading section is the main load-bearing structure. Four wing sections of the trailing edge are driven by four electrical servo motors in series. In the interior of deflecting wing section, pentahedron truss structure is adopted, and in the interior there is laid on the surface a composite elastic skin. Connecting rods with stop function is arranged to limit the relative rotation angle of the four trailing sections. A kinematics analysis model of the variable camber wing is established, and the drive speed is calculated. An aerodynamic analysis model of the wing is built, and the aerodynamic performance of four typical flight status is analyzed, and their performance is compared with that of the wing with conventional flight control surfaces. The results show that under the same flight status, the actuation time of the variable camber wing with fourstage tandem drive along chordwise is only 25% of that of the conventional wing. The lift-drag ratio increases by 71.94% for takeoff. The maneuver moment increases by 12.46% for roll. The lift increases by 11.19% for approach, and the drag increases by 104.83% for deceleration after touchdown. Tandem drive variable camber wing is superior relatively to the conventional control wing in handling characteristics and in aerodynamic performance.

Abstract:The common problem of static calibration and dynamic measurement remaining in domestic aircraft landing gear load measurement, the causes of static calibration in dynamic load measurement by strain method are analyzed theoretically and mechanically. At the same time, the focuses, in consideration of carrier based aircraft being subjected to severe dynamic loads due to fixed point landing, is on the static and dynamic measurement of impact loads on carrier based aircraft landing. By simulating the process of aircraft landing through dynamic drop tests and analyzing the measured load on the force measuring platform, the degree of influence of dynamic load on the accuracy of strain method measurement is obtained,and an improved inertia correction method is proposed. The identification of the mass matrix is done by the drop test data, and the correction of the measured load is made by the strain method through the identified mass matrix and measured acceleration. The experimental results show that the improved inertia correction method further improves the measurement accuracy of vertical loads and significantly improves the measurement accuracy of heading and lateral loads

Abstract:Aimed at the problems that in the process of bayesian network structure learning, the network structure size increases in exponential with the number of nodes, in leading to the expansion of the network structure search space, and, in turn, hampering the efficiency of network structure learning algorithms, a bayesian network hybrid structure learning method, MMPC-FPSO, is introduced in combination with maximum-minimum parent-child set constraints (MMPC) and firefly particle swarm optimization (FPSO). Firstly, in view of addressing the issues of low algorithm efficiency and inaccurate network structure due to random initialization of the network structure population in the process of bayesian network structure learning using particle swarm algorithms, a population constraint method is proposed based on the improved MMPC algorithm. Secondly, in view of tackling the problems of slow speed, low accuracy, and susceptibility to local optima in traditional particle swarm-based scoring search methods, a particle optimization strategy based on the firefly algorithm is presented. Finally, in order to validate the correctness and superiority of the proposed method, the three standard networks are applied to the structure learning. The simulation results demonstrate that the gap between the obtained BIC scores and the scores of standard networks is reduced by 68.7%, 65.5%, 34.1%, respectively by the proposed algorithm, compared to the traditional particle swarm-based structure learning methods.

Abstract:In view of hole edge crack initiation-monitoring of porous aluminum alloy plates in aviation structures under fatigue load, a method of hole edge crack initiation-monitoring is proposed based on the fiber optic sensing system in combination with wavelet decomposition, density based spatial clustering of applications with noise and Gaussian mixture model. Firstly, a fiber optic grating sensing system is used to collect the micro strain at the edge of a porous aluminum alloy plate during the entire process from crack initiation to structural fracture under cyclic loading conditions, and a micro strain curve at the edge of the hole is constructed. Wavelet decomposition on the micro strain curve at the hole edge is performed to obtain the low-frequency and high-frequency components of the micro strain curve, and the minimum value of the low-frequency component and the sudden change of the high-requency component are taken as the characteristics of crack initiation at the hole edge. The crack initiation being analyzed, the number of fatigue loading cyclic number is calculated by DBSCAN algorithm and GMM theory when the crack at the hole edge is initiated, and the initiation position of the main crack at the hole edge of the porous aluminum alloy plate and the number of fatigue loading cyclic number are compared and analyzed when the main crack at the hole edge is initiated. The test results show that this monitoring method is capable of accurately locating the initiation position of the main crack at the hole edge, and calculating the fatigue loading cyclic number when the main crack at the hole edge initiates, and the calculation error of the fatigue loading cyclic number is within the range of 5%. In the future, the method can be applied to the ground fatigue test of a whole-aircraft, structural health monitoring and other scenarios.

Abstract:In view of the problems lying ahead of “low slow small” target detection, a grid based concept is proposed, a definition of grid based perception system is given, and a grid based perception system is designed, including sensor subsystem, communication subsystem, management and control center, and comprehensive support subsystem. The paper analyzes the key technologies of grid based perception systems, including low-cost sensor design, “low slow small” target detection, data fusion processing, and other technologies. The deployment principles of grid based perception systems are researched and a deployment principle model is established. And the above-mentioned reasons have, to a certain extent, practical guidance significance for solving the problem of “low slow small” target detection.

Abstract:In order to solve the problem of highly similar data in the condition of small data set expansion, the dimensionality reduced kernel density estimation method is utilized for expanding the small data set, obtaining more accurate expanded data.In addition, in order to solve the problems of low efficiency and weak convergence of CSO, an improved ICSO is proposed to learn the structure:L􀆧vy flight is introduced into the position update formula of rooster to make the algorithm jump further;the dynamic adjustment inertia weight with exponential decline is adopted to hasten local search and augmenting convergence speed; by introducing the most advantageous individual guidance approach, the likelihood of discovering the ideal position is increased.The experimental results show that the proposed algorithm is superior to the MCMC algorithm, the BPSO algorithm, the CSO algorithm, the ADLCSO-I algorithm and the SA-ICSO algorithm in terms of BIC score, accuracy and Hamming distance under conditions of small data set.

Abstract:Aimed at the problems that military unmanned aerial vehicle (UAV) data link communication is poor in anti-interference performance and weak in anti-captured capability, a narrow cross-section patternreconfigurable antenna is proposed based on an active meta-surface radome with excellent aerodynamic performance.The antenna is comprised of a broadband planar omnidirectional antenna, a narrow cross-section active meta-surface radome with excellent aerodynamic performance, and a dual-frequency impedance matching network. When all the diodes on the meta-surface radome are off (without bias voltage applied), the radome is in a fully transparent state, and the antenna operates in a broadband omnidirectional communication mode. However, when specific diodes on the meta-surface radome are turned on, the corresponding area of the radome becomes fully shielded, and the antenna works in a dual-frequency directional communication mode. In this case, the impedance matching of the antenna is improved significantly by introducing a dual-frequency impedance matching network. In the omnidirectional communication mode, the antenna exhibits a relative bandwidth of 44.6%, a maximum gain of 1.37 dBi, and an out-of-roundness of less than 2.5 dBi. In the directional mode, the dual-frequency antenna has upper and lower frequency bands of 1.4 GHz and 1.8 GHz, respectively, with relative bandwidths of 9.1% and 15.3%. The maximum directional gain can reach 5.2 dBi. The proposed antenna offers the advantages of a narrow cross-section and low cost while allowing flexible switching between broadband omnidirectional communication mode and dual-frequency directional communication mode. The proposed antenna is expected to enhance the anti-interference and anti-capture performance of UAVs.

Abstract:Missile formation baseline measurement is the premise of missile cluster attack.In view of the problems in missile formation baseline measurement, a high-performance lightweight baseline measurement method is proposed based on BDS-3 DGNSS/RDSS/INS.Taking the BDS RDSS short message as a formation data transmission link, a pseudo-range single-difference observation model is established based on the BDS-3 DGNSS/INS. Under conditions of continuous normal GNSS signal or signal interruption, the DGNSS and INS integrated navigation is capable of achieving a stable baseline measurement output.The simulation results show that the DGNSS/INS integrated navigation can achieve stable baseline measurement output in the observation epoch of continuous normal GNSS signal. With the GNSS signal interrupting in 20 seconds, the baseline measurement error of DGNSS/INS integrated navigation in the east (E) and north (N) directions is less than 2.5 m(1σ), and the baseline measurement error in the up (U) direction is less than 3.0 m (1σ). The requirement of pseudo-range single-difference model is reduced by 70%~80% compared with the RTK algorithm.

Abstract:In order to make a microstrip line liquid crystal phase shifter loaded with defective ground structure(DGS) good in performance, small in insertion loss, suitable in return loss, and larger in phase coverage.the DGS microstrip line liquid crystal phase shifter is modeled and simulated by utilizing HFSS simulation software for changing the phase shifting capability of a single phase shifting unit and changing the shape of the DGS, achieving the same performance with fewer phase shifting units. Taking a dumbbell DGS liquid crystal microstrip line phase shifter as a reference, the differences in phase shifting capability and insertion loss of five shapes of DGS (dumbbell, reduced DGS area, first-order fractal, triangular, and crossover) are compared. The first-order fractal and crossover DGS microstrip line liquid crystal phase shifters show that the phase shifting is good in capability in comparison, and finally the results are verified by simulating phase shifters with different dielectric constants to observe their S-parameters and phase shifting capability