Automatic modulation recognition of radio fuzes using a DR2D-based adaptive denoising method and textural feature extraction

The identification of intercepted radio fuze modulation types is a prerequisite for decision-making in interference systems.However,the electromagnetic environment of modern battlefields is complex,and the signal-to-noise ratio(SNR)of such environments is usually low,which makes it difficult to implement accurate recognition of radio fuzes.To solve the above problem,a radio fuze automatic modulation recognition(AMR)method for low-SNR environments is proposed.First,an adaptive denoising algorithm based on data rearrangement and the two-dimensional(2D)fast Fourier transform(FFT)(DR2D)is used to reduce the noise of the intercepted radio fuze intermediate frequency(IF)signal.Then,the textural features of the denoised IF signal rearranged data matrix are extracted from the statistical indicator vectors of gray-level cooccurrence matrices(GLCMs),and support vector machines(SVMs)are used for classification.The DR2D-based adaptive denoising algorithm achieves an average correlation coefficient of more than 0.76 for ten fuze types under SNRs of-10 d B and above,which is higher than that of other typical algorithms.The trained SVM classification model achieves an average recognition accuracy of more than 96%on seven modulation types and recognition accuracies of more than 94%on each modulation type under SNRs of-12 d B and above,which represents a good AMR performance of radio fuzes under low SNRs.

Synergistic effect of carbon nanotube and encapsulated carbon layer enabling high-performance SnS_2-based anode for lithium storage

Tin disulfide(SnS_(2)),due to large interlayer spacing and high theoretical capacity,is regarded as a prospective anode material for lithium-ion batteries.Nevertheless,the poor electron conductivity of SnS_(2) and huge volumetric change during the lithiation/delithiation process lead to a rapid capacity decay of the battery,hindering its commercialization.To address these issues,herein,SnS_(2) is in-situ grown on the surface of carbon nanotubes(CNT)and then encapsulated with a layer of porous amorphous carbon(CNT/SnS_(2)@C)by simple solvothermal and further carbonization treatment.The synergistic effect of CNT and porous carbon layer not only enhances the electrical co nductivity of SnS_(2) but also limits the huge volumetric change to avoid the pulverization and detachment of SnS_(2).Density functional theo ry calculations show that CNT/SnS_(2)@C has high Li^(+)adsorption and lithium storage capacity achieving high reaction kinetics.Consequently,cells with the CNT/SnS_(2)@C anode exhibit a high lithium storage capacity of 837mAh/g after 100 cycles at 0.1 A/g and retaining a capacity of 529.8 mAh/g under 1.0 A/g after 1000 cycles.This study provides a fundamental understanding of the electrochemical processes and beneficial guidance to design high-performance SnS_(2)-based anodes for LIBs.

Research on aiming methods for small sample size shooting tests of two-dimensional trajectory correction fuse

The longitudinal dispersion of the projectile in shooting tests of two-dimensional trajectory corrections fused with fixed canards is extremely large that it sometimes exceeds the correction ability of the correction fuse actuator.The impact point easily deviates from the target,and thus the correction result cannot be readily evaluated.However,the cost of shooting tests is considerably high to conduct many tests for data collection.To address this issue,this study proposes an aiming method for shooting tests based on small sample size.The proposed method uses the Bootstrap method to expand the test data;repeatedly iterates and corrects the position of the simulated theoretical impact points through an improved compatibility test method;and dynamically adjusts the weight of the prior distribution of simulation results based on Kullback-Leibler divergence,which to some extent avoids the real data being"submerged"by the simulation data and achieves the fusion Bayesian estimation of the dispersion center.The experimental results show that when the simulation accuracy is sufficiently high,the proposed method yields a smaller mean-square deviation in estimating the dispersion center and higher shooting accuracy than those of the three comparison methods,which is more conducive to reflecting the effect of the control algorithm and facilitating test personnel to iterate their proposed structures and algorithms.;in addition,this study provides a knowledge base for further comprehensive studies in the future.

Underdetermined direction of arrival estimation with nonuniform linear motion sampling based on a small unmanned aerial vehicle platform

Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.

Automatic modulation recognition of radiation source signals based on two-dimensional data matrix and improved residual neural network

Automatic modulation recognition(AMR)of radiation source signals is a research focus in the field of cognitive radio.However,the AMR of radiation source signals at low SNRs still faces a great challenge.Therefore,the AMR method of radiation source signals based on two-dimensional data matrix and improved residual neural network is proposed in this paper.First,the time series of the radiation source signals are reconstructed into two-dimensional data matrix,which greatly simplifies the signal preprocessing process.Second,the depthwise convolution and large-size convolutional kernels based residual neural network(DLRNet)is proposed to improve the feature extraction capability of the AMR model.Finally,the model performs feature extraction and classification on the two-dimensional data matrix to obtain the recognition vector that represents the signal modulation type.Theoretical analysis and simulation results show that the AMR method based on two-dimensional data matrix and improved residual network can significantly improve the accuracy of the AMR method.The recognition accuracy of the proposed method maintains a high level greater than 90% even at -14 dB SNR.

Suppression of low-frequency ultrasound broadband vibration using star-shaped single-phase metamaterials

In order to suppress the low-frequency ultrasound vibration in the broadband range of 20 k Hz—100 k Hz,this paper proposes and discusses an acoustic metamaterial with low-frequency ultrasound vibration attenuation properties,which is configured by hybrid arc and sharp-angle convergent star-shaped lattices.The effect of the dispersion relation and the bandgap characteristic for the scatterers in star-shaped are simulated and analyzed.The target bandgap width is extended by optimizing the geometry parameters of arc and sharp-angle convergent lattices.The proposed metamaterial configured by optimized hybrid lattices exhibits remarkable broad bandgap characteristics by bandgap complementarity,and the simulation results verify a 99%vibration attenuation amplitude can be obtained in the frequency of20 k Hz—100 k Hz.After the fabrication of the proposed hybrid configurational star-shaped metamaterial by 3D printing technique,the transmission loss experiments are performed,and the experimental results indicate that the fabricated metamaterial has the characteristics of broadband vibration attenuation and an amplitude greater than 85%attenuation for the target frequency.These results demonstrate that the hybrid configurational star-shaped metamaterials can effectively widen the bandgap and realize high efficiency attenuation,which has capability for the vibration attenuation in the application of highprecise equipment.

Process and performance of DAAF microspheres prepared by continuous integration from synthesis to spherical coating based on microfluidic system

In order to improve the energy output consistency of 3, 3’-diamino-4, 4’-azoxyfurazan(DAAF) in the new insensitive booster and the safety and efficiency in the preparation process, a continuous preparation system of DAAF from synthesis to spherical coating was designed and established in this paper, which combined ultrasonic micromixing reaction with microdroplet globular template. In the rapid micromixing stage, the microfluidic mixing technology with ultrasonic was used to synergistically strengthen the uniform and rapid mass transfer mixing reaction between raw materials to ensure the uniformity of DAAF particle nucleation-growth, and to prepare high-quality DAAF crystals with uniform structure and morphology and concentrated particle size distribution. In the microdroplet globular template stage, the microfluidic droplet technology was used to form a droplet globular template with uniform size under the shear action of the continuous phase of the dispersed phase solution containing DAAF particles and binder. The size of the droplet template was controlled by adjusting the flow rate ratio between the continuous phase and the dispersed phase. In the droplet globular template, with the diffusion of the solvent in the dispersed phase droplets, the binder precipitates to coat the DAAF into a ball, forming a DAAF microsphere with high sphericity, narrow particle size distribution and good monodispersity. The problem of discontinuity and DAAF particle suspension in the process was solved, and the coating theory under this process was studied. DAAF was coated with different binder formulations of fluororubber(F2604), nitrocellulose(NC) and NC/glycidyl azide polymer(GAP), and the process verification and evaluation of the system were carried out. The balling effects of large, medium and small droplet templates under different binder formulations were studied. The scanning electron microscope(SEM) results show that the three droplet templates under the three binder formulations exhibit good balling effect and narrow particle size distribution. The DAAF microspheres were characterized by powder X-ray diffraction(XRD), differential scanning calorimetry(DSC), thermo-gravimetric(TG) and sensitivity analyzer. The results showed that the crystal structure of DAAF did not change during the process, and the prepared DAAF microspheres had lower decomposition temperature and lower mechanical sensitivity than raw DAAF. The results of detonation parameters show that the coating of DAAF by using the above three binder formulations will not greatly reduce the energy output of DAAF, and has comparable detonation performance to raw DAAF. This study proves an efficient and safe continuous system from synthesis to spherical coating modification of explosives, which provides a new way for the continuous, safe and efficient preparation of spherical explosives.

Design and evaluation of a kind of polymer-bonded explosives with improved mechanical sensitivity and thermal properties

The emergence of TKX-50,an energetic ionic salt with a high enthalpy of formation and low sensitivity,has opened a new path for the development of high-energetic,insensitive composite explosives.However,due to the poor interfacial binding properties of TKX-50 with conventional binders,there is a lack of effective guidance for the design of TKX-50 based composite explosives.To address the above issues,the interactions between carboxymethyl cellulose acetate butyrate(CMCAB)and other binders with explosives TKX-50/HMX were compared using the molecular dynamics method.Based on the simulations,TKX-50/HMX/CMCAB-based polymer-bonded explosives(PBXs)were prepared with CMCAB as binder,which displays a high binding energy(Ebind)with TKX-50 and high cohesive energy density(CED),and the effect of TKX-50 content on the performance of PBXs was investigated.The physical properties of PBXs,specifically the morphology,mechanical sensitivity,and thermal conductivity,were analyzed by SEM,sensitivity apparatus,and thermal conductivity meter,respectively.The specific heat capacity(Cp)and non-isothermal decomposition temperature of PBXs were tested by DSC,and then the corresponding thermal kinetic parameters were analyzed to evaluate their thermal safety.The adiabatic thermal decomposition processes of PBXs were tested using an ARC instrument.The decomposition mechanism and kinetics were also explored to further analyze their thermal stability and thermal safety under adiabatic conditions.The computer code EXPLO5 was used to predict the detonation parameters of PBXs.The results showed that CMCAB and TKX-50 displayed favorable interfacial bonding properties,and TKX-50 can be bonded with HMX to form a molding powder with a desirable morphology and safety profile.The TKX-50 in PBXs effectively improves the mechanical sensitivity and thermal safety of PBX and has a significant effect on the detonation performance of PBX.This research demonstrates a novel method suitable for screening and investigating high-energetic insensitive explosive systems compatible with TKX-50.

Study on damage mechanism and damage distribution of the rear plate under impact of debris cloud

The debris cloud generated by the hypervelocity impact(HVI)of orbiting space debris directly threatens the spacecraft.A full understanding of the damage mechanism of rear plate is useful for the optimal design of protective structures.In this study,the hypervelocity yaw impact of a cylindrical aluminum projectile on a double-layer aluminum plate is simulated by the FE-SPH adaptive method,and the damage process of the rear plate under the impact of the debris cloud is analyzed based on the debris cloud structure.The damage process can be divided into the main impact stage of the debris cloud and the structural response of the rear plate.The main impact stage lasts a short time and is the basis of the rear plate damage.In the stage of structure response,the continuous deformation and inertial motion of the rear plate dominate the perforation of the rear plate.We further analyze the damage mechanism and damage distribution characteristics of the rear plate in detail.Moreover,the connection between velocity space and position space of the debris cloud is established,which promotes the general analysis of the damage law of debris cloud.Based on the relationship,the features of typical damage areas are identified by the localized fine analysis.Both the cumulative effect and structural response cause the perforation of rear plate;in the non-perforated area,cratering by the impact of hazardous fragments is the main damage mode of the rear plate.

Damage assessment of the target area of the island/reef under the attack of missile warhead

Under the background of vigorously developing facilities of island/reef in the world,the economic value and strategic significance of the island/reef have become increasingly important.Unfortunately,they may easily become the attacking target of missiles in the war time.Therefore,aiming at the damage quantification of the targets in the island/reef under the missile attacking,a macroscopic damage assessment model for the target area is proposed in this paper.The model focuses on the construction of the assessment model framework.Firstly,the analytic hierarchy process and the grey relational analysis are applied to measure the importance of each target in the region through four indicators of the target hazard,striking urgency,damage advantage and mission relevance,respectively.Secondly,based on the damage mechanism of shock wave and fragments to target,the corresponding damage model is established,and the damage grade of each target in the evaluated area is obtained according to the damage criteria and grading standard.Finally,the model obtains the overall damage grade of the target area by employing the fuzzy comprehensive evaluation method,with synthesizing the importance and the damage grade of each target.Through the verification of an example,it demonstrates the certain feasibility of the model and provides a certain basis and reference for the subsequent research.

Manipulator-based autonomous inspections at road checkpoints:Application of faster YOLO for detecting large objects

With the increasing number of vehicles,manual security inspections are becoming more laborious at road checkpoints.To address it,a specialized Road Checkpoints Robot(RCRo)system is proposed,incorporated with enhanced You Only Look Once(YOLO)and a 6-degree-of-freedom(DOF)manipulator,for autonomous identity verification and vehicle inspection.The modified YOLO is characterized by large objects’sensitivity and faster detection speed,named“LF-YOLO”.The better sensitivity of large objects and the faster detection speed are achieved by means of the Dense module-based backbone network connecting two-scale detecting network,for object detection tasks,along with optimized anchor boxes and improved loss function.During the manipulator motion,Octree-aided motion control scheme is adopted for collision-free motion through Robot Operating System(ROS).The proposed LF-YOLO which utilizes continuous optimization strategy and residual technique provides a promising detector design,which has been found to be more effective during actual object detection,in terms of decreased average detection time by 68.25%and 60.60%,and increased average Intersection over Union(Io U)by 20.74%and6.79%compared to YOLOv3 and YOLOv4 through experiments.The comprehensive functional tests of RCRo system demonstrate the feasibility and competency of the multiple unmanned inspections in practice.

Adsorption Performance of Sliding Wall-Climbing Robot

Sliding wall-climbing robot （SWCR） is applied worldwide for its continuous motion, however, considerable air leakage causes two problems： great power consumption and big noise, and they constraint the robot＇s comprehensive performance. So far, effective theoretical model is still lacked to solve the problems. The concept of SWCR＇s adsorption performance is presented, and the techniques of improving utilization rate of given adsorption force and utilization rate of power are studied respectively to improve SWCR＇s adsorption performance. The effect of locomotion mechanism selection and seal＇s pressure allocation upon utilization rate of given adsorption force is discussed, and the theoretical way for relevant parameters optimization are provided. The directions for improving utilization rate of power are pointed out based on the detail analysis results of suction system＇s thermodynamics and hydrodynamics. On this condition, a design method for SWCR-specific impeller is presented, which shows how the impeller＇s key parameters impact its aerodynamic performance with the aid of computational fluid dynamics （CFD） simulations. The robot prototype, BIT Climber, is developed, and its functions such as mobility, adaptability on wall surface, payload, obstacle ability and wall surface inspection are tested. Through the experiments for the adhesion performance of the robot adsorption system on the normal wall surface, at the impeller＇s rated rotating speed, the total adsorption force can reach 237.2 N, the average effective negative pressure is 3.02 kPa and the design error is 3.8% only, which indicates a high efficiency. Furthermore, it is found that the robot suction system＇s static pressure efficiency reaches 84% and utilization rate of adsorption force 81% by the experiment. This thermodynamics model and SWCR-specific impeller design method can effectively improve SWCR＇s adsorption performance and expand this robot applicability on the various walls. A sliding wall-climbing robot with high adhesion efficiency is developed, and this robot has the features of light body in weight, small size in structure and good capability in payload.

Discharge characteristics of a needle-to-plate electrode at a micro-scale gap

To understand the discharge characteristics under a gap of micrometers,the breakdown voltage and current–voltage curve are measured experimentally in a needle-to-plate electrode at a microscale gap of 3–50 μm in air.The effect of the needle radius and the gas pressure on the discharge characteristics are tested.The results show that when the gap is larger than 10 μm,the relation between the breakdown voltage and the gap looks like the Paschen curve;while below 10 μm,the breakdown voltage is nearly constant in the range of the tested gap.However,at the same gap distance,the breakdown voltage is still affected by the pressure and shows a trend similar to Paschen＇s law.The current–voltage characteristic in all the gaps is similar and follows the trend of a typical Townsend-to-glow discharge.A simple model is used to explain the non-normality of breakdown in the micro-gaps.The Townsend mechanism is suggested to control the breakdown process in this configuration before the gap reduces much smaller in air.

New Hybrid AD Methodology for Minimizing the Total Amount of Information Content:A Case Study of Rehabilitation Robot Design

Converting customer needs into specific forms and providing consumers with services are crucial in product design.Currently,conversion is no longer difficult due to the development of modern technology,and various measures can be applied for product realization,thus increasing the complexity of analysis and evaluation in the design process.The focus of the design process has thus shifted from problem solving to minimizing the total amount of information content.This paper presents a New Hybrid Axiomatic Design(AD)Methodology based on iteratively matching and merging design parameters that meet the independence axiom and attribute constraints by applying trimming technology,the ideal final results,and technology evolution theory.The proposed method minimizes the total amount of information content and improves the design quality.Finally,a case study of a rehabilitation robot design for hemiplegic patients is presented.The results indicate that the iterative matching and merging of related attributes can minimize the total amount of information content,reduce the cost,and improve design efficiency.Additionally,evolutionary technology prediction can ensure product novelty and improve market competitiveness.The methodology provides an excellent way to design a new(or improved)product.

Design and implementation of robot serial integrated rotary joint with safety compliance

In order to guarantee safety and stability during physical human-robot-interaction(p HRI) in the occasion of service or industrial operation, a serial integrated rotary joint with the characteristics of passive and active compliance is proposed. Passive compliance is achieved by a designed elastic element, such that the compliant joint may minimize large force which occurs during accidental impacts and, further, may offer more accurate and stable force control and a capacity for energy storage. Meanwhile, the modeling of the compliant joint is comprehensively analyzed, including the effect of the motor model on the overall control system. In order to realize the active compliance, a new method of impedance control is proposed. On the basis of PD control, a more compliant impedance controller is introduced. Experimental results show that the serial integrated rotary joint can provide more effective safety compliance during physical interaction, which has also been well applied in our designed massage robot and rehabilitation robot.

Weak wide-band signal detection method based on small-scale periodic state of Duffing oscillator

The conventional Duffing oscillator weak signal detection method, which is based on a strong reference signal, has inherent deficiencies. To address these issues, the characteristics of the Duffing oscillator＇s phase trajectory in a small- scale periodic state are analyzed by introducing the theory of stopping oscillation system. Based on this approach, a novel Duffing oscillator weak wide-band signal detection method is proposed. In this novel method, the reference signal is discarded, and the to-be-detected signal is directly used as a driving force. By calculating the cosine function of a phase space angle, a single Duffing oscillator can be used for weak wide-band signal detection instead of an array of uncoupled Duffing oscillators. Simulation results indicate that, compared with the conventional Duffing oscillator detection method, this approach performs better in frequency detection intervals, and reduces the signal-to-noise ratio detection threshold, while improving the real-time performance of the system.

Weight distribution of sub-munitions fuze design

In order to explore the unexploded ordnance problem of cluster munitions and find the so- lutions, an M85 sub-munitions reliability model was established by applying the Monte Carlo method. Simulation and experimental statistics matched the proportion of unexploded ordnance, so the hy- pothesis was feasible. The causes of failure and influencing factors of the dual-purpose improved conventional munitions M85 were analyzed according to experimental data. The sensitivity of each device in fuze was also analyzed. The sorting of weight of each device influence in M85 sub-muni- tions fuze was determined. Stabilization device with the maximum weight is the key components of sub-munitions fuze, so these results provide a reference to the analysis and redesign of other sub- munitions fuzes.

Effect of microstructure on short pulse duration shock initiation of TATB and initial response mechanism

Micro-TATB particles with different sizes and 3D nanoporous TATB architectures with different specific surface areas were prepared through recrystallization to study short pulse duration shock initiation properties by electric gun technology.For micro-TATB,the initiation threshold significantly decreases with TATB average size ranging from 79.7μm to 0.5μm.For 3D nanoporous TATB architecture,the initiation threshold decreases and then increases with specific surface areas increased from 9.6 m^2/g to36.2 m^2/g.The lowest initiation thresholds are obtained for the micro-TATB with average sizes of 1.3μm and 0.5μm,and 3D nanoporous TATB architecture with specific surface area of 22.4 m^2/g.The shock initiation thresholds of micro-TATB and 3D nanoporous TATB architectures show significantly decreases with the porosity increased.The decomposition reaction and thermal conductivity properties were further investigated to understand the initial response mechanism.High porosity provides more collapse sites to generate high temperature for formation of hot spots.The low thermal conductivity and decomposition temperature could enhance the formation and ignition of the hot spots,and initial decomposition reaction of TATB.The effect of the decomposition temperature is higher than that of the thermal conductivity on the shock initiation properties.The enhanced decomposition reaction could pro mote energy release and transfer process from the ignition to the combustio n.This work offe rs a new insight to understand the effects of microstructure on the shock initiation properties and the initial response mechanism of TATB.

A trajectory shaping guidance law with field-of-view angle constraint and terminal limits

In this paper, a trajectory shaping guidance law,which considers constraints of field-of-view(FOV) angle, impact angle, and terminal lateral acceleration, is proposed for a constant speed missile against a stationary target. First, to decouple constraints of the FOV angle and the terminal lateral acceleration, the third-order polynomial with respect to the line-ofsight(LOS) angle is introduced. Based on an analysis of the relationship between the looking angle and the guidance coefficient,the boundary of the coefficient that satisfies the FOV constraint is obtained. The terminal guidance law coefficient is used to guarantee the convergence of the terminal conditions. Furthermore, the proposed law can be implemented under bearingsonly information, as the guidance command does not involve the relative range and the LOS angle rate. Finally, numerical simulations are performed based on a kinematic vehicle model to verify the effectiveness of the guidance law. Overall, the work offers an easily implementable guidance law with closed-form guidance gains, which is suitable for engineering applications.

Characteristics and underlying physics of ionic wind in dc corona discharge under different polarities

During a dc corona discharge, the ions’ momentum will be transferred to the surrounding neutral molecules, inducing an ionic wind.The characteristics of corona discharge and the induced ionic wind are investigated experimentally and numerically under different polarities using a needle-to-ring electrode configuration.The morphology and mechanism of corona discharge, as well as the characteristics and mechanism of the ionic wind, are different when the needle serves as cathode or anode.Under the different polarities of the applied voltage, the ionic wind velocity has a linear relation with the overvoltage.The ionic wind is stronger but has a smaller active region for positive corona compared to that for negative corona under a similar condition.The involved physics are analyzed by theoretical deduction as well as simulation using a fluid model.The ionic wind of negative corona is mainly affected by negative ions.The discharge channel has a dispersed feature due to the dispersed field, and therefore the ionic wind has a larger active area.The ionic wind of positive corona is mainly affected by positive ions.The discharge develops in streamer mode, leading to a stronger ionic wind but a lower active area.