For tilt-rotor aircraft with coaxial rotors (coaxial rotor aircraft), reduction of radar cross section as well as acoustic noise can be essential for stealth design, and the rotation of the coaxial ...rotors can have an influence on noise and dynamic radar cross section (RCS) characteristics. In this paper, an approach to the prediction of both the sound pressure level (SPL) of noise and the dynamic RCS of coaxial-tilt aircraft is carried out, based on the theories of the FW-H equation, the physics optics method (PO) and the physical theory of diffraction (PTD) method. In order to deal with the rotating parts (mainly including coaxial rotors), a generated rotation matrix (GRM) is raised, aiming at giving a universal formula for the time-domain grid coordinate transformation of all kinds of rotation parts with arbitrary rotation centers and rotation axis directions. Moreover, a compass-scissors model (CSM) reflecting the phase characteristics of coaxial rotors is established, and a method of noise reduction and RCS reduction based on the phase modulation method is put forward in this paper. The simulation results show that with proper CSM parameter combinations, the reduction of noise SPL can reach approximately 3~15 dB and the reduction of dynamic RCS can reach 1.6 dBsm at most. The dynamic RCS and noise prediction and reduction method can be meaningful for the radar-acoustic stealth design of coaxial tilt-rotor aircrafts.
The development of quantum radar technology presents a challenge to stealth targets, so it is necessary to study the quantum detection probability. In this study, an analytical expression of the ...quantum radar cross section (QRCS) for complex targets is presented. Based on this QRCS expression, a calculation method for the detection probability for quantum radar is creatively proposed. Moreover, a self-designed flying-wing stealth aircraft is adopted to obtain the detection probability distributions of the conventional radar and the quantum radar in different directions. As revealed by the result of this study, the detection probabilities of the quantum radar and the conventional radar are significantly different, and the detection probability of the quantum radar has obvious advantages in most regions with a certain distance.
Quantum radar is a novel detection method that combines radar and quantum technologies. It exceeds the detection threshold and poses a threat to conventional stealth targets. This work aims to derive ...the expression of the quantum radar cross-section of a new complex target. The calculation formula of QRCS was derived after introducing the relative photon parameters and vector dot product. Subsequently, a comprehensive optimization model of quantum stealth and lift–drag ratio based on a genetic algorithm was proposed for the waverider warhead. During the optimization process, we proposed an optimization method with the objective function of the QRCS pioneering design value and achieved better outcomes than the optimization method using the average value in terms of QRCS performance and lift–drag ratio in the important azimuths of the waverider. By changing the design variables of the waverider warhead and using this new optimization method, the QRCS of the waverider in the forward and lateral angles were minimized, remarkably improving the aerodynamic performance of the waverider. Similarly, the optimization results show that the proposed design value optimization method is feasible.
Active tracking control is essential for UAVs to perform autonomous operations in GPS-denied environments. In the active tracking task, UAVs take high-dimensional raw images as input and execute ...motor actions to actively follow the dynamic target. Most research focuses on three-stage methods, which entail perception first, followed by high-level decision-making based on extracted spatial information of the dynamic target, and then UAV movement control, using a low-level dynamic controller. Perception methods based on deep neural networks are powerful but require considerable effort for manual ground truth labeling. Instead, we unify the perception and decision-making stages using a high-level controller and then leverage deep reinforcement learning to learn the mapping from raw images to the high-level action commands in the V-REP-based environment, where simulation data are infinite and inexpensive. This end-to-end method also has the advantages of a small parameter size and reduced effort requirements for parameter turning in the decision-making stage. The high-level controller, which has a novel architecture, explicitly encodes the spatial and temporal features of the dynamic target. Auxiliary segmentation and motion-in-depth losses are introduced to generate denser training signals for the high-level controller’s fast and stable training. The high-level controller and a conventional low-level PID controller constitute our hierarchical active tracking control framework for the UAVs’ active tracking task. Simulation experiments show that our controller trained with several augmentation techniques sufficiently generalizes dynamic targets with random appearances and velocities, and achieves significantly better performance, compared with three-stage methods.
In this study, the analytical expression of quantum radar cross section (QRCS) for three-dimensional (3D) convex targets is presented. The QRCS simplified calculation equation is derived numerically ...after the introduction of the correlation photon parameters and vector dot product, and the computing efficiency of the proposed equation increases significantly. In this study, two types of the 3D convex target were selected to verify the accuracy and efficiency of the equation, and an optimization approach is presented to analyze QRCS of the stealth missile based on the genetic algorithm (GA) unprecedentedly. The aim of this study is to achieve the minimum forward QRCS of the stealth missile through GA and to adjust the geometry design variables on the head of the missile. As revealed by the optimized results, the proposed technique is confirmed to be effective and acceptable.
•It is becoming important to study the quantum radar scattering characteristics.•The Fourier transform and the QRCS of the triangular prism plane are solved.•The analytical expression of triangular ...prism is obtained.•The results by this method are in agreement with the numerical solutions.
In this study, the analytical expression of the triangular prism is obtained by solving the Fourier transform of the respective plane of the triangular prism, as well as their quantum radar scattering cross section. On that basis, a solution to the equivalent transformation of the elevation angle and azimuth angle of the plane is proposed. The QRCS of the triangular prism is simulated, the distribution characteristics of QRCS are obtained in these ways, and the numerical and analytical solutions of the QRCS of the prism are compared. The results indicate that the QRCS simulation results obtained using the analytical expression method are well consistent with the numerical solution, and the QRCS cloud map indicates the correlation between the number of waves and the change in frequency. The above-described results reveal that the analytical expression derived in this study exhibits high computational accuracy, and the calculation time is significantly shortened.
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The application of absorbing materials on military aircraft has greatly improved the aircraft’s survivability and operational effectiveness on the battlefield. The coating method of absorbing ...materials affects the stealth performance of the aircraft. Therefore, a zoning coating method for absorbing materials is proposed in this paper, and it reduces the amount of the absorbing materials and achieves purpose of reducing the aircraft’s cost and weight by reducing the coating thickness of the weak scattering source. In this paper, CAD software is used to build a stealth aircraft model. Then through calculating and analyzing the surface current distribution characteristics of the aircraft under different electromagnetic wave irradiation angles, the aircraft’s zoning coating design scheme is determined. Later, the electromagnetic scattering characteristics of the aircraft are simulated by the Multi Level Fast Multipole Method (MLFMM) under the circumstance that the electromagnetic wave horizontal illumination azimuth angle is 0–45˚ and the frequency is 3 GHz and 8 GHz. At the same time, the RCS of the aircraft in uncoated and 1.5 mm full coating and zoning coating are obtained. The simulation results indicate that, when the pitch angle is 0˚ and the azimuth angle is within the range of 0–45˚, compared with 1.5 mm-thickness full-fuselage scheme, as for the stealth aircraft after zoning coating design, its RCS average is basically the same as 1.5 mm-thickness full-fuselage coating when the electromagnetic wave frequency is 3 GHZ with 8 GHZ under the circumstance that the amount of absorbing materials reduces by 40 %, and compared with no coating, it reduces by 17dBsm and 22dBsm in the vertical polarization; While compared with no coating, it reduces by 19dBsm and 18dBsm in the horizontal polarization.
Purpose
By reducing the coating thickness of the weak scattering source, the coating weight of the absorbing material can be reduced by 35% with little effect on the RCS.
Design/methodology/approach
...To alleviate the weight-increasing problem caused by a large number of coating of absorbing materials, a method for zonal coating of absorbing materials for a stealth helicopter was proposed. By appropriately reducing the thickness of the coating at the secondary scattering locations, the amount of coating used is significantly reduced.
Findings
Compared with the full-coated, the zonal coating scheme achieves the corresponding RCS reduction effect.
Practical implications
Zonal coating design can achieve the effect of reducing coating weight and cost.
Originality/value
The effects of different coating methods on RCS were verified by electromagnetic scattering simulation, and the applicability of the zonal coating design of the absorbing material to the stealth helicopter was verified.
A new model on the mechanism of anti-Stokes fluorescent cooling is proposed, based on which incident laser induces a phonon-assisted energy transfer from one luminescent center to another in an ...optical medium and causes medium cooling when the energy transfer is an anti-Stokes process and absorbs phonons. Here, we develop the model in two cases: two-phonon-assisted energy transfer for a small energy mismatch and one-phonon-assisted energy transfer for a large energy mismatch. The dependence of relative cooling efficiency on photon energy and temperature is also discussed in evaluating the new mechanism.
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