The Joint Airport Weather Studies (JAWS) field experiment was carried out in 1982 near Denver. An analysis is presented of aircraft performance in the three-dimensional wind fields. The fourth dimension, time, is not considered. The analysis seeks to prepare computer models of microburst wind shear from the JAWS data sets for input to flight simulators and for research and development of aircraft control systems and operational procedures. A description is given of the data set and the method of interpolating velocities and velocity gradients for input to the six-degrees-of-freedom equations governing the motion of the aircraft. The results of the aircraft performance analysis are then presented, and the interpretation classifies the regions of shear as severe, moderate, or weak. Paths through the severe microburst of August 5, 1982, are then recommended for training and operational applications. Selected subregions of the flow field defined in terms of planar sections through the wind field are presented for application to simulators with limited computer storage capacity, that is, for computers incapable of storing the entire array of variables needed if the complete wind field is programmed.

Simulated flight through JAWS wind shear - In-depth analysis results. [Joint Airport Weather Studies]

Planar microwave sensors have become increasing developed in recent decades, especially in material characterization (solid/liquid) as they provide regions highly sensitive to the surrounding medium. However, when it comes to deciphering the content of practical biological analytes or chemical components inside a host medium, even higher sensitivities are required due to their minute concentrations. This review article presents a comprehensive outlook on various methodologies to enhance sensitivity (e.g., coupling resonators, channel embedding, analyte immobilization, resonator pattern recognition, use of phase variation, using coupled line section, and intermodulation products), resolution (active sensors, differential measurements), and robustness (using machine learning) of arbitrary sensors of interest. Some of the most practical approaches are presented with prototype examples, and the main applications of incorporating such procedures are reported. Sensors with which the proposed techniques are implemented exhibit higher performance for high-end and real-life use.

https://www.mdpi.com/1424-8220/22/18/6946/pdf?version=1663294245

Techniques to Improve the Performance of Planar Microwave Sensors: A Review and Recent Developments

Most reported metasurfaces operate in single propagation direction mode (either transmissive mode or reflective mode), which hamper practical application. Here, we proposed a bi-directional operation coding metasurface based on a phase change material of a vanadium dioxide (VO2) assisted metasurface. It can realize a dynamically invertible switch between the transmissive mode or reflective mode in the terahertz regime by changing the external ambient temperature. The proposed structure consists of a silicon column, polyimide dielectric substrate layer, and VO2 film bottom layer. When VO2 is in dielectric state, the designed metasurface possesses the functions of transmission beam splitting and deflection and generates a transmission vortex beam. When VO2 is in metallic state, the proposed metasurface exhibits many functions such as reflection beam splitting, deflection, radar scattering surface (RCS) reduction and reflection vortex beam generation. The proposed metasurface can solve transmissive and reflective bi-direction terahertz encoding regulation. This scheme provides a new method to realize multi-function terahertz devices.

Transmission and reflection bi-direction terahertz encoding metasurface with a single structure

Unique applications of carbon materials in infrared stealth: A review

Parameter adjustment through numerical optimization has become a commonplace of contemporary microwave engineering. Although circuit theory methods are ubiquitous in the development of microwave components, the initial designs obtained with such tools have to be further tuned to improve the system performance. This is particularly pertinent to miniaturized structures, where the cross-coupling effects cannot be adequately accounted for using equivalent networks. For the sake of reliability, design closure is normally performed using full-wave electromagnetic (EM) simulation models, which entails considerable computational expenses, often impractically excessive. Available mitigation techniques include acceleration of the conventional (e.g., gradient-based) routines using adjoint sensitivities or sparse sensitivity updates, surrogate-assisted and machine learning algorithms, the latter often combined with nature-inspired procedures. Another alternative is the employment of variable-fidelity simulations (e.g., space mapping, co-kriging), which is most often limited to two levels of accuracy (coarse/fine). This work discusses an EM model management approach coupled with trust-region gradient-based routine, which exploits problem-specific knowledge for continuous (multi-level) modification of the discretization density of the microwave structure at hand in the course of the optimization run. The optimization process is launched at the lowest discretization level, thereby allowing for low-cost exploitation of the knowledge about the device under study. Subsequently, based on the convergence indicators, the model fidelity is gradually increased to ensure reliability. The simulation fidelity selection is governed by the algorithm convergence indicators. Computational speedup (i.e., reduction in the number of EM simulations required by the optimization process to converge) is achieved by maintaining low resolution in the initial stages of the optimization run, whereas design quality is secured by eventually switching to the high-fidelity model when close to concluding the process. Numerical verification is carried out using two microstrip circuits, a dual-band power divider and a dual-band branch-line coupler, with the average savings of almost sixty percent when compared to single-fidelity optimization.

/pdf/reduced-cost-microwave-design-closure-by-multi-resolution-em-29usan8649.pdf

Reduced-Cost Microwave Design Closure by Multi-Resolution EM Simulations and Knowledge-Based Model Management

In this article, a multiple diffuse coding metasurface (MDCM) of independent polarization is designed to control the propagation direction of diffuse reflections under different polarizations and to improve the monostatic and bistatic RCS (radar cross section) reduction effect. First, a method for controlling the distribution range and propagation direction of the diffuse field is studied, and the diffuse field distribution of the random phase metasurface is optimized by a genetic algorithm to improve the uniformity of the diffuse scattering distribution. Then, the random phase distribution is superimposed on the periodic gradient phase distributions of the linear and hedge types in the orthogonal direction so that the main propagation direction of the diffuse metasurface deviates from the specular reflection region under different polarizations, showing single and two diffuse beams. Finally, the anisotropic unit cell with a rectangle inside and an improved Jerusalem cross on the outside is employed as the basic coding element of the MDCM due to its independent polarization phase response. The numerical and experimental results show that the MDCM features multiple diffuse scattering, independent polarization and angle insensitivity and can efficiently improve the monostatic and bistatic RCS reduction effect simultaneously. Because the scattered energies are redirected away from the specular reflection direction, the specular scattering reduction effect is better than the isotropic diffuse metasurface. The proposed method increases the difficulty of detection by single or netted radar and has the potential for the applications of stealth techniques.

/pdf/multiple-diffuse-coding-metasurface-of-independent-5dism6x4p6.pdf

Multiple Diffuse Coding Metasurface of Independent Polarization for RCS Reduction

At present, low emissivity coating has been widely used in various fields, but damage will greatly reduce the efficiency of low emissivity coating, so the damage detection of low emissivity coating becomes an important work. Based on convolution neural network, a model for automatic identification of coating damage with low emissivity is proposed. Firstly, the optical image data set of low emissivity coating is constructed and extended by means of data enhancement. After that, VGG-19 and ResNet-50 models are built based on tensorflow, and the cross entropy loss function is used in the models. Then, SGD, momentum, RMSprop and Adam are used to optimize the model. In the process of model optimization, the learning rate is adjusted to get the optimal model. The results show that when the learning rate is $5\times 10^{-5}$ and Adam method is used to optimize the model, the recognition accuracy of VGG-19 model is 90.64%, while that of ResNet-50 model is 94.14%. This paper is of great significance for the study of automatic damage identification of low emissivity coatings.

/pdf/damage-identification-of-low-emissivity-coating-based-on-wychgz0ed8.pdf

Damage Identification of Low Emissivity Coating Based on Convolution Neural Network

Investigation on the parameter distribution of Ar/O2 inductively coupled plasmas

To investigate the parameters distribution and electromagnetic scattering characteristics by plasma sources is the basis to develop plasma stealth technology of radar. In this paper, a radome inductively coupled plasma (ICP) source is designed. The fluid model of ICP discharge is established by COMSOL. The Boltzmann equation solver is introduced to correct the inaccuracy of the electron energy distribution function (EEDF) in the fluid model. The distribution of electron density (Ne) and electron temperature (Te) in ICP under different external conditions is obtained, and the Ne is diagnosed by microwave interference method. Then the Ne and Te under steady-state are introduced into the Z-transform finite difference time-domain model to simulate the propagation characteristics of electromagnetic waves. The results indicate that the amplitude and spatial distribution of ICP parameters change significantly under different external conditions (i.e., the pressure, the gas electronegativity, and the power). Moreover, the frequency bands of wave attenuation are adjusted over a broader range by control the discharge conditions. Additionally, the wave vector gradient of ICP induced the reflected wave to form the pseudo point source in the high Ne region.

Haojun Xu

Papers

Multiple Diffuse Coding Metasurface of Independent Polarization for RCS Reduction

Damage Identification of Low Emissivity Coating Based on Convolution Neural Network

Investigation on the parameter distribution of Ar/O2 inductively coupled plasmas

Investigation on the parameters distribution and electromagnetic scattering of radome inductively coupled plasma

Study on the influence of thin plasma thickness on electromagnetic wave attenuation