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A finite element simulation model of terahertz wave propagation in plasma is developed. The equivalence of treating the plasma as a dielectric and an electrical conductor is studied in comparison. The propagation characteristics of terahertz waves in a unmagnetized plasma obtained from experimental measurements or simulations are simulated by interpolating the distribution of key parameters such as electron density and collision frequency of the external plasma. The validity of this open simulation model is verified by using the simulation data of plasma electron density generated by the independent electrochemical plasma generation model as external data. Using this model as a research tool, the propagation characteristics of terahertz waves in plasma measured by laser Thomson scattering are studied. The simulation results of the terahertz wave propagation characteristics in the plasma with and without considering the collision frequency are compared by this model. The terahertz transmission model in plasma can be used to study the propagation characteristics of terahertz waves in various inhomogeneous plasmas, which would be helpful to solve the communication "blackout" problem. [ABSTRACT FROM AUTHOR]

High-order spoof surface plasmon (SSP) mode on corrugated metallic surfaces can find many interesting applications, such as in imaging, sensing, transmission and enhanced radiation source, etc. In this paper, an efficient excitation method of the high-order SSP mode by using an injected electron beam on the uniform rectangular metallic grating is proposed and investigated numerically. Based on the matched wave momentum between the SSP mode and the electron beam, both the fundamental and high-order SSP modes can be excited on the structure by using a single injected electron beam. Numerical simulation results indicate that the maximum electric field intensity of the generated high-order SSP mode is about two orders higher than that of the fundamental SSP mode. In addition, the peak power of the excited high-order SSP mode is almost two times that of the fundamental SSP mode power by the same energy electron beam, which demonstrates the obvious advantage of the high-order SSP electronic excitation approach compared to the previous fundamental SSP mode excitation on the structure. The central working frequency of high-order SSP power spectrum is about three times that of the fundamental SSP power spectrum. Moreover, the influences of the injected electron beam energy on the excited SSP power spectrum are analyzed specifically. It is shown that the generated SSP power spectrum demonstrates a blue shift with the decreased working voltage of the electron beam simultaneously, with its peak power increasing. However, the working bandwidth is narrowed with decreased beam voltage, which further reveals its working mechanism of presented electronic excitation of the SSP mode. The presented studies provide a new method to excite a high-order SSP mode on the metallic grating, which can find some potential applications in high-sensitivity sensing, deep sub-wavelength waveguide, and many others in terahertz spectra. [ABSTRACT FROM AUTHOR]

Fast construction of the 3-D scattering centers of ship targets on the sea surface is important for many radar applications, including the fast signature prediction, feature extraction, and automatic recognition of targets. Combining the “four-path” model for target-surface coupling scattering with modified Fresnel reflection coefficient model in the stochastic sea surface and ray tube integration method, we propose a 3-D image formation method for ship-surface compound targets. Using the CLEAN technique on 3-D image, we develop a fast algorithm for establishing 3-D scattering center model for ship targets on the sea surface. Because this algorithm realizes 3D imaging of targets at a single frequency and single aspect angle, and adopts simplified surface model to avoid the need to construct a large number of surface elements, the computational efficiency of the proposed alogrithm is greatly increased to meet the needs of practical engineering applications. Simulation experiments of a typical ship target show that the proposed algorithm can increase the speed by four orders of magnitude under typical conditions, as compared with the traditional FFT-based 3D imaging method. We validate the accuracy of this algorithm by comparing reconstructed 1-D range profiles and ISAR images obtain by the scattering center model with the ones that are directly simulated.

Classification of drones is important due to their increasing popularity and potential threats. The micro-Doppler signatures that depend on the rotation of rotor blades facilitate the classification of drones. To enhance the robustness of micro-Doppler based classification of drones, dual radar sensing classification scheme is proposed in this paper. First, time-frequency spectrograms are obtained by performing a short-time Fourier transform on the radar data collected by two radar sensors that have similar angular diversity. Then, principal components analysis is utilized to extract the features from the time-frequency spectrograms and the features obtained by the two radar sensors are fused together. Finally, the classification results are obtained by using the support vector machine. The experimental results show that the classification accuracy obtained by the fusion of dual radar sensors is 5% higher than that obtained by only using a single radar sensor.

The phonon dispersion spectrum, eigenvector, and lattice vibration frequency of cadmium telluride with a zinc blende structure have been investigated using the density functional theory, and the permittivity of cadmium telluride crystal is numerically calculated. The permittivity of the crystal is measured using the terahertz time-domain spectroscopy system. The experimental results are consistent with the theoretical calculations on the modified local density approximation, the general gradient approximation, and the modified general gradient approximation. Finally, the differences among the three approximate exchange correlation potentials indicate that in the terahertz region, the permittivity of cadmium telluride is dominantly contributed by the coupling between electron and phonon; however, the phonon frequencies of transverse wave and longitudinal wave were sensitive to electron density distribution.

The measurement system has been built with Stepped Frequency Continuous Wave (SFCW) signal for Radar Cross Section (RCS) measurements in free-space at 220～330 GHz. The system consists of vector network analyzer, Millimeter-Wave Converters and target support structure. The measurement techniques which are used in scattering measurements are verified by RCS measurement data. The system measurement accuracy is control within about ±3 dB at –23.6 dBsm.

When the hypersonic vehicle is flying, the plasma in the area near the stagnation point of the front end of the vehicle can be approximately seen as the fully ionized dusty plasma. Due to the existence of dust particles, dusty plasma affects the communication quality of the hypersonic vehicle. In this paper, the general Boltzmann equation applicable to dusty plasmas containing electrons and the Fokker–Planck–Landau collision model are combined to derive a general formula for the electron distribution function of fully ionized dusty plasmas. Considering the contribution of the collision effect and charging effect to the dispersion relationship of fully ionized dusty plasma, the dielectric constant of fully ionized dusty plasma under an external magnetic field is solved. The Wentzel–Kramers–Brillouin method is used to calculate the attenuation coefficient (α) of the THz wave in fully ionized dusty plasma, and the influence of the external magnetic field strength and other dusty plasma parameters on the attenuation characteristics of the THz circularly polarized wave is analyzed. The research results show that the α of the THz left-hand circularly polarized wave decreases with the increase in the external magnetic field strength, while the α of the THz right-hand circularly polarized wave increases. In addition, increasing the dust particle radius, dust particle density, and electron density in a certain frequency range can increase the α of the THz circularly polarized waves. These research results provide theoretical guidance for the exploration of the interaction mechanism between the THz waves and fully ionized dusty plasma. [ABSTRACT FROM AUTHOR]

Automatic Target Recognition (ATR) is one of the most difficult problems in Synthetic Aperture Radar (SAR) data interpretation. In recent years, the model-based SAR target recognition method has attracted much attention because of its good performance in the extended operation condition. Based on the research of a few domestic research institutes, this paper briefly introduces the preliminary research results and gives some thoughts about SAR ATR problem. First of all, the development of parametric scattering model are discussed from three aspects. Next, two ways to model the parametric electromagnetic scattering for complex target are put forward. Finally, we propose a new framework for a Three-Dimensional (3D) parametric scattering model based SAR ATR. In the end, the future research direction of model-based SAR target recognition is prospected.