3-D time-varying and spatially nonuniform plasma is applied using the finite-difference time-domain algorithm in investigating the effects of electromagnetic (EM) wave scattering in the plasma sheath. The plasma sheath is stratified in space, and three types of electron density in time-varying forms are assumed. The characteristics of different time-varying forms are analyzed using radar cross section (RCS). In addition, the effects of RCS change with time at Sand L-bands are investigated using electron density as the time variable. In the condition of timevarying and spatially nonuniform plasma sheath, the attenuation of EM wave is affected by different time-varying regularities of electron density (n _e ). The RCS varying with time is related to the change rate of n _e .

The influence of static eccentricity (SE) and dynamic eccentricity (DE) on the electromagnetic forces in internal- and external-rotor permanent magnet synchronous motors (PMSMs) is investigated in this article. First, the analytical model of the electromagnetic force is derived. By introducing the eccentricity coefficient, the influence of eccentricity on the electromagnetic force is then analyzed. The results show that SE changes the spatial component of the electromagnetic force in internal-rotor motors, while the frequency remains unchanged. While for the external-rotor motors, both the spatial order and frequency of electromagnetic force are affected by SE. Contrary to SE, DE introduces additional spatial components and sideband frequency harmonics to the electromagnetic force of internal-rotor motors. For external-rotor motors, only the spatial order is changed. In addition, axial-flux PMSMs suffer from the extra unbalanced bending moment (UBM), which is a unique feature that differs from traditional radial-flux PMSMs. The expression of UBM caused by eccentricity is further derived. Finally, the theoretical analysis is validated by the simulation and test results, respectively. This study will benefit the researchers and designers in terms of source identification and reduction of acoustic noise in PMSMs.

Dusty plasma differs from ordinary plasma, and its unique properties have always been an active research branch of plasma science. In this article, a finite-difference time-domain (FDTD) method is used to study the propagation characteristics of terahertz (THz) waves in spatially inhomogeneous and time-varying weakly ionized and weakly colliding dusty plasma. The reflection and transmission coefficients are analyzed for the concentration and radius of dust particles, the time-varying rate of electron density, and the effective collision frequency. Results show that increasing the concentration and radius of dust particles will enhance the adsorption ability of the dust particles toward electrons, thereby weakening the electron density in dusty plasma, which will increase the penetration ability of THz waves into the dusty plasma layer. The increase in the effective collision frequency in the dusty plasma will enhance the collisional absorption of dusty plasma and restrain the ability of electromagnetic (EM) waves to penetrate the plasma layer. However, the ability of EM waves to penetrate the dusty plasma layer can be effectively improved by increasing incident wave frequency. Therefore, using THz technology to penetrate spatially inhomogeneous and time-varying dusty plasma is feasible.

In this paper, a novel photonic-assisted Doppler frequency shift (DFS) measurement scheme based on an integrated dual-polarization Mach–Zehnder modulator is presented. In the proposed scheme, the DFS to be identified is transformed into a low-frequency electrical signal through an optical frequency-conversion link. The value of the DFS can be acquired by analyzing the spectrum of the low-frequency electrical signal. Meanwhile, the orientation of the DFS can be easily determined utilizing a 90° hybrid coupler. If the receiver is moving toward the transmitter, only the positive port has an output signal, while only the negative port has an output signal if the receiver is moving away from the transmitter. The scheme can simultaneously obtain the value and the orientation of the DFS. In addition, to investigate the frequency tunability of the proposed scheme, the DFS, which varies from $-100$ to 100 KHz at a step of 10 KHz for different microwave signals at frequencies of 10, 15, and 18 GHz, is demonstrated experimentally, and the errors are within $\pm 5\times {10}^{-6}\mathrm{Hz}$.

The theory of random phase screen is adopted to establish the propagation model of power-exponent-phase airy (PEPA) beams in plasma sheath turbulence (PST) conditions. The propagation model can determine the changes in intensity, phase, and orbital angular momentum (OAM) mode distribution of PEPA beams under PST. Simulation results reveal that PEPA beams in multiple OAM modes at the source field can better suppress PST than the conventional vortex beams because the influence of turbulence is dispersed in different OAM modes. Moreover, compared with power-exponent-phase Laguerre – Gaussian (PEPL) beams, PEPA beams are better suited for transmission under plasma turbulence because of their self- focusing and self-healing properties. The results provide a theoretical basis for studying communication problems during PST.

The face-centered cube (FCC) grid has more sampling points than the traditional Yee cell (as it contains a total of 14 grid points, of which six are center points and eight are vertices, and each grid point has three field components). Thus, FCC is better than the former in dealing with the dispersion error of anisotropic media. On the basis of this feature, this article first derived the FCC-finite-difference time-domain (FDTD) iterative formula for nonuniform plasma on the basis of FCC grid and verifies the accuracy of the algorithm. This algorithm is combined with the nonuniform plasma flow field model of hypersonic vehicles, and the backward single-station radar cross sections (RCSs) of vertical polarization (VV) and horizontal polarization (HH) are calculated under different flight altitudes, flight velocities, and external conditions. Results showed that as flying height increased or flying speed decreased, it results in an increase in RCS. Different external magnetic fields and incident angles also had an obvious impact on the electromagnetic scattering characteristics. From the perspective of electromagnetic wave polarization, both VV polarization and HH polarization have a great impact on RCS. These results provide a theoretical basis for studying the electromagnetic scattering characteristics of nonuniform plasma targets.