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Two kinds of fluorides are proposed innovatively to modulate the dielectric property of the plasma by reducing the electron density. There is a maximum of 74.41% electron density reduction after the fluorides are injected into the plasma at a magnitude of 1019 m−3, and the corresponding plasma frequency reduction is 49.42%. The fluorides proposed in this paper exhibit a wider modulation range, a faster modulation speed, and a longer maintenance time compared with SF6. The electromagnetic (EM) wave transmission characteristics in plasma are modulated correspondingly. The attenuation of S21 is reduced by 15.11–20.11 dB in 6–18 GHz, and an enhancement in the whole experimental frequency range is observed compared with SF6. The results of the paper can be applied in the mitigation of reentry vehicle's EM wave attenuation induced by the over-dense plasma sheath covering the vehicle. In addition, it also has a potential in broad applications of EM wave and plasma interactions. [ABSTRACT FROM AUTHOR]

The integrative design of scattering and radiation characteristics of antennas is of great practical significance for modern wireless communication. In this work, from the perspective of separate and cooperative modes, we comprehensively discussed the possibility of simultaneously and harmoniously implementing scattering suppression and radiation enhancement for an electrically small antenna by subwavelength plasmas. For the separate mode where the two functions are decoupled based on a two-layer structure, it is shown that an overdense–underdense core–shell density profile is preferred to achieve the optimal synergism between radiation enhancement and plasmonic-cloaking-induced invisibility, where the angular frequency of detecting waves (ωd) is supposed to be lower than that of communication signals (ωc). For the cooperative mode where the two functions are coupled within one plasma shell, the collaborative strategies between plasmonic-cloaking/Fano-resonance-induced invisibility and radiation enhancement are analyzed. The results show that the plasmonic-cloaking type requires ωd > ωc, while for the Fano-resonance type, ωd is larger/less than ωc when radiation enhancement is dominated by the symmetrically/asymmetrically coupled plasmon modes. Also, we provided clearer perspectives to distinguish the physical differences between plasmonic-cloaking and Fano-resonance-induced invisibility and between radiation enhancement underlying the two modes. Our results provide promising solutions for designing next-generation plasma-based tunable and intelligent stealth antennas. [ABSTRACT FROM AUTHOR]

The ground-based device, the Space Plasma Environment Research Facility (SPERF), is established for experimentally simulating magnetosphere plasma processes, with one of its major components, asymmetric reconnection experiment (AREX), for three-dimensional physics relevant to dayside asymmetric magnetopause reconnection. As an outstanding property of fast magnetic reconnection in collisionless plasmas, the Hall effect and its geometric features can be experimentally investigated in SPERF-AREX with various magnetic configurations related to different driven scenarios for simulating interplanetary magnetic field (IMF) conditions. In this work, the Hall effect and its geometric characteristics in such proposed experiments are numerically studied based on a Hall MHD model. The simulation results reveal that in the X-line geometry relevant to southward IMFs, the Hall field features in cross section perpendicular to the X-line are mostly analogous to typical two-dimensional Hall quadrupole structures, clearly an "anti-parallel reconnection" feature. In the separator (A-B null-line) geometry relevant to arbitrary IMF orientations, along the separator between magnetic nulls, the magnetic field configuration near a magnetic null also demonstrates the typical quadrupolar pattern. However, the pattern is distorted away (> 10 d i , here d i = c / ω p i is the ion inertial length) from the nulls, in a way similar to that in "component reconnection." Furthermore, the Hall effect induces a dawn-dusk asymmetry for both the X-line and the separator geometries. [ABSTRACT FROM AUTHOR]

Tunability is an important feature for the filter. As a special electromagnetic medium, the plasma has its permittivity being altered in a wideband range. In this work, based on the surface plasmon polaritons of plasma–dielectric–plasma waveguides, we propose a double-stubs structure submerged in a gaseous discharge plasma medium to realize tunable filtering properties in the giga-hertz (GHz) regime. The finite element method is applied to numerically compute filtering properties. The coupled mode theory and orthogonal design method are introduced to verify simulation results and estimate the effect of simulation parameters on the filtering properties. It is shown that the height of two stubs has the most important influence on filtering performance. Although once the filter is fabricated, its size cannot be modified, one can, nevertheless, vary the plasma frequency to effectively adjust the plasma frequency for the best filtering. Thus, such a plasma-modified filter provides a feasible scheme to dynamically adjust the filtering frequency. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharges (DBDs) are commonly used as efficient sources of large volume diffuse plasmas with moderate temperature and plenty of reactive particles, but the synergistic linkage of some key plasma parameters in single frequency driven systems sometimes limits their application fields and accessible operating ranges. The discrete control of certain key plasma parameters by multi-frequency, i.e., dual frequency (DF), voltage waveform excitations is of increasing requirement and importance for both application-focused and fundamental studies on DBD plasma. In this paper, a significant nonlinear coupling modulation of the discharge evolution process and characteristics caused by the HF oscillation of the high-frequency component in the DF DBD system is observed and investigated, which provides a simple and efficient approach to realize the independent control of the target key plasma parameters such as gas temperature and electron density. Based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of the tiny high frequency component on the properties modulation of atmospheric DF DBD are reported. The driving voltage waveform is characterized by a 50 kHz fundamental sinusoidal low-frequency signal superimposing a small amount of 2 MHz high-frequency signal [HF component changing from 0 to 100 V with a low-frequency (LF) component fixed at 1 kV as a constant], and the effects of the high-frequency voltage amplitude and phase shift on the discharge characteristics, sheath dynamics, impact ionization of electrons, and key plasma parameters are investigated. Particularly, the effects of phase modulation on the discharge evolution and characteristics for DF DBDs are discussed and revealed. The results have demonstrated that a slight and proper parameter variation of the high-frequency oscillation can provide a high electron seed density, and trap electrons within the sheath, thus achieving required plasma parameters. The sheath dynamics can be effectively modulated by tuning the phase shift, which enables a possible alternative approach to optimize the independent control of the key plasma parameters under atmospheric pressure. [ABSTRACT FROM AUTHOR]

In the giga-Hz (GHz) regime, not only does an advanced electromagnetic platform need a stealth function to shield itself from radar detection, similar to the "invisible" cloak in the visible light regime, but also an enhanced transmission function to communicate with others. To satisfy the seemingly contradictory requirements, we here propose a multi-functional mode of plasma cloaking, invisible to radar detection but signal-enhanced in communication bands. Such a synergistic effect is achieved by combining a "detour" layer of cloaking and an enhancement layer of communication. Thus, with such a design we can successfully apply an ideal "cloak" to the low frequency detecting regime (in the P-band) and improve signal transmission capabilities in a higher frequency communication regime (in the L-band) at the same time. Furthermore, the tunability and limitations of the multi-functional system are discussed, and the principles of designing inner and outer plasma layers are acquired. [ABSTRACT FROM AUTHOR]

Energy absorption of electromagnetic (EM) waves in collisional dusty plasmas is attracting much attention from researchers due to its applications in many fields, such as plasma antennas, blackout research during reentry, plasma stealth technology, and the design of microwave transmission in plasmas. In this paper, the propagation characteristics, in particular, the energy absorption effects of EM waves in partially ionized unmagnetized collisional dusty plasmas, are investigated. The results show that the effective energy absorption of EM waves is mainly due to the interaction between electrons and waves, and the plasmas with proper collisional frequencies can be used as a broadband frequency EM wave absorption medium with moderate absorption efficiency. Quantitative analyses of the characteristics of the EM waves that propagate in the collisional dusty plasmas are also included in this study. [ABSTRACT FROM AUTHOR]