Plasma-added intensification of radio frequency (RF) signals toward the future generation of compact antennas with wide-range requests has been studied experimentally in this paper. A technology based on modulation and enhancement effects of subwavelength plasma structures on application-focused RF electromagnetic radiation is developed. An inductively coupled plasma is applied to provide appropriate subwavelength structures, aiming at enhancing the electromagnetic radiation of an omnidirectional ellipse dipole antenna. The plasma mediated radiation enhancement on RF antenna signals of ~1 GHz is observed experimentally for the first time. It is shown that this technology is capable to obtain a significant gain up to nearly 10 dB higher than the free-space radiation without the plasma structure. And an enhanced frequency band of the typical GSM900 frequency range can be extended from 0.89 to 1.05 GHz. Meanwhile, electromagnetic signals transmitted by the plasma-added antenna still maintain good quality for communication. In addition, numerical simulations are also taken to reveal the mechanism of the radiation enhancement effects.

The bird-streamer caused failures have become one of the major causes of transmission line outages. It is more common and widespread than generally believed, and greatly threatens the reliability of transmission lines. The laboratory study of such failures mechanism is seldom reported especially for long gaps such as 500 kV insulators. Presented in this paper are the results of long air gaps bird streamer flashover experiments conducted on 500 kV and 220 kV transmission line insulators. The experimental results demonstrated that bird-streamer caused surface flashover can happen in 500 kV insulators, however space flashover, because the bird streamer will split into different jets under high electric field cannot short circuit the long air gaps. The high risk areas of flashover for 220 kV and 500 kV insulators were defined in this paper: an elliptical area for 220 kV I string insulator and a symmetrical area beside the central line for 500 kV V string insulator. The influence of some main factors on flashover processes is also elucidated, such as volume, conductivity and viscosity of the streamer, and the insulator type and configuration. The paper has significant value in understanding the bird caused failure mechanisms and designing remedies.

The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath structure. The strategic modulation of harmonics number and phase shift is capable of raising the electron density significantly (e.g., nearly three times in this case), but without a significant increase in the gas temperature. Moreover, by tailoring the fluctuation of harmonics with a steeper slope, a more profound efficiency in electron impact ionization can be achieved, and thus enhancing the electron density effectively. This method then enables a novel alternative approach to realize the independent control of the key plasma parameters under atmospheric pressure.

The interaction between electromagnetic (EM) waves and plasma sheaths of re-entry vehicles has attracted widespread attention for solving the blackout problem in re-entry control and communication. In this paper, an integrated model is proposed to study EM wave transmission and scattering characteristics in plasma sheaths for typical altitude and velocity regimes. The key plasma parameters and their distributions of the plasma sheath are investigated based on the previously reported flying data. Reflection, transmission, and absorption coefficients as well as radar cross sections (RCSs) in studied cases are calculated by the integrated model. The results show that multi-effects of the plasma sheath, including the high-density, strong-collision, wide-dispersion, sub-wavelength thickness, etc., can synergistically affect the transmission and scattering characteristics. EM signals of control and communication are then reflected, transmitted, or absorbed differently in various parameter regimes of the plasma sheath. The backward RCS of re-entry vehicles may decrease or increase due to variations of feature EM shapes of the plasma sheath. Communication and control properties of the re-entry vehicles are also revealed by synergy of multi-effects of the sheath on EM waves in various regimes.

Resonant absorption is a process that electromagnetic (EM) energy is converted to plasma energy with a mode conversion on the resonant layer where the incident EM wave frequency equals to the local frequency of a plasma normal modes. With a finite collision between charged and background neutral particles in a plasma, the plasma oscillation is dissipated to widen the resonance layer and heat the plasma. In this work a modified scattering matrix methods (SMM) are applied to study the effects of the collision frequency, incident angle, and plasma thickness on resonant absorption. We analyze the energy absorption caused by resonance in comparison with collisional absorption for different parameters. It is found that the resonant absorption dissipates about nearly half of the incident EM energy in an overdense inhomogeneous plasma when the collision is weak, and the rest half portion is reflected. If the collision is strong, however, the collisional absorption is then more significant than the resonant and affects the entire wave propagation process.

The performance of atmospheric pressure dielectric barrier discharge (DBD) driven by dual-frequency sources of 200 kHz/13.56 MHz has been investigated numerically here in a one-dimensional fluid model. By varying the ratio of dual frequency excitation amplitudes, strong nonlinear coupling in the discharge is observed, with the electron density rising significantly due to the synergistic effect governing the ionization process. Moreover, it is shown that the phase shift between the dual frequencies also has an influence on the electron temperature and density. As to different high frequency components, the modulation of the electron temperature and density induced by the phase-shift also varies significantly. Those results then demonstrated the possibility of applying amplitude and/or phase modulations in a wide operation window to optimize the plasma parameters in dual-frequency DBDs with fixed frequencies.