Liu Ming-Hai

Multi-band microwave metamaterial absorber based on coplanar Jerusalem crosses

The influence of the gap on the absorption performance of the conventional split ring resonator (SRR) absorber is investigated at microwave frequencies. Our simulated results reveal that the geometry of the square SRR can be equivalent to a Jerusalem cross (JC) resonator and its corresponding metamaterial absorber (MA) is changed to a JC absorber. The JC MA exhibits an experimental absorption peak of 99.1% at 8.72 GHz, which shows an excellent agreement with our simulated results. By simply assembling several JCs with slightly different geometric parameters next to each other into a unit cell, a perfect multi-band absorption can be effectively obtained. The experimental results show that the MA has four distinct and strong absorption peaks at 8.32 GHz, 9.8 GHz, 11.52 GHz and 13.24 GHz. Finally, the multi-reflection interference theory is introduced to interpret the absorption mechanism.

Electromagnetic Wave Attenuation in Atmospheric Pressure Plasmas

The properties of electromagnetic waves in atmospheric pressure plasmas are investigated with the Lorentz model. The effects of the electromagnetic wave frequency, plasma density, and the electron-neutral collision frequency on the attenuation of electromagnetic waves are discussed. The numerical results indicate that the wave attenuation is stronger at the region of the longer wavelength and at the higher plasma density.

A Novel Structure of Slot-Antenna Array for Producing Large-Area Planar Surface-Wave Plasmas

The principle of surface wave plasma discharge in a rectangular cavity is introduced and the distribution of the electromagnetic field within a rectangular waveguide is analysed. A novel structure of a slot antenna array is presented. In comparison with the traditional slotantenna, it is shown that the designed slot antenna array can excite effectively the surface wave coupling into the chamber, and generate a stable large-area high-density plasma. These results are useful for exploring the optimized design of the slot-antenna for surface wave plasmas.

Electromagnetic interaction between local surface plasmon polaritons and an atmospheric surface wave plasma jet

We analyze the electromagnetic interaction between local surface plasmon polaritons (SPPs) and an atmospheric surface wave plasma jet (ASWPJ) in combination with our designed discharge device. Before discharge, the excitation of the SPPs and the spatial distribution of the enhanced electric field are analyzed. During discharge, the critical breakdown electric field of the gases at atmospheric gas pressure and the surface wave of the SPPs converted into electron plasma waves at resonant points are studied. After discharge, the ionization development process of the ASWPJ is simulated using a two-dimensional fluid model. Our results suggest that the local enhanced electric field of SPPs is merely the precondition of gas breakdown, and the key mechanism in maintaining the discharge development of a low-power ASWPJ is the wave-mode conversion of the local enhanced electric field at the resonant point.

Numerical Reproduction of Spatio-Temporal Evolution of Surface Plasmon Polaritons at Dielectric-Plasma Interface

Discharges in planar-type overdense plasmas caused by resonant excitation of surface plasmon polaritons (SPPs) are presented. The spatio-temporal evolution of surface waves of SPPs at the dielectric-plasma interface is reproduced numerically. It is found that different discharge light patterns are excited by different spatio-temporal wave fields. Moreover, the corrugation surface included in the proposed plasma sources plays a significant role in producing large-area uniform plasmas.

Surface Wave Analysis of Planar-Type Overdense Plasma with Surface Plasmon Polariton Resonance

Surface waves (SWs) in planar-type overdense plasmas are analyzed and the invariable SW mode caused by the resonant excitation of surface plasmon polaritons (SPPs) is presented. It is found that the electric field peaks at the location where the plasma density equals the cut-off density while the plasma density gradient and the collision rate have different influences on the field amplitude and the peaks width. Moreover, the mode conversion between SW of SPPs and electron plasma waves play a significant role in production of overdense plasma.

Early Stage of Pulsed Discharge in Water

The bubble radius at the early stage of discharge in water is investigated using high-speed photography. Some simulation results on the bubble radius are presented, which are in agreement with the experimental results, with a maximum difference of about 10%. The reasons why the peak pressure of the first shock wave is only related to the energy released in the bubble during the first half period are addressed. The energy released in the bubble after the first half period increases the bubble pulsation period, but it produces no more than 10% under the peak pressure of the second shock wave.

Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons*

Atmospheric lower-power pulsed microwave argon cold plasma jets are obtained by using coaxial transmission line resonators in ambient air. The plasma jet plumes are generated at the end of a metal wire placed in the middle of the dielectric tubes. The electromagnetic model analyses and simulation results suggest that the discharges are excited resonantly by the enhanced electric field of surface plasmon polaritons. Moreover, for conquering the defect of atmospheric argon filamentation discharges excited by 2.45-GHz of continued microwave, the distinctive patterns of the plasma jet plumes can be maintained by applying different gas flow rates of argon gas, frequencies of pulsed modulator, duty cycles of pulsed microwave, peak values of input microwave power, and even by using different materials of dielectric tubes. In addition, the emission spectrum, the plume temperature, and other plasma parameters are measured, which shows that the proposed pulsed microwave plasma jets can be adjusted for plasma biomedical applications.

Propagation of Electromagnetic TM (S-Polarization) Mode in Two-Dimensional Atmospheric Plasma

The finite-difference-time-domain (FDTD) method is applied to simulate the two-dimensional propagation of electromagnetic TM (S-polarization) mode in atmospheric plasma and in metal layer for strong electron-neutral collisions. Dependence of the wave attenuation on both plasma parameters and incident wave angle are obtained. It is indicated that for a given electron density profile the attenuation depends strongly on the incident angle, the wave frequency, the width of plasma layer, and the collision frequency between electrons and neutrals.

Self-consistent three-dimensional modeling and simulation of large-scale rectangular surface-wave plasma source

A self-consistent and three-dimensional (3D) model of argon discharge in a large-scale rectangular surface-wave plasma (SWP) source is presented in this paper, which is based on the finite-difference time-domain (FDTD) approximation to Maxwells equations self-consistently coupled with a fluid model for plasma evolution. The discharge characteristics at an input microwave power of 1200 W and a filling gas pressure of 50 Pa in the SWP source are analyzed. The simulation shows the time evolution of deposited power density at different stages, and the 3D distributions of electron density and temperature in the chamber at steady state. In addition, the results show that there is a peak of plasma density approximately at a vertical distance of 3 cm from the quartz window.