Search

A new honeycomb absorbing superimposed structure based on inductively coupled plasma (ICP) is proposed in this study. The superimposed structure is composed of a thin-layer honeycomb absorbing structure (HAS) and a square plasma discharge cavity with a maximum thickness of 3 cm. External conditions such as RF power,pressure and cavity thickness of ICP can adjust the absorbing frequency band and reflectivity of the superimposed structure. The model of the inductively coupled plasma superimposed honeycomb absorbing structure (ICP-HAS) is analyzed and simulated by CST software, and the reflectivity test system is built. The simulation and experimental results show that increasing the RF power and pressure can improve the absorbing effect of the superimposed structure, and changing the thickness of the cavity will change the absorbing frequency band and reflectivity valley. The maximum −10 dB absorbing bandwidth of the proposed superimposed absorbing structure can reach 12.6 GHz. In addition, the multiple reflection and refraction of the electromagnetic wave by ICP can give full play to the microwave absorption performance of the HAS. Therefore, the proposed ICP-HAS can achieve broadband actively adjustable microwave absorption without using magnetic materials and low thickness.

Adding electronegative gas to the inert gas is an important means of adjusting the plasma parameter distribution. In this paper, a fluid model of the Ar/O 2 inductivly coupled plasma (ICP) is used to investigate the parameter distribution, while the electron energy distribution function (EEDF) and the transport coefficients are obtained by the Boltzmann equation solver module to improve the accuracy. The spatial-temporal evolution of the electron density and the electron temperature of the ICP are obtained and the influence of the discharge power and the oxygen mole ratio on the distribution of the ICP parameters is compared. Additionally, the physical mechanism is researched using the diffusion-transport theory of the plasma. In order to verify the reliability of the model results, an experiment is carried out to diagnose the discharge parameters. The results of the simulation and the experiment are performed for different power and oxygen mole ratios and a good qualitative and numerical agreement is obtained, indicating that the inclusion of the simulation results in a high accuracy.

Plasma stealth technology has the advantage of real-time regulation of the absorbing band and does not affect the aerodynamic performance. The thin-layer cavity facilitates installation on special parts such as the surface of the aircraft body. However, the thickness of plasma directly determines the transmission distance of the radar wave in the plasma. When the thickness is decreased, the attenuation effect of the plasma on electromagnetic waves is reduced. In response to this problem, we studied the influence of thickness on electromagnetic wave scattering parameters, and established a fluid model of a planar transparent cavity ICP source using the multi-physics coupling method COMSOL in this paper. The accuracy of the fluid model is improved by adding the Boltzmann solver. COMSOL combined with ZT-FDTD method was used to establish the calculation model of ICP electromagnetic scattering parameter. The results of simulation show that the thickness has a significant influence on the ICP electromagnetic scattering parameters. When the thickness of plasma decreases, the central area of n e keeps deviating from the center of the cavity, the ring feature is enhanced, and the attenuation effect is generally in a downward trend. The main attenuation bandwidth in the frequency band also shows a shrinking trend. Through comparative experiments, the increase of pressure on the improvement of the main attenuation bandwidth compensates for the reduction of the main attenuation bandwidth caused by the decrease in thickness.

Aiming at the limitation of frequency selective surface (FSS) used in radome, a new type of active frequency selective surface (AFSS) based on inductively coupled plasma (ICP) is proposed. The structure consists of a square plasma discharge cavity with a size of 20 × 20 × 5 cm3 and a FSS with broadband bandpass response. By comparing the simulation results of COMSOL Multiphysics with the experimental results of microwave interference diagnosis, the influence of coil configuration on the characteristic parameters of ICP source is analyzed. The transmissivity of ICP-FSS with different coil configurations was measured by time domain measurement system. The experimental results show that the bandwidth of passband of the structure is 6.4 GHz–19.1 GHz when the ICP source is not excited. When the ICP source is excited, the ICP-FSS structure presents different stopband transmission characteristics under different coil configurations. The bandwidth of stopband widens as the RF power increases, and the transmission coefficient valley also increases, which can effectively reduce the detection probability of the radar in the off state. Therefore, the proposed AFSS based on inductively coupled plasma is an effective candidate for radome application.

The electromagnetic wave propagation in plasmas has been investigated based on the hypothetical parameters in a number of previous literature, but the results can't mirror the feature of real plasma sources for waves. In this paper, the two-dimension parameters of Ar inductively coupled plasma (ICP) are investigated under high and low pressure by multi-physics coupling analysis method. Meanwhile, the profiles of electron density are diagnosed by the Langmuir probe for comparison with the simulated. The increasing pressure induces the significant increase of oscillation frequency and collision frequency, while a large density gradient causes the more nonuniform distribution. The wave propagation in ICPs is calculated with Z-transform finite-different time-domain method. The curves of attenuation, transmission and reflection coefficient are obtained versus pressure, frequency and power. The low pressure ICP induces the relative more attenuation of wave in the frequency band (1 GHz–6 GHz), while the high pressure ICP is more effective to the frequency band (6 GHz–17 GHz). The increasing power is conductive to the attenuation within limits. The reflection is complicated due to the high degree of wave vector gradient over a wavelength. Moreover, the pseudo secondary wave source is created inside high electron density region of ICP.

To investigate the parameters distribution characteristics of the plasma sources with high electron density is a prerequisite to developing the plasma radar stealth of military objects. In this paper, the multi-physics coupling models of O2/Ar ICP and a Langmuir probe are employed to investigate the impacts of the discharged conditions (i.e., the radio frequency (RF) power, the pressure, and the Ar/O2 gas ratio) on parameters distribution. The problem of the inaccuracy of EEDF in COMSOL plasma fluid module is corrected by introducing Boltzmann equation solver. The thickness of ICP decreases with the increase in pressure. The electron motion is restricted by gas collision, and the peak of electron density N e is transferred to the top of the skin layer. In addition, the N e in Ar increased first and then decreased with the increase of pressure, and the gradient of N e in the core region increased. Besides, the N e decreases with increasing molar ratio of oxygen, but the uniformity of the N e distribution in the core region is significantly enhanced. Moreover, T e increases with the increase of electronegative gas ratio and decreases with the rise of pressure. The results indicate that the amplitude and spatial distribution of ICP parameters change significantly with the external conditions.