Applied Science and Convergence Technology 2021; 30(5): 141-145
Published online September 30, 2021
Copyright © The Korean Vacuum Society.
aApplied Physics Laboratory for PLasma Engineering (APPLE), Department of Physics, Chungnam National University, Daejeon 34134, Republic of Korea
bDepartment of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea
cAgency for Defense Development (ADD), Daejeon 34186, Republic of Korea
dInstitute of Quantum Systems (IQS), Chungnam National University, Daejeon 34134, Republic of Korea
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In this experimental research, the characteristics of the discharge generated using a flexible electrode at intermediate pressure were investigated. We confirmed the discharge patterns according to the pulse width and frequency of a pulse generator with a fixed voltage under a pressure of 0.3 atm, which is the pressure at a typical flight altitude. Uniform discharge was found to occur at a frequency of 10 kHz with a pulse width of 4 µs and at a frequency of 20 kHz with a pulse width of 3 µs. To analyze the trend of discharge patterns, the voltage and current waveforms of the discharge in each condition were measured. In addition, the power dissipated by one cycle was calculated from the measured voltage and current waveforms. From the measurement and calculation results, it was confirmed that the dissipated power was large when the discharge occurred at a frequency of 20 kHz with a pulse width of 3 µs, that is, the brighter and more uniform discharge pattern, which was found to be the optimal discharge condition for the flexible electrode at a pressure of 0.3 atm.
Keywords: Flexible electrode, Intermediate pressure, Plasma, Radar cross section
Plasma can be employed in stealth technology because of its wide absorption bandwidth and high absorption efficiency. The key principle is to surround the target with a plasma layer, which reflects or absorbs the incident radar signal, thereby reducing the radar cross section (RCS) as an indicator of the stealth capabilities of the target surrounded by the plasma layer. Based on this principle, many studies on RCS reduction using plasma have been conducted. Koretzky and Kuo demonstrated that plasma torches can effectively attenuate EM waves [1, 2]. Wolf and Arjomandi measured the RCS by generating a dielectric barrier discharge at atmospheric pressure and calculated the attenuation effect of plasma using the Lorentz model to compare the measured RCS . He
Although much research has been conducted to improve the process of RCS reduction by plasma, there are still problems that must be solved in order to apply plasma stealth technology to targets such as aircraft and aerospace vehicles. Most of the reported plasma sources for RCS reduction are rigid plates and cannot be used on curved surfaces. As a result, they generally cannot be applied to all surfaces on a target. Research on RCS reduction using plasma arrays applied to curved surfaces has been reported through simulation calculations , but experimental studies have not yet been reported. Therefore, it is necessary to use a component such as a flexible electrode as a source that can generate plasma even on a curved surface.
There have been many studies related to plasma using flexible electrodes. Cho and Kim developed a flexible sheet capable of generating plasma at atmospheric pressure and studied the discharge characteristics according to the applied voltage and dielectric thickness . Kim
In this study, the characteristics of the discharge generated using a flexible electrode at intermediate pressures were investigated. The discharge patterns according to the pulse width and frequency of a pulse generator with a fixed voltage under a pressure of 0.3 atm, which is the pressure at a typical flight altitude of 30,000 ft (approximately 9,000 m) , were confirmed. In addition, the voltage and current waveforms of the discharge in each condition were measured, and the power dissipated by one cycle was calculated from the measured voltage and current waveforms. From the measurement and calculation results, the effects of the pulse width and frequency on the discharge were analyzed.
Figure 1 shows the configuration of the flexible electrode used as the plasma source in our study. The flexible electrode consists of a 100 µm thick polyimide film with a meshed electrode printed on one side and a plane electrode on the other side. The electrodes are made of copper, and the mesh lines are 70 µm thick and 1 mm wide, with 4 mm of spacing between adjacent lines.
A schematic of the experimental setup is shown in Fig. 2. To study the characteristics of discharge on the flexible electrode at intermediate pressure, the flexible electrode was placed inside a 20 mm thick acrylic cube with dimensions of 200 mm × 200 mm × 27 mm. The pressure in the chamber was maintained at 0.3 atm using a rotary pump connected with an angle valve. A high-voltage pulse generator (IHP-1002, ITM) with an output voltage of 0–10 kV, a frequency of 0–40 kHz, and a pulse width of 2–5 µs was used to generate the plasma on the flexible electrode. We used an oscilloscope (TDS3052A, Tektronix Inc.) connected to the experimental device with a voltage probe (TekP5100, Tektronix Inc.) and a current probe (TCP202, Tektronix Inc.) to measure the voltage and current waveforms during the experiments. Figure 3 shows the voltage waveform according to the pulse width of the generator used in this study at a fixed voltage of 2.5 kV and a frequency of 20 kHz. Under this condition, the output voltage of the pulse generator was applied with a rise time of approximately 1.6 µs and a peak of 3.0 kV during the set pulse width (on-time), and attenuated and oscillated with a decay time of approximately 4.0 µs during the off-time. It can be seen that some ringing occurred in the on-time range, and the ringing increased as the pulse width increased.
Figure 4 shows the discharge patterns on the flexible electrode according to the pulse width (
To analyze the discharge pattern results, voltage and current wave-forms under each condition were measured. Figure 5 shows the measured waveforms according to the pulse width at a frequency of 10 kHz. The current waveform led the voltage waveform. When the voltage was applied (
Figure 6 shows the measured voltage and current waveforms as a function of the pulse width at a frequency of 20 kHz. Compared with Fig. 4(b), as in the case of
When the frequency was 30 kHz, the measured voltage waveforms exhibited a complex waveform (Fig. 7). The voltage waveforms were similar in amplitude under all pulse width conditions and did not exceed 0.8 kV. Compared with Fig. 4(c), these results are interpreted to indicate that the glow discharge did not occur at
As shown in Fig. 8, the discharge voltage and current waveforms at
Figure 9 shows the calculation of the power dissipated in the discharge according to the frequency with different pulse widths. The dissipated power was calculated as follows:
The characteristics of discharge generated on a flexible electrode as a plasma source for RCS reduction were experimentally studied according to the frequency and pulse width of a pulse generator with a fixed voltage at a pressure of 0.3 atm. When the pulse width was lower (
This research was supported by the Aerospace Low Observable Technology Laboratory Program of the Defense Acquisition Program Administration and the Agency for Defense Development of the Republic of Korea.
The authors declare no conflicts of interest.