A dielectric barrier discharge (DBD) in atmospheric pressure air was excited by a high-voltage pulse power supply. Capacitors with different capacitance were connected in the discharge circuit and their effects on discharge power calculation were evaluated. The average power deposited into the discharge were calculated by three different methods: 1) Lissajous figure; 2) product of voltage and current; and 3) watt-hour meter. Further studies showed that the capacitor with 10 nF was suitable for power calculation. At applied voltage of 9 kV, discharge power calculated by three methods were similar (around 25-27 W). However, with the increase of applied voltage, the discharge power obtained by product of voltage and current was far beyond the real value. Lissajous method has proven more appreciable for discharge power calculation in a pulsed plasma at high voltage. This study provides a practical guide for power calculation in a pulsed-driven DBD system.

Charge transportation expressed as a Lissajous figure usually is a standard method for the analysis of discharge power and energy in surface dielectric barrier discharge (SDBD). In this paper, the charge transportation characteristics under different parameters of power supply and actuator configurations are investigated, and the mechanisms of two typical Lissajous figures are discussed theoretically. Experimental results show that when the plasma distribution is quasi-diffuse mode, the Lissajous figure is almond shape correspondingly, while the plasma distribution looks like separated-channel mode, the Lissajous figure presents a parallelogram shape. Based on an improved time-varying lumped-element circuit model, two equivalent circuits of SDBD under two plasma distributions are built, and the Lissajous figures are calculated theoretically. Calculations and analysis results indicate that the two kinds of Lissajous figures under different plasma distribution modes are due to the current pulse durations and equivalent dielectric capacitances caused by plasma distributions acting together. The protrusions of Lissajous figures are caused by the current narrow pulses in the characteristics of separated-channel mode, while Lissajous figures under quasi-diffuse mode have no protrusions.

The primary aims of this paper are to provide a better understanding of surface dielectric barrier discharge based on annular geometry and to investigate the effect of segmented grounding electrodes on their electrical and optical properties. To this end, four grounding electrode conditions are considered: 10-segment, 20-segment, and 30-segment ones as the experimental conditions, and an unsegmented (termed 0-segment) one as the control. A great number of current pulses with lower amplitudes are observed under the segmented conditions compared to the 0-segment condition. In the former case, the current pulse number and the peak value are observed to be inversely and directly proportional to the number of segments, respectively. However, the average currents corresponding to the various segmentations are observed to be nearly identical, and each of them is lower than that under the 0-segment condition. Secondly, the discharge uniformity under the 30-segment condition is observed to be better than under the 0-segment condition, because even though the discharge is usually concentrated at covered regions, it spreads spanwise to the adjacent uncovered regions as the number of segments is increased. Consequently, the airflow induced by spanwise-spread plasma extends the effective range of plasma action. Moreover, the Lissajous figures corresponding to the four conditions are ascertained to be approximately parallelogram-shaped. However, the slopes of the discharge phases are dependent on the voltage, as the variations of equivalent capacitance in dark and discharge phases are distinct. A higher amount of power is consumed under the 30-segment condition than under the 0-segment condition, although the maximum transported charge is much lower in the former case. Finally, in the quasi-sinusoidal external electric field distribution induced by the segmented grounding electrode, a slightly lower-than-average electric fields avoid the creation of obvious separated channels, while a moderate peak-to-peak difference of electric field improves the electric field distortions caused by existing micro-discharges. This phenomenon serves as a satisfactory explanation of the differences between the discharge channel developments and the plasma distributions under different conditions. Based on the obtained results, we conclude that the performance of discharge plasma can be improved by arranging the electrodes optimally.

Nanosecond pulsed surface dielectric barrier discharge (SDBD) is a hot topic in many fields, but the mechanisms of discharge evolution and micro-channel propagation are still not clearly understood. In this paper, a plasma fluid model of nanosecond pulsed SDBD is established, and the deductions of the two current spikes are verified and improved by simulation. The two current spikes correspond to the two stages of the discharge: the ionization wave propagation and the repeated re-ignition in the gap between the ionization wave and the dielectric surface. In the first stage, the ionization wave develops rapidly at first and propagates very slowly in the end, which produces the first current spike with a very short rise time and a tailing falling edge. The curve profile of the ionization wave velocity is very similar to that of the first current spike. A certain distance is maintained between the bottom of the ionization wave and the dielectric surface in this stage, which forms the gap for the next stage. In the second stage, the charged particle cloud induced by the quasi-uniform electric field in the middle of the gap and the new micro-channel from the edge of the high-voltage electrode propagate at first, and then merge together to establish a new discharge channel. The reverse electric field in the gap induced by the accumulated charges on the dielectric surface restricts the expansion velocity of the second discharge channel, which results in a longer rise time and falling time of the second current spike.

Surface discharge induced by metal particles is a common insulation failure in many high-voltage equipment. In order to further understand the mechanisms of this surface discharge, a 2D simulation model of a plate–surface–plate structure with a pin is established and verified by experiments in this paper to simulate the actual discharge configurations, and the evolution characteristics of the positive and negative surface discharges are compared. The evolutions of both positive and negative discharges could be divided into two phases: the bridging phase and the expansion phase. As the electric field in the gap between the streamer and the dielectric surface is strengthened by the effect of the space charge, the ionization sources and the secondary electrons excited on the dielectric surface, the dielectric surface presents attraction to the streamer, and subsequently the two streamer routes first touch the dielectric surface and then arrive at the grounding electrode. However, the channel branching is the most distinctive characteristic of the positive and negative discharges. In the positive discharge, the channel first branches, then merges, and finally expands, and the gaps of pin to dielectric surface and pin to grounding electrode are broken down by two slender positive branches, respectively. The negative discharge presents a stout channel without branching, which develops and expands simultaneously. This is ascribed to the thinner space charge layer, the weaker shielding effect of the internal electric field and the more active movement of the internal charges in the positive discharge. Another important factor for the discharge branching is the appropriate matching of the sheath thickness and the curvature radius of the channel’s head.

Real-time modification is a promising method for improving the clinical surface performance of titanium (Ti) implants, which requires a simple structure, short treatment time, and long duration of hydrophilicity. Hence, a novel diffuse jet without airflow was developed in this paper to address these three requirements. The diffuse jet produces cone-shaped plasma with a maximum radial size of 16 mm and a typical characteristic of diffuse discharge. Due to the absence of airflow, the diffuse jet with a simple structure and a mild discharge meets the first requirement. The diffuse jet remains quasiuniform and stable when contacting with metals. The effective modification area is approximately 200 mm $^{2}$ , which is seven times larger than that of the current plasma jets. A super-hydrophilic surface with the original multilevel microporous structure can be obtained after just 40 s of treatment with the diffuse jet, and remain viable for at least 30 mins, which meets the other two requirements. The carbon-cleaning effect and oxygen-attaching effect of the diffuse jet, along with the higher intensities of the C $=$ O/O-H together with the lower intensities of C-C/C-H after modifications, are responsible for the super-hydrophilicity. Because the slow expansion and the long reaction time of the active particles caused by the absence of airflow, a longer treatment time is more beneficial for the duration of the super-hydrophilicity. The results above successfully meet all the requirements and present a novel efficient method for the clinical real-time surface modification of Ti.