Effect Of Voltage Amplitude Research Articles

Preparation and optical characterization of 3D-TiO2 thin films with brilliant colors

In this paper, three-dimensional titanium dioxide (3D-TiO2) thin films with periodic structure were obtained by periodic pulse anodization of high-purity titanium wafers under specific alternating voltage (AV) using asymmetric sawtooth waveforms. The effect of voltage amplitude and electrolyte concentration on the structural color of the 3D-TiO2 thin films were investigated. It is shown that the nanotubes grown by asymmetric sawtooth wave at a specific AV have a “bamboo” shape, and the cycle length, as well as the inner and outer tube diameters of the nanotubes are closely related to the AV. The structural color of the samples was different at varying voltages and electrolyte concentrations for the same oxidation cycle time. The structural color of films grown under low voltage is analyzed to be related to the scattering and absorption of light on their surfaces. The thickness of the film grown under high voltage satisfies the conditions for light interference. The maximum reflected wavelength is red-shifted and then blue-shifted as the electrolyte concentration decreases. The study shows that the microstructure is the main influence on the color change of 3D-TiO2 thin films.

Charge distribution on polymer insulator surface under AC voltage

Charge accumulation on an insulator surface under AC electric field is uncertain and is different from DC. In this paper, a method of extracting the phase of voltage truncation time is proposed. The characteristics of charge distribution on an insulator surface under AC voltage is obtained, and the relationship between the voltage phase and the surface charge distribution is investigated. The measurement results of charge distribution and the microscopic discharge process are compared and analyzed which can overcome the deficiency of the traditional off-line measuring method. In addition, the effect of voltage amplitude and insulator material characteristics on the surface charge are studied. It is shown that the charge distribution on an insulator surface shows a three-tier concentric circular structure, and the distribution characteristic of the charge is closely related to the phase of the AC voltage truncation time and the insulation material. The charge density is also affected by the voltage amplitude.

An Investigation of the Control of Electron Energy in the Atmospheric-Pressure Helium Plasma Jet

In this paper, an investigation of the control of electron energy in the atmospheric-pressure helium plasma jet produced by a needle–plane discharge system has been performed by means of the numerical simulation based on a 2-D self-consistent fluid model. Due to the consideration of practical application of the cold atmospheric-pressure plasma jet (CAPPJ) in the fields of biomedicine, in this paper, the mean electron energy (MEE) nearby the cathode plane is accounted for. The parameter dependences of the MEE have been systematically calculated. The considered parameters include the voltage amplitude and rising time $t_{r}$ of the applied voltage pulse as well as needle electrode radius. The voltage amplitude is changed in the range from 3 to 19 kV, and $t_{r}$ is from 1 to 200 ns. The spatial electric field has also been analyzed in detail because of its dominant role in controlling electron energy. In addition, the effect of electron energy on the production of the reactive species OH, O3, and H2O2 has also been investigated when considering the addition of humid air to the working gas helium. This paper gives the following significant results. For a given $t_{r}$ , the MEE increases almost linearly with increasing voltage amplitude. The effect of voltage amplitude on the MEE becomes much more evident for smaller $t_{r}$ and is obviously weak for the $t_{r}$ with a few hundreds of nanoseconds. Fixing the voltage amplitude, the MEE decreases with the increase in $t_{r}$ . The dependence of the MEE on $t_{r}$ is evident for a high voltage amplitude and the reverse is true for the lower voltage amplitudes. As a whole, the higher voltage amplitude and smaller rising time $t_{r}$ or their synergism should be considered for obtaining high electron energy. Especially, an MEE of about 10 eV can be obtained, which covers the energy thresholds inducing all the processes of dissociative electron attachment to water molecule and thus is of essential importance for the production of the reactive species such as OH, H2O2, and O3 in the interactions of plasmas with the aqueous solution embedded in biofilms or tissues. The needle electrodes with different radii result in a minor variation of the MEE under the fixed voltage amplitude and $t_{r}$ . Therefore, changing the radius of the needle electrode is not an effective solution to the control of electron energy in the CAPPJ. Furthermore, the parameter dependence of the spatial electric field is similar to that of the MEE, which reveals the dominant role played by the spatial electric field in controlling electron energy in CAPPJs. Considering the addition of humid air to the working gas helium, with the increase in electron energy, the averaged densities of OH and O3 increase, but that of H2O2 decreases.

Effect of voltage amplitude on gas density variation in an atmospheric pressure streamer discharge

Gas density variation in an atmospheric-pressure streamer discharge was visualized using the Schlieren method and was simulated by a two-dimensional axisymmetric simulation. The Schlieren images visualized the occurrence of shock waves and decrease in the gas density after the discharge. The axial distribution of the gas density was compared between experimental and simulation models, and we found that the two were in good agreement. Additionally, this paper discusses the effect of the pulse voltage amplitude on the decrease in the gas density. Our simulation results show that the pulse voltage amplitude affects the ratio of energy loss fractions of electrons by electron-impact collision processes.