Dielectric Barrier Discharge Lamp Research Articles

Parametric Studies of a Mercury-Free DBD Lamp

Mercury discharge lamps are often used because of their high efficiency; however, the usage of mercury lamps will be restricted or forbidden for safety and environmental purposes. Finding alternative solutions to suppress mercury is of major interest. The aim of this work is to increase the luminous efficacy of a commercial-free mercury flat dielectric barrier discharge lamp (Planilum, St Gobain) in order to reach the necessary conditions for the lamp to be used as a daily lighting source. The lamp is made of two glass plates separated by a gap of 2 mm. The gap is filled by a neon xenon mixture. The external electrodes made of transparent ITO (indium tin oxide) are deposited on the lamp glass plates. The electrical signal applied to the electrodes generates a UV-emitting plasma inside the gap. Phosphors deposited on the glass allow the production of visible light. The original electrode geometry is plane-to-plane; this induces filamentary discharges. We show that changing the plane-to-plane geometry to a coplanar geometry allows the plasma to spread all over the electrode surface, and we can reach twice the efficacy of the lamp (32 lm/W) as compared to the original value. Using this new electrode geometrical configuration and changing the electrical signal from sinusoidal to a pulsed signal greatly improves the visual uniformity of the emitted light all over the lamp. Electrical and optical parametric measurements were performed to study the lamp characteristics. We show that it is possible to develop a free mercury lamp with an efficacy compatible with lighting purposes.

10 kV SiC MOSFET Evaluation for Dielectric Barrier Discharge Transformerless Power Supply

At low pressure, cold plasmas are used for a wide range of applications such as coating, flow control, or microelectronics. Currently, this industry requires expensive vacuum systems which consume energy and time, and therefore it is very appealing to develop similar processes at atmospheric pressure. Under this condition, dielectric barrier discharge (DBD) is one of the best ways to obtain a cold plasma. The dielectric barriers naturally limit the current, and then the plasma temperature. Unfortunately, at atmospheric pressure the discharge ignition between the electrodes requires high voltage, which is generally obtained through a step-up transformer. The parasitic elements of this device exclude a smart control for the discharge. In order to overcome this default, we analyze the performance of a transformerless power supply developed with a recently released single-chip high-voltage semiconductor. The circuit uses only two high-voltage switches synthesized by means of the 10 kV SiC MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The design and implementation of the electric converter are presented and validated with experiments carried out on UV excimer DBD lamps. Then, the performances of the 10 kV SiC switches are analyzed and the relevance of this device for DBD applications is discussed.

External Electrode Fluorescent Lamp (EEFL) Driving Methods

External electrode fluorescent lamps (EEFLs) are used as backlight source for large screen size liquid-crystal displays. Since electrodes are outside of the discharge tube, lifetime is enhanced when compared with cold cathode fluorescent lamps. Also, a single inverter can drive multiple EEFL tubes, leading to a compact design, driven by sinusoidal or square waveforms. Luminance can be enhanced by synchronizing the moment of the self-discharge of the dielectric wall charge with voltage rising and falling. This paper presents luminance measurements for different driving alternatives and lamp voltages, showing that EEFLs have an electrical behavior similar to dielectric barrier discharge lamps and light emission similar to the conventional fluorescent lamps. It is also shown that sinusoidal operation is more efficient than square wave operation in the light emission sense for the explored conditions.

Efficiency of an Exciplex DBD Lamp Excited Under Different Methods

Three different electrical generators have been designed and used to supply an exciplex dielectric barrier discharge lamp in order to elucidate the influence of each one of these supplying strategies over the system performance; the first method consists on supplying the lamp with short bipolar voltage pulses; the second and third methods are based on semiresonant converters were current pulses, of controlled duration and magnitude, are injected into the lamp. For each one of the generators, measurements of the lamp and supply efficiency, are performed and analyzed, at different levels of power (up to 130 W) and operating frequencies (60–90 kHz). From the experimental results, the pulsed voltage-mode approach has allowed obtaining the highest lamp efficiency (7%), yet the maximum supply efficiency is offered by the resonant mode supplies. On the basis of the lamp and the supply efficiencies, the whole system performance is analyzed.

Optimum transformer turns ratio for the power supply of dielectric barrier discharge lamps

This study is focused on studying a resonant current converter for the electrical supply of dielectric barrier discharge devices. To understand the impact of parasitic capacitances and incorporate them into the design of an optimised power supply, this approach theoretically analyses a boost-based resonant converter, considering switch capacitance and analysing the impact of the transformer turns ratio on the system's electrical efficiency. The theoretical loss analysis shows a considerable variation in efficiency for different transformer turns ratios (between 38 and 90%). At low turns ratios, most of the losses are caused by switching, whereas at high turns ratios, the conduction losses outweigh the switching losses. The impact of the transformer stray capacitance is analysed via simulation and the optimised converter is used for the experimental validation of the theoretical study.

Repetitive High-Voltage All-solid-state Marx Generator for Excimer DBD UV Sources

In order to develop an efficient and reliable pulsed power supply for excimer dielectric barrier discharge (DBD) ultraviolet (UV) sources, a pulse generator using Marx topology is adopted. MOSFETs are used as switches. The 12-stage pulse generator operates with a voltage amplitude in the range of 0-5.5 kV. The repetition rate and pulsewidth can be adjusted from 0.1 to 50 kHz and 2 to 20 μs, respectively. It is used to excite KrCl* excilamp, a typical DBD UV source. In order to evaluate the performance of the pulse generator, a sinusoidal voltage power supply dedicated for DBD lamp is also used to excite the KrCl* excilamp. It shows that the lamp excited by the pulse generator has better performance with regard to radiant power and system efficiency. The influence of voltage amplitude, repetition rate, pulsewidth, and rise and fall times on radiant power and system efficiency is investigated using the pulse generator. An inductor is inserted between the pulse generator and the KrCl* excilamp to reduce electromagnetic interference and enhance system reliability.

Square-Shape Current-Mode Supply for Parametric Control of the DBD Excilamp Power

With the aim of providing a power supply for the study of dielectric barrier discharge (DBD) excimer lamps (excilamps), a current-mode converter that allows for an accurate adjustment of the electrical power injected into one of those lamps is designed and implemented. Starting from the electrical model of the DBD lamps, the convenience of using a current-mode supply to control the lamp power is demonstrated. With the proposed converter, the current supplied to the lamp has a trapezoidal almost-square shape controlled by means of three parameters, namely, amplitude, duty cycle, and frequency, which provides full control of the lamp electrical power. Implementation is made considering a step-up transformer interfacing the high-voltage lamp with the converter. Experiments demonstrate the operating principle of this converter, including ultraviolet power measurements for a DBD XeCl excilamp. The capabilities of the converter are used to analyze the lamp behavior under different combinations of these three parameters, illustrating its capabilities for finding the optimal operating point of a DBD reactor.

Decontamination Efficiency of a DBD Lamp Containing an UV-C Emitting Phosphor.

Among different physical and chemical agents, the UV radiation appears to be an important route for inactivation of resistant microorganisms. The present study introduces a new mercury-free Dielectric Barrier Discharge (DBD) flat lamp, where the biocide action comes from the UV emission produced by rare-earth phosphor obtained by spray pyrolysis, following plasma excitation. In this study, the emission intensity of the prototype lamp is tuned by controlling gas pressure and electrical power, 500 mbar and 15 W, corresponding to optimal conditions. In order to characterize the prototype lamp, the energetic output, temperature increase following lamp ignition and ozone production of the source were measured. The bactericidal experiments carried out showed excellent results for several gram-positive and gram-negative bacterial strains, thus demonstrating the high decontamination efficiency of the DBD flat lamp. Finally, the study of the external morphology of the microorganisms after the exposure to the UV emission suggested that other mechanisms than the bacterial DNA damage could be involved in the inactivation process.

Pilot Plant Results with Three Different Types of UV Lamps for Advanced Oxidation

Three different types of ultraviolet lamps were tested for the advanced oxidation process application on pre-treated surface water in a pilot plant. The pilot setup consisted of three parallel reactors with either medium pressure, low pressure or dielectric barrier discharge UV lamps. Four model compounds (atrazine, bromacil, ibuprofen and N-nitroso-dimethylamine (NDMA)) and 0, 5 or 10 ppm hydrogen peroxide were dosed. Low pressure lamps were shown to have the lowest energy demand, calculated as electrical energy per order, followed by dielectric barrier discharge lamps and then medium pressure lamps. Medium pressure lamps gave the highest formation of genotoxic activity and nitrite formation, whereas no formation of genotoxic activity was observed for either of the other lamp types.

Starting Mechanism of Inductively Coupled Electrodeless Lamp Operating at 135 kHz

The present electrodeless lamp system operates at 135 kHz and has a higher efficiency and output than the high pressure mercury lamp system, which is currently very popular in the market. However, in terms of the starting performance, the 135 kHz electrodeless lamp system needs a much higher voltage than its 13.56 MHz predecessor. With regard to the ignition for inductively coupled electrodeless lamps, it has been reported that there are theoretically two types of ignition: E-discharge and H-discharge. E-discharge uses capacitively coupled plasma and is utilized for plasma processing as the dielectric barrier discharge lamp (DBD lamp) or for back lighting as the external electrode fluorescent lamp (EEFL). This lamp plasma is sustained by the electric field passing through the glass wall from the power source. H-discharge uses inductively coupled plasma and is utilized for lighting. This lamp plasma is sustained by the electromotive force generated by the alternating magnetic field. The ignition of this lamp is defined as the time when the H-discharge occurs, as this is an inductively coupled electrodeless lamp. The starting voltage of the 135 kHz electrodeless lamp system is higher than 1 kV, so it is expected to reduce the starting voltage because of the insulation. Observation of the starting state of the 135 kHz electrodeless lamp system showed that discharge occurred at a relative low coil voltage. It was also shown that the starting voltage could be decreased when the turns of the coil wire are decreased under the condition that the product of the wire turns and the frequency and current are both kept constant.

Evaluation of Photocatalytic Active Coatings on Sintered Glass Tubes by Methylene Blue

A comparative study between ten different photocatalytic active coatings was done. The effectiveness and photocatalytic activity of the coatings were studied by degradation experiments of methylene blue (MB) dye under UV light illumination. The reactor design consisting of sintered glass packed in a borosilicate tube placed between two planar dielectric barrier discharge lamps (Osram Planon) is reported for the first time. The coatings consisted of either titania, silica, or zinc on sintered borosilicate glass. The advantage of sol-gel in catalyst preparation was exploited to combine catalyst to act as cocatalyst. TiO2-P25 widely applied in suspension systems was effectively immobilized on sintered glass support with the aid of tetraethylorthosilicate (TEOS) solution which acted as support material. Results indicated that TiO2-P25+SiO2, TiO2-P25+SiO2+Pt, and TiOSO4_30,6wt% films showed highest degradation rates close to 100% after 90 min illumination with degradation rates exceeding 50% after 30 minutes. TTIP+Pt showed lowest degradation rate.

Characterization and modelling of low-pressure rf discharges at 2–500 MHz for miniature alkali vapour dielectric barrier discharge lamps

Low-pressure dielectric barrier discharge (DBD) alkali vapour lamps are of particular interest for portable atomic clocks because they (1) could enable low-power operation, (2) generate the precise required wavelength, (3) are planar simplifying chip-level integration and (4) use external electrodes, which increases the lifetime. Given the stringent requirements on lamps for atomic clocks, it is important to identify the parameters that can be optimized to meet these performance requirements (size, power consumption, stability, reliability). We report on the electrical and optical characteristics of dielectric barrier plasma discharges observed in two configurations: (1) in a vacuum chamber over a wide low-pressure range (2–100 mbar) for three different buffer gases (He, Ar, N2) driven at different frequencies between 2 and 500 MHz and (2) on microfabricated hermetically sealed Rb vapour cells filled with 30 and 70 mbar of Ar. We discuss the optimum conditions for a low-power and stable operation of a Rb vapour DBD lamp, aimed at chip-scale atomic clocks. We also present the electrical modelling of the discharge parameters to understand the power distribution mechanisms and the input power to discharge power coupling efficiency.

Prediction of advanced oxidation performance in various pilot UV/H2O2 reactor systems with MP- and LP- and DBD-UV lamps

The UV/H2O2 advanced oxidation process is increasingly applied as a barrier against organic micro pollutants in drinking water treatment. Adequate modeling of the purification process, resulting in a reliable prediction of the reactor performance, would make it possible to optimize the operating parameters as a function of seasonal or diurnal fluctuations in the influent composition, and thus save energy while still guaranteeing safe drinking water. We recently developed two design tools to predict full scale performance of UV/H2O2 reactors: the UVPerox I and II models. UVPerox I is based on a kinetic model, describing both photolysis and oxidation. By means of Computational Fluid Dynamics (CFD) calculations of the reactor the UV dose distribution inside the reactor can be calculated, while the kinetic model gives the conversion as a function of the UV dose. UVPerox I is shown to be applicable to reactors equipped with Low Pressure (LP) or Dielectric Barrier Discharge (DBD) UV lamps, using a broad range of organic compounds, resulting in a <5–10% deviation from experimental data for different water matrix compositions. The conversion of micro pollutants as a function of the UV dose can also be experimentally determined, using a collimated beam (CB) set-up. The dose response curves thus obtained can also be directly implemented in the CFD-model of the reactor (UVPerox II). Using several model compounds UVPerox II is shown to be applicable to reactors equipped with three kinds of UV lamps (LP-, MP- UV and DBD lamps), each with its own emission spectrum. The deviation from experimental data was found to be <5–10%, independent of the composition of the water matrix. Both models were applied to several reactor geometries. Good agreement was obtained between both models and the actual conversion data for three types of UV lamps in various pilot reactors and water types.

Synthesized High-Frequency Thyristor for Dielectric Barrier Discharge Excimer Lamps

Dielectric barrier discharge (DBD) lamps, being capacitive loads, must be associated with bidirectional current sources for an appropriate control of the transferred power. Pulsed current source supplies, which are known to offer very interesting performances, require specific power switches that are able to manage bidirectional voltage and unidirectional current at much higher frequencies (several hundreds of kilohertz) than commercial thyristors. This paper proposes the detailed design of such a high-speed synthesized thyristor, using discrete components: a MOSFET in series with a high-voltage (HV) diode and a logic circuit that controls its gate. This switch is associated with an optimized self-powered driver, which is a very efficient solution to handle the perturbations associated with the HV and high-frequency operation. Experimental application of this device for DBD excimer lamp supply is proposed.

Wet chemical preparation of YVO4:Eu thin films as red-emitting phosphor layers for fully transparent flat dielectric discharge lamp

Highly transparent YVO4:Eu thin films were deposited via dip coating of liquid nanoparticle dispersions on glass substrates. Annealing of the nanoparticle layers resulted in restructuring of the material into oriented crystalline films. The crystallinity was confirmed using powder X-ray diffraction. Film thickness was adjusted to 467nm by multiple deposition. The resulting coatings show >99% absorbance for wavelength below 300nm and >90% transmission in the visible spectral range. Under UV-light excitation a bright red photoluminescence with a quantum efficiency of 20% is observed. A planar, transparent dielectric barrier discharge lamp was constructed using YVO4:Eu coated glasses and transparent electrodes made from antimony-doped tin dioxide thin films.

Control of the UV flux of a XeCl dielectric barrier discharge excilamp through its current variation**Reported at the IX International Conference on Atomic and Molecular Pulsed Lasers (Tomsk, 2009).

The efficiency of the electrical power transfer to the gas mixture of a XeCl dielectric barrier discharge (DBD) exciplex lamp is analysed. An equivalent circuit model of the DBD is considered. It is shown that the excilamp power can be controlled by applying current to the lamp. This highly desired property isensured by means of a specific power supply topology, whose concepts and design are discussed. The experimental prototype of a current-mode converter operating in the pulsed regime at pulse repetitionrate of 50 kHz is presented and its capability to control the amount of energy transferred during each current pulse is demonstrated. The capability of this power supply to maintain specific operating conditions for the DBD lamp, with a very stable behaviour (even at a very low current, in the regime of a single discharge channel), is illustrated. The experimental results of a combined use of this converter and a XeCl excilamp are presented. The influence of the supply parameters on the 308-nm XeCl excilamp is analysed.The shape of the UV pulse of the lamp is experimentally shown to be similar to that of the current, which actually flows into the gas mixture. The UV radiation power is demonstrated to be tightly correlated to the current injected into the gas and controlled by the available degrees of freedom offered by the power supply. The measured UV output characteristics and performance of the system are discussed. Time resolved UV imaging of a XeCl DBD excilamp is used to analyse the mechanisms involved in the production of exciplexes at various power supply regimes. It is shown that a pulsed voltage source leads to formation of short high intensity UV peaks, while current pulses lead to formation of sustained discharge filaments. Based on the results of modelling of the above-mentioned operation conditions, the two power supply regimes are compared and analysed from the point of view of the UV power and radiative control.

Streak Images of the Breakdown Phase of a Pulsed Dielectric Barrier Discharge in Nitrogen

Streak images of the visible/ultraviolet emission from a pulsed excited N2 dielectric barrier discharge lamp are presented revealing streamer-type breakdown characteristics.

Dynamics of the Electrical Breakdown Phase of a Pulsed Dielectric Barrier Discharge in Neon

Streak images of the visible emission from a pulsed excited Ne dielectric barrier discharge lamp are presented.

Preliminary Investigation of a Dielectric Barrier Discharge Lamp in Open Air at Atmospheric Pressure

A dielectric barrier discharge (DBD) lamp is investigated by using sinusoidal power with a 10 kHz frequency in open air at atmospheric pressure. With increasing applied voltages, the different discharge phenomena appear. At relatively low voltages, the discharge states are general stochastic filamentary discharges with weak light. However, at relatively high voltages, the walls of quartz tubes are heated sharply by plasma, and then the dazzling light is emitted very quickly to form the DBD Lamp, corresponding to the low maintaining voltage that is lower than the ignited voltage. The discharge state or mode of the DBD lamp that corresponds to the glow discharge is deduced according to the wave form of the circuit current, which is evidently different from the filamentary discharges. Under these conditions, the spectrum of the DBD lamp is continuous in the range 400–932 nm, which is scanned in the range 300–932 nm. It is also shown that there is another discharge state or mode that is different from the traditional filamentary discharges. Therefore, it is concluded that the discharge state or mode of the DBD lamp is a glow discharge.

A novel ZVS double switch flyback inverter and pulse controlled dimming methods for flat DBD lamp

To reduce the voltage stress on the switching device and improve the converter efficiency, a zero-voltage switching (ZVS) double switch flyback inverter is proposed. Moreover, two kinds of voltage pulse density modulation dimming methods with the double switch flyback inverter for the driving of flat dielectric barrier discharge (DBD) lamp were presented to improve the dimming performance of DBD lamp. The luminance of the DBD lamp was adjusted by controlling an adopted auxiliary switch. The dimming circuits were built and demonstrated. The luminance and luminous efficacy with variation of input power and dimming ratios were provided. The experiment results show that a ZVS was achieved with the proposed double switch flyback inverter and the flicker caused by the uncontrolled voltage oscillation during the turn-off time of dimming pulse could be reduced. Therefore, a wider dimming range about 100% to 2% could be achieved with the proposed method and the power consumption was reduced.