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A dielectric barrier discharge (DBD) is an electric discharge that occurs between a pair of electrodes with at least one dielectric material in between. The discharges that form in DBD’s are known as microdischarges, which are small streamers that typically have a radius of 0.1 mm and travel on a timescale of less than 100 ns. The properties of the dielectric materials used in a DBD configuration can affect the formation of the discharges. For example, a low density porous dielectric material may have discharges that tend to form in a particular area where a small hole exposes the electrode that the dielectric is covering. Other properties such as gas composition, gas pressure, electrode separation distance, and the applied voltage frequency/waveform can influence the properties of the discharge.

Abstract  

Materials  and  Methodology  

The affordability and advancements in 3D printing technology make it the method of choice for prototyping and development. We investigate how the thickness and density of 3D printed electrodes affects the formation of microdischarges inside a dielectric barrier discharge (DBD) surface modification reactor. We use a Makerbot Replicator II 3D printer to manufacture the electrodes by encasing thin pieces of copper tape in PLA plastic. The DBD setup consists of a cylindrical aluminum HV electrode which is surrounded by a layer of 6 mm thick Alumina and is connected to a 15 kV, 75-300 kHz, AC power supply. The printed electrodes are grounded and held 5 mm beneath the Alumina, forming a discharge gap. The DBD is operated with an Ar/Air gas mixture at atmospheric pressure. A PI-MAX 3 ICCD camera is used to image the microdischarges at various stages of their development. The image analysis suggests that that the printed electrodes with a thicker and denser plastic layer have a greater number discharges per discharge period. Quickfield electric field simulations suggest that the field inside the discharge gap is distorted near the surface of the electrodes due to irregularities in the printed material. These results can be used to guide the future design of 3D printed electrical components.

Introduc9on  

QuickfieldTM Student Edition modeling software was used to model the electric field around the electrodes with different densities of PLA. ● The simulations show that the non-uniformities in the printed material tend to distort the electric field strength near the surface of the electrode. ● A higher density electrode will distort the field less than a electrode with a lower density.

Conclusion/Discussion  

References  

Above: Discharge image of 2mm low density holder with the corresponding oscillogram.

Experimental  Set-­‐up  

● The Alumina is modeled as a cylindrical capacitor along the region where it covers the HV electrode. ● The air gap is modeled as a 5 mm wide planar capacitor. ● The printed electrode is modeled as a 2 mm wide planar capacitor with PLA as a dielectric material on the inside (using the 2mm thick electrode).

Robert Albertson1, Sophia Gershman2 and Andrew Zwicker2  1Mercer County Community College, West Windsor NJ, 08550; 2Princeton Plasma Physics Laboratory, Princeton NJ, 08543-0451  

3D  Printed  Electrodes  for  a  Dielectric  Barrier  Discharge  

● A gas line attached compressed Argon gas to a shut off valve and then to an Omega mass flow controller and was inserted into the back flange. ● A gas line connected a Robinair vacuum pump to a shut off valve and was inserted in the front flange. ● During operation, the DBD was first evacuated with the vacuum pump, with pressures dropping as low as 500 torr. ● After evacuation, Argon was flowed into the DBD to a pressure of 1 atm.

Electrode    Configura9on  

• A Rigol DS6104 oscilloscope captured traces of the applied AC voltage and discharge current. • A Tektronix  P6105  HV  voltage  probe  was  aPached  to  the  HV  electrode • A Link  DSO-­‐P150  voltage  probe    was  aPached  in  series  with  130 Ohm resistor to give current values. • Oscilloscope was triggered by discharge current with a 1.31 V trigger level. ● PI-MAX 3 ICCD camera was triggered by the oscilloscope when the scope itself was triggered by the discharge current. ● Ocean Optics USB 4000 spectrometer was inserted in the back flange of DBD system and used to take spectra in visible and UV range.

Printed Electrodes Two sets of electrodes were printed with a Makerbot Replicator II 3D printer: one set consisted of electrodes with a width of 4mm and the other set consisted of electrodes with a width of 2mm. ● Each set had a high, medium and low density printed electrode. ● The copper tape was inserted by pausing the printer halfway through the print while carefully placing it along the half-finished electrode so that the printer could extrude on top of it. ● All electrodes were printed in polylactic (PLA) plastic.

Problem  Statement  This research project investigates whether 3D printers are capable of printing quality electrical components. This is tested by printing electrodes for a DBD while analyzing various properties of the discharges that form. The thickness of the electrodes and the density of the infill are the only parameters that are altered in the experiment. Each of the electrodes is imaged using the PI-MAX 3 ICCD camera and a statistical analysis is used to evaluate the discharge. Using 3D printers to create electrical components allows for greater efficiency in professional applications by allowing one to create the components on spot without having to spend the time of creating them by hand.

Electric field inside air gap

Properties of the microdischarges

Spectra

Capacitance Estimation

Statistical Results

The number of microdischarges was counted for each image along with the number of current spikes per discharge period in the matching oscillogram. These values were average over all obtained images.

𝑘↓𝑎 =1  

𝐴↓𝑎 =11.6  𝑐𝑚↑2   𝑑↓𝑎 =0.5  𝑐𝑚  

 

𝐶↓𝑎 =   𝑘↓𝑎 𝜀↓𝑜 𝐴↓𝑎 /𝑑↓𝑎  =2.05  𝑝𝐹      

Air Capacitor

𝑘↓𝑐 =9.3  

𝐿=9.5  𝑐𝑚  

𝑎=2.25  𝑐𝑚  

𝑏=2.9  𝑐𝑚  

 

𝐶↓𝑐 =   2𝜋𝑘↓𝑐 𝜀↓𝑜 𝐿/ln 𝑏/𝑎   =0.19  𝑛𝐹  

 

Alumina Capacitor

𝑘↓𝑝 =2.5  

𝐴↓𝑝 =11.6  𝑐𝑚↑2   𝑑↓𝑝   =0.2  𝑐𝑚  

 

𝐶↓𝑝 =   𝑘↓𝑝 𝜀↓𝑜 𝐴↓𝑝 /𝑑↓𝑝  =12.83  𝑝𝐹  

PLA  Capacitor  

Measurement  Methodology  

Electrical  system  

Gas  system  

DIDRIV10/PVM500DC pulsed half power resonant AC power supply was used to power the DBD. ● Connected to the HV electrode via a high voltage cable connector. ● 15 kV max output voltage with adjustable frequency /duty cycle. ● During DBD operation, the frequency was always set to the resonance frequency of the system.

The DBD set-up consists of a cylindrical aluminum HV electrode encased by 0.6 cm thick alumina. ● The printed electrodes are supported by resting them on the edges of the alumina, which forms a 0.5 cm wide discharge gap.    

Materials  and  Methodology  con9nued  

Electrical  measurements  

● A Rigol DS6104 oscilloscope captured traces of the applied AC voltage and discharge current. ● A Tektronix P6105 HV voltage probe was attached to the HV electrode. ● A Link DSO-P150 voltage probe was attached in series with 130 Ohm resistor so that the current could be measured. ● The oscilloscope was triggered by the discharge current with a 1.31 V trigger level.

Imaging  A PI-MAX 3 ICCD camera was used to image the discharges with a 5 µsec exposure time. ● The camera was triggered by the oscilloscope when the scope itself was triggered by the discharge current. ● Each image was taken manually by taking singles on the oscilloscope in sets of 10, 20, or 40 images at a time. ● Any electrical data obtained by the scope corresponding to an image was saved onto a flash drive.

Spectroscopy  A Ocean Optics USB 4000 spectrometer was used to attain spectra of the discharge in the UV and visible range. ● The spectrometer probe was inserted in the back flange of the DBD and outfitted with a compression fitting. ● The flange itself supported the spectrometer probe. ● The spectrometer probe was held about 2 inches from discharge.

Theory/Calcula9ons  

𝐶↓𝑡𝑜𝑡𝑎𝑙 = (1/𝐶↓𝑎  +   1/𝐶↓𝑐  +   1/𝐶↓𝑝  )↑−1 =1.75  𝑝𝐹  

Results  

The charge transported in a single microdischarge was estimated by integrating the area under the curve of the current waveform captured by the oscilloscope using Logger Pro.

Princeton  Plasma  Physics  Laboratory  

Above:  Discharge  image  of  2mm  low  density  holder  with  the  corresponding  oscillogram.  

Above: Discharge image of 2mm high density holder with the corresponding oscillogram.

Above: Discharge image of 4mm medium density holder with the corresponding oscillogram.

DBD  Current  and  Images  

Images/Oscillograms  con/nued  

Above: Discharge image of 2mm medium density holder with the corresponding oscillogram.

Above: Discharge image of 4mm low density holder with the corresponding oscillogram.

The following are discharge images and the corresponding oscillograms for each of the electrodes. The vertical axis on the oscillograms are in mA while the horizontal axis represents the datapoint number.

Becker, K. H., et al. eds. Non-equilibrium Air Plasmas at Atmospheric Pressure. Bodmin: Institute of Physics Publishing, 2005. Print. H.E Wagner, R. Brandenburg, et al. ‘The barrier discharge: basic properties and applications to surface treatment’. Vacuum. 71:417-436 (2003). QuickfieldTM Student Edition, 5.10.1.1140 Copyright © 1993-2012, Tera Analysis Ltd.

Electrodes with a greater density had a higher number of microdischarges forming than their lower density counterparts for a given thickness. The low density electrodes had the greatest tendency for arcing: both the 2mm and 4mm low density were damaged extensively. It is worth noting that the resonance frequency of the DBD system changed drastically after several minutes of continuous use. In the future, it will be useful to test different plastics besides PLA with greater dielectric strengths.

Above: Schematic diagram of the electrodes.

To the left: Picture of DBD used to test the printed electrodes. To the right: Picture of printed electrode inserted inside the alumina chamber.

Above: Schematic diagram of the DBD configuration.

Above: Diagram describing how the PI-MAX 3 was triggered.

To the left: Quickfield electric field strength simulation of low density electrode (red represents an area of strongest E-field strength and blue represents and area of weakest E-field strength). To the right: Quickfield electric field strength simulation of a perfectly uniform electrode.

Above: Schematic diagram of DBD modeled as capacitors in series. To the left: Alumina capacitor.

● The displacement current was subtract out from the current. ● Typical values for the amount of charge passed by a microdischarge is on the order of 0.1 – 1 nC of charge. ● The low density electrodes had microdischarges that passed the most charge. ● Typically decay time for the microdischarges was about 100-200 ns.

The  electrical,  material,  and  geometrical  proper/es  of  the  simula/ons  were  made  to  match  the  actual  DBD  as  closely  as  possible.  

● These value agrees within the same order of magnitude of that given by Quickfield’s capacitance calculator.

Above: A microdischarge from the 4mm high density holder. The amount of charge passed is 0.3 nC and the decay time is about 220 ns.

Above: Table displaying the results of the statistical analysis.

To the left: Picture of all the printed electrodes.

Above: Table of electrode properties

● The spectra show that Ar, O, H, OH, and N2 are active species in the discharge.

Above: Spectrum of discharge for 4mm low density holder in visible range (left) and the UV range (right).