Vol. 125 (2014) ACTA PHYSICA POLONICA A No. 6

Proc. of the 8th International Conference NEET 2013, Zakopane, Poland, June 18�21, 2013

Experimental Investigation of Low Power Microwave

Microplasma Source

D. Czylkowskia,∗, B. Hrycaka, M. Jasi«skia and J. Mizeraczyka,b

aThe Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Centre for Plasma

and Laser Engineering, J. Fiszera 14, 80-231 Gda«sk, PolandbGdynia Maritime University, Department of Marine Electronics, Morska 81-87, 81-225 Gdynia, Poland

The aim of this paper is to present a novel microwave microplasma source generated in di�erent gases at atmo-spheric pressure. The design, rule of operation and experimental investigations of the new microwave microplasmasource are described. The main advantage of the presented microwave microplasma source is its small size, simplic-ity, and low cost of construction and operation. The microplasma has a form of a small plasma jet of dimensionsof a few mm, depending on the kind of gas, gas �ow rate, and absorbed microwave power. Presented in this paperresults of experimental investigations were obtained with an atmospheric pressure argon, krypton, nitrogen, andair microplasma, sustained by microwaves of standard frequency of 2.45 GHz. The absorbed microwave power wasup to 70 W. The gas �ow rate was from 2 to 25 l/min. The miniature size, simplicity of the source and stabilityof the microplasma allow to conclude that the presented new microwave microplasma source can �nd practicalapplications in various �elds.

DOI: 10.12693/APhysPolA.125.1323

PACS: 52.50.Dg, 52.70.Ds, 52.70.Kz, 52.80.Pi

1. Introduction

These days we observe a growing interest in the at-mospheric pressure microplasma sources operated withvarious gases like argon, nitrogen, and air. Microplasmahas dimensions in the range from µm to mm. Thereare many merits of the use of microplasma sources: eco-nomics, portability, easy to use, less made and opera-tion costs, and small size. They are needed for surfacemodi�cations, gas cleaning, hydrocarbon reforming, mi-crowelding, light sources, atomic spectroscopy and manyothers [1�5]. They can be also used in the biomedicalapplications such as sterilization of medical instruments,high-precision surgery, cells treatment and deactivationof bacteria and viruses [6, 7].

Among di�erent methods of microplasma generation,microwave microplasma sources (MmPSs) are of highpromising. They are simple and have long lifetime, com-pared to other microplasma systems. Due to this lastyears we designed, built and tested experimentally asmall, portable and easy to use MmPS [8�10]. It hadstructure of a coaxial line, formed by an inner conduc-tor, made of a brass rod with a tungsten rod top andouter conductor in the form of a brass cylinder. TheMmPS was operated at standard microwave frequencyof 2.45 GHz. In this paper we present a novel coaxialMmPS which is much smaller than that previously men-tioned. The design, rule of operation, and experimentalinvestigations of the new MmPS are described.

∗corresponding author; e-mail: dczylkowski@imp.gda.pl

2. Experimental setup

The diagram of the experimental setup used in thesemeasurements is presented in Fig. 1. Its main parts wereequipped with circulator, low power microwave genera-tor of frequency of 2.45 GHz, bi-directional coupler withdual-channel power meter, the MmPS, gas supplying and�ow control system, temperature, ultraviolet (UV) ra-diation and electromagnetic (E-M) �eld meters. In theexperiment the microwave power PA absorbed by the mi-croplasma was determined from PI�PR, where PI and PR

are the incident and re�ected microwave powers, respec-tively. The incident and re�ected microwave powers PI

and PR were measured directly using bi-directional cou-pler equipped with dual-channel power meter.

Fig. 1. The diagram of the setup for experimental in-vestigations of MmPS.

The photo and sketch with main dimensions of ournovel MmPS is presented in Fig. 2. It is based on acoaxial line formed by the inner conductor, made of a

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1324 D. Czylkowski et al.

tungsten rod, and outer conductor in the form of a brasscylinder. The long (length 87 mm) and thin coaxial line(5 mm of outer diameter) allows to reach by plasma thehardly to access cavities e.g. in stomatology applications.

Fig. 2. Photo and sketch with dimensions of MmPS.

The operating gas is introduced through a duct be-tween the inner and outer conductors. The MmPS issupplied from a typical low power 2.45 GHz microwavegenerator through a coaxial line using an N -type connec-tor. The generated microplasma has a form of a smallplasma jet of dimensions of a few mm, depending on thekind of gas, gas �ow rate and absorbed microwave power.

3. Results

The results concerning experimental investigations ofnovel MmPS included: in�uence of operating conditions(kind of operating gas, gas �ow rate, absorbed microwavepower) on the size and shape of the microplasma; depen-dence of the re�ected microwave power on the incidentmicrowave power and on the operating gas �ow rate; mi-croplasma temperature measurements as a function ofabsorbed microwave power and operating gas �ow rate;E-M �eld measurements around the MmPS and UV ra-diation measurements versus gas �ow rate, absorbed mi-crowave power and distance from microplasma �ame.In this paper only selected experimental results are

presented. In Fig. 3 photos of the Ar, Kr, N2, and airmicrowave microplasma for various operating conditionsare shown. As it can be seen the size and shape of themicroplasma �ame depends on the kind of the operatinggas and absorbed microwave power (PA). Also, di�erentvalue of minimal absorbed microwave power is needed togenerate microplasma in di�erent gases. In the case ofAr and Kr a few W of absorbed microwave power is su�-cient to initiate the discharge while in the case of N2 andair tens of W are needed.The dependence of the re�ected microwave power (PR)

on the incident microwave power (PI) and on the oper-ating gas �ow rate was measured to estimate e�ciency

Fig. 3. Photos of the microwave microplasma gener-ated in di�erent gases and for various operating condi-tions. (a) Ar, Q = 10 l/min, PI = 12 W, PR = 10 W,(b) Kr, Q = 10 l/min, PI = 15 W, PR = 12 W, (c) N2,Q = 10 l/min, PI = 300 W, PR = 230 W, (d) air,Q = 10 l/min, PI = 330 W, PR = 260 W.

of microwave power transfer from the microwave gener-ator to the plasma and thus to describe the stability ofMmPS operation. Measurements were done for argon mi-croplasma of gas �ow rate up to 25 l/min and incident mi-crowave power up to 125 W. As it was observed, althoughthe MmPS was not equipped with any impedance match-ing element the re�ected microwave power, for choosingexperimental conditions, stays at acceptable level.

Fig. 4. Electromagnetic �eld intensity (a) and UV ra-diation (b) measurements around MmPS.

The photo showing electromagnetic �eld intensity mea-surements around the MmPS is shown in Fig. 4a. Inthe photo the Holaday EMF Measurement type HI-1600meter and meter probe could be seen. Results of mea-surements show that all the time during the experimentsthe electromagnetic �eld intensity was never higher than5 mWcm−2. Thus it makes our MmPS safe for personneland instrumentation. Figure 4b shows photo of UV ra-diation measurements around Ar microplasma �ame. Inthe measurements the Sonopan UVB-20 meter was used.In the �gure the meter detector placed parallel to themicroplasma source can be seen.Dependence of the UV radiation intensity on the ab-

sorbed microwave power is presented in Fig. 5a. The UVdetector was placed perpendicularly to the MmPS. Mea-surement was done for two values of Ar �ow rate, 5 and10 l/min. The distance of the UV detector to the Ar mi-croplasma �ame was equal to 10 cm. From the �gure theincrease of the UV radiation intensity with increase ofthe absorbed microwave power can be seen. Dependenceof the UV radiation intensity on the distance from Armicroplasma �ame is shown in Fig. 5b. The Ar �ow rate

Experimental Investigation of Low Power Microwave Microplasma Source 1325

Fig. 5. Dependence of the (a) UV radiation intensityon the absorbed microwave power and (b) UV radiationintensity on the distance from MmPS.

was 5 l/min and absorbed microwave power was equalto 13.5 W. Figure shows that UV radiation strongly de-pends on the distance from the MmPS and decreases withincreasing the distance.

Fig. 6. Photos of the (a) Ar microplasma treatment ofthe human skin and (b) Ar microplasma operated in awater.

In Fig. 6a the photo showing human skin treatment us-ing low power Ar microplasma is presented. The Ar �owrate was 10 l/min and absorbed microwave power wasequal to 10 W. Figure 6b shows the photo of the possi-bility of Ar microplasma operating in a water. As well asthe possibility of living organism treatment as possibilityof operation in wet environment allows to conclude thatour MmPS is a promising device for the biomedical ap-plications. Among them, potential use in dental hygieneseems to be very interesting.

4. Conclusions

The results of our experimental work show that theinvestigated novel MmPS can be operated with a goodstability and safe level of electromagnetic �eld intensity.It can be operated in di�erent gases like argon, kryp-ton, nitrogen, and air with gas �ow rates of up to tensl/min. We showed that our MmPS can be used in hu-man skin treatment and can be operated in water. The

simplicity of the presented in this paper novel MmPSgenerator, operation stability and parameters of the mi-croplasma allows to conclude that the presented devicecan �nd practical applications in various �elds.

Acknowledgments

This research has been supported by the Szewalski In-stitute of Fluid-Flow Machinery, Polish Academy of Sci-ences under the program IMP PAN O3Z1T1.

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