4 Torr argon, 1.8 GHz

Upper Energy Level (eV)

13.0 13.2 13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8

ln( I

/gA

)

15

16

17

18

19

20

21

22

PS-TuP8

Frequency and Dimensional Scaling of Microplasmas Generated by Microstrip Transmission LinesIstvan Rodriguez, Jun Xue, and Jeffrey Hopwood, Northeastern University Boston, MA 02115

Goals• Decrease the size of microplasma generators

• Increase the frequency of operation from 900 MHz to 1800 MHz

• Compare measured and modeled electromagnetic behavior

• Compare light intensity as a function of operating frequency

Motivation• A possible application for microplasma is a portable gas analyzer

• Ideal microplasma properties

• Low power consumption (< 1 watt)

• High optical brightness

• Long, stable operating lifetime: no sputter erosion

Background• The microplasma is formed in the gap (g) of a split-ring resonator

• The split-ring resonator is one-half wavelength in circumference

• The electric field is most intense in the region of the gap

Groundplane

Lineplane

Section AA’

Groundplane

Lineplane

Section BB’

A’A B’

B

Magnitude of the electric field |E|Simulation using HFSS from Ansoft

Discharge gap Ground Plane

Dielectric

g

h

Microstrip

Eg

Eo

g o

hE 2 E

g

Voltage CurrentV, I

λ2

V, I

Experiment• Compare two microstrip split-ring resonators (MSRR): 900 MHz, 1800 MHz

• Designed and simulated using Ansoft Ensemble

• 900 MHz: = 20 mm, width = 1 mm, g = 100 um.

• 1800 MHz: = 10 mm, width = 0.5 mm, g = 100 um.

• Fabrication

• CNC Milling of RT/Duroid (R = 10.2) with 17 m copper cladding

• SMA connector at ~12° for 50 RF input

• Electronics

• VCO – Raltron RQRA 0810-0900 (810 – 900 MHz @ 2dBm)

• VCO – Minicircuits MOS-1825pv (1766 – 1826 MHz @ 2dBm)

• PA – Anadigics AWT6108 – Quad Band GSM Cell Phone Power Amplifier

Results

Comparison between 0.9 GHz and 1.8 GHz MSRR

• Quality Factors (Q~170) and RF losses are comparable

• Excitation Temperatures (Texc~0.65 eV) are equal within experimental error

• Optical Emission Intensity is several times higher at 1.8 GHz than 0.9 GHz

• emission intensity is proportional to electron density, I ~ ngas K(Te) ne

• increasing the frequency also increases the electron density

Power Control

MSRR

Frequency Control

Power Amplifier

Low Band VCO

1.8 GHz MSRR

10 Torr argon

Wavelength (Angstroms)

6500 7000 7500 8000 8500

Inte

nsity

0.0

5.0e+4

1.0e+5

1.5e+5

2.0e+5

2.5e+5

3.0e+5

Intensity (1.8GHz) Intensity (0.9GHz)

760 Torr argon

Wavelength (Angstroms)

6500 7000 7500 8000 8500

Inte

nsity

0.0

1.0e+4

2.0e+4

3.0e+4

4.0e+4

5.0e+4

Intensity (1.8GHz) Intensity (0.9 GHz)

EM Model

EM Measurement

OpticalEmissionIntensity

1.8 GHz 0.9 GHz

100 um discharge gaps

VCO

Comparision of 0.9 GHz and 1.8 GHzSplit-Ring Resonator Optical Emission Intensity

Argon Pressure

4 Torr 10 Torr 100 Torr 760 Torr

Inte

grat

ed O

ptic

al E

mis

sion

Int

ensi

ty

0

1e+6

2e+6

3e+6

4e+6

Pabs = 0.25 W

0.9 GHz

0.9 GHz

0.9 GHz0.9 GHz

1.8 GHz

1.8 GHz

1.8 GHz

1.8 GHz

0.9 GHz Results 1.8 GHz Results

4x more intensity!

Discussion and ConclusionThe OES intensity I ~ ne since Texc is nearly constant. This implies that doubling

results in doubling ne at low pressure and increasing ne by 4x at 1 atm.

Hypothesis:Simple Ohmic Heating Model for Capacitive Discharges (Lieberman and Lichtenberg, p. 344)

Pohm 0.76 A[o2memg/e2] (2V2)/(s2ne) ~ A2/ne

…where A is the electrode area: A ~ (microstrip width) for diffusive plasma conditions observed at low pressures, but A ~ constant for filamentary discharge at 1 atm

2x more intensity

0.9 GHz (low pressure) 1.8 GHz (low pressure)1.8 GHz (high pressure)0.9 GHz (high pressure)

ne2nene4ne

1 mm0.5 mm

100 um gap @ 1W 1 MV/m

Coaxial Probe

Glass tube(chamber)

Manifold

PlasmaSourceGas outlet

To pressure gauges

Gas inlet

Needlevalve

30dB

900.000 -7.3

MKS

0.53

0.53 - - -

Source: F. Iza, PhD Thesis, 2004.

AWT6108 GSM cell phone power amplifier (~4W)

Voltage-controlled oscillator

4 Torr argon, 0.9 GHz

Upper Energy Level (eV)

13.0 13.2 13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8

ln( I

/gA

)

15

16

17

18

19

20

21

22

10 Torr argon, 1.8 GHz

Upper Energy Level (eV)

13.0 13.2 13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8

ln( I

/gA

)

15

16

17

18

19

20

21

2210 Torr argon, 0.9 GHz

Upper Energy Level (eV)

13.0 13.2 13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8

ln( I

/gA

)

15

16

17

18

19

20

21

22

eVTexc 13.067.0 eVTexc 10.069.0

eVTexc 08.063.0 eVTexc 10.060.0

ElectronExcitation

Temperatures

This work is supported by the National Science Foundation under Grant No. CCF-0403460

20 mm

10 mm

900 MHz in 1 atm. air

argon

power

optical spectrometer

lightprocess gas

plasma