PS-TuP8

1
PS-TuP8 Frequency and Dimensional Scaling of
Microplasmas Generated by Microstrip Transmission
Lines Istvan Rodriguez, Jun Xue, and Jeffrey
Hopwood, Northeastern University Boston, MA 02115
0.9 GHz Results
1.8 GHz Results

• Experiment
• Compare two microstrip split-ring resonators
  (MSRR) 900 MHz, 1800 MHz
• Designed and simulated using Ansoft Ensemble
• 900 MHz f 20 mm, width 1 mm, g 100 um.
• 1800 MHz f 10 mm, width 0.5 mm, g 100 um.
• Fabrication
• CNC Milling of RT/Duroid (eR 10.2) with 17 mm
  copper cladding
• SMA connector at 12 for 50 W RF input
• Electronics
• VCO Raltron RQRA 0810-0900 (810 900 MHz _at_
  2dBm)
• VCO Minicircuits MOS-1825pv (1766 1826 MHz _at_
  2dBm)
• PA Anadigics AWT6108 Quad Band GSM Cell
  Phone Power Amplifier

• 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

100 um discharge gaps
EM Model
1.8 GHz
0.9 GHz

• Motivation
• A possible application for microplasma is a
  portable gas analyzer
• Ideal microplasma properties
• Low power consumption (lt 1 watt)
• High optical brightness
• Long, stable operating lifetime no sputter
  erosion

EM Measurement
VCO
Electron Excitation Temperatures
Power Control
MSRR

• 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

Power Amplifier
Low Band VCO
Frequency Control
Optical Emission Intensity
10 mm
900 MHz in 1 atm. air
argon
4x more intensity!
2x more intensity
100 um gap _at_ 1W ? 1 MV/m
Discussion and Conclusion The OES intensity I
ne since Texc is nearly constant. This implies
that doubling w 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 Aeo2menmg/e2 (w2V2)/(s2ne)
Aw2/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

• Results
• Comparison between 0.9 GHz and 1.8 GHz MSRR
• Quality Factors (Q170) and RF losses are
  comparable
• Excitation Temperatures (Texc0.65 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

1 mm
0.5 mm
1.8 GHz (high pressure)
0.9 GHz (high pressure)
0.9 GHz (low pressure)
1.8 GHz (low pressure)
ne?4ne
ne?2ne
This work is supported by the National Science
Foundation under Grant No. CCF-0403460