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 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 Ground plane Line plane Section AA’ Ground plane Line plane 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 EgEg EoEo VoltageCurrent 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 (T exc ~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 ~ n gas K(T e ) n e increasing the frequency also increases the electron density Power Control MSRR Frequency Control Power Amplifier Low Band VCO 1.8 GHz MSRR EM Model EM Measurement Optical Emission Intensity 1.8 GHz0.9 GHz 100 um discharge gaps VCO 0.9 GHz Results 1.8 GHz Results 4x more intensity! Discussion and Conclusion The OES intensity I ~ n e since T exc is nearly constant. This implies that doubling  results in doubling n e at low pressure and increasing n e by 4x at 1 atm. Hypothesis: Simple Ohmic Heating Model for Capacitive Discharges (Lieberman and Lichtenberg, p. 344) P ohm  0.76 A[  o 2 m e m g/e 2 ] (  2 V 2 )/(s 2 n e ) ~ A  2 /n e …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) n e  2n e n e  4n e 1 mm 0.5 mm 100 um gap @ 1W  1 MV/m Coaxial Probe Glass tube (chamber) Manifold Plasma Source Gas outlet To pressure gauges Gas inlet Needle valve 30dB 900.000 -7.3 MKS 0.53 - - - Source: F. Iza, PhD Thesis, 2004. AWT6108 GSM cell phone power amplifier (~4W) Voltage-controlled oscillator Electron Excitation 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 light process gas  plasma