Harmonic Generation in Microwave Microplasma

Harmonic generation in microplasmas is explored theoretically and experimentally, and then compared with a 2D fluid model. A microstrip split ring resonator with 150 ?m gap is designed to provide a microplasma source at around 1 GHz. Electrode area asymmetry is a known factor in harmonic generation in plasmas and is explored. Gas pressures of 0.2 Torr to 760 Torr in argon with power levels of 0.5 to 3 W are examined. Experimental results show third harmonic output of greater than 10 mW is achieved with 3 W of net input power in 0.3 Torr of argon and with asymmetric electrode areas. Experimental results of a microstrip split ring resonator in a frequency mixer configuration are also shown. Fluid model simulations of Gregorio reveal that the small electrode area of an asymmetric discharge forces a higher voltage, which strongly modulates the sheath width and creates hot electrons. A nonlinear voltage-capacitance relationship, as well as hot electrons causing large conduction current spikes, are the sources of harmonic current in the plasma. Results of experiments and fluid model simulations are compared and are found to compare reasonably well.