Microplasma antennas: characterizing capillary plasma discharges as potential monopole antennas

This thesis investigates the use of capillary plasma elements, in glass and quartz with sub-millimeter inner diameters and 1-5 cm in length, as monopole antenna elements. Plasma elements of this size have not been demonstrated before, as most plasma antennas use fluorescent tubes with inner diameters greater than 2 cm and longer than 30 cm. In order to validate that capillary plasma elements function well as the conductive element in antenna structures, spectroscopic electron density measurements of the Stark broadening in the Balmer series were performed for two capillary antenna elements. Glass tubes operated as a dielectric barrier discharge, or DBD, driven by an AC voltage of 10--40 kHz showed peak electron densities of n_e = 10^(15) cm^(-3). Time-averaged electron densities and conductivities in these tubes remained well below n_e = 10^(14) cm^(-3) and σ_p = 100 S/m, two threshold values for adequate antenna operation. Quartz tubes driven by a 140 MHz RF voltage maintained time-averaged electron densities of 8 x 10^(14) cm^(-3). This result indicates that capillary microplasma discharges in capillary tubes can be used as monopole antennas with electronically variable resonances and radiation patterns, as well as the opportunity to investigate microplasma monopole elements incorporated into arrays once the engineering problems of plasma breakdown and stability have been solved