Interaction and control of millimetre-waves with microplasma arrays

Propagation of electromagnetic waves in several types of microplasmas has been examined experimentally in a frequency range 10?75?GHz. Firstly, the fundamental characteristics of the propagation were investigated using a planar geometry of microplasma assembly, and the electron density was derived by a comparison of the transmittance with the theoretical analyses using a Drude type model with collisional effects. Secondly, an extraordinary propagation phenomenon such as the focusing effect was observed in a two-dimensional periodical microplasma array. This kind of anomalous refraction cannot be interpreted only by predictions based on the dielectric property of bulk plasma, and it is suggested that a photonic-crystal-like periodical dielectric structure may play a significant role. Thirdly, it was demonstrated that the T-junction formed by a microplasma connected to a microstrip line can control the transmission of microwaves. An attenuation (or modulation) depth of about 35% was obtained with a series of two T-junctions connected to the strip line at the right-angled corners. All the above features come from (a) the relatively high electron density of the microplasmas near 1013?cm?3, (b) the complex dispersion relation with collisional effects and (c) the spatial arrangement with a characteristic scale of the same order of the wavelength of microwaves.