Microwave absorption on thin films and contaminants

Summary form only given. This paper examines the RF heating of the contaminants on a diamond window, and of TiN coatings on ceramic windows. This model has been extended to account for discontinuous surface films which have a patchy or island structure. An analysis of a 4 nm TiN film with an island structure showed that the average, global absorption coefficient of order 0.1-0.3 percent, which is on the same order of magnitude as that for diamond windows. An isolated contaminant, depending on its size and its complex electrical permittivity, may absorb RF power primarily through the electric field, or primarily through the time-varying magnetic field. It turns out that an internal graphite inclusion in a diamond window absorbs only a small amount of mm wave power primarily through the electric field, which results in negligible heating within the diamond window. On the other hand, aluminum contaminant of 100 /spl mu/m size near the surface of the maximum RF magnetic field (1 MA/m) of a microwave cavity (at X-band) may absorb significant RF power from the time-vary magnetic field to cause melting or even vaporization of the aluminum sphere.