Time delay for the electric breakdown of polyethylene at 3300 megacycles

The electric strength of polyethylene has been reported as being 17 kv/mil at dc and 3300 megacycles (1), at room temperature. The measurements that were made at the microwave frequencies were carried out in a “dished in” conical shaped resonant cavity. The three-quarter wavelength TEM mode of the cavity was used. The one-half wavelength section was filled with air and the remaining quarter wavelength was filled with the dielectric sample. A special dielectric-imbedded feedloop had been designed to permit matching the cavity impedance to the 7/8" coaxial transmission line. Tuning stubs in the air filled section were used to tune the cavity. Another feature of the cavity was the ease with which the electrode surfaces were renewed after each test (1).