Adjustable resonant cavity for measuring the complex permittivity of dielectric materials

An adjustable resonance cavity was developed to measure the complex permitt ivity of dielectric materials. The cavity has an inner diameter of 16.400 c m and an inner height of 2.54 cm. The aluminum stationary wall holder was p ositioned about 10.8 cm above the top of the cavity. It was fixed into plac e by three 1.27-cm-diam linear shafts. By suspending from the wall holder, the movable wall moved vertically by sliding on 1.27 cm bore-closed ball bu shings. By turning a 1 in.-12 nut, the movable wall could be positioned so that the cavity height equaled the height of the sample. Therefore, this en ables the measurement of the permittivity of samples with heights between 0 .88 and 1.91 cm and radius between 1.27 and 3.18 cm. The complex permittivi ty of the sample was calculated based upon the sample dimensions, central f requency of TMono modes, and Q factor of the resonance curve using an exact solution. The complex permittivity was measured at the three lowest modes, where the frequency span is 1-4 GHz. (C) 2000 American Institute of Physic s. [S0034-6748(00)01108-4].