Unloaded quality factor

In general, electromagnetic resonators are of common use for material characterization at microwave frequencies. In addition, a resonator represents a basic element of a multipole filter or an oscillator circuit. Any type of electromagnetic resonator is characterized by the resonant frequency /o and the unloaded quality factor Qo of the selected resonant mode and its spectrum of spurious modes. In order to measure the resonator properties or to use a resonator as part of a filter structure, the resonator needs to be equipped with one or two... 

The information about the losses in the material under investigation lies within the unloaded quality factor. In case of measurements at low levels of rf power weak coupling (Qexti, Qext2 Ql) resulting in Qo Ql is of common use. For measurements of the power dependence matched input coupling (Qexti Qo) and weak output coupling conditions should be adjusted (e.g. by a mechanical adjustment of coupling antennae position inside a cavity resonator). 

Two procedures described in BS4443, Part 2, 1988 [48] are suitable in particular for latex, PVC, and polyurethane foams. One is faster to carry out and can be used as a quality control method (Procedure A). Procedure B can be used to determine the load to give indentations of 25, 40, and 65% deflections and hence the sag factor can be determined. In addition, by measuring the load for specified indentations of the foam on loading (as with Procedure B), followed by measuring the indentations on unloading, a measure of the foam hysteresis can be determined. Hysteresis is a measurement of the energy absorbed by a foam when subjected to a deformation. 

---