Abstract
This paper describes the construction, principle, and features of a precise variable capacitor capable of obtaining a very small capacitance change and its applications.
There are two types of such a precise variable capacitor. One is the cylindrical type, and the other is the plate type.
For example, in our experiments, a variation of about 1×10-4pF was obtained by a displacement of 100μm of the micrometer head at the cylindrical type. And a variation of 3.5×10-4 pF was obtained by a displacement of 100μm of the movable metal electrode at the plate type.
This precise variable capacitor is very simple and compact in its construction and this can also be placed directly in the measuring circuit.
To show its application, a measurement of dielectric constant and thickness (less than 1000Å) of Langmuir films of stearic acid is presented.
As for another application, we measured Q factor of very low loss dielectrics at 2.5MHz by capacitance substitution method using this precise variable capacitor as standard. Both experiments were performed yielding good results.
