The Trimmer capacitor is the parts that its capacitance can be changed freely. The Trimmer capacitor is used in some applications that generally have no need to adjust again after the initial adjustment. The trimmer capacitor has an adjustable structure adding to general ceramic capacitor to adjust capacitance.
There are basically three different principles shown in the below that can be used to adjust capacitance.
Generally most of the commercial products are using the first principle.
Principle 1: change the overlap electrode area between parallel facing electrodes.
Principle 2: change the distance between parallel facing electrodes.
Principle 3: change the dieelectric constant of ceramics.
The actual trimmer capacitor product has a dielectric ceramic between two parallel facing electrodes. One side of electrode is movable (can be rotated) so that a capacitance can be changed by adjusting the overlap electrode area between the movable and the fixed electrode. According to this process, a capacitance value can be changed linearly depending on the rotation angle of a movable electrode. Murata trimmer capacitor is also using above the Principle 1 and has more than 50% market share in the world.