In mechanically controlled variable capacitors, the distance between the plates, or the amount of plate surface area which overlaps, can be changed. The most common form arranges a group of semicircular m. Very often, multiple stator/rotor sections are arranged behind one another on the same axis, allowing for several tuned circuits to be adjusted using the same control, e.g. a preselector, an input filter and the corresponding os. The variable capacitor with air dielectric was invented by the engineer. He received a patent for the invention on 13 December 1893. The thickness of the depletion layer of a reverse-biased semiconductor varies with the DC voltage applied across the diode. Any diode exhibits this effect (including p/n junctions in transistors), but devices specifical.