Homemade air variable capacitor

What is an air variable capacitor?

In some applications, a capacitor is required to provide a variable capacitance value. Variable capacitors are used in such cases. They allow the capacitance value to be changed repeatedly mechanically and electronically. Air variable capacitors use air as a dielectric and are composed of two sets of metal sheets, one of which is fixed and the other can be rotated. The metal plates are arranged in a network. The overlap between the two sets of metal plates can be adjusted by rotating the moving plate, and the capacitance changes accordingly. But the air gap remains the same.

Application of air variable capacitor

Due to its simple design and powerful functions, air variable capacitors are widely used. Its most important use is in the radiofrequency field, for example, to tune a radio by setting a resonance frequency. They are also important components of radiofrequency matching networks, magnetic resonance imaging (MRI) equipment, and precision capacitance meters. In addition, they are used to test the performance of air and other gases.

Homemade air variable capacitor

Making an air variable capacitor is very simple. To make an air variable capacitor at home, follow these steps:

Design layout

The first step before performing the hardware steps is to design the structural layout and precise measurements. The layout can be designed through Cadvance or any other open-source software.

Marking metal sheet

Put the aluminum sheet on the table and draw a 5cmx5cm box. Mark the center of the first plate of aluminum and use it as a reference, marking a hole every 5cm. A compass is fixedly placed at the marked hole, and a circle is drawn on each square aluminum sheet with an equal diameter. Then, draw a vertical line with the center point of the arc as the tangent point on the arc of each circle to the end of the aluminum sheet. There should be one more moving film than the fixed film.

Cut aluminum

After drawing, cut the aluminum sheet. Take an aluminum sheet and draw a line connecting the center of the circle to the corner on the left. Mark the midpoint of the line between the arc and the left corner. Mark another hole at the corresponding position in the right corner. For reference, mark the same holes on all aluminum sheets.

Separate moving film from fixed-film

Draw a smaller inner circle from the center of each circle and cut off the upper half of the inner circle. Make sure there are no arches, twists, and curls on the aluminum sheet.

Rear plate drilling

Take a moving plate and a fixed plate, and put them in a fully meshed position on the endplate. Mark the positions of the holes on the endplate according to the positions of the holes on the two aluminum sheets. Place one of the two endplates over the other and drill holes in the marked holes.

Assembling aluminum sheet

The next step is the assembly of moving and fixed plates. When assembling the moving blade, remove the bolt head. Put the nut on one end of the bolt and screw it to 5 cm from the end of the bolt. Then, insert the first spacer, two washers, the second spacer, two washers, and so on, until all the spacers are inserted. Finally, insert the stop nut. Repeat the same process to mount the stator to the backplane.

Capacitor assembly

The capacitor's case consists of two endplates or covers some insulating material. Take out the moving film group and insert the rotating shaft into the rear plate (connected to the fixed film group). Put the spacers on the shafts on both sides of the endplate. Turn the shaft to the full mesh position and tighten the other endplates. Use stop nuts and washers for fixing.

Related article about variable capacitor:  https://www.utmel.com/blog/categories/capacitors/what-is-a-variable-capacitor