Constructing a capacitive sensor using springs 3

If the thickness of the covering layer is 2 millimeters or thicker, the sensitivity of the spring sensor will be higher. Figures 4 to 6 present the physical dimensions of the spring that are more suitable for achieving optimal capacitance characteristics.

Suggestions for selecting the physical dimensions of springs

The height of the spring should be 5 millimeters or more. Beyond this range, sensitivity will no longer increase with the height of the spring, but it will not lead to a decrease in performance; Therefore, the distance between the circuit board and the cover layer can be extended accordingly as needed. If the height of the spring is less than 5 millimeters, its elasticity, sensitivity, and side sensitivity will be affected.  diode

For a 4mm thick cover layer, in order to achieve optimal spring sensitivity, the diameter of the spring must not be less than 10mm (as shown in Figure 5). In specific situations, if the sensitivity of the spring is sufficient relative to the selected cover layer, a spring with a smaller diameter can be selected.

As shown in Figure 6, when the range of FTC variation is only between a few hundredths of a picofarad, the thickness of the spring wire will not have a significant impact on the capacitance characteristics. Therefore, the thickness of the spring wire should be determined by the required strength of the spring. Overall, the thickness of the spring wire should be between 0.3 and 1.5 millimeters.

According to the intermediate results of the simulation, the self capacitance of the spring sensor is generally larger than that of a solid-state conductive sensor with the same diameter. When using the CSD method, compensation can be achieved by protecting the electrode.

The use of springs of different shapes

In practical applications, springs of different shapes can be used. Each shape has its advantages and disadvantages. Common springs include circular springs, variable diameter circular springs, and rectangular springs.  diode