It is used in many lamps and wall switches that have a metal exterior as well as on public computer terminals.
The switch keeps charging and discharging its metal exterior to detect changes in capacitance.
When a user’s finger or another object approaches these electrodes, it disrupts the electric field between them, resulting in a change in capacitance value.
The advantages of mutual capacitance technology include tight electric field coupling, allowing for more flexible design.
However, mutual capacitance also has its limitations, such as its measurement noise being generally greater than self-capacitance.
A resistance switch needs two electrodes to be physically in contact with something electrically conductive (for example a finger) to operate.
Current commercial solutions construct the piezo in such a way that touching it with approximately 1.5 N is enough, even for stiff materials like stainless steel.