capacitor basics

In a recent webinar, a number of questions came up concerning capacitive touch. I thought I would cover some of the questions and provide some insight into the physics of capacitive touch along the way in some upcoming posts. Likewise, if you have questions or topics that you’d like us to address, drop us a note.

Let’s start by reviewing a few capacitor basics. A capacitor is basically any two conductors separated by an insulator; the area of the conductors, the spacing between the conductors, and the characteristics of the insulating material, all combine to determine the amount of capacitance created. So, any two pieces of metal, which are not connected to one another, exhibit capacitance. The two pieces of metal can be two plates in a tuning capacitor, two cars sitting in the parking lot, or two bits of iron in adjacent red blood cells.

hat this means for capacitive touch is that every surface of an average human being is capacitively couple every other surface. So, if I touch a capacitive switch sensor, I am actually capacitively coupling the touch sensor, through my body, to ground beneath my feet. Or, in the case of a hand held device, I am capacitively coupling the sensor, to the ground of the circuit through my other hand that is holding the device.