Operating Principle of 3M Surface Capacitive Touch Screen

To achieve multi-touch on a capacitive screen, it relies on adding mutual capacitance electrodes. Simply put, it divides the screen into blocks and sets up a set of mutual capacitance modules in each area to work independently, so the capacitive screen can detect touch conditions in each area independently and realize multi-touch easily after processing.

Capacitive technology touch panel CTP (Capacity Touch Panel) uses human body's current induction to work. The capacitive screen is a four-layer composite glass screen. The inner surface and interlayer of the glass screen are each coated with a layer of ITO (nano indium tin metal oxide). The outermost layer is a silica glass protective layer with only 0.0015mm thick. The interlayer ITO coating serves as a working surface, four electrodes are drawn out from the four corners, and the inner ITO layer is a screen layer to ensure the working environment.

When the user touches the capacitive screen, due to the electric field of the human body, the user's finger and the working surface form a coupling capacitor. Because the working surface is connected to a high-frequency signal, the finger absorbs a very small current. This current flows from the four corners of the screen respectively. It flows out from the electrodes on the finger, and theoretically the current flowing through the four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position through precise calculation of the ratio of the four currents. It can reach 99% accuracy and has a response speed of less than 3ms.