Touch screens are everywhere around us. How do they work?

There are many technologies. The two main ones are:

• Resistive technology: The screen (glass plate) is covered with one (and even two) transparent conductive layers based on indium tin oxide (ITO). When the user presses the screen, it momentarily deforms both layers and creates a contact. A voltage is applied to the ends of the screen and a controller calculates a position from the voltage measured at the point of contact.
• Capacitive technology: When the user touches the screen with their finger, it creates a local (capacitive) discharge. Four sensors located at the corners of the screen detect this deficit of electrical charges. A controller calculates the point of contact.

Every technology has its advantages and disadvantages. For example, capacitive technology does not allow for the use of gloves or any stylus. It is also not suitable for large formats. Resistive technology is less expensive but wears out over time and the multilayers degrade image quality.

In both cases a rare metal, indium, is used. It is classified as a critical raw material. For this reason, we need to control our consumption of digital devices.