Q. What is the mechanism that opens an automatic door without touching it?

A. Although there are many types of automatic doors, those that use infrared ray sensors are common. The human eyes can see various colors of light from blue to red. Each light has a different wave length. Light with a longer wave length than red is called an infrared ray and this cannot be seen by the human eye. Every warm substance, including human beings, emits infrared rays. In the case of automatic doors, when a person approaches the door, an infrared ray sensor detects the rays the person emits and transmits an electrical signal to open the door.

Infrared rays are used for other purposes as well. For example, infrared rays can measure the temperature of something in a remote location or detect a site with unusually high temperatures. A semiconductor ceramic is an important part of an infrared ray sensor because its electrical resistance changes with a change in temperature.