Any AC circuit emits electromagnetic energy into the surrounding space, creating a space with electric and magnetic forces, known as an electromagnetic field. Electromagnetic fields propagate through space from far and near, forming electromagnetic waves. The process of emitting electromagnetic waves outward is called electromagnetic radiation. Electromagnetic waves can be divided into ionizing radiation (cosmic rays, X-rays, Y-rays) and non-ionizing radiation (ultraviolet, visible light, infrared and radio frequency radiation). With the popularization of electrical equipment and electrical equipment power continues to increase, electromagnetic radiation pollution is becoming more and more serious. Electromagnetic radiation has the characteristics of "invisible, unheard, untouchable", has become the fourth major public health hazard.