Among them, electromagnetic waves below 10GHz can penetrate human body, be absorbed by tissues and be converted into heat. You can refer to the domestic microwave oven (working at 2.45GHz) to heat meat, and the relative SAR is measured by W/kg. According to WHO, 4W/ kg is the lowest dose to cause thermal damage to human body.
Electromagnetic waves with frequencies above 10GHz are difficult to penetrate tissues, and the absolute part will be absorbed by the skin, so W/m2 is used to measure SAR. WHO believes that 1kW/m2 is the lowest dose that can cause harm to human body, which may lead to cataract or skin burn.
According to WHO, there is no scientific evidence that wave paths in electromagnetic frequencies will shorten human life, or cause or promote cancer.
Extended data:
The appearance of radar was due to the war between Britain and Germany during World War I, and Britain urgently needed a radar (technology) that could detect metal objects in the air and help search for German aircraft in anti-air strikes. During World War II, radar technology with the functions of ground-to-air, air-to-ground (search) bombing, air-to-air (interception) fire control and friend or foe identification appeared.
After the war, radar developed new radar systems, such as monopulse angle tracking, pulse Doppler signal processing, high-resolution synthetic aperture and pulse compression, friend or foe identification combined system, computer automatic fire control system, terrain avoidance and terrain following, passive or active phased array, frequency agility and multi-target detection and tracking.