Microwave basic knowledge small classroom

What is microwave?

Microwave refers to the electromagnetic wave whose wavelength is between infrared and radio waves. The frequency range is about 300MHz to 300GHz, and the corresponding wavelength is between 1 meter and 1mm.

Two, the characteristics of microwave

As a kind of electromagnetic wave with wave-particle duality, the basic nature of microwave usually presents three characteristics: penetration, reflection and absorption. In the case of glass, plastic and porcelain, microwaves almost pass through without being absorbed. For water and food will absorb microwave and make their own heat. For metals, it reflects microwaves.

Therefore, the microwave sensor induction surface can not be shielded by metal objects because of the need to emit microwave.

Three, the principle of microwave detection - Doppler effect

Any wave reflection characteristics, meets the obstacle when waves of a certain frequency, there will be a part of the wave is reflected back, if the obstacle is stationary, the wavelength of reflected wave is constant, if the obstacle is to the waves, the reflection wavelength is shorter than the wavelength of waves, if the obstacle is to stay away from the waves in the direction of the movement, The wavelength of the reflected wave is longer than the wavelength of the source wave, and a change in wavelength means a change in frequency. Microwave sensors know when a moving object is approaching or moving away from them by the changes in the reflected waves.

In addition to body movement, microwave detection technology can also detect your breathing and heartbeat by detecting the surface of your breathing body and the expansion and contraction of your heart.

Frequency band of microwave detection

The frequency bands commonly used for microwave detection are as follows:

C band: 5.8ghz +/75MHz

X band: 10.525GHz+/-25 MHZ

K band: 24.125GHz+/-200MHz

The three bands belong to the ISM band and are available to industrial, scientific, and medical organizations. They are Free licenses and do not require authorization. The higher the frequency, the better the sensitivity, but the higher the technology, material and price requirements. Considering cost and detection capability, C-band is usually used for intelligent induction control of lamps in the lighting industry, X-band is usually used for industrial, security and automatic door control, and K-band is usually used for speed measurement, ranging, obstacle avoidance and other applications.

Fifth, the main difference between microwave detection and infrared PIR

Compared with infrared detection, microwave detection has overwhelming advantages in environmental adaptability, speed detection, accuracy and detection range.

Main applications of microwave detection

Smart lighting, smart Internet of things, smart home and smart pension and other fields.