Electromagnetic radiation with frequencies band in between 0.3Hz to 3THz (wavelength rage between 1mm to 100um) is known as Terahertz radiation. The frequencies of Terahertz are higher than microwave and lower than infrared.

The spin frequencies and vibration frequencies of many organic large molecule is at the terahertz that can give opportunities and information to scientists and engineers to investigate the characteristics of the materials.

All kinds of materials will emit and receive the terahertz radiation. A portion of the terahertz received by the materials will transmit and pass through the materials. Different Materials have different transmission ratiao.

With this characteristic, one of the Terahertz applications is security inspection.