In recent years many studies have been done in terahertz (THz) limits of how to a science and technology and its advantages have been studied and how to a developed. One of the most interesting applications is imaging. Terahertz waves fall in between infrared waves and microwaves, and have shared with both frequency bands. These waves are non-ionizing and can penetrate in wide range of non-conducting materials such as cloth, cardboard, wood, plastic and ceramic. The interesting properties of THz waves have caused that these waves are used in many fields such as medical and security. For example, one of the equipment applications in this frequency domain is detection of objects on a person's body without physically removing clothes or making physical contact. This system can detect unauthorized objects such as weapons, drugs, explosives on a person, remotely. Interestingly, many materials have unique spectral "fingerprints" in the terahertz range. Some terahertz frequencies can have a penetration depth of several millimeters in some body tissues and reflect. Unlike X-rays, terahertz waves are non-ionizing and in general, their low photon energy , does not damage to body tissue and DNA. Other medical applications of these waves are safe and painless imaging of epithelial cancer. Also, by using the THz waves more accurate imaging of the teeth can be THz waves more accurate imaging of the teeth can be obtained compared to X-rays. obtained compared to X-rays.