Terahertz cameras can visualize differences in plastic types.
© Fraunhofer FHR
Terahertz cameras can visualize differences in plastic types.

General information on terahertz technology

Terahertz waves: Broad range of applications in safety technology

The terahertz range is a part of the electromagnetic spectrum between microwaves and infrared with a frequency of one billion oscillations per second. The so-called terahertz gap was an issue for many years as there were no practical radiation sources for this part of the spectrum until well into the 1990s. Due to its special properties, terahertz radiation has become an important technology of the future: it can be used to detect concealed explosives or drugs and it can identify which substances are flowing through a plastic pipe. It is capable of monitoring the thickness of a layer in a nondestructive manner and visualizing material flaws in ceramics or plastics. Due to its low energy characteristics, terahertz radiation is non-hazardous for humans and animals. There is practically no limit to the areas in which it can be used.

Proximal and remote detection of hazardous substances

In contrast to UV radiation or X-rays, terahertz waves do not change the chemical structure of the substances that are being investigated. Hence, they are not harmful for humans and are therefore suitable for people screening. Terahertz spectroscopy can be used to specifically detect a large number of hazardous substances through numerous commonly used packaging materials or clothing. Detection is possible at distances of up to a few meters without sampling. Thanks to the short wavelengths, the spatial resolution is far superior to that which can be achieved in the microwave range. The material of a suspicious object can be analyzed by the spectrum of the radiation.

Active or passive methods

Terahertz scanners function on the basis of active or passive methods. When using a passive method, scanning is restricted to the natural terahertz radiation that is emitted by the human body. The active method on the other hand uses an additional artificial radiation source via terahertz radiation. The system uses the variation of the wavelength from the backscatter to reconstruct an image.

Numerous application possibilities

Scientists have developed practical and easy-to-handle terahertz scanners and detectors. In addition to applications in safety technology, terahertz radiation can also be used in the areas of laboratory analytics, process measurement technology and quality control.