Terahertz waves, also called submillimeter waves, T-Rays, T-Waves are electromagnetic waves in the frequency band between 300 GHz and 10 THz (1THz=10^12 Hz). Wavelengths of radiation in the terahertz band range from 30 µm to 1 mm. That’s why they are also known as submillimeter waves.
Terahertz radiation lies between microwaves and infrared light regions of the spectrum and it shares some properties with each of these. Like infrared light, terahertz waves can travel in a direct path from the source to the receiver, and manipulated with optical elements. On the other side, like microwave radiation, they are non-ionizing (they don’t carry enough photon energy to ionize (remove an electron) atoms or molecules) and can penetrate a wide variety of non-conducting materials. Among them there are clothes, skin, paper, cardboard, wood, plastics, ceramics etc. On the other hand, Terahertz waves cannot penetrate metal, water and liquids.
These properties are making the T-Waves attractive candidates for the brand-new applications in a various fields (imaging, non-destructive testing, healthcare, security and defense…). For example, due to a non-ionizing property, Terahertz waves can penetrate some distance inside the body tissue, and as they are inoffensive for living organisms, they can be a good replacement of the X-Ray imaging.
Still, we don’t see the Terahertz waves; they are naturally occurring and surrounding us in everyday life. Yet this region of spectrum remains the least explored mainly due to the technical difficulties. But recently, thanks to advances in a technology, new systems were developed to both generate and measure/detect those waves. These decisive advances are promising for a number of applications.
Some interesting physical properties of Terahertz waves:
- High depth of penetration (like radio waves)
They can be transmitted through various types of materials including plastic, paper, ceramic, textile and wood. This allows non-destructive analysis of hidden objects or substances, and detects their defects, inclusions, contaminations.
- Directivity (like light waves)
They can be manipulated as laser/light waves and so can be diffracted, refracted and reflected. Wavelengths are from 30µm to 1 mm, so it allows imaging with resolution, near of our eyes vision resolution of the visible light.
- Identification of chemical substances (molecular fingerprint)
When exposed to electromagnetic radiation, molecules vibrate (rotate) with characteristic frequencies. These frequencies are unique and specific to each molecule (molecular fingerprint). Measuring these frequencies (spectrum) allows the identification of the molecules and chemical substances.
- Non-ionizing
This property allows using Terahertz waves by and for humans. Non destructing analysis with T-waves will be much more cost effective and safe than with X-Rays.
- Propagation in the air
Terahertz waves can propagate in the air, without showing significant attenuation. This property gives a possibility of non-contact measurements (more advantageous than ultrasound) and control (for ex. products on a production line).
- Thermal radiation of human body
Humans (and other animals) naturally emit terahertz radiation. This allows the use of passive imaging techniques, where the detection device is not emitting the waves in observed region. This can be particularly advantageous in the military field, since the detection device will be undetectable, in contrast to conventional radars.
Terahertz waves are the future !