What are terahertz waves
Situated between millimeter waves and far-infrared rays, terahertz waves are a type of electromagnetic radiation with frequencies ranging roughly from 100GHz and 10THz and wavelengths spanning 0.03mm to 3mm. They can easily pass through materials, exhibit high linearity, and unlike X-rays are considered safe for biological tissue. As a result, practical application is advancing in various fields, such as non-destructive testing, component analysis, medical diagnostics, and wireless communication.
Methods for generating terahertz waves include frequency multiplication that multiplies a frequency by an integer, photomixing, where light of different frequencies are combined, and resonant tunneling diodes suitable for miniaturization.
Future challenges range from improving the efficiency and output of oscillators to achieving miniaturization and reducing overall system costs. Addressing these issues is expected to lead to further practical applications.
Terahertz Wave Frequency Band
Terahertz waves are a type of electromagnetic radiation that occupies the region between radio waves and light on the electromagnetic spectrum. Their frequency ranges from approx. 100GHz (0.1THz) to 10THz, corresponding to wavelengths between 0.3mm and 3mm.
*Electromagnetic waves: Waves that propagate through synchronized oscillations of electric and magnetic fields.
*Frequency: Represents the number of times an electromagnetic wave oscillates per second; the higher the frequency the greater the energy of the wave. The unit is Hertz.
*Wavelength: The distance between the peaks of an electromagnetic wave. The longer the wavelength, the lower the frequency and smaller the wave’s energy. Expressed in units of meters (m).
Characteristics of Terahertz Waves
Now let’s take a closer look at the characteristics and applications of terahertz waves.
1. Permeability: Able to pass through dielectric materials
Terahertz waves can easily penetrate substances like paper, plastic, ceramics, wood, and textiles, allowing them to ‘see’ inside. This property being explored for non-destructive material analysis. For example, it can be used to detect foreign objects in food or identify hidden wiring and obstacles within building walls.
*Dielectric: A material similar to an insulator, capable of storing electric charge while exhibiting poor conductivity.
2. Linearity: Possesses higher linearity than radio waves
Like laser beams, terahertz waves feature a high degree of linearity and can be optically processed through reflection with mirrors or focused using lenses. This property makes them ideal for sensing and imaging technologies to visualize objects. For instance, research is underway towards practical applications such as defect detection in materials and cancer diagnosis in the medical field.
3. Absorptivity: Strong absorption by water
Terahertz waves are highly absorbed by water. This characteristic can be used for detecting the moisture content in skin or fruit, as well as for analyzing the composition of substances. What’s more, detecting trace amounts of atmospheric moisture can improve the accuracy of weather forecasts, such as predicting localized rainfall.
4. Fingerprint spectrum: Ability to distinguish substances
Different substances absorb terahertz waves at varying frequencies, creating a unique pattern in terahertz spectroscopy known as the fingerprint spectrum. Biomolecules, proteins, and polymers have distinct absorption characteristics. By measuring these absorption rates, specific substances can be identified. Potential applications include detecting illegal drugs, authenticating artwork, and analyzing the composition of unknown materials.
5. High-speed communication: Enables fast transmission of large amounts of data
Using terahertz band signals for communication allows for significantly faster data transmission compared to conventional wireless communication systems. At the same time, properties such as moisture absorption (rain, humidity) and high linearity that makes signals susceptible to obstacles like buildings and people can pose challenges. Despite these technical hurdles, research is ongoing towards the practical implementation of wireless terahertz networks as a next-generation communication standard that promises faster, high-capacity data transmission.
6. Safety: Does not damage materials or the human body
Generally, high-energy electromagnetic waves such as ultraviolet and X-rays can potentially damage cells, raising concerns about the harmful effects on the human body with excessive exposure. In contrast, terahertz waves feature lower energy than visible light that poses no risk to human health. As such they are expected to be used in security screening at airport gates and in medical diagnostics.
Towards practical application
While terahertz waves possess excellent characteristics and show promise in areas where radio waves and light have proven difficult to use, several challenges remain before practical implementation can be achieved. Research and development of new materials and technologies is currently underway to address these issues and further expand the range of applications. As we move towards a more convenient and safer future, the emergence of new devices and systems utilizing terahertz waves is highly anticipated.
