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Terahertz radiation falls between infrared and microwaves on the electromagnetic spectrum but is less widely used, due to a variety of key technological and practical challenges.
These waves can penetrate materials such as clothing or packaging but unlike X-rays, for example, THz radiation is non-ionizing, making it safe for living tissue. This means THz scanners could safely be used in airports to pick up the unique spectral signatures of several types of explosives, many compounds used in pharmaceutical ingredients and illegal narcotics.
An EU-funded initiative has now laid the foundations for transformative applications in biology, medicine, material science, quality inspection and security using this radiation. By testing novel solutions to efficiently harness the unique properties of THz waves, the THEIA project has driven important research in the field.
‘The results can be used to develop novel types of scanners or imaging systems,’ says Marco Peccianti, THEIA’s lead researcher at the University of Sussex in the UK. ‘Many complex materials possess unique fingerprints in the THz spectrum, including compounds such as polymers, proteins, amino acids, drugs or explosives. For instance, terahertz radiation will be of paramount importance in next-generation airport security scanners. Scanners based on THz radiation would increase our ability to recognise drugs, explosives and other illicit substances, with notable societal and economic benefits.’
Obstacles to be overcome
Other applications include analysing the composition of a wide range of complex materials, creating imaging systems to diagnose defects in manufacturing and peering inside building walls to detect structural problems. In medicine and medical research, imaging systems using THz spectroscopy, which can detect differences in water content and density of tissue, would provide an alternative means of looking inside the human body, particularly into some types of soft tissue to detect diseases such as cancer.
To bring these applications to fruition, several obstacles to efficiently exploit the properties of THz radiation need to be overcome.
In the THEIA project, the team devised a novel technique for channelling THz waves using waveguides, a structure that controls the direction and dimension of the waves. Instead of generating a THz wave and coupling it to a waveguide using a lens or similar optical components, the researchers developed a way to generate the wave directly inside the waveguide.
Improved speed and efficiency
‘The investigation has been performed by simulating the waveguide structure using high-performance computing solutions, and matching the prediction to experimental observations,’ says Peccianti. ‘Practically, we compared different technological solutions, from embedding wave generation in a high-performance waveguide to fabricating the waveguides with terahertz-emitting materials. The key result is the creation of an active terahertz waveguide system.’
The THEIA solution not only delivers a THz signal where needed, but also serves to remove many of the large and bulky components of existing THz systems. ‘This could potentially enable THz imaging to be used in ways that would previously have been impossible,’ Peccianti says.
Researchers are now focusing on improving the efficiency, speed and resolution of their THz imaging techniques in TIMING, a follow-up EU-funded project. The research will aim to develop a next generation of THz imaging devices as unique diagnostic tools to unambiguously discriminate molecular compounds with improved speed and resolution.
The THEIA project received funding from the EU’s Marie Skłodowska-Curie Actions programme.