Terahertz technology may be in its relative infancy but fortunately the scientist leading the National Physical Laboratory’s pioneering work, Dr Mira Naftaly boasts more than two decades experience in this nascent field.
It’s well under a year since the National Physical Laboratory in Teddington was designated by the Engineering and Physical Science Research Council (EPSRC) as its approved facility for testing applications and technology harnessing Terahertz – THz or T-wave – frequency.
Much has been said about the potential of this region of the electromagnetic spectrum.
As the NPL describes it, THz could provide pioneering approaches to a host of applications including electronic components, next-generation 6G mobile networks, atmospheric and environmental monitoring, plus non-destructive material testing in sectors including pharmaceuticals, electronics and petrochemicals.
Leading this work is NPL Senior Research Scientist, the spectroscopist and laser physicist Dr Mira Naftaly, who took time out to shed light on the work being done by her team.
How would you define THz to the layperson, in terms of its uses within the electromagnetic frequency spectrum?
The THz band of frequencies lies between microwaves and infrared light. As such, it has some of the properties and behaviour of both radio waves and visible light.
Many materials that are opaque to visible light are to some degree transparent to THz, which makes it possible to use THz to image internal structures of opaque objects.
In such cases, THz imaging provides much higher spatial resolution than microwaves because of its shorter wavelength. As a consequence, THz is being increasingly employed for non-destructive testing.
Many substances, especially biological molecules (e.g. amino acids, proteins, sugars) and pharmaceuticals have characteristic spectral signatures at THz frequencies and therefore can be identified and studied using THz spectroscopy.
THz also has important advantages for wireless communications, due to its higher frequency and larger available bandwidth than microwaves. THz wireless links are envisaged to play a central role in future communications and 6G+, capable of providing wireless speeds of terabits per second and secure links.
What do you regard as the key developments in the understanding and application of terahertz measurement over the last two decades?
With regard to applications, the key development has been the availability of robust, compact, reliable, fibre-coupled THz instruments that do not require expert operators and can be installed in a variety of environments, including industrial production lines.
With regard to understanding, first and foremost, better understanding of THz sources and detectors, and engineering aspects of THz instruments. Also, better understanding of interactions of THz radiation with different types of materials, including metamaterials, semiconductors, quantum materials and biological systems.
Taking the example of petrochemicals, could you explain how THz technologies can impact positively the testing processes – whether in terms of accuracy, speed or sustainability?
THz sensing as applied to petrochemicals has been used to detect composition, moisture content down to 0.01%, a variety of contaminants, oxidation products, octane number of petrol and diesel, ethanol content in fuels and viscosity of lubricants.
Accuracy and speed are comparable with other optical techniques. However, there are many cases where other optical techniques are unsuitable or do not provide the desired information. We have a current commercial project using THz to test aviation fuels.
Many substances, especially biological molecules and pharmaceuticals have characteristic spectral signatures at THz frequencies and therefore can be identified and studied using THz spectroscopy
Environmental monitoring and climate observation is also cited as an area in which THz measurement can bring value. What are the gains provided over and above other methods that might be employed?
THz measurements can be used to detect some environmentally significant gases and pollutants. Depending on the target gas and the measurement conditions, in some cases THz may be more suitable than other techniques, or provide additional information, especially in earth observation.
NPL emphasises the contribution of feedback from collaborators, industry and academia as well as its own ‘foresighting’ – what challenges do these stakeholders identify in harnessing THz tech?
There are different implementation challenges for THz, depending on its application.
For non-destructive testing: 1) equipment is bespoke, and must be specially configured for each use case scenario; 2) equipment is expensive; 3) there is a lack of general implementation and validation processes, so each user has to develop these for their own use case.
For wireless comms: 1) the current state of the art is still quite far from integrated on-chip devices, so the equipment is bulky and requires multiple devices; 2) equipment is very expensive compared with microwave comms; 3) operation is line-of-sight only.
Which are the key collaborations and services in which the EPSRC terahertz facility is currently involved?
So far, eight proposals have already been submitted and and are awaiting EPSRC review and approval. Some examples of submitted projects include semiconductor devices for THz wireless communications, THz monitoring of plant quality, using quantum materials to generate THz, and quantum behaviour of living cells at THz frequencies. We are working with the UK academic community and industry to support innovative research projects and the development of applications.
Drawing on your own lengthy experience working in terahertz measurement, how do you see it developing in terms of research and industrial applications over the next 20 years?
Twenty years is far too long to predict. In the next five years: rapid growth of THz non-destructive testing in the industry; rapid development of THz wireless communications, approaching mass roll-out; some on-chip THz devices becoming available as useful commercial products. THz is on the threshold of breakthrough growth. It is a very exciting time to be in this field and I am looking forward to engaging with the UK academic and industrial communities as a national state of the art facility.
