Oxford University researchers have developed a sensor made of sapphire fiber that can tolerate extreme temperatures, with the potential to enable significant improvements in efficiency and emission reduction in aerospace and power generation.
The work, published in the journal Optics Expressuses a sapphire optical fiber – a thread of industrially grown sapphire less than half a millimeter thick – which can withstand temperatures over 2000°C.
When light is injected onto one end of the sapphire fiber, some is reflected back from a point along with the fiber, modified to be sensitive to temperature (known as a Bragg grating). The wavelength (color) of this reflected light measures the temperature at that point.
Sapphire fibre. Credit: Julian Fells, University of Oxford
The research resolves a 20-year-old problem with existing sensors that, while the sapphire fiber seems very thin, it is enormous compared to the wavelength of light. This means that the light can take many different paths along with the sapphire fiber, which results in many different wavelengths being reflected at once.
The researchers overcame this problem by writing a channel along the length of the thread, such that the light is contained within a tiny cross-section, one-hundredth of a millimeter in diameter. With this approach, they were able to make a sensor reflecting predominantly a single wavelength of light.
The initial demonstration was on a short length of sapphire fiber 1 cm long. Still, the researchers predict that sizes of up to several meters will be possible, with a number of separate sensors along this length. For example, this would enable temperature measurements to be made throughout a jet engine.
Using this data to adapt engine conditions in-flight can significantly reduce nitrogen oxide emissions and improve overall efficiency, reducing the environmental impact. The sapphire’s resistance to radiation also gives applications in the space and fusion power industries.
Research team member Dr. Mohan Wang, Department of Engineering ScienceUniversity of Oxford, said:
‘The sensors are fabricated using a high-power laser with extremely short pulses, and a significant hurdle was preventing the sapphire from cracking during this process.’
The work is part of a £1.2M EPSRC Fellowship Grant held by Dr. Julian Fells at the University of Oxford’s Department of Engineering Science and was carried out in partnership with Rolls-Royce, the UK Atomic Energy Authority (Remote Applications in Challenging Environments – RACE), Cranfield University, Halliburton and MDA Space and Robotics.
Mark Jefferies, Chief of University Research Liaison at Rolls-Royce plc, said:
‘This is exciting news and yet another important scientific achievement resulting from our long-standing partnership with Oxford University. This fundamental research could enable more efficient and accurate multi-point temperature measurement in harsh environments, improving control, efficiency, and safety. We look forward to working with the University of Oxford to explore its potential.’
Rob Skilton, Head of Research at RACE, UK Atomic Energy Authority, said:
‘These sapphire optical fibers will have many different potential applications within the extreme environments of a fusion energy powerplant. This technology can significantly increase the capabilities of the future sensor and robotic maintenance systems in this sector, helping UKAEA in its mission to deliver safe, sustainable, low carbon fusion power to the grid.’
Dr. Fells, who is leading the research, said:
‘We are very grateful to the UK Engineering and Physical Sciences Research Council (EPSRC) for supporting this work and the reviewers who saw the potential for the challenging work we proposed. We are now working with our partners to further develop the technology to the point where it can be integrated into the suitable infrastructure.’
Source: University of Oxford
