Microwave measurement

A device that uses microwaves to measure impurities in liquids could be used to detect contaminants in blood, moisture in aircraft fuel and let drivers know when brake fluid needs changing.

Oxford University’s technology transfer company, Isis Innovation, is planning to commercialise its active microwave cavity sensors to market. Isis claims that unlike similar devices, its solution can test fluid in situ without having to remove a sample, and offers a high Q (quality) factor.

The Q factor of a resonator is a function of the energy stored per cycle of oscillation compared with the energy dissipated per cycle of oscillation. A high Q factor means that the loss in the active cavity resonators is significantly smaller, giving a high signal-to-noise ratio — a measure of sensitivity.

The sensor, or Rhumbatron, sprang from research carried out by Oxford University’s Prof John Gregg, an expert on RF and spintronic devices. There are two main types: a fixed cavity device, and a tuneable version. Cavity length can be changed in the latter by screwing the top down — a mechanical process that could be automated.

Dr Rakesh Roshan, a project manager in Isis’s technology transfer group, said: ‘As the liquid flows in one end and out the other, we input RF waves and examine the changes in the frequency whenever a liquid with a contaminant passes through in comparison with a pure liquid.’

The active nature allows real-time dynamic measurement, meaning it could, for example, be installed in a car and continually monitor the health of the brake fluid then automatically notify the driver when it needs changing. As it can detect liquid as well as solid contaminants, in avionics it could accurately measure the moisture content of fuel, giving advance warning of the threat of it freezing before it reaches dangerous levels.

Most work to date has been on non-biological samples, but a researcher is currently working with a prototype device to see the effect of contaminants in a blood sample. It could also be adapted to detect cancerous tissue, and other life-sciences applications.

Isis is seeking to commercialise the device and has signed development contracts with four companies. It is also working with an electronic design company, which will make a more commercial prototype.

‘What we have in the lab at the moment is a very “Heath Robinson” kind of thing,’ said Roshan. ‘They are trying to tidy it up and make it look more commercially attractive for their own client, but we hope the prototype will lead to a licensing deal with that client.’

The prototyping process will take another six months. ‘The time from there to the market depends on the appetite of any aerospace or automobile company for this kind of sensor, although the fact is their business is not so healthy at the moment,’ said Roshan.

Berenice Baker