Wireless temperature sensors can be interrogated remotely

The sensors themselves are essentially just modified crystals that split light to give temperature readings in the order of millikelvins over a broad range from around -120°C to +680°C.

‘The point about this is that the crystals can be anywhere in the area where we’re measuring the temperature,’ said project collaborator Prof Mike Glazer of Oxford University.

‘We can pump the light in from anywhere and we can interrogate from anywhere, with no wires and no cable, and we can work at huge distances away if we want.’

The phenomenon of birefringence, where a non-uniform ‘anisotropic’ crystal splits light into two separate rays, is complex but well characterised.

Indeed, previous research has already shown that the size of the effect will increase or decrease in proportion to the temperature of the crystal. Therefore, in theory, you could calibrate such crystals to be highly accurate temperature gauges.

However, the use of birefringence in this way has significant problems in practice. This temperature-measuring ability of highly birefringent crystals is badly compromised by changes in the thickness and orientation of the crystal. This adds expense to the manufacture and calibration of such crystals and makes them almost unusable in situations where, for example, vibration could alter the orientation of the crystal.