Crystal takes temperatures to extremes

U. WARWICK (UK) — Researchers have developed a form of crystal that can deliver highly accurate temperature readings, ranging from -120 to +680 degrees centigrade.

Researchers at the University of Warwick and Oxford University used a “birefringent” crystal, which splits light passing through it into two separate rays.

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.

Researchers Pam Thomas and Mike Glazer have developed a way to very accurately measure temperatures, down to individual milli-kelvins, in extreme environments using a “birefringent” crystal, which splits light passing through it into two separate rays. (Credit: University of Warwick)

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.

However the Warwick and Oxford researchers have developed a reproducible and low-cost method of modifying the properties of crystalline lithium tantalate so that its birefringence is virtually independent of the crystal’s thickness and position. The modification makes it resistant to vibration and cheaper to manufacture.

In fact, they have made the birefringence almost zero in magnitude in all directions (the material is close to being optically isotropic just like ordinary glass). However, the slightest temperature change induces a rapid increase in birefringence in these materials, making this a reliable, robust ,and very sensitive method for measuring temperature.

The inventors have named their device a Zero-Birefringence Optical Temperature Sensor (Z-BotS) and are currently seeking follow-on funding to develop the device from the bench-top proof-of-concept to a miniaturized, commercially viable package.

“This advance . . . allows us to create a new generation of robust reliable birefringent crystal-based temperature sensing equipment which will be particularly valuable in electromagnetic, radio frequency, and high voltage environments, where other types of sensor are subject to large errors due to interference,” says Pam Thomas, a Warwick professor. “Examples are temperature measurement within the vicinity of MRI scanners in hospitals, industrial microwave dryers, and the human body.”

“This opens new possibilities for remote temperature sensing of challenging environments,” says Mike Glazer of Oxford. “As the birefringence changes detection in these crystals can actually be operated remotely as only the crystal itself needs to be in the environment. All the other components: light source, measurement, and processing electronics can be situated remotely.”

The invention is now the subject of a patent application, and the researchers are working with Isis Innovation and Warwick Ventures to explore licensing opportunities.

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