Photo: University of Warwick |
Researchers at the University
of Warwick and Oxford University
have developed a form of crystal that can deliver highly accurate temperature
readings, down to individual milli-kelvins, over a very broad range of
temperatures: -120 to 680 C.
The researchers 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.
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 making 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.
Professor Pam Thomas of the University of Warwick says: “This
advance, which has come out of research funded by EPSRC, 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. Examples are temperature
measurement within the vicinity of MRI scanners in hospitals, industrial
microwave dryers, and the human body.”
Professor Mike Glazer of the University of Oxford
says, “This opens new possibilities for remote temperature sensing of
challenging environments. 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.”