The principle of operation of liquid crystal sensors is based on the fact that liquid crystals change their state in such way that they modify passive scattering or absorption of light. As the crystal melt, the three-dimensional order becomes a two-dimensional or one dimensional order, layers or strands form that can be seen as a clarification of the previously turbid melt.
For instance, in one medical application, the patient’s body is painted with a black water-soluble varnish to show up the colour of the liquid crystals better. Liquid crystals are painted over the varnish and any inflammation causes arise in temperature that is indicated by a colour pattern.
Related: Types of Transducers used in Biomedical Measurement Applications
Liquid crystals are employed in disposable thermometers in the measurement of oral temperatures. They are also commonly used in wrist watches because a low-voltage (1-15 V) low power (1 μW/cm2) electric field causes observable changes in digital displacements.
