An ultra-sensitive heat sensor was developed that is based on the fact that certain materials are thermoelectric. The electrons in a thermoelectric material move from the cold side to the warm side when a temperature difference arises between the two sides and a voltage difference arises. In this project, researchers developed a thermoelectric material that uses ions as charge carriers instead of electrons, and the effect is 100 times larger.
A thermoelectric material that uses electrons can develop 100 µV/K (microvolt per Kelvin), compared with 10 mV/K from the new material. The signal is thus 100 times stronger, and a small temperature difference gives a strong signal.
The new material is an electrolyte that consists of a gel of several ionic polymers. Some of the components are polymers of p-type, in which positively charged ions carry the current. A highly conductive polymer gel of n-type was discovered in which negatively charged ions carry the current. Very few such materials have been available until now.
With the aid of previous results from work with electrolytes for printed electronics, the researchers have now developed the first printed thermoelectric module to use linked n- and p-legs, where the number of leg connections determines how strong a signal is produced. The scientists have used screen-printing to manufacture a highly sensitive heat sensor based on the different and complementary polymers. The heat sensor has the ability to convert a tiny temperature difference to a strong signal: a module with 36 connected legs gives 0.333 V for a temperature difference of 1 K.