Printed thermocouple, multiple wired integrated in poliymide.
Printed thermocouple, multiple wired on LTCC.

Thermocouples measure in a wide temperature range. They have a high linearity of the measurement signal and a high robustness. In the point of connection between two conductors, containing metals or alloys, is a thermoelectric voltage generated which is the measuring signal for temperature. Conductors in commercial thermocouples are normally cables, connected at the measurement point, which are non-elastic and hard to miniaturize.

Using the Aerosol-Jet printing technology, thermocouples can be applied directly on the surface or components to be measured. The Fraunhofer IKTS developed printable inks (Ag, Ni, CuNi), which are activated below 300 °C. The direct-printing method applies structures contactless and miniaturized on planar or 3D-objects. Multiple wired printed thermocouples realize high thermoelectric voltages above 35 µV/K close to the standardized thermocouples. The embedding of the thermocouples in polyimide shields against environmental influence. A longtime temperature treatment of 1000 h at 150 °C showed a slightly drift of the thermoelectric voltage under 5 %.  This will be a future point of investigation.