TY  - THES
AU  - Hamacher, Stefanie
TI  - Development of a New, Miniaturized and Flexible Temperature Sensor
VL  - 303
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Jülich
M1  - FZJ-2025-04468
SN  - 978-3-95806-863-6
T2  - Schriften des Forschungszentrums Jülich Reihe Schlüsseltechnologien / Key Technologies
SP  - XXII, 153
PY  - 2025
N1  - Dissertation, RWTH Aachen University, 2025
AB  - Temperature is one of the most important scientific quantities and plays a fundamental part in our daily life. While permanent temperature sensors were primarily used to control air conditioning, fridges and freezers, nowadays they are utilized in many more fields, such as healthcare, manufacturing and agriculture. Over the centuries several different devices were developed that were able to determine changes in temperature. In the beginning, such a thermometer was simply based on the expansion and contraction of air or water and the dilation of liquids is still in use in the common mercury thermometer. However, many more devices are known today that are based on the change of different physical quantities that can be related to temperature. Common examples are the change in resistance used in resistance temperature detectors (RTDs) or thermistors or the change in spectral characteristics detected via IR measurements. Depending on the purpose of the temperature measurement an appropriate technique is chosen, since all of the known devices have their advantages and drawbacks, e.g. a small temperature range or low relative change of the specific parameter per degree. To overcome such drawbacks, a miniaturized temperature sensor based on a new approach was developed in this work. As a sensing principle, the dependence of the diffusion coefficient on fluid viscosity, which in turn is temperature dependent, was exploited. Using Faradaic electrochemical currents from a redox mediator dissolved in fluid, a relation between current and temperature can be obtained. Here, three different ionic liquids (ILs) and mixtures of them were investigated along with different redox species, such as ferrocene, hydroquinone and methylene blue to establish a stable temperature sensor that is suitable over a large temperature range and shows long-term stability. Several thin-film sensor prototypes were fabricated and characterized using custom-made electronics as well as a potentiostat. First, the peak current dependence on temperature using cyclic voltammetry (CV) was demonstrated. Afterwards a screening of the most feasible redox species was conducted using CV. Thereby it was found that ferrocene is not stable over a longer period of time, which is why other redox couples were examined and methylene blue was found to be the best. Additionally, the IL 1-ethylimidazolium nitrate ([EIM][NO3]) was used as redox species and solvent medium simultaneously. In order to establish an easy to handle sensor, the sensitive layer had to be fixed upon the substrate. This was achieved by adding two monomers and a photo initiator to the IL mixture that were cured using UV light. Finally, the prepared temperature sensors were characterized using the chronoamperometric technique and four different pulse lengths. Compared to standard resistance temperature detectors, this novel sensor shows a higher per degree sensitivity and can be utilized in a broad temperature range, for example for cold-chain monitoring of perishables.
LB  - PUB:(DE-HGF)3 ; PUB:(DE-HGF)11
DO  - DOI:10.34734/FZJ-2025-04468
UR  - https://juser.fz-juelich.de/record/1047702
ER  -