Investigation of a microheater on a thin PDMS layer as an attachable thermal conductivity sensor
The mechanical and thermal properties of a polymer medium can be greatly increased through the addition of micro- and nano-sized solid particles. In such materials, the orientation of the additives can become a complicated function of the sample configuration, manufacturing method, thermal history, and so on. Consequently, thermal analysis by conventional techniques may lead to varying results due to the difference between the configuration of the measurement specimen and the actual target material. In order to minimize such discrepancy, an in situ thermal characterization technique is needed. In this study, a microheater on a thin polydimethylsiloxane (PDMS) layer is proposed as an attachable thermal conductivity measurement device. The proposed device can simply be attached to the target of interest and measurement can be performed similar to the conventional “3-omega” method. A sensitivity analysis is performed to provide insight and guideline on the sensor design and testing, and to study the effect of the sample thermal conductivity on the temperature oscillation measured at the microheater. The relationship between the substrate thermal conductivity and the temperature oscillation at the microheater is analyzed through comparing sensitivity parameters calculated for different values of design variables: input frequency, thickness of the PDMS layer, and microheater width. The results suggest that measurement at low temperature oscillation frequency (2 W/m/K), both amplitude and phase lag of the temperature oscillation should be utilized.
Keywords: attachable sensor, thermal conductivity measurement, the 3-omega method, in situ measurement, thin PDMS layer, sensitivity analysis