Printed Heating and Temperature-Sensing Film in Transient Plane Source Sensor and Its Application in Measuring Thermal Conductivity

The transient plane source (TPS) method for thermal conductivity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula>) measurement has been growing in popularity because of few limits on sample shape, size, and state. The accuracy and reliability are determined on TPS sensors and data analysis, and various modified models have been put forward for data processing, but there are scarcely any improvements proposed on sensor fabrication. In this study, screening printing is adopted as a new and economical method to fabricate the nickel film with a bifilar spiral arrangement in TPS sensors for heating and temperature-sensing. The functional nickel film is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu $ </tex-math></inline-formula> m in thickness and the formed TPS sensor has a total thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 30~\mu $ </tex-math></inline-formula> m after being sealed in polyimide films. The TPS sensor shows good linearity between relative resistance change and temperature from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~^{\circ }$ </tex-math></inline-formula> C to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~^{\circ }$ </tex-math></inline-formula> C with a considerable temperature coefficient of resistance (TCR), <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.69\times 10^{-{3}}$ </tex-math></inline-formula>/°C. After calibration, five kinds of materials are measured by the TPS method: silica aerogel, polystyrene (XPS), stainless steel, alumina, and copper. The results are then compared with a steady-state heat flowmeter or transient laser flash measurement. It is found that the errors can be kept within 3%, and the results are highly identical with different time windows selected for fitting analysis, which proves the excellent accuracy and reliability of the TPS sensor fabricated by screen printing. Also, according to various output power, the measurement repeatability reaches 99.10% as the ultrathin sensor could effectively reduce heat loss during transient measurement.