Optimization of Thin-Film Thermopile Heat Flux Sensor to Accelerate the Response Time

Heat flux sensors offer precise measurements of heat flux density, playing a significant role in thermal management systems. Among them, thin-film thermopile heat flux sensors have attracted significant attention due to their outstanding performances, such as small size and rapid response time. The spatial distribution of hot and cold junctions holds paramount importance in determining the performance characteristics of thin-film thermopile devices. This study presents the design of a 3-D thermopile device fabricated using copper (Cu) and constantan (Cu55Ni45) with vertical distribution of hot and cold junctions, aiming at achieving a synergistic enhancement of response speed and sensitivity. The thin-film thermopiles were fabricated using an alumina (Al2O3) ceramic substrate, with Al2O3 thin-film serving as the thermal resistive layer. A water-cooled metal heat sink package was specifically designed to create a Cu/Cu55Ni45 thin-film heat flux sensor. The sensitivity of the device was calibrated by the heat radiation method, yielding a value of $37.84~\mu $ V/(kW/m2) and exhibiting a linearity of 0.99924. Within a heat flux density range of 300 kW/m2, the maximum error was found to be 1.22%. The response time of the device was evaluated using a laser calibration system, revealing a response time of 2 ms and a recovery time of 104 ms. This study provides a significant reference for heat management and transient heat flux testing methodologies across various domains, including aerospace and industrial safety.