A Novel Liquid-Enhanced Micro Thermal Expansion-Based Angular Motion Sensor With Ultrahigh Sensitivity

This article presents the development of highly sensitive micro thermal expansion-based angular motion (TEAM) sensors utilizing water and ethanol as the working fluids. Theoretical analysis demonstrates that replacing the gas medium with liquids significantly increases the sensitivity of TEAM sensors, attributed to the larger Rayleigh number (Ra*). Among the two liquids studied, the ethanol-based TEAM sensor exhibits greater sensitivity to fluctuations in thermal properties than the water-based sensor. To ensure waterproofing, a Parylene-C coating was applied as the encapsulation layer for developing the novel liquid-based sensors. Experimental results identify a critical Ra* of 2950, which distinguishes the linear and nonlinear regions of operation for both the water-based and ethanol-based sensors. In the linear region, the water-based and ethanol-based sensors exhibit normalized sensitivities of 0.1638 and 0.37 mV/°/s/mW, respectively, which are more than 10 times and 20 times higher than those of conventional air-based sensors, supporting the theoretical predictions and confirming the feasibility of the proposed design strategy. Furthermore, the ethanol-based TEAM sensor outperforms the sulfur hexafluoride (SF6)-based sensor, currently the most sensitive gas-based thermal angular motion (TAM) sensor, by over five times. The experimental comparisons of single-heater and dual-heater configurations further highlight the importance of the dual-heater setup in minimizing heat loss and enhancing sensor performance, particularly for liquid-based sensors. These findings demonstrate the potential of the liquid-enhanced TEAM sensor for developing more accurate and reliable angular motion detection systems in complex environments.