A novel microsensor for measuring thermal conductivity of fluid based on three omega method.

A novel microsensor has been designed for the measurement of thermal conductivity of fluids based on the three omega (3ω) method. First, we theoretically analyzed the heat conduction using the 3ω method to demonstrate the mechanism of the microsensor to measure the thermal conductivity of a fluid. For the main structure of the microsensor, a heater was supported by the thin dielectric layers. In order to obtain the optimal parameters, we used the finite element method to simulate the working condition of the microsensor. In the simulation model, the effects of the thicknesses of the heater and dielectric layers on the thermal conductivity λ of the fluid were analyzed. The simulation results confirmed the validity and accuracy of conventional analytical calculations. Based on the simulation and theoretical calculation, a microsensor was optimally designed and fabricated to measure the thermal conductivity of fluids. Experimental data are consistent with those reported in the literature and demonstrate that the proposed sensor is effective for measuring thermal conductivity of fluids, including conductive ones.

A Novel Slope Method for Measurement of Fluid Density with a Micro-cantilever under Flexural and Torsional Vibrations.

A novel method, which was called a slope method, has been proposed to measure fluid density by the micro-cantilever sensing chip. The theoretical formulas of the slope method were discussed and established when the micro-cantilever sensing chip was under flexural and torsional vibrations. The slope was calculated based on the fitted curve between the excitation and output voltages of sensing chip under the nonresonant status. This measuring method need not sweep frequency to find the accurate resonant frequency. Therefore, the fluid density was measured easily based on the calculated slope. In addition, the micro-cantilver was drived by double sided excitation and free end excitation to oscillate under flexural and torsional vibrations, respectively. The corresponding experiments were carried out to measure the fluid density by the slope method. The measurement results were also analyzed when the sensing chip was under flexural and torsional nonresonant vibrations separately. The measurement accuracies under these vibrations were all better than 1.5%, and the density measuring sensitivity under torsional nonresonant vibration was about two times higher than that under flexural nonresonant vibration.