In-Situ Measurement of Fluid Density Rapidly Using a Vibrating Piezoresistive Microcantilever Sensor Without Resonance Occurring

Abstract

The Micro Electro Mechanical Systems (MEMS) density sensor is developed to achieve in-situ measurement of fluid density rapidly. The sensor's sensitive chip with a rectangular microcantilever is fabricated using MEMS technology. In the sensitive chip, an Au coil and four piezoresistors are fabricated on the rectangular microcantilever. When the sensitive chip is placed in the uniform magnetic field and the Au coil is powered with alternating input-voltage, the alternating Lorentz force is generated to drive the microcantilever to vibrate. Then, the powered Wheatstone full bridge consisting of four piezoresistors generates alternating output-voltage based on the piezoresistive effect. The sensor is tested when it is immerged in the silicone oil and in air under local atmospheric pressure. According to the experiment results, it is found that the data of alternating input-voltage of Au coil and alternating output-voltage of the Wheatstone bridge have a linear relationship. The linear function can be fitted easily through least-squares fitting to obtain slope and intercept. We also discover that every slope is inversely proportional to the corresponding fluid density. Hence, the fluid density can be measured rapidly by the calculated slope. The experimental results show that the absolute deviations of the measured densities from the reference densities are .