Abstract

Being able to accurately measure oil viscosity in real time is critical for multiple applications. It can ensure that the oil being used to protect and lubricate gears and other mechanical elements is good. To do this a thermally actuated micro electromechanical systems (MEMS) based sensor has been previously developed. The sensor is able to measure viscosity by having the fluid couple with the oscillating diaphragm and monitoring the frequency, amplitude and quality factor of the waveform. To improve the accuracy of the sensor, 5 different versions were created to study the effects of heating area and the sensing material used in the Wheatstone bridge. To also improve the repeatability of the sensors and reduce sensor to sensor variation the fabrication process was improved. This included the use of SOI wafers and better diaphragm alignment through the use of a contact aligner with an IR attachment to show alignment marks through the wafer. For the Wheatstone bridge polysilicon and P+ diffusion resistors were evaluated. For the heater material polysilicon and P+ diffusion were evaluated. For the heater area 3 separate designs were made with different size polysilicon heaters but with the same P+ Wheatstone stone to allow just the heater size to be evaluated. To remove the effects of temperature on the sensors each sensor was run through a temperature sweep in air. The data was used to create a correction factor that applied to the fast Fourier transform (FFT) frequency to produce more accurate results for measurements taken above room temperature. To determine how sensitive each type was to changes in viscosity each type was placed in N100, N35 and N10 oils while their temperature went from 25°C to 80°C. These oils were used because they made specific ASTM standards to ensure they have a set viscosity for a given temperature. From testing it was determined that higher initial deflection of the diaphragm does not equate to a higher sensitivity.

Library of Congress Subject Headings

Viscosimeter--Testing; Microelectromechanical systems; Wheatstone bridge--Materials

Publication Date

7-19-2023

Document Type

Thesis

Student Type

Graduate

Degree Name

Electrical Engineering (MS)

Department, Program, or Center

Department of Electrical and Microelectronic Engineering (KGCOE)

Advisor

Ivan Puchades

Advisor/Committee Member

Karl Hirschman

Advisor/Committee Member

Robert Pearson

Campus

RIT – Main Campus

Plan Codes

EEEE-MS

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