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Author

Simon Loane

Date of Award

7-2009

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Mechanical Engineering

Supervisor

C.Y. Ching

Co-Supervisor

Ravi Selvananagathy

Language

English

Abstract

There is currently a lack of quality sensing techniques that can provide the required spatial and temporal resolution for use in microfluidic devices. The development of such micro sensors will allow real time monitoring and control of many processes at the micro level, and play a crucial role in expanding microfluidics to novel applications. For example, integration of sensors within the microfluidic device itself will allow active control of processes within these devices. The overall objective of this study was to develop a micro temperature and micro flow sensor for use in microfluidic devices. The specific objectives were to develop, design and micro fabricate a micro thermocouple and micro heater, and integrate these within a microchannel to show proof of concept of a micro thermal pulse flow sensor. A platinum-constantan (PT-NiCu) micro thermocouple was developed and fabricated using a three mask process. The micro fabrication protocols and procedures were developed for potentiostatically electroplating the constantan leg of the micro thermocouple. The thermocouples were characterized and the Seebeck coefficient (sensitivity) was found to be 39.04 μV/゜C and 41.75 μV/゜C for non compensated and a compensated thermocouple arrangement respectively.

A meandering resistive type micro heater was developed. The power consumption for the 400 Å thick gold micro heaters on the silicon oxide and on the glass substrates was compared. The power required for the glass substrate was 46mW, 112mW and l60mW for 5V, 8V, 10V respectively, while for the silicon oxide was 499.5 mW, 1.27 W and 1.943 W respectively.

The thermal flow sensor was developed by integrating the micro heater and micro thermocouple within a microchannel to show proof of concept of the sensor. The flow sensor was operated in three modes; time of flight, temperat1ll'e difference and pulsed thermotransfer calibration mode. Essentially the thetmotransfer principle occurs as the heat loss from the micro heater source to the fluid will increase with the flow rate, thereby giving greater voltage amplitude of the thetmocouple response with increasing flow velocities.

The flow sensor performance was characterized using methanol/water as the working fluid for mass flow rate in the range of no flow to 0.7 ml/min. The device has several unique operating and physical characteristics, including the novel pulsing scheme developed that compensates against temperature drift, resulting in high repeatability.

The flow sensor was calibrated using the thermotransfer principle for three pulse modes; single, multiple pulses with change in input voltage and multiple pulses with change in pulse duration. The comparative results showed that the multiple pulse modes generated a more detectable signal than the single pulse mode. The multiple pulse regimes allowed for a larger dynamic flow range. The flow sensor can be duplicated relatively easily so that multiple sensors can be distributed within a microfluidic device to allow simultaneous flow measurements at different locations within the device.

McMaster University Library

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