Fully Screen Printed Thermocouple and Microheater Applied for Time-of-Flight Sensing in Microchannels

Abstract

In order to control the flow inside microchannels, measuring the flow velocity of fluids is an important task. A possible way to determine flow velocity is by measuring the thermal time-of-flight. To this end, in this paper, a full screen printed combination of microheater and thermocouple is presented. Screen printing represents a technology that is attractive for fabricating low-cost sensor systems for microfluidic devices which can be directly integrated into the channel. The structure presented here has been manufactured using high-temperature stable screen printing inks. The thermocouple is calibrated and then the sensor setup is used to determine the flow velocity in a microchannel at various flow rates. The measurement is performed using a frequency domain approach by evaluating phase shifts of slow steady-state oscillations, and alternatively in the time-domain by estimating the heat transfer function from a step response measurement. The measurement results are compared to theoretically predicted values and show good agreement for a flow velocity range from 20 $\mu 1$ /min to 70 $\mu 1$ /min.