Hot thermistor flow sensor

In collaboration with Dr. Amir Harandi at Potomac Photonics, Inc. we have investigated localized heating and temperature and fluid flow monitoring in microfluidic systems.  Very small  0201 thermistors were used in a self-heating mode to simultaneously heat and monitor the temperature of a microfluidic channel.  This microfluidic analog of a hot wire anemometer  show the simplicity and cost benefits associated with integration of microfluidics with SMD electronic components.

Emphasizing simplicity, a single NTC surface mount thermistor was mounted outside a thin flow channel wall of a microfluidic device constructed from COC (cyclic olefin copolymer).  Flow channel dimensions were 300 microns width  x 500 microns height and the footprint of the thermistor was 300 microns x 600 microns.  Biasing the thermistor with the circuit shown below and using its resistance to measure its temperature, we found good agreement with predictions obtained from Comsol modeling and obtained a relatively large electrical signal proportional to flow.


Figures and data courtesy of Amir Harandi, Potomac Photonics, Inc. 

Flow monitor experiment using heated thermistor and a series bias circuit.

Self-heated thermistor mounted on a FR4 substrate and in contact with a microfluidic flow channel.

Variation of thermistor temperature with flow using the thermistor bias circuit shown at left.