A. Petropoulos1, D.N. Pagonis2, G. Kaltsas1,3
(1) Technological Educational Institution (TEI) of Athens, Department of Electronics, 12210, Athens, Greece
(2) Technological Educational Institution (TEI) of Athens, Department of Naval Architecture, 12210, Athens, Greece
(3) Institute of Microelectronics, NCSR Demokritos, P.O. Box 60228, 15310 Aghia Paraskevi, Athens, Greece
A polymer-based microfluidic flow sensor with controllable sensitivity over a wide measurement range
The fabrication technology as well as the detailed characterization of a polymer microfluidic flow sensor is presented. The device fabrication is based on a combination of PCB and MEMS techniques, enabling effective thermal isolation and direct communication to the macroworld. The sensor operation can be tuned to custom specifications by precise definition of structural and operational parameters, so that maximum sensitivity in pre-specified flow rate regions can be achieved throughout an extended measurement range [150nL/min-140μL/min].
2.Motivation and results
Flow rate determination within a microchannel via the quantification of convective heat transfer is a concept with its origin traced in the mid ‘90s . Precise knowledge of the flow rate within a microchannel is a critical factor in a variety of applications associated with lab-on-a-chip and POC systems. In order to facilitate differentiated applications, a microfluidic flow sensor should have the flexibility of operating in distinct flow rate regions. Furthermore a move from silicon to polymer-based structures is a necessity in order to assure compatibility with the modern microchannel fabrication methods . In this work we present the fabrication and evaluation of a polymer microfluidic flow sensor. The sensor heating and sensing elements are directly integrated on a PCB substrate, while the microchannel walls are formed via SU-8. Inherent characteristics of the specific fabrication technology , are the direct electrical communication of the Pt sensing elements to the macroworld (no wire bonding), the highly effective thermal isolation achieved and the full two-dimensional control on the crossection and the shape of the integrated microchannels. The distinctive characteristic of the presented microfluidic flow sensor is the ability to adjust the operational sensitivity in varying flow rate regions, by the appropriate definition of specified parameters. These are: 1. The operating principle (hotwire or calorimetric) 2. The input power 3. The height and the width of the microchannel 4. The distance from the sensing elements to the heater. The individual device measurement range is subject to parameter configuration, within a wider frame spanning from 150nL/min up to 140μL/min. The maximum sensor sensitivity in terms of the recorded flow-induced temperature changes is amongst the highest ones reported in the literature. Overall, the presented sensor can act as a high-performance standalone flow measuring device. Furthermore it can be easily implemented in a more complex detecting system, due to the polymer based fabrication technology, the direct electrical communication to the macrowold and the ability for on-demand tuning into predefined operation specifications.
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