A4.1 - Fully Integrated Micro Coriolis Mass Flow Sensor Operating at Atmospheric Pressure

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A4 - Flow Sensors I
J. Lötters, R. Wiegerink, T. Lammerink, J. Haneveld, T. Hagemann - T. A. G. Hagemann, University of Twente, AE Enschede (Netherlands)
89 - 94


Outline of the problem
We have fabricated a micro Coriolis mass flow sensor using silicon nitride as the tube material. We demonstrated that a silicon nitride sensor could reach a resolution of the order of 10 milligram/hour. In the meantime, we added an integrated capacitive read-out. However, actuation was still done using Lorentz forces in combination with large external magnets.

Innovation of the solution
We have realised a micromachined micro Coriolis flow sensor with integrated electrodes for both electrostatic actuation and capacitive read-out. A comb-shaped electrode design is used to prevent squeezed film damping so that the sensor can operate at atmospheric pressure, thus eliminating the need for vacuum packaging. The new sensor chip no longer requires large external magnets and the size of the chip itself has been reduced from 15 × 15 to 7.5 × 7.5 mm2.

Technical realisation
A Coriolis type flow sensor consists of a vibrating tube. The tube is actuated in a torsion mode or flapping mode by applying voltages to capacitors at the inside of the rectangular loop. A mass flow inside the tube induces Coriolis forces that excite the other vibration mode, resulting in a vibration amplitude proportional to the mass flow. Both the actuation and the Coriolis movements are detected using capacitors at the outside of the loop. The mass flow can be extracted from the two output signals by detecting the phase difference, which is exactly proportional to the amplitude ratio of the Coriolis and actuation movements.

Measurements have been performed with both torsion and flapping actuation. With both actuation principles it was found to be possible to measure flows between 10 milligrams / hour and 1 g/h. The measurements clearly show that the structure is more sensitive with torsion actuation. This is in agreement with the theoretical model of the sensor structure since the flapping mode is more efficiently excited by the Coriolis force. Research now focuses on increasing the actuation amplitudes in order to improve the signal-to-noise ratio.