An Angstrom-sensitive, differential MEMS capacitor for monitoring the milliliter dynamics of fluids

A device, with MEMS sensors at its core, has been fabricated and tested for measuring low fluid pressure and slow flow rates. The motivation was to measure clinically relevant ranges of slow-moving fluids in living systems, such as the cerebrospinal fluid in the brain. For potential clinical utility, the device can be read transcutaneously by inductive coupling to MEMS capacitive sensors in circuits with resonance frequencies in the MHz range. Signal shifts for flow rates in the range of 0–42 mL/h and differential pressure levels between 0.1 and 2 kPa have been measured, because the sensitivity in the capacitance gap measurement is about 1 Å. The sensors have been used successfully to monitor simulated cerebrospinal fluid dynamics. The device does not utilize any internal power, since it is powered externally via the inductive coupling.