Flow-induced frequency shifts in suspended microchannel resonators with ultra-thin walls and large hydraulic diameter

A suspended microchannel resonator (SMR) is an unconventionally designed microelectromechanical system mass sensor that allows internal fluid flow in its suspended structure. This device is operated at its resonance conditions and registers a frequency shift corresponding to the mass flowing through the channel. Presented here is a dynamic SMR fluid–structure phenomenon that has not been reported to date. SMR devices were fabricated with ultra-thin walls and large hydraulic diameter using thermo-compression wafer bonding, and optical characterization of these SMRs with internal fluid flow using a laser Doppler vibrometer revealed frequency shifts of various vibration modes with variation in fluid flow rate, gas species, and device geometry. The underlying physics is modeled semi-analytically and is found to match some of the experimental observations, while others are unanticipated. This study shows that SMRs can be used to sense flow rate by measuring the change in resonant frequency resulting from the flow, aside from standard Coriolis-based measurement. Furthermore, it is shown that fluctuations in fluid flow due to inlet pressure noise create noise in the frequency measurement, which, in turn, sets the resolution that can be achieved in mass sensing.