A self-resonant micro flow velocity sensor based on a resonant frequency shift by flow-induced vibration

We report the development of a self-resonant flow sensor based on a resonant frequency shift due to flow-induced vibrations. The vibration of a microcantilever beam, induced by a turbulent flow, is modulated with its own natural frequency, and the resonant frequency is shifted by a surface stress on the beam due to fluid drag force. The vibration induced by air flow is measured by using a piezoelectric PZT material on a silicon cantilever beam. The theoretical resonant frequencies of two cantilever beams (lengths: 610 mu m and 2000 mu m) are 12416 Hz and 1155 Hz, respectively. For the air flow velocities of 2.8 m s(-1) and 9.7 m s(-1), the shifted resonant frequencies of the cantilever beam whose length is 610 mu m are 12 810 Hz and 15 602 Hz, respectively. Sensitivities of the two self-resonant flow sensors with the 610 and 2000 mu m long beams are approximately 384 +/- 15 Hz/(m/s) and 20.4 +/- 0.6 Hz/(m/s), respectively.