Sail-shaped piezoelectric micro-resonators for high resolution gas flowmetry

This work presents sail-shaped thin film aluminum nitride resonators operating as high resolution gas flow meters. Deformation of the sail-like structure of the resonator due to the gas flow changes the effective stiffness and consequently the resonant frequency of the resonator. For a 10.2 MHz resonator engaged in a simple oscillator configuration Allan deviation as small as 10^-8 (df/f₀) was achieved for measurement periods less than one minute. Sensitivity of frequency to flow velocity was measured to be 0.5Hz/mm/s leading to minimum detectable velocity of 0.2mm/s. In addition, transient behavior of the sensor was investigated showing a rise time of approximately 20 ms. The presented sensors with frequency modulated output are much less susceptible to noise compared to the conventional sensors with amplitude modulated output. Furthermore, the output of such sensors can be directly fed into a digital readout/control system without the need for analog to digital conversion.