Highly Stable Piezoelectric Resonator Based Airflow Sensor Using Time Of Flight Technique

This paper presents a novel airflow sensor that measures respiration airflow using time-of-flight sensing modality. This is achieved using two high quality factor (Q~3000), low insertion loss (IL<10 dB), 25MHz thin-film piezoelectric-on-silicon resonators placed at a known fixed distance (~1cm) and integrated into two distinct oscillator circuits. The respiration airflow is accurately measured by dividing the fixed distance over the time difference in frequency shift of the resonators in response to the humidity of the exhaled air and the temperature drift of the resonators. The use of dual oscillator architecture could guarantee signal stability and high signal-to-noise ratio (SNR) whilst maintaining excellent sensitivity.