A Hybrid Fabrication Technique of Capacitive Flow Meters Using Three-Dimensional Printing for Rectifying Airflows

In this study, a simple manufacturing method was developed for fabricating a multifunctional capacitive flow meter (CFM), which can act as a check valve for flow channels. By using three-dimensional (3D) printing technology, a hybrid advanced manufacturing process is realized. As the gas flows in the forward direction, the initially closed polymer membrane opens and allows airflow. The flexible and dielectric membrane is normally closed. It opens in response to the airflow direction and changes the capacitance according to the airflow rate. The sensing performance of four different CFMs were characterized according to the thickness of the membrane. From an analysis of the static and transient responses, the sensing range, sensitivity, and signal-to-noise ratio were calculated and compared. The CFM with a 600
$\mu \text{m}$
thick membrane was adopted as the sensing component for a human respiratory (inhalation and exhalation) monitoring system as one of the applications. The 3D printed system successfully measured the respiratory rate and tidal volume (~442.3 ml), supporting the applicability of CFMs in diverse fields such as human healthcare, mass flow controllers, and smart wearable devices.