Capacitive sensor based on PCB technology for air bubble inside fluidic flow detection

This paper presents the design and performance of a low-cost high-accuracy three-electrode capacitive sensor based on a printed circuit board (PCB) capable for detecting an air bubble inside a fluidic channel. The electrodes of the sensor are designed and fabricated on the copper via of the PCB to detect an air bubble inside the liquid flowing through the PCB. With the proposed sensing structure, i.e., fluid vertically across the capacitive sensor, not only the present of an air bubbles inside the liquid flow can be monitored through the unbalance signal between the three electrode potential voltages, but also the volume and velocity of the bubble can be recognized from the amplitude and width of the obtained signal. The sensitivity and resolution of the sensor to detect air bubble inside water channel are estimated to be 23.5 mV/mm³ and 0.34 mm³, respectively, showing its potential of being used in microfluidic system and medical applications.