A bubble detector is used in systems where air or gas bubbles are unwanted in the fluid flowing through a pipe, for example for critical medical equipment like dialysis machines, infusion pumps, and blood transfusion systems. Beside this, a bubble detector can also detect the development of foams in a fluid.

The major advantage of using an ultrasonic transducer for bubble detection is that measuring method is non-invasive and functions through the tubing wall. The sensor has no direct contact to the fluid, which prevents a potential risk of contamination or leakages. So, the bubble detection can easily be mounted on top of the tubing without any additional tools or modification to the existing system.

For this application also the two transducers are used in bi-static configuration and are placed on either side of the tube, one for transmitting and other for receiving.

When there are no bubbles, the ultrasonic signal passes through the tube and the fluid without much attenuation, but if any bubble is present in the fluid and as the bubble passes in between the transducers, the ultrasound signal gets scattered or reflected as the bubbles hits the bubble as a result the signal reaching the receiver get attenuated. This attenuation in the signal can be detected by the receiver circuit and can be processed to count the number of bubbles, the size, and even the volume of air in the bubble.