Development of tube flow sensor by using film transfer technology and its application to in situ breathing and surface image evaluation in airways

A micro-electro-mechanical systems flow sensor was integrated onto an optical fiberscope to enable in situ breathing and surface image evaluations in small airways. The tube flow sensor was developed to be easily attached to an optical fiberscope. Firstly, two heaters working as flow rate sensors were formed on thin film by using a lift-off process. Then the fabricated film sensor was assembled onto the outer tube surface by film transfer technology. The flow rate vs. sensor output characteristics under both the forward and backward flow conditions were confirmed to be coincident. Thanks to thermal capacity reduction by 1.0 μm-thickness film substrate and thermal isolation by cavity formation around the heaters, a short response time of less than 20 ms was obtained. This was sufficient to follow the temporal airflow rate change during breathing. The fabricated tube flow sensor was attached to the outside of a fiberscope 1.6 mm in diameter, and it was inserted into a tube that was connected to the airway of a rat. An optical image of the rat was captured, and its breathing airflow rate was successfully detected.