Fabrication of a stent-type thermal flow sensor for measuring nasal respiration

A stent-type flow sensor is presented for evaluating nasal respiration. To enable the thermal flow sensor to be fixed at inner nasal passage surfaces, it was integrated onto a stent structure, which is normally used as a medical tool. The monolithically integrated sensor was fabricated on a Ti substrate by photolithography and wet etching processes, an advantageous procedure in that both the thermal isolation cavity and the stent structure can be fabricated during the same etching process. The sensor was mounted onto a silicone tube's inner surface by inflating a balloon tube, and then its characteristics were evaluated. A study of the cylindrical stent's mechanical strength under compression conditions showed that elastic deformation occurs when the compression force is 0.08 N or less. The sensor can detect the flow direction at a flow range of 0-2000 ccm. A response time of 260 ms or less was obtained by forming a cavity under the sensor. The sensor characteristics under oscillating flow were studied by using a ventilator, and it was confirmed that the sensor was able to measure the oscillating flow at an output frequency of 2.0 Hz.