Energy-less respiration monitoring device using thermo-sensitive film

We propose an easy-to-use energy-less respiration monitoring device for monitoring the breathing flow using a thermo-sensitive film. Thermo-sensitive film less than 0.01 mm thick with thermo-sensitive ink and a base film were wrapped over the aperture and partially produced in the tube for monitoring the breathing status. The aperture used as the respiration monitoring area, also worked as thermal isolation to shorten the response time and to decrease thermal capacity in the monitoring area. The response time was investigated using a response evaluation device (designed and produced using MEMS technology) to follow the temperature change with the breathing cycle of 0.3 Hz. The response time depended on the thickness of both the ink and the base film and decreased with the decrease of the thickness due to thermal capacity reduction. The obtained minimum response time was 373 ms when the ink thickness was 6.8 μm and the base film thickness was less than 5.0 μm. The color of the ink at the breathing monitoring area formed on the aperture successfully changed from blue to transparent according to the temperature change of the airflow.