Low power consumption design of micro-machined thermal sensor for portable spirometer

There are great needs for a low cost and low power consumption portable spirometer for the home care of respiratory diseases. Thermal anemometer has the advantage of possible miniaturization by modem microfabrication processes. However, its optimal design remains to be a technical challenge for the trade off between required sensitivity and power consumption. The designed features of such a sensor include low thermal conduction via substrate, wide dynamic range (0∼180 L/Min) to cover high peak flow rate and possible low cost mass production. To meet these requirements, we used both surface and bulk micromachining techniques to fabricate the sensor for optimal performance. Testing of constructed prototype showed that it can be used under low operating voltage of 3 volts. According to the American Thoracic Society (ATS) guidance for the measurement of pulmonary functions, including dynamic volume of forced expiratory vital capacity (FVC) and flow during forced expiration: peak expiratory flow rate (PEFR), it has necessary accuracy (≤ 3% variation) for diagnosis requirements.