Solid polymer electrolyte membrane flow sensor for tracheal tube

Solid polymer electrolyte membrane (SPM) acts not only as an actuator but as a small, voltage generating, and fast response sensor. Sensing characteristics of SPM as applied to a flow sensor for a ventilator was studied. SPM was prepared by chemically plating with gold on the surface of Nafion membrane. A new technique using Nafion R-1100 resin was applied to fabricate SPM with an arbitrary thickness between 200-1000 μm. Flow sensing unit and signal amplifier was constructed to measure the induced voltage by bending SPM with air-flow from the ventilator. Induced voltage by SPM ranged 1-100 μV over a ventilator air-flow range of 20-100 L/min. SPM sensor showed linear increase of induced voltage by the increase of flow. This relationship was tested over a range of SPM thickness, length and width. The result was compared with an electro-mechanical coupling model of SPM transducer: data showed consistent result on the relation between the induced voltage and membrane length and thickness while a discrepancy was observed in the relation of membrane width and induced voltage. The result, however, was consistent with the assumption of capacitive component model.