Bidirectional subminiature thermistor sensor for analog control by breath flow.
A subminiature airflow sensor is described, which can discriminate between exhalation and inhalation, has good linearity and stability, and is small enough to fit inside the stoma button of a laryngectomee. The system employs two fast-response self-heated thermistors placed on opposing sides of an aerodynamic obstacle inside a tube; flow polarity discrimination is based on differences between the heat exchange patterns under laminar vs. turbulent flow. An output proportional to airflow is achieved by the connection of a circuit with a piecewise-linear transfer characteristic in cascade with the thermistors. Developed in-house, this circuit may be adjusted to create an arbitrary range of input-output characteristics. Applications are suggested for an input device for various handicapped aids, for medical diagnostics and in industrial control.
D000403:Airway Resistance; D004738:Engineering / Q000295:instrumentation*; D005069:Evaluation Studies as Topic; D006801:Humans; D007825:Laryngectomy; D008433:Mathematics; D008904:Miniaturization; D012119:Respiration; D012129:Respiratory Function Tests / Q000295:instrumentation*