An optical fiber based flow transducer for infant ventilation: Measurement principle and calibration

The measurement principle, design and static calibration of a flow transducer for neonatal ventilation is here described. The sensing element is constituted by an optical fiber that conveys the radiation emitted by a LED to a position sensitive detector (PSD). The measurement principle enables a differential output signal obtained through the processing of the photocurrents generated by the PSD: two different analog circuits were used, based on a differential amplification and a logarithmic amplification respectively. With the first circuit, the transducer shows a parabolic calibration curve in good agreement with theoretical data (R²>;0.95) at flow rate ranging from -8 L·min^-1 to +8 L·min^-1. The sensitivity has a mean value of about 120 mV·min·L^-1 and a discrimination threshold lower than 1 L·min^-1. Using the logarithmic amplification, the transducer shows a linear behavior between 2 L·min^-1 and 8 L·min^-1 with a sensitivity equal to 70 mV·L^-1·min. The fluid dynamic resistance is negligible. These preliminary experimental results, together with the known advantages of optical fiber-based sensors, encourage further studies for the application of this measurement principle in neonatal artificial ventilation.