report OF eddy current based flexible sensor for contactless measurement of breathing

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Changes in the volume of pulmonary air change the conductivity distribution in the thorax. On the basis of this effect, we describe an instrument without contact to measure the volume of the lung which is suitable for applications such as monitoring of respiration in patients of sleep for the sleep apnea. The instrument is based on a magnetic coil and is positioned in a soft mattress below the subject. Current AM frequency is applied to the coil to generate eddy currents in the tissue near the drivers, which in turn generate a magnetic field opposed to the transmitted field. This effect makes changes in the distribution of thoracic conductivity due to respiration and blood circulation change the effective inductance of the coil. We describe a new design to measure this effect using a single program and receiving coil. The coil forms part of a granted Colpitts oscillator to be its margin of stability, in order to give great changes of frequency of changes in the conductivity. The output of the oscillator is then demodulated using a frequency counter. This device has been tested in healthy volunteers and showed a good correlation with pneumotachographe measures