Development of non-invasive optical transcutaneous pCO2 gas sensor and analytic equipment

We have studied the development of an optical transcutaneous pCO₂ gas sensor and analyzer using a non-invasive method. The basic principle of the pCO₂ measurement adapted Beer-Lambert´s law and the embodied system using the NDIR (non dispersive infrared) method. CO₂ gas reacts with a 4.3 μm wavelength, so we selected this wavelength by an optical filter, and used energy decrease by molecule oscillations. We measured the CO₂ concentration using the MFC (mass flow controller) in basic steps instead of the pCO₂ gas that can collect by inflicting heat on the outer skin. This measuring system consisted of an IR lamp, an optical filter, an optical reaction chamber, a pyroelectric sensor and a signal processing system. We minimized the volume of the optical reaction chamber in order to make the sensor portable. We made an optical reaction chamber with a Si wafer using MEMS technology and it was shortened to 1 mm. We carried out an experiment in photoreaction length variation from 1 mm to 10 mm. We confirmed the linear graph of CO₂ concentration variation from 1,000 ppm (parts per million) to 100,000 ppm at 1 mm photoreaction length. The response time of this system was within 2 seconds, which is fairly fast.