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

This paper presents an optical transcutaneous pCO₂ gas sensor and analyzer using a non-invasive method. The basic principle of the pCO₂ measurement method adapts Beer-Lambert´s law and the embodied system uses the NDTR (non-dispersive infrared) method. Since CO₂ gas reacts to a 4.3 μm wavelength, this wavelength is selected using an optical filter, and used energy decrease by molecule oscillations. The CO₂ concentration is then measured by a MFC (mass flow controller) using basic steps, instead of collecting pCO₂ gas by inflicting heat on the outer skin. The measuring system consists of an IR lamp, optical filter, optical reaction chamber, pyroelectric sensor, and signal process part. To make the sensor system portable, the length of the optical reaction chamber is minimized to 1 mm using a Si wafer based on MEMS technology. When CO₂ gas is injected into the optical reaction chamber, a result of 4.3 mV was confirmed when using a photoreaction path of 1 mm with a CO₂ gas reaction. The response time of the system was within 2 seconds, which is fairly fast.