New CO2 sensor with high resolution and fast response

The most common principles for CO₂ sensors are only partially fulfilling the requirements of cardiovascular and respiratory applications. A new acoustic sensor principle is claimed to be favorable in several respects, such as size, resolution, response time, reliability and cost. The sensor makes use of an electro acoustic element coupled to a Kundt resonator. The resonance frequency is determined by the mean molecular mass of the gas contained in the resonator, which may, in turn, be dominated by the variations of CO₂ concentration. A phased locked loop (PLL) oscillator provides both voltage and frequency outputs of the sensor. In this paper, a prototype design is presented, along with experimental results demonstrating that resolution, linearity and response time adequate for biomedical applications may be achieved.