A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels

Abstract

Please cite this article as: T.A.Vincent, J.W.Gardner, A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels, Sensors and Actuators B: Chemical http://dx.doi.org/10. 1016/j.snb.2016.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels Highlights  MEMS based NDIR system for ppm CO2 detection with lock-in amplifier.  Fast 1.3 s response time for breath-by-breath analysis.  Portable breath analyser designed for measuring metabolic rate of subjects.  Effect of path length on NDIR system investigated with novel sensor housing.  Silicon on insulator IR emitter used for low power, low cost gas detection. AbstractThe molecules in our breath can provide a wealth of information about the health and well-being of a person. The level of carbon dioxide (CO2) is not only a sign of life but also when combined with the level of exhaled oxygen provides valuable health information in the form of our metabolic rate. We report upon the development of a MEMS-based non-dispersive infrared CO2 sensor for inclusion in a hand held portable breath analyser. Our novel sensor system comprises a thermopile detector and low power MEMS silicon on insulator (SOI) wideband infrared (IR) emitter. A lock-in amplifier design permits a CO2 concentration of 50 ppm to be detected on gas bench rig. Different IR path lengths were studied with gases in dry and humid (25 % and 50 % RH) in order to design a sensor suitable for detecting CO2 in breath with concentrations in the range of 4 to 5 %. A breath analyser was constructed from acetal and in part 3D printed with a side-stream sampling mechanism and tested on a range of subjects with two data-sets presented here. The performance of the novel MEMS based sensor was validated using a reference commercial breath-by-breath sensor and produced comparable results and gave a response time of 1.3 s. Further work involves the detection of other compounds on breath for further metabolic analysis and reducing the overall resolution of our MEMS sensor system from ca. 250 ppm to 10 ppm.

A Phase-Domain Readout Circuit for a CMOS-Compatible Hot-Wire CO2Sensor

“…The total accumulated noise charge is related to the noise charge q n accumulated in one cycle as q 2 n,acc = N ·q 2 n . By substituting this in (8), the standard deviation of μ can be expressed as…”

“…However, they are quite expensive, difficult to miniaturize (large sensing length), and power hungry (>100 mW) [5]- [7]. Efforts have been made to realize compact MEMS-based infrared emitters in SOI technology [8]- [10]; however, the resulting resolution is inferior to that achieved by conventional microbulb-based IR emitters [8]. A fiber-optic CO 2 sensor operating in the near-IR spectrum has been proposed in [11] to reduce the sensing length to 8 cm.…”

A Low-Cost Breath Analyzer Module in Domiciliary Non-Invasive Mechanical Ventilation for Remote COPD Patient Monitoring

“…Arterial-blood gas (ABG) test, measuring the amounts of arterial CO 2 and O 2 , is the gold standard technique, but it is relatively invasive [20]. There is a growing interest in applying non-invasive technologies that could measure physiological parameters, as end-tidal CO 2 (capnography) and blood oxygen saturation level SpO 2 (oximetry) [21][22][23]. However, for domiciliary NIV, capnograph is an optional module of the mechanical ventilator, not included in the kit supplied to home assisted COPD patients.…”

A NDIR Mid-Infrared Methane Sensor with a Compact Pentahedron Gas-Cell

“…Incandescent lamp is one kind of mid-infrared source which has been demonstrated to be successfully employed in gas detectors based on infrared absorption due to its small size and low cost (a few US dollars) [ 18 , 19 ]. Non-dispersive infrared (NDIR) is a proper method for this kind of sensor [ 20 , 21 , 22 ]. However, due to the large divergence angle, such a kind of source cannot be condensed into the multi-pass gas cell for hundreds of reflections without mode overlap.…”