The 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.

/pdf/a-low-cost-mems-based-ndir-system-for-the-monitoring-of-4kwhh1jivt.pdf

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

Gas sensor is a device that converts the information of an analyte species into electrical signals using various detection principles. Electrical conductivity is one of the crucial properties of sensing materials. This basic property is modified with the formation of p-n and n-n heterostructures or by the inclusion of dopants. Surface morphology of a sensing material plays a vital role in the adsorption of analyte species for effective gas sensing behavior, further this can be improved with proper surface treatment viz., surface reactions by decorating with nanoparticles composed of various noble metals. The sensing mechanism differs owing to various morphologies with sensing materials. Sensing materials can either be polymers, metal oxides, nanoparticles or pertinent combination of these constituents. The sensor properties like selectivity, sensitivity, stability, response time and detection limits are influenced by morphology, material exposed to target gas and operating conditions. This review focusses on sensing mechanism and monitoring of nanostructures (nanorods, nanosheets, nanobelts, nanoribbons, nanowires, nanoflowers, spinel etc.) by appropriate combination of materials and dopants. The performance of numerous metal oxide-based gas sensing devices and their market trends are reviewed.

A review on metal-oxide based p-n and n-n heterostructured nano-materials for gas sensing applications

The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff's law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO(2) absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO(2) gas sensor.

/pdf/a-highly-efficient-cmos-nanoplasmonic-crystal-enhanced-slow-38ayqxq50a.pdf

A highly efficient CMOS nanoplasmonic crystal enhanced slow-wave thermal emitter improves infrared gas-sensing devices

Emergency personnel, such as firefighters, bomb technicians, and urban search and rescue specialists, can be exposed to a variety of extreme hazards during the response to natural and human-made disasters. In many of these scenarios, a risk factor is the presence of hazardous airborne chemicals. The recent and rapid advances in robotics and sensor technologies allow emergency responders to deal with such hazards from relatively safe distances. Mobile robots with gas-sensing capabilities allow to convey useful information such as the possible source positions of different chemicals in the emergency area. However, common gas sampling procedures for laboratory use are not applicable due to the complexity of the environment and the need for fast deployment and analysis. In addition, conventional gas identification approaches, based on supervised learning, cannot handle situations when the number and identities of the present chemicals are unknown. For the purpose of emergency response, all the information concluded from the gas detection events during the robot exploration should be delivered in real time. To address these challenges, we developed an online gas-sensing system using an electronic nose. Our system can automatically perform unsupervised learning and update the discrimination model as the robot is exploring a given environment. The online gas discrimination results are further integrated with geometrical information to derive a multi-compound gas spatial distribution map. The proposed system is deployed on a robot built to operate in harsh environments for supporting fire brigades, and is validated in several different real-world experiments of discriminating and mapping multiple chemical compounds in an indoor open environment. Our results show that the proposed system achieves high accuracy in gas discrimination in an online, unsupervised, and computationally efficient manner. The subsequently created gas distribution maps accurately indicate the presence of different chemicals in the environment, which is of practical significance for emergency response.

https://www.mdpi.com/1424-8220/19/3/685/pdf

Towards Gas Discrimination and Mapping in Emergency Response Scenarios Using a Mobile Robot with an Electronic Nose.

Gas sensors are critical components when adhering to health safety and environmental policies in various manufacturing industries, such as the petroleum and oil industry; scent and makeup production; food and beverage manufacturing; chemical engineering; pollution monitoring In recent times, gas sensors have been introduced to medical diagnostics, bioprocesses, and plant disease diagnosis processes There could be an adverse impact on human health due to the mixture of various gases (eg, acetone (A), ethanol (E), propane (P)) that vent out from industrial areas Therefore, it is important to accurately detect and differentiate such gases Towards this goal, this paper presents a novel electronic nose (e-nose) detection method to classify various explosive gases To detect explosive gases, metal oxide semiconductor (MOS) sensors are used as reliable tools to detect such volatile gases The data received from MOS sensors are processed through a multivariate analysis technique to classify different categories of gases Multivariate analysis was done using three variants—differential, relative, and fractional analyses—in principal components analysis (PCA) The MOS sensors also have three different designs: loading design, notch design, and Bi design The proposed MOS sensor-based e-nose accurately detects and classifies three different gases, which indicates the reliability and practicality of the developed system The developed system enables discrimination of these gases from the mixture Based on the results from the proposed system, authorities can take preventive measures to deal with these gases to avoid their potential adverse impacts on employee health

https://www.mdpi.com/2072-666X/11/6/597/pdf

Wireless E-Nose Sensors to Detect Volatile Organic Gases through Multivariate Analysis.

A gas sensor system for harsh environment applications

In this paper we demonstrate the use of a CMOS infra-red emitter in a low power Non Dispersive Infra Red (NDIR) based carbon dioxide sensor for application in domestic boilers. Compared to conventional micro-bulbs as IR wideband sources, CMOS IR emitters offer several advantages: They are faster, smaller, have lower power consumption and can have integrated circuitry. The emitter is a 1.16 mm × 1.06 mm chip with an integrated FET drive and consists of a tungsten heater fabricated in a CMOS process followed by Deep Reactive Ion Etching (DRIE) to form a thin membrane to reduce power consumption. The NDIR sensor consists of the emitter and a commercial detector placed 5 mm apart in a simple tube. Operating the emitter at 10 Hz with a power consumption of only 40 mW, the sensor was measured in the range of 6-14% by volume of CO2, showing a resolution of 0.5%, a response time of 20 s, and low cross-sensitivity to humidity.

Low power NDIR CO 2 sensor based on CMOS IR emitter for boiler applications

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A gas sensor system for harsh environment applications

Low power NDIR CO 2 sensor based on CMOS IR emitter for boiler applications