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June 20, 2022

Exploring Market Demand for Pervasive Gas Monitoring

A body of new knowledge about the health effects of gaseous or volatile pollutants has highlighted the need for monitoring air quality outdoors and indoors. Different volatiles, even at their trace levels over short exposures, have been found to be harmful to human health. More consumer and industrial products may emit volatiles that now are known to be harmful, including furniture, passenger cars, and industrial trucks. Interest in detecting and measuring the gaseous pollutants is growing in order to create relevant and effective responses to reduce or eliminate health risks. 

Both national and international organizations have been developing guidelines, regulations, and standards for monitoring air in industrial, medical, outdoor, and indoor office and residential settings. The guidance allows manufacturers to certify their products while educating users about acceptable levels of gaseous pollutants. For example, the U.S. Environmental Protection Agency (EPA) uses cutting-edge science to establish regulations to reduce and control air pollution with cost-effective approaches. For the most common pollutants, EPA compiles data every five years to assess the adequacy of air regulations. The agency also identifies specific chemicals and sources such as cars, trucks and power plants that can impact air quality. A major goal is to tie pollutants to the sources most responsible for health risks.

RegulationsThe four main outdoor air pollutants – O3, NO2, SO2, and CO gases – are monitored with EPA-approved instruments.  These measurement results are further used to calculate an Air Quality Index (AQI) in combination with data from particle detectors. For indoor air, the volatiles are more use-case specific depending on several factors such as residential versus office buildings, human occupancy, furniture type, ventilation systems. Illustrative volatiles include CO2, formaldehyde, and benzene.

While the importance of monitoring air pollutants is growing, technology solutions have not met yet the expectations of modern customers in data quality and cost effectiveness.   

Sensor Choices

There are two broad categories of gas analyzers for air quality monitoring (AQM). Ranked first, based on the regulatory acceptance, is traditional analytical instrumentation such as gas chromatography (GC), mass spectrometry (MS), chemiluminescence (CL), ultraviolet/visible UV/VIS, laser, and photo-acoustic systems. Over the years, these conventional technologies have achieved superior performance capabilities in field-portable and even wearable formats. However, they are cost-prohibitive for consumer use, have large power demands, and generally require frequent maintenance, limiting their broad adoption for pervasive gas monitoring. Many such instruments are approved or endorsed by the EPA, World Health Organization (WHO) and other national and international organizations.

Ranked second are conventional gas sensors based on design principles ranging from electrochemical and metal oxides (MOx) to pellistors, non-dispersive infrared (NDIR) and many others. Affordable higher performance sensors are needed in order to address diverse gas sensing applications such as consumer-usable indoor and outdoor AQM, medical diagnostics, and homeland security.

In recent years, gas sensor makers have adopted new technologies and manufacturing practices, including non-aqueous electrolytes in electrochemical sensors and microfabricated MEMS technologies for MOx, pellistors, and NDIR sensors. These advances have driven reductions in power, cost, and, most importantly, size – shrinking from the size of a cherry to a grain of rice for some contemporary sensors.  
 

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Identifying Trends in the Gas Sensor Markets

To understand trends in this growing market, the SEMI MEMS and Sensors Industry Group (MSIG) contacted several developers of gas sensor-based systems to see if the current crop of sensor modules meets their needs. Our objective was to identify common pain points that the sensor manufacturers need to address in order to create products for new, demanding applications.

The target applications for the companies surveyed ranged from personal heath monitoring to large-scale environmental monitoring for Smart Cities. Most companies noted that air quality was the main parameter of interest. Although there were various use cases, most companies wanted their applications to work in both indoor and outdoor environments with similar accuracy.

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The survey resulted in no one size fits all solution. Pollutants for indoor and outdoor are different and certain technologies can be better than others at detection.

The survey collected data on individual parameters of the sensors – including accuracy, sizedata rate, power consumption, calibration, and price – and how each impacted their application. The companies included comments on bare sensing elements as well as the sensor systems that include auxiliary components such as calibration, data transfer and sensor logic.

Accuracy: About half of the companies surveyed were satisfied with the accuracy of the sensors available on the market when performing measurements in the absence of confounding gases. Gas sensor manufacturers are working to improve the selectivity of the sensors to the gas of interest and eliminate the interference of other gases. Other problems reported in the survey included drift and calibration.

Gas sensors have been undergoing significant improvement in most key performance parameters in the recent past. New technologies like MEMS increasingly employ a combination of sensor hardware, integrated gas filters, and software techniques to improve performance with the goal to reach performance levels comparable to solutions using traditional analytical instruments.
 

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Multi-gas sensors based on diaelectric excitation. Courtesy of GE Research.

 

Size: The responses ranged anywhere from 3mm x 3mm to 10mm x 10mm for the sensor package footprint. The gas sensor size is dictated by the technology used within the device. Metal oxide sensors can be small, meeting the 3mm x 3mm footprint requirement, while NDIR, electrochemical, and pellistor sensors are larger.

Data Rate: Most companies did not report a preferred data rate, and responses ranged from once per second to once every 10 minutes. As a rule, the data rate of a gas sensor should be comparable to expected time constants of the monitored changes in gas concentrations. For example, Smart Office buildings can detect changes in CO2 concentrations with data rates of once every 1 to 10 minutes depending on the volume of the monitored room and air-exchange speed. By contrast, data rates for detecting sudden changes near bus stops in Smart City urban environments should be about once per second to take into account the dynamics of the outdoor wind patterns.

Power Consumption: With responses ranging from 100 µW to 1 W, we suspect this wide range is attributable to whether the device is battery- or line-powered. Considering the gas sensor as a part of the system, the system power consumption is often a direct trade-off with the data rate, so having a lower data rate helps reduce power consumption. Modern gas sensor system designs optimize power consumption by exploiting sleep mode, power down, or other similar techniques now possible thanks to digital interface and programmability.

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Calibration: Responses applied to the bare sensing elements as well as the sensor systems with stored calibration parameters for specific applications. While most companies wanted the gas sensor system to be calibrated when shipped from the manufacturer, all agreed to an option to perform end-of-line calibration. It is surprising that the companies are willing to do end-of-line calibration before shipping, since this usually adds cost – a willingness indicating that accuracy is highly important, and that companies are willing to work with sensor manufacturers to achieve it.

Price: Companies responses were mixed regarding satisfaction with the current pricing of gas sensors, and varied depending on whether they are purchasing bare sensing elements or the sensor system that including calibration, data transfer, sensor logic, or other features. The expectations ranged anywhere from a couple of dollars for mass-volume consumer devices to over $10 for industrial or automotive use cases. 

Recent gas sensing technology advancements make cost reduction a definite possibility. For instance, MEMS-based solutions that typically use bulk silicon processes have the potential to drive down costs, even though these technologies are not the prevalent gas sensor solutions in use today. Furthermore, most MEMS platforms in non-gas sensors integrate digital functionality, making it easier for them to be controlled by or integrated into larger sensor networks, potentially reducing the total cost of ownership (TCO) of these sensors for end users. The sensor system calibration forms a significant portion of a MEMS and any other sensor system cost, and the industry has identified this step as a key way to reduce cost.

StandardsGas Sensor Testing Standards: When asked about the importance of gas sensor testing standards, most companies supported their use. Gas sensors with well-established performance standards have been available in residential and industrial safety markets for more than half a century. For gas sensor applications targeting various new markets today, standardization helps customers use gas sensors more effectively.

The SEMI MSIG Device Working Group recently released a summary of gas sensor parameters for general standardization to help users and manufacturers of gas sensors when using the common metrics of sensors performance (SEMI MS14, Guide to Critical Parameters of Gas Sensors).

Summary

MedtechMakers of modern gas sensors can draw lessons from sensors that are already bringing high-quality data to low-cost formats. For example, early wearable physiological sensors had poor accuracy that initially went unnoticed due to the excitement over potential applications. However, the industry soon realized that to be broadly accepted and sustainable, wearable physiological sensors needed to a significantly improved accuracy. Thus, the number of wearable sensors with accuracy that matches medical devices or hospital equipment is increasing, for example wearable sensors for electrocardiography (EKG) or electromyography (EMG) and for blood glucose monitoring.

In another example, once the accuracy of physical sensors – such as microphones, accelerometers, gyroscopes, compasses – reached that of in-market solutions, mass markets adopted the devices. For example, ∼1 billion mobile devices ship annually, with adoption driving the price of these sensors to under $1 each.

For the gas sensors revolution to take off, accuracy must also improve. Contemporary cross-disciplinary approaches are also facilitating the development of new gas sensors capabilities and growing markets. Advancements in electronics, gas filters and packaging and on-board data analytics indeed could increase sensor stability and accuracy. More robust predictive models and algorithms using AI technology and on-board data analytics are also greatly improving performance.

About the Authors

HeadshotRadislav Potyrailo is a Principal Scientist at GE Research and Chair of the Device Working Group of the MEMS and Sensors Industry Group, a SEMI Technology Community. Radislav has been leading multiple programs for gas, chemical, and biological detection on inventing new sensing systems and bringing them from lab feasibility studies, to field validation, and to commercialization. He has MS degree in Optoelectronics from Kyiv Polytechnic Institute and Ph.D. in Analytical Chemistry from Indiana University.

HeadshotRyotaro Sakauchi is a Senior Manager at Robert Bosch LLC and is responsible for Business Development of Bosch Sensortec’s MEMS sensors for the consumer market. He has been in the MEMS sensor sector for the last 13 years and has previously held technical and business positions at Bosch’s U.S. and Japan locations. He has a Bachelor’s degree of Liberal Arts from International Christian University in Japan.

HeadshotSreeni Rao is a Senior Director at TDK responsible for its Gas and Environmental Sensing products and business. He has been in the MEMS sensing and semiconductor sector for the last 25 years, and has previously held technical and business leadership positions at Texas Instruments, IBM, Analog Devices, and Qualtre, Inc. He has a Ph.D. in ECE from University of California, Irvine and an MBA from Northeastern University.

HeadshotChristian Meyer is a Senior Product Marketing Manager at Renesas. His roles in the last 18 years included responsibilities in analyzing different gas technologies, as well as sensor development. His background is in Applied Physics and Engineering for Atmospheric Measurements.