Precise mass flow enables novel pollution sensing technologies

Alicat Mass Flow provides accurate control of gasses under test

The growth of the IoT (Internet of Things) is driving the need for smaller and more ubiquitous sensors. Normally, one thinks of optical or electrical sensors in this context. This type of measurement has typically been in the province of automotive and process control industries and is largely unavailable at the consumer level. Presently, IoT is creating a need for low-power, low-cost gas sensors that can be utilized for consumer level applications. There are potential applications in the area of household air-quality monitoring, personalized healthcare, breath analysis and a multitude of other applications. However, existing sensors that could be used for these applications are generally not suitable due to large size, higher power demands and/or high cost. There are a number of competing technologies focused on providing sensors for this market; one of the most promising sensor types is the field-effect transistor (FET). In a recently published paper, Fahad et. al. describe a novel FET that promises to meet many of the requirements where existing sensors fall short. Many of the experiments described in the paper require highly accurate mass flow of measured gases – precisely provided by a set of Alicat mass flow controllers. 1

Fahad et. al. demonstrate a novel chemically-sensitive FET capable of detecting H2S as low as 10ppb. Sulfur Dioxide is an invisible gas that readily forms harmful compounds, including sulfuric acid and sulfate particles. Sulfur dioxide is a toxic air pollutant and is especially dangerous to asthma sufferers. The US, in particular, has made great strides in reducing sulfur emissions from powerplants. However, in excess of 500 million tons were still produced in 2011 from powerplants and other sources. 2 The same series of experiments showed detection of NO2 down to 1ppm levels.  Nitrogen Dioxide is another common air pollutant that can impact personal health.  NO2 reacts with other airborne substances to form particulate matter and ozone, both of which have significant negative effects on respiratory health.  The US EPA has recently tightened standards for NO2. These newer standards will require increased monitoring of ambient air levels to ensure compliance. Implementing these new standards will, in turn, require increased training and proper calibration of equipment used to ensure the required accuracy. Alicat makes a range of products specifically designed to help state and local environmental analysts and technicians ensure the needed levels of accuracy.3

These experiments demonstrate the efficacy of the novel low-power FET sensor. The experiments were conducted using known gasses from commercial suppliers; control of the gas input was critical to making accurate assessments of FET function. Alicat Scientific Mass Flow Controllers were used to ensure the accuracy of these measurements by precisely regulating the input flow of the gas mixture. The extremely high controllable range of Alicat’s mass flow meters allowed control of flow rates from 1-100 sccm. Our latest flow controllers boast an increased controllable range of up to 10,000:1, which can be helpful for any experiment where a range of flow rates is required.

As scientists and engineers continue to develop novel sensors to enable IoT technologies, precise, reliable mass flow will continue to be required. At Alicat, increasing the pace of scientific innovation is our greatest passion. All of our instruments are custom built to the needs of your science and ship in days, months.

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1) “Room temperature multiplexed gas sensing using chemical-sensitive 3.5-nm-thin silicon transistors” Fahad HM, Shiraki H, Amani M, Zhang C, Hebbar VS, Gao W, Ota H, Hettick M, Kiriya D, Chen YZ, Chueh YL, Javey A. Science Advances  24 Mar 2017: Vol. 3, no. 3, e1602557 DOI: 10.1126/sciadv.1602557

2) “Sulfur Dioxide Emissions.” Sulfur Dioxide Emissions, US EPA, 2014,

3) “Ambient Air Monitoring.” Alicat Scientific,