Carbon-nanotube-based gas detectors paved the way for interchangeable smartphone-savvy sensors.

In 2007, when the Department of Homeland Security (DHS) issued a call for a sensor that could equip a smartphone with the ability to detect dangerous gases and chemicals, NASA Ames Research Center scientist Jing Li had a ready response. She had been developing the use of single-walled carbon nanotubes that respond to various gases and compounds for use in NASA applications such as evaluating planetary atmospheres, detecting chemicals around rocket launch pads, and monitoring the performance of life-support systems. Her proposal was awarded funding in 2008, but she needed a way for the device to “sniff” the air for samples, and a system that would allow it to interface with a smartphone.

The NODE platform can be outfitted with an array of different sensor modules for detecting light, gases, temperature, motion, and more. It can store data or transmit it to a smart device using Bluetooth wireless technology.
Li approached George Yu of Genel Systems. “Genel had the technology to provide a very small sample collection system,” Li said, noting that the company was subcontracted shortly after funding was awarded. In the end, however, that sampling jet proved too noisy, and Li and her team settled on a tiny fan. Then a separate contract for the cellphone interface system fell through. “That contract didn’t work out, so I asked George to do it — I know he is good at electrical circuit design,” Li said.

The team settled on the iPhone, which was new at the time, and Li convinced the DHS program manager that the sensor should be a module attached to the outside of the phone, rather than a system built into the phone’s guts. “This is a very new technology, and there will be a lot of iterations. Making it interchangeable will make it easier to update,” she explained.

This modular design not only paved the way for future smartphone chemical sensors, but also presaged the line of interchangeable, smartphone-savvy sensors Yu commercialized a few years later after founding Variable Inc. in Chattanooga, TN.

Yu figured out how the sensor module could draw its power from the cellphone battery, and use the phone to digitally process the data it gathered and transmit it to a central location such as a cloud platform. Most of the design for the microprocessor, memory, communication protocol, back-end Web structure, data storage, and cloud technology he developed for NASA and DHS under a NASA subcontract would later appear in Variable’s NODE wireless sensor platform.

NODE’s Therma modules detect temperature at a distance, and have proven popular in the food service, auto repair, manufacturing, and home inspection industries.
Ultimately, Li’s team outfitted each of 40 iPhones with a tiny chip containing 32 carbon nanotube sensors that react to potentially harmful chemicals such as ammonia, hydrogen chloride, and chlorine, as well as volatile organic compounds such as benzene. Most of the phones have been delivered to DHS, and are being tested by technical first responders.

“DHS wants to utilize chemical detection technology incorporated with a cellphone to do global or regional chemical detection,” Li said. If firefighters arrive at a scene involving a toxic gas leak, for example, the collective data from multiple firefighters carrying the technology can map the extent and boundary of the chemical hazard.

Building on the integration system he created for DHS, Yu developed his NODE platform — a cylinder not much bigger than a man’s thumb — that transmits data from sensors to a smartphone or other smart device, and that has its own memory port capable of storing data to be uploaded to any computer. Unlike the sensor developed for DHS, NODE operates independently of the cellphone, and transmits the data to the phone or other device using Bluetooth wireless technology.

Variable converted off-the-shelf sensors such as infrared thermometers, motion sensors, and barcode readers into interchangeable modules that can be snapped onto either end of NODE so it can use two modules simultaneously. There is a module for carbon dioxide detection and another that senses gases such as carbon monoxide, chlorine gas, and hydrogen sulfide. Another module measures ambient light, room temperature, humidity, and barometric pressure.

The product line went on the market in 2012, and by summer of 2014, it was in its second generation, NODE+, which is faster, uses less power, has more memory, and is compatible with Android devices as well as Apple smart devices. The sensors have found extensive use in the areas of supply-chain management, transport, and logistics.

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