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Thin, Flexible, Lower-Cost Motion Sensors Developed

Joshua DeGraff

Joshua DeGraff holds printed flexible motion sensor. (Florida State University)

17 November 2017. Engineers in the U.S. and France created and tested motion-detecting sensors more flexible and thinner than today’s sensors, and made with a low-cost process. A team from the High-Performance Materials Institute at Florida State University in Tallahassee and Institut National des Sciences Appliquées, or INSA, in Lyon, France describe the sensors in the November issue of the journal Materials & Design (paid subscription required).

The team led by INSA’s Pierre-Jean Cottinet is seeking highly sensitive wearable sensors for rehabilitation, robotics, and internet-of-things applications that need to capture motions, sometimes subtle,  made by people wearing the devices. Many current motion-detecting sensors on the market, however, are produced like semiconductors, which can detect motions, but are stiff and inflexible. Other motion detectors are made with more flexible metals, but they tend to be less sensitive and require more costly manufacturing processes.

To meet these needs, the INSA-Florida State researchers designed a sensor technology they say provides the needed flexibility for integration into wearable fabrics and sensitivity to detect subtle motions, but can also be produced inexpensively. Their solution uses multi-wall carbon nanotubes known as BuckyPaper, made into films only 7 microns — 7 millionths of a meter — thick. The team made the BuckyPaper sensors with a commercially available ink-jet printer, adding in silver ink electrodes during the printing process.

The result say the researchers is a motion-detecting sensor that is more sensitive than metallic devices, yet still more flexible than semiconductors. The team tested a prototype device woven into a fabric glove for testing, with encouraging results.

“We measure sensors by gauge factor,” says Florida State doctoral candidate and first author Joshua DeGraff in a university statement, “which indicates how much resistance value changes as a material is strained or bent. Our gauge factor has been up to eight times higher than commercial sensors and 75 percent higher than many other carbon nanotube sensors.” Gauge factor is calculated as the ratio of per-unit change in resistance to per-unit change in length.

Tests with the prototype may have proved the concept of the new motion detector, but the device still needs to be refined before it’s ready for commercialization. The researchers want to make the sensor even thinner to better integrate into fabrics, with more real-world testing to guarantee the device fits into the many curves and shapes of the human body.

“We’re not quite there yet, but this is an important step,” adds Richard Liang, director of the High Performance Materials Institute. “Consumers want great quality and affordable prices, and this material provides both of those things.”

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