Thread-based sensors measure body metrics

Engineers have demonstrated flexible thread-based sensors that can measure neck movements to provide data on the direction, angle of rotation and degree of displacement of the head. 

thread-based sensors
Scanning electron microscopy of carbon ink-coated threads. Straight thread on left. Bending the coated threads creates strain (right), which changes their electrical conductivity – a quantity that can used to calculate the degree of deformation (scale bar 200 microns) (Image: Yiwen Jiang, Tufts University)

The development at Tufts University in Massachusetts raises the potential for thin, inconspicuous tattoo-like patches that could, according to the team, measure athletic performance, monitor worker or driver fatigue, assist with physical therapy, enhance virtual reality games and systems, and improve computer-generated imagery in cinematography.

Thread-based transistors promise fully flexible electronics

Described in Scientific Reports, the technology adds to thread-based sensors developed at Tufts that can be woven into textiles, measuring gases and chemicals in the environment or metabolites in sweat.

According to Tufts, the researchers placed two threads in an “X” pattern on the back of a subject’s neck during experiments. Coated with an electrically conducting carbon-based ink, the sensors detect motion when the threads bend, creating strain that changes the way they conduct electricity. When the subject performed a series of head movements, the wires sent signals to a Bluetooth device, which then transmitted data wirelessly to a computer or smartphone for analysis.

The data analysis involved machine learning approaches to interpret the signals and translate them to quantitate head movements in real-time, with 93 per cent accuracy.

Specialised algorithms will be needed for each location on the body, but the proof-of-principle demonstrates that thread sensors could be used to measure movement in other limbs, according to the researchers. Skin patches or form-fitting clothing containing the threads could be used to track movement in settings where the measurements are most relevant, such as in the field, the workplace, or a classroom.

“This is a promising demonstration of how we could make sensors that monitor our health, performance, and environment in a non-intrusive way,” said Yiwen Jiang, an undergraduate student at Tufts University School of Engineering and first author of the study. “More work needs to be done to improve the sensors’ scope and precision, which in this case could mean gathering data from a larger array of threads regularly spaced or arranged in a pattern and developing algorithms that improve the quantification of articulated movement.”

Other types of wearable motion sensor designs have included 3-axis gyroscopes, accelerometers, and magnetometers to detect movement of the subject in relation to their surroundings. Those sensors are based on inertial measurements and tend to be bulkier and more inconvenient.

In use, a thread sensor patch could alert a lorry driver of fatigue or other situations where tracking operator alertness is critical, monitoring the head movements of someone about to fall asleep. For athletes, thin tattoo-like patches placed different joints could contain motion sensors that detect their physical movement and form, while thread-based sweat sensors could potentially track their electrolytes, lactate, and other biological markers of performance in sweat.

“If we can take this technology further, there could be a wide range of applications in healthcare as well,” said Jiang. “For example, those researching Parkinson’s disease and other neuromuscular diseases could also track movements of subjects in their normal settings and daily lives to gather data on their condition and the effectiveness of treatments.”