CNT-based wearable strain sensor relies on light transmittance
The sensor is capable of sensitive, stable, and continuous measurement of physical signals, including subtle human motions for the real-time monitoring of body postures.
Doing away with conventional piezo-resistive strain sensors, the researchers led by Professor Inkyu Park from the Department of Mechanical Engineering designed an optical-type stretchable strain sensor instead, based on the light transmittance changes of a CNT-embedded elastomer.
transmittance changes of the CNT-embedded Ecoflex
thin film.
The new sensor is reported to exhibit high stability and is less affected by environmental disturbances. In order to achieve a large dynamic range for the sensor, Professor Park and his team chose Ecoflex as an elastomeric substrate with good mechanical durability and flexibility, into which they embedded multi-walled CNTs.
Under tensile strain, microcracks propagate within the embedded CNT matrix, changing the optical transmittance of the film which can be measured using a LED on one side and a photodiode on the other side. Such an optical wearable strain sensor has a dynamic range of 0 to 400%, the researchers report, with a sensitivity 10 times higher than conventional optical stretchable strain sensors.
The sensor’s response after 13,000 sets of cyclic loading was stable without any noticeable drift. This suggests that the sensor response can be used without degradation, even if the sensor is repeatedly used for a long time and in various environmental conditions.
Next, the research used the sensor to measure the motion of a bending finger, for robot control. They also developed a three-axes sensor array for body posture monitoring, offering the possibility to monitor human motions with small strains such as a pulse near the carotid artery and muscle movement around the mouth during pronunciation.
This work was supported by the National Research Foundation (NRF) of Korea.
KAIST – www.kaist.edu
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