You can now add wearable human-motion sensor to the list of uses for carbon nanotubes.
Researchers at the National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba, Japan have created a wearable electronic sensor that can detect human motions such as breathing patterns. The wearable sensor was made using stretchable carbon nanotube films.
Carbon nanotubes are sheets of graphene that have been rolled into a cylinder. They are typically a few microns (millionths of a meter) long and a nanometer (billionth of a meter) in diameter. This high surface area to volume ratio contributes to the high electrical conductivity of the carbon nanotubes, making them useful in applications such as lithium-ion batteries and fuel cells.
The high conductivity is one of the main reasons researchers chose carbon nanotubes to make the new wearable sensor. The sensor consists of single-walled carbon nano tube (SWCNT) films, single rolled up layer of graphene, on top of a polydimethylsiloxane (polymer) substrate. The SWCNT sensor behaves like a single stretchable object because the carbon nanotubes are first aligned perpendicular to the direction the sensors are pulled, improving the film’s stretchiness.
The sensor can be stretched up to 280 percent, meaning it can be drawn out to almost four times the original size. Because the sensor is so flexible, it can be embedded into clothing and does not restrict your motion when you wear it. The sensor can distinguish a range of motions from marching to jumping, simply by taping it onto stockings over the knee joint. This kind of device would be useful for human rehabilitation applications.
Photograph of the wearable sensor used to detect knee motion
The team also used the sensor to monitor human respiration by attaching it directly on the chest to record chest expansion and contraction (inhalation and exhalation). This technology could be used in the future as a breathing monitor for detecting sudden infant death symptom (SIDS) in sleeping infants.
Researchers at Stanford University in California, USA also used carbon nanotubes to make a skin-like sensor that’s stretchable, transparent, and conductive. The sensor can sense touch and also detect pressures of ~50 kPa, which is about the same as pinching your fingers together. The researchers believe their sensor could be used in the future as an implantable device, because it can be stretched and wrapped around a patient’s skin and organs.
Like the wearable sensor developed by AIST, the key to the skin-like sensor’s stretchability is also the aligned single-walled carbon nanotubes; which allow the sensor to keep its properties after being stretched.
Electronic sensors were traditionally rigid devices made from silicon wafers and have now evolved to stretchable sensors made from carbon nanotubes. The wide range of health monitoring and therapeutic applications will continue to the drive the research of stretchable electronic sensors. In the future, a better understanding and control of carbon nanotube alignment will likely lead to sensors with greater stretchability and sensitivity.
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