An international team of researchers led by Dr. Sungwon Lee and Professor Takao Someya of the University of Tokyo's Graduate School of Engineering has developed a nanofiber-type pressure sensor that can measure pressure distribution of rounded surfaces such as an inflated balloon and maintain its sensing accuracy even when bent over a radius of 80µm, equivalent to just twice the width of a human hair. The sensor is roughly 8µm thick and can measure the pressure in 144 locations at once.
The device demonstrated in this study consists of organic transistors, electronic switches made from carbon and oxygen based organic materials, and a pressure sensitive nanofiber structure. Carbon nanotubes and graphene were added to an elastic polymer to create nanofibers with a diameter of 300nm to 700nm, which were then entangled with each other to form a transparent, thin and light porous structure.
According to the researchers conventional pressure sensors are flexible enough to fit to soft surfaces such as human skin, but cannot measure pressure changes accurately once they are twisted or wrinkled, making them unsuitable for use on complex and moving surfaces. Additionally, it is difficult to reduce them below 100µm thickness because of limitations in current production methods.
Figure: University of Tokyo - Flexible organic pressure sensors
This work was conducted in collaboration with the research group of Professor Zhigang Suo at Harvard University, USA.
Japan Science and Technology Agency (JST) Exploratory Research for Advanced Technology (ERATO) Someya Bio-Harmonized Electronics Project
Sungwon Lee, said, "We've also tested the performance of our pressure sensor with an artificial blood vessel and found that it could detect small pressure changes and speed of pressure propagation." Sungwon Lee added, "Flexible electronics have great potential for implantable and wearable devices. I realized that many groups are developing flexible sensors that can measure pressure but none of them are suitable for measuring real objects since they are sensitive to distortion. That was my main motivation and I think we have proposed an effective solution to this problem."
Sungwon Lee | Amir Reuveny | Jonathan Reeder | Sunghoon Lee | Hanbit Jin | Qihan Liu, Tomoyuki Yokota | Tsuyoshi Sekitani | Takashi Isoyama | Yusuke Abe | Zhigang Suo | Takao Someya
Nature Nanotechnology (2016) | doi:10.1038/nnano.2015.324
Received 07 January 2015 | Accepted 11 December 2015 | Published online 25 January 2016
Measuring small normal pressures is essential to accurately evaluate external stimuli in curvilinear and dynamic surfaces such as natural tissues. Usually, sensitive and spatially accurate pressure sensors are achieved through conformal contact with the surface; however, this also makes them sensitive to mechanical deformation (bending). Indeed, when a soft object is pressed by another soft object, the normal pressure cannot be measured independently from the mechanical stress. Here, we show a pressure sensor that measures only the normal pressure, even under extreme bending conditions. To reduce the bending sensitivity, we use composite nanofibres of carbon nanotubes and graphene. Our simulations show that these fibres change their relative alignment to accommodate bending deformation, thus reducing the strain in individual fibres. Pressure sensitivity is maintained down to a bending radius of 80 μm. To test the suitability of our sensor for soft robotics and medical applications, we fabricated an integrated sensor matrix that is only 2 μm thick. We show real-time (response time of ∼20 ms), large-area, normal pressure monitoring under different, complex bending conditions.Links