In collaboration with Yamaha Corporation, we have developed a soft sensor that detects movement by expanding and contracting. A composite material in which CNT sheets arranged in one direction are sandwiched by urethane resin is used for sensing. The elastic modulus of the sensor part is 5 MPa or less, which is softer than human skin, and the thickness is 0.2 mm or less, which is very thin. It is a soft rubber-like substance that fits well on clothing and is comfortable to use.
How to use CNT sensor
The electrical resistance of CNT urethane composite rubber increases when stretched. It is used by attaching it to a thing whose shape changes. It measures the change in resistance when it is deformed and senses how much it is deformed.
It can be stretched to twice its original length. There is a good linear relationship between the amount of strain (deformation) and the resistance, and hysteresis is also small. Sensor sensitivity is expressed by a quantity called the gauge factor (GF), which is the resistance change rate divided by the strain. The GF of this sensor is 10 or more, which is highly sensitive compared to general metal strain gauges.
The dynamic characteristics of resistance change with strain are also good. Even when expanded and contracted at 29 Hz, there is no delay in resistance change to strain. This sensor realizes high linearity and responsiveness by sandwiching a rigid CNT with a relatively large diameter between urethane resin layers and dynamically changing electrical contact within a confined area.
Sensing the fine finger motion by “Data glove”
Strain sensors are attached to the joints of the five fingers to detect finger movements. Data is acquired in real-time by wireless communication such as Bluetooth. Until now, there have been methods such as motion capture that detect body movements, but since finger movements are complicated, data gloves can be used to make accurate measurements.
Rapid-response, widely stretchable sensor of aligned MWCNT/elastomer composites for human motion detection
Katsunori Suzuki, Koji Yataka, Yasuro Okumiya, Shingo Sakakibara, Keisuke Sako, Hidenori Mimura, and Yoku Inoue
ACS Sensors 1, pp.817-825 (2016).