Scientists have developed a new type of electronic skin that can detect touch, pressure and even nearby objects, while allowing its sensitivity to be electronically adjusted.
The technology could eventually give robots and prosthetic limbs a more sophisticated sense of touch and make interactions between people and machines safer.
The research was led by Associate Professor Jaekyun Kim of Hanyang University in South Korea and published in the journal Nano Energy.
Electronic skin, sometimes called e-skin, uses thin and flexible sensors to imitate some of the sensing abilities of human skin. Researchers hope such technology could one day allow robots to handle delicate objects, help prosthetic limbs respond to their surroundings and improve wearable health-monitoring devices.
One promising technology for electronic skin is the triboelectric nanogenerator, or TENG. These devices turn mechanical actions, such as touching, pressing or separating two surfaces, into electrical signals. The basic effect is similar to the static electricity that can build up when different materials rub against each other.
However, existing triboelectric sensors have important limitations. Their sensitivity can be difficult to adjust, and their designs can take up too much space when thousands of individual sensors need to be combined into a large surface.
The researchers addressed these problems by creating a vertically stacked sensor containing a special transistor with two electrical “gates.” The design allows different components to be placed on top of one another rather than spread across a larger area, potentially making it easier to build dense arrays of sensors.
The upper sensing layer is made from a flexible silicone-like material called PDMS. When a metal surface touches this layer, electrical charges build up where the two materials meet. As the metal moves away, these charges create an electrical voltage that changes the amount of current flowing through the transistor underneath.
When an object approaches the surface again, the electrical conditions gradually change. By measuring the resulting change in current, the sensor can determine whether something has touched the surface or is simply very close to it.
The second, lower gate provides another important ability: adjustable sensitivity. Researchers can change the voltage applied to this gate to control the sensor’s starting electrical current. Increasing the voltage makes the device more sensitive.
The sensor can also detect differences in pressure. Pressing harder creates a larger contact area with the sensing surface, producing more electrical charge and a stronger signal.
In tests, the device responded in 127 milliseconds and recovered in 212 milliseconds. It continued working reliably after 1,000 contact-and-release cycles.
The team also built a 10-by-10 array containing 100 individual sensing points. It successfully detected finger touches at specific locations and sensed a metal probe approaching from distances of up to 500 micrometers, or half a millimeter.
The researchers believe the compact design could eventually allow much larger and denser electronic skin systems to be produced.
Such technology could help future robots, prosthetic devices and wearable electronics sense their surroundings more precisely, bringing machines another step closer to having a practical artificial sense of touch.
