Electronic skin mimics human-like sense of touch
Inspired by human skin, Chinese researchers have constructed a tactile sensor that detects pressure and pulses, replicating the experience of pressurised human touch.
Described in the journal Science Robotics, the technology may represent a critical step forward in the development of smart prosthetics that can functionally replace — or potentially even surpass — the sensing ability of natural limbs.
Human skin perceives pressure as part of touch, which is subsequently transformed into signals to nerves that finally reach the brain, creating a pulse-like feeling. Restoring this sense of pressurised touch remains an important feature needed to make artificial limbs more lifelike and thus more acceptable for their users.
Yuanzhao Wu and colleagues from the Chinese Academy of Sciences developed an ‘e-skin’ that can convert pressure from touch to internal electric signals. Based on giant magneto-impedance (GMI) material embedded with an air gap, the skin encases a magnetic sensor and is composed of a hollow polymer membrane with magnetic particles on its top surface.
When pressure is applied to the magnet-dotted membrane roof, the membrane inverts, causing the magnetic particles on the top to inch towards the magnetic sensor on the inside. The resulting resistance created is transmitted as signals using an electrical circuit, and these signals are converted as pulses with various frequencies that increase with greater pressure.
Mounted on a mechanical arm, an artificial finger equipped with the e-skin was able to perceive the subtlest touches, such as the wind blowing. In subsequent experiments, the e-skin was also able to detect and pulse in response to drops of water that contained different volumes, as well as a moving trail of ants. In some cases, the pulses responded to pressures exceeding even the sensing threshold value of humans.
“The proposed tactile sensor not only showed desirable sensitivity and low detection limit but also exhibited transduction of digital-frequency signals like human stimuli responses,” the researchers wrote. “These features of the GMI-based tactile sensor show potential for its applications in smart prosthetics, especially prosthetic limbs that can functionally replace natural limbs.”
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