Artificial electronic skin recognizes surface texture and responds to pressure, temperature and sound
Welcome to the iCover Blog Pages ! A group of professors Hong San Lee from the Dong-A University Busan Institute in South Korea offered their vision of what electronic skin of the future should look like . E-skin or electronic skin - just one of the varieties of artificial leather, which in the future can be used by both humans and robots. How promising is the option proposed by Professor Hon and what are the fundamental differences between his proposed version of artificial electric skin and alternative solutions proposed earlier?
One of the main areas that Professor Hong San Lee’s laboratory is engaged in today is polymer nanomaterials. The nanocomposites obtained within its walls - transparent conductive films, ferroelectric (ferroelectric) films, gas-tight films can already be used in the very near future in various fields, in particular, as part of the construction of an organic LED display or mobile phone display, in prosthetics and robotics .
Artificial Leather
Unlike alternative, already existing versions of artificial leather, E-skin, proposed by a group of South Korean scientists, is made of a ferroelectric material that generates electricity in response to external stimuli, such as pressure, temperature, sound. The structure of the final product, a thin film that senses temperature and pressure, was based on the use of ferroelectric nanocomposites made from polyvinylidene fluoride (PVDF) and reduced graphene oxide, which retains ferroelectric properties even after a processing cycle (alloy formation or casting from a solution) , developed by scientists, without the need for additional "Teasing."
The ability to “feel” the pressure and temperature of a film from such a composite acquires precisely due to ferroelectricity. Two layers of such a film after micro-embossing allow one to obtain a relief structure with significantly improved characteristics of sensitivity to external influences. A ribbed surface, like a pattern on our palm or fingers, gives the skin multifunctionality, which manifests itself in the ability to feel both dynamic and static pressure and temperature effects. The sensitivity of the artificial electronic skin created by a group of Korean scientists, according to Professor Hong, is so great that even one hair lying on it and the surrounding sounds can be felt.
How ferroelectricity is generated
An electric charge in a ferroelectric nanocomposite can be accumulated in polar phases during mechanical action. It was proposed to form polar phases in nanocomposites based on reduced graphene oxide and polyvinylidene fluoride by incorporating PVDF into the structure. The magnitude of the generated voltage is proportional to the ratio of the generated charge to the electric capacity.
Having imitated a fingerprint, scientists linked together the epidermal and dermal structures of human skin. In this case, the inner skin layer included mechanical receptors recording stationary pressure, the rest - fixing pressure changes and vibration. Due to the relief of micro-embossing, a two-layer ferroelectric film acquires increased sensitivity to sound and texture. The resistance of the electronic skin changes when the contact area of the outer and inner layers changes due to changes in the applied static or dynamic pressure.
The ability to respond to temperature changes is generated due to mechanisms similar to those that stimulate the accumulation of electric charge in the polar phases. Thermodynamic changes in the composites lead to a change in the contact resistance between the layers of reduced graphene oxide (rGO), which makes it possible to sense temperature changes.
“Thus, our electronic skin,” says Professor Hon, is multifunctional, like the tip of a human finger, which senses static and dynamic pressure, temperature and texture at the same time. ”
Development in this direction has been ongoing for more than a year and certain results have already been achieved. But it is precisely in multifunctionality that the fundamental difference between electronic artificial leather created by Korean scientists and the options proposed by the scientific community up to this point and providing sensitivity at the level of one or a maximum of two key characteristics consists of dynamic pressure, static pressure and temperature. The development of the Hon laboratory allows us to provide not only all three sensitivity parameters characteristic of human skin, but also the ability to respond to vibrations of sound waves and recognize the features of surface texture.
How electronic skin “feels” sounds
Everything is quite simple. Sound is nothing more than time-varying air pressure. The sensitivity of the electronic skin e-skin, which significantly exceeds the sensitivity of a conventional microphone, is enough to sense changes in such vibrations, to reveal the laws of frequency response and generate the corresponding currents.
The nanocomposites created in Professor Hon's laboratory have reduced electrical resistance due to the distribution of reduced graphene oxide in PVDF and piezoresistive (piezoelectric semiconductor) sensors can also be used as ferroelectric sensors. The material is thermoplastic. Using technology of molding from a melt or casting from solution films, it is possible to force it to take and repeat any shape (for example, micromodel structures) without prejudice to ferroelectric and piezoresistive properties.
Thus, it is possible to create coupled microstructures on a ferroelectric film, which can enhance piezoresistive, piezoelectric and pyroelectric sensitivity to dynamic and static thermomechanical signals. In alternative experiments in which researchers used passive graphene foam, field effect transistors, and polarized ceramic polymers, artificial leather samples with sensitivity to pressure and temperature were used to create artificial leather, Professor Hon said, but there’s no question to reproduce the microrelief while maintaining ferroelectric properties.
Such areas as anthropomorphic robotics, prosthetics, the creation of mobile devices with the function of monitoring human health, the Internet of things, and others are very promising for the use of electronic skin with similar properties. At the same time, depending on the application, it will be possible to shift the focus on the prevalence of the desired properties. For example, the E-skin used in robotics will have to have increased resistance to significant pressure drops without loss of sensitivity, and when used for prosthetics, it should have an additional interface for transmitting signals to the brain.
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