Artificial electronic skin recognizes surface texture and reacts to pressure, temperature and sound
Welcome to the pages of the blog iCover ! The group of Professor Hon San Lee from the Dong-A University Busan Institute in South Korea offered their vision of how the e-skin of the future should look. E — skin or electronic skin is just one of the varieties of artificial leather, which in the future can be used both by humans and by robots. How promising is the version proposed by Professor H. and what are the fundamental differences between the version of artificial electric skin offered by him and the alternative solutions proposed earlier?
One of the main areas in which the laboratory of Professor Hon San Lee is today is polymeric nanomaterials. Nanocomposites produced in its walls - transparent conductive films, ferroelectric (ferroelectric) films, gas-tight films can be used in various fields in the very near future, in particular, as part of the design of an organic LED display or mobile phone display, in prosthetics and robotics .
Professor Hon's artificial leather
Unlike alternative, already existing variants of artificial leather, the 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 used by scientists developed ferroelectric nanocomposites from polyvinylidene fluoride (PVDF / PVDF) and reduced graphene oxide, which retains its ferroelectric properties even after a processing cycle (forming from an alloy or casting from a solution) without the need for additional “Teasing”.
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The ability to “feel” the pressure and temperature of the film from such a composite becomes due to the ferroelectricity. Two layers of such a film after micro-embossing make it possible to obtain a relief structure with significantly improved sensitivity to external effects. The ribbed surface, like the pattern on our palm or fingers, gives the skin multifunctionality, which manifests itself in the ability to feel both dynamic and static pressure, as well as temperature effects. Sensitivity created by a group of Korean scientists of artificial e-skin, according to Professor Hon, is so great that one can even feel the hair lying on it and the surrounding sounds.
How ferroelectricity is generated
Electric charge in a ferroelectric nanocomposite can be accumulated in polar phases under mechanical action. Polar phases in nanocomposites based on reduced graphene oxide and polyvinylidene fluoride were proposed to be formed by incorporation of PVDF into the structure. The magnitude of the generated voltage is proportional to the ratio of the charge to the electric capacity.
Having simulated a fingerprint, the scientists tied the epidermal and dermal structures of human skin together. At the same time, the inner skin layer included mechanical receptors recording stationary pressure, the rest - fixing changes in pressure 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 with changes in the contact area of ​​the outer and inner layer due to changes in the applied static or dynamic pressure.
The ability to react to temperature changes is generated due to mechanisms similar to those that stimulate the accumulation of electric charge in polar phases. Thermodynamic changes in composites lead to a change in the contact resistance between the layers of reduced graphene oxide (rGO), which makes it possible to sense changes in temperature.
“Thus, our e-skin,” says Professor Hon, is multifunctional, like the tip of a human finger that senses static and dynamic pressure, temperature and texture at the same time.
Developments in this direction have been carried out for more than a year, and certain results have already been achieved. But it is precisely in the multifunctionality that the fundamental difference of electronic artificial leather, created by Korean scientists from the options proposed by the scientific community up to this point and providing sensitivity at the level of one or at most two key characteristics: dynamic pressure, static pressure and temperature, is. The development of the Khon laboratory allows not only to ensure all three parameters of sensitivity characteristic of human skin, but also the ability to respond to fluctuations in sound waves and to recognize features of the surface texture.
How e-skin "feels" sounds
Everything is quite simple. Sound is nothing more than time-varying air pressure. The sensitivity of an e-skin e-skin, which greatly exceeds the sensitivity of a conventional microphone, is enough to sense changes in such oscillations, identify patterns of frequency response and generate the corresponding currents.
Nanocomposites created in Prof. Hohn's laboratory have a reduced electrical resistance due to the distribution of reduced graphene oxide in PVDF and piezoresistive (piezo-semiconductor) sensors can be used as ferroelectric sensors. The material is thermoplastic. Using the technology of molding from the melt or casting from the solution films, it is possible to make it accept and repeat any shape (for example, micro-model structures) without harming the ferroelectric and piezoresistive properties.
Thus, it is possible to create cohesive microstructures on a ferroelectric film, which allow to enhance the piezoresistive, piezoelectric and pyroelectric sensitivity to dynamic and static thermomechanical signals. In alternative experiments, in which the researchers used passive graphene foam, field-effect transistors, and polarized ceramic polymers, artificial skin samples that are sensitive to pressure and temperature were obtained in the creation of artificial skin, Professor Hon said, but to reproduce the microrelief with the preservation of ferroelectric properties.
Such areas as anthropomorphic robotics, prosthetics, the creation of mobile devices with the function of monitoring the state of 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 emphasis on the predominance 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 being used for prosthetics will have an additional interface for transmitting signals to the brain.
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Source: https://habr.com/ru/post/391515/
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