An ultra-thin wearable device capable of reproducing the localized sensation of touch has been developed at the Italian Institute of Technology (IIT) and described in a recent paper published in the journal Advanced Electronic Materials.
The new system, developed by IIT researchers Arianna Mazzotta and Virgilio Mattoli, is an electronic tattoo a few micrometers thick, which is designed to arouse a tactile sensation, thus to generate a force that pushes on the skin of the person who is wearing it, enabling them to perceive a touch.
The research team has demonstrated the functioning of a single 'tactile' dot, and they are working on the implementation of displays that will include several tactile pixels, called taxels, which can be activated independently one from each other, and which will allow reproduction on the skin of letters, numbers, as well as directional and dynamic patterns.
The electronic temporary tattoo — like those used by children — is small and easy to wear, allowing it to be applied in everyday life to generate a very localized force, capable of applying a tactile sensation on the skin to which the device adheres perfectly.
The tactile device is based on an electro-thermo-pneumatic actuation strategy, which consists of electrically heating, in a fast and very localized manner, a small volume of air enclosed between two very thin films. As it expands, the air generates forces and displacements on the skin placed in contact with the tattoo, producing the tactile sensation. Due to its very low thickness, the tattoo is virtually undetectable once transferred onto the skin, which is crucial for its potential final application as a tactile display.
Moreover, unlike most other devices designed and proposed so far to generate tactile sensations through forces and deformations, this system is able to operate powered by a small battery, at low voltages, ensuring complete safety for the person who is wearing it.
Preliminary usage test results showed great promise in terms of functionality, suggesting the use of this technology as a possible new standard in the manufacture of lightweight, portable, and energy-efficient tactile displays.
Here is an exclusive Tech Briefs interview — edited for length and clarity — with Mazzotta and Mattoli.
Tech Briefs: Can you explain in simple terms how it works?
Mazzotta and Mattoli: The structure is very simple: We print on the tattoo paper, an electrode that heats up when activated, thus causing a localized increase of temperature at the center of the device (just below the “white” circle). We created a “pocket” of air thanks to the use of microparticles (white circle) and a very thin layer of a plastic material. The air expands thanks to the increase in temperature, and this causes the movement of the very thin layers which push toward the skin. This movement gives the tactile sensation.
Tech Briefs: I’m certain there were way too many to count, but what was the biggest technical challenge you faced while developing this electronic temporary tattoo?
Mazzotta and Mattoli: One of the biggest challenges was to find a way to trap air between the very thin layers of the device, that is at the base of its working principle. After a few not-very-successful attempts, we came up with the idea to use microparticles (the white circle) to help create space for trapping air in the thin device. The microparticles are deposited on the tattoo substrate, and then covered and encapsulated by a thin plastic membrane.
Tech Briefs: The research article says, “The research team has demonstrated the functioning of a single 'tactile' dot, and they are working on the implementation of displays that will include several tactile pixels, called taxels…” How is that coming along? Any updates you can share?
Mazzotta and Mattoli: Yes, we are developing a new device that includes more active dots. You can think about it as a matrix of taxels — instead of only one, as in the case of the tattoo. The higher number of taxels enables reproducing more complex information like, for example, alphabet characters/numbers (also Braille for visually impaired people) or dynamic patterns for haptic feedback in virtual reality, gaming, or navigation. The new device will be still wearable and low power-consuming.
Tech Briefs: The article also says, “Preliminary usage test results showed great promise in terms of functionality, suggesting the use of this technology as a possible new standard in the manufacture of lightweight, portable, and energy-efficient tactile displays.” How far away from that do you estimate we are?
Mazzotta and Mattoli: We have provided the first proof of concept of the principle that can be used. There is still a lot of work to do toward a full integration of commercially exploitable technology. Nevertheless, we are working in this direction and the temporal horizon could be in the order of few years.
Tech Briefs: Going from that, what are your next steps?
Mazzotta and Mattoli: We are now working to translate the single point actuation strategy used for this electronic tattoo into the fabrication of a more complex tactile display that will be capable of giving a larger amount of tactile information — thanks to a higher number of active points.
Tech Briefs: Do you have any advice for engineers aiming to bring their ideas to fruition?
Mazzotta and Mattoli: Be committed on your idea, do not give up at the first difficulty, be open-minded and be ready to change strategy toward your goal if necessary or if you find some valid alternatives along the way (don’t be afraid to explore new possibilities).
Tech Briefs: Anything else you’d like to add?
Mazzotta and Mattoli: In our group we have some expertise in tattoo electronics. We had already developed an electrode for recording bioelectrical signals by using temporary tattoos, and at certain point we started to think about, not only acquiring signals, but also using them as active devices. In particular, we were playing with the tattoos for heating up some substrates, and we noticed that in certain cases, when a small volume of air remained trapped under the tattoo, a movement occurred when powered. We noticed this and understood that the principle could be used to implement a tattoo haptic device.