Lightweight, flexible patch conveys a tactile sensation directly to the skin

Adding a sense of touch can make virtual reality experiences feel more real.

A woman sits at a computer, video chatting with her young son while she gently pats an interface on a separate screen. In response, a wireless patch on the child’s back vibrates in a pattern that matches his mother’s fingers, allowing him to “feel” her physical touch.

The new patch is a type of haptic device, a technology that remotely conveys tactile signals. A common example is video game controllers that vibrate when the player’s avatar takes a hit. Some researchers think more advanced, wearable versions of such interfaces will become a vital part of making virtual and augmented reality experiences feel like they are actually happening. “If you take a look at what exists today in VR and AR, it consists primarily of auditory and visual channels as the main basis for the sensory experience,” says John A. Rogers, a physical chemist and material scientist at Northwestern University, whose team helped develop the new haptic patch. “But we think that the skin itself—the sense of touch—could qualitatively add to your experience that you could achieve with VR, beyond anything that’s possible with audio and video.”

Scientists, technology companies and do-it-yourself-ers have experimented with wearable haptic devices, often vests or gloves equipped with vibrating motors. But many of these require heavy battery packs connected by a mess of wires. Because of their weight, most have to be attached loosely to the body instead of adhering securely to the skin. So, Rogers and his colleagues developed a vibrating disk, only a couple millimeters thick, that can run with very little energy. These actuators (a term for devices that give a system physical motion) need so little energy that they can be powered by near-field communication—a wireless method of transferring small amounts of power, typically used for applications like unlocking a door with an ID card.

“The power required for mechanical actuators has oftentimes been a limiting factor to making really massive and scalable use of these technologies in mobile applications,” says Jürgen Steimle, a computer scientist at Saarland University in Germany, who was not involved in the new patch project. The researchers “state that the individual actuators require less than two milliwatts of power, which is more than an order of magnitude less than what is typically used in prior work…. And this is a step change in my opinion, because it allows us to create new types of mobile devices that could be both effectively driven with a battery or they could even, like in this case, use wireless powering.”

The resulting product looks like a lightweight, soft patch of fabric-like material that can flex and twist like a wet suit, maintaining direct contact with the wearer’s skin as their body moves. It consists of thin layers of electronics sandwiched between protective silicone sheets. One layer contains the near-field communication technology that powers the device. This can activate another layer: an array of actuators, each of which can be activated individually and tuned to different vibration frequencies to convey a stronger or weaker sensation. This stack of electronics, slightly thinner than a mouse pad, culminates in a tacky surface that sticks to the skin. The device is described in a Nature paper published Wednesday.

Rogers notes that aspects of this technology already exist in other devices, but he says his group’s patch combines them in a new way. “The miniaturized actuators; the wireless control strategies; the thin, flexible, soft construction; the soft, gentle interface with the skin; the battery-free operation—this is a collection of technology features that we don’t think have been reported in the past,” he says. “When you put them all together, you end up with a completely different type of platform that I think will serve as a really powerful starting point for what could ultimately be a full-body suit where you have maybe 1,000 actuators and they’re all controlled simultaneously, with a form factor that people are actually going to want to use.”

Steimle points out that other teams have developed thinner actuators, but those used different methods of stimulating the skin. Modules that physically vibrate “tend to be heavy, rigid, bulky, and power-hungry, because you need to have this mechanical movement that is that is realized,” he says. “Within the constraints of mechanical movement, this is outstanding work.”

So far, the researchers have tested prototype patches of different shapes and sizes to fit on various parts of the body—a circular one for the back of the hand and an X-shaped one for the upper back, for example. In one demonstration a family video-chatted while using the patch to touch remotely. In another, a lower-arm amputee gripped a beer koozie with his prosthetic hand. Each fingertip was equipped with sensors that communicated with a patch on his upper arm, providing tactile information about the object his robotic arm was holding. Finally, a test subject wore multiple haptic patches while playing a combat video game, so virtual strikes on his avatar’s limbs could be transmitted to the corresponding parts of his real body.

Although Rogers and his colleagues have established a start-up business to potentially commercialize their device, they say this is not the focus of their continuing research. In the near future, Rogers says, they hope to make the patch lighter, thinner and more flexible. They are also experimenting with its sensitivity: because the actuators can be tuned to vibrate at frequencies to which the skin is more or less perceptive, they could theoretically convey a stronger or weaker touch (although that would require a more refined system for inputting the signal, one that could distinguish a gentle stroke from a rougher push). Rogers also thinks future versions of the haptic patch could produce more types of sensations. In addition to a perpendicular touch on the skin, it might be able to convey a twisting motion or a temperature change.

“I think the application space is quite versatile, and it’s also quite obvious that we need this type of tactile output,” Steimle says. He notes that the most common commercially available haptic devices are smartphones, which just have two modes: vibrating or not vibrating. “And of course, this is not very expressive; it is not really doing justice to us human beings and how we touch, how we feel, how we perceive the world around us,” he says. “Anything that helps us improve the expressivity of the tactile channel, the haptic channel, will help us realize more advanced computing interfaces in the future.”

Via ScientificAmerican.com