Virtual reality is already widespread in entertainment and is beginning to expand into areas ranging from education to healthcare. But while visual and auditory interfaces are extremely advanced and touch, or “haptics,” improves, one key sense is missing from the virtual world: smell.
That may be about to change. Engineer Xinge Yu from City University of Hong Kong and colleagues have developed a lightweight, flexible and wireless scent interface that can accurately deliver scents such as lavender, pineapple or green tea to virtual reality users and immersing them more completely in scented virtual worlds. “Bringing scent into virtual reality extends it into another dimension,” says Yu. “We wanted to develop something in a portable, skin-integrated format that people can go anywhere and use at any time.”
The design of the team was described in an article published Tuesday in Nature Communication. A key advantage is that it can control the intensity of odors. One demonstration of the study involved increasing the intensity of the smell generated when a woman in a four-dimensional film held a rose to her nose.
Previous olfactory interfaces typically used bottles of liquid perfume, an atomizer (a device that turns liquids into a fine mist), and a method for blowing out the atomized droplets. It works, but it’s stiff and has a limited run time between recharges, and it doesn’t easily control the intensity. These drawbacks have made the devices less practical for VR systems.
The new design uses small scent-infused paraffin wax pads that are heated by an electrode to release a scent. A temperature dependent resistor, or thermistor, senses temperature, which controls the intensity of the odor. And a magnetic induction coil controls a metal plate that conducts heat away from the electrode to quickly cool it and extinguish the smell. Arrays of these smell generators, which measure millimeters, are embedded in thin, flexible sheets of electronics.
The study describes two different device formats. The first is small enough to stick to a user’s upper lip, but it only includes two scent generators. The second is worn as a face mask and has nine. Both are customizable with a selection of 30 scents, including gardenia, caramel, ginger, clove, mojito, and coconut milk. Different combinations can be mixed at varying intensities to create a palette of thousands of possible scents.
Proximity to the user’s nose, combined with clever engineering, allows delays between activation and reception of a scent as short as 1.44 seconds. Atomizers are faster than that, but they don’t have the control of new devices and are as small as they’ll ever be, says Judith Amores, senior researcher at Microsoft Research and affiliated with the Massachusetts Institute of Technology, who studies olfactory interfaces for health applications but did not participate in the study. “One advantage of this system is that they could miniaturize it even further,” she says. “That’s what’s exciting.”
The study includes demonstrations of possible applications beyond simply augmenting virtual reality, including communicating messages through smell and evoking emotions. The researchers suggest the devices could even be used to alleviate depressed mood or aid recall in people with age-related cognitive decline. “Scent is directly linked to the emotional and memory parts of the brain, so there are many applications related to well-being and health,” says Amores. “It could also be used as a way to do scent training to help people who have lost their sense of smell due to COVID.”
Researchers have already started narrowing things down further. They have a system that’s two to three times smaller now, and they’re aiming to shrink it down to something five to ten times smaller in the future. “That’s the next step,” Yu said.
