A group of independent researchers built a device that can artificially induce smell using ultrasound, with no consumable cartridges required.
Current virtual reality is focused on stimulating your vision and hearing, with some limited haptics depending on exactly what accessories you’re using, leaving your other senses untouched.
One such sense not addressed with today’s technology, with extremely niche exceptions, is smell. Scientists describe smell as the most primal sense, with the olfactory nerve directly connecting to your limbic system, bypassing your higher-level cerebral cortex that other senses pass through first. The limbic system includes the hippocampus, where memories are formed, which is why smell can often trigger vivid recall of old memories in a far more visceral way.
One could argue that even when the Visual Turing Test is eventually passed, your subconscious won’t truly feel like it’s in another place if you’re still smelling the physical room you’re in, with the smells that should be coming from the virtual world entirely absent.
David Matthews
There have been many attempts to solve this over the years. Famously, long before modern virtual reality, in the 1950s, systems with branding like “Smell-O-Vision” and “AromaRama” wanted to bring smell to theaters, with very poorly received results, leaving them short-lived, though recently some “4D cinemas” have started doing the same for a few films.
Riding the VR hype wave spawned by the launch of the Oculus Rift and HTC Vive in 2016, multiple startups tried to bring smell to VR as a widespread clip-on accessory for headsets, including Feelreal and Vaqso, but all of them failed, beyond some niche medical use cases.
The reason all these attempts failed is that they relied on physically emitting chemicals towards your nose, typically from aromatic liquid cartridges. As well as putting them in the same strict regulatory space as e-cigarettes, presenting significant legal roadblocks, this also requires the user to continuously buy refills, inherently limits which smells can be represented, and means that some smells will linger far too long. It’s simply not a viable approach for smell to become a widespread part of virtual reality.
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That’s why the new approach of a small group of independent researchers seems so promising and is arguably revolutionary. When I say “new”, I should be clear that the team first presented this in November, but we think it’s more than worth bringing to your attention regardless.
The team of four are Lev Chizhov, Albert Yan-Huang, Thomas Ribeiro, Aayush Gupta. Chizhov is a neurotech entrepreneur with a background in math and physics, Yan-Huang is a researcher at Caltech with a background in computation and neural systems, and Ribeiro and Gupta are co-researchers on the project with software engineering and AI expertise.
Instead of targeting your nose at all, the device directly targets the olfactory bulb in your brain with “focused ultrasound through the skull”. The researchers say that as far as they’re aware, no one has ever done this before, even in animals.
A challenge in targeting the olfactory bulb is that it’s buried behind the top of your nose, and your nose doesn’t provide a flat surface for an emitter. Ultrasound also doesn’t travel well through air. The solution the researchers came up with was to place the emitter on your forehead instead, with a “solid, jello-like pad for stability and general comfort”, and the ultrasound directed downward towards the olfactory bulb.
To determine the best placement, they say they used an MRI of one of their skulls to “roughly determine where the transducer would point and how the focal region (where ultrasound waves actually concentrate) aligned with the olfactory bulb (the target for stimulation)”.
We found our “sweet spot” to be low-frequency ultrasound focused right below the forehead and angled downward toward the bulbs. Specifically:
• 300 kHz frequency (low enough to penetrate the skull well)
• Focal depth of about 39 mm (where the ultrasound energy converged beneath the forehead)
• 50–55° steering angles (to point the focus down toward the bulbs)
• 5-cycle pulses at a 1200 Hz repetition rate (short, rapidly repeating bursts)
According to the researchers, they were able to induce the sensation of fresh air “with a lot of oxygen”, the smell of garbage “like few-day-old fruit peels”,
an ozone-like sensation “like you’re next to an air ionizer”, and a campfire smell of burning wood.
“We distinguish between a smell and a sensation here because, subjectively, they feel different. The smells are strong and localized to the noise, almost like you could sniff around and find the source. The sensations are more diffuse: a weak, slow-onset impression of a smell, often paired with other (likely placebo) feelings, such as a light tingling on the face.
Both smells and sensations are strongest on a light in-breath, so we tested by sitting there, with a probe to the forehead, mildly sniffing. Sometimes there is a slight waft of a smell that comes on over a few breaths, and sometimes it just hits you. The first time Albert smelled the garbage, he jerked his eyes open thinking a garbage truck just drove in!”
While technically head-mounted, the current device does require being held up with two hands. But as with all such prototypes, it likely could be significantly miniaturized.
Fascinatingly, but somewhat outside our purview, the researchers also speculate that their approach could be used for far more than VR. Current functional BCI (brain computer interface) systems are squarely focused on reading from the brain. This approach, technically sending signals to the brain, falls into the realm of writing to the brain non-invasively – the stuff of science fiction. While admitting that the idea is “speculative”, they suggest that a more advanced implementation of their approach might be able to go far further than smell, given the olfactory bulb’s direct connection to key regions of the brain.
In a far less theoretical future though, the approach explored by these researchers could allow future headsets to induce smells without refills. While it’s unlikely that anyone in the consumer space will find the cost of this worth it any time soon, it’s not out of the question that an enterprise headset maker could tackle this in coming years – something we’ll keep a close eye out for.
