Caption: Dr Mengyang Zhu measuring ultrasound in a public place.
On 6 September 2024 the Journal of the Acoustical Society of America published a research paper* co-authored by members of SWT, on the ability of airborne ultrasound to cause unpleasant sensations in people. Safety is a key concern at SWT, and this topic is important to SWT because our devices are ultrasonic, and we have ensured there is no measurable ultrasound emitted into the surrounding air. We also are keen to ensure that there are guidelines in place that industries and building managers can follow in order to ensure the safety of people.
However, many common devices now do emit ultrasound into the air around them, and some do so in public spaces, exposing members of the public, without their knowledge, to airborne ultrasound. Numerous commercial devices do this, and a proportion of the population suffer adverse effects (migraines, headaches, dizziness) as a result. The fact that usually the member of the public did not know the source of the problem, or that they had been exposed to airborne ultrasound, and their colleagues and families occupying the same location at the same time felt no ill effects, led to isolation in sufferers who were disbelieved, or to individuals being labelled in the school or workplace as malingerers or ‘difficult’.
This new paper* compared the response of volunteers to high frequency sound and ultrasound in air. The study quantified the extent to which the volunteers found the higher frequencies more unpleasant than the lower frequencies. It also provided new evidence to support the recent theory that, for people without hearing loss, at the very highest frequencies a person can hear, the sound tends to be unpleasant as soon as it becomes loud enough to hear. This contrasts with the lower frequencies used for speech, where there is a wide range loudness between the quietest sound a person can hear, and the loudness of the quietest sound at the same frequency that they can hear without suffering an adverse reaction. This finding has implications for future guidelines [TL1] used to protect people from airborne ultrasound, on which Professor Leighton has been working.
In 2016, Professor Leighton was the first to publish the extent of how the public were being exposed in this way without their knowledge. He was particularly concerned about the exposure of children, because of their potential to be susceptible, and because they could well not be empowered to improve their situation (especially if the adults around them are unaffected). He brought together the team that just published this 2024 paper.
He advertised how to adapt a smartphone to detect such ultrasound in air, which resulted in the public tracking down sources of problems, from Australia to Japan to the USA. This was particularly beneficial, because with only a minority of the public suffering adverse reactions, they tended to be disbelieved by family and co-workers who occupied the same location at the same time.
* Lineton, B., Al Balushi, R. A. R., Lloyd Jones, S., Leighton, T. G and Fletcher, M. D. (2024) Sensory unpleasantness of very-high frequency sound and audible ultrasound. J. Acoust. Soc. Am., 156 (3), 1565–1574 (doi: 10.1121/10.0028380). The electronic dataset is at https://eprints.soton.ac.uk/492940/.