June 24, 2022
Anecdotal reports of adverse human effects of industrial ultrasound in air date back to the 1940s. Whilst high levels could produce quantifiable temporary or permanent hearing loss, humans usually encountered lower levels and some reported less quantifiable symptoms: headache, nausea, tinnitus, migraine, an unpleasant feeling of ‘pressure in the ear’. Poor science, and contamination of the sound field by high levels of audio-frequency noise, meant that the slight amounts of credible data (dating from the 1960s) were swamped by the incredible, providing a poor basis for safety guidelines. The best guidelines were produced in 1984, 18 years after the 1960s reports, and these were entitled ‘interim guidelines’ in the expectation that new data would be taken to fill the data gaps that were so evident, and so provide more authoritative guidelines.
In the 37 years from then to today, those data gaps have not been filled. About 8 years ago, members of the public approached the author complaining of adverse effects in public spaces (museums, shops, railway stations etc.) and on inspection, these were shown to contain airborne ultrasound that was exposing the public without their knowledge. Guidelines for public exposures need to take into account the fact that, unlike industrial exposure, the age range, medical history, susceptibility, pre-existing conditions, and duration of exposure cannot be known or logged, and there is no possibility of monitoring for adverse during exposure, or offering hearing protection. The plethora of devices emitting ultrasound in air had arisen from the fall in price of powerful emitters and digital signal processing and control, and their deployment resulted from the mistaken belief that the lower frequency limit for ultrasound is 20 kHz, and that humans cannot hear above this (both of which are untrue). The devices range from the expected (e.g. rodent and bird deterrents, automatic door opening systems), to the unexpected (e.g. covert surveillance of an individual’s viewing habits at home). Some cannot work without exposing humans to high levels of ultrasound (e.g. acoustic spotlights, deterrents to keep teenagers from luxury stores, haptic feedback systems).
Interest in the topic increased with the unvalidated attribution, from 2017, of ultrasound in reports of attacks on the USA Embassy in Cuba.
This presentation will outline how the convolution of myth and data led to a state where public exposures are being undertaken without warning, how the real phenomenon might be distinguished from misinformation, to what extent the protecting guidelines are inadequate, and the experimental challenges in filling the data gaps to correct this situation.
Timothy Leighton FRS FREng FMedSci ScD is the founder and Chair of the Global Network for AntiMicrobial Resistance and Infection Prevention (Global-NAMRIP). He is Professor of Ultrasonics and Underwater Acoustics at the University of Southampton; and the Executive General Director and Inventor-in-Chief of Sloan Water Technology Ltd., a UK manufacturer and R&D establishment founded on his patents. A fellow of three National Academies, he has been awarded 8 international medals, and 6 international prizes. His fundamental discoveries have led to changes in practice, and the introduction of new technology, for ocean and space exploration; for climate change prediction; for infection prevention and pandemic research; for the safety of human exposure to ultrasound; for marine mammal communications and behaviour; for the treatment of osteoporosis, kidney disease and migraine; and for advanced radar and sonar. The Institute of Physics Paterson medal citation (2006) describes “Timothy Leighton’s contribution is outstanding in both breadth and depth. He is an acknowledged world leader in four fields”.