Symptoms like headache and dizziness, and nausea can be experienced with prolonged exposure to ultrasounds of low frequencies, and may cause some discomfort and lead to hearing damage. But to clearly differentiate the extent of impact due to audible and ultrasonic noise needs to be studied.

Especially in industrial environment where you have different kinds of machines generating various types of sound, and the level of comfort experienced by human beings when suddenly some machines are switched off (although they were not producing any audible noise) while operating, is  clear example of human comfort when ultrasonic noise is not present.

I feel it is a nice interesting topic for research.

K. Sreenivas

It depends on their intensity or amplitude and tieme of exposure. There is a device of frequency around 20 kHz that were used in public squares in France some years ago to keep younger people out of the square at night, the principle of this device is that only younger people could hear that frequency so in emitting a “semi”-high ultrasonic wave (that propagate in air) the younger people couldn’t stay near the source of the sound causing dissing and headcheese, this work in the same way to keep away mice and mosquitoes.

The ultrasound that medicine use in the human body are in the domain of NDT and their intensity is very low, in order to cause small deformations in tissues that don’t break them

However if you use high intensity ultrasound you could have acoustic cavitation, and that could cause damage (i.e, acoustic cavitation bubbles can destroy objects near them) and the HIFU ultrasound also can make damage to the tissues

To add to Szymon's comment.  Mechanical and Thermal indicies and the method by which they are measured are covered by AIUM/NEMA standard UD2 and the IEC standard 606061-2-37.  However these relate to diagnostic ultrasound equipment ONLY.

Therapeutic ultrasound (which is explicitly designed to cause bioeffects) is covered by other standards with separate documents for physiotherapy, lithotripsy and HIFU.

As a correction to Szymon's comment manufacturers of diagnostic ultrasound equipment are only required to display MI and TI if either of these values exceed 1.0. Furthermore MI is NOT intended to evaluate the damage due to tissue rupture.  Instead MI is intended to correlate with the likelihood of a gas emboli undergoing ultrasonically induced cavitation.  Now, whilst I agree that under very high field amplitudes, an intertial cavitation event may cause tissue damage, tissue rupture is not the only form of tissue damage.  Thus MI is intended to advise about the risk of any form of mechanical effects - not just rupture.

As a general observation, diagnostic ultrasound is one of the least harmful imaging methodologies, but its use is predicated upon the principle of ALARA (As Low As Reasonably Acceptable).  As such, ultrasonographers are required to use the lowest output levels they can to achieve the required diagnostic outcome.  However as these are trained professionals, they are expected to use their judgment to assess when diagnostic need justifies higher ultrasonic output levels.  MI and TI are displayed so that this data can form part of their risk assessment

I also whole-heartedly agree with Szymon's closing comment:  that greater study is recommended.  This is a deep subject.  A good starting point may be the text "Ultrasonic Exposimetry" by Marv Ziskin and Peter Lewin

YES and NO. All depends on frequency range,  intencities and conditions. It is necessary know the area of concrete applications of ultrasound you are using

Thank you all

All answers are very interesting and stimulating but still I cannot see a clear answer to the original question. Are ultrasonic waves harmfull to humans ? At what frequency range ? and at what distance from source ? and for how long time of exposure?

The problem is serious as now air conditioners are being manufactured with a built-in ultrasonic device to keep insects away as claimed .

Dear Kamal,

Research in this area is currently in its infancy but there are some interesting research results coming out. I will point you in the direction of a project which our group has recently been involved with - https://www.ptb.de/emrp/ears-project.html.

The aim of one half of this project was to explore whether hearing thresholds could be extended into the infrasound and ultrasound ranges making use of various approaches including looking for brain activation through the use of MEG and fMRI imaging. From the results in this project it is clear that some people are much more affected by low frequency ultrasound than others. At the upper frequency limit of human hearing there is a very steep drop in the sensitivity of the ear but the frequency of onset can vary significantly between different people. As a result some people are very sensitive to frequencies above 20 kHz whilst others have no conscious perception at all. However, a lack of perception does not mean that there is no brain activity. As the MEG ultrasound testing was the last part of the project the full set of results are yet to be published but hopefully they will give us some insight and help with developing improved guidelines on ultrasound exposure.

In conclusion I would say that anecdotal evidence shows that high amplitude ultrasound does have an impact on humans but there is currently not enough research to answer the questions of what frequency range, what amplitude, what exposure time and at what distance. The work in the EARS project is a first step towards developing a dose-response relationship but there is plenty more to be done and if you find personally that you experience negative effects from the presence of an ultrasound source currently the best solution is to avoid the source as much as possible.

Finally, a working group on the health effects of ultrasound in air has recently been formed in the UK, led by ISVR and NPL, to look at this problem - https://sites.google.com/site/hefua2/home

I hope that you find some of this information useful.

Kind Regards,

Ben

Ben

Thank you very much. I do appreciate your prompt response.

The question may be motivated by things like waves of ionizing radiation, which are undeniably harmful. Ultrasonic waves are mechanical, not electromagnetic, and could conceivably be harmful under the right circumstances by their mechanical effects, inducing heat, inducing phase changes that give rise to bubbles, shock effects of high amplitude waves, etc. The ultrasonic waves typically used in laboratory studies are harmless.

Tu sum up, ultrasound have an effect on human tissues, and that is why they are used in medecine. As far as I know (I am not a specialist), it seems that frequencies for these applications are from 0.8 to 3Mhz. The effects are both mechanical and thermical. If applied improperly, it can burn the tissues (I have an exemple of that in my own family) and results in severe injuries.

I have a question to ask to Researchgate community. I am retired Ear ,Nose & Throat Professor from JIPMERy , Medical Institute from Pondicherry, India. I want to know whether multiple " serous bubbles implosions in serous otitis media"-- can cause damages to delicate tissues in middle ear from release of acoustic energy , particularly thin autonomic nerve plexuses in "Shrapnell's membrane area --which do not have insulating myelin sheath.

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