Why are some broadband routers emitting ultrasound?

Mostly buzzing and feezling of ferrite cores in switching  step-down regulators. The mains is stepped down to 12V or something that can sensibly be piped a few metres, but inside the router a no of other voltages are required for logic  typically 3.3V 5V and perhaps higher voltages for a pseudo phone line if one is fitted.

At each stage, where there is a voltage change, a linear regulator would have to dissipate significant heat, and a switching design is more suitable.

some theory 
https://learnabout-electronics.org/PSU/psu31.php  stepping down

https://learnabout-electronics.org/PSU/psu32.php stepping up.

Usually the raw switching is at a far higher frequency, typically hundreds of kHz, with fast switching MOSFETs in modern commercial electronics, (or in military stuff, low MHz and gallium nitride devices....) 

What happens with many such stages on a common supply is that there are beat frequencies generated between them and these are however lower, and quite often in the region you suggest. Additionally, loads vary with network traffic and flashing lights etc and this leads to additional lower frequency modulation of the switching wave-forms. Also when lightly loaded some deigns can  'squegg' i.e. stop altogether when the output target is exceeded, and then restart as the voltage on the reservoir capacitor falls leading to burst of a a few cycles of operation interspersed with pauses again this can occur at lower ultrasound frequencies but in a very hard to predict way.

The main acoustic generation mechanism is magnetostriction in inductors (the same same reason 50Hz transformers buzz at 50Hz and click and thud when switched on and off), additionally some semiconductors and certain designs of ceramic capacitor are mildly piezo electric.

Mike.

Thanks Mike for your answer, much appreciated.

That's how, now it's a question about whether the designers of these switching electronic circuits and the companies that sell or pass on devices using these circuits (I fear lots more than just broadband routers) know what they are inflicting upon the public? For the record, ultrasound is known to cause the following symptoms:

• Fatigue
• Persistent headache
• Migraine
• Nausea
• Tinnitus
• Sensation of fullness or pressure in the ears
• Dizziness
• Light-headedness
• Anxiety
• Temporary or permanent hearing threshold shifts

Ref: International Commission on Non-Ionizing Radiation Protection (ICNIRP). "Validity of the 1984 Interim Guidelines on Airborne Ultrasound and Gaps in the Current Knowledge". Health Phys. 2024 Aug 1;127(2):326-347. doi:10.1097/HP.0000000000001800  Epub 2024 May 17. PMID: 38768315.

Yes, that what's none other than what the ICNIRP have to say about the International Radiation Protection Association (IRPA) interim guidelines dating back to 1984 that are still current and now in the care of the ICNIRP. In 1984, how many electronic devices were to be found in homes creating ultrasound, whether deliberately or incidentally as in the case of routers? There's plenty of science backing up these symptoms as being a consequence of ultrasound exposure, including this as posted by Mike in my aforementioned discussion on electricity meters causing tinnitus and symptoms that are included in the above list:

T. G. Leighton; "Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?" Proc. A 1 January 2016; 472 (2185): 20150624. https://doi.org/10.1098/rspa.2015.0624

The ICNIRP know they need to update the IRPA guidelines, but surely the electronics industry should act responsibly and not wait for ages for that to happen when there are worrying numbers of people suffering tinnitus, migraines (both estimated currently to be 1 in 7 of the UK population), fatigue, anxiety, dizziness etc? Note, I am finding other tinnitus sufferers who are experiencing a combination of these symptoms, including recently someone who reported worsening tinnitus and the feeling pressure on their ears while in their own home. 

Andrew

Thanks Andy for your response. The more harmful frequencies are I believe, those below 100 kHz, but ultrasound hearing has been found to extend as far as 225 kHz. This study cites an earlier study concerning the limit, but unfortunately that one is available in Russian only and very difficult to translate due to the way it was scanned:

Gavrilov, Leonid & V., Gersuni & al, Pudov. (1980). Gavrilov L. R., Gersuni G. V., Pudov V. I. et al. "Human hearing in connection with the action of ultrasound in the megahertz range on the aural labyrinth." Sov. Phys.-Acoust., 1980, 26, 4, 290-292.. Sov. Phys.-Acoust. (Acoustical Physics). 26. 290-292

I don't want to go into EFs and EMFs in this 'Question', but can ultrasound be similarly suppressed?

I presume you are aware that https://www.researchgate.net/publication/14466051_Application_of_focused_ultrasound_for_the_stimulation_of_neural_structures 

is online and is a quick summary flyover of the areas that had been looked at in the early 80s. Note that whiile that paper is a bit vague about it, the power levels used when triggering nerves to erroneously report heat, cold touch etc are quite high, as a percentage of the levels that would lead to tissue damage (~watt  per cm2) which is very high compared to SPL where an Lw of 0dB is normally taken as 1 picowatt, - so a 120dB source is 1 watt of at the source.

Of  course when thinking in terms of power density, spread out over an ever increasing area with distance. (not to be confused with loudspeaker input power - 1kW of electrical power producing a few watts of acoustic energy filling the whole night club is quite common, the rest goes as heat ! )

The acoustic conversion of rattling inductors that are not deliberate loudspeakers is very low, sub 0.1%, and that means the effect on circuit efficiency is not normally considered. It also allows us to put an upper bound on what power levels you are hearing  - the router DC input power is likely to be less than 10W, and of that perhaps 50% is stepped up or down, say 5W, of that say 500uW to  5mW is converted to sound, that is somewhere between a traditional dual  bell alarm clock and a revving car engine. If that was in the audible range, we'd all notice it at a few inches ! but it is still 3-4 orders of magnitude lower than levels that induce false sensation in nerves below the skin in normal test subjects,

Yes, ultrasound can be suppressed in much the same way as normal sounds can by baffles, and acoustic absorbers, and closing doors and windows, but it tends to get through proportionally  smaller gaps and holes, as the wavelength is shorter.  To make equipment harder to detect from its acoustic  emissions, internal modifications   as simple as blobbing mastic or conformal coat (a heavy varnish) over the inductors and even hot melt glue  are a common initial strategy and can be quite effective.

regards Mike.

TDK, an inductor maker, give some advice in this publication https://product.tdk.com/en/techlibrary/solutionguide/acoustic-noise.html

Mike.

Hi Mike,

Thanks for your 2 further replies.

I rather doubt sound proofing will be practical as the devices will need air flow to cool any components that can get hot and ultrasound is going to get through some small gaps. I was wondering if there were electronics that could prevent or substantially reduce the vibrations and therefore the emissions. The TDK advice shows there are choices that can be made to reduce noise, but do the manufacturers of electronic devices, particularly those we are putting in our homes, realise the consequences of the polluting emissions their devices are generating?

Re Gavrilov's paper on focused ultrasound stimulation of neural structures; ultrasound has its good medical effects, but it also has its bad effects as those of us with ultrasound hearing can testify. Having any device in the living room, study, possibly bedroom emitting frequencies in the tens and low hundreds of kilohertz is potentially a health disaster and how many people with this sensitivity actually know that they've got it? The medical profession doesn't seem to be aware of it at all and therefore unable to diagnose it.

I wouldn't have had a clue about ultrasound sensitivity without the major problem I have with unsuppressed SMPSs in electricity meters. Take dental descalers for instance, which of course deliberately use ultrasound: I always hear a high-pitched tone during descaling and used to think it was normal and that everybody did. It didn't result in tinnitus fortunately, but it was exactly the same tone as the tinnitus that began with the first smart/digital electricity meter installed in my house. Descaling since the tinnitus started has been painful and the dentist once asked me what was wrong. He had no idea some people could hear a tone while having their teeth cleaned, even though the dental nurse with us at the time told us that she too hear a tone during descaling. There are people complaining of actually suffering tinnitus after having their teeth ultrasonically cleaned. Here's an example of a case from PubMed: 

Andersen TL. Tinnitus na behandeling met ultrasone scaler [Tinnitus following treatment with ultrasonic scaler]. Ned Tijdschr Tandheelkd. 2023 Nov;130(11):447-450. Dutch. doi: 10.5177/ntvt.2023.11.21080. PMID: 37933721.)

Without previous experience of suffering ultrasound hearing and tinnitus, I would have installed the new router and slowly developed tinnitus and other symptoms. Depending on how quickly the tinnitus developed and it's variation in volume with location in terms of being in the house or not, I might have suspected the router was the cause and turned it off to see what happened, but the chances are that it wouldn't have made any noticeable difference. I would have gone to a GP, told them I had this horrid tone ringing in my ears keeping me awake most of the night, to which they would not doubt responded; "tinnitus is all about stress, go and have a holiday" etc. (That's what they told me when I knew the meters had caused the tinnitus that I still have 4 years later.) Stress and tinnitus do go together, but with ultrasonic inflicting tinnitus, the stress comes from having the tinnitus, not the other way around, plus a bucket load extra due to not being believed.

Of the ultrasound symptoms listed earlier, only the ear pressure I previously suffered responded quickly to leaving the house and returning, or by turning off the electricity in the house and back on again. Eventually I found the surround sound system was the source of the ultrasonic emissions (probably as EMFs rather than acoustically), but even that wasn't noticeable for the first 15 hours. Working out that an electronic device is the source of symptoms such as tinnitus, fatigue, dizziness and insomnia can be virtually impossible and of course, everything we buy and install ourselves or by utilities is of course made to British Standards, so officially deemed "safe" to use. However, the more I find out about my sensitivities and finding others suffering similarly, whether they understand they are sensitive or not to these frequencies, the more alarmed I'm becoming about the true scope of this problem.

Andrew

Really low acoustic noise  has to be designed from the outset at board level , and as above if you want to be stealthy then a heavy varnish and mastic over the offending components is the way forward or even potting the whole PSU module.  Unless you are happy to open the box however such measures are  not a practical retrofit.

It is possible to identify many designs of switch-mode devices using a similar  sort of set-up to that used for detecting bat calls. (and even the vibration of 32kHz watch crystals with some difficulty and an fft

)

M.

Hi Mike,

I think we'd better issue a warning:

Anyone thinking of opening up electronic devices and using things like mastic to cover components and block ventilation holes up to baffle any type of noise being generated, acoustic or ultrasonic, this may lead to overheating issues and hence be dangerous. This should not be attempted unless you are sure about what you are doing and of course, utility provided equipment like routers are the property of the utility and should not be interfered with. If you can gather enough evidence that utility equipment is causing you to hear noises that you should not be hearing, please complain to the utility and ask them to replace it. The more people who do this, the more likely action will be taken to stop such devices being issued and installed in the first place.

There are at least 2% of the population with ultrasound hearing, that's 1.4m in the UK, most of whom will have routers, electricity meters and other electronic kit that incorporate these ultrasound generating switched-mode electronics in their design, that risks these people suffering from a combination of the symptoms I listed earlier, plus other symptoms if they are also electro-sensitive. (That's if ultrasound hearing is not considered a form of ES itself. It certainly indicates a higher risk.) Most of the people affected will not understand why they have acquired their symptoms and the medical profession will not be able to diagnose them let alone provide useful treatment. Hence, awareness of this problem is needed on all sides and the use of circuitry that generates hidden ultrasound at levels that can cause awful symptoms in humans and pets, ought to be stopped.

I calculated the cost of fitting suppression in smart/digital electricity meters and compared it against the cost of the health care provided to myself during the time I had them in my home. (See:RE: Reasons why I suffered tinnitus, insomnia, chronic fatigue, and other health problems after having digital electricity meters installed) The health care costs for the minority affected is hugely more expensive compared to the cost of the suppression for all meters and there's no way I can put a cost to the utter misery caused by suffering the symptoms.

Andrew

I've wondered if some members of EngX who've read this question might have had a go at seeing whether their broadband routers also emit ultrasound. There are free apps for smartphones that let you check up to 22 kHz. I'll guess there's also a few who have even better kit that will pick up higher frequencies of ultrasound and also have meters that will detect EFs and EMFs in the ultrasonic range.

Please put the microphone 7 inches away from the router when taking measurements so that the distance is pretty much consistent to enable a fair comparison without having to worry about the inverse square law. Also, make sure it has completed its boot up sequence if turning on before measuring.

It doesn't matter if you or anyone in your household have any of the symptoms mentioned or not, but it would be interesting to know if you do find ultrasound being emitted, providing you are happy to share the information.

Please mention details of the model and type (FTTC/FTTP/POTS etc). Results showing no or very low ultrasonic emissions are as valuable as those that reveal relatively high emissions in order to find the prevalence. Happy to take results behind the scenes if you don't want to post them here yourself.

The router I tested: SR203 - FTTP.

Thanks,

Andrew

Any particular group of ultrasonic/bat detector apps that have been found to be usable?

Lots of apps have poor interfaces or are targeting the 'wrong' sorts of sounds (relative to this application)

2 or 3 'suggested' apps might be a useful start. (along with noting the recoding of the actual phone make & model, and any actual method of calibration)

Hi Philip,

I didn't want to promote one app over another, nor be told the app(s) I advise come with security flaws etc. People need to make sure they are happy to download the most suitable one they can find for their phone and their personal requirements for permissions. I believe the one I use most often is good, the waterfall chart is quite useful. It is available in the Android Store without much effort by searching for "ultrasound analyser". I don't think it has an Apple Store version, but I might be wrong. There are lots to choose from. (Try "ultrasonic sound detector" also.)

I think stating phone make and model will complicate things too much. I'm not expecting many people to take up my request (but the more the merrier) and collating by type of measuring equipment will lead to an array of results that probably wouldn't mean a lot. I understand your suggestion and it would be necessary if I was carrying out a full scientific study, but all I am looking for at the moment is: Is your router emitting an undue amount of ultrasound? Anything above 10 dB would indicate a lack of suppression. Maybe use two apps and compare. If both agree, then that's a result.

One additional thing for all who do this: Please check that any ultrasound found is coming from the router. I'm sure we are going to find other things in the home producing ultrasound. Move the phone/microphone around to check that the signal strength varies with distance away from the router only. The suggested distance of 7 inches is chosen because that is how far away I measured the ultrasound in the screenshot in the opening post. I no longer have the router, I had to return it when I cancelled the transfer of ISP, so I can't repeat the test at another distance.

Cheers,

Andrew

Hi Philip,

I didn't want to promote one app over another, nor be told the app(s) I advise come with security flaws etc. People need to make sure they are happy to download the most suitable one they can find for their phone and their personal requirements for permissions. I believe the one I use most often is good, the waterfall chart is quite useful. It is available in the Android Store without much effort by searching for "ultrasound analyser". I don't think it has an Apple Store version, but I might be wrong. There are lots to choose from. (Try "ultrasonic sound detector" also.)

I think stating phone make and model will complicate things too much. I'm not expecting many people to take up my request (but the more the merrier) and collating by type of measuring equipment will lead to an array of results that probably wouldn't mean a lot. I understand your suggestion and it would be necessary if I was carrying out a full scientific study, but all I am looking for at the moment is: Is your router emitting an undue amount of ultrasound? Anything above 10 dB would indicate a lack of suppression. Maybe use two apps and compare. If both agree, then that's a result.

One additional thing for all who do this: Please check that any ultrasound found is coming from the router. I'm sure we are going to find other things in the home producing ultrasound. Move the phone/microphone around to check that the signal strength varies with distance away from the router only. The suggested distance of 7 inches is chosen because that is how far away I measured the ultrasound in the screenshot in the opening post. I no longer have the router, I had to return it when I cancelled the transfer of ISP, so I can't repeat the test at another distance.

Cheers,

Andrew