# Effect Of Electronic Devices In Close Proximity

From reading other posts, it seems like electromagnetic induction is the greatest threat to electronic devices these days with either traditional HDDs or newer SSDs. Since current in a wire creates an electromagnetic field, I assume most electronic devices create their own field (albeit probably a weak one). Electromagnetic induction could be created by moving the devices around each other in a rapid fashion. Is there any danger to electronic devices (including their memory/storage and microchip functionality) when they are placed in close proimity to each other... say stacked on top of one another while operating?

Bonus Points: Assuming I was able to measure the electromagnetic field, what values would cause concern?

• I'd say static discharge is the biggest threat. – Andy aka Jan 7 '15 at 12:14
• Greatest threat of what? – Phil Frost Jan 7 '15 at 12:17
• Greates threat of causing damage to the device. Any damage: memory loss, inoperability, etc. – user58446 Jan 7 '15 at 12:32

This is a pretty broad question... so the answer is... it depends how intense the EM field is. At one extreme, you could have a very strong EMP like the one caused by detonation of a hydrogen bomb! On the more mundane level, the EM interference that electronic devices cause to each other is commonly a concern and studied under the (obvious) name(s) of electromagnetic interference/electromagnetic compatibility. I also agree with the comments below your question that while this is a concern, whether it is the biggest... it depends on the application.

The computer components that you mention (HDD, SSD) almost certainly have been tested for both EM emissions and susceptibility (to those), so they're very unlikely to affect each other that way in close proximity. You're more likely to have issues with heat dissipation (or rather accumulation) when you pack a lot of devices like those close together. Also, (mutual) vibration is a common concern in HDD arrays; the RAID-grade HDDs will typically have some firmware features not present in desktop HDDs to better cope with that.

EDIT: As user/consumer there is one (software/firmware) bit that you can do to limit EM emissions from computing (and similar) devices: make sure your computer has enabled spread-spectrum clock generation its BIOS/firmware; it should be on by default precisely due to EMI regulatory compliance issues.

Since you (now) ask in the comment below about a cell phone affecting computer components... that's a more dicey issue. A cell radio will emit a lot more than (other) computer components... by design! It can certainly affect some critical-care electronic equipment (although almost exclusively older ICU equipment/designs) and supposedly electronics on-board airplanes (again a controversial issue; the fairly recent [2013] relaxation of FAA rules still prohibits the use of the cellular radios inside the [smart]phones, however the even more recent 2014 decision of EASA does allow the cell radio to be left on) etc. Obviously the cell phone itself (which if it's a smartphone is basically a computer with flash memory like in a SSD etc.) works well enough in the presence of its own cell radio, but I honestly don't know if typical desktop computer components get tested (by their manufacturer) for correct operation with a cell phone radio right on top of them. Maybe you should ask that as a separate question.

• Well, the truth is I thought about this while I had a tablet and a cell phone sitting on my laptop while charging. So, no high-frequency movement or high-powered magnets. Just casual use... but I knew I would get a solid answer if I asked here to relieve my ridiculous concerns. Thank you. – user58446 Jan 7 '15 at 13:48

This is at the heart of FCC Part 15 regulations for consumer (Class B) electronic devices with a clock rate of 9 KHz (note: not MHz) and greater. This applies to devices which are unintentional radiators, such as computers (i.e. they are no intended to produce radio waves, but they do so anyway):

Operation is subject to the following two conditions:

• The device may not cause harmful interference, and

• The device must accept any interference received, including interference that may cause undesired operation.

'Accept' in this context means that the equipment must be able to tolerate without catastrophic failure any interference that is thrown at it, even though it is not guaranteed to function normally under these circumstances.

Normally anyone going to market with an electronic device has it tested that it meets these conditions. Such testing can cost several thousand dollars (but not as much, say, as you would incur if the product contains intentional radiators, such as cell modules or Bluetooth modules, which call for a lot more testing.)

Advertising or selling a electronic product that fails Part 15 can subject the manufacturer to severe fines: $100,000-$200,000 plus $10,000/day per violation. • +1 Very informative... if you care to, can you please elaborate (in your answer) on what kind of testing is done and how exactly it is performed. Can this sort of thing be done by an amateur, or do you need a white lab-coat? It sounds like an interesting aspect of EE. – user58446 Jan 8 '15 at 7:23 • @user58446 en.wikipedia.org/wiki/Electromagnetic_compatibility#EMC_testing is a bit sketchy, but should get you give you an idea how testing is done. There are whole books dedicated just to the topic of EMC test. By the way, there is a pretty long list of standards on EMC compatbility worldwide at en.wikipedia.org/wiki/List_of_EMC_directives – Fizz Jan 10 '15 at 4:03 • @user58446: If you want to read a somewhat more techincal article than Wikipedia (but not book-lenght) electronicdesign.com/test-amp-measurement/… appears resonable, although it's a little dated. It has a few photos too, but you have to click the links and they have rather low resolution. Anyway, it should give you an idea that it's not something the average Joe or even the average DYI electronist can afford to do at home... at least not to certification standards. "Economically" and "in-house" refers to businesses of a certain size. – Fizz Jan 10 '15 at 4:35 • @user58446: and if wonder what a GTEM cell is: en.wikipedia.org/wiki/GTEM_cell The previously mentioned "economical" cell from the aforementioned electronicdesign.com article was around$200K. For something more high-tech, costing nearly ten times that, you could have a look at youtube.com/watch?v=ZM3jWYGNoLU – Fizz Jan 10 '15 at 4:49

No. The field emitted by most devices is very small, and there are legal limits on high-frequency EM emissions. Metal casework goes a long way towards absorbing emission and radiation. The exceptions are things like high-power radio/TV transmitters and train-sized electric motors.

However, if noisy electric devices are using the same power supply as sensitive devices, they may cause damage through spikes and surges. Again this only applies to extreme cases and not normal consumer electronics. Consumer electric tools are generally fine, but it's probably not a good idea to plug your laptop and arc welder into the same supply.