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EMF [electromagnetic field] shield fabric?

Does anyone know how to make EMF [electromagnetic field] shield fabric?

Question by lindaoak    |  last reply


Has anyone any advice on building a Faraday cage for VHF - 20GHz or higher?

Hi, I've found lots on the 'net about building Faraday cages, but most of these are a couple of years old and targeted at lower frequencies up to around around the 2.4GHz range. I'm looking at making a Faraday cage for a room, to shield against a recent phone tower upgrade with transmissions now in the 19GHz range. (I've seen some other towers, fortunately not near me, recently approved for transmissions at 38GHz.) From what I've read so far, I'd need about 20 layers of heavy duty alfoil to come close to getting effective shielding, or wire with holes less than 7.5mm wide, which is going to be pretty tricky. Just wondering if anyone's tackled this problem before and, if so, how?

Question by powerup    |  last reply


Accessing SD memory on data logging shield

Hey again, I finished my first project recently and was looking to expand on the design. It's an EMF detector (https://www.instructables.com/community/First-project-completednow-lets-expand-it/) and it's working great. Now, I want to add memory and a USB charger to turn it into an self-contained EMF data logger. The project looks easy enough, but I have a question that I wasn't able to find answers for. Here's the question: Can the memory installed on the data logging shield be accessed through the Arduino USB port? On my cell phone, whenever I plug the USB into my laptop, it connects as a drive. I'd like to do the same thing with the EMF data logger. Or will I just have to remove the SD card every time I want to extract data from it? Thanks LorienD

Topic by LorienD    |  last reply


Very old shielding materials and techniques for permanent magnets and resulting possibilities

Forromagnetic meterials are not just called that for no reason.It comes from ferrous - iron.Iron has the highest permeability at normal temperatures.That means a magnet is attracted to it very strongly.We utilise this for transformer cores, the stuff inside a relay and the moving latch of the relay itself.Like current from an electrical system magnetic fields like to take the easiest route possible.Air is a very bad medium, so any iron close by will be prefered even if it is at a slight distance.You can check with a magnet, a steel bar and some iron shavings - please cover the are with plate first ;)Slightly less known is the option to also guide and extend the magnetic field this way.If you check how far the magnetic field of a magnet reaches and note that distance,then you can add some steel bars or rods at the poles - the field will extend through the metal.The most powerful example of this are the shielded magnets used for hooks or speakers.Except for a tiny area the entire magnetic flux goes through the metal.So in this lefover area the magnetic flux density will my many times greater than what the magnet alone would be able to.What most people don't know is that magnets also interact with other magnets in terms of their fields changing and distorting.The Halbach Array is a good example of this.Seen as a single magnet the array would have one weak and one strong side instead of even strenght for both.Wherever magnetic fields change a conductor can produce electricity or current.This in return causes an electromagnetic field that opposes the one from the magnets.Just drop a magnet through a copper or aluminium pipe ;)Since these distortions are widely unknow to the hobby tinkerer mistakes can happen ;)In the early days of exploring science some people already knew about shielding.And they also knew that certain metals have certain properties.Where it is quite hard to create a good coil from steel wire, copper works fine as it is not magnetic.What would then a copper shielding do?If you have two moving magnets with only a tiny gap then the resulting field distortions are quite huge.A copper shield around the magnet like a pipe would then react to these changes and also create a megnetic field that works in relation to the enclosed magnet.In simple terms it means the shield would let the magnet appear weaker or stronger depending on the field change.A quite old document I found gave some hints on how people thought in different directions back then.It was in regards to the design of a magnet motor by the way.Here various magnets were shielded in tube made of a copper-bismuth-alumium alloy.These tubes were then electrically connected so it created a single loop conductor.The claim was that the resulting electromagnetic field of this ring would drive the fields of the enclosed magnets sideways out of alignment.Like bending straight pastic tubes sideways.This "pulsating" would always happen when the magnetic binding forces reach max and so basically drastically weaken this binding effect.Another document talks about a "magnetised brass rod".A holes of the rod diameter is drilled through a block magnet.Not from north to south but through the middle where the flux is greatest.The claim here was that if that rod rotates fast enough a very low voltage with a very high current will be generated.Sounds easy and interesting enough that I might have to test one myself one day.The best one however is what I consider a hoax or being as good as Starlite.Someone back in 1908 claimed to have created a material the reflects magnetic fields.In lame man's terms it would be like an insulator around some electrical wire.The claim and some pics showed it, was that no magnetic field can pass the material.Or to be correct only a tiny fraction of what would be possible through air.A small magnet inside a longer tube of this material would create almost the same attraction to steel at the tubes ends as on the magnet itself.Measurements showed the field strength would be almost equal to a long mangnet of the same field strength.Imagine guiding the field of a big and powerful magnet through a tube around some corners or other magnets and then end in just a tiny hole for the entire flux...Too bad he never shared his secret formula to anyone knows to mankind.Isolation...Imagine you have an array of changing magnetic fields and quite strong magnets.Then you might face the problem that your focus on the "working" end neglected the other end of the magnet (stack).Providing some iron core material will keep thes field lines contained and away from interfering with your setup ;)But it also allows to use te otherwise unused end of your magnets more directly.For example by guiding to another magnet to affect its field strenght ;)Placing a sheet or steel between two magnets in a setup provides a "shared pole" so to say.If you have a north and south pole on a rotor at a distance of 5mm then a sheet of steel between will drastically weaken the strenght and reach of this combined field.It is like pulling the arch between the magnets down to make it more flat.And at and an angle the resulting field will also be slightly angled ;)Capping...When I first encounter this many years ago I couldn't really make sense of it.Quite complex..If you check the magnetic field lines with iron filings or similar then you notice how they go in a rounded manner from pole to pole.This is because the single field lines are of equal polarity and will dirve apart like opposing magnets.By capping the ends of a magnet you provide a short.Instead of diverting out like mad they will follow the cap and create very intersting magnetic field in return.If both poles are capped it is like pressing the magnet flat but without having a field on top of the oles - only aorund the center part.For this the thickness much must match what is required for the flux density.As a rule of thumb: if the end is still very magnetic then it is not enough material tickness ;)Interacting fields in a tube...This one is quite old too and seemed to have found no usable inventions apart from simple magnetic spring replacement systems.But it gave me some clues about Tesla "earthquake machine" ;)If you place a magnet in a tube and at it's ends magnets with opposing fields to the one inside then you can fix this magnet in place.Push one magnet deeper and the distance from the inner magnet to the other end will shrink the same amount.In this old paper two coils were around the pipe with the inner magnet between them.In this gap and at about the same width as the magnets length another coil was placed.Violent shaking would then create electrical energy at much higher level then modern shaker torches.In return an AC current on the outer coils would cause the inner magnet to move back and forth to create electricity in the center coil.According to the paper possible uses include: core less transformer, measuring minute changes in AC voltages, providing free power from a running motor...The last one had me stumbled for a very long time.Until I considered a different configuration.The whole thing is basically a linear DC motor - with correct timing of course.And in some motors we use permanent magnets.I am starting to wonder what would happen if we would design a rotor magnet like this?The running motor would be subject to constant field changes that affect the rotor.And a normal motor is always "even".By using four magnets instead of one we can push the field really flat.This means the area where the coil would operate (about 1/5 of the magnets area) will have a much stronger field.The resulting torque should be higher by about 25% !!Even a simple two coil model setup should show a significant increase in performance here.Timing is critical here but I tried some calculations based on 8 poles and the required "on times" for the coils.In a standard motor configuration with a single rotor magnet the coil is active for about 12° of the rotation.With a 4 magnet configuration this "on time" can be reduced to under 8° of the rotation to get the same amount of torque.An energy reduction of about 4% if you neglect losses and only think in time.If you think in terms like impulse energy then we are talking of about 15% !Shorter on time but still much higher flux density overall than for the long standard timings.Going the long run now:If you check how most DC motors work then you realise soon that for most one rule seems to followed.Only use one coild pair at a time.This is quite contradictive if you consider the geometry and options.A dual commutator would allow to use a second coil pair with a field OPPOSING the magnets instead of being attracted to it.After all: on you bike you pedal with both legs and not just one...And if you do it professionally then yu do the same as I suggested for the motor - you use the up pull of your legs as well.Doing it brushless only requires amodified h-bridge desing to drive the second coil pair at the right timing.Some will now say that it requires twice the energy, I say that for the same motor size your get twice the torque!Just imagine what that means in possible weight reduction for a motor - or its size to deliver the same torque at the same power levels when a normal motor is used ;)The more poles the more complicate the precise timing but no big deal really with modern electronics.Can it be improved even further?I though long and hard about that one until I considered EMF.A DC motor produces a lot of it when the elecromagnetic field collapses in the the coils.We do not utilise this energy...There is a tiny delay until the released energy levels are at max.My theory is that it should be possible to divert this energy into another coil set.If that coil is not the next active but still within a strong enough field area then the EMF would actually add to the drive of the motor.Only downside is that according to my calculations at least 16 poles would be required to get an optimum result.Way above of what I can create in my little garage :(In theory it should then be possible to reach about 98% efficiency for the motor....

Topic by Downunder35m    |  last reply


So, EMF blocking Stickers, Pendants or Death-Crystals? Answered

Uh, how to start with this one... Local health store started carrying the latest line of emf blocking stickers and pendants. At first I thought good grief, if people are that gullible as to not look into the science behind they perhaps deserve to have there money parted from them. Several weeks later though, a symposium was booked in the local convention hall. I was surprised to learn how many people actually went to this, and were indeed parted with a fair chunk of change. If you look into to it there are numerous if not hundreds of these anti-emf scams abound on the internet all claiming only theirs works... That alone would send my spidey senses tingling. I really don't want to get in to the science behind why this is a scam, and would appreciate answers from people who know what they are talking about rather then those have been duped. Moving on... I am afraid the owner of the health store is going to get slammed on this one eventually. Normally I would say the owner of the store has a good head on her shoulders with an excellent BS sensor. Not so much, this time around. Guess my question would be how to inform her of why its a scam with out her eyes rolling into the back of her head. "Had a friend go the symposium for kicks, "she has a doctorate in bio-engineering, health science and is pursing her latest degree in occupation health sciences." To her shock and delight it was simple for her to see through the scam, but she had to admit his did provide a technical sounding argument, mixing truth with techno babble, that perhaps someone with an understanding of only layman’s terms could be persuaded by. Oh, what to do...

Question by iminthebathroom    |  last reply


Printer disconnecting or USB port disappearing in Windows

First I thought to make an Instructable out of it but realised there are too many different printer models out there, so this time no images. What is this about you might wonder? Well, let me tell you my story first and you might see similarities to your problem. It all started with me getting a new PC as the old one got memory problems (RAM modules failed). After a few successful prints I noticed errors coming up in the log window. Mainly things like communication problems and that some data is sent again. Realised that on my new PC I did not check the speed settings for the COM ports, so I adjusted them to match the printer board and moved on without even bothering to check the logs. Then, half way through a bigger print, it all stopped and I could not even connect to the printer anymore. After a power cycle on the printer all was fine again but the error kept coming back every now and then. At this point I started to read up on the problem and the most common recommendation is to print over SD - too bad if your printer does not support it and too bad it does not address the issue at all! A few more technical answers pointed to the Logitech drivers, especially mouse, keyboard and 3D vision. As I was using the same outer hardware as before and also the same drivers (and same version numbers) I simply ruled this one out too, although it might be a vital clue for others. When starting to get frustrated and after opening a cold blonde I remembered that I had a similar issue a long time ago and that it was related to loose wires on the screw terminals for the power connection. Measured it all but according to my trusty multimeter all was fine. Now comes the fun part: I friend of mine with a HiFi fetisch was here when I testing the connection and he started laughing at my attempts. He explained that ALL his connections, no matter if power or audio signal are oversized! Here I started to wonder if he is up to something and looked up similar circuit board mounted power plugs. To my surprise they are all rated for anything between 1 and 5Amps. Even without a heated bed powered by the printer board I think everyone will agree that a max 5A connections is not enough. My frined then offered to check the plug and connector at his place - what a great thing to have friends :) He used a signal generator and small speaker with the plug as a connector between them. With an oscilloscope connected to both input and speaker you could see, while moving the plug, that the audio signal become somehow unclean - there where spikes and missing bits everywhere depending which way you wobble the plug. After taking the whole thing apart the destructive way we saw the cause: overheated contact areas with discolored surfaces. I replaced the plug now with a 250V/20A one from an old laser printer and had no USB or connection issues ever since. Ok, what's the thing with power and USB problems on a 3D printer? Almost all printer boards have the ground connections bridged to avoid interference on the USB signals. This mean, in case of a faulty power connection or one that is "dirty", the USB port on the computer can receive back EMF signal or even a voltage spike. In return a smart bios either disconnects the port or disables it until the problem is solved, in our case by restarting / reconnecting the printer. But even with no obvious signs of power problems you can get  a so called "dirty" connection. Dirty covers all from corrosion, worn springs for battery compartments, overheating or in the old days burnt relay contacts. For our printer it usually means that either the soldering connection on the board or a screw came loose, in rare cases like mine an undersized connector can burn out due to being unable to handle the currents. The bad thing is that you can not always spot these problems the easy way... Is there an easy way to tell that my USB problem is caused by a faulty power connection? Yes and no. Some boards offer indicating LED's, you connect power and the LED stays on even if the printer is disconnected from the PC. If it is more than just a Power on" indicator" this LED will be off after the printer stops working and in the device manager your serial port for the printer is gone. You might also hear the warning sound from Windows in regards to a device being disconnected. If all the above is true than most likely your power connection has a problem somewhere - if in doubt replace all screw and plug connectors for the power. Sometimes the problem is less obvious. Your print software might show communication problems in the log window or re-send a lot of commands. If the speed selection for the com port is the same as for the firmware of the printer board and as set in the printer software, it could also be a power connection problem. But to be on the save side try a shielded cable with ferrite cores on both ends first for the connection between computer and printer. Can I take any measures to prevent the problem? Sure, you could solder everything and make sure the wires are fixed in place so they won't move. But a simple indicator might be enough: Solder a piece of LED strip to the power connection on the circuit board - if the connection has trouble the LED's will show it in most cases by changing light levels or flickering. On top they act as a nice light to see what's happening during a print.

Topic by Downunder35m