How do you shield electronics from EMF?

[Classsy]

Hello all,

I have an issue which I believe all you smart electrical engineers can help me with: How do you shield electronics from emf?

I have a tablet pc with an active digitizer. The digitizer becomes inaccurate towards the peripheries of the screen --the closer to the bezel you are-- around the wifi radios and various electronics stuffed around the screen. Apparently the wacom digitizer does this because it picks up EMF signals from the rest of the computer. I want to shield my screen from these waves.

My questions:

1. What is the difference between EMF and EMI in this application?

2. Is the tape I've seen online what i need to remedy this issue? To me, the layman, it just seems like aluminum or copper foil. If I need this, is there a place to get this cheap?

3. Anything else I should consider? Could I possibly short my screen out?

4. Does this sound like it may actually help with my digitizer?

Thank You.

 

[the_emi_guy]

Is this a tablet PC that you are developing, or one that you have purchased?

We do not know what online tape your are referring to.

 

[yungman]

You talking about this?

http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l2632&_nkw=copper+tape&_sacat=3858&_from=R40

EMF is not EMI. EMF is electro motive force! That is for battery, voltage source etc.!

There are many ways of shielding, copper tape is only one of many. My first suggestion is to return it if you just bought it. It is not necessary easy to fix the problem without knowing more detail. Is it a total stand alone unit with no connection to anything, and if you move it close to something, it will act up? If there is a cord that connect to something, I'd try putting a ferrite toroid on the cord and see whether it will help or not.

I don't know what are you digitizing, does it connect to something? Any connection to external device can pickup noise, not just the basic shielding of the unit. I hate to see you order the copper tape and find it's useless. The first thing I would do is to return it if possible.

 

[Classsy]

We do not know what online tape your are referring to.

Sorry. I am referring to the 3M branded tape.

The unit is an x230t lenovo tablet laptop


Thanks again.

 

[Ouabache]

EMF is not EMI. EMF is electro motive force! That is for battery, voltage source etc.!

Just a clarification - acronyms have more than one meaning.
In this instance EMF refers to "ElectroMagnetic Field". Electromagnetic fields are generated in various parts of electronic circuits, typically around transformers, RF coils, oscillators. Modern electronics take this into account and in good design, shield these sources. To distinguish EMF from EMI; electromagnetic fields can be thought of as a potential source of EMI (electromagnic interference).

 

[the_emi_guy]

Apparently the wacom digitizer does this because it picks up EMF signals from the rest of the computer.

How do you know this?

 

[Classsy]

How do you know this?

People on lenovo forums have diagnosed the EMI as the culprit and have tried to remedy this issue with aluminum foil-- with various levels of success. Thus far, they have stuck the foil over the outside of the computer. I want to actually open the bezel and stick it inside, around the digitizer circuits. I know it sounds risky, but I've already opened the case and am confident in my ability to root around inside the computer. I just need to know what type of emf shielding tape i should buy. I've seen a mesh which looks promising. Would copper tape suffice? Thanks

 

[the_emi_guy]

Has Lenovo come clean on this issue? Are you sure there is no driver update or calibration procedure that will improve the situation?

Anyway, regarding the type of tape:

If you do not need it to have adhesive and you do not need to solder to it you can use aluminum foil from the grocery store and a pair of scissors.

If you want to be able to solder to it you will need copper tape.

You may want to buy some low static Kapton tape to cover areas that may be shorted by your experiments. Don't use household tape, it generated lots of static electricity when you pull it off of the roll.

Let us know how you make out, maybe you will become the hero on that Lenovo forum.

 

[yungman]

You follow the link I posted? They are quite good price, I myself just ordered the 10m X 50mm for $14.50.

 

[Classsy]

You follow the link I posted? They are quite good price, I myself just ordered the 10m X 50mm for $14.50.

Yes, is this sufficient? Thank you

 

[yungman]

Yes, is this sufficient? Thank you

I did a lot of CE test and fix emission problem, that's the kind I use. The good thing is the adhesive is conductive, you can build up a total shield without soldering.

If you put it inside, one cheap trick is using double sided scotch tape to line the inside, then use kitchen aluminum foil ( get Renolds, they are thicker. to line and stick onto it. Then screw the ground on. That's what I do to line the cavity inside the electric guitar on the pickguard where the area is large and takes a lot of copper tape to build up the size.

 

[G.Dutcher]

The issue may be much lower than RF frequencies, in which case one must ask is the interference due to magnetic or electric near field crosstalk of circuits. Conductive metals (if grounded) will shield electric fields well, but not magnetic fields which requires a materia with permeability (a magnet must attact it) and aluminum does not qualify. If the source and victim circuits are low impedance, it is probably inductive crosstalk due to currents rather than electric field capacitive crosstalk due to voltages.

 

[the_emi_guy]

The issue may be much lower than RF frequencies, in which case one must ask is the interference due to magnetic or electric near field crosstalk of circuits. Conductive metals (if grounded) will shield electric fields well, but not magnetic fields which requires a materia with permeability (a magnet must attact it) and aluminum does not qualify.

The OP is talking about a tablet PC not an electric power drill. Noise sources in computer technology equipment that are in the KHz couple into victim circuits galvanically, not via fields.

If the source and victim circuits are low impedance, it is probably inductive crosstalk due to currents rather than electric field capacitive crosstalk due to voltages.

Metals do not need to be permeable in order to shield inductive crosstalk.