EMI shield

[green]

https://learnemc.com/shielding-theory https://cecas.clemson.edu/cvel/emc/c...tor/index.html

(numbers) on right side. (17) absorption and reflective + a calculator. Entered aluminum, .64mil and 10kHz, 100kHz and 1MHz in calculator. Absorption loss was low, reflective loss >100db. If I look at amplifier out, coil connected to amplifier with a scope(Tx off, just looking for EMI pickup). I see a noise level. Covered coil with regular strength aluminum foil both sides, saw some reduction in noise. No where near 100db. What should I expect to see? Maybe something I'm doing wrong?

[Tinkerer]

https://learnemc.com/shielding-theory https://cecas.clemson.edu/cvel/emc/c...tor/index.html

(numbers) on right side. (17) absorption and reflective + a calculator. Entered aluminum, .64mil and 10kHz, 100kHz and 1MHz in calculator. Absorption loss was low, reflective loss >100db. If I look at amplifier out, coil connected to amplifier with a scope(Tx off, just looking for EMI pickup). I see a noise level. Covered coil with regular strength aluminum foil both sides, saw some reduction in noise. No where near 100db. What should I expect to see? Maybe something I'm doing wrong?

Thank you for starting a shielding thread. The shield, in your case, the aluminum foil, needs to be connected to the ground of the detector. Aluminum foil has a thin layer of aluminum oxide covering it. Aluminum oxide is a very good insulator. Since it is a very thin layer, it can be broken with some friction, but new oxide forms very quickly, there is always a risk of bad electrical contact unless there is a solder connection.
I used to make a simple test to check the shielding on a PI coil. Approaching my hand to the coil without shielding, produces a lot of noise. With shielding the hand should not be seen by the coil. Not much of a precise science.

I would like to opportunity of this thread to consult the forum experts about PI coil shielding:

What should the resistance of the shield, from the tip of the coil, to the connection of the RX board be?

Is the main purpose of the shield for electrostatic shielding between the soil and the coil?

How critical is the capacitive coupling between the soil and the coil?

The shield should not absorb much of the TX magnetic pulse. Does this mean that the shielding frequency should be higher than the highest frequency of the TX pulse?

There are many other aspects to shielding to be considered, but let's discuss these initial questions.

[erte123]

thanks for starting this thread, anyone know what's the best type emi shield material between these- aluminum, copper, or mix of nickel/copper/cobalt material. i'm asking just to see if its possible to shield the top half of an existing detector from middle of coil wire all the way to the top around control housing using emi tape- i've read the nickel/copper/cobalt tape is good but maybe aluminum or copper tape works the same? i think emi effects a detector the most at the coil so maybe wrapping a detector halfway to top with emi tape won't change anything... any advice?

[kt315]

sorry we do not protect a detector from emi. why you want protect from emi if a nature of transmitter coil energy is emi?

[green]

https://learnemc.com/shielding-theory https://cecas.clemson.edu/cvel/emc/c...tor/index.html

(numbers) on right side. (17) absorption and reflective + a calculator. Entered aluminum, .64mil and 10kHz, 100kHz and 1MHz in calculator. Absorption loss was low, reflective loss >100db. If I look at amplifier out, coil connected to amplifier with a scope(Tx off, just looking for EMI pickup). I see a noise level. Covered coil with regular strength aluminum foil both sides, saw some reduction in noise. No where near 100db. What should I expect to see? Maybe something I'm doing wrong?

Trying to learn something about shielding. It was suggested in another thread that I should shield the detector circuit. Using the coil as a transducer for noise pickup. The test is to determine drop in noise from shielding. Wrapping the detector coil in aluminum foil wouldn't work because it would act like a large long TC target. Another test: covered both sides of a 20cm 26turn flat spiral coil with cardboard cut from a cardboard box. Connected coil with 30cm twisted pair lead to TRT preamp. Tx coil not connected. Coil located about 1.2m from scope and .4m from a 10W CFL lamp(on or off). Distance to scope and lamp has a large effect on noise pickup. A long piece of regular strength aluminum foil was folded around the coil to shield it. Shielding better today than what I remembered last time, still along way from 100db(reflective loss) Should loss be closer to 100db?. Reflective loss not effected by thickness. If foil was thin enough to not act as a target, maybe could shield the coil? Is there another or better test for determining emi reduction from shielding?

[Tinkerer]

sorry we do not protect a detector from emi. why you want protect from emi if a nature of transmitter coil energy is emi?

So you say that the shielding should be for electrostatic field?

[Tinkerer]

Trying to learn something about shielding. It was suggested in another thread that I should shield the detector circuit. Using the coil as a transducer for noise pickup. The test is to determine drop in noise from shielding. Wrapping the detector coil in aluminum foil wouldn't work because it would act like a large long TC target. Another test: covered both sides of a 20cm 26turn flat spiral coil with cardboard cut from a cardboard box. Connected coil with 30cm twisted pair lead to TRT preamp. Tx coil not connected. Coil located about 1.2m from scope and .4m from a 10W CFL lamp(on or off). Distance to scope and lamp has a large effect on noise pickup. A long piece of regular strength aluminum foil was folded around the coil to shield it. Shielding better today than what I remembered last time, still along way from 100db(reflective loss) Should loss be closer to 100db?. Reflective loss not effected by thickness. If foil was thin enough to not act as a target, maybe could shield the coil? Is there another or better test for determining emi reduction from shielding?

Any type of shielding will absorb a certain amount of TX power and generate eddy currents within. We try to have these eddy currents with a very short TC, so that they are not interfering with our targets.

Attached is a shielding tape sold by Aliexpress. It does an excellent job at shielding, but it also reduces the TX pulse a bit.
It also adds capacitance to the coil and cable. As I use a 10 feet twisted pair cable, shielded with this tape, to add distance from the scope and the computer, the capacitance is very notable.

To reduce coil to shielding capacitance there is no better way than adding distance or space between shield and coil or cable. Even 1 mm makes a big difference. The capacitive coupling seems to follow an exponential relationship.

[WM6]

Attached is a shielding tape sold by Aliexpress.

Hi Tinkerer

What sort of (safe?) payment you chose with Aliexpress?

[Tinkerer]

Hi Tinkerer

What sort of (safe?) payment you chose with Aliexpress?

Alipay. After hundreds of buys, I fully trust the Aliexpress Escrow system.

[kt315]

So you say that the shielding should be for electrostatic field?

electrostatic process of charge adsorbcy is always around you if you moving. coil is moving. that gives potencial.
this potencial can discharge.

[Tinkerer]

http://www.mogami.com/e/paper/shield/shield.html

Here is an article about shielding.

[kt315]

ok. we are living under the Sun and we are kids of the Sun. we see be cause there is a LIGHT. yes?
put on impermeable glasses. now do you see something around? NOT NOT AND AGAIN NOT. FULL DARKNESS.
why you do not see nothing? be cause NO LIGHT INTO YOUR EYES.

light is ELETROMAGNETIC FIELD FROM-TO A COIL.
darkness is YOUR impermeable glasses on your BLIND MIND and EMI shield .

you just vainly wasted time in your american schools guys.

[Koala]

thanks for starting this thread, anyone know what's the best type emi shield material between these- aluminum, copper, or mix of nickel/copper/cobalt material. i'm asking just to see if its possible to shield the top half of an existing detector from middle of coil wire all the way to the top around control housing using emi tape- i've read the nickel/copper/cobalt tape is good but maybe aluminum or copper tape works the same? i think emi effects a detector the most at the coil so maybe wrapping a detector halfway to top with emi tape won't change anything... any advice?

I don't have a lot of success by just adding shielding. Its easy to create ground loops and make the situation worse. For example the coil cable should already have a shield. Why add a shield to a shield.

Do you have a particular problem your trying to fix ?

[Ferric Toes]

Any type of shielding will absorb a certain amount of TX power and generate eddy currents within. We try to have these eddy currents with a very short TC, so that they are not interfering with our targets.

Attached is a shielding tape sold by Aliexpress. It does an excellent job at shielding, but it also reduces the TX pulse a bit.
It also adds capacitance to the coil and cable. As I use a 10 feet twisted pair cable, shielded with this tape, to add distance from the scope and the computer, the capacitance is very notable.

To reduce coil to shielding capacitance there is no better way than adding distance or space between shield and coil or cable. Even 1 mm makes a big difference. The capacitive coupling seems to follow an exponential relationship.

This is the tape I use very successfully. I buy it from a company called 'cidimall' on eBay. Woven cloth is nickel plated copper and another good feature is that it is backed with conductive adhesive. I wrap the bare coil with PVC spiral cable wrap and then helically wrap the tape on top of this which gives mm or so spacing. For the last few turns of shielding, I wrap it over a couple of inches of bared 7/0.2 stranded wire which connects to the shielding via the conductive adhesive. the tail of the wire, with a bit of the retained original insulation, is then connected to coax ground/coil end ground. There must be a small gap of course to prevent a shorted turn effect. Wrap around shielding is by far the best, because coaxial construction around the coil bundle results in minimal eddy currents in the shield and least effect on the TX waveform.

Eric.

[Koala]

I have got confuses

are we talking about EMI shielding of the electronics

or the coil shield ?