Reducing EMI

[CAS]

I just came across these http://www.rs-online.com/designspark...pressor-sheets and wondered if they would be useful in coil design? Any ideas?

[WM6]

Such sheet will reduce detection of targets too. Shield should not suppress magnetic field.

[golfnut]

Not really, as these will reduce the magnetic flux emanating from your Tx coil.

These work by having millions of tiny particles each sustaining eddy currents - it would be like energising a billion tiny targets - so no feild/flux lines would be left to energise your target.

[CAS]

I thought as much. I was looking at using it around an experimental TX circuit to reduce any radiated emissions from entering a very sensitive RX circuit

[kt315]

please read ITMD BEFORE you ask or open new thread.

yours Anatloy

[CAS]

please read ITMD BEFORE you ask or open new thread.

yours Anatloy

I have read the book several times but as new products are constantly coming onto the market and people are coming up with new ideas, I figured that a forum such as this would be a good place to open up a discussion. Obviously I should just stick to re-reading the book and working on new ideas without discussing it with others.

[kt315]

using EMI protection is bad idea. a coil is itself EMI transmitter. you decrease EMI field and low the sensitivity of a detector.
simple rule - if brand firm CAN so it DOES, if NOT brand is not able to release it.
why someone handyman at kitchen or hangar CAN do something MORE best that for example Garrett or White's??? ivconic tells us only about
''There is only one detector better than Deus - it is Deus with larger coil!

-- no chance to do better than a brand.

[golfnut]

It would have uses in a detector but it would normally be used off the back of poor design practise.

Say your lcd data bus was parallel ribbon and you had a nice colour LCD with decent update rates... The noise from the LCD could degrade the Rx performance.

You could clad the LCD ribbon in the absorber.. So it does have its uses, as does other emi techniques such as effective ground plane structures, decoupling, screening, filtering, conductive gaskets, reducing ground loops, separate analog and dig GNDS, star points etc, etc.

They all have their place.

The stick on films are normally an expensive kludge to get you out of a hole until the root cause is identified and designed out. Thats my experience anyway.

[CAS]

using EMI protection is bad idea. a coil is itself EMI transmitter. you decrease EMI field and low the sensitivity of a detector.
simple rule - if brand firm CAN so it DOES, if NOT brand is not able to release it.
why someone handyman at kitchen or hangar CAN do something MORE best that for example Garrett or White's??? ivconic tells us only about
''There is only one detector better than Deus - it is Deus with larger coil!

-- no chance to do better than a brand.

EMI protection within a circuit where you have a high voltage circuit in close proximity to a very sensitive RX circuit is a good idea. Good circuit design can only go so far when you have physical size constraints.

While I agree that your average handyman may not be able to come up with a better idea, some of us are more than handymen. Some of us own our own electronics business and that while we may not have experience with MD coils etc, we do have a lot of electronics experience in other fields and with a little lateral thinking sometimes new ideas ARE better than those who have constraints due to what the market will pay for a product.

[kt315]

EMI protection will give backing effect like a some target gives EMI reply in RX coil because some kinda EMI protection itself.
take a massive metal plate and set near a coil - this is EMI protection and this is THE TARGET, for the coil.

[Qiaozhi]

Flex Suppressor sheets are intended to screen EMI above 1MHz, and up into the GHz region. I suspect they would be almost invisible to a metal detector.

In the article it states: "A Flex Suppressor sheet is composed of magnetic powder that is suspended in a flexible polymer material. This magnetic powder is a proprietary mixture made primarily of iron and silicon. The iron flakes are so thin that eddy currents are not able to form on the skin, causing the electromagnetic field to collapse. Because the metallic flakes are separated from each, the overall sheet is non-conductive."

However, even if they might be suitable as a Faraday shield (due to their inability to form eddy currents), the cost is prohibitive. Even the thinnest (240mm x 240mm x 0.03mm) is £18.78 for one sheet.

[CAS]

Flex Suppressor sheets are intended to screen EMI above 1MHz, and up into the GHz region. I suspect they would be almost invisible to a metal detector.

However, even if they might be suitable as a Faraday shield (due to their inability to form eddy currents), the cost is prohibitive. Even the thinnest (240mm x 240mm x 0.03mm) is £18.78 for one sheet.

That's why I thought they may be able to shield out stray signals from for eg mobile phones etc that may have an impact on a very sensitive RX circuit. I know they are expensive but some of the equipment we work on has some fitted and I can get some as a spare part.

[godigit1]

please read ITMD BEFORE you ask or open new thread.

yours Anatloy

Just curious is it a requirement to have read ITMD before you can post a new thread on this forum?

I think the tape sounds interesting.

[kt315]

Just curious is it a requirement to have read ITMD before you can post a new thread on this forum?

I think the tape sounds interesting.

you know the answer. certainly no it is not. the copy is fat and has all detailed information on metal detecting principles, best of the best book for everybody -
from kitchen women to guru doc with PHD in electronics. 1-3GHz EMI range is given harmonics above 1-3 GHz, do you agree with this rule?
those harmonics MAY make a noise, but ONLY in electronics like a processor, not a coil. while a coil has simplest RC filter from any kind of EMI, that is
above VLF (very low frequency, thousands of Hertz).

Anatloy

[Qiaozhi]

I think that what kt315 is trying to say, is that any external high frequency signal [in the GHz region] will not affect the detector, due to the limited bandwidth of the preamp. For example, the NE5532 has a 10MHz unity-gain bandwidth. Even if the preamp is a two-stage configuration with 33x gain per stage, the cutoff frequency is limited to 10MHz / 33, which equals 303kHz.

That's why I thought they may be able to shield out stray signals from for eg mobile phones etc that may have an impact on a very sensitive RX circuit. I know they are expensive but some of the equipment we work on has some fitted and I can get some as a spare part.

If you have access to samples of the Flex Suppressor sheet, it would be easy to confirm / deny whether there are any benefits to using this material in a metal detector. In particular, it would be interesting to know the dc resistance of the material, and whether it could be used as a Faraday shield.