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Guru
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Plastic For Explosion prone areas

01/24/2008 11:50 PM

Can any body suggest the source for plastic, which should have resistivity less than 10e9 per sq, so that no static charge will get developed and resisticity more than 10e6, so that wireless signal from transmitter can pass through, without getting earthed.

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Guru
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#1

Re: Plastic For Explosion prone areas

01/25/2008 4:41 AM

Well, if it forms a container that becomes a Faraday Cage as a result of its conductance, then a radio signal will not get through it. Better to place an antenna on the outside and feed the signal through the container.

Plastics can be made conductive by filling them up with carbon. Antistatic bags can be made in this stuff, for the protection of static-sensitive devices while in transit and storage.

Electronic assemblers sometimes have loads of it in their waste bins.

It depends upon what thickness is required.

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Guru
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#2
In reply to #1

Re: Plastic For Explosion prone areas

01/25/2008 5:07 AM

It is container and no antenna is possible. Thats why I specified the limits of resistivity.

It should be transperent to 2.4 GHz transmission but should not be so high in resistivity to allow static.

The upper range of resitivity is defined by EN 60079:0

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Guru
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#3

Re: Plastic For Explosion prone areas

01/26/2008 3:16 AM

You can load many plastics with conductive particles as has already been suggested. You can also coat the plastic with a thin film of metal to make a conductive surface. You can also treat the surface with chemicals to cause surface adsorption of water which will create a conduction path. Look into anti-static container technology and you will pick up many suggestions.

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Guru

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#4

Re: Plastic For Explosion prone areas

01/26/2008 2:25 PM

If I reformulate your question, it can be readily answered:

"What happens to radio waves going thru a plastic of a given conductivity?"

The first answer is, that it will exponentially decay in its passage, the degree depends only of its thickness.

How can we calculate that? Well, there is a formula to calculate the Skin Depth, which is where the wave decayed 1/2.7:

depth = 500 sqrt (res / freq)

depth in millimeter

sqrt is square root of (...)

res is resistivity in Ohmmeter (sheets are expressed this way)

freq is frequency in Hertz

So, for aluminum at 50 Hertz is 500 sqrt (2.8*10^-8 / 50) = 12 mm

For a conducting plastic 10^7 Ohmmeter at 10 Mhz:

500 sqrt (10^7 / 10^7 ) = 500 mm = 0.5 meters

So, the bottom line is, that within a wide range conductivity to drain static electricity is just fine and do not dampen the radio waves much. I hope you are aware, that a radio of any significant power (that is forbidden for safety reasons) will get thru too, potentially crating mayhem.

By the way, this is the reason, why antennas laid underground (!?!) work just fine.

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Guru

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#5

Re: Plastic For Explosion prone areas

01/28/2008 2:51 AM
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Guru

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#6

Re: Plastic For Explosion prone areas

01/28/2008 10:24 PM

Go and have a look for "Durapol" G-10 Fiberglass or "ESLON DC PLATE" which is a Anti-static Perspex material we use in the PCB industry for protective enclosures.

http://www.eslondc.com/

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