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Author Topic: Akula eternal lantern 4  (Read 277686 times)

MarkE

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Re: Akula eternal lantern 4
« Reply #300 on: March 12, 2015, 07:51:03 AM »
@MarkE,

Give up!
Synchro1 go ahead and explain this idea of yours.  Then maybe you can explain why it is that products are designed exactly opposite of your idea. 

forest

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Re: Akula eternal lantern 4
« Reply #301 on: March 12, 2015, 08:11:30 AM »

MarkE

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Re: Akula eternal lantern 4
« Reply #302 on: March 12, 2015, 08:58:26 AM »
That is a very good video that demonstrates a several very good points:

1) A Faraday cage attenuates, it does not completely block RF energy transfer between the input and the output.
2) Sealing off openings makes a big difference in shielding effectiveness.
3) Shielding effectiveness is multiplicative.

Something that he did not mention is that the effectiveness of a given layer of shielding is depends on:  How conductive the shield material is, how thick the shielding material is, and what frequency range of the signals one is trying to block.  A couple of mils of aluminum blocks effectively down to around 2MHz below which the image cancellation drops off rapidly.  The same thickness of copper is effective to much lower frequencies due to the higher conductivity of copper.

forest

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Re: Akula eternal lantern 4
« Reply #303 on: March 12, 2015, 05:35:56 PM »
MarkE


What would you propose to block EMI from 8kW radio transmitter put inside a box ? :-\




I heard Richard Willis has such problems with EMI radiation.

synchro1

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Re: Akula eternal lantern 4
« Reply #304 on: March 12, 2015, 07:02:52 PM »
@MarkE,

The interior ítem has to be completely insulated from the cage to protect against the EMP. Connecting the item to the cage turns the cage into an antenna, just like connecting the item to the aluminum tray.

@MarkE,

A transistor radio with a retractable aluminum antenna would be protected while completely isolated from the cage conductor. Extending the radio antenna enough to make contact with the cage conductor would turn the cage into an antenna! Got it?

MarkE

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Re: Akula eternal lantern 4
« Reply #305 on: March 12, 2015, 08:40:05 PM »
MarkE


What would you propose to block EMI from 8kW radio transmitter put inside a box ? :-\




I heard Richard Willis has such problems with EMI radiation.
I heard that Richard Willis' dropped phone numbers months ago, and now his web site registry has expired.
The shielding methods that will be most effective depends on whether wires have to come out of the box or not.  If they do, and they are long, then they are likely the biggest source of EMI.

In the case that no wires come out of the box:  An ordinary steel box with EMI gasket material around all seams, where the EMI gasket material makes gas tight contact with the box material (preferably with a tin or other conductive plating) will make the box pretty EMI tight. 

In the case that wires come out of the box, then in addition to the box above, the wires need to pass through a suitable EMI filter that is bonded to the box.  There are many off the shelf filters available.  The filter design depends on:  The voltage and currents that must be supported, the frequency of the current that must be passed, and the amount of noise that is on the lines unfiltered.

MarkE

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Re: Akula eternal lantern 4
« Reply #306 on: March 12, 2015, 09:01:43 PM »
@MarkE,

A transistor radio with a retractable aluminum antenna would be protected while completely isolated from the cage conductor. Extending the radio antenna enough to make contact with the cage conductor would turn the cage into an antenna! Got it?
An antenna works by having energy impinge on it that gets guided to a sensing circuit.  The energy travels along the surface and for MHz and up signals penetrates only a tiny bit into the surface of the metal.  The better the conductor, the less the penetration at any given frequency.  Deeper inside the metal there is virtually no net energy because the impinging field is virtually completely canceled by the image current of the surrounding metal. 

If you have a strong enough signal, the finite resistance and inductance of the metal structure will develop detectable voltage drops.  Those voltage drops conduct current through capacitance to whatever circuit is inside the box.  That capacitance reacts with the inductance of the box and circuit board structures establishing resonances.  EMC engineers push those resonant frequencies up by making multiple connections to the metal structure at spacings that are as small as possible and/or insert energy absorbing materials like carbon loaded foam to damp the resonances.  In extreme situations more than one level of box is used.

forest

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Re: Akula eternal lantern 4
« Reply #307 on: March 12, 2015, 09:14:39 PM »
MarkE


The problem is when device has output wires carrying high frequency currents of many amps.A shield like copper tube around wire ?

MarkE

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Re: Akula eternal lantern 4
« Reply #308 on: March 12, 2015, 10:10:33 PM »
MarkE


The problem is when device has output wires carrying high frequency currents of many amps.A shield like copper tube around wire ?
If the wires are contained end to end in sealed metal enclosures then there will be very little radiation.  If the shielding were superconducting there would be no radiation.  In effect what you have is one big sealed Faraday Cage.  Except for rigid coax, the cable shielding is never perfect, and the bond to the metal enclosure is almost never solid.  That means that an antenna or antennae exist, and then the task is to decouple the internal noise from those antennae.

synchro1

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Re: Akula eternal lantern 4
« Reply #309 on: March 12, 2015, 10:38:34 PM »
@MarkE,

You're a nauseating and obnoxious fraud. Get a life!

MarkE

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Re: Akula eternal lantern 4
« Reply #310 on: March 12, 2015, 10:49:21 PM »
MarkE


The problem is when device has output wires carrying high frequency currents of many amps.A shield like copper tube around wire ?
Forest, if you have a closed volume of metal, then currents flow on the inside surface of that metal.  Those currents make a magnetic image that is opposite and very nearly equal to the field that induced them.  So if you have a voltage generator sealed up in a metal box where the box itself is one of the conductors and a wire inside of the box is another of the conductors to a load resistor that also connects to the metal box, then what happens is that metal box creates an image (nearly) identical to the field from the wire.  So at that interior box boundary the two fields cancel and what gets outside is zero.  In reality the cancellation isn't quite perfect because of the finite resistivity of the box material.  That means that the exterior surface of the metal carries virtually no net high frequency current.

MarkE

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Re: Akula eternal lantern 4
« Reply #311 on: March 12, 2015, 10:49:54 PM »
@MarkE,

You're a nauseating and obnoxious fraud. Get a life!
Is that your best effort at a reasoned argument?

synchro1

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Re: Akula eternal lantern 4
« Reply #312 on: March 13, 2015, 01:48:10 AM »
Is that your best effort at a reasoned argument?

@MarkE,

Start a new thread. The current thread topic here is "The Led Generator"! You're running a "Faraday Cage" snout rut through it.

forest

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Re: Akula eternal lantern 4
« Reply #313 on: March 13, 2015, 09:55:34 AM »
Forest, if you have a closed volume of metal, then currents flow on the inside surface of that metal.  Those currents make a magnetic image that is opposite and very nearly equal to the field that induced them.  So if you have a voltage generator sealed up in a metal box where the box itself is one of the conductors and a wire inside of the box is another of the conductors to a load resistor that also connects to the metal box, then what happens is that metal box creates an image (nearly) identical to the field from the wire.  So at that interior box boundary the two fields cancel and what gets outside is zero.  In reality the cancellation isn't quite perfect because of the finite resistivity of the box material.  That means that the exterior surface of the metal carries virtually no net high frequency current.


Device I'm working on is a high frequency few kW power generator with output wires to power resistive heaters inside second chamber.I guess I should enclose those wires in copper tube(s) and connect all chambers together then to ground to eliminate EMI.

MarkE

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Re: Akula eternal lantern 4
« Reply #314 on: March 13, 2015, 10:32:06 AM »

Device I'm working on is a high frequency few kW power generator with output wires to power resistive heaters inside second chamber.I guess I should enclose those wires in copper tube(s) and connect all chambers together then to ground to eliminate EMI.
You could, but that would be entirely unnecessary overkill.  If you generate DC output to the heaters then ordinary EMI filters can easily attenuate the high frequency noise.