so then, does RF Tx inside a Non-grounded, 100% sealed, metal enclosure radiate out? like with Van De graaff

Thread Starter

genekuli

Joined Oct 21, 2018
103
in the Van De graaff the charge migrates to the outside of the metal enclosure (Non-grounded), is that possible for RF Tx ? maybe with change in frequency perhaps? the Tx antenna inside the metal enclosure is not touching the metal enclosure
 

nsaspook

Joined Aug 27, 2009
8,531
According to the emDrive people it should start to fly. ;)


The RX/TX shielding effectiveness is the same but it might get a little hot if you put the transmitter inside the RF sealed enclosure.
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
According to the emDrive people it should start to fly. ;)


The RX/TX shielding effectiveness is the same but it might get a little hot if you put the transmitter inside the RF sealed enclosure.
thanks, but i need to know the converse effect; if the RF escapes out from inside
 

BobTPH

Joined Jun 5, 2013
3,506
If it could, we could make a great refrigerator. No energy comes in. Energy goes out. Temperature keeps dropping.

Seems like Maxwell’s demon to me.

Bob
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Why would you think it would be any different?
because another answer from a RF engineer that i received elsewhere and also by putting my phone inside a fully sealed metal pot with lid (no plastic or gaps) and it still working like normal.
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
If it could, we could make a great refrigerator. No energy comes in. Energy goes out. Temperature keeps dropping.

Seems like Maxwell’s demon to me.

Bob
but then why does my phone work to receive calls inside a metal pot with lid and no gaps and no plastic sections?
 

nsaspook

Joined Aug 27, 2009
8,531
because another answer from a RF engineer that i received elsewhere and also by putting my phone inside a fully sealed metal pot with lid (no plastic or gaps) and it still working like normal.
The obvious answer is the POT is not RF sealed at the frequency in question because for a cell phone to work it needs to transmit and receive. so neither is being totally blocked. Post a picture of the pot and sealing procedure.
 

nsaspook

Joined Aug 27, 2009
8,531
it is metal on metal, NO gap, with overlap, it is a good stainless steel pot, phone works inside as normal
Very small air gaps at cell phone frequencies allow RF energy flow. Notice the Trash Can video of the test without RF sealing tape on the metal to metal 'seal' .

It seems to me (from your questions and the responses you have to correct answers given to those questions) you are making assumption without the proper knowledge to make them. The most important thing is to minimize gaps with seamless conductive materials.
 
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upand_at_them

Joined May 15, 2010
766
Why doesn't the ungrounded metal box just re-radiate the RF? Isn't that what the ungrounded/unconnected elements of a Yagi antenna do?...They re-radiate the RF.
 

nsaspook

Joined Aug 27, 2009
8,531
Why doesn't the ungrounded metal box just re-radiate the RF? Isn't that what the ungrounded/unconnected elements of a Yagi antenna do?...They re-radiate the RF.
It's mainly because of skin effect in the RF case (at low frequencies and DC the charge distribution and ground effects are more into play) of a sealed Faraday cage. The conductive inner and outer surfaces are effectively two separate conductors separated by a nonconductor of RF (shielding) because of a boundary condition between free space and a good conductor beginning at some value of RF. The RF energy is reflected back into space or is absorbed as heat in the increasing effective resistance of the conductor as the RF energy enters the surfaces of the connector and moves deeper.
media-1200849-skin-effect-3.jpg

https://www.edn.com/skin-effect/

 
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SamR

Joined Mar 19, 2019
3,455
That and that the box is not constructed to be at the resonant frequency. Any possible radiated RF would be at a signal level so insignificant it would be virtually impossible to separate it from the greater strength background noise. Hence, effectively none.
 

sparky 1

Joined Nov 3, 2018
565
The cost of transmission of electrical power requires that the equipment be safe and last a long time.
The electrical behavior should not be so violent and erradic to exceed the dielectric strength of the wires and insulators. Van de graaff.
Conventional electrical systems do not penetrate a metal enclosure by design.

We can find technical specifications for conventional RF requirement such as what an RF linear power amplifier enclosure must meet.
There are rules that include safe distance from an antenna and it's various parts used in part, a radiative surface.
We can see the expense of milling out a solid block of aluminum which is mostly used to keep noise out of sensitive equipment.
Mu metal sheet can be placed around equipment (scope ect) that are sensitive to Van de Graaff, HV generators and other.
It is the high permeability of material like Ni80FeMo5 that attracts the magnetic field part, the e field might find a path so your ground is important.
 
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nsaspook

Joined Aug 27, 2009
8,531
That and that the box is not constructed to be at the resonant frequency. Any possible radiated RF would be at a signal level so insignificant it would be virtually impossible to separate it from the greater strength background noise. Hence, effectively none.
Actual physical antenna resonance (a special condition but not a necessary condition for EM radiation) is not a much of a factor in the totally enclosed shielding effect just like it's not in the small gap leakage case. The leakage dimensions needs to be on the order of 1/50 of a wavelength for significant direct radiation escape from the crack but the skin effect of the conductors on the crack surfaces provides a transmission line short to the exposed outer surface for energy transfers across the RF nonconducting middle of the shielding.

https://palomar-engineers.com/non-resonant-vs-resonant-antennas
 
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SamR

Joined Mar 19, 2019
3,455
I really can't even conceive of an enclosure archiving resonance. Since it can't and most probably is nowhere near resonance the SWR would have to be enormous with effective radiation near zero. Resonance is the Golden Ring for antennas and 100% actually near impossible if not truly impossible. As you fall away from that ideal the antenna effectiveness diminishes rapidly. Even with small bands of frequency for an antenna, tuners are used to improve matching and radiation effectiveness.
 
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