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Question about a Faraday Cage

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I hope I'm contributing by posting these vids:

 

 

$15 Faraday cage:

Part2 (an experiment):

 

Some of what he says in the video seems to disagree with a lot of what I have read by others on this forum and seen in other vids.

1. He says a ground is unnecessary because the EMP travels around the cage and not through it.

2. The objects inside do NOT have to be insulated from the cage.

 

I have a hard time believing I will have a faraday cage simply by purchasing a metal trashcan and putting my electronics inside. Yet, he asserts this in the vids and also in the comments on the youtube page. He admits it sounds counter to what one would expect, but this is what he is stating based off his sources.

 

Your thoughts guys?

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Sorry before anyone yells because I zipped over them HEMP means High Altitude Electro Magnetic Pulse this is the standard that Uncle Sam uses as they have not developed a ground based unit that can deliver as powerful an event as a high altitude event and for the scientifically inclined DIYer here is the formula for Shielding Effectiveness -

 

S.E. dB = 20 Log10( E1 / E2 ) Decibels

 

Where E1 is the properly measured field strength in volts/meter without the shield and E2 is measured field strength with the shield in place at a fixed test distance. In the case of a homogeneous material, total shielding effectiveness of a material is a function of:

 

 

 

SE dB = (R + A + B) Decibels

 

 

Where R is Total Reflection Loss, A is Total Absorption Loss, and B is Re-Reflection Loss. Reflection Loss occurs due to the impedance mismatch at the air-to-metal interfaces. Absorption Loss is a function of thickness and frequency for a given material. Where Absorption Losses are greater than 10 dB, Re-Reflection Loss can be disregarded.

 

How do I figure out R, A, and B for a particular material? (Say a Metal trash-can)

 

and what do you mean by frequency of a given material?

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How do I figure out R, A, and B for a particular material? (Say a Metal trash-can)

 

and what do you mean by frequency of a given material?

 

In general you probably don't have to do the math. Since you are not interested in taking scientific data, any conductor should work. You misread

frequency of a given material?

 

The actual quote is

Absorption Loss is a function of thickness and frequency for a given material.

Any conduct has a resistance to electrical current (low temp super conductors are different and not of concern) flow that is dependent on the frequency of the current. Ham operators have tables that give signal loss per foot. Important stuff in matching circuits. The higher the frequency, the more the 'skin effect' becomes apparent.

 

The best cage would be a safe made out of gold. During WW2, gold from Fort Knox was used as buss bars in some power plants because of the shortage of copper (needed for war production) There was a minor problem in that the gold was a much better conductor than copper so some recalibration was needed.

 

Hams have 'matching' units to adjust for impedance mismatch; if he does it wrong or the mismatch is too great you get arching, sparking, and the magic blue smoke escapes. (Magic blue smoke is what makes electrical things work. I can prove it! Every time the magic blue smoke escapes from a piece of gear, the gear stops working!)

 

The key to re-reflection is that, given enough energy, the cage acts like an antenna and re-emits the signal. With enough absorption, this effect is trivial. Sorta like one of my antennas - it's radiation was trivial!

 

In general, copper is the best cage, iron/steel up next, aluminum down the way a bit. That said, aluminum will get the job done. Remember that the trash can MUST be properly bonded to the lid - any gaps and the cage may be ineffective.

Edited by Capt Bart

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In general you probably don't have to do the math. Since you are not interested in taking scientific data, any conductor should work. You misread

Good eye, I see now.

 

Any conduct has a resistance to electrical current (low temp super conductors are different and not of concern) flow that is dependent on the frequency of the current. Ham operators have tables that give signal loss per foot. Important stuff in matching circuits. The higher the frequency, the more the 'skin effect' becomes apparent.

 

The best cage would be a safe made out of gold. During WW2, gold from Fort Knox was used as buss bars in some power plants because of the shortage of copper (needed for war production) There was a minor problem in that the gold was a much better conductor than copper so some recalibration was needed.[/Quote]

I think you have it backwards, copper is a better conductor than gold, but I see your point.

 

Hams have 'matching' units to adjust for impedance mismatch; if he does it wrong or the mismatch is too great you get arching, sparking, and the magic blue smoke escapes. (Magic blue smoke is what makes electrical things work. I can prove it! Every time the magic blue smoke escapes from a piece of gear, the gear stops working!)

Can you buy more of this magic blue smoke that escapes?

 

 

kidding. lol

The key to re-reflection is that, given enough energy, the cage acts like an antenna and re-emits the signal. With enough absorption, this effect is trivial. Sorta like one of my antennas - it's radiation was trivial!

 

In general, copper is the best cage, iron/steel up next, aluminum down the way a bit. That said, aluminum will get the job done. Remember that the trash can MUST be properly bonded to the lid - any gaps and the cage may be ineffective.

 

But that still leaves two important questions: Does it have to be grounded? Does it have to be insulated on the inside?

According to the guy in the vids the answer is no to both. However, a lot of people say differently.

 

(I made two posts back to back... I think you missed the first one Capt)

Edited by exit

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Capt. Bart is absolutely on the money and yes gold is a muct better conductor than copper wich is why it is used in hi end conductors microelectronics and the reason circuit boads and micrchips have gotten so small

 

If you do some google searches, you'll find that many sources says that the best conductors in order are:

1. Silver

2. Copper

3. Gold

 

Your point about gold being used in microelectronics because its a better conductor doesn't make any sense. First, its not the most commonly used (Copper is). Second, Just because its used in microelectronics doesn't mean its a better conductor.

 

1. Silver is cheaper than gold

2. Silver is a better conductor

 

and like I said... a lot of sources say copper is a better conductor.

 

Here are some sources:

 

http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

http://answers.yahoo.com/question/index?qid=20080918194651AApbo2w

 

and if those sources seem questionable in validity you can read this research article here:

http://www.sjsu.edu/faculty/selvaduray/page/papers/mate234/yingzheng.pdf

 

page 9 at the bottom under Electrical Properties, it concludes:

 

"The copper wire has approximately 33% more conductivity than the gold wire."

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Exit,

Can you buy more of this magic blue smoke that escapes?

 

Yes you can but it is VERY EXPENSIVE (I'll sell you all you want for a HUGH price) but the problem is getting it back in the device that leaked it:rolleyes:

 

As to which is better; my old physics references say gold. Won't argue the point simply because I may be wrong and I can't afford 24 carat gold wire in any case. If I could it wouldn't be strong enough to be useful. Additionally, conductivity is highly dependent on the frequency of the applied voltage.

 

The use of gold, silver, or copper in solid state devices(SSD) depends a lot on what they need to do. Remember most (all?) SSDs are "semi-"conductors. They are basically an insulator (silicon or other insulator) that has been contaminated (doped) with a conducting material. The various labels (CMOS, gallium arsenide (GaAs), AlSb, GaSb, InAs, and PbSe are just a few: see http://en.wikipedia.org/wiki/List_of_semiconductor_materials for a more complete list) tell you what the doping agent is. Depending on need, they are light emitting, light detecting, and various forms of junctions. Most of the doping agents are poisons by the way which is why most land fills want you to dispose of electronics differently than just dumping.

I only have a working physicist's knowledge of the solid state stuff. I liked the field but was more interested in other areas.

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Capt Bart: Many years ago I had to decide whether I would major in physics or EE. From an introductory course in physics I learned that matter is fundamentally lazy - it always takes the path of least effort - and that matter is fundamentally stupid - it tries every other path first. I concluded that these two observations were the heart of physics - the rest is just details. I majored in EE.

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Exit,

 

 

Yes you can but it is VERY EXPENSIVE (I'll sell you all you want for a HUGH price) but the problem is getting it back in the device that leaked it:rolleyes:

[/Quote]

I'm currently broke. I don't think I can afford this huge price. Besides, I still need a Ham radio :)

As to which is better; my old physics references say gold. Won't argue the point simply because I may be wrong and I can't afford 24 carat gold wire in any case. If I could it wouldn't be strong enough to be useful. Additionally, conductivity is highly dependent on the frequency of the applied voltage.

 

The use of gold, silver, or copper in solid state devices(SSD) depends a lot on what they need to do. Remember most (all?) SSDs are "semi-"conductors. They are basically an insulator (silicon or other insulator) that has been contaminated (doped) with a conducting material. The various labels (CMOS, gallium arsenide (GaAs), AlSb, GaSb, InAs, and PbSe are just a few: see http://en.wikipedia.org/wiki/List_of_semiconductor_materials for a more complete list) tell you what the doping agent is. Depending on need, they are light emitting, light detecting, and various forms of junctions. Most of the doping agents are poisons by the way which is why most land fills want you to dispose of electronics differently than just dumping.

I only have a working physicist's knowledge of the solid state stuff. I liked the field but was more interested in other areas.

Not just electronics! Even the new light bulbs have certain chemical/elements (mercury?) that they are trying to avoid getting into the land fills. I can't remember exactly what but I saw a documentary about it.

 

Mea culpa my. High school science is a tad rusty the rest is correct

 

Np! I'm only giving you guys a hard time about it because I like to be corrected when I make incorrect assumptions (which I do all the time lol) or when I'm misinformed.

 

OH and some people might find this interesting/entertaining

 

A professor demonstrating faraday cages

 

Edited by exit
add link

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I am very new here so please excuse my ignorance. Will any of us even have any warning of an incoming nuke? for me I am not in any financial condition to start building anything resembling a faraday shed. I think I may have to resign myself to the fact that I am screwed and nothing (including my BOB) is going to work, so I need to start thinking more about my Bug In preps.

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Capt Bart: Many years ago I had to decide whether I would major in physics or EE. From an introductory course in physics I learned that matter is fundamentally lazy - it always takes the path of least effort - and that matter is fundamentally stupid - it tries every other path first. I concluded that these two observations were the heart of physics - the rest is just details. I majored in EE.

 

I like that quote - that really isn't a bad description of matter or entropy.

 

As Ernest Rutherford ( http://en.wikipedia.org/wiki/Ernest_Rutherford ) Nobel Prize Winner in Chemistry said, "All science is either Physics or stamp collecting"! http://www.quotationspage.com/quote/26219.html

 

At the cutting edge of science you'll find people doing physics and that was part of what took me in that direction. That and the fact that I've always been a sucker for BIG explosions and the biggest bangs of all times occur in the Cosmos. I started as an aeronautical engineer but could not get past the mechanical drawing requirement! Later everybody used CAD but that was after I had learned about exploding galaxies and I was thoroughly hooked into astrophysics.

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I am very new here so please excuse my ignorance. Will any of us even have any warning of an incoming nuke? for me I am not in any financial condition to start building anything resembling a faraday shed. I think I may have to resign myself to the fact that I am screwed and nothing (including my BOB) is going to work, so I need to start thinking more about my Bug In preps.
That's completely dependent on who launched it, the delivery system, the point of origin. According to Wikipedia the most credible of all sources ICBMs travel around 1500mph. With that in mind the distance from Korth Korea to Colorado is about 6000 miles. That gives you about 3 to 4 hours warning for missiles coming out of that part of the world. But if you launch a short range missile from a submarine that is found its way into the gulf of Mexico or any of our coast line you have about 15 to 20 minutes in your in a coastal city. Worst case scenario for warnings the delivery system is a semi truck and has no early warning.

 

Those are just travel time estimates based off the numbers I could find. You still have to factor in the response time. So if the guy locked behind the satellite feed sees a confirmed launch his immediate response is to get his supervisor to make the phone calls. If there's a direct line to the white house from that room great if they spend 4 minutes running threw the building not so great. From there you have to factor in who's where. Secrete service guy who answers the phone is not paid enough to decide if you need to know his job is to get everyone to their assigned dooms day bunkers. By the time they start deciding whether or not you need to know it could be 30 minutes later. The the probable answers is you don't need to know until the last minute. What ever building your in offers more protection then being stuck in traffic and if the word comes threw you have 10 minutes to shelter in place thats not enough time to go out and loot what you 'need'.

 

So after all of that there's a good chance you will get little to no warning that a nuke is coming. Capt bart would have better info on this.

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Capt Bart: Many years ago I had to decide whether I would major in physics or EE. From an introductory course in physics I learned that matter is fundamentally lazy - it always takes the path of least effort - and that matter is fundamentally stupid - it tries every other path first. I concluded that these two observations were the heart of physics - the rest is just details. I majored in EE.

 

Capt Rob, You're absolutely right. Although, the concept generalizes to things that behave and are made up of matter.

 

For example, human/animal behavior. I've studied principles of behavior extensively as an undergraduate and I will hopefully begin my Ph.D soon (waiting to see whether I'm accepted into a program at the moment).

 

I just want to point out that its not really laziness that drives matters and overall behavior of anything to 'behave' in a way which results in the least amount of effort, its logic in its purest form. Organisms (and matter I'm guessing) behave in a way which produces the most amount of reward at the least cost. The only difference between organismic behavior and that of matter is perspective. Everything has a purpose, affect, and effect.

 

I find it hard not to be amazed and humbled by our universe. We and everything around us may be lazy, but logical at the very least.

 

We just don't understand nature until we ask the right questions.

 

I like that quote - that really isn't a bad description of matter or entropy.

 

As Ernest Rutherford ( http://en.wikipedia.org/wiki/Ernest_Rutherford ) Nobel Prize Winner in Chemistry said, "All science is either Physics or stamp collecting"! http://www.quotationspage.com/quote/26219.html[/Quote]

lol if thats not a jab at other sciences then I don't know what is...

I can understand why someone would be so enthralled with physics though, of all sciences it will probably impact society the most technologically, though not socially. By that I mean some other sciences will produce better teachers, professionals, and students.

At the cutting edge of science you'll find people doing physics and that was part of what took me in that direction. That and the fact that I've always been a sucker for BIG explosions and the biggest bangs of all times occur in the Cosmos. I started as an aeronautical engineer but could not get past the mechanical drawing requirement! Later everybody used CAD but that was after I had learned about exploding galaxies and I was thoroughly hooked into astrophysics.

Agreed, most scientists are drawn to physics and astrology. Its not my field and I love to learn about it.

 

That's completely dependent on who launched it, the delivery system, the point of origin. According to Wikipedia the most credible of all sources ICBMs travel around 1500mph. With that in mind the distance from Korth Korea to Colorado is about 6000 miles. That gives you about 3 to 4 hours warning for missiles coming out of that part of the world. But if you launch a short range missile from a submarine that is found its way into the gulf of Mexico or any of our coast line you have about 15 to 20 minutes in your in a coastal city. Worst case scenario for warnings the delivery system is a semi truck and has no early warning.

 

Those are just travel time estimates based off the numbers I could find. You still have to factor in the response time. So if the guy locked behind the satellite feed sees a confirmed launch his immediate response is to get his supervisor to make the phone calls. If there's a direct line to the white house from that room great if they spend 4 minutes running threw the building not so great. From there you have to factor in who's where. Secrete service guy who answers the phone is not paid enough to decide if you need to know his job is to get everyone to their assigned dooms day bunkers. By the time they start deciding whether or not you need to know it could be 30 minutes later. The the probable answers is you don't need to know until the last minute. What ever building your in offers more protection then being stuck in traffic and if the word comes threw you have 10 minutes to shelter in place thats not enough time to go out and loot what you 'need'.

 

So after all of that there's a good chance you will get little to no warning that a nuke is coming. Capt bart would have better info on this.

 

I don't think its very likely we could be attacked by an ICBM. Even if North Korea could launch a nuclear device with an ICBM (which it can't last I checked), we have freakin airplanes with lasers to shoot that shit down.

 

Didn't we invent ICBM defense?

 

A nuclear device being detonated in the United States would most likely be on the ground. Its practically impossible to detonate one in space above us, at least by my reckoning. We should be more worried about a CME :)

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EXIT

Agreed, most scientists are drawn to physics and astrology. Its not my field and I love to learn about it.

Astrology is the predicting of the future based on the position of planets within the signs of the Zodiac. Astronomy/Astrophysics is the application of the scientific method to the study of the cosmos and the physical processes that makes it function. I actually had a friend put on a letter of recommendation that I was very interested in Astrology. I got the job anyway but it was embarrassing.

 

Autonomous,

According to Wikipedia the most credible of all sources ICBMs travel around 1500mph.

This is one of those cases where Wikipedia is full of it. ICBM, following a ballistic path can reach velocities of up to 5 miles/sec. The SR-71 Blackbird exceeds by a sizable margin 1500 miles an hour. Time of flight from the old Soviet missile fields to the US was on the order of 45 minutes. If ICBMs are coming over the pole, they show up on DEW line radars about 30 minutes before impact. That is part of why the early warning satellites are so important. They can detect a launch and give extra warning. SLBMs (Sea Launched Ballistic Missile) can have as little as 7 minutes warning.

 

As you note, a truck bomb gives zero warning.

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The thing to remember about a Faraday cage is that it only works while the device is actually inside the cage with no connection to the outside world. Take it out to update the content of your kindle and it is not protected during the time it is outside the cage.

 

The only way to be certain that you've built an EMP proof box is to check it against the EMP. There is no way to do that for civilians. All we can do is out best and be prepared if we are wrong about the integrity of our cage.

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EXIT

 

Astrology is the predicting of the future based on the position of planets within the signs of the Zodiac. Astronomy/Astrophysics is the application of the scientific method to the study of the cosmos and the physical processes that makes it function. I actually had a friend put on a letter of recommendation that I was very interested in Astrology. I got the job anyway but it was embarrassing.

I stand corrected!

 

That's a pretty funny story by the way lol

 

Autonomous,

 

This is one of those cases where Wikipedia is full of it. ICBM, following a ballistic path can reach velocities of up to 5 miles/sec. The SR-71 Blackbird exceeds by a sizable margin 1500 miles an hour. Time of flight from the old Soviet missile fields to the US was on the order of 45 minutes. If ICBMs are coming over the pole, they show up on DEW line radars about 30 minutes before impact. That is part of why the early warning satellites are so important. They can detect a launch and give extra warning. SLBMs (Sea Launched Ballistic Missile) can have as little as 7 minutes warning.

 

As you note, a truck bomb gives zero warning.

 

We woudn't have to worry about an EMP on the ground though... radiation would be the bigger problem

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hey i did ok on estimates considering the sources i had to work with.

 

Exit, now the question is what if you take the truck bomb and put it in a plane. Not like a jumbo jet but a private plane that a corporation or a disgruntled nuclear power could afford or a corporation owned by the former. The plane wont get you into orbit but it would be a hell of a way to hide a missile and you can expect about 5 minutes of movement off your flight plan to get it into position.

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I don't know enough about airport security to give you a good answer.

 

However, I'm pretty sure that would be extremely unlikely to happen in the U.S.

Maybe I'm being optimistic but I assume there is a certain level of security to get into any airport. I'm also assuming airplanes coming into the U.S. airspace have met stringent security requirements to be allowed in, especially after 9/11.

 

Even so, I remember reading that the atomic bombs that were dropped on Hiroshima and Nagasaki did not explode on the ground like a typical bomb, rather, they exploded at a high altitude to cause the most ammount of damage and to avoid leaving a huge crater (wasted blast energy). So I'm assuming based on this tid-bit info I've learned way back (who knows when) that in order for an nuclear device inflicted EMP to be effective, it would HAVE to be extremely high altitude.

 

To get a better idea of how high the plane has to be.... here is a pic

 

post-1642-13851497790469_thumb.jpg

 

Now figure out how high (altitude) most planes (private jets and commercial airliners) can get and you'll have an idea how far an EMP would go.

Edited by exit
clarification

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just did some digging. The record for highest altitude plane is 67 miles. But that was a military plane.

 

1 mile = 5280 feet

 

Most planest are not able to fly higher than 45,000 feet. Which is roughly 8.5 miles. Lets push it to 9.

 

Judging by the picture, the EMP would effect a decent size of the U.S. (a few cities) but probably not even half. It would be much easier to recover from than a High Altitude EMP from an ICBM.

 

I wouldn't worry about it too much. The CME is what worries me.

Edited by exit

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I believe the Hiroshima bomb was fused to explode at 900 ft. Best EMP altitude is 200 to 250 miles.

 

Swampfox, yes, a metal military ammo can would work well as long as there were no significant holes in it. The object being protected MUST not be touching the metal of the can. It should be on double thick cardboard or some sort of insulation holding it away from the inside walls.

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