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In Reply to: RE: From Wiki: posted by d3vkb on April 04, 2011 at 15:41:36
What's at issue is EMI/RFI.
Depending on the source and distance from the source, the interference will predominantly be either E-field or H-field. A material that's effective for E-field shielding won't be as effective at H-field shielding, and vice versa.
Since crystals aren't electrically conductive to any degree and have no permeability to speak of, their effects with regard to H-field interference will be virtually nill.
A lump of iron would be far more effective than any lump of crystal. Though a lump of anything isn't terribly effective unless the receiving circuit happens to be in its "shadow."
se
Follow Ups:
by Carl Johnk, admittedly an older text, but then again I'm, pretty old:
Carl states that the magnetic moment in diamagnetic material is zero in absence of a magnetic field. Application of a magnetic field exerts a a force ( Lorentz force) on the orbiting electron which will generate a small magnetic field. "Diamagnetism is presumed to exist in all materials...."
Typical values are -0.95X10^-5 for copper, -.8X 10^-5 for germanium. Paramagnetic material has a much higher susceptibility: FeSO4, FeO3, magnetite and hematite being on the order of 10^-3. In both cases the net magnetism at rest with no magnetic field applied is Zero.
Stu
If you do, then simply regurgitating something from some physics text isn't the way to make it.
se
to your statement that quartz has no electrical or magnetic effects?
Just wondering,. because I can find reference in a standard electrical engineering text about the magnetic properties of all materials, but you have stated that quartz can have no affect at all.
Please quote your reference. I would greatly appreciate that rather than a shot in the dark formed by only your intellect.
Stu
to your statement that quartz has no electrical or magnetic effects?
Here's what I actually said:
Since crystals aren't electrically conductive to any degree and have no permeability to speak of, their effects with regard to H-field interference will be virtually nill.
Just wondering,. because I can find reference in a standard electrical engineering text about the magnetic properties of all materials, but you have stated that quartz can have no affect at all.
Great. Then get out your "standard electrical engineering text" and tell us what the relative permeability of quartz is.
Because I have several myself as well as texts specifically relating to the electrical properties of materials. None of them give the relative permeability of quartz. Nor do any Google searches turn up anything.
Here's why.
Quartz is diamagnetic.
However the most diamagnetic material outside of a superconductor is bismuth. And even then bismuth is only VERY VERY weakly diamagnetic. For all intents and purposes, it's about as effective as air at shielding from magnetic fields, save for eddy current losses due to the fact that bismuth is a conductor rather than an insulator as quartz is.
So as I said, their effects as far as H-field interference goes is virtually nill.
se
Same thread you state quartz has no magnetic properties at all.
"Virtually nil" seems to be a highly subjective statement, at least in my thinking. I stated the permeability, but now you are stating it is negligible. Now what numerical measurement is significant for you? At what point does the human ear distinguish any change? If you can not answer that question then you have no means of determining what is negligible. Just because a number is numerically small does not mean it may be negligible.
After all, in the medical field there are drugs which can affect the human body in what could be deemed negligible amounts (amount of plutonium to kill you for example,as taken from the headlines).
Stu
Same thread you state quartz has no magnetic properties at all.
No, I did not.
"Virtually nil" seems to be a highly subjective statement, at least in my thinking.
When you're talking about magnetic properties on the order of that of air, then I think it's safe to call such magnetic properties "virtually nil."
I stated the permeability, but now you are stating it is negligible.
No, you didn't state the permeability. You simply said the book said it was similar to that of copper. And didn't mention the permeability of copper either.
The relative permeability of a vacuum is 1.
The relative permeability of copper is 0.999994.
The relative permeability of sapphire is 0.99999976.
Now what numerical measurement is significant for you? At what point does the human ear distinguish any change?
A change in what exactly?
se
your post earlier in this same thread where you refer to a wikipedia entry.
Stu
your post earlier in this same thread where you refer to a wikipedia entry.
In that post I said crystals had "no permeability to speak of."
That's NOT the same as saying they have absolutely NO permeability. Only that it is very very small. So small that it doesn't warrant any mention.
You seem to have problems with comprehension, which would explain why you came up with the erroneous notion that permeability was measured in Webers per meter per second.
se
is a subjective statement. The text gives the permeability of Germanium, a crystal as being about the same as copper.
Where is your text and statement? You criticize but present no backing for your statements.
Stu
The text gives the permeability of Germanium, a crystal as being about the same as copper.
And the permeability of copper is, for all intents and purposes, about the same as air.
se
It is significantly higher being a solid.
Also have you examined the units used to measure permeability? Webers per square meter per second. A Weber is equivalent to a Tesla. That's a huge unit. The only speaker I know that measures its magnetic field in Teslas is the neodymium magnet Lowthers.
Stu
It is significantly higher being a solid.
No, it's not. Copper's permeability is measured as a solid. As I said previously, copper's relative permeability is 0.999994. For all intents and purposes, no better than air.
Also have you examined the units used to measure permeability?
Yes, I have.
Webers per square meter per second.
*BZZZZZZZZZZZT!*
Wrong.
The SI unit for permeability is Henries per meter (H/m).
The Weber is the unit for magnetic flux.
You simply don't have a clue what you're talking about.
se
"Since crystals aren't electrically conductive to any degree and have no permeability to speak of, their effects with regard to H-field interference will be virtually nill."
I don't think anyone would argue that with you Steve. Apparently they are believed to behave as lossy space to E-fields with the mechanism being them squirming around from the field and thus converting some of it's energy to heat. Naturally that would mean that they need to be at a high-Z node to do their thing.
Rick
Piezo electricity is simply a figment of a physicist's imagination.
Stu
Piezo electricity is simply a figment of a physicist's imagination.
You're good at creating straw men, I'll give you that.
se
beginning to sound like Geoff Kait: any relation?
Stu
Didn't you accuse me pretty much the same? But now you're harping on someone else!
Flavor of the month. So much for intellectual honesty.
beginning to sound like Geoff Kait: any relation?
Surprise, surprise. Another straw man.
se
and yawn again
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