El 10-11-14 0:32, escribió:
wrote:
El 09-11-14 23:01, escribió:
wrote:
El 08-11-14 8:03, escribió:
In rec.radio.amateur.antenna wrote:
"Brian wrote in message
...

His whole grasp of antenna theory is flawed.
He was trying to (indirectly) argue the other day via his his
interpretation of Maxwell's Equations you could generate an EM wave
by waving a magnet about. When corrected, he introduced another
variation.

Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your
posts these days are personal attacks aimed at one or another.

Why do you behave like that?

Certainly, as I corrected myself, if you wave a magnet about fast enough,
say, 1000,000,000 times per second, you will certainly generate an EM wave
and no-one has corrected me on that point because that point is true.

No, that point is utterly, completely, and absolutely false and goes
once again to show you have no clue as to the difference between an
electric field, a magnetic field, and an electromagnetic field.



Without doing the math, can we be sure that there is no radiation from
a rotating magnetic dipole?

You could ask someone who understands the math.

It is not that I don't understand the math, but I don't want to spend
time if we can get an answer by using reciprocity (the part of my text
you skipped).

Back to reciprocity:

When using reciprocity, a permament magnet will rotate in an EM
radiation field (produced by an antenna-transmitter combination, far
field distance). Of course you need to spin-up the magnet as you don't
have a rotating field. Once it is synchronized, you can extract power
from it (resulting in a slip angle).

So the other way around, using reciprocity, the rotating magnet will
generate power in a load connected to the antenna that was used to
generate the EM field.

None of which has a permanet magnet spinning in empty space, which is
why I snipped it.

If we can't prove that reciprocity (or other assumption) doesn't hold
for this case, then the rotating permanent magnet produces EM radiation.

And rigously proving any of that is much more complex then F=ma.


Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.


--
Wim
PA3DJS
Please remove abc first in case of PM

Wimpie wrote:

snip

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

You mean like in a pulsar?

For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Again, not talking about any "electromechanical system", just a permanet
magnet spining.

Also implied is the macro level, i.e. a magnet one can hold in one's
hand and velocities well below any relativisitc effects.


--
Jim Pennino

El 10-11-14 19:39, escribió:
wrote:

snip

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

You mean like in a pulsar?
To be more precise, I mean the radiation with same frequency as pulsar
rotation, of course only present when there is a net magnetic dipole
moment. I am not pointing to the pulsed RF radiation.


For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Again, not talking about any "electromechanical system", just a permanet
magnet spining.

That just spinning magnet produces dB/dt, hence an E-field (not
conservative).

Superposition of two quadrature magnetic oscillating dipoles (small
loop antnenas) gives a rotating magnetic dipole field. Such a
quadrature setup can be exchanged by a rotating permanent magnet.


Also implied is the macro level, i.e. a magnet one can hold in one's
hand and velocities well below any relativisitc effects.

I considered non-relativistic velocities only.



--
Wim
PA3DJS
Please remove abc first in case of PM

Wimpie wrote:
El 10-11-14 19:39, escribió:
wrote:

snip

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

You mean like in a pulsar?
To be more precise, I mean the radiation with same frequency as pulsar
rotation, of course only present when there is a net magnetic dipole
moment. I am not pointing to the pulsed RF radiation.


For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Again, not talking about any "electromechanical system", just a permanet
magnet spining.

That just spinning magnet produces dB/dt, hence an E-field (not
conservative).

Superposition of two quadrature magnetic oscillating dipoles (small
loop antnenas) gives a rotating magnetic dipole field. Such a
quadrature setup can be exchanged by a rotating permanent magnet.


Also implied is the macro level, i.e. a magnet one can hold in one's
hand and velocities well below any relativisitc effects.

I considered non-relativistic velocities only.

Did you concider it is difficult to hold a pulsar in one's hand?



--
Jim Pennino

wrote in :

Did you concider it is difficult to hold a pulsar in one's hand?


Nevrr mind the context, you could sell that! Imagine the T-shirt trade
alone...

On 11/10/2014 6:00 PM, Wimpie wrote:
El 10-11-14 19:39, escribió:
wrote:

snip

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

You mean like in a pulsar?
To be more precise, I mean the radiation with same frequency as pulsar
rotation, of course only present when there is a net magnetic dipole
moment. I am not pointing to the pulsed RF radiation.

I want to be clear on this. You are saying that a rotating magnetic
dipole *does* create EM waves just the same as any antenna? The only
difference between a Pulsar and a handheld magnet is one of scale?


For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Again, not talking about any "electromechanical system", just a permanet
magnet spining.

That just spinning magnet produces dB/dt, hence an E-field (not
conservative).

Superposition of two quadrature magnetic oscillating dipoles (small loop
antnenas) gives a rotating magnetic dipole field. Such a quadrature
setup can be exchanged by a rotating permanent magnet.


Also implied is the macro level, i.e. a magnet one can hold in one's
hand and velocities well below any relativisitc effects.

I considered non-relativistic velocities only.

I'm not interested in Jim's hand waving. Either a magnet can or can't
generate EM waves. If a big one does it, then a little one does it too.

--

Rick

"Sn!pe" wrote in message
.uk...
Wimpie wrote:

[...]

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Would such radiation *propagate* though? I have a vague recollection
from many years ago that there's a difference between a proper *radio*
wave and another sort of oscillating field that one also gets close to
an antenna. Was it something to do with the phase relationship between
the electric and magnetic components of the field perhaps?

I may well have imagined this, it was a very long time ago.

What you appear to be discussing is the difference between the Near Field
and the Far Field