Re: Magnetic field transmitters and receivers.
- From: Benj <bjacoby@xxxxxxxxxxx>
- Date: Sat, 19 Jul 2008 21:52:49 -0700 (PDT)
On Jul 19, 10:25 pm, "Timo A. Nieminen" <t...@xxxxxxxxxxxxxxxxx>
wrote:
Surely a loop antenna qualifies as such? Fine, once you're in the far
field, all you have is an everyday EM wave, but in the near field, it
would be hard to argue successfully that you don't have a genuine magnetic
field receiver/transmitter.
Not really, but one would have to examine the configuration to be
sure. There is some magnetic field "transmission" in the near field
but it would have to be separated from EM components.
Look. I know MIT just invented "magnetic power transmission" and
everybody is oooing and ahhhing! Bollocks! Bunkies, it's called
magnetic induction and it's been around for a LONG time!
Yes, you can detect static magnetic fields, but in thhat case, there isn't
any _transmission_.
Absolutely. A DC field does indeed proceed out into space when turned
on, but carries only one bit of information so it's hardly a
'transmission"!
If you're detecting changing magnetic fields, then you
aren't doing anything fundamentally different from a loop antenna.
Not so. Generally inductive pickups work differently from loop
antennas. Antennas are designed to work with EM waves. An inductive
pickups is designed to work with ONLY a changing magnetic field. But
let me point out here that there is a certain advantage to inductive
transmission. While EM waves fall off as r squared induction falls
off only as r. A loop around a long solenoid has the same output
voltage no matter how large you make it! Magnetic fields can indeed
be picked up at large distances with properly sensitive apparatus. A
common application some time ago was tapping of telephone
conversations using inductive pickups at considerable distance from
the wires. [which is why it's always funny when people think they
heard "clicks" that mean their phone is tapped by the CIA!]
Bottom line: Magnetic "transmission" is just plain old magnetic
induction! Period.
.
- References:
- Magnetic field transmitters and receivers.
- From: jonas . thornvall
- Re: Magnetic field transmitters and receivers.
- From: Timo A. Nieminen
- Magnetic field transmitters and receivers.
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