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Re: LF: Magnetometers

To: <[email protected]>
Subject: Re: LF: Magnetometers
From: "Markus Vester" <[email protected]>
Date: Sun, 27 Apr 2014 08:18:37 +0200
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Hi Edgar,
in principle, yes. But:
The question is on how much improvement you would get, compared to a simple induction loop. A loop responds to the time derivative of the field, so doesn't respond to DC and very low frequencies. That's where sensors which respond to the field itself are needed (eg compass needles, Hall effect, fluxgates, NMR, squids). For example, the noise of a fluxgate is more or less flat with frequency, and there is a crossover frequency above which the simple loop wins (usually around 100 Hz, depending on factors like the size, copper mass, or ferrous core of the loop).
A proton NMR magnetometer with a large enough sample is sensitive at DC, and has the additional advantage of absolute calibration referenced to the NMR Larmor frequency. But it actually responds to the integral of the field, so SNR falls off more rapidly at with frequency.
Superconducting quantum interference devices (squids) have been used as very low noise magnetometers up to a several 100 kHz. But this makes sensse only in a shielded room. In the open, atmospheric background noise dominates by orders of magnitude, and a copper coil of less than a square meter is able to provides ample SNR at VLF. Narrowband resonant matching doesn't improve the SNR from the coil itself (induction voltage vs resistive noise), but it helps to bring down the noise contribution from the attached preamplifier.
Best 73,

From: edgar
Sent: Sunday, April 27, 2014 7:05 AM
Subject: LF: Magnetometers

Possibly a silly question but,

Is it possible to detect low frequency electromagnetic waves with
Fluxgate or Proton Magnetometer?

e.g. waves with frequency of 8 kHz to 29 kHz?

Regards, Edgar
Moonah, Tasmania.

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