http://www.flickr.com/photos/53399890@N05/6341068132/in/
Well, I know that in a toroid, the magnetic field is zero in the center, and zero outside of it.
I think the current enclosed would be zero. But again, I'm not too sure here.
Well, I know that in a toroid, the magnetic field is zero in the center, and zero outside of it.
I think the current enclosed would be zero. But again, I'm not too sure here.
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Absolutely. We used to fly over subs tied up to piers to get our MAD gear calibrated. MAD (magnetic anomaly detection) was used by S2 and P3 aircraft in the U.S. and other navies to detect subs while the subs were submerged. [See source.]
But let's set the record straight, it's not the sub's magnetic field that is detected, it's an anomaly in Earth's magnetic field that is detected. Because a sub is a huge chunk of metal, it causes the smooth flux of Earth's magnetic field to make sharp abnormal (one might even say anomalous) bends. And those are what MAD detects... the anomalies.
As to B fields from the electronics on board a sub, you are right. They are not detectable above or below the surface. The hull does a nice job of shielding whatever spurious fluxes there might be, but most of the fields are closed fields and cancel out. So there really is very little if anything outside the hulls of subs to detect.
By the way, think about i, if there were B fields all over the place, what would that do to the skipper's Rolex? We couldn't let that happen could we?
But let's set the record straight, it's not the sub's magnetic field that is detected, it's an anomaly in Earth's magnetic field that is detected. Because a sub is a huge chunk of metal, it causes the smooth flux of Earth's magnetic field to make sharp abnormal (one might even say anomalous) bends. And those are what MAD detects... the anomalies.
As to B fields from the electronics on board a sub, you are right. They are not detectable above or below the surface. The hull does a nice job of shielding whatever spurious fluxes there might be, but most of the fields are closed fields and cancel out. So there really is very little if anything outside the hulls of subs to detect.
By the way, think about i, if there were B fields all over the place, what would that do to the skipper's Rolex? We couldn't let that happen could we?
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This page gives a very brief overview of the once top-secret anti-submarine harbour defence technology known as "Indicator Loops":
http://indicatorloops.com/loopworks.htm
Cheers ebs
http://indicatorloops.com/loopworks.htm
Cheers ebs