There is iron in our blood, which is magnetic. Roughly how strong would a magnet have to be to induce a noticeable attraction? It would be nice to know this for several distances. Also, do electromagnets that strong exist?
Biophysics – How Strong a Magnetic Field Needs to Be to Noticeably Attract a Person
biophysicselectromagnetism
Related Solutions
To modify the distribution of magnetic field (irrespectively of the source - PMs or coils), you need some material with non-unit magnetic permeability, such as steel. These materials 'concentrate' the field lines, pulling them in away from the surrounding air (which has a permeability of very nearly 1). So to shield the outside world, you'd need to create a 'circuit' of permeable material (let's say steel), which channels the magnetic flux from the north pole of your magnet to its south pole. If you leave a little gap in one part of your circuit, the field will be enhanced in the gap.
Short answer: No.
The iron in the body is not magnetic because it is not in metallic form nor magnetite form. It is instead an ion complexed to nitrogen atoms in turn bonded to proteins.
The human body repels magnets very slightly because it has water, which is diamagnetic. Powerful enough magnets have been used to make frogs float, but unfortunately only small objects can be levitated this way.
Diamagnetic materials will seek out regions of lower field strength. The diamagnetic acceleration goes as B*dB/dx, where B is the magnetic field and dB/dx is the gradient. Larger objects need more total B because the B gradient must persist over a longer distance. Because the force is B*dB/dx and not dB/dx, the maximum B required follows a square-root field strength scaling law. For a human, ~25 times larger than a frog, you will need a field 5 times as intense. Ten tesla will levitate a frog, so 50 to for a human. 45 is our limit (national high magnetic field lab) for now. It requires megawatts of power for the resistive inside, liquid helium for the superconductive outside, and probable lots of care to make sure the whole thing doesn't explode due to the magnetic forces. In the future, it is not infeasible that we will produce 50 tesla, but it would probably have a small bore/coil size ratio.
Far more important is that 10 tesla MRI will make a person quite dizzy. The vestibular system (ear motion detector) runs a DC electric (ionic) current through a fluid. If you put this in a static magnetic field, you will get a Lorentz force, which will swirl the liquid. If you rotate in the field, other magnetic effects on conductors would apply as well. 50 tesla would be much harder, if not dangerous.
The shape is also important. You would need to build a static machine so that you can sit or stand in the "gravity", but you can't walk around.
Finally, your magnet would attract ferromagnetic projectiles with 25 times the force of a 2T MRI. Shrapnel!
Lets stick to rotating space stations for now.
Best Answer
Humans are weakly diamagnetic. Rather than being attracted by a magnetic field we would tend to repel the lines of force.
Look at the work of the High Field Magnet Laboratory http://www.ru.nl/HFML/, in particular http://www.ru.nl/hfml/research/levitation/diamagnetic/ where they demonstrate levitation of a living frog. It took about 16T to levitate the frog.