Your typical Foucault's current brakes operate on a disk, which is placed in an electromagnetic field in order to transform kinetic energy into heat without friction. The problem is that the disk still overheats, just like an usual disk brake. In the case of railways this also needs that the wheels have adherence to rail.
Theoretically, it would be as simple as to place two huge magnets around both rails in order to brake the train. A simple mechanical design could move the magnets up and down whether we want braking or not. The magnetic field would turn kinetic energy into heat, but this would not overheat as the heat would advance along the train itself. Also this would not require any friction, and as thus, no mechanical parts have to be changed due to use. (Friction braking is still required for stopping the train once a low speed would has been attained with Foucault's current braking).
This would have the following advantages :
- Braking doesn't rely on rail adherence
- Since permanent magnets can be used, no electricity needed to operate the braking device (work on non-electrified railways, or in emergency when there's damage to the overhead lines)
- No risk of overheating in the long run since the dissipated heat moves along the rail.
- Don't damage brake pads, and don't damage rails as does the usual emergency brake which applies friction to the rails.
The only major problem I'd see with such a system is that the magnets would also attract the rail itself (made from steel) - but if magnets on both rails are in reverse directions each force will cancel the other, so the magnets just have to be very solidly attached.
Is such a system possible or have I missed something ? If it's possible, why isn't it more widely used ? Or would the magnets needs to be too strong for this idea to be any effective, and this would have effects on passengers or their belonging ?