A Homemade Magnetohydrodynamic Thruster (MHDT)
Based on the image on the left, it is possible to make a simple MHD thruster, just powerful enough to propel a toy boat.
This type of thruster generates magnetic fields by passing an electric current through a liquid conductor, such as sea water. Using another magnetic field, the liquid can be pushed in a chosen direction, therefore generating thrust. You can easily make one of these devices from household materials and a couple of neodymium magnets. In the diagram below the small arrows represent the intersecting electric and magnetic fields. the large blue arrow represents the flow of water.
Two opposing inner faces of a rectangular plastic tube are covered by metal strips. These are the main electrodes and should have a connection for a battery. Magnets are attached on the outside of the tube so that they are attracting each other, and are at 90° to the electrodes.
The metal strips here are cut from a thin Aluminium sheet, but you can just use foil although it wont last as long. The electrolysis and salt water corrosion soon eats away at the metal, but foil should last just long enough to see it working. The best sort of electrode would possibly be made from carbon. A good power source for this device would be a pulse width modulated supply such as our power pulse modulator. This would allow you to adjust the frequency and width of electical pulses so that you could get the optimum thrust from your design.
This setup shows the electrodes closer together than the magnets. The combination of magnets used in this device were not strong enough to move the electrified water with any decent force. At only 1.5V in salty water, large amounts of electrolysis occurs, but the water does generally flow in one direction.
The key to getting the best performance it to have the strongest magnetic field you can get across the gap between the electrodes.
Also make sure the magnets are behind the plastic or insulated somehow. You don't want them shorting out the electric current in the water.