Physicists have developed a superconducting coil capable of transmitting more than five kilowatts of contactless electricity with only small losses. Conceivable applications include autonomous industrial and service robots, medical equipment, vehicles, and even aircraft.
Contactless power transmission has already established itself as a key technology for charging small devices such as mobile telephones and electric toothbrushes. However, users would also like to see contactless charging made available for larger electric machines.
The researchers developed a special coil design to ensure that temperature increases don't disrupt the superconductivity. It involves separating individual windings of the coil from one another by spacers. This trick significantly reduces alternating current loss in the coil. As a result, nearly lossless power transmission as high as the kilowatt range is possible.
The team chose a coil diameter for their prototype that resulted in a higher power density than is possible in commercially available systems. The basic idea with superconducting coils is to achieve the lowest possible alternating current resistance within the smallest possible winding space and thus to compensate for the reduced geometric coupling.
To do so the researchers had to resolve a fundamental conflict. If they made the distance between the windings of the superconducting coil small, the coil would be very compact, but there would be a danger of superconductivity collapse during operation. Larger separations would, on the other hand, result in lower power density.
They optimized the distance between the individual windings using analytical and numerical simulations. The separation is approximately equal to half the width of the winding conductor. The researchers now want to work on further increasing the amount of transmittable power. If they succeed, the door will open to a large number of very interesting application areas, for example, uses in industrial robotics, autonomous transport vehicles and high-tech medical equipment.
The large-scale applicability of the system still faces an obstacle, however. The coils require constant cooling with liquid nitrogen, and the cooling vessels used cannot be made of metal. The walls of metal vessels would otherwise heat up considerably in the magnetic field, much like a pot on an induction stove.
There are as yet no cooling vessels like this, which are commercially available. This will mean an extensive amount of further development effort, but the achievements up to now represent major progress for contactless power transmission at high power levels.