0 Members and 4 Guests are viewing this topic.
The magnetic field at a distance r from a very long straight wire, carrying a steady current I, has a magnitude equal to[attachment=11603]
I started looking into it because when we discussed wireless chargers on the radio programme I suggested that this technology is only useful over short distances; the reason I put forward was that the base coil (the driver) produces an alternating field that dies away according to 1/r^2 and that therefore the slave coil - resident in the device and which picks up the power from the changing field - needs to be sufficiently close to feel the changing field and hence generate a charging current.
At first glance, such a power transfer is reminiscent of relatively commonplace magnetic induction, such as is used in power transformers, which contain coils that transmit power to each other over very short distances. An electric current running in a sending coil induces another current in a receiving coil. The two coils are very close, but they do not touch. However, this behavior changes dramatically when the distance between the coils is increased. As Karalis, a graduate student in electrical engineering and computer science, points out, "Here is where the magic of the resonant coupling comes about. The usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system."
Wireless power transfer over two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Members of the team that performed the experiment are obstructing the direct line of sight between the coils.
BTW If a Hollywood movie is made of this 'scientific breakthrough' Kelsey Grammer is ideal to play Professor Joannopoulos  ...[attachment=11620]
It's hard to tell more without having more technical information on their setup.
This work was funded by the Army Research Office (Institute for Soldier Nanotechnologies), National Science Foundation (Center for Materials Science and Engineering), and the Department of Energy.
I wonder what these folks http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebContentAreaLanding/Page/1153822623782(or their local equivalent) would think of that demonstration.