"German inventor Dirk Strothmann has created what he claims is a small, no-contact, self-contained dynamo bike light.  According to Strothmann, his fork- or brake caliper-mounted Magnic Light works with any type of metallic wheel rims. While other contactless dynamos do exist, those incorporate wheel-mounted magnets. Dirk's product, however, has the magnets in the dynamo, and utilizes eddy currents. In a nutshell, these are electrical currents that are induced in a conductor, when that conductor is exposed to a changing magnetic field."

http://www.gizmag.com/magnic-light-contactless-dynamo/21494/