A wireless power receiver includes a power receiver configured to wirelessly receive power, and including a direct current -to-DC converter, and a power detector configured to detect power detection information from a front end of the DCDC converter. In this apparatus, the length and the inclination of the support surface is selected to, in combination, impart a minimum critical rotational velocity to an object rolled on the support surface. An implantable medical device incorporating such an electrical contact assembly is also disclosed.