A device for wireless transfer of information includes a data carrier in the form of a thin card, and a transponder that receives a first microwave signal, modulates it and codes it with data, and reradiates a second microwave signal without adding new energy thereto. The transponder includes at least...http://www.google.de/patents/US5552790?utm_source=gb-gplus-sharePatent US5552790 - Device for wireless transfer of information
