A ring antenna (10) for resonant circuits for identifying metallic containers has an annular core (11) having at least one core surface (11a') corresponding to at least one surface of the container and made from ferrite. The core may be U-shaped, having a base portion and a first and second arm portions,...http://www.google.cl/patents/US5864323?utm_source=gb-gplus-sharePatent US5864323 - Ring antennas for resonant circuits
