An animal restraining system includes a radio frequency transmitter adapted to be located adjacent an area in which the animal is to be restrained, a transmitting antenna, and a collar unit worn by the animal. The collar unit has a multiplicity of radio signal receivers each having a highly directional...http://www.google.fr/patents/US5067441?utm_source=gb-gplus-shareBrevet US5067441 - Electronic assembly for restricting animals to defined areas
Electronic assembly for restricting animals to defined areas
