US Patent 8248263 Personnel safety utilizing time variable frequencies

A system to improve safety of workers who are in proximity to mobile machines includes a machine mountable radio-frequency identification reader that wirelessly monitors radio-frequency identification tags worn by workers moving relative to and in proximity to a mobile machine when the reader is mounted on the machine. The reader includes a processor and an antenna front-end which is switchable between an omni-directional antenna or at least one directional antenna. The omni-directional antenna is mountable so as to monitor a machine circumference completely around the mobile machine. Each directional antenna is mountable so as to monitor only either a front or a back of the mobile machine relative to the machine's direction of motion.