US Patent 10359786 UAV shutdown constraint near overhead lines

FIG. 1 shows airframe (10) with powertrain (11) supporting electromagnetic field strength sensor (12), reference electromagnetic field strength (14), comparator (16), and shutdown (18) flying along a transmission line with towers (40, 42, and 44), phase conductors (46, 48), and 50, and shield wires (52 and 54). Reference electromagnetic field strength (14) is adjusted before the flight to set the minimum electromagnetic field strength before shutdown (18) reduces the power to powertrain (11). The reference electromagnetic field strength (14) corresponding to a characteristic radial dimension (58), and thus virtual tunnel (22), outside of which airframe (10) cannot fly without automatic shutdown (18), regardless of the state of the autopilot, GPS signal, or radio link.