Patent ID: 7563054

Claim:
Marking tape comprising a plurality of passive resonant circuits each having a selected resonance frequency and having a sufficient size and dimensioning to be wirelessly detected when positioned in a hidden place such as an underground position, each resonant circuit comprising an inductive coil formed by a conductive material layer on one surface of a dielectric plastic film, and a capacitor formed by a conductive layer on one side of the dielectric plastic film and an oppositely positioned conductive layer on the opposite side of the dielectric plastic film, wherein the conducting material layers providing the coils and capacitors are formed on the surfaces of the dielectric plastic film in such a way that the coil of each resonant circuit comprises an elongate substantially rectangular coil which is of a longitudinal extent such as to overlap the coil of the next subsequent resonant circuit in the longitudinal direction of the marking tape in order that a possible break in the marking tape results in a loss of resonance or displacement of resonance frequency of at least one of the resonant circuits.