Method and apparatus for providing permanent magnetic signatures in buried cables and pipes to facilitate long-range location, tracking and burial depth determination

A method of producing magnetization in ferromagnetic material of an elongated object, comprising applying to said object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle, and that results in multiple cycles of a radial external magnetic field around the object that is substantially cylindrically symmetric and that extends along the length of the object, wherein the magnetic field is applied during relative lengthwise movement of the object and a magnetizer, and the field applied by the magnetizer has a polarity that varies repetitively.

A method of producing magnetization in ferromagnetic material of an elongated object, comprising applying to said object a magnetic field that magnetizes the ferromagnetic material in a manner that results in a radial external magnetic field around the object that is substantially cylindrically symmetric and that varies along the length of the object, wherein the magnetic field is applied during relative lengthwise movement of the object and a magnetizer, and the field applied by the magnetizer has a polarity that varies repetitively, wherein the magnetizer includes a pair of mirror-image magnets disposed at opposite sides of the object and the polarity of which adjacent to the object varies repetitively during the relative movement.

Apparatus for producing magnetization in ferromagnetic material of an elongated object, comprising a magnetizer that includes a pair of mirror-image magnets arranged to be disposed adjacent to the object at opposite sides thereof, a mechanism that provides guided relative movement of the object and the magnetizer along the length of the object, and a mechanism that repetitively varies the polarity of the magnets adjacent to the object as the object is moved relative to the magnets.

A method of providing ferromagnetic material of an elongated object with an external magnetic field for passive magnetic detection, comprising using a magnetizer to apply to a portion of said object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle, and that results in multiple cycles of a radial external magnetic field around the object that is substantially cylindrically symmetric and that extends along the length of the object, and providing relative movement between said object and said magnetizer along the length of said object to apply the magnetic field of the magnetizer to another portion of said object.

Apparatus for producing magnetization in ferromagnetic material of an elongated object, comprising a magnetizer, a mechanism for providing guided relative movement of the object and the magnetizer along the length of the object, and means for operating the magnetizer to apply to a portion of the object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle, and that results in multiple cycles of a radial external magnetic field around the object that is substantially cylindrically symmetric and that extends along the length of the object.

A method of providing a magnetic signature in ferromagnetic material of an elongated object, comprising, applying to said object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle, so an to produce multiple cycles of a radial external magnetic field around the object that extends along the length of the object and so that the fall-off of the magnitude of the radial external field with distance R from the center line of the object is in accordance with 1/Rn, where n is less than 2 and greater than or equal to one, irrespectice of the radial direction from the object.

A method of providing a magnetic signature in ferromagnetic material of an elongated object, comprising magnetizing the ferromagnetic material in a manner that results in multiple cycles of a radial external magnetic field around the object that extends along the length of the object over a plurality of meters, wherein each cycle includes a portion extending between polarity reversal points in which radial flux lines of one polarity emanate from the object throughout that portion and another portion extending between polarity reversal points in which radial flux lines of opposite polarity emanate from the object throughout the other portion, and wherein the magnitude of the radial external magnetic field varies progressively throughout each portion.

A method of providing a magnetic signature in ferromagnetic material of an elongated object, comprising magnetizing the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object over a plurality of meters, in which the magnitude of the longitudinal magnetization varies progressively throughout each cycle, and wherein the longitudinal magnetization results in multiple cycles of a radial external magnetic field around the object, each cycle of the radial external magnetic field including a portion in which radial flux lines of one polarity emanate from the object throughout 360° and another portion in which radial flux lines of opposite polarity emanate from the object throughout 360°.

A method of providing a magnetic signature in ferromagnetic material of an elongated object, comprising magnetizing the ferromagnetic material in a manner that produces multiple cycles of a radial external magnetic field around the object that extends along the length of the object and in a manner such that the fall-off of the magnitude of the radial external magnetic field with distance R from the center line of the object is in accordance with 1/Rn, where n is between 2 and 1.

Apparatus for producing magnetization in ferromagnetic material of an elongated object, comprising, a magnetizer constructed to apply to said object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle, and that results in multiple cycles of a radial external magnetic field around the object that is substantially cylindrically symmetric and that extends along the length of the object, said magnetizer having a mechanism that provides relative movement between said object and said magnetizer along the length of said object.

Apparatus for producing magnetization in ferromagnetic material of an elongated object, comprising, a magnetizer that applies to said object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle, and that results in multiple cycles of a radial external magnetic field around the object that is substantially cylindrically symmetric and that extends along the length of the object, said magnetizer having a mechanism that moves the object lengthwise relative to the magnetizer.

Apparatus for providing a magnetic signature in ferromagnetic material of an elongated object, comprising, a magnetizer that applies to said object a magnetic field that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization that extends along the length of the object and that varies continually over each cycle so as to produce multiple cycles of a radial external magnetic field around the object that extends along the length of the object and so that the fall-off of the magnitude of the radial external field with distance R from the center line of the object is in accordance with 1/Rn, where n is between 2 and 1, irrespective of the radial direction from the object.

Apparatus for providing a magnetic signature in ferromagnetic material of an elongated object, comprising, a magnetizer that magnetizes the ferromagnetic material in a manner that results in multiple cycles of a radial external magnetic field around the object that extends along the length of the object over meters, wherein each cycle includes a portion extending between polarity reversal points in which radial flux lines of one polarity emanate from the object throughout that portion and another portion extending between polarity reversal points in which radial flux lines of opposite polarity emanate from the object throughout the other portion, and wherein the magnitude of the radial external magnetic field varies progressively throughout each portion.

Apparatus for providing a magnetic signature in ferromagnetic material of an elongated object, comprising a magnetizer that magnetizes the ferromagnetic material in a manner that creates multiple cycles of longitudinal magnetization along the length of the object over meters, wherein the magnitude of the longitudinal magnetization varies progressively throughout each cycle, and wherein the longitudinal magnetization results in multiple cycles of a radial external magnetic field around the object, each cycle of the radial external magnetic field including a portion in which radial external flux lines of one polarity emanate from the object throughout 360° and another portion in which radial flux lines of opposite polarity emanate from the object throughout 360°.

Apparatus for providing a magnetic signature in ferromagnetic material of an elongated object, comprising a magnetizer that magnetizes the ferromagnetic material in a manner that produces multiple cycles of a radial external magnetic field around the object that extends along the length of the object, and in a manner such that the fall-off of the magnitude of the radial external magnetic field with distance R from the center line of the object is in accordance with 1/Rn, wherein n is between 2 and 1.