Semi-rigid airborne electromagnetic transmitter antenna system

Patent metadata

Field	Value
Publication number	US-9903976-B2
Application number	US-201514930335-A
Country	US
Kind code	B2
Filing date	Nov 2, 2015
Priority date	Nov 2, 2015
Publication date	Feb 27, 2018
Grant date	Feb 27, 2018

Abstract

An apparatus for airborne electromagnetic surveying is provided, comprising a central hub defining an equatorial plane, a transmitter loop, and radials connecting the hub to the transmitter loop. The loop generally lies in a plane during flight, and comprises loop sections, some of which are connected with flexible joints allowing the loop to flex out of the plane during lift-offs and landings. A loop section comprises current conducting elements connected to current conducting elements of adjacent loop sections forming a transmitter loop circuit. A radial connects to the hub at a point that is substantially offset from the transmitter loop plane, thereby contributing to the stability of the transmitter loop connection point in an up-down direction relative to the hub. Additionally, a loop section comprising rigid conductive elements retained in a spaced-apart relationship by a frame member is also provided.

First claim

What is claimed:

1. An apparatus for airborne electromagnetic surveying, the apparatus comprising:
a rigid central hub having a vertical extent and defining an equatorial plane;
a transmitter loop disposed around the rigid central hub;
a plurality of radials connecting the rigid central hub and the transmitter loop, a distal end of each radial being connected to the transmitter loop at a transmitter loop connection point and a proximal end of each radial being connected to the hub at a hub connection point;
the transmitter loop comprising:
a plurality of substantially rigid loop sections connected in an end-to-end manner with joints, wherein a plurality of the joints are flexible joints and the loop sections are disposed to lie in a transmitter loop plane during flight and may flex out of the transmitter loop plane at the flexible joints during lift-offs and landings,
wherein, each loop section comprises one or more current conducting elements electrically connected to current conducting elements in an adjacent loop section to collectively form a transmitter loop circuit into which current may be driven by a transmitter, and
wherein the proximal end of at least one radial connects to a hub connection point that is substantially offset from the transmitter loop plane along the vertical extent of the rigid central hub, whereby the offsetting contributes to the stability of the transmitter loop connection point in an up-down direction relative to the equatorial plane of the hub, and
wherein the transmitter loop plane and the equatorial plane of the hub are substantially parallel during flight.

2. The apparatus of claim 1 wherein at least one of the radials is a rigid radial.

3. The apparatus of claim 2 wherein the rigid radial is a truss, the truss comprising a plurality of spars, the plurality of spars comprising an upper spar connected at its proximal end to the hub at an upper hub connection point located at or above the equatorial plane of the hub, and a lower spar connected at its proximal end to the hub at a lower hub connection point located at or below the equatorial plane of the hub, and wherein distal ends of the upper and lower spars are conjoined for connection at a transmitter loop connection point, whereby the truss resists upward and downward movement of the transmitter loop connection point relative to the equatorial plane of the hub.

4. The apparatus of claim 3 wherein at least one rigid radial truss is pivotally connected to the rigid central hub so that the distal end of the pivoting rigid radial truss may move into a position raised above the equatorial plane of the rigid central hub.

5. The apparatus of claim 4 , further comprising a biasing mechanism for biasing the distal end of the pivoting rigid radial truss towards the equatorial plane of the hub.

6. The apparatus of claim 5 , wherein the biasing mechanism selectively provides a variable biasing force to adjust the flexibility of movement of the pivoting rigid radial truss relative to the rigid central hub.

7. The apparatus according to claim 3 , comprising a plurality of rigid radial trusses including a pivoting first rigid radial truss connected to the transmitter loop at a leading end of the transmitter loop, and a second rigid radial truss connected to the transmitter loop at the trailing section of the transmitter loop.

8. The apparatus of claim 7 wherein the pivoting rigid radial truss comprises at least one upper and two lower spars, wherein the distal ends of the upper and lower spars are conjoined for connection at a transmitter loop connection point, and wherein the proximal end of the upper spar is pivotally connected to an upper region of the hub, and wherein the proximal ends of the lower spars are variably connected to one or more lower regions of the hub to allow a distance between the transmitter loop connection point and the lower region of the hub to change in response to upward or downward movement of the pivoting rigid radial truss relative to the equatorial plane of the hub.

9. The apparatus of claim 1 wherein a flexible joint is a hinged joint, the hinged joint comprising first and second hinge members rotatably connected with a hinge pin defining a hinge axis, wherein the hinge axis lies substantially in the transmitter loop plane.

10. The apparatus of claim 9 comprising a plurality of hinged joints, wherein the hinge axes of the joints are oriented substantially perpendicular to a longitudinal axis of the transmitter loop, the longitudinal axis extending between leading and trailing ends of the transmitter loop.

11. The apparatus of claim 10 wherein a plurality of transmitter loop connection points are located at the hinged joints of the transmitter loop.

12. The apparatus of claim 9 further comprising a bushing rotatably engaged with the hinge pin for rotation about the pin independently of the first and second hinge members.

13. The apparatus of claim 12 wherein the bushing is connected to at least one of the plurality of radials, a chord, a lift rope, or a yoke.

14. The apparatus of claim 13 wherein the bushing is coupled to a yoke and the yoke is coupled to a rigid radial, the rigid radial extending between and connecting the hub at a hub connection point and the transmitter loop at a transmitter loop connection point.

15. The apparatus of claim 9 further comprising at least one biasing mechanism for biasing the angle formed by the first hinge member relative to the second hinge member.

16. The apparatus of claim 1 , comprising a tow line, and a plurality of lift ropes connecting the transmitter loop and the hub to the tow line for suspending the apparatus from an aircraft.

17. The apparatus according to claim 1 , wherein the hub comprises a closed, weatherproof shell.

18. The apparatus of claim 17 , wherein the weatherproof shell contains a magnetometer, the magnetometer being connected to a controller and a data recorder.

19. The apparatus of claim 18 , wherein the magnetometer is mounted on a stabilization system for stabilizing the motions of the magnetometer against motions of the hub.

20. The apparatus of claim 18 wherein a bucking coil is located at the rigid central hub substantially in its equatorial plane for bucking a primary magnetic field of the transmitter loop circuit within the shell, wherein the bucking coil is serially connected to the transmitter loop circuit.

21. The apparatus according to claim 1 , comprising a plurality of distinct transmitter loop circuits.

22. A loop section for forming part of an apparatus for airborne electromagnetic surveying, the loop section comprising:
a plurality of rigid conductive elements extending between first and second ends of the section, the conductive elements capable of conducting electrical current;
at least one frame for securely retaining the rigid conductive elements in a spaced apart relationship, the frame comprising non-conductive material for providing electrical isolation between the rigid conductive elements; and
a section terminator connected to a frame and extending from an end the loop section for connecting to an adjacent loop section at a joint.

23. The loop section of claim 22 comprising:
at least a first and a second frame, where the first frame is disposed towards one end of the loop section and the second frame is disposed towards the opposite end of the loop section; and
a first section terminator disposed at the first end of the loop section and supported by the fi

Assignees

• Vale Sa

Inventors

• West Gordon Fox
• Walker Peter Whyte
• Polzer Benjamin David

Classifications

• G01V3/165 Primary

  operating with magnetic or electric fields produced or modified by the object or by the detecting device (with electromagnetic waves G01V3/17) · CPC title

• G01V2003/084

  Sources · CPC title

• G01V3/081

  the magnetic field is produced by the objects or geological structures (characterised by the method of magnetic field measurement G01R33/00) · CPC title

• G01V3/28

  using induction coils · CPC title

• G01V3/18

  specially adapted for well-logging · CPC title