Stc, Inc

Standard Telephones and Cables Public Limited Company

Standard Telephones & Cables Limited

Standard Telephone & Cables

Philip Extance

Roger E Jones

Gilles D Pitt

Gillies D Pitt

Rosamund C Neat

David Wilson

Stewart O Martin

In a fiber optic interferometric magnetic sensor or magnetic gradient detector a magnetic bias field is applied to a magnetically sensitized portion of an optical fiber by means which are driven by optical power whereby a completely passive sensor head arrangement may be achieved. In a magnetic gradient detector optical power from a high power laser (34) may be supplied via an optical fiber (35) to illuminate a solar cell 27 to whose electrical output terminals solenoids (25,26) are connected. A portion of a respective optical fiber (21, 22) which is magnetically sensitized, by for example bonding to a strip of magnetostrictive material (23, 24), is disposed inside each solenoid (25, 26).

Magnetic field sensors, in particular optical fiber magnetometers

Amorphous metallic material in ribbon form is employed to provide hermeticity of cable elements, particularly optical fibres. The metallic glass CuZr has a low permeability for hydrogen, particularly when erbium is included. Thus sealing optical fibres (1) in amorphous metal tubes (3) will prevent increase in attenuation of such fibres when used in submarine cables by preventing contact with hydrogen generated in such cables during use thereof.

Optical fiber cable having a low permeability to hydrogen

A magnetic field sensor is comprised by a length of magnetically sensitized single mode optical fibre wound in substantially random directions on a sphere of non-magnetic material, so that an omnidirectional response is obtained. Specific directionality can be obtained by application of a dc bias field in the desired direction. All three perpendicular components can be measured by applying three perpendicular ac fields at different frequencies. The sensor is intended for use in all fibre Mach-Zehnder interferometer types of magnetometer or magnetic gradient detector, examples of which are described.

Spherical shell fibre optic magnetic field sensors and magnetometers and

An alternating magnetic excitation field is generated in the flux concentrators (11,12) of a Hall effect device, including a Hall element (13), by passing an a.c. current through a coil (14). This alternating field serves to drive the flux concentrators into and out of saturation. In the presence of a d.c. magnetic field and when a Hall current is applied to the Hall element, a second harmonic component is generated in the output voltage of the Hall element (13); the amplitude of the second harmonic component providing a measure of the d.c. magnetic field. In an alternative arrangement (FIG. 4) the flux concentrator means is in loop form rather than in a flat configuration as in FIG. 3.

Magnetic field sensor having a Hall effect device with overlapping flux

Certain materials (e.g. polymers, glasses) exhibit the photo-elastic effect, whereby when they are subject to stress become birefringent, which influences a light beam passing through the glass. This beam, e.g. from a laser is collimated and circularly polarized as it approaches the glass and is again polarized as it leaves the glass. This stress is applied, according to this invention, by magnetostrictive strips on the glass which are influenced, by the magnetic field to be measured or the AC bias field. A miniaturized arrangement using this principle is described.

Photo-elastic sensor

Two portions (B,C) of one arm of an optical fibre Mach-Zehnder interferometer are magnetically sensitized and each has applied thereto an a.c. bias fields at a respective different frequency (w.sub.1, w.sub.2). One portion (A) of the other arm of the interferometer is magnetically sensitized and has two a.c. bias fields applied thereto, each at one of the different frequencies (w.sub.1,w.sub.2). The fields for portion A and C are aligned with a first direction (x) whereas those for A and B are parallel, A and B being separated in a second direction (y). The detected output of the interferometer at frequency w.sub.1 is related to the magnetic gradient in the y direction, whereas the detected output at frequency w.sub.2 is related to the magnetic gradient in the x direction. Thus using two bias frequencies allows one interferometer to be used to detect two gradients (FIG. 8).

Optical fibre magnetic gradient detector

A solid-state heading sensor is comprised by a three-axis Hall effect magnetometer and a three-axis accelerometer. The magnetometer is comprised by a cube-like structure (10) of non-magnetic material on each of three orthogonally related faces of which is located a respective Hall effect device (11, 12, 13), for example of GaAs. The three-axis accelerometer may be comprised by a three-axis module (15) disposed in a recess in the cube-like structure, or by three separate accelerometer structures (23, 24, 25), for example planar etched silicon accelerometers, each disposed on a respective one of the orthogonally related faces adjacent the Hall effect device (20, 21, 22) thereon.

Heading sensor

A Hall effect device for responding to weak magnetic fields uses a small chip of gallium arsenide located between the overlapped ends of two flux concentrators. The spacing between the concentrators may be as small as 95 micrometers. The flux concentrator, which serve to enhance the device's sensitivity are made of amorphous magnetic material, i.e. a metallic glass, which has high permeability.

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Cambridge, United Kingdom

Philip Extance