This application relates to methods and apparatus for distributed fibre optic sensing that can provide an indication of the absolute value of pressure acting on a sensing portion of a fibre optic cable. A sensor apparatus (600) has a first fibre optic cable structure (102) comprising a first optical fibre (101) and an interrogator (103) configured to perform distributed acoustic sensing on the first optical fibre (101) to provide a measurement signal from at least one sensing portion of the first optical fibre. The first fibre optic cable structure (102) is configured such that a sensitivity of a sensing portion (603, 604) to an incident pressure stimulus (ΔP1, ΔP2) depends on the ambient pressure (AP1, AP2) at the location of the respective sensing portion. A processor (104) is configured to process the measurement signal in response to an incident pressure stimulus (ΔP1, ΔP2) based on a predetermined sensitivity profile (504, 701) to determine an indication of the ambient pressure at the respective sensing portion.

A field detector (2) comprises a field-responsive element (10) which undergoes a dimensional change when exposed to a predetermined field; and an interferometric read-out arrangement arranged to detect the dimensional change of the field-responsive element. A light source (4) is arranged to provide a measurement beam reflected from the field-responsive element (10) and a reference beam not reflected from the field-responsive element (10), an optical detector (6) being disposed so as to detect at least part of an interference pattern produced by the measurement beam and the reference beam. The field-responsive element (10) has a shape comprising a curved surface and is constrained at least one edge (12) thereof such that the dimensional change causes the curved surface to be displaced in a direction which changes an optical path length of the measurement beam relative to the reference beam, thereby changing the interference pattern detected by said optical detector.

A stress distribution measurement device includes: a first magnetostrictive sensor and a second magnetostrictive sensor each including an excitation coil that excites AC magnetism in a measurement target using alternating current, and a detection coil to which alternating current is induced due to the AC magnetism flowing in the measurement target; an excitation circuit that applies a first excitation voltage to the excitation coil of the first magnetostrictive sensor and applies a second excitation voltage to the excitation coil of the second magnetostrictive sensor, the second excitation voltage having a phase or a waveform different from the first excitation voltage; and a detection circuit that includes a first detector that performs synchronous detection of current flowing in the detection coil of the first magnetostrictive sensor based on the first excitation voltage and a second detector that performs synchronous detection of current flowing in the detection coil of the second magnetostrictive sensor based on the second excitation voltage.

A fully distributed magnetic adsorption multi-parameter sensing cable, which is configured to be installed on the wall of a metal pipeline, includes an outer sheath, a sensing component arranged in the outer sheath, and a fully distributed magnetic adsorption reinforcement (FDMAR) arranged in the outer sheath and on a peripheral side of the sensing component. The outer sheath is attached to the wall of the metal pipeline by the FDMAR. A magnetic adsorption force between the FDMAR and the wall of the metal pipeline is able to be adjusted by changing the size of the FDMAR and the distance between the FDMAR reinforcement and the wall of the metal pipeline. The fully distributed magnetic adsorption multi-parameter sensing cable has the advantages of good adsorption effect and high sensitivity.

This application relates to a fibre optic cable structure suitable for use as a sensing fibre optic for distributed acoustic sensing and having an improved sensitivity to transverse pressure waves. The application describes a fibre optic cable (300) having a longitudinal cable axis and comprising at least one optical fibre (301). The cable also comprises a compliant core material (303) mechanically coupled to the optical fibre(s), possible via a buffer (302) such that a longitudinal force acting on the compliant core material induces a longitudinal strain in the optical fibre(s). At least one deformable strain transformer (304) is coupled to the compliant core material and configured such that a force acting on the strain transformer in a direction transverse to the cable axis results in a deformation of the strain transformer thereby applying a longitudinal force to the compliant core material.

This application relates to methods and apparatus for monitoring power cables (100) carrying multiple AC phases to detect deformation of the power cable. A distributed fibre optic interrogator unit (302) is used to interrogate a sensing optical fibre (301) coupled to the power cable to provide a measurement signal from each of a plurality of longitudinal sensing portions of the sensing optical fibre. An analyser (602) is configured to analyse the measurements signals to detect a characteristic of an imbalance in magnetic fields. The characteristic may be a signal component with a characteristic frequency related to the power frequency and number of AC phases, the sensing optical fibre may be sensitised to magnetic fields and the characteristic frequency may be 2n times the power frequency where n is the number of phases, e.g. six times the power frequency for three phase AC.

A sensor for detecting an amount of current flowing in a wire wherein displacement of a sensing mirror is used in an interferometer to enable determination of the amount of current. The sensor includes a magnetostrictive element located within a magnetic field formed by the wire. The sensor also includes a position sensor that detects a size increase of the magnetostrictive element. In addition, the sensor includes an amplifying device that amplifies the size increase of the magnetostrictive element by a predetermined amplification factor to provide an amplified size increase. Further, the sensor includes a displacement device that displaces the sensing mirror by an amount corresponding to the amplified size increase.

This application relates to methods and apparatus for distributed fibre optic sensing that can provide an indication of the absolute value of pressure acting on a sensing portion of a fibre optic cable. A sensor apparatus (600) has a first fibre optic cable structure (102) comprising a first optical fibre (101) and an interrogator (103) configured to perform distributed acoustic sensing on the first optical fibre (101) to provide a measurement signal from at least one sensing portion of the first optical fibre. The first fibre optic cable structure (102) is configured such that a sensitivity of a sensing portion (603, 604) to an incident pressure stimulus (P1, P2) depends on the ambient pressure (AP1, AP2) at the location of the respective sensing portion. A processor (104) is configured to process the measurement signal in response to an incident pressure stimulus (P1, P2) based on a predetermined sensitivity profile (504, 701) to determine an indication of the ambient pressure at the respective sensing portion.

An acoustically driven ferromagnetic resonance (ADFMR) device includes a piezoelectric element, a pair of transducers arranged to activate the piezoelectric element to generate an acoustic wave, a magnetostrictive element arranged to receive the acoustic wave, and a readout circuit to detect one of either a change in the magnetostrictive element or a change in the acoustic wave.

An acoustically driven ferromagnetic resonance (ADFMR) device has a piezoelectric element comprised of piezoelectric material, first and second electrodes arranged in a vertical stack with the piezoelectric element to activate the piezoelectric element to generate an acoustic wave, a radio frequency voltage source electrically connected to the first electrode, a magnet comprised of a magnetostrictive material in the vertical stack with the first and second electrodes and the piezoelectric element to receive the acoustic wave, wherein the acoustic wave resonates at a ferromagnetic resonance of the magnetostrictive material, and a readout circuit to detect a change in the acoustic wave by detecting one of an output voltage amplitude, a change in impedance or a reflection of the acoustic wave in the magnet to measure an unknown magnetic field in which the ADFMR device resides and as experienced at the magnetostrictive element.