There is described a method of making an acoustic sensor having a frequency response approximating a desired frequency response. The method comprises wrapping optical fiber around a core according to a wrapping pattern. The wrapping pattern is determined from an impulse response of the acoustic sensor. The impulse response is determined from the desired frequency response of the acoustic sensor.

This application describes a fibre optic cable structure which is advantageous for distributed fibre optic sensing, for example distributed acoustic sensing (DAS). The fibre optic cable structure includes an optical fibre for distributed fibre optic sensing and is configured to comprise at least one longitudinal section of a first type, which exhibits a change in effective optical path length of the optical fibre of one polarity in response to a given applied force, and which is adjacent to at least one longitudinal section of a second type, which exhibits a change in effective optical path length of the optical fibre of the opposite polarity in response to an equivalent applied force. When used for DAS, the response of a sensing portion that includes sections of both the first and second types, will include or exclude certain wavenumber by summation, which provides a directional sensitivity to incident waves.

A fiber optic distributed acoustic sensing (DAS) system for detecting a red palm weevil (RPW) includes an optical fiber configured to be wrapped around a tree and a DAS box connected to the optical fiber. The DAS box includes a processing unit that is configured to receive a filtered Rayleigh signal reflected by the optical fiber, and run the filtered Rayleigh signal through a neural network system to determine a presence of the RPW in the tree.

A method and apparatus for monitoring a structure using an optical fiber based distributed acoustic sensor (DAS) extending along the length of the structure. The DAS is able to resolve a separate acoustic signal with a spatial resolution of 1 m along the length of the fibre, and hence is able to operate with an acoustic positioning system to determine the position of the riser with the same spatial resolution. In addition, the fiber can at the same time also detect much lower frequency mechanical vibrations in the riser, for example such as resonant mode vibrations induced by movement in the surrounding medium. By using vibration detection in combination with acoustic positioning then overall structure shape monitoring can be undertaken, which is useful for vortex induced vibration (VIV) visualisation, fatigue analysis, and a variety of other advanced purposes. The structure may be a sub-sea riser.

A system and method to assess utility pole integrity, by using existing telecom fiber optic cable as a sensor cable, instant mechanical impact on the pole(s), DAS technology and a machine learning model. An instant mechanical impact creates a vibration event on the optical fiber cable mounted/suspended on a target pole, which is detected/recorded by DAS. By applying a machine learning model on the DAS signals, the target pole's integrity condition is obtained.

An optical fiber sensing system according to the present disclosure includes: an optical fiber network (10) configured to detect first sensing information related to a first monitoring target and second sensing information related to a second monitoring target; a reception unit (21) configured to receive an optical signal from the optical fiber network (10); a specification unit (22) configured to specify a first monitoring target based on first sensing information superimposed on the optical signal and specify a second monitoring target based on second sensing information superimposed on the optical signal, and a provision unit (23) configured to provide information related to the first monitoring target and information related to the second monitoring target specified by the specification unit (22) for a service providing destination.

An improved optical fiber distributed acoustic sensor system uses an optical fiber having reflector portions distributed along its length in at least a first portion. The reflector portions are positioned along the fiber separated by a distance that is equivalent to twice the distance an optical pulse travels along the fiber in a single sampling period of the data acquisition opto-electronics within the sensor system. No oversampling of the reflections of the optical pulses from the reflector portions is undertaken. The sampling points for data acquisition in the sensor system are aligned with the reflections that arrive at the sensor system from along the sensing fiber. Adaptive delay componentry adaptively aligns the reflected optical signals (or their electrical analogues) with the sampling points. Control over the sampling points can re-synchronise the sampling points with the returning reflections. Reflection equalisation componentry may reduce the dynamic range of the returning reflections.

A sensor. In some embodiments, the sensor includes a first waveguide, a flexible support element, and a second waveguide. A first portion of the first waveguide may be supported by the flexible support element and separated by a first gap from a second portion of the first waveguide. The flexible support element may be capable of bending so as to cause an effective index of refraction of the first waveguide to change. The first waveguide may be coupled to the second waveguide through a second gap, the second gap being at an end of the first waveguide and an end of the second waveguide.

A sensor. In some embodiments, the sensor includes a first waveguide, a flexible support element, and a second waveguide. A first portion of the first waveguide may be supported by the flexible support element and separated by a first gap from a second portion of the first waveguide. The flexible support element may be capable of bending so as to cause an effective index of refraction of the first waveguide to change. The first waveguide may be coupled to the second waveguide through a second gap, the second gap being at an end of the first waveguide and an end of the second waveguide.

A variable-frequency light source is configured to emit a light beam and modulate a frequency of the light beam. A fiber optic cable is attached to the variable frequency light source. The fiber optic cable is configured to receive the light beam at an inlet and pass the light beam to an exit. Multiple optical detectors are attached to the fiber optic cable. Each of the optical detectors is configured to detect a specified frequency of light that is backscattered through the fiber optic cable. An actuation mechanism is attached to the fiber optic cable. The actuation mechanism is configured to deform the fiber optic cable in response to a stimulus.