Sensor Deployment

As a result of many years of experience in a wide range of applications we have accumulated considerable expertise in the design of sensors and their deployment methods. This enables us to supply sensors that not only perform accurately and reliably in the operating environment, but are also easy to install in the case of existing structures, or easily integrated into the manufacturing process, in the case of new structures.

The principal methods of deployment are:

  • Surface bonded sensor patches
  • Embedded sensors
  • Discrete sensing devices

This expertise and know-how is equally applicable to sensors designed to work with TDM or WDM type FBG interrogators and so Epsilon Optics can supply and support either type in order to suit the requirements of the particular application. We have a number of international patents which cover sensor embedment, temperature sensors and discrete fibre optic sensing devices.
Key Features

Surface Bonded Sensor Patches

  • Ease of installation, reducing time and cost, rigged and can be used on both metallic and composite structures

Embedded Sensors

  • No impact on the component’s external surface, measurement of strains within the component and are very well protected

Sensor Carriers

  • Ease of installation, easily removed for re-use with a very high degree of robustness
 
Surface Bonded Sensor Patch

The optical fibre is mounted within a patch normally manufactured from low modulus glass fibre. The patch is shaped to suit the component to which it is to be attached and the FBGs are located in their required positions.

Standard strain sensor patch Patented temperature sensor patch
Standard Strain Sensor Patch
Flexible, rugged and easy to handle.
Patented Temperature Sensor Patch.
Custom strain sensor patch Custom strain sensor patch
Multi Sensor Patch
Single patch with 4 FBGs comprising a strain rosette with 0, +45, -45 degree sensors and a temperature compensation sensor.
Custom Strain Sensor Patch
Manufactured to conform accurately to the shape of the structure.

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Key Features

Surface Bonded Sensor Patch:

  • Ease of installation which significantly reduces both time and cost
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  • The patch’s low stiffness and relatively large bond area greatly reduces the shear strain on the bond when compared with conventional resistive strain gauges, significantly improving the life of the sensor
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  • The ingress and egress of the optical fibre can be engineered into the patch adding to the robustness of the installation
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  • Sensor patches can be used on both metallic and composite structures
 
Embedded Sensors:

The optical fibre with its FBGs can be embedded in composite structures with minimal intrusion and no detrimental effect on the mechanical properties of the structure (see note). Although the diameter of an optical fibre is much larger than that of a glass or carbon fibre used in a composite structure, their mechanical properties are very similar. In this way a properly embedded sensor can be considered an integral part of the structure and will last the lifetime of the structure, even over many millions of fatigue cycles.

Embedded Sensor Installing
Picture taken by electron microscope showing the cross section
of an optical fibre embedded in e-glass/epoxy composite
Installation of FBG sensors in pre-preg composite

For a successful installation a number of factors need to be considered, including:

  • The fibre type used, in particular the coating type needs to be selected to match the temperatures and pressures of the cure cycle
  • The fibre needs to be positioned such that the risk of micro-bending is minimised
  • The ingress / egress point needs to be engineered into the component which may require modification of mould tooling
Key Features

Embedded Sensors:

  • No impact on the component’s external surface. This is important where the component provides an aerodynamic surface such as a helicopter rotor blade
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  • It is possible to measure strains within the component
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  • The embedded sensor is very well protected and is available for the life of the component
Sensor Veil
Sensor Veil Array (dry un-impregnated),

Successfully embedding bare optical fibre into a composite structure during manufacture can be challenging with risk of high optical losses, fibre breakage and inaccurate placement of the sensors. For this reason it usually requires the specialist skills of a technician with extensive experience in handling optical fibre.

In order to avoid both the technical problems and the need for a fibre optics specialist to install the sensors, Epsilon Optics has developed the Sensor Veil which comprises of a dry (un-impregnated) veil cloth in e-glass or carbon fibre, with a fibre-optic sensor array fixed to it. The optical fibre layout and sensors are all precisely located and the optical fibres brought out via a suitable cable which can be pre-connectorised. Whilst not being as robust as a surface bonded sensor patch, the Sensor Veil is resilient enough to be installed with confidence by a suitably trained laminator. In this way the entire array which may include many sensors can be accurately positioned in the laminate stack.

The Sensor Veil concept is suitable for pre-preg, wet lay-up, vacuum infusion, resin transfer moulding and similar processes. Where closed moulds are being used there will need to be provision made for the cable exit. Where a vacuum bag is used the Sensor Veil can be combined with one of our surface mounted connector housings located on the final laminate under the vacuum bag.
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Epsilon Optics has worked with a number of manufacturers of composite components to successfully embed optical sensors and has developed techniques for all common composite manufacturing processes including:
  • ● Hand lay-up       ●  Vacuum infusion       ●  Resin transfer moulding       ●  Filament winding       ●  Pultrusion       ●  Pre-preg       ●  Autoclave processing

Note: A number of trials have been conducted by several of our Aerospace customers, comparing the strength and resistance to fatigue of components, with and without Epsilon Optics embedded sensors. Provided the sensors are embedded in accordance with Epsilon Optics best practice, no measureable knock-down in performance was detected.
 
Surface Mount Connectors:

The ingress/egress point of the optical fibre from the composite can be particularly vulnerable to damage both during manufacture and subsequent use if not properly engineered. To address this problem Epsilon Optics has developed a number of connector enclosures suitable for surface mounting and being fully compatible with most production process (vacuum bagging, autoclave, vacuum infusion etc.).

Embedded connectors Diamond Mini Avim Embedded connectors FC-APC Embedded connectors Diamond Avim
Diamond miniAVIM FC-APC Diamond AVIM

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Key Features

Surface Mount Connectors:

  • Available to suit a range of Aerospace and communications type connectors
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  • Provides a ruggedised fibre-optic connection from a composite structure
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  • Ease of termination ideally suited to manufacturing environments
 
Discrete Sensing Devices:

The optical fibre and its FBGs are mounted within a composite carrier which is shaped such that it can be locked or clamped to the structure. The carrier follows the changes in shape of the parent structure and thus measures the loads applied to it. A number of variations have been developed including sensors for detecting cracks and for measuring displacements of civil engineering structures. They have also been used on complex metallic structures such as aircraft landing gear.
Pultruded Rod Embedded Sensor Long guage Sensor
Micro-Tenex © pultruded rod sensor In-axle sensor for aircraft landing gear Long Guage Length Displacement Sensor

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Key Features

Sensor Carriers:

  • Ease of installation
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  • High degree of robustness
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  • Pre-connectorised (optional)
 
Design and implementation of complete fibre optic sensing solutions