Sensors

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
  • Sensor carriers

This expertise and know-how have resulted in the registering of a number of patents and are equally applicable to Time Division Multiplexing and Wavelength Division Multiplexing sensor systems. We therefore build sensors which are optimised for use either with our own TDM interrogators or for WDM interrogation systems from other suppliers.

 

 

 

 

Sensor Deployment Methods

1. 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   Custom strain sensor patch   Standard temperature sensor patch
Standard strain sensor patch
 
Custom strain sensor patch
 
Standard temperature sensor patch
Note: When compared with an installation using conventional resistive strain gauges sensor patches can offer significant weight savings as only a single optical fibre is required to multiple measurement points compared with conventional gauges, each of which requires a minimum of 3 connecting wires.

Click here for more information

 
Key Features Heading

Surface bonded sensor patch:

  • Ease of installation which significantly reduces both time and cost.
  • 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 sensors life.
  • The ingress and egress of the optical fibre can be engineered into the patch adding to the robustness of the installation.
  • Sensor patches can be used on both metallic and composite structures

 

2. 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 moulding process.
  • 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.

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

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 fully compatible with most production process (vacuum bagging, autoclave, vacuum infusion etc.).

Cables and Connectors
Surface mounted
sub-sea connector
Surface-mount connector,
suitable for vacuum bagging
During lay-up

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.

 

 
Key Features Heading

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.
  • It is possible to measure strains within the component
  • The embedded sensor is very well protected and is available for the life of the component.

 

3. Sensor Carriers:

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 gears.

Sensor Carriers
In-axle sensor for aircraft landing gear
Long guage length displacement sensor
Micro-Tenex © pultruded rod sensor

Click here for more information

 
Key Features Heading

Sensor Carriers:

  • They are easy to install
  • Can be removed for re-use
  • Very robust

 

     
Design and implementaion of complete fibre-optic sensing solutions

OR

Email:

Fiber-optic sensing for smarter, stronger, safer structures. Call us on +44 (0) 1425 655027