Optical fibre for sensing structures
Optical fibre for sensing structures
Keywords: Sensors, Optics
With the embedding of optical fibre (OF) sensors it is possible to create integrated sensing structures. These systems make it possible to monitor changes in the structure or in its environment. A large number of conditions of the structure can be monitored such as deformations and loads, crack growth,vibrations, wear, impact, pressure, and temperature.
Furthermore, OF sensors can also be used for the following measurements:
liquid level measurement,
leak detection,
pH-values, salt concentrations or the presence of hydrocarbons,
linear and angular acceleration, and
electrical fields.
Composite materials (fibre reinforced plastics) are most suitable for embedding the optical glass fibres. Structures made of advanced composite materials are superior in weight, chemical resistance, lifetime and structural performance. Even more efficient and safer structures can be made when the functionality of on-line measurement of the environmental conditions of the structure is added.
The main advantages of OFs as sensors are said to be:
small size of the OF (0.15-0.25 mm diameter),
robust and reliable for a long time,
no risk of fire or explosion by short-circuit,
no electromagnetic interference,
high accuracy,
multiplexing possible (multiple sensors on one fibre),
wide operational temperature range (from about 200°C to about +300°C),
high chemical resistance,
high speed and long-distance data transmission.
The OF technology is very suitable to be applied in load-carrying structures. Another promising application is the integration of optical sensors in composite pressure vessels to ensure the safety of the vessel. In combination with special rotary optical joints it is possible to apply the technique in rotating objects. Examples are rolls in paper machines, drive shafts and flywheels. The application of optical sensors in composite pipe systems or storage bins can also be very interesting, for example to detect leaks, measure pH-values,measure the pressure and temperature or to detect specific chemicals.
A demonstrator of this technology is developed by Airborne in cooperation with TNO-TPD. Two OFs with optical strain sensors are integrated in the wall thickness of a carbon fibre reinforced pipe. The characteristics of this demonstrator are:
total length 1,200 mm,
outer diameter 93 mm,
inner diameter 85 mm,
roller weight 2.04 kg,
longitudinal E modulus 39,800 Mpa, and
transverse E modulus 23,200 Mpa.
The detection system developed by TNO TPD has the following specifications:
- 1.
high sensitivity: better than 1 micro strain for strain measurement,
- 2.
frequency range: DC >10 kHz, and
- 3.
multi-sensor configuration: up to 40 sensors.
The TNO-TPD system is developed for high-speed structural monitoring and for multi-point measurement in process industry. Airborne is a development company specialised in advanced structures and systems. One of the activities is to create self-sensing systems by embedding sensors in composite structures, for which OF sensors are the most used technology. Future developments are to embed controllers (chips) for stand-alone sensing structures, and to add actuation functionality by embedding active materials (piezo-electric, shape memory materials and magnetostrictive polymers).
For further details contact: TNO TPD. Tel: +31 (0)15 2692000; Airborne International B.V. Tel: +31 (0)70 3017400.
