Activities
Fibre optic sensors are a technologically advanced solution for particularly complex applications where traditional electric sensors are inadequate. The boom in commercial and scientific production confirms the strategic importance of:
- keeping laboratories up-to-date
- innovating through the development of new sensors designed to satisfy specific needs
- forming a bridge between the world of research and that of industry
- identifying predictive diagnostic methods for mechanical, civil and aerospace structures suited to the particular characteristics of fibre optic sensors
There are numerous technologies that allow the use of fibre optics for measuring purposes, such as Fibre Bragg Grating sensors (FBG), Fabry-Perot sensors (FP), Optical Backscatter Reflectometry sensors (OBR), Interferometric sensors (IS) and, in general, Coherent sensors (including the Synoptic version), as well as Raman and Brillouin sensors and many others. Each technology can provide additional information or can be adapted to specific applications.
Fibre optic sensors are used at locations where traditional sensors would be at a disadvantage, in terms of number of sensors required, cable lengths, cable sizes, sensor dimensions, presence of electromagnetic disturbance, high voltages, explosive materials, etc.
Application examples:
- instrument monitoring of large structures (bridges, buildings, aeroplanes, trains)
- improving the efficiency of wind turbines, oil extraction, turbine engines
- monitoring of tunnels, chemical and industrial plants for safety purposes
- control of mechanical systems by embedding in smart structures
- distributed or quasi-distributed strain measurements on laboratory specimens
Location
The Laboratory is located in building Sesini-A, Department of Mechanical Engineering. The actual location of the instrumentation may vary, however, according to projects being undertaken by the four departments involved (Mechanical Engineering; Aerospace Science and Technology; Electronics, Information and Bioengineering; Civil and Environmental Engineering).
Equipment
The instrumentation chosen for the LAFOS Laboratory employs different technologies in order to be able to adapt to a wide variety of needs. For example, Optical Backscatter Reflectometry (OBR) technology can measure the strain distributed along a long length of fibre, with a spatial resolution of a few millimetres. Fibre Bragg Grating (FBG) technology can be used to measure local strain and temperature with a high degree of accuracy and high sampling rate. Fabry-Perot (FP) technology enables the use of interferometric sensors. Coherent interferometric sensor technology allows complete and distributed information to be obtained along a length of fibre. FBG technology used with a Linear Attenuating Filter (LAF) technology allows the acquisition of very high frequency signals for impact studies. The instrumentation purchased for the LAFOS Laboratory supplement an already vast collection of instruments available to the departments involved. A detailed list of the equipment is provided below.
Instrumentation purchased by the laboratory
- Optical Backscatter Reflectometer (OBR): a tool used to measure strain and temperature along a length of fibre in continuous mode. Up to 16 analogue signals can be output, corresponding to measurements at 16 specific points. Length, resolution and acquisition frequency depend on the method used. The following are available:
- 2 m, 5 mm, 250 Hz
- 20 m, 5 mm, 50 Hz
- 10 m, 1.25 mm, 23.8 Hz
- Dynamic interrogator for FBG (Fibre Bragg Gratings): 1 kHz sampling frequency, 4 optical channels, maximum 80 FBG per channel, 20 dB dynamic optical range, measures both the spectrum and the peak wavelengths of the sensors
- Static interrogator for FBG (Fibre Bragg Gratings) and FP (Fabry-Perot interferometer): 2 Hz sampling frequency, 4 optical channels, maximum 80 FBG per channel, 50 dB dynamic optical range, measures both the spectrum and the peak wavelengths of the sensors
- Random waveform generator for use with coherent interferometric sensors. High temporal resolution for preparing pulses for distributed sensors
Instrumentation already available to the departments
A number of interrogators, sensors and accessories for fibre optics are available in each participating department. These include 3 dynamic interrogators for 1 kHz FBG, a linear filter FBG interrogator for 4 sensors with 0.1 pm resolution and 2 kHz acquisition frequency, optical spectrum analysers (OSA), 4 draw wire optical encoders for measuring motion, 12 FBG optical accelerometers, 12 FBG load cells for measuring force, torsion and temperature, fibre arc fusion joining system, 850/1300 nm LED sources, fibre optic rotary joints (FORJ), optical amplifiers, 3 kW and 1 kW stabilised fibre laser sources, Raman pump, polarization scrambler, waveshaper.
Services provided
The Laboratory provides the University with a design service for complex measuring systems, from design to development, installation, monitoring campaigns and data analysis. The systems will be based principally on fibre optic sensors for particularly critical measuring environments (live electrical components, motors, alternators, railway pantographs, overhead railway and electricity distribution lines, aeroplanes, buildings, bridges, tunnels, chemical plants, wind turbines, oil and gas plants, natural gas transport, smart materials, etc.).
Procedures and costs of using equipment
Custom supply of instrumentation and qualified personnel, with methods and costs to be agreed according to requirements and in line with the terms of use. For more information and details, contact Prof. Mario Martinelli (Laboratory coordinator, mario.martinelli@polimi.it) and Ing. Lorenzo Comolli (head of operations, lorenzo.comolli@polimi.it).