Wolfgang Ecke

Fibre Bragg grating sensor system monitors operational load in a wind turbine rotor blade

A fibre Bragg grating sensor system has been installed in a horizontal axis wind turbine and was successfully tested for already more than one year. We report the requirements, system design and realisation of the sensor system for continuous on-line load monitoring of the rotor blades, and provide examples of strain measurement results.

Highly sensitive micro-mechanical fiber Bragg grating acceleration sensor combined with a new multiplexable interrogation principle

The paper describes a micro mechanical Bragg grating acceleration sensor with enhanced sensitivity by force amplification. A new multiplexable and affordable interrogation scheme that uses two overlapping Bragg gratings within the sensor will be demonstrated.

Fiber-optic bragg grating sensors for structural health monitoring at cryogenic temperatures

While conventional resistance strain gages show increasing cross-sensitivities to temperature and magnetic field with decreasing temperature down to liquid helium, it has been found that fiber optic Bragg grating strain sensors show negligible thermo-optic and magneto-optic effects in cryogenic environment and allow, therefore, reliable strain measurements. These specific application advantages of optical fiber Bragg grating sensors at low temperatures, together with the electrical isolation and low electro-magnetic interference, low thermal conductivity to a large number of multiplexed sensors, make them attractive for structural health monitoring of super-conductive magnets, e.g., for super-conductive motors, magnetic levitation transport, nuclear fusion reactors, or for measurement of material parameters at low temperature, and, if using special sensor substrates, also for temperature measurements and hot spot detection on superconductors.

On-line characterization of impacts on electrical train current collectors using integrated optical fiber grating sensor network

A sensor network consisting of unified fiber grating based temperature and strain sensor pads has been developed for integration in carbon/aluminum composite current collector strips, and has been tested in electrical trains on commercial railways. The fiber optic sensor network measures value and position of both con-tact forces and impacts under real-time conditions, immediately at the high voltage location of the interface between overhead contact line and current collector.

Spectrally encoded optical fibre sensor systems and their application in process control, environmental and structural monitoring

Different types of advanced optical fibre sensor systems using similar spectral interrogation principles and potential low-cost polychromator optoelectronic signal processing instrumentation will be presented, and examples of their industrial application are demonstrated. These are such sensors as multimode fibre based humidity, temperature, and pressure sensors with extrinsic microoptical Fabry-Perot transducers for process control in gas industry, UV absorption evanescent field sensors for organic pollution monitoring in groundwater, and single mode fibre Bragg grating (FBG) multiplexed strain & vibration and temperature sensor networks for structural health monitoring applications in electric power facilities, aerospace, railways, geotechnical and civil engineering. Recent results of current investigations applying FBGs and microstructured fibres for chemical sensing will be discussed.

Micro bending beam based optical fiber grating sensors for physical and chemical measurands

We propse the application of sensors based on the intrinsic bend sensitivity of Bragg gratings inscribed in D-shaped fibers. The first example is a viscosity sensor, consisting of the D-shaped fiber with a sphere attached to the tip of the fiber. The force exerted on the sphere by the laminar flow of a fluid with unknown viscosity bends the fiber, and with this shifts the Bragg wavelength of the inscribed Bragg grating. The other one is a hydrogen senosr, which uses the influence of hydrogen on a palladium foil attached to the Bragg grating. The palladium foil, which is frictionally connected to the flat surface of the D-shaped fiber, is stretched under the influence of hydrogen and with this stretches/bends the fiber.

Separation of refractive index and temperature measurements using surface plasmon-coupled fiber grating

A new fiber optic sensor based on Bragg reflection influenced by a surface plasmon is presented. This arrangement allows for self-referencing due to its highly polarization-resolved response.

Fiber Bragg grating sensor system for operational load monitoring of wind turbine blades

A fiber optic Bragg grating sensor system has been installed in the blades of a wind turbine and was successfully tested for several years. We report the requirements, system design and construction parameters of a sensor system for continuous on-line monitoring of bending loads of the rotor blades, and provide characteristic examples of monitoring results.

Fiber optical sensor network embedded in a current collector for defect monitoring on railway catenary

In order to identify defects of the electrical infrastructure during train operation, a fiber Bragg grating based sensor system performs measurements of the distribution of short time force changes in vertical and horizontal (driving) direction between current collector and overhead contact line. The actual model calculations and the practical design of a 2-dimensionally arranged strain sensor network have been especially enhanced to the calculation of impact directions. The well-known advantages of fiber-optic sensors - embedding capability in the composite carbon/aluminum collector strip, multiplexing of distributed sensor networks, electrical isolation - are of particular importance for detection and characterization of fast impacts immediately at the position of incidence. Tests under everyday operating conditions with trains on high-speed tracks as well as under high load in mountain regions proved the application of this sensing technology. Problems and solutions for the sensor network embedment, the fast Bragg sensor interrogation algorithms, and actual lab test results with their application-orientated analysis will be presented.

Optical fiber sensor research and industry in Germany: review and outlook

Since more than 30 years, the increased research, technology development and commercialization of optical fiber sensors combined with their continuously growing technical applications have become a story of success worldwide and in Germany as well. German fiber sensor research and industry achieved remarkable milestones in the 1980ies and 1990ies, such as first field tests of magneto-optic current sensors in power facilities or of micro-bending fiber strain sensors in a highway bridge. Recent progress and the state of the art of optical fiber sensing in Germany are demonstrated by examples of advanced fiber Bragg grating and distributed sensor system applications, fiber gyroscopes and other interferometric sensors, chemical and bio-medical sensors, and sensors based on polymer fibers as well. In context with the growing international cooperation, the potential of German research and industry will be discussed in terms of novel fiber-optic sensor system concepts, of increasing maturity and reliability of this exciting sensor technology and of new applications and markets.