A concept for fiber optic measurement of strain in rotating structures where the fiber cannot access the central rotation axis is described. Various interrogation techniques are considered, and the use of a fast spectrometer-based interrogator is preferred. An automated algorithm for optical alignment while the structure is rotating is described.
A novel sensitive and fast technique is described for monitoring pm scale shifts of narrow Bragg grating features. The technique is based on a grating pair and heterodyne measurement, and offers inherent compensation of temperature variations under strain measurement.
Fiber Bragg Grating (FBG) sensors may probe ultrafast changes in pressure caused by shock waves propagating in solid and liquid media impacted by high velocity projectiles. The FBG spectra are measured using an optical system comprising economically priced electro-optical components offering 5 nsec temporal resolution and 0.8 – 1.6 nm spectral resolution. We present results showing evolution of 5 kBar shock wave pressure in approx. 100 nsec, as well as the dependence of the FBG response on the physical length of the sensor (1mm and 0.1mm), and on the relative orientation between the FBG axis and the shock wavefront.
FBGs respond to external pressures in ways that reflect both the strain-optic effect and the geometrical variations, both induced by the applied pressure. While the response to static isotropic pressure is quite straight forward and intuitive, the response to anisotropic shock waves is much more complex and depends also on the relative orientation between the fiber and the shock propagation direction. We describe and explain experimental results for both cases.
A multi-wavelength fiber-optic confocal position sensor, employing a diffractive optical element (DOE), is described.
The DOE was designed with the aim of enhancing the chromatic dispersion of the optics, and thus improving the
measurement range of the technique. A proof-of-principle experiment is presented, yielding a five-fold enhancement in
the dispersion and thus in measurement range in excellent agreement with design simulation.
A white light interferometric system for remote monitoring of the expansion of a pressured foil membrane is described. The membrane will serve as a transmission "window" in liquid and gaseous target chambers for the production of radio-isotopes in an accelerator. Alternative commercial solutions are unsuitable in this environment. We describe some feasibility experiments which have been performed on a model cell pressurized to expand the foil. Pressures of up to 25 bar induce expansions of up to 1.5 mm in the center of the foil, which the optical probe, positioned 100 mm away, detects with a precision of 20 μm. The results fit well to an accepted model, yielding also the Young's modulus of the foil and its transition from elastic to plastic behavior.
Imaging a single optical fiber onto a remote, reflective target using several wavelengths - while exploiting the chromatic dispersion of the imaging optics - can be used to sense displacements of the target. Light of each wavelength is back-reflected into the fiber at a unique target position. The basic principles of the method and the optical considerations to optimize its accuracy are described. Experimental demonstrations are presented, showing precisions of around 10-20 micrometers.
The construction and the operation properties of an organically doped, sol-gel cladded optical fiber pH sensor, are described. The silica-entrapped indicator in the fluorescence-based device was fluorescein, pumped with a continuous wave (cw) argon 488 nm laser. The transmitted signal through the sensing fiber yielded a response in the pH range of 4 - 7, where signal level increased from acid to base. The device is durable and renewable. When tested over more than 8 weeks it retained its response, as demonstrated by dozens of cycles of measurements each lasting a few hours. The probe is easily prepared under regular room conditions by simple decladding of the fiber and sol-gel recoating. System design and setup are attractive due to modularity and discardable low cost probe tips.
The concept of using embedded sensors based on optical fibre technology for condition
monitoring in fibre reinforced composites is no longer novel. Extensive literature is available on the topic, and
several development programmes have demonstrated concept feasibility. No routine service application has yet
An interdisciplinary team in Israel, comprising industry and academic partners, has been
developing various aspects of the technology, with the ultimate aim of real time monitoring of aircraft structural
components during flight. Aspects studied have included optical signal processing and analysis, optical signal
correlation with mechanical loading, micromechanical modelling of composites containing optical fibres, optical
fibre to composite matrix stress transfer and techniques for embedding optical fibres during conventional
composite manufacturing processes.
The linear birefringence exhibited by the wound fiber in a Faraday rotation current sensor is shown to be responsible for a significant dependence of the output signal on the location of the conductor within the fiber loop, and for non-zero outputs for conductors outside the loop. Numerical calculations show a signal variation of up to approximately equals 10% as the conductor is moved around the circumference of the loop.
We present a ruggedized portable fiber-optic Faraday-rotation current
sensor, that exhibits good and stable performance characteristics. The
sensor has been tested and calibrated against a commercial induction-coil
type device. The resultant scale-factor is in a very good agreement with
the theoretical one, calculated following extensive fiber birefringence
measurements. The measured sensor noise equivalent current is