This paper introduces a novel method to simultaneously measure the cores of a multi-core fiber, enabling higher acquisition rates in shape sensing. The two-dimensional shape of the optical fiber is determined from the distributed strain measurements performed with the optical frequency domain reflectometry technique.
Luca Schenato, Pedro J. Vidal-Moreno, Marco Santagiustina, Andrea Galtarossa, Luca Palmieri, Efren Diez-Jimenez, Sonia Martin-Lopez, Miguel Gonzalez-Herraez
This paper introduces and numerically investigates a special optical fiber cable with zero temperature-induced phase shift. The cable structure consists of stacked layers of two materials with opportune mechanical, thermal, and geometrical properties. This structure allows adjusting the thermal-induced strain to the fiber, resulting in a broad tunability of the bare thermal expansion, including the negative range. By a proper choice of materials, the thickness of each layer, and the radius of the cable, the induced thermal strain can fully compensate for the thermo-optic effect, resulting in a complete temperature insensitivity of the phase shift. This cable may be of great interest in the sensing fields in all those applications where the temperature compensation is critical, such as in low-frequency distributed acoustic sensing. Moreover, it could be relevant for a wide range of telecom applications that require precise thermal control.
We present the design and field test of a rugged FBG sensor prototype for high-sensitivity measurement of underground water level. Pressure sensors have many fields of application, ranging from environmental monitoring to the oil and gas industry. In particular, pressure sensors can be used to monitor the stability of dikes and embankments by measuring the inner phreatic level at their foot to detect anomalous filtration and excess of pore pressures. For this application, rather high sensitivity at an affordable cost is required. Fiber optic pressure sensors have been explored with different solutions, but the technologies proposed so far have either small sensitivity, and hence are befitted for large pressure ranges, or are based on interferometry, and hence require rather expensive laser sources. The sensor described in this paper exploits a 3D-printed mechanical transducer to convert external pressure in longitudinal strain along the fiber. A second FBG, embedded in the sensor, is used to compensate for temperature cross-sensitivity. The structure is enclosed in an aluminum alloy case to withstand harsh environments and installation procedures. Pressure and temperature sensitivities of the sensor are about 20 pm/cm H2O and 17 pm/°C respectively. Three sensors of this kind have been successfully tested in a large scale dike at the Flood Proof Holland facility, in Delft, Netherlands.
In this paper, we describe an optical fibre cable for distributed pressure sensing. The cable structure encodes the local pressure into strain exerted onto a standard optical fibre, embedded inside the cable following a meandering path. The cable has been designed and preliminarily tested by means of optical frequency domain reflectometry. Nonetheless, the cable can be interrogated by any optical fibre distributed strain sensing technique. Up to our knowledge, the proposed cable is the first real distributed fibre optic pressure sensing cable embedding standard fibres, capable of providing high- pressure sensitivity.
This paper describes the application of a commercial distributed optical fiber sensing system to a large scale physical model of landslide. An optical fiber cable, deployed inside the landslide body, is interrogated by means of optical frequency domain reflectometry with very high spatial density. A shallow landslide is triggered in the physical model by artificial rainfall and the evolution of the strain is measured up to the slope failure. Precursory signs of failure are detected well before the collapse, providing insights to the failure dynamic.
In this work a quasi-distributed optical fiber load sensor based on a semi-auxetic structure is presented. By concatenating sections with positive Poisson’s ratio to sections with negative one it is possible to precisely encode the distributed load into a strain exerted on a fiber. The sensor is described and a simple proof of concept is built and tested. The fiber is interrogated by means of optical frequency domain reflectometry. The proposed sensor represents just one example of the potential applications of auxetic and semi-auxetic structures and materials in optical fiber sensors development.
In this work, a low cost optical fiber sensing system for cracks growth monitoring in the concrete lining of a road tunnel is presented. A plastic optical fiber (POF), with large dynamic strain range, is used for sensing by means of phase measurement of a RF modulated optical signal. Preliminary results suggest that the system represents a viable solution to the aim of crack monitoring.
An optical fiber sensor for the simultaneous measurement of hydrostatic pressure and temperature in soil embankments is presented. The sensor exploits a dual chambers transduction mechanism and is based on the optical measurement of the differential strain induced in the fiber by temperature and pressure in the two chambers. A prototype has been built and interrogated by means of optical coherent frequency domain reflectometry and the results of a preliminary experimental characterization are presented and discussed. Temperature and pressure sensitivities are approximately -7.1 GHz/°C and -4.4 GHz/kPa, respectively.
A simple, yet effective, setup for the simultaneous interrogation of multiple ferrule-top-cantilever sensors for acoustic sensing is here presented and experimentally tested with two ferrule-top-cantilever sensors; results confirm the feasibility of the approach.
Two fiber optic sensors (FOSs) for detection of precursory acoustic emissions in rockfall events are proposed and
experimentally characterized. While both sensors are interferometric, the first one use a fiber coil as sensing element,
whereas the second sensor exploits a micro-machined cantilever carved on the top of a ferrule. Preliminary
experimental comparison with standard piezo-electric transducers shows the viability of such FOSs for acoustic
emission monitoring in rock masses.
Process variations, incurred during the fabrication stage of MEMS structures, may lead to substantially different performance than the nominal one. This is mainly due to the small variation of the geometry of the structure with respect to the ideal design. In this paper we propose an approach to estimate performance variations for general planar suspended MEMS structure for low frequency applications. This approach is based on two complementary techniques, one probabilistic and the other deterministic. The former technique, based on the Monte-Carlo method, defines a random distribution on the geometric variables and evaluates the possible outcome performance by sampling that distribution. The latter technique, based on robust optimization and semidefinite programming (SDP) approximations \cite{EOL:98}, finds bounds on performance parameters given the bounds on the geometric variables, i.e. it considers the worst case scenario. Both techniques have been integrated with SUGAR, a simulation tool for MEMS devices available to the public \cite{Zhou98} \cite{Sito}, and tested on different types of folded springs.
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