ES2419579B1 - TRANSDUCTION SYSTEM BASED ON DIFFERATION NETWORKS IN FIBER OPTIC - Google Patents

Abstract

A transduction system (10) comprising: an optical fiber (1) engraved with at least one diffraction grating (2); a resin block (3) in which at least one diffraction grating (2) is fully embedded. The resin block (3) comprises a plurality of reinforcing filaments (4) arranged longitudinally to said optical fiber (1) and to the diffraction grating (2) engraved therein, said reinforcing filaments (4) being located on both sides of the optical fiber (4) and configured to isolate the diffraction grating (2) from vertical pressures. A structure (40) of a composite material comprising at least one transduction system (10) embedded therein.

Description

TRANSDUCTION SYSTEM BASED ON DIFRACTION NETWORKS IN FIBER OPTIC FIELD OF THE INVENTION

The present invention belongs to the field of monitoring and measurement of deformations in composite structures using fiber optic techniques, and in particular with transducers based on fiber optic diffraction networks.

BACKGROUND OF THE INVENTION

Composite materials have a high impact in today's industry. Specifically, in sectors such as aeronautics or wind power, fiber-reinforced plastics (carbon, glass, wood, etc.) abound.

Despite the fact that there are several methods of manufacturing fiber-based composite materials, most manufacturing methods involve placing a series of fiber fabrics so that they intermingle with plastics, typically epoxy or polyester resins.

One of these methods is resin infusion molding, in which fiber fabrics (carbon, glass, etc.) are deposited on a mold, covered with a bag and performed empty. Subsequently, the resin is allowed to enter the tissues during the infusion process. This resin is then allowed to cure to obtain a plastic block reinforced with the shape of the mold.

Measuring deformations in structures is key in new designs. Knowing the response of a structure during its useful life can reduce costs both in

manufacturing as well as maintenance, anticipating when it will fail and allowing

more efficient designs.

There are numerous proven fiber optic techniques for measuring structural responses, including those based on diffraction gratings. Using these techniques, the deformations suffered at key points of a structure can be detected with great precision.

The standard telecommunications optical fiber is silica and has a coating, generally acrylate, that protects it mechanically. In the optical fiber, the typical acrylate coating is around 250 f.1m in diameter, approximately. Other coatings can be used to enable the application of fiber technology in other application areas, such as optical sensors.

Fiber optic diffraction grating technology starts from the periodic deformation of the fiber core so that, in the altered zone (transduction zone), the properties of light linearly dependent on the deformation period are modified. Taking these effects into account, if the transduction zone is subjected to a mechanical deformation in the longitudinal axis of the optical fiber, the period of the alteration of the nucleus is modified, changing the properties of light correspondingly both in transmission and in reflection .

In the particular case of short-period diffraction or Bragg (FBG) networks, the central wavelength of the light reflected by the transduction zone is proportional to the period of the alteration of the nucleus. Thus, by measuring the central wavelength returned by the diffraction grating, the level of deformation to which the transduction zone is subjected can be obtained, either by mechanical deformation or by thermal expansion.

Given the high sensitivity of the diffraction gratings, the deformation is generally required to be homogeneous in the transduction zone to obtain a reliable measurement of said parameter. Achieving a homogeneous strain distribution directly by performing the installation process can be very complex in some scenarios.

Furthermore, taking into account that due to the manufacturing process of the diffraction grating, it may be necessary to remove the coating, leaving the silica fiber at its 125 Jlm diameter, it is necessary to protect the transduction zone again before incorporating it into the structure.

To try to solve these problems of integration of fiber optic technologies with the fidelity of structural measures, different proposals have been found in the state of the art:

In US patent application US2003 / 0066356-Al a fiber optic based device for measuring loads is described, in which the transduction zone is covered with a composite block to protect the optical fiber and homogenize the deformation transfer adjusting the elastic modulus of the block to that of the structure to be sensed. Said device is intended to be incorporated into a concrete structure, therefore additional means are incorporated in the design to fix the transducer to said structure to be measured, for example superficially glued or inserted in concrete.

In the international patent application W02010001255-A2 an idea similar to the previous one is presented within the field of composite materials, and more specifically within the renewable energy sector. A fiber optic based sensor is described for the measurement of deformation by means of. Bragg diffraction. It consists of a resin block in which the optical fiber is inserted. The design of this device is oriented to be glued to the surface of the structure to be monitored. For this, an assembly area is incorporated that separates the sensing block from the surface and with which a better homogeneity of the deformation is achieved by further separating the anchor points.

On the other hand, in the European patent application EP1148324-A2 a transducer based on FBG is described in which the optical fiber is protected by incorporating it into a "patch". This process can be carried out in several ways, one of them being a resin coating. With this "patch" it is possible to homogenize the deformation in the transduction zone and prevent the optical fiber from micro-breaks. Said device is oriented to be adhered to the surface to be monitored and the wired output of the optical fiber is specified for better mechanical protection.

In turn, in the international patent application W02009144341-Al another implementation of a composite materials sensor based on Bragg diffraction gratings (FBG) for the measurement of deformations is presented. This design is oriented to be glued to the surface of the structure. It is based on a composite material carrier element in which an FBG is incorporated in an asymmetric arrangement in order to bring the optical transduction zone closer to the surface to be characterized.

Focusing more on the application of fiber optic techniques to the field of composite materials, several examples of structural monitoring systems can be found. For example, the European patent application EP1677091-Al describes a method based on FBG technology to detect failures in structures of composite materials. An attempt is made to detect inhomogeneities in the structure response by characterizing the evolution of the FBG spectra. Although it is true that it is contemplated to place the optical fiber inside the laminates, it is more aimed at monitoring the evolution of critical points such as the joints between components. In any case, only the method is described, without going into details on the physical implementation of the transduction zone.

Specializing more in composite materials, the renewable energy sector stands out, where you can find several examples of applications of fiber optic techniques. Thus, the European patent application EP1780523-Al describes a monitoring system for wind turbine blades based on fiber optic technologies. Losses introduced into the optical fiber when deforming with the structure are characterized. By incorporating optical fibers of different diameters, different breaking stresses can be achieved to record when certain deformations are exceeded at some point. From an implementation point of view, the options of gluing or imbibing the fiber to the laminates are cited, but the way to do it is not specified, nor are implementation examples provided.

International patent application W02008101496-A2 describes a wind turbine blade with optical sensing means. From the optical point of view, it is not particularized that the technology used is diffraction gratings. Regarding its implementation, it is based on a device designed to be glued to the internal surface of the wind turbine blade. For this, it starts from a support to which the optical fiber is fixed to facilitate installation and alignment and protect it mechanically.

International patent application W02008020242-A2 describes a wind turbine blade with optical deformation sensors based on FBGs. A monitoring system with at least one measuring point for each part of the wind turbine blade is detailed. For its installation it is contemplated that it be incorporated into a part of the wind turbine blade. Although this installation can be carried out before the infusion, it is conceived only as a method of mechanical protection, since it is located on the surface of the component. It is further specified that the component is mounted on a substrate. To insert the component into the shovel, marks or holes are used.

In the international patent application W02009095025-Al a sensing method and optical system oriented to wind turbine components is described. It starts from Bragg diffraction grating (FBG) technology and describes a tunable laser-based wavelength multiplexing method.

In view of the work carried out previously, it is observed that the optical monitoring of composite material structures is not a new discipline. However, in no work of the found are the characteristic problems of the integration of fiber optic diffraction networks with composite materials solved.

In the previous documents different solutions to problematic characteristics of the optical fiber are exposed, such as its mechanical protection to avoid micro-breaks in view of its manipulation or to facilitate the alignment of the transduction zone during the installation process of the transducers.

However, when trying to introduce the fiber optic diffraction gratings in blocks of composite materials, another series of problems arise during the manufacturing process, in addition to those exposed in the previous documents.

Due to the manufacturing conditions of the pieces of composite materials, the optical fiber is subjected to transverse forces that can be of significant non-homogeneous spatial distribution, since by pressure, either mechanical or by vacuum processes, the compactness of the laminate. From a mechanical point of view, the fiber without its protection would break under these circumstances in an industrial environment, so it is necessary to re-protect weak areas, such as the transduction zone.

The sensitivity of fiber optic diffraction networks is high to mechanical deformations, so the roughness introduced by the fabrics used in the manufacturing processes of laminates apply a heterogeneous deformation on the diffraction network, so that the optical properties they are degraded. This effect is increased by having to apply pressure to compact the laminate so, apart from mechanically protecting the optical fiber, means are required to isolate the diffraction grating from possible inhomogeneities present in composite materials that can modify its optical response .

It is also a necessary condition that the transducer embedded in the structure is as invasive as possible so that it does not modify the mechanical characteristics of the structure. The aforementioned is particularly vital when it has to be installed at critical points of the structures that should not be disturbed; which leads to the transducer having to be made in such a way that it is "naturalizable" within the aforementioned structures. With this in mind, there are limitations in both shape and size (especially in thickness) and valid materials to protect the base diffraction network (s) of the transducers.

SUMMARY OF THE INVENTION

The present invention tries to solve the aforementioned drawbacks by means of an innovative form of protection of the diffraction grating, which isolates the grating from the aggressions of the manufacturing system. This overcomes the major limitations of conventional transduction systems, which are imposed by thicknesses and materials, which can degrade the behavior of the composite structure.

Based on these limitations, it was decided to opt for a resin block with longitudinal reinforcements in which the diffraction grating is embedded and which isolates the grating from the aggressions of the manufacturing system. With this design, the thickness restrictions are met, proposing a simple geometry for a better adaptation to the laminate fabrics that also allows a better installation of the fiber optic system.

Specifically, in a first aspect of the present invention, there is provided a transduction system comprising: an optical fiber that has at least one diffraction grating recorded; a resin block in which at least one diffraction grating is fully embedded. The resin block comprises a plurality of reinforcing filaments arranged longitudinally to the optical fiber and to the diffraction grating engraved therein, the reinforcing filaments being located on both sides of the optical fiber and configured to isolate the network from diffraction of transverse forces that may disturb the fidelity of the transducer response.

Preferably, the ream block is a plastic ream block, and more preferably the plastic resin is epoxy or polyester.

The reinforcing filaments, without neglecting other possibilities, may preferably be: groups of glass fibers, groups of carbon fibers, groups of aramid fibers

or groups of optical fibers.

Preferably the reinforcing filaments are symmetrically located on both sides of the optical fiber.

Also preferably the diameter of the reinforcements is at least 1.5 times greater than the diameter of the optical fiber.

The resin block preferably has a constant thickness from at least the reinforcing filament located on one side of the diffraction grating and closest to it and at least the reinforcing filament located on the other side of the diffraction grating and more close to it.

In a possible embodiment, the transduction system comprises a plurality of diffraction gratings recorded on the optical fiber.

The system is configured to be integrated into a composite material structure. during the manufacturing process of the structure.

The invention also provides a composite material structure comprising at least one transduction system embedded therein, that transduction system being any of those described above.

Preferably the composite material that forms that structure is compatible with the resin block of the at least one transduction system embedded in the structure.

In a possible embodiment, the structure carries embedded a plurality of transduction systems, forming a quasi-distributed transducer.

In another aspect of the invention, a blade for a wind turbine made of blades of the structure described above is provided.

The advantages of the invention will become apparent in the following description.

BRIEF DESCRIPTION OF THE FIGURES

In order to help a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment thereof, and to complement this description, a set of drawings is included as an integral part thereof, the character of which is illustrative and not limiting. In these drawings:

Figures 1 a and 1 b show diagrams of a transduction block or system according to a possible embodiment of the invention.

Figure 2 shows a possible embodiment of the invention, in which N transduction blocks are linked in the same fiber optic channel, so that a quasi-distributed transducer is obtained as the basic structure sensing unit.

Figure 3 illustrates a process of embedding the transduction block in a composite material structure, according to the invention.

Figure 4 schematizes how each block or transduction system is

fully embedded in the material in the desired position, according to the

invention.

DETAILED DESCRIPTION OF THE INVENTION

In this text, the term "comprises" and its variants should not be understood in an exclusive sense, that is, these terms are not intended to exclude other technical characteristics, additives, components or steps.

Also, the terms "approximately", "substantially", "around", "some", etc. they should be understood as indicating values close to those that these terms accompany, since due to calculation or measurement errors, it is impossible to achieve these values with complete accuracy.

The following preferred embodiments are provided by way of illustration, and are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments herein.

'

indicated. For those skilled in the art, other objects, advantages, and features of the invention will emerge in part from the description and in part from the practice of the invention.

The scope of the invention is focused on the industry of composite materials or "composites", understood as composite materials all those materials formed by a plastic resin, such as epoxy or polyester, with reinforcing materials such as fiberglass, fiber carbon, aramid, etc.

Starting from the aforementioned limitations of conventional transduction systems, that is, the thicknesses and materials, the device of the invention comprises a block of plastic resin with longitudinal reinforcements in which the diffraction grating is embedded. As described below, this block isolates the network from the aggressions of the manufacturing system. This design complies with the thickness restrictions characteristic of composite material manufacturing systems, typically less than a few millimeters, proposing a simple geometry for better adaptation to the laminate fabrics, which also allows for a better installation of the fiber optic system .

Figure 1 a shows a schematic of a 1 O transduction block or system according to a possible embodiment of the invention. Specifically, the figure is outlined by an optical fiber 1 in which a diffraction grating 2 has been recorded. The diffraction grating 2 (and part of the fiber 1) is covered with a block of plastic resin 3 (for example, but not limitingly, epoxy resin). Parallel to the diffraction grating 2 along the optical fiber 1 reinforcement filaments 4 are incorporated, which can be of various materials, such as fiberglass, carbon, aramid, etc. Said reinforcements 4 are positioned on both sides of the diffraction grating 2 with a substantially symmetrical distribution, in order to homogenize the deformation in the diffraction grating 2. That is, the deformation in the measurement zone is intended to be distributed uniformly when measuring. At least one reinforcement 4 must be placed on each side of the fiber 1 that bears the diffraction grating 2. Said reinforcements 4 must have a height greater than the diameter of the optical fiber 1 and must be positioned leaving the diffraction grating 2 at the central point of the vertical axis in order to isolate the diffraction grating 2 from transverse forces. A recommended configuration is to use stiffeners 4 whose diameter is at least 1.5 times greater than the diameter of fiber 1, and more preferably at least twice the diameter of fiber l. To guarantee the homogeneity of the measurement, the resin block 3 must have a constant thickness between the reinforcements 4 (at least in the closest ones) and the diffraction grating 2.

From an optical point of view, the diffraction grating 2 of the transduction system 1 O must be of the minimum possible length that the technique allows, typically a few millimeters, to minimize the possible effects of inhomogeneities on the deformation during the measurement. It has been observed that with diffraction gratings 2 of a few millimeters the deformation in the measurement zone remains constant.

In order to facilitate the integration of the transduction system in composite materials, the general geometry of the block must be simple, not presenting abrupt shapes that favor the appearance of inhomogeneities in the material to which the transduction system is incorporated. A possible embodiment of a transduction system 10 analogous to that of figure la is shown in FIG. 1 b. Figure lb includes a chamfer transition 6 on the sides of the transduction system (following the outermost reinforcements 4) to improve its integration in reinforced plastics. The thickness of the transduction system is constant 7 in the area between the reinforcements 4 and

10 fiber 1, in this way a homogeneous response to deformation is achieved.

In view of the drawbacks observed when trying to reproduce the integration of diffraction gratings from the state of the art in composite structures, the inventors have imposed the following requirements on the transduction system of the invention:

fifteen

•

If necessary, protect the fiber optic areas that are not covered (for example, acrylate) to offer better mechanical consistency.

•

Isolate the diffraction grating from the irregularities introduced by pressing

later, during the embedding phase in the laminate, for which 2 O the block is designed.

•

Homogenize the deformation offered to the diffraction grating to obtain a measurement with the highest signal-to-noise ratio and highest fidelity and reliability.

•

Facilitate the management and positioning of the transduction point.

On the other hand, from the point of view of the structure in which the transduction block is to be included, more restrictions are derived:

• Integration of the 1 O transduction block must not degrade the mechanical response of the structure or at least not significantly degrade it. This implies small thicknesses (less than a few millimeters) and simple shapes

30 little mvastvas.

•

The materials used must be composite materials, so as not to degrade the behavior of the structure.

•

The installation process must be compatible with the manufacture of laminates, such as vacuum infusion.

Observing these requirements, a transduction system based on diffraction gratings in fiber optics and reinforced plastic has been developed. The system obtained has sufficient mechanical resistance for handling in production environments.

Due to the constant thickness in the area of the diffraction grating 2 and the symmetrical arrangement of the reinforcements 4, a homogeneous distribution of the deformation is achieved. Likewise, with the correct dimensioning of the reinforcements 4, the diffraction grating 2 is protected from the transverse forces or pressures characteristic of the manufacturing process of the structure.

In order to minimize problems of degradation of the optical properties of the diffraction grating, it is a question of using grids of the shortest possible length, within the limits of the technique used. A diffraction grating 2 with a length of less than a few millimeters is preferably chosen and designed. With this choice, the measurement resolution is penalized a little, in exchange for greater robustness to inhomogeneities in the deformation.

The 1 O transduction system must have a shape that facilitates its integration between the tissues of the composite material of the structure in which it is to be integrated. Simple geometries without abrupt transitions and chamfered ends 6 (figure 1-b) allow better integration in the composite materials of the target structure, avoiding possible inhomogeneities created during the embedding process.

In a possible embodiment of the invention, as schematized in figure 2, N transduction systems 10 are linked (in the scheme of figure 2, N = 3) in the same fiber optic channel 1, so that a "quasi-distributed transducer" is obtained as the basic structure sensing unit. The quasi-distributed transducer as described in figure 2 (or a transducer formed by a single transduction block 1 O as described in figures 1 a and 1 b) must be positioned between the fabrics of the laminate 8 of the target structure before to finish the structure.

Various quasistribution transducers are embedded in the structure of composite materials depending on the points of interest to be monitored. Each quasi-distributed transducer is wired at both ends to make the output of the composite material structure endowing the optical fiber with greater mechanical robustness.

Although it is true that transducers based on fiber optic diffraction networks are usually interrogated by a single end, preferably both ends are extracted in order to apply other interrogation techniques, the scope of which is outside the present invention and / or to add redundancy to the system and therefore improve its reliability.

A manufacturing process of the transduction system 1 O of the invention is described below: It starts from a telecommunications optical fiber 1. A diffraction grating 2 is etched therein by any conventional etching method. Subsequently, it is covered with resin block 3 by the described process:

l. The diffraction grating 2 is positioned in a non-stick plastic mold in the shape of the transduction block 1 O. When positioning, the diffraction grating 2 is centered with symmetrical distribution within the mold.

2.

The reinforcements 4 are incorporated in longitudinal arrangement, aligned with the optical fiber l.

3.

Low-viscosity plastic resin 3 is poured covering all the mold holes.

Four.

The mold is closed and allowed to cure following the requirements of the resin.

5.

The mold is opened and the finished transduction block 1O is removed.

To manufacture a quasi-distributed transducer, simply scale the manufacturing system to the number of transducer measurement points.

The process of embedding the transduction block 1 O into a composite structure 40 is described below, as illustrated in Figure 3: The incorporation of the transduction system - semi-distributed or not-in a composite structure has to be carried out during the manufacturing process.

The composite material that forms structure 40 (which after the embedding process will incorporate the transduction block 1 O) may be, without limitation, one of the following: fiberglass laminate or carbon fiber laminate, plus the corresponding resin. One of the methods for manufacturing the composite material of the structure 40 in which the system or block 1O, known in the state of the art as "dry lamination", is to be embedded, consists of stacking the reinforcing fabrics (or fabrics ), then a pressure is performed that compacts the laminate and the plastic resin is added, to thus form the authentic composite material that will form the structure 40. If the manufacturing process is by vacuum infusion, the pressure to compact is carried out using a vacuum bag before adding the plastic resin. Another option is to use fabrics already impregnated with resin. A person skilled in the art will understand that any other method known in the state of the art can be used as the manufacturing process for the composite material.

As shown in Figure 3, the transduction system 10 (which can be quasi-distributed) has to be introduced between the reinforcing fabrics or laminate fabrics 8 before compacting the laminate. For this, during the placement of the reinforcing tissues 8, the transduction system 10 is placed in the position of the structure to be characterized. Due to the reinforcements (plastic resin 3 and reinforcements 4) incorporated into the transduction system 1 O, the optical fiber 1 with the diffraction network 2 is protected from the pressures exerted during the compaction of the tissues that make up the laminate 8.

To fix each transduction system 1 O in position, it is fixed to one of the tissues 8 with plastic resin, preferably similar to that used in the manufacture of the structure to be monitored with the translation system, such as epoxy resins or polyester. Once compacted, the 1 O transduction blocks are completely embedded in the material in the desired position, as illustrated in Figure 4.

4 shows a cross section of a composite structure 40 with embedded transduction system 1 O. It can be seen how the reinforcing fabrics or laminate fabrics 8 conform to the transduction system 1O. Figure 4 shows four laminate fabrics 8, but this number reflects only one possibility of implementation, more or less laminate fabrics 8 may be included. .

The reinforcements 4 incorporated into the transduction system 1 O protect the optical fiber 1 and the diffraction grating (not illustrated in Figure 4) from the pressures exerted during the manufacture of the structure 40. Also, due to the substantially symmetrical position of the diffraction grating with respect to the reinforcements 4, the deformation of the structure is transmitted homogeneously. Since the transduction system 1 O has a simple shape, the resin 3 is distributed homogeneously in the transition zones 5, favoring better integration of the device. This effect is dramatically improved by introducing a small chamfer on the sides of the transduction system (reference 6 in figure 1.b) that facilitates tissue adjustment 8.

The transduction system can be used to monitor any structure, preferably made of composite materials, making it possible to embed it. A possible example is its application to wind turbine blades. This example of implementation is detailed below:

In a wind turbine blade, the load typically falls on the central area.

Characterizing the deformations in said central area may be of interest in order to diagnose the current state and useful life of the structure. Due to the topology of a blade, the thickness of the composite material in which the 1 O transduction system is embedded is highly variable, for example between about 150 and 15 mm for an intermediate case. In the most restrictive case, a 1 O transduction system is embedded in a sheet of composite material (such as fiberglass) about 15 mm thick without degrading its mechanical behavior. For this, a 1 O transduction system is used based on a 5 mm Bragg diffraction grating recorded in standard telecommunications optical fiber with an acrylate cover (250 um in diameter).

To implement the transduction system, it starts from the diffraction grating and is encapsulated in a block of low-viscosity epoxy resin, specifically the same one used in the manufacture of the wind turbine blade. Two 800 um fiberglass reinforcements are incorporated into the resin block, as shown in figure la. These reinforcements fix the thickness of the resulting resin block to 800 um.

Once the transduction system is finished, it is incorporated into the structure during the manufacturing process, positioning it on the tissues as illustrated in Figure 3. At the end of the composite structure, the quality of the embedding process is analyzed as no discontinuities are detected in the structure. resulting.

The described transducer and transducer block can be used to monitor any structure made of composite materials. A clear example where its utility is relevant is in the blades of wind turbines. In wind turbine blades, its design is very important to achieve, with the minimum amount of material and less weight, to manufacture a blade that meets the minimum requirements in its mechanical performance. When working at the limit of the design, it is very useful to be able to have information on the state of the blade, either during storage or during its useful life. If transducers are strategically integrated into the blade manufacturing process

As described, it is possible to extract this information about the mechanical state of the

shovel and be able to predict more precisely what the life time of the

itself, predicting possible repairs, or replacements thereof in the

5 wind turbine or suspend a periodic replacement if the measurements obtained

reflect the correct operation of it. Therefore, although the installation

of this type of transducers supposes an additional cost in the manufacture of the blades,

This investment ends up being amortized with the measures obtained, since this will not

act on them periodically but only when it is really necessary. In addition, data will be obtained that can help optimize and improve the

design of the same.

Claims (12)

l. A transduction system (lO) comprising: - an optical fiber (1) engraved with at least one diffraction grating (2); - a resin block (3) in which said at least one diffraction grating (2) is fully embedded; characterized in that said resin block (3) comprises a plurality of reinforcing filaments (4) arranged longitudinally to said optical fiber (1) and to the diffraction grating (2) engraved therein, said reinforcing filaments ( 4) located on both sides of the optical fiber (4) and configured to isolate the diffraction grating (2) from vertical pressures.

2.

The system of claim 1, wherein said resin block (3) is a plastic resin block.

3.

The system of claim 2, wherein said plastic resin is epoxy or polyester.

Four.

The system of any of the preceding claims, wherein said reinforcing filaments (4) are chosen from the following group: groups of glass fibers, groups of carbon fibers, groups of aramid fibers or groups of optical fibers.

5.

The system of any of the preceding claims, wherein said reinforcing filaments (4) are located symmetrically on both sides of the optical fiber (4).

6.

The system of any of the preceding claims, wherein the diameter of said reinforcing filaments (4) is at least 1.5 times greater than the diameter of said optical fiber (1).

7.

The system of any of the preceding claims, wherein said resin block (3) has a constant thickness from at least the reinforcing filament (4) located on one side of the diffraction grating closest to it and up to at least the reinforcing filament (4) located on the other side of the diffraction grating (2) closest to it.

8.

The system of any of the preceding claims, comprising a plurality of diffraction gratings (2) recorded on said optical fiber (1).

9.

The system of any of the preceding claims, which is configured to be integrated into a structure (40) of a composite material during the manufacturing process of said structure (40).

1O. A structure (40) of a composite material comprising at least one transduction system (10) embedded therein, said transduction system (1 O) being any one of claims 1 to 9.

eleven.

The structure of claim 1 O, wherein the composite material that forms it is compatible with the resin block (3) of said at least one transduction system (1 O) embedded in said structure (40).

12.

The structure of any one of claims 10 or 11, comprising a plurality of transduction systems (10) forming a quasi-distributed transducer.

13.

A blade for a wind turbine formed by blades (8) of the structure (40) of any one of claims 10 to 12.