BACKGROUND

The present invention pertains to a sensor assembly for monitoring an artifact.

The present invention further pertains to an optic sensor system

comprising such a sensor assembly.

The present invention still further pertains to an application wherein the optic sensor system is used to monitor an artifact.

Use of fiber optic sensors is known for purpose of monitoring

infrastructures. For example EP2372322 notes that a reduction in the amount of cabling can be achieved by employing optic sensors for example, designed as Fiber Bragg Gratings disposed in a single optic fiber. The sensor device disclosed therein comprises an elongated support, which is disposed transversely in relation to the carriageway under the carriageway. The support is provided with a plurality of measuring zones, which are separated from one another in the longitudinal direction of the support by intermediate zones. The axial rigidity of the measuring zones in a direction perpendicular to the carriageway is greater than the axial rigidity of the intermediate zones in a direction perpendicular to the carriageway. Each measuring zone is provided with at least one sensor to measure deformation of this measuring zone in response to a force exerted substantially perpendicular to the carriageway. The elongated support is provided by an I-beam. When a vehicle traverses the carriageway, the I-beam subsequently deforms in a first direction, assumes a neutral state and deforms in a second direction opposite to the first direction. During deformation in the first direction, an optic sensor on the front side of the I beam subsequently is compressed by the I-beam, assumes a neutral state, and is stretched. An optic sensor on the opposite side of the I-beam subsequently is stretched, assumes a neutral state and is compressed. The optic sensors are, for example, designed as Fibre Bragg Gratings. The support may be provided with a protective sleeve to protect the operation of the sensors against environmental influences, the support is optionally incorporated in a trough-shaped housing with a base and vertical side walls. The known sensor device is relatively costly. The protective sleeve is not strictly necessary. In the absence of this protective sleeve, the space between the flanges of the I-beam will be filled with asphalt, or other material used for construction of the carriage way. Often the space between the flanges will only be filled partially, and to an extent which can not be predicted. This is unfavorable for the reliability and accuracy of the measurement results obtained with the sensor device. Also, it is to be noted that the I-beam is an intermediate element that changes the physical characteristics to be measured, in consequence, the characteristics measured are indirect effects of the traffic on the infrastructure not reflecting the true behavior of such infrastructure.

Moreover, the use of an I-beam requires more space to be installed properly which limits the amount of sensors per linear meter that can be placed on a monitoring device.

Furthermore, the use of I-beams due to their continuous form-factor can result in cross-talk subsequent sensors thereby inducing errors into the measurement.

It is a still further disadvantage of the known sensor arrangement that it occupies a large volume. Therewith is only suitable for a limited class of applications. Whereas a carriageway provides ample space for the massive construction as proposed in the cited document EP’322, this may not always be the case. For example for the purpose of monitoring parts of a building, e.g. a floor in a storage house or a container only a hmited amount of space may be available for the sensor arrangement.

SUMMARY OF THE INVENTION It is an object of the invention to provide a sensor assembly for monitoring an artifact that at least partially mitigates one or more of the above-mentioned disadvantages.

In order to meet this object, a sensor assembly is provided as claimed in claim 1. Therein a measurement zone is formed by an at least one deformable section of the carrier and an at least one longitudinal optic fiber section of the optic fiber. A change of deformation of the elastically deformable carrier section in the longitudinal direction of the at least one longitudinal optic fiber section is detectable as a change in longitudinal strain in the longitudinal optic fiber section. Hence, contrary to the known assembly, the measuring zones have a longitudinal rigidity that is smaller than a longitudinal rigidity of the

intermediate zones between the measuring zones. This renders it possible to manufacture the sensor assembly in a substantially more hghtweight and compact construction.

In an embodiment, of the sensor assembly the at least one deformable section is integrally formed with the pair of mounting sections. This is

advantageous in that the carrier can be provided from a single strip of material.

In an embodiment the carrier may be formed in its entirety as a

deformable strip of material. Alternatively, the carrier may be provided such that the deformable sections are deformable more easily than the mounting sections. For example this can be achieved in that the deformable sections have a reduced cross-sectional area as compared to the mounting sections. A reduced cross- sectional area in the deformable sections can be obtained with relatively simple operations, e.g. by punching, mechanical drilling, (laser or waterjet) cutting or laser drilling or by molding the carrier in a form providing for the deformable sections. Alternatively it is possible to provide the deformable sections in the carrier by rolling the carrier in those sections to locally obtain a reduced thickness.

In an application, the sensor assembly provided from a strip of material is preferably arranged with its main surfaces substantially parallel to a surface of the artifact, e.g. the surface of a road. Therewith the sensor assembly, mounted in its mounting portions to the artifact will typically flex with the artifact in a direction transvers to the artifact surface and not move longitudinally. In the absence of a mounting in the mounting portions such longitudinal movements probably due to the embedding of the fiber in viscoelastic material in the asphalt may occur and introduce measurement errors. While the latter can be partially mitigated by signal processing the measurement accuracy would still be significantly impaired. The mounting portions of the carrier prevent longitudinal movements.

In a particular form of this embodiment the at least one elastically deformable longitudinal carrier section has a first and a second curved portion. Therein the first curved portion connects the longitudinal mounting sections at a first lateral side of the carrier, and the second curved portion connects the longitudinal mounting sections at a second lateral side of the carrier that is opposite to the first lateral side. In the absence of a mechanical tension, the first and the second curved portion are curved towards each other in between the longitudinal mounting sections. Therewith a well controllable elastic behavior in the longitudinal direction is achieved. The curved portions maybe for example omega shaped, and have a shortest distance between each other halfway their length. Alternatively, the curved portions may be formed otherwise to achieve a desired controlled elastic behavior in the longitudinal direction, for example with S-shaped curved portions. Embodiments may further be contemplated wherein, in the absence of a mechanical tension, the first and the second curved portion are curved away from each other in between the longitudinal mounting sections, i.e. outside lateral boundaries defined by the mounting portions. This would however involve a less efficient use of material.

Alternatively the at least one deformable section and the pair of mounting- sections may be formed of mutually different materials. For example a first material used for the at least one deformable section may have a lower modulus of elasticity than that of a second material used for the pair of mounting sections. Also it may be contemplated to additionally provide the at least one deformable section of the first material with a reduced cross-sectional area as compared to the cross-sectional area of the mounting sections manufactured of the second material. In an embodiment of the sensor assembly a change of deformation of the elastically deformable carrier section in the longitudinal direction of the at least one longitudinal optic fiber section is detectable as a change in longitudinal strain in the longitudinal optic fiber section through an indirect mechanical coupling between the elastically deformable carrier section and the at least one longitudinal optic fiber section. For example the at least one longitudinal optic fiber section is mechanically coupled to the deformable section via the pair of mounting sections.

In an embodiment the elastically deformable longitudinal carrier sections is axially pre-compressed. Therewith it pre-tensions the longitudinal optic fiber section, and it is achieved that the optic strain-sensor element also is capable of measuring deformations that result in compressive loads.

As a further aspect an optic sensor system is provided as claimed in claim 10, that comprises an interrogator in addition to at least one sensor assembly as specified above. In the optic sensor system the optic fiber of the sensor assembly is coupled to the interrogator and the interrogator is configured to transmit an optical interrogation signal into the optic fiber. In response it receives a response optical signal that has been modulated by the optic strain-sensor element of the at least one longitudinal optic fiber section of the optic fiber.

In an embodiment of the optic sensor system the at least one longitudinal optic fiber section is one of a plurality of longitudinal optic fiber section, and the at least one deformable longitudinal section is one of a plurality of deformable longitudinal carrier sections. Each pair of mutually subsequent deformable longitudinal carrier sections is coupled to each other via a respective longitudinal mounting section of the carrier. In this embodiment a change of deformation of each of the elastically deformable longitudinal carrier sections is detectable as a change in longitudinal strain in an optic strain-sensor element of a respective one of the longitudinal optic fiber sections. The optic strain-sensor elements of the longitudinal optic fiber sections have mutually different optical properties, for example mutually different characteristic wavelengths. Accordingly a change in strain of a particular longitudinal optic fiber section is detectable as a change in its associated unique characteristic wavelength. Also other optical properties may be used to modify the optical interrogation signal into a response signal, for example an amount of absorption. For example the optic strain-sensor elements could have a same characteristic wavelength, but change the absorption of light in response to strain to a different extent.

According to a further aspect of the present invention, an application is claimed in claim 12, wherein the sensor assembly is arranged within a

constructive part of an artifact. In an exemplary embodiment the sensor assembly is arranged within a constructive part of an artifact. For example the artifact is a civil engineering asset, such as a road, a railway support, a bridge and a tunnel. Advantageously therein the carrier is fixed to the artifact with one or more anchoring elements.

In addition, the optic sensor system is highly suitable for the purpose of monitoring parts of a building, e.g. a floor in a storage house or a container where only a limited amount of space may is available.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects are described in more detail with reference to the following drawings. Therein:

FIG. 1 schematically shows an embodiment of a sensor assembly according to a first aspect of the invention, FIG. 1A, IB show in more detail examples of a fastening element in said assembly;

FIG. 2 shows a part of another embodiment of the assembly in more detail;

FIG. 2A, 2B respectively show a cross-sections according to A21-A21 and A23-A23 in FIG. 2;

FIG. 2C shows in a cross-section according to IIC-IIC in FIG. 2 an alternative embodiment of a sensor assembly according to the first aspect;

FIG. 3 shows a still further embodiment of the sensor assembly according to the first aspect;

FIG. 4 shows characteristic wavelengths of optic strain sensors in an exemplary embodiment of the sensor assembly according to the first aspect, therein the horizontal axis indicates the wavelength in nm and the vertical axis indicates a magnitude in arbitrary units;

FIG. 5 schematically shows an optic sensor system according to a second aspect of the invention in a typical application;

FIG. 5A shows a cross-section according to VA-VA in FIG. 5;

FIG. 6 shows a further alternative embodiment of a sensor assembly according to the first aspect;

FIG. 7, 7 A, 7B, 7C show an example of another fastening element for use in the sensor assembly, therein FIG. 7 A, 7B are a first and a second cross-section according to VIIA-VIIA and VIIB-VIIB in FIG. 7 respectively, FIG. 7C shows the fastening element mounted on a carrier in the same cross-section as FIG. 7A;

FIG. 8A, 8B show a further example of a fastening element;

FIG. 9 shows a still further example of a fastening element.

DESCRIPTION OF EMBODIMENTS

FIG. 1 schematically shows a sensor assembly 1 for measuring movement of a surface of an artifact A. Therein the upper portion of FIG. 1 shows a top-view of the sensor assembly and the lower portion shows a side-view according to arrow SV in the upper portion. The sensor assembly 1 comprises an optic fiber 10 and a carrier 20. The sensor assembly comprises longitudinal sections. I.e. the optic fiber 10 may have one or more one longitudinal optic fiber sections. In the embodiment shown the optic fiber 10 has a longitudinal optic fiber section 11a with an optic strain-sensor element 12a and a further longitudinal section at each end of this section 11a. The carrier 20 has at least one elastically deformable longitudinal carrier section 23a and a pair of longitudinal mounting sections 21a, 21b that are mechanically coupled to mutually opposed ends of the at least one longitudinal optic fiber section 11a. I.e. each of the mutually opposed ends is mechanically coupled to its associated mounting section 21a, 21b, and the mounting sections 21a, 21b. On their turn, the mounting sections are configured to be mechanically coupled to the artifact A, for example by means of one or more anchoring elements 24a, 24b provided via at least a connection opening 27a, 27b provided in the mounting section 21a, 21b. In the case that movements, e.g. by deformation of the artifact A occur, the elastically deformable longitudinal carrier section 23a deforms accordingly, which in turn results in a change of deformation of the elastically deformable longitudinal carrier section 23a in its longitudinal direction, which is detectable as a change in longitudinal strain in the

longitudinal optic fiber section 11a.

Alternatively the carrier may be configured to be mounted to the artifact by using an adhesive. For this purpose the carrier may be configured in that its surface has been treated to allow for a good adherence to the adhesive, for example by a chemical treatment or by providing the carrier with a surface relief, e.g. by roughening. Alternatively, the carrier can be attached to the artifact by spot welding to the artifact or to a pre-attached welding point on the artifact

As a further alternative, the carrier may be configured to be mounted to the artifact in a plurality of positions in each mounting section, for example by providing the mounting sections with ribs that anchor the mounting sections in a plurality of positions to the artefact.

In the embodiment shown each of the mutually opposed ends of the longitudinal optic fiber section 11a is mechanically coupled to its associated mounting section 21a, 21b by a fastening element 25a, 25b. The fastening elements 25a, 25b may for example clamp the mutually opposed ends.

Alternatively, the ends of the longitudinal optic fiber section 11a may have ribs that cooperate with a rim of complementary shape in the fastening elements 25a, 25b. This is schematically shown for an end with rim 1 lab of a longitudinal optic fiber section 11a in FIG. 1A. In a variation of the embodiment of FIG. 1A, the fastening element 25b may additionally clamp the rim llab.

Typically the longitudinal optic fiber section 11a is axially pre-tensioned.

In this way a detection threshold for the deformation of the elastically deformable longitudinal carrier section 23a is avoided. This may be achieved for example by applying a pretension to the optical fiber 10 when fastening it to the fastening elements 25a, 25b. Alternatively, or additionally, the elastically deformable longitudinal carrier section 23a may be slightly compressed in the longitudinal direction when fastening the optical fiber thereto.

In some cases it may be desirable to tune the amount of pretension in a longitudinal optic fiber section 11a, for example to adapt its characteristic wavelength or other characteristic optical property. Also this may be desirable in case a too high value of the pretension is likely to result in damages. FIG. IB shows an example of a fastening element that allows for a tuning of a pretension in the longitudinal optic fiber section 11a, by a screwing movement of inner portion 25b 1 of the fastening element with an outer portion 25b2.

In the embodiment shown (see lower portion of FIG. 1) the assembly 1 is mechanically coupled to the artifact by the mounting sections 21a, 21b of the carrier 20. In this embodiment the mounting sections 21a, 21b are fastened to the artifact A by nails 24a, 24b. In another embodiment the mounting sections 21a, 21b may be provided with ribs, e.g. circumferential ribs that anchor the mounting sections within the artifact. This embodiment is very suitable in applications wherein the artifact is molded or comprises molded portions. For example, in case the artifact is a carriageway a sensor assembly according to this embodiment may be accommodated in a slit which is subsequently filled with a curable liquid filler material. Upon curing the assembly is mounted to the artifact by the ribs within the cured filler material.

FIG. 2 shows an embodiment of the carrier 20 as used in FIG. 1 in more detail. Additionally, FIG. 2A shows a cross-section according to A21-A21 of a longitudinal section 21a of the carrier 20 and FIG. 2B shows a cross-section according to A23-A23 of a longitudinal section 23a of the carrier 20. These FIGs.

2, 2A and 2B illustrate that the longitudinal section 23a has a cross-sectional area that is smaller than that of the longitudinal portions 21a, 21b. For example, the cross-sectional area of the longitudinal section 23a may have value that is 5 to 20 smaller than that of the longitudinal portions 21a, 21b. This value

may for example be closer to 5 for a relatively long longitudinal section 23a and be closer to 20 for a relatively short longitudinal section 23a.

Due to its relatively small cross-sectional area, the section 23a forms a deformable longitudinal section, whereas section 21a, hke section 21b is substantially non- deform able. This renders it possible that an elastically deformable longitudinal carrier section 23a is integrally formed with the pair of longitudinal mounting sections 21a, 21b of the carrier 20 and obviates the use of different materials.

The carrier 20 may for example be manufactured of an elongate strip 20” of a metal, such as stainless steel, or another resilient material. Also polymers may be considered for this purpose. In the example of FIG.2 portions removed from the strip 20” are shaded. In the embodiment shown, the carrier 20 has a total length of 150-160 mm. The length of deformable section is 50-70 mm and the width of the carrier, measured between the mutually opposite lateral sides 26L, 26R is in the order of 50 to 55 mm.

In the embodiment as shown in FIG. 2, 2 A and 2B, the elastically deformable longitudinal carrier section 23a has a first and a second curved portion 23al, 23a2. The first curved portion 23al connects the longitudinal mounting sections 21a, 21b at a first lateral side 26L of the carrier 20. The second curved portion 23a2 connects the longitudinal mounting sections 21a, 21b at a second lateral side 26R of the carrier that is opposite to the first lateral side. In the absence of a mechanical tension, the first and the second curved portion 23al, 23a2 are curved towards each other in between the longitudinal mounting sections 21a, 21b. Therewith a well controllable elastic behavior in the

longitudinal direction is achieved. The carrier 20 as shown in FIG. 2, 2A and 2B, may for example be manufactured from a metal strip 20’for example having a thickness of 0.5 to 2 mm by removing thereof the hatched areas 23al’, 23a’ and 23a2’, for example by punching, laser cutting or other material processing method. In this example, the width of each of the curved portions 23al, 23a2 is in the order of a few mm. Similarly, first mounting holes 27a, 27b for mounting the carrier 20 to the artifact can be provided, as well as second and third mounting- holes 28a, 28b for mounting fastening elements 25a, 25b to the carrier 20. In the embodiment shown the third mounting holes 28b are provided as slits, therewith allowing a longitudinal positioning of the fastening element 25b. A positioning of the fastening element 25b in this way may facihtate tuning a pre-tensioning of the longitudinal optic fiber section 11a with the elastically deformable longitudinal carrier section 23a. This may be used as an alternative or in addition to the measure as proposed with reference to FIG. IB.

It is noted that the optic fiber 10 need not be pre-tensioned over its entire length. For example a portion of the optic fiber 10 at the right of the sensor assembly of FIG. 1 may extend with play towards a next sensor assembly.

Whereas in the embodiment of FIG. 2 the portions 23al, 23a2 are omega shaped, alternative shapes may be employed to achieve a desired controllable elastic behavior in the longitudinal direction. For example if a lower elasticity modulus is desired the portions 23al, 23a2 could be S-shaped.

FIG. 2C shows an alternative embodiment according to cross-section IIC- IIC in FIG. 2. When molding the carrier 20 into the artifact, or with a (curable) filling material into a slit in the artifact, these elements 24a, 24b serve as anchors that mount the carrier with its mounting portions to the artifact. In the example shown, the anchoring elements 24a’, 24b’ are provided with through holes to feed through the optic fiber 10. By way of example FIG. 2C shows how the optic fiber is fastened at portions l laa, l lab with fastening elements 25a,

25b to the carrier 20. The fastening elements 25a, 25b are mounted to the carrier 20 with set of screws 29a, 29b, but may alternatively be welded, e.g. by spot welding for example

By way of example, FIG. 3 shows a sensor assembly 101, wherein the longitudinal optic fiber section 11a is one of three longitudinal optic fiber sections 11a, l ib, 11c. The deformable longitudinal section 23a is one of a plurality of deformable longitudinal carrier sections 23a, 23b, 23c. Each of the deformable longitudinal carrier sections is coupled to a longitudinal mounting section 21a, 21b; 21b, 21c; 21c, 2 Id at its mutually opposed ends. In this embodiment a change of deformation of each of the elastically deformable longitudinal carrier sections is detectable as a change in longitudinal strain in an optic strain-sensor element of a respective one of the longitudinal optic fiber sections 11a, l ib, 11c. The optic strain-sensor elements of the longitudinal optic fiber sections 11a, lb, 11c have mutually different optical properties. For example, the optic strain sensor elements are fiber bragg gratings (FBG), having a mutually different characteristic frequency. In another embodiment, also distance measurement between anchors can be detected using fiber optic interferometry techniques.

It is noted that the example of the sensor assembly with three longitudinal optic fiber sections 11a, l ib, 11c is merely provided by way of illustration. In practical implementations another, typically higher , number of longitudinal optic fiber sections may be provided. By way of practical example, a sensor assembly may be provided with tens of optic strain sensor elements is respective

longitudinal optic fiber sections arranged in respective elastically deformable longitudinal carrier sections. Such a sensor assembly may for example have 30 FBG’s having a spacing between subsequent characteristic frequency in the order of 1 nm as schematically shown in FIG. 4, within a total wavelength range of for example 1530 nm to 1570 nm. Such a sensor assembly may be provided on a reel, and be unwind thereof at the location of its application, for example to be arranged in a sht provided into a road, a wall of a tunnel or a floor of a

warehouse. Once the sensor assembly is mounted therein, the slit can be filled with a filler material. Additionally, or alternatively, it is possible that the mounting portions are provided with anchor elements, for example with transversally extending ribs, so that the sensor assembly is mounted with these ribs within the filler material.

FIG. 5 schematically shows an optic sensor system 200. The optic sensor system 200 comprises an interrogator 40) and at least one sensor assemblies 1A, here a plurality of sensor assemblies 1A, IB,..., IN for example comprising a sensor assembly 1 as specified above with reference to FIG. 1, 1A, IB, 2, 2 A, 2B or as specified with reference to FIG. 3, 4. As shown in FIG. 5, the optic fibers 10A, ... , 10N of the sensor assemblies IA,. . , IN are coupled to the interrogator 40. The interrogator 40 is configured to transmit an optical interrogation signal into the optic fibers 10A,..., 10N and to receive a response optical signal that has been modulated by the optic strain-sensor elements therein. In an embodiment as shown in FIG. 1 it would suffice that the interrogator 40 is configured to transmit a single optical interrogation signal for example an optic signal at a characteristic wavelength of the single optic strain-sensor element 12a. In that case it is not even necessary that the optic strain-sensor element 12a is responsive at a specific wavelength. It is sufficient if for example the interrogator 40 can detect a change in absorption in the response signal. Even for a sensor assembly with a plurality of optic strain-sensor elements it may be sufficient if the response of these optic strain-sensor elements as such can not be distinguished from each other, provided that other information is available for disambiguation. For example, if the sensor assembly is arranged in a longitudinal direction of a one way street with low traffic density, the interrogator can detect a passing by vehicle as a sequence of response signals from the subsequent optic strain-sensor elements, and infer from the order in which the sensor are arranged and the direction of the traffic which of the optic strain-sensor elements has provided each of the response signals. In this way the location and speed of the vehicle can be determined.

To allow for a wider range of applications however it is advantageous that the optic strain-sensor elements of the longitudinal optic fiber sections have mutually different optical properties, for example as discussed with reference to FIGs. 3, 4. For this purpose for example an FBG interrogator 40 having a measurement range of 40 nanometers with a recording speed of 1000 Hz and a wavelength tracking resolution of approximately 0.1 picometers may be used.

In the application shown in FIG. 5, the sensor assemblies 1A, IB, ..., IN are arranged within a constructive part of an artifact. In this case, the artifact is a civil engineering asset, in particular a road 50, but the skilled person will appreciate that the artifact should not be limited to the embodied road. In fact, the artifact could be a side wall of a railway support, a bridge, a tunnel, the sealing of said tunnel or any other surface that could be subjected to movement. The embodied road 50 has traffic lanes 51, 52 for carrying vehicles 90. In this case the deformation of a surface of the road 50, due to the load of the wheels 92 exerted thereon is detected. In this exemplary embodiment, each of the sensor assemblies 1A, IB, ..., IN is arranged in its longitudinal direction transverse with respect to a longitudinal direction of the road 50, and sensor assemblies 1A, IB, ..., IN are arranged at a distance from each other in the longitudinal direction of the road 50. For example, within a sensor assembly, e.g. 1A, the optic strain-sensor elements may be mutually spaced at a distance of 10 to 50 cm, and subsequent sensor assemblies 1A, IB, IN, for example 1A, IB, may be arranged at a distance in the range of lm to 100m from each other. FIG. 5A schematically shows a cross-section according to VA-VA in FIG. 5, illustrating how the sensor assembly 1A is arranged within the material 55 of the road 50, below its surface 51.

Typically the sensor assemblies 1A, ..., IN are formed as a strip having its main surfaces substantially parallel to the surface of the road. The sensor assembly, mounted in its mounting portions to the road will typically flex with the road in vertical direction and not move longitudinally.

In the embodiment shown, the sensor assemblies 1A, IB, ... , IN may be responsive in a common wavelength range. E.g. the wavelength range covered by the optic strain-sensor elements in any of the sensor assemblies for example as illustrated in FIG. 4, may be the same as that of each of the other assemblies. In that case, the interrogator 40 may be provided with a multiplexer allowing it to subsequently interrogate each of the sensor assemblies. Alternatively, the sensor assemblies may be assigned mutually different wavelength ranges for

interrogation, e.g. 1485 to 1525 nm, 1530 to 1570 nm, 1575 to 1615 nm and 1620 to 1660 nm and the interrogator 40 may interrogate each of the sensor

assemblies by a sweep over the combined wavelength range, in this case form 1485 to 1660 nm.

In the embodiment shown, the interrogator 40 provides an output signal to a transmission unit 80, for a wired or wireless transmission to a monitoring center for example. Alternatively, or additionally, the interrogator 40 may be provided with storage means and/or display means to allow an operator to read out measurement data from the interrogator 40.

Depending on a required sensitivity and spatial resolution of the sensor assembly, a length of the mounting portions may be dimen ioned shorter or longer. For example if a high resolution is required the length Lm of these portions may be relatively small, e.g. 50 to 100 mm. However, if a higher sensitivity is obtained by increasing the length, for example to value in a range of 100 to 150 mm, or a range of 150 to 200 mm. The sensitivity is determined in particular by the ratio of this length Lm and the length Ld of the deformable longitudinal portions. The length of the deformable longitudinal portions may be varied, e.g. from a value in a lower range of 2 to 10 mm to a value in a higher range of 10 to 30 mm, 30 to 50 mm or even up to 200 mm. Therewith a

multiplication factor for the sensitivity can be varied for example within a range of 0.25 with Lm=50 mm and Ld=200 mm to about 100 with Lm=200 mm and Ld = 2 mm. In the embodiment shown the length Ld of the deformable sections is about 20 mm and the length Lm of the mounting sections is about 50 mm.

Therewith the ratio Lm/Ld is about 2.5, which is within a range of 1 and 10. It is not necessary that the dimensions of the deformable mounting portions and the longitudinal deformable portions is uniform of the length of the sensor assembly. Embodiments may be contemplated wherein for example mounting portions are short in a first longitudinal range for the purpose of a high resolution and longer in a second longitudinal range for the purpose of a higher sensitivity.

FIG. 6 shows an alternative embodiment of a sensor assembly. Therein a plurality of optic fibers 10A, 10B, 10C is provided that extend along mutually different longitudinal ranges 20A, 20B, 20C of the carrier 20. Each of the plurality of optic fibers, for example optic fiber 10A may have a plurality of longitudinal optic fiber sections that coincide with an associated elastically deformable longitudinal carrier section within its longitudinal range 20A. The optic fibers 10A, 10B, 10C may be provided in a bundle 15 of optic fibers that extends towards the interrogator and branch off the bundle at the start of their corresponding longitudinal range 20A of the carrier 20. The optic fibers 10A, 10B, 10C, will typically only be provided with optic sensor elements in a longitudinal range wherein it cooperates with the carrier 20, and be free from sensor elements in the remaining longitudinal range wherein it extends towards the interrogator. The optic fibers 10A, 10B, 10C may have mutually overlapping responsive frequency ranges and be coupled via a multiplexer to the interrogator. In this way, the assembly 102 can extend over a relatively substantive distance, while requiring an interrogator with only a modest wavelength range.

FIG. 7, 7 A, 7B, 7C show an example of another fastening element 25 for use in the sensor assembly. Therein FIG. 7 A, 7B are a first and a second cross- section according to VHA-VILA and VIIB-VIIB in FIG. 7 respectively. FIG. 7C shows the fastening element mounted on a carrier in the same cross-section as FIG. 7 A.

The embodiment of the fastening element 25 as shown therein is formed of a metal strip, e.g. from stainless steel, and has a v-shaped central portion 25C, to hold an optic fiber 10 and laterally extending into planar peripheral portions 25P for mounting the fastening element to the carrier 20. To facilitate said mounting, the peripheral portions 25P of the fastening element are provided with a plurality of first openings 252. In addition, second openings 254 are provided at both sides of the central portion 25P that enable access of a clipping element 258 to fix the optic fiber 10 within the space defined between the fastening element 25 and the carrier. The fastening element 25 is further provided with a centrally arranged top opening 256, that facilitates filling the remainder 250 of the defined space with a protective fluid, e.g. a gel or the adhesive.

The first openings 252, the second openings 254 and the top openings 256 may be formed for example by mechanical drilling, or laser drilling. In an embodiment openings in particular the first openings may be formed chemically, e.g. by an etching process, to achieve an optimal mechanical integrity.

An inner surface of the central portion 25C of the fastening element 25 is provided with a first and a second row 2511, 2512 of blunt protrusions 251 at mutually opposite side of a length axis of the fastening element. The protrusions of the second row 2512 are staggered with respect to the first row 2511. As shown in FIG. 7 A, the optic fiber is pressed against these protrusions, for example by clipping element 258, so that the protrusions longitudinally fix the optic fiber 10 within the fastening element 25.

FIG. 7C, in the same cross-section as FIG. 7 A, shows the fastening element 25 mounted by mounting elements 257 on a carrier 20.

FIG. 8A, 8B show another embodiment. Therein FIG. 8A shows a longitudinal portion of a fiber 10 with a coating 14, for example a polymer coating, e.g. of polyimide which is clamped between parts 25a, 25b of a fastening element. FIG. 8B shows a cross-section according to VIIIB-VIIIB in FIG. 8A. As can be seen in FIGs 8A, 8B, the parts 25a, 25b define an opening 25o with an diameter that is smaller than an outer diameter of the coating 14, but at least as large as a diameter of the fiber 10. Therewith the mechanical parts 25a, 25b tightly grip the fiber tightly without the need for the adhesive. An adhesive can still be added as additional adhesion.

FIG. 9 shows again another embodiment. Therein the fiber 10 is clamped between a first and a second fastening part 25c, 25d, of which at least one is pivotably arranged with pivot axis 25e. The at least pivotable fastening part 25d grips the fiber 10 at contact point 25f. Therewith, upon exerting a pulling force F upon the fiber 10 in a longitudinal direction from the contact point 25f, towards the pivot axis 25e, the fiber is locked into position as the pulling force F on the fiber result in a mechanical squeezing or increased grip on the fiber such that any movement of the fiber in the mechanism, i.e. slip, is prevented.