EP3625550A1 - Optical sensor, process for making such sensor and evaluation system comprising at least one of such sensors - Google Patents

Optical sensor, process for making such sensor and evaluation system comprising at least one of such sensors

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Publication number
EP3625550A1
EP3625550A1 EP18735425.3A EP18735425A EP3625550A1 EP 3625550 A1 EP3625550 A1 EP 3625550A1 EP 18735425 A EP18735425 A EP 18735425A EP 3625550 A1 EP3625550 A1 EP 3625550A1
Authority
EP
European Patent Office
Prior art keywords
optical fiber
section
optical
terminal
optically
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP18735425.3A
Other languages
German (de)
French (fr)
Inventor
Milena Salvo
Marco Sangermano
Bellot Cristian MARRO
Massimo Olivero
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Politecnico di Torino
Original Assignee
Politecnico di Torino
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Politecnico di Torino filed Critical Politecnico di Torino
Publication of EP3625550A1 publication Critical patent/EP3625550A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G01N2021/7706—Reagent provision
    • G01N2021/7736—Reagent provision exposed, cladding free
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N2021/8472—Investigation of composite materials

Definitions

  • the present invention refers to an optical sensor, in particular for evaluating the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments.
  • the present invention further refers to a process for making such optical sensor.
  • the present invention further refers to an evaluation system of the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments comprising at least one of such optical sensors .
  • composite and polymeric materials represent an important class of materials for multiple industrial applications, since they are capable of providing a high degree of protection against the corrosion from chemical agents.
  • deterioration of composite materials is deemed a source of risks (for example, underwater structures and equipment and in the petrol -chemical industry)
  • maintenance is difficult, the cost of repair interventions is very high and the safety of operations is linked to the high long-term stability of a few millimeters of polymer.
  • the diffusion of seawater, humidity or other chemical species in polymers and in composites thereof is therefore an important technologic problem.
  • An active and constant monitoring of these materials however allows highly timely foreseeing their deterioration and performing efficient and economic interventions.
  • the monitoring system must however have some specific features, such as remote monitoring, safety and minimum invasiveness .
  • the continuous monitoring of humidity and chemical compounds in the polymeric materials and polymeric composites is further essential for evaluating their long-term behavior, in particular when they are use in hostile environments.
  • sensors into polymeric materials and composites introduces the concept of "smart composite” , capable of providing indications about its properties and a possible permeation of corrosive agents, thereby allowing an accurate evaluation of their ageing.
  • the optical fibers are a valid tool for remote monitoring applications of polymeric materials and composites and for making smart composites. Due to some peculiar features, such as immunity to electromagnetic interferences intrinsic fire-proof safety (this latter one deriving from the fact that the optical fiber does not transport electric signals and therefore there is no chance of triggering sparks) . Moreover, the optical fibers can be easily embedded into composite materials without changing their mechanical performances.
  • FBG Fiber Bragg Gratings
  • - US8348611 discloses a sensor aimed for monitoring the mechanical properties of a manufactured product
  • - US5144690 discloses a sensor in which the fiber has a double core and monitoring is based on a signal coupling between the two cores
  • JP2000321169 discloses a method for monitoring the deterioration of mechanical properties
  • the prior art further proposes optical fiber-based optical sensors of the so-called "D-shaped" type, in which the related operating portion is placed in an intermediate position of such fiber and only a lateral surface portion of the fiber core is exposed to external contacts .
  • object of the present invention is solving the above prior art problems, by providing an optical sensor made of low-cost optical fiber to detect, in a continuous and non-destructive way, the diffusion of water or corrosive chemical species through polymeric materials and polymeric composites, in order to monitor and foresee the degrading of their chemical -structural characteristics .
  • Another object of the present invention is providing an optical sensor whose operation is based on a measure of spectral attenuation of the fiber.
  • an object of the present invention is providing an optical sensor comprising a single-core, silica-based fiber.
  • Another object of the present invention is providing an optical sensor not containing potentially toxic elements .
  • an object of the present invention is providing a process for making an optical sensor starting from optical fibers made of silica easily available as commercial products used for telecommunication applications .
  • Another object of the present invention is providing an optical sensor which allows monitoring the ageing and/or the deterioration of a polymer or of a composite material in an initial phase and not invasively.
  • an object of the present invention is providing an optical sensor which can operate in aggressive environments and which can be remotely queried without needing an electric supply.
  • Another object of the present invention is providing a system which, comprising at least one optical sensor according to the invention, allows the evaluation of the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments.
  • Figure 1 shows a schematic perspective view of a preferred embodiment of the optical sensor according to the present invention
  • Figure 2 shows a schematic perspective view of the optical sensor of Figure 1 compared with a reference sensor
  • Figure 3 shows a schematic block diagram of a preferred embodiment of the system according to the present invention.
  • Figure 4 shows a schematic block diagram of the system according to the present invention of Figure 3 in an example of its application environment.
  • the optical sensor according to the present invention is aimed, in particular, to evaluating the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments .
  • the optical sensor according to the present invention is an Evanescent Wave Optical Sensor, "EWOS” , since it is based on the principle of the evanescent wave according to which part of the light guided in a sensitive section made of optical fiber core is diffused in the material surrounding the section of optical fiber.
  • the diffused optical signal is changed if chemical -physical modifications of the material occur.
  • the diffusion of water or other corrosive substances is detected by recording the spectral attenuation in the sensitive section of optical fiber.
  • an optical sensor 1 comprises at least one terminal operating portion 3 aimed to be preferably integrated or incorporated into at least one matrix 2, preferably in a solid shape, composed of one or more polymeric materials and/or composites thereof, to optically guide at least one incoming optical signal Lj and at least one outgoing optical signal L 0 .
  • the operating portion is placed in a terminal position and non in an intermediate position as, instead, in the prior art "D-shaped" optical sensors.
  • such terminal operating portion 3 comprises :
  • the optically reflecting terminal section 7 comprises at least one layer of optically reflecting substance, such layer of optically reflecting substance being made through chemical deposition of silver particles through Tollen reagent; - at least one protecting covering section 9 of the optical fiber.
  • the terminal operating portion 3 can further comprise at least one section of non-worked optical fiber 11 interposed between the sensitive section made of optical fiber core 5 and the protecting covering section 9.
  • the optically reflecting terminal section 7 is composed of the terminal portion of the sensitive section made of optical fiber core 5 covered by at least one layer of optically reflecting substance.
  • such optically reflecting substance is chosen among noble metals such as, for example, silver and gold.
  • the protecting covering section 9 of the optical fiber is optically opaque and composed of at least one polymeric sheath or protective coating.
  • the terminal operating portion 3 can be integrated, incorporated or immersed into the matrix 2 during its production and in particular before the step of curing the one or more polymeric materials which compose it.
  • the optical sensor according to the present invention can be made with selective and/or fluorescent coatings in order to make it sensitive to particular chemical species .
  • optical sensor 1 Through the optical sensor 1 according to the present invention as previously described, it is then possible to detect the diffusion of humidity or chemical species in the polymeric or composite matrix 2 by observing the modifications of the spectral attenuation of the outgoing optical signal L 0 with respect to the incoming optical signal L x once having crossed the sensitive section made of optical fiber core 5.
  • Figure 2 schematically shows an empiric experience performed by comparing an optical sensor 1 according to the present invention with a reference sensor 100, made as the optical sensor 1 but in which the sensitive section made of optical fiber core has been afterwards coated with at least one layer of copper 101 to cancel its sensitivity, and then inserted into the same matrix 2 to verify that possible variations of the spectral attenuation cannot be ascribed to a real diffusion of water or chemical species, but are rather imputable to fluctuations in the optical source or in the optical measuring system.
  • the functionality of the optical sensor 1 according to the present invention can further be extended to specific chemical substances, such as for example hydrogen sulfide (3 ⁇ 4S) , hydrochloric acid (HCl) , hydrocarbons and other chemical substances: for such purpose, the sensitive section made of optical fiber core 5 could comprise at least one nanometer coating layer of at least one metal such as, for example, aluminum (Al) or zinc (Zn) or with organic and inorganic substances for selectively producing a sensitive coating.
  • specific chemical substances such as for example hydrogen sulfide (3 ⁇ 4S) , hydrochloric acid (HCl) , hydrocarbons and other chemical substances: for such purpose, the sensitive section made of optical fiber core 5 could comprise at least one nanometer coating layer of at least one metal such as, for example, aluminum (Al) or zinc (Zn) or with organic and inorganic substances for selectively producing a sensitive coating.
  • the sensitive section made of optical fiber core 5 could also comprise at least one nanometer layer containing carbon nanotubes .
  • the present invention further deals with a process for making an optical sensor 1 as previously described.
  • an optical sensor 1 preferably starting from a commercial optical fiber for telecommunications to make it sensible to variations of the material of the matrix 2 in which it is embedded, incorporated or immersed.
  • the process according to the present invention therefore comprises the following steps:
  • optical fiber can be a low-cost, commercial silica-based multi-mode optical fiber for telecommunications ;
  • such step provides, for example, for mechanically or chemically removing at least one portion of the polymeric coating from a terminal of such optical fiber;
  • such step can obviously be performed with different techniques such as, for example, mechanical lapping, laser ablation or chemical attack with hydrofluoric acid (HF) ;
  • the process according to the present invention comprises the step of covering at least partially the sensitive section made of optical fiber core with at least one nanometer layer containing carbon nanotubes and/or with at least one nanometer coating layer of at least one metal such as, for example, aluminum (Al) or zinc (Zn) , for example through Physical Vapor Deposition, PVD, techniques and/or a coating layer with organic and inorganic substances;
  • such step can provide for covering the terminal portion of the sensitive section made of optical fiber core with at least one layer of optically reflecting substance, such optically reflecting substance being preferably chosen among noble metals such as, for example, silver and gold.
  • such step can obviously be performed with different manufacturing techniques or processes such as, for example, plasma-assisted physical deposition, chemical deposition through Tollen reagent or painting with a reflecting solution containing silver particles.
  • optical sensor made as described above can then be embedded, incorporated or immersed in the polymeric matrix when this latter one is made, and in particular before the step of curing the one or more polymeric materials composing it.
  • the optical sensor according to the present invention made through the above described process, provides for a potential reduction of costs by a factor 10 with respect to currently marketed optical fiber sensors.
  • being relatively simple to make with rather inexpensive laboratory equipment makes it very interesting for applications on industrial scale.
  • optical sensor according to the present invention can be several such as, for example, in the oil or gas industries and in applications in which the polymeric materials or composites are used in hostile environments (for example, underwater applications, aerospace and renewable energies) .
  • the optical sensor according to the present invention could also be used for developing accelerated ageing tests of polymeric materials and composites.
  • a key aspect of the present invention is making sensors starting from relatively inexpensive materials, such as the commercial optical fiber, which brings about an estimated cost of £0.60/sensor in terms of materials. To this, it is possible to add the production process, which could be partially automatized for large scale productions.
  • the present invention also deals with an evaluation system of the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments. With particular reference to Figures 3 and 4, it is possible to note that the system 200 according to the present invention comprises:
  • At least one coupling device 205 of optical fibers 207 which operates, preferably, in the near infrared region of the spectrum around (but not limited to) 1550 nm, such coupling device 205 being operatively connected to the wide-band light source 201, to the spectrometer device 203 and to the optical switch 209;
  • optical sensors 1 - one or more optical sensors 1 according to the present invention, at least one of which being operatively connected to the optical switch 209 and having at least the respective terminal operating portion (3) integrated or incorporated in a polymeric matrix 2.
  • At least one of the optical sensors 1 according to the present invention comprises a respective terminal connector, mobile or adapted to be installed in field.
  • the coupling device 205 takes care of sending at least one optical signal generated by the wide-band light source 201 to the optical switch 209 which, in turn, takes care of sending it to each optical sensor 1 present in the system 200 according to the present invention as incoming optical signal.
  • the optical switch 209 receives from each optical sensor 1 the related outgoing optical signal and takes care of sending them to the optical switch 209, which transmits them to the spectrometer device 203 for their necessary processing .
  • system 200 can also be used when the polymeric matrix 2 incorporating or embedding one or more sensors 1 is immersed in at least one chemically aggressive liquid environment 211, comprising one or more chemical species to be monitored, contained in a suitable tank (becher) 213.

Abstract

An optical sensor (1) is described, comprising: an operating portion (3) aimed to be integrated, incorporated or immersed in at least one matrix (2) composed of one or more polymeric materials and/or composites thereof to optically guide an incoming optical signal (LI) and an outgoing optical signal (LO), the operating portion (3) comprising a portion (4) for entering the incoming optical signal (LI) and/or for exiting the outgoing optical signal (LO); a sensitive section made of optical fiber core (5) externally placed in direct contact with the matrix (2); an optically reflecting terminal section (7) placed in direct contact with the matrix (2), the terminal section (7) being adapted to optically reflect the incoming optical signal (LI) to transform it into the outgoing optical signal (LO); and a protecting covering section (9) of the optical fiber. A process for making of such optical sensor (1) and an evaluation system comprising at least one of such optical sensors (1) are also described.

Description

OPTICAL SENSOR, PROCESS FOR MAKING SUCH SENSOR AND
EVALUATION SYSTEM COMPRISING AT LEAST ONE OF SUCH SENSORS
The present invention refers to an optical sensor, in particular for evaluating the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments. The present invention further refers to a process for making such optical sensor. The present invention further refers to an evaluation system of the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments comprising at least one of such optical sensors .
As known, composite and polymeric materials represent an important class of materials for multiple industrial applications, since they are capable of providing a high degree of protection against the corrosion from chemical agents. In specific environments of use, wherein the deterioration of composite materials is deemed a source of risks (for example, underwater structures and equipment and in the petrol -chemical industry) , maintenance is difficult, the cost of repair interventions is very high and the safety of operations is linked to the high long-term stability of a few millimeters of polymer.
The diffusion of seawater, humidity or other chemical species in polymers and in composites thereof is therefore an important technologic problem. An active and constant monitoring of these materials however allows highly timely foreseeing their deterioration and performing efficient and economic interventions. The monitoring system must however have some specific features, such as remote monitoring, safety and minimum invasiveness .
The continuous monitoring of humidity and chemical compounds in the polymeric materials and polymeric composites is further essential for evaluating their long-term behavior, in particular when they are use in hostile environments.
The insertion of sensors into polymeric materials and composites introduces the concept of "smart composite" , capable of providing indications about its properties and a possible permeation of corrosive agents, thereby allowing an accurate evaluation of their ageing.
In such context, the optical fibers are a valid tool for remote monitoring applications of polymeric materials and composites and for making smart composites. Due to some peculiar features, such as immunity to electromagnetic interferences intrinsic fire-proof safety (this latter one deriving from the fact that the optical fiber does not transport electric signals and therefore there is no chance of triggering sparks) . Moreover, the optical fibers can be easily embedded into composite materials without changing their mechanical performances.
The currently most used optical fiber technology for monitoring in composite materials is the one of Fiber Bragg Gratings, "FBG" . FBGs are therefore a class of sensors with features of sturdiness and easy installation and use, above all due to the fact that the sensible part of the fiber is coated with a polymer which reduces the chances of mechanically damaging it. In any case, these sensors are costly, as well as the related optical - electronic monitoring system.
Alternative technologies to FBG are also known, used for the chemical and structural monitoring, among which:
- US4634856 discloses a sensor aimed for monitoring ground humidity, made by placing a reflecting material, sensible to humidity, at the end of an optical fiber, whose monitoring principle is based on the measure of the variation of the reflection coefficient at its terminal;
- US8348611 discloses a sensor aimed for monitoring the mechanical properties of a manufactured product; - US5144690 discloses a sensor in which the fiber has a double core and monitoring is based on a signal coupling between the two cores;
- JP2000321169 discloses a method for monitoring the deterioration of mechanical properties;
- US4827121 discloses an optical fiber sensor based on chalcogenides which are potentially toxic elements.
The prior art further proposes optical fiber-based optical sensors of the so-called "D-shaped" type, in which the related operating portion is placed in an intermediate position of such fiber and only a lateral surface portion of the fiber core is exposed to external contacts .
Therefore, object of the present invention is solving the above prior art problems, by providing an optical sensor made of low-cost optical fiber to detect, in a continuous and non-destructive way, the diffusion of water or corrosive chemical species through polymeric materials and polymeric composites, in order to monitor and foresee the degrading of their chemical -structural characteristics .
Another object of the present invention is providing an optical sensor whose operation is based on a measure of spectral attenuation of the fiber.
Moreover, an object of the present invention is providing an optical sensor comprising a single-core, silica-based fiber.
Another object of the present invention is providing an optical sensor not containing potentially toxic elements .
Moreover, an object of the present invention is providing a process for making an optical sensor starting from optical fibers made of silica easily available as commercial products used for telecommunication applications .
Another object of the present invention is providing an optical sensor which allows monitoring the ageing and/or the deterioration of a polymer or of a composite material in an initial phase and not invasively.
Moreover, an object of the present invention is providing an optical sensor which can operate in aggressive environments and which can be remotely queried without needing an electric supply.
Another object of the present invention is providing a system which, comprising at least one optical sensor according to the invention, allows the evaluation of the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments.
The above and other objects and advantages of the invention, as will appear from the following description, are obtained with an optical sensor, a process and a system as claimed in the respective independent claims. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims .
It is intended that all enclosed claims are an integral part of the present description.
It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention, as appears from the enclosed claims.
The present invention will be better described by some preferred embodiments thereof, provided as a non- limiting example, with reference to the enclosed drawings, in which:
Figure 1 shows a schematic perspective view of a preferred embodiment of the optical sensor according to the present invention;
Figure 2 shows a schematic perspective view of the optical sensor of Figure 1 compared with a reference sensor;
Figure 3 shows a schematic block diagram of a preferred embodiment of the system according to the present invention; and
Figure 4 shows a schematic block diagram of the system according to the present invention of Figure 3 in an example of its application environment.
As stated, the optical sensor according to the present invention is aimed, in particular, to evaluating the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments .
In particular, the optical sensor according to the present invention is an Evanescent Wave Optical Sensor, "EWOS" , since it is based on the principle of the evanescent wave according to which part of the light guided in a sensitive section made of optical fiber core is diffused in the material surrounding the section of optical fiber. The diffused optical signal is changed if chemical -physical modifications of the material occur. The diffusion of water or other corrosive substances is detected by recording the spectral attenuation in the sensitive section of optical fiber.
Therefore, with particular reference to Figures 1 and 2, it is possible to note that an optical sensor 1 according to the present invention comprises at least one terminal operating portion 3 aimed to be preferably integrated or incorporated into at least one matrix 2, preferably in a solid shape, composed of one or more polymeric materials and/or composites thereof, to optically guide at least one incoming optical signal Lj and at least one outgoing optical signal L0. It can be noted how, in the optical sensor 1 according to the present invention, the operating portion is placed in a terminal position and non in an intermediate position as, instead, in the prior art "D-shaped" optical sensors.
Advantageously, such terminal operating portion 3 comprises :
- a portion 4 for entering the incoming optical signal Lj and/or exiting the outgoing optical signal L0;
- a sensitive section made of silica-based multi-mode optical fiber core 5 externally placed in direct contact with such matrix 2: in particular, as it is possible to clearly note at least in Figures 1 and 2, contrary to what occurs in prior art "D-shaped" sensors, in the optical sensor 1 according to the present invention the direct contact is obtained on the whole external surface axially symmetrical with respect to a longitudinal axis of symmetry R-R of the sensitive section made of optical fiber core (5) ;
- an optically reflecting terminal section 7 placed in direct contact with such matrix 2, the terminal section 7 being adapted to optically reflect the incoming optical signal Lj to transform it into the outgoing optical signal L0. Advantageously, the optically reflecting terminal section 7 comprises at least one layer of optically reflecting substance, such layer of optically reflecting substance being made through chemical deposition of silver particles through Tollen reagent; - at least one protecting covering section 9 of the optical fiber.
Possibly, the terminal operating portion 3 can further comprise at least one section of non-worked optical fiber 11 interposed between the sensitive section made of optical fiber core 5 and the protecting covering section 9.
Preferably, the optically reflecting terminal section 7 is composed of the terminal portion of the sensitive section made of optical fiber core 5 covered by at least one layer of optically reflecting substance.
Preferably, such optically reflecting substance is chosen among noble metals such as, for example, silver and gold.
Preferably, the protecting covering section 9 of the optical fiber is optically opaque and composed of at least one polymeric sheath or protective coating.
The terminal operating portion 3 can be integrated, incorporated or immersed into the matrix 2 during its production and in particular before the step of curing the one or more polymeric materials which compose it.
Moreover, differently from FBG sensors, which are essentially sensitive to temperature and mechanical deformations, the optical sensor according to the present invention can be made with selective and/or fluorescent coatings in order to make it sensitive to particular chemical species .
Through the optical sensor 1 according to the present invention as previously described, it is then possible to detect the diffusion of humidity or chemical species in the polymeric or composite matrix 2 by observing the modifications of the spectral attenuation of the outgoing optical signal L0 with respect to the incoming optical signal Lx once having crossed the sensitive section made of optical fiber core 5. For such purpose, Figure 2 schematically shows an empiric experience performed by comparing an optical sensor 1 according to the present invention with a reference sensor 100, made as the optical sensor 1 but in which the sensitive section made of optical fiber core has been afterwards coated with at least one layer of copper 101 to cancel its sensitivity, and then inserted into the same matrix 2 to verify that possible variations of the spectral attenuation cannot be ascribed to a real diffusion of water or chemical species, but are rather imputable to fluctuations in the optical source or in the optical measuring system.
It is also possible to provide that the functionality of the optical sensor 1 according to the present invention can further be extended to specific chemical substances, such as for example hydrogen sulfide (¾S) , hydrochloric acid (HCl) , hydrocarbons and other chemical substances: for such purpose, the sensitive section made of optical fiber core 5 could comprise at least one nanometer coating layer of at least one metal such as, for example, aluminum (Al) or zinc (Zn) or with organic and inorganic substances for selectively producing a sensitive coating.
The sensitive section made of optical fiber core 5 could also comprise at least one nanometer layer containing carbon nanotubes .
The present invention further deals with a process for making an optical sensor 1 as previously described.
In general, as can be seen below in more detail, through the process according to the present invention it is possible to make an optical sensor 1 according to the present invention preferably starting from a commercial optical fiber for telecommunications to make it sensible to variations of the material of the matrix 2 in which it is embedded, incorporated or immersed.
The process according to the present invention therefore comprises the following steps:
- providing at least one section of optical fiber: advantageously, such optical fiber can be a low-cost, commercial silica-based multi-mode optical fiber for telecommunications ;
- removing at least one portion of the external protecting covering layer of the optical fiber to uncover at least one section of non-worked optical fiber: such step provides, for example, for mechanically or chemically removing at least one portion of the polymeric coating from a terminal of such optical fiber;
- reducing the circular section of the section of non- worked optical fiber to expose the sensitive section of core of the optical fiber: such step can obviously be performed with different techniques such as, for example, mechanical lapping, laser ablation or chemical attack with hydrofluoric acid (HF) ;
- working a terminal section of the sensitive section of core of the optical fiber to obtain a surface with reduced roughness: such step can be performed, for example, through etching with diamond-coated blade; it is also possible to provide that the process according to the present invention comprises the step of covering at least partially the sensitive section made of optical fiber core with at least one nanometer layer containing carbon nanotubes and/or with at least one nanometer coating layer of at least one metal such as, for example, aluminum (Al) or zinc (Zn) , for example through Physical Vapor Deposition, PVD, techniques and/or a coating layer with organic and inorganic substances;
- making an optically reflecting terminal section in a terminal portion of the sensitive section made of optical fiber core: in particular, such step can provide for covering the terminal portion of the sensitive section made of optical fiber core with at least one layer of optically reflecting substance, such optically reflecting substance being preferably chosen among noble metals such as, for example, silver and gold. Also in this case, such step can obviously be performed with different manufacturing techniques or processes such as, for example, plasma-assisted physical deposition, chemical deposition through Tollen reagent or painting with a reflecting solution containing silver particles.
The optical sensor made as described above can then be embedded, incorporated or immersed in the polymeric matrix when this latter one is made, and in particular before the step of curing the one or more polymeric materials composing it. In particular, the optical sensor according to the present invention, made through the above described process, provides for a potential reduction of costs by a factor 10 with respect to currently marketed optical fiber sensors. Moreover, being relatively simple to make with rather inexpensive laboratory equipment, makes it very interesting for applications on industrial scale.
In fact, the possible uses of the optical sensor according to the present invention, as well as of the process for making it, can be several such as, for example, in the oil or gas industries and in applications in which the polymeric materials or composites are used in hostile environments (for example, underwater applications, aerospace and renewable energies) .
Moreover, given its easy fabrication and use, the optical sensor according to the present invention could also be used for developing accelerated ageing tests of polymeric materials and composites.
Finally, a key aspect of the present invention is making sensors starting from relatively inexpensive materials, such as the commercial optical fiber, which brings about an estimated cost of £0.60/sensor in terms of materials. To this, it is possible to add the production process, which could be partially automatized for large scale productions. The present invention also deals with an evaluation system of the diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments. With particular reference to Figures 3 and 4, it is possible to note that the system 200 according to the present invention comprises:
- at least one wide-band light source 201;
- at least one spectrometer device 203;
- at least one optical switch 209;
- at least one coupling device 205 of optical fibers 207 which operates, preferably, in the near infrared region of the spectrum around (but not limited to) 1550 nm, such coupling device 205 being operatively connected to the wide-band light source 201, to the spectrometer device 203 and to the optical switch 209;
- one or more optical sensors 1 according to the present invention, at least one of which being operatively connected to the optical switch 209 and having at least the respective terminal operating portion (3) integrated or incorporated in a polymeric matrix 2.
Advantageously, in order to avoid costly "splicing" procedures, it is possible to provide that at least one of the optical sensors 1 according to the present invention comprises a respective terminal connector, mobile or adapted to be installed in field. In particular, as it is possible to clearly note in Figures 3 and 4, the coupling device 205 takes care of sending at least one optical signal generated by the wide-band light source 201 to the optical switch 209 which, in turn, takes care of sending it to each optical sensor 1 present in the system 200 according to the present invention as incoming optical signal. In turn, the optical switch 209 receives from each optical sensor 1 the related outgoing optical signal and takes care of sending them to the optical switch 209, which transmits them to the spectrometer device 203 for their necessary processing .
For example, with particular reference to Figure 4, it is possible to note how the system 200 according to the present invention can also be used when the polymeric matrix 2 incorporating or embedding one or more sensors 1 is immersed in at least one chemically aggressive liquid environment 211, comprising one or more chemical species to be monitored, contained in a suitable tank (becher) 213.

Claims

1. Optical sensor (1) aimed to evaluate a diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments comprising at least one terminal operating portion (3) aimed to be integrated or incorporated into at least one matrix (2) composed of one or more polymeric materials and/or composites thereof to optically guide at least one incoming optical signal (Lx) and at least one outgoing optical signal (L0) , characterized in that said terminal operating portion (3) comprises:
- a portion (4) for entering said incoming optical signal (Lj) and/or exiting said outgoing optical signal
( Lo ) ;
- a sensitive section made of silica-based multi-mode optical fiber core (5) externally placed in direct contact with said matrix (2) , said direct contact being obtained on a whole axial symmetrical external surface of said sensitive section made of optical fiber core (5) ;
- an optically reflecting terminal section (7) placed in direct contact with said matrix (2) , said terminal section (7) being adapted to optically reflect said incoming optical signal (Lj) to transform it into said outgoing optical signal (L0) , said optically reflecting terminal section (7) comprising at least one layer of optically reflecting substance, said layer of optically reflecting substance being made through chemical deposition of silver particles through Tollen reagent; - at least one protecting covering section (9) of said optical fiber.
2. Optical sensor (1) according to the previous claim, characterized in that said terminal operating portion (3) comprises at least one section of non-worked optical fiber (11) interposed between said sensitive section made of optical fiber core (5) and said protecting covering section (9) .
3. Optical sensor (1) according to any one of the previous claims, characterized in that said optically reflecting terminal section (7) is composed of a terminal portion of said sensitive section made of optical fiber core (5) covered by at least one layer of optically reflecting substance.
4. Optical sensor (1) according to any one of the previous claims, characterized in that said protecting covering section (9) is optically opaque and composed of at least one polymeric sheath or protective coating.
5. Optical sensor (1) according to any one of the previous claims, characterized in that said sensitive section made of optical fiber core (5) comprises at least one nanometer layer containing carbon nanotubes and/or at least one nanometer coating layer of at least one metal and/or at least one coating layer with organic or inorganic substances.
6. Process for making an optical sensor (1) according to any one of claims 1 to 5, characterized in that it comprises the steps of:
- providing at least one section of optical fiber;
- removing at least one portion of an external protecting covering layer of said optical fiber to uncover at least one section of non-worked optical fiber;
- reducing a circular section of said section of non- worked optical fiber to expose a sensitive section of core of said optical fiber;
- working a terminal section of said sensitive section of core of said optical fiber to obtain a surface with reduced roughness;
- making an optically reflecting terminal section in a terminal portion of said sensitive section made of optical fiber core.
7. Process according to the previous claim, characterized in that said optical fiber is a commercial multi-mode optical fiber for silica-based telecommunications .
8. Process according to claim 6, characterized in that said step of removing at least one portion of an external protecting covering layer of said optical fiber provides for mechanically or chemically removing at least one portion of a polymeric coating from a terminal of said optical fiber.
9. Process according to claim 6, characterized in that said step of reducing a circular section of said section of non-worked optical fiber is performed through mechanical lapping, laser ablation or chemical attack with hydrofluoric acid (HF) .
10. Process according to claim 6, characterized in that said step of working said terminal section of said sensitive section of core of said optical fiber is performed through etching with diamond-coated blade.
11. Process according to claim 6, characterized in that said step of making said optically reflecting terminal section provides for recovering a terminal portion of said sensitive section made of optical fiber core with at least one layer of optically reflecting substance.
12. Process according to the previous claim, characterized in that said optically reflecting substance is chosen among noble metals such as, for example, silver and gold.
13. Process according to claim 11 or 12, characterized in that said step of making said optically reflecting terminal section is performed through plasma-assisted physical deposition, chemical deposition through Tollen reagent or painting with reflecting solution containing silver particles.
14. System (200) for evaluating a diffusion of chemical species inside polymeric materials and composites thereof in aggressive environments comprising:
- at least one wide-band light source (201) ;
- at least one spectrometer device (203);
- at least one optical switch (209) ;
- at least one coupling device (205) of optical fibers (207) , said coupling device (205) being operatively connected to said wide-band light source (201) , to said spectrometer device (203) and to said optical switch (209) ;
- one or more optical sensors (1) according to any one of claims 1 to 5, at least one of said optical sensors (1) being operatively connected to said optical switch (209) and having at least its respective terminal operating portion (3) integrated or incorporated in said polymeric matrix (2) .
EP18735425.3A 2017-05-17 2018-04-24 Optical sensor, process for making such sensor and evaluation system comprising at least one of such sensors Withdrawn EP3625550A1 (en)

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IT102017000053268A IT201700053268A1 (en) 2017-05-17 2017-05-17 OPTICAL SENSOR AND PROCEDURE FOR REALIZING SUCH A SENSOR.
PCT/IT2018/000059 WO2018211539A1 (en) 2017-05-17 2018-04-24 Optical sensor, process for making such sensor and evaluation system comprising at least one of such sensors

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