WO2012140179A1 - Hydrophone tout optique insensible a la temperature et a la pression statique - Google Patents
Hydrophone tout optique insensible a la temperature et a la pression statique Download PDFInfo
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- WO2012140179A1 WO2012140179A1 PCT/EP2012/056740 EP2012056740W WO2012140179A1 WO 2012140179 A1 WO2012140179 A1 WO 2012140179A1 EP 2012056740 W EP2012056740 W EP 2012056740W WO 2012140179 A1 WO2012140179 A1 WO 2012140179A1
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- Prior art keywords
- cavity
- hydrophone
- frequency
- optical fiber
- plugs
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
- G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
- G01V1/186—Hydrophones
- G01V1/188—Hydrophones with pressure compensating means
Definitions
- the invention relates to the general field of acoustic transducers underwater or hydrophone. It relates more particularly optical hydrophones based on optical fiber laser.
- optical fibers With regard to the production of underwater acoustic transducers, the use of optical fibers is a known solution which has recognized advantages among which we find in the first place the small bulk of a hydrophone made using such a technology, as well as that the possibility of making a hydrophone assembly from the same fiber by multiplexing on the same fiber the pressure variation information detected by the various hydrophones forming this assembly, each hydrophone being associated with a given wavelength.
- hydrophones optical fiber coil interferometers optical fiber laser cavity hydrophones.
- the measured optical quantity is the cumulative optical phase variation over the total length of an optical fiber (typically 20 to 100m), wound on a conformal mandrel, configured so that its diameter varies under the effect of the acoustic pressure to be measured which induces a variation dynamic length of the optical fiber wound therein, an air chuck for example.
- the dynamic variation of the length of the optical fiber results in a variation of the phase of the signal carried by the fiber.
- the relative variation of the phase of the signal is equal to about 0.78 times the relative strain of the length of the fiber.
- This phase variation can be measured with the necessary precision by placing the hydrophone in the arm of an interfera m be unbalanced optical fiber type Michelson for example.
- This type of hydrophone has the main disadvantage of not being sufficiently miniaturized. Indeed, in order to transmit the information relating to the pressure measurements made by each hydrophone constituting a network, different interrogation and multiplexing techniques well known to those skilled in the art can be implemented. Their purpose is to connect, by means of a single optical fiber, all the associated hydrophones within the same network to the system responsible for exploiting these measurements.
- the multiplexing on a single optical fiber of a large number of hydrophones requires that insertion losses thereof along the optical fiber be low, typically less than 1 dB. This implies that, in each hydrophone, the optical fiber is wound on a mandrel having a minimum diameter, so as to minimize losses due to the curvature of the fiber.
- microstructured optical fibers with a very small allowable curvature radius fiber for FTTH applications
- good sensitivity and insertion loss performance is difficult to achieve with a substantially lower winding diameter of 15 or more. 20mm.
- each hydrophone constituting the network measures a simple pressure value
- This method has the disadvantage of having to add additional sensors and limit the range of use of the immersion hydrophone (limited dynamic sensor)
- Fiber-optic laser cavity hydrophones make it possible to produce hydrophones with high sensitivity, ie capable of listening to a low level of sea noise. Their use makes it possible to implement coherent optical processing techniques for accurately measure the frequency variations of the optical signal conveyed by the fiber. Such variation is here consecutive to the reception of an acoustic signal by a Bragg grating inscribed in an active optical fiber, an Erbium or Erbium / Yttrium doped optical fiber for an emission around 1.5 ⁇ for example.
- a Bragg grating includes, near its center, a phase jump substantially equal to ⁇ so as to constitute a single-frequency laser cavity, the optical pumping of the cavity being carried out via a diode (diode pumping) which can be remote-transported via a standard optical fiber.
- the emission frequency of the laser cavity thus formed depends on the pitch of the Bragg grating and the phase of the central phase shift. As a result, if the laser cavity is uniformly deformed, the emission frequency of the laser will vary in the same proportions with a coefficient of 0.78 related to the elasto-optical properties of the silica constituting the fiber.
- the axial deformation induced by an acoustic pressure applied directly to the external surface of the laser cavity is not sufficient to obtain the compatible hydrophonic sensitivity of a level lower than the sea noise force 0, taking into account the DSP (density spectral power) of the intrinsic noise of the laser (of the order of 20 Hz / VHz to
- the hydrophone retains an intrinsic sensitivity to the temperature at least equal to that of the laser cavity and a sensitivity to the static pressure, unless associated with a large hydrostatic filter.
- the invention relates to a laser optical cavity hydrophone of the type comprising a Bragg grating optical fiber element forming the laser cavity.
- Said hydrophone comprises a mechanical structure forming a cavity filled with a fluid, inside which the optical fiber element is placed along the longitudinal axis of the cavity, the mechanical structure further comprising:
- a substantially cylindrical hollow rigid body forming the cavity inside which the optical fiber element is placed;
- Two plugs configured and arranged to close the ends of the rigid body, traversed by the optical fiber element, said optical fiber element being fixed to the plugs at the crossing points so as to be permanently in tension.
- the two plugs are configured, given the material in which they are made, so as to present a longitudinal deformation when they are subjected to:
- a through-orifice configured to make the cavity communicate with the external medium and to achieve a balancing of the static pressure between the external medium and the fluid contained in the cavity.
- the rigid body and the two plugs are configured so that the hydrophone has symmetry planes arranged to minimize its sensitivity to parasitic accelerations.
- the dimensions of the rigid hollow body are defined so that the formed mechanical cavity can accommodate the optical fiber element and that, given their dimensions, the plugs undergo, under the action of dynamic variations of the pressure exerted by the external medium, a deformation sufficient to induce on the optical fiber element a variation in length to obtain the desired sensitivity of the hydrophone to dynamic pressure variations.
- the dimensions, length, hole and section S t rou, of the through orifice are determined so that, given the viscosity of the fluid contained in the cavity of the hydrophone, the latter has, in view of its volume V caV ity, a law of variation of its sensitivity to pressure variations, as a function of the frequency of these variations, having a given range of frequency of variation of the pressure a substantially constant sensitivity, this frequency range being located before the frequency F2 corresponding to the peak of mechanical resonance of the cavity.
- the dimensions of the through orifice are determined so that the range of frequencies of variation of the pressure for which the sensitivity of the cavity of the hydrophone is substantially constant being between the frequency F2 and a resonance peak (51) at a frequency F1 equal to the frequency of Helmholtz f H of the cavity defined by:
- the frequency f H is the lowest possible.
- the dimensions of the through-orifice are determined so that the range of frequencies of variation of the pressure for which the sensitivity of the cavity of the hydrophone is substantially constant being between the frequency F2 and a frequency F1 equal to the cutoff frequency f p of the cavity defined by the relation:
- the frequency fp is the lowest possible.
- the two plugs closing the cavity constituted by the rigid body have a hollow cylinder shape open at one end, said cylinder, configured to be inserted into the cavity so as to close the end and having a substantially cylindrical side wall and a resilient disc-shaped end wall perpendicular to the longitudinal axis of the cavity, and closing off the end of the plug inserted in the cylindrical body, the resilient end wall being configured to deform under the action variations in the pressure exerted by the external environment; the side wall having at least two segments:
- the side wall of the plug further comprises a terminal segment A whose thickness defines a shoulder which abuts on the end of the rigid body when the plug is put in place thereon.
- the dimensions of the cavity and the nature of the materials constituting the rigid body and the plugs are determined so as to obtain the highest possible frequency F2.
- the cavity housing the optical fiber element contains an open foam, said foam being impregnated with the fluid contained in the cavity, the material constituting the foam being defined so as to dampen the natural modes of resonance of the optical fiber element.
- the through orifice is a circular orifice made through the wall of the rigid body.
- the through hole is a circular orifice made longitudinally in the thickness of the side wall of a plug.
- the rigid body is made of titanium or glass.
- the plugs are made of PPO plastic or polyoxymethylene (POM) or polyformaldehyde.
- the rigid body or plugs being made in whole or in part of a porous material, the through hole is constituted by the pores of the material.
- FIGS. 3 and 4 are illustrations showing the behavior of the hydrophone according to the invention under the action of the dynamic variations of the pressure exerted by the external medium
- FIG. 5 a curve showing the shape of the variation law of the sensitivity of a hydrophone according to the invention as a function of the frequency of variation of the pressure exerted by the external medium;
- FIGS. 1 to 6 The following description presents the characteristics of the optical hydrophone according to the invention, through a preferred embodiment, taken here as a non-limiting embodiment of the scope or scope of the invention.
- the structure of this particular embodiment as well as the explanation of its operating principle is illustrated in particular by FIGS. 1 to 6.
- the hydrophone according to the invention comprises a protective mechanical structure defining a cavity January 1 within which a Bragg grating optical fiber element 12 is placed.
- this cavity also serves, in known manner, to amplify the axial deformation imposed on the optical fiber element 12 by the dynamic pressure exerted by the external environment.
- the optical fiber element 12 constituting the Bragg grating optical fiber single frequency cavity which forms the sensitive part of the hydrophone, fulfills three distinct functions: a pressure sensor function exploiting the variation in the emission frequency of the laser cavity associated with axial elastic deformation, in stretching and / or retraction, of the optical fiber cavity which constitutes the main element of the sensor;
- the optical hydrophone according to the invention thus consists of a mechanical structure comprising a rigid body of cylindrical shape. 13 closed on each side by a plug 14 or 15.
- cylinder In general, in the context of the invention, the notion of cylinder is considered in its most general definition.
- the mathematical definition of the cylinder it can for example be a right prism in the case of a polygon-shaped base or a cylinder of revolution in the case of a circular base.
- the rigid body is a right cylinder of revolution whose generating line is the axis of the optical fiber.
- the rigid body is a hyperboloid or a generalized ellipsoid.
- a geometry of revolution makes it possible to minimize the sensitivity to parasitic transversal accelerations.
- the plugs 14 and 15 are configured so as to form two pistons located at the two ends of the cylindrical body whose displacement, the deformation, under the action of the variations of the pressure exerted by the medium, varies the volume of the cavity 1 1 as well as the length of the Bragg grating optical fiber element 12 housed in this cavity.
- the optical fiber element 12, forming the active part of the hydrophone is placed along the central axis of the cylindrical body 13 defining the cavity January 1. It thus enters and leaves the cavity 1 1 through the walls of the plugs 14 and 15, walls to which it is attached in such a way that when the hydrophone is assembled, it undergoes a pre-tension. In this way, the deformation (displacement) of the plugs 14 and 15 under the action of the pressure exerted by the medium systematically causes a variation in the length of the optical fiber element 12 enclosed in the cavity January 1.
- the device according to the invention also comprises one or more through holes 16 whose function is to put the internal medium contained in the cavity 1 1, delimited by the cylindrical body 13 and the two plugs 14 and 15, permanently in contact with the external environment.
- the orifices 16 advantageously allow the pressures prevailing inside and outside the cavity 1 1 to equilibrate so that the device is thus insensitive to static pressure.
- the static pressure being identical inside and outside the cavity 1 1, the pistons formed by the plugs 14 and 15 do not undergo its influence.
- the Bragg grating optical fiber element 12 does not suffer from the plugs any stress resulting from the static pressure exerted on them.
- the dimensional characteristics of the cavity 1 1 formed as well as the size and the arrangement of the plugs 14 and 15 and the communication orifices 16 are determined so as to achieve the following functionalities:
- a low-pass hydrostatic filtering for placing the laser cavity constituted by the optical fiber element 12 in equi-pressure with the pressure of the medium surrounding the hydrophone, for the variations of pressure of frequency lower than a frequency of given break;
- the cylindrical body 13 is constituted by a cylindrical tube made of a rigid material making it little deformable under the effect of pressure.
- titanium is made of titanium, titanium being chosen for its rigidity and low thermal expansion.
- it can also be made in any suitable rigid material, compatible with the filling fluid.
- the cylindrical body 13 thus advantageously takes only a negligible part in the overall deformation. It thus has no part in the amplification of the deformation exerted by the structure on the optical cavity constituted by the optical fiber element 12, this amplification being provided by the plugs 14 and 15.
- the thickness E of the wall of the cylindrical body 13, generally constant, is also defined to provide the necessary rigidity given the maximum pressure that it must undergo.
- length L is in turn imposed by the length of the optical fiber portion that it must accommodate, this length preferably being sufficient for the optical fiber element 12 to be fixed to the plugs 14 and 15 in a zone 18 or 19 of simple light conduction, which does not correspond to the Bragg grating forming the laser cavity, the Bragg grating, of length h, thus not being directly attached to the plugs 14 and 15 by its ends.
- the internal diameter D of the cylindrical body 13 is in turn defined according to the dimensional characteristics imposed on the plugs 14 and 15 to fulfill their function of amplification and compensation of the effects of temperature variations on the behavior of the optical cavity formed by the optical fiber element 12.
- the plugs 14 and 15 are, in turn, configured to perform different functions:
- a piston function making it possible to vary the length of the optical fiber element 12 housed in the cavity 1 1 under the action of the dynamic pressure variations exerted on the hydrophone, an increase in pressure resulting in a displacement of plugs, or at least the inner end of the plugs, towards the inside of the cavity
- plugs 14 and 15 are conceivable, in particular embodiments implementing plugs having a portion rigidly connected to the cylindrical body 13, for holding the plug in place on the latter, and a mobile or free-deforming part able to move inside the cavity, towards the center of the cavity or towards its end, by driving in its movement the optical fiber element 12 which is attached.
- the plugs 14 and 15 may therefore, for example, consist, at least in part, of an elastic material, a material substantially less rigid than the material constituting the cylindrical body 13, Noryl® PPO plastic by example or polyoxymethylene (POM) or polyformaldehyde, Deirin® for example.
- Noryl® PPO plastic by example or polyoxymethylene (POM) or polyformaldehyde, Deirin® for example.
- FIG. 2 shows the structure of the plugs implemented in the preferred embodiment taken as an example.
- each plug 14 or 15 is formed by a hollow body comprising a wall 21.
- This wall 21 defines a cylindrical cavity 23 in the mathematical sense of the term. In the case where this cylindrical cavity is a cylinder itself, it has a constant internal diameter d.
- the cylindrical cavity 23 has an axis of symmetry coincident with that of the cylindrical body and a resilient wall D 22, for example disc-shaped, perpendicular to the axis of symmetry of the cylindrical cavity January 1 and closing one of the ends of the cavity 23, the other end being open.
- the plug thus formed is intended to be inserted into the cavity 1 1 by its end closed by the wall 22.
- the hollow body and the wall 21 are, for example cylindrical bodies in the mathematical sense of the term.
- the wall 21 is a wall whose non-constant thickness essentially defines two distinct segments B and C for which the plug has distinct outside diameters.
- this wall could also include only the free segment C.
- the wall 21 of the plug thus comprises a first segment B whose thickness is defined so that when it is inserted into the cavity 1 1 of the hydrophone its wall, at the segment B, is put in contact narrow, preferably sealed, with the inner wall of the cylindrical body 13, by tight fitting for example, so that the wall of the plug is held in a fixed position in the cavity 1 1 of the hydrophone at the segment B.
- the wall 21 may further comprise a terminal segment A whose thickness defines a shoulder which abuts on the end of the cylindrical body 13 when the plug is placed on the cylindrical body 13.
- the plugs may be of cylindrical, hyperboloid or ellipsoid shape, provided however that they have the 3 segments: the segment B in close and tight contact with the rigid body, the segment C free to expand with temperature variations and whose projected length on the axis of the fiber is equal to x and the wall D, 22 perpendicular to the fiber.
- the plug comprises a portion rigidly connected to the body 13.
- This portion rigidly connected to the cylindrical body 13 comprises the parts A and B but could equally well be made differently as long as the plug is rigidly connected to the cylindrical body 13.
- the portion of the plug free to deform which can move within the cavity, causing in its movement the optical fiber element 12 comprises the portion C which is free to expand or contract longitudinally depending on the variations of temperature.
- This part also includes the membrane D.
- Each of the two plugs must in fact have a portion rigidly connected to the body 13 and a portion movable relative to the body 13 comprising a deformable wall capable of being deformed when it is subjected to variations in the pressure exerted by the external environment in which is immersed the hydrophone; the deformation of the plugs causing a change in the length of the optical fiber element 12.
- the deformable wall has an inner face 221 facing, that is to say facing, the interior of the cavity and a face external 222 facing outwardly of the cavity.
- the deformable wall is the elastic wall 22. This wall is movable in translation along the longitudinal axis under the effect of temperature variations because the part C is able to contract or expand freely in the longitudinal direction under the effect of temperature variations which causes a displacement of the elastic wall 22 in the longitudinal direction relative to the body 13.
- the caps could be made differently.
- the operation of the device according to the invention comprises three states:
- This resulting pressure is intended to effect of causing a deformation of the elastic walls 22 of the plugs 14 and 15, which results, in the case of the preferred embodiment taken as an example, by a bending ⁇ 2 of the elastic wall 22 of the plug inside the the cavity of the hydrophone.
- This deformation which induces a decrease in the volume of the cavity and which has the effect of increasing the internal pressure, continues until the internal and external pressures balance again.
- the initial position of the plug is shown in dashed line.
- FIG. 4 A second dynamic state, illustrated in FIG. 4, for which the pressure exerted by the external medium undergoes a rapid decrease resulting in the appearance of a resulting pressure, indicated by the arrows 41 in FIG. 4.
- This resulting pressure has the effect of effect of causing a deformation of the plugs 14 and 15 which results, in the case of the preferred embodiment taken as an example, by a reverse bending ⁇ 3 of the elastic wall 22 of the plug.
- This deformation which induces an increase in the volume of the cavity and which has the effect of reducing the internal pressure continues until the internal and external pressures balance again.
- the initial position of the plug is shown in dashed line.
- the optical fiber element 12 is, as has been said above, attached to the wall 22 of each of the plugs which closes the cavity so that, when the hydrophone is assembled, it undergoes a meadow. -voltage.
- the value of this pre-tension is defined so that when the plug undergoes its maximum elongation under the action of an increase in the pressure of the external medium, possibly cumulative elongation, with the length variations due to the temperature, the optical fiber element 12 retracts but remains nevertheless under the effect of a residual voltage which keeps it rectilinear, in tension, as illustrated in FIG. 3.
- the optical fiber element 12 sees its length vary from a maximum value l 3 to a minimum value l 2 passing, at the balance, by a length while always remaining in tension and this, regardless of the temperature considered in the temperature range.
- the device according to the invention is defined so as to meet different requirements.
- the length L of the cylindrical body 13 is determined, in a preferred embodiment, both by the length of the Bragg grating optical fiber element 12 housed in the cavity, length imposed by construction, and in a lesser extent, by the resonant frequency of the cavity.
- the dimensions of the orifice (orifices) through 16 orifice (s) implemented according to the invention so as to ensure the insensitivity of the device to the static pressure are defined so as to have an optimum range of frequency of use, that is to say a frequency range on which the sensitivity of the device is in accordance with the expected value.
- the dimensions of the orifice 16 can be determined by assimilating the latter to a cylinder of radius R tr0 u and length l hole and considering the curve of variation of the sensitivity of a cavity to pressure variations depending the frequency of these variations.
- a cavity such as that constituted by the device according to the invention has, under the effect of variations of the pressure and because of the presence of the orifice 16 and the viscosity of the medium inside the cavity in particular, one or two resonance peaks 51 and 52 at frequencies f 1 and f 2 , these frequencies being defined both by the volume of the cavity and the dimensions (R tr0 u and l tra u) -
- the first behavior corresponds to that of the low-viscosity or non-viscous fluids
- the second behavior illustrated by the solid line curve
- the first behavior results in the presence of two peaks 51 and 52, while the second behavior is reflected by the presence of a single peak 52.
- the peak 51 indicates that the behavior of the cavity at the very low frequencies is comparable to that of a Helmhoitz cavity.
- the resonance peak 51 appears for low frequency variations, in particular when the fluid inside the cavity is considered to be non-viscous and / or when the hole is of relatively large diameter, of the order of 1 mm, for example. It is observed that, for these low frequencies, the cavity has a behavior similar to a Helmhoitz cavity and that the resonance frequency corresponding to the peak 51 is close to the Helmhoitz resonance frequency of the cavity.
- the cavity is generally modeled by a mass-spring system, the hole behaving like a mass and the cavity acting as a stiffness. According to this model, if we consider that the cylinder is rigid, the resonance frequency is then defined by the following relation:
- the orifice 16 behaves as if it were closed so that the variations in the external pressure are transmitted to the internal environment that by the piston movements followed by the two plugs, or more precisely by the elastic wall 22 of the plug free to deform, movements that are transmitted to the optical fiber element 12.
- the second resonance peak here corresponds to a purely mechanical resonance which has the two plugs for origin, resonance whose frequency therefore depends essentially on the geometry of the plugs.
- the geometry of the cavity is optimized to obtain the widest possible use band.
- the geometry of the cavity is optimized to obtain that the frequency fi of the first peak, or the cutoff frequency f p in the case of a viscous fluid, is as low as possible and that the frequency f 2 of the second peak is the highest possible.
- the diameter of the orifice 16 does not significantly affect the frequency f 2 of the second peak 52.
- the frequency f 1 of the first peak 51 increases with diameter of the orifice. It is therefore advantageously possible to adjust the value of the frequencies f1 or fp of the cavity by choosing the diameter of the orifice appropriately.
- the diameter of the cavity influences the values of the frequencies fi or fp on the one hand and f 2 on the other hand. It is more precisely observed that the values of f- ⁇ , or fp, and f 2 vary in the same direction as a function of the diameter of the cavity, towards values that are smaller as the diameter is greater. It is thus advantageously possible to adjust the position of the useful frequency range by choosing the diameter of the cavity appropriately.
- the length of the cavity simultaneously influences the values of the frequencies f 1 or f 2 , and f 2 , the values of f 1 or f 2 , and f 2 varying towards values of lower than the length of the cavity is larger.
- the diameter, or more generally the opening, of the cylindrical body 13 determines the dimensions of the plugs and in particular the dimensions of the cylindrical wall 21 of a plug.
- the dimensions of a plug are, in turn, determined so as to obtain the desired amplification of the longitudinal deformation imposed on the optical fiber element by the pressure variations and to compensate for the effects of the variations of the temperature on the length I of the optical fiber element.
- the insensitivity of the device according to the invention to temperature variations is achieved by adjusting the geometry of the plugs.
- the temperature variations cause on the one hand a variation of index in the fiber 12 and on the other hand a variation in the length of the plugs 14 and 15 at the origin of the elongation or retraction of the fibre12.
- the variation of the length Lfibre for a temperature variation ⁇ must cause a variation of the wavelength ⁇ opposite the variation caused by the variation of T'indice n.
- the variation of the length Lfibre is thus defined by the following equality:
- the cylindrical body defining the cavity is rigid and insensitive to the temperature variations considered, it is advantageously possible to express the elongation.
- ALf ib is undergone by the optical fiber element 12 housed in the cavity, an integral element of the plugs 14 and 15, as a function of the length variation of the plugs under the effect of the temperature variation ⁇ and thus to size the plugs appropriately so that their variation in length causes the variation ⁇ _ 3 ⁇ 4 ⁇ of length of the fiber making it possible to compensate exactly or substantially the variation of the index n. This can be achieved in several ways.
- t be and P i S t represent the coefficients of thermal expansion of the materials respectively constituting the cylindrical body 13 and the plugs 14 and 15 or, at least, the free section C plugs and ⁇ the temperature variation.
- the length x is the length of the moving part which is, here, the length of the free section C.
- the dimensions of the plugs must be determined so that the length x is defined by the following relation:
- L fiber is the length of the fiber, that has tU b e and ⁇ ⁇ ⁇ 3 ⁇ 0 ⁇ represent the thermal expansion coefficients of the materials respectively constituting the cylindrical body 21 and the plugs 14, 15 or, at least, free section C, n represents the index of the cavity, dn / dT the variation of the index of the cavity per unit of temperature.
- this length x is independent of ⁇ and depends only on the properties of the materials used and the fiber length I fiber fixed between the plugs.
- the plug may have different shapes, but it is still possible to find a material and a geometry of the moving part of the plugs which satisfies the relation 9 in a wide temperature range.
- a three-dimensional thermal calculation by the finite element method makes it possible to arrive at the optimal length of the mobile plugs.
- a length x equal to 4.7 mm is then obtained.
- the device according to the invention is therefore defined from a structural point of view, as a device comprising a cylindrical body 13 made of rigid material, with a low coefficient of expansion, and plugs 14 and 15 made of high coefficient of expansion, these elements defining a cavity in which is housed the Bragg grating optical fiber element 12.
- the device is advantageously insensitive to temperature variations and static pressure variations. It advantageously makes it possible to amplify the length variations imposed on the optical fiber element 12 by dynamic pressure variations.
- studies carried out elsewhere highlight that the nature of the fluid contained in the cavity conditions the sensitivity of the device.
- the sensitivity of this hydrophone depends little geometric parameters. It depends mainly on the compressibility of the fluid used. As a result, it is possible to increase the sensitivity of the hydrophone according to the invention by using a more compressible fluid than water to fill the cavity of the hydrophone. For example, an oil can be chosen instead of water.
- the curve of FIG. 6 gives the appearance 61, for a dynamic variation of pressure equal to 1 kHz, of the variation of the sensitivity of an optical hydrophone according to the invention as a function of the compressibility of the fluid used to fill the cavity.
- the optical fiber element 12 housed in the cavity is fixed to the plugs 14 and 15 so as to undergo a voltage prestress whose value is defined so that whatever are the dynamic pressure variations imposed by the external environment and regardless of the elongation of the temperature changes, it is maintained in tension.
- the fiber element 12 behaves like a vibrating wire whose resonant frequency depends on its free length and its linear density as well as the prestress applied thereto.
- the voltage prestress applied to the fiber directly depends on the operating temperature range.
- the temperature insensitivity of the device according to the invention is obtained by varying the length of the fiber element so that the wavelength ⁇ remains constant.
- the variation in the length of the fiber is itself induced by the deformation of the plugs to which it is fixed under the action of temperature, the axial deformation in particular.
- the tensile force F applied to the fiber element 12 being fixed, it is the same for the natural modes of vibration of the fiber element 12.
- one or more of these eigenmodes can correspond to frequencies resonance located in the range of use of the device so that for these frequencies, the sensitivity of the device is altered.
- eigenmodes can be determined in a known manner by considering the tensile force F applied to the fiber element 12 to maintain it in pre-tension and the speed of propagation of a deformation wave along the vibrating rope. what constitutes this element.
- the traction force F applied to the fiber element 12 can be defined by the following relation: [12] where E represents the Young's modulus of silica (material constituting the fiber), where S and I respectively represent the section and the length of the fiber, and where ⁇ _ represents the elongation imposed on the fiber. This elongation is determined by taking into account the elongation of the fiber as a function of the temperature variation considered.
- the propagation velocity v of a wave in the vibrating string formed by the fiber element 12, subjected to the tension force F is further defined by the expression:
- the eigen modes of vibration of the string are obtained for wavelengths such that: where L is the length of the fiber and n is an integer.
- the resonant natural frequencies of the vibrating string constituted by the optical fiber element 12 are defined by the following relation:
- I 42mm made from a silica fiber of diameter equal to 250 ⁇ and having a relative variation of length equal to 9.36 ⁇ / ⁇ / ⁇ ⁇ , the elongation ⁇ _ of the fiber obtained for a temperature variation of 50 ° C is substantially equal to 23.4 ⁇ and the voltage F to be applied is substantially equal to 0.6N.
- the application of this voltage itself induces the appearance of natural resonance frequencies at the level of the optical fiber element 12, eigenfrequencies of which the first at a value substantially equal to 1500 Hz.
- this natural mode of resonance will be excited as soon as a transverse acceleration of identical frequency will be exerted by the external medium.
- Such an acceleration due essentially to mechanical disturbances caused, for example, by the movements of the acoustic antenna in which the hydrophone is integrated, introduces a disturbance of the sensitivity of the hydrophone. As a result, in such a configuration, it becomes necessary to dampen the natural modes of vibration of the optical fiber element 12.
- this damping can be obtained by varying the viscosity of the fluid contained in the cavity of the hydrophone.
- FIGS. 7 and 8 show schematically the structure of an alternative embodiment of the device according to the invention.
- the cylindrical body 13 has no orifice 16.
- through-holes 71 are here used in the thickness of the plugs 14 and 15.
- this embodiment advantageously makes it possible, on the one hand, to leave the cylindrical body 13 free of any piercing and, on the other hand, to obtain orifices presenting a length l hole greater than the thickness of the wall of the cylindrical body and therefore to design hydrophones with a frequency of Helmhoitz lower than in the previous embodiment (see relation [3]).
- the device according to the invention comprises such orifices regardless of the embodiment envisaged.
- the function of the through orifices 16 may, in an alternative embodiment where the rigid body 13, or a part of the rigid body is made of a porous material, to be filled by the pores of the materials.
- the function of the through holes 16 can be filled by the pores of the material.
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BR112013026180-3A BR112013026180B1 (pt) | 2011-04-14 | 2012-04-13 | Hidrófono com cavidade laser |
AU2012241768A AU2012241768B2 (en) | 2011-04-14 | 2012-04-13 | All-optical hydrophone that is not sensitive to temperature or static pressure |
SG2013077482A SG194525A1 (en) | 2011-04-14 | 2012-04-13 | All-optical hydrophone that is not sensitive to temperature or static pressure |
JP2014504334A JP6083074B2 (ja) | 2011-04-14 | 2012-04-13 | 温度又は静圧の影響を受けない全光ハイドロホン |
ES12713995T ES2904681T3 (es) | 2011-04-14 | 2012-04-13 | Hidrófono totalmente óptico insensible a la temperatura y a la presión estática |
KR1020197003158A KR20190015602A (ko) | 2011-04-14 | 2012-04-13 | 온도 또는 정압에 대해 민감하지 않은 전광 하이드로폰 |
US13/642,519 US9103713B2 (en) | 2011-04-14 | 2012-04-13 | All-optical hydrophone insensitive to temperature and to static pressure |
KR1020137026973A KR102112366B1 (ko) | 2011-04-14 | 2012-04-13 | 온도 또는 정압에 대해 민감하지 않은 전광 하이드로폰 |
EP12713995.4A EP2697612B1 (fr) | 2011-04-14 | 2012-04-13 | Hydrophone tout optique insensible a la temperature et a la pression statique |
CN201280018164.6A CN103492842B (zh) | 2011-04-14 | 2012-04-13 | 对于温度或静压不灵敏的全光水听器 |
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FR1101165A FR2974263B1 (fr) | 2011-04-14 | 2011-04-14 | Hydrophone tout optique insensible a la temperature et a la pression statique |
FR1101165 | 2011-04-14 |
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WO2012140179A1 true WO2012140179A1 (fr) | 2012-10-18 |
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PCT/EP2012/056740 WO2012140179A1 (fr) | 2011-04-14 | 2012-04-13 | Hydrophone tout optique insensible a la temperature et a la pression statique |
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US (1) | US9103713B2 (fr) |
EP (1) | EP2697612B1 (fr) |
JP (1) | JP6083074B2 (fr) |
KR (2) | KR102112366B1 (fr) |
CN (1) | CN103492842B (fr) |
AU (1) | AU2012241768B2 (fr) |
BR (1) | BR112013026180B1 (fr) |
ES (1) | ES2904681T3 (fr) |
FR (1) | FR2974263B1 (fr) |
SG (1) | SG194525A1 (fr) |
WO (1) | WO2012140179A1 (fr) |
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- 2012-04-13 US US13/642,519 patent/US9103713B2/en active Active
- 2012-04-13 KR KR1020197003158A patent/KR20190015602A/ko not_active Application Discontinuation
- 2012-04-13 CN CN201280018164.6A patent/CN103492842B/zh active Active
- 2012-04-13 WO PCT/EP2012/056740 patent/WO2012140179A1/fr active Application Filing
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Cited By (10)
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CN103438979A (zh) * | 2013-08-14 | 2013-12-11 | 武汉普惠海洋光电技术有限公司 | 一种光纤水听器固定装置 |
CN106030269A (zh) * | 2013-11-19 | 2016-10-12 | 辉固技术有限公司 | 用于检测流体介质中压力波的具有静态压力补偿的传感器 |
EP3002613A1 (fr) * | 2014-10-03 | 2016-04-06 | PGS Geophysical AS | Appareil optique noyable, procédés et systèmes |
US10101481B2 (en) | 2014-10-03 | 2018-10-16 | Pgs Geophysical As | Floodable optical apparatus, methods and systems |
FR3034207A1 (fr) * | 2015-03-27 | 2016-09-30 | Thales Sa | Dispositif de capteur a fibre optique |
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CN108106713A (zh) * | 2017-12-19 | 2018-06-01 | 威海北洋电气集团股份有限公司 | 一种含空气腔的芯轴型光纤水听器 |
CN111039087A (zh) * | 2019-12-26 | 2020-04-21 | 北京航天控制仪器研究所 | 一种光纤激光水听器“有源”光纤光栅封装张力控制方法及系统 |
CN111039087B (zh) * | 2019-12-26 | 2021-09-07 | 北京航天控制仪器研究所 | 一种光纤激光水听器“有源”光纤光栅封装张力控制方法及系统 |
Also Published As
Publication number | Publication date |
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SG194525A1 (en) | 2013-12-30 |
EP2697612B1 (fr) | 2021-11-10 |
CN103492842A (zh) | 2014-01-01 |
FR2974263A1 (fr) | 2012-10-19 |
JP6083074B2 (ja) | 2017-02-22 |
BR112013026180B1 (pt) | 2021-08-17 |
ES2904681T3 (es) | 2022-04-05 |
AU2012241768B2 (en) | 2015-05-07 |
KR20190015602A (ko) | 2019-02-13 |
US20140036635A1 (en) | 2014-02-06 |
EP2697612A1 (fr) | 2014-02-19 |
KR20140015467A (ko) | 2014-02-06 |
JP2014519014A (ja) | 2014-08-07 |
FR2974263B1 (fr) | 2014-10-24 |
US9103713B2 (en) | 2015-08-11 |
KR102112366B1 (ko) | 2020-05-18 |
AU2012241768A1 (en) | 2013-11-07 |
CN103492842B (zh) | 2016-08-24 |
BR112013026180A2 (pt) | 2020-11-03 |
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