(19)
(11)EP 3 511 723 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
30.03.2022 Bulletin 2022/13

(21)Application number: 19161095.5

(22)Date of filing:  26.08.2014
(51)International Patent Classification (IPC): 
G01P 15/09(2006.01)
G01H 11/08(2006.01)
(52)Cooperative Patent Classification (CPC):
G01H 11/08; G01P 15/0922

(54)

PIEZOELECTRIC ACCELEROMETER

PIEZOELEKTRISCHER BESCHLEUNIGUNGSMESSER

ACCÉLÉROMÈTRE PIÉZOÉLECTRIQUE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 29.08.2013 US 201361871482 P
31.12.2013 US 201314145093

(43)Date of publication of application:
17.07.2019 Bulletin 2019/29

(62)Application number of the earlier application in accordance with Art. 76 EPC:
14182330.2 / 2843421

(73)Proprietor: PGS Geophysical AS
0216 Oslo (NO)

(72)Inventor:
  • FERNIHOUGH, Robert Alexis Peregrin
    Manor, TX 78653 (US)

(74)Representative: Gill Jennings & Every LLP 
The Broadgate Tower 20 Primrose Street
London EC2A 2ES
London EC2A 2ES (GB)


(56)References cited: : 
EP-A1- 0 882 987
DE-A1- 4 135 369
US-A- 4 431 935
US-A1- 2011 310 698
EP-A2- 0 675 365
GB-A- 1 435 125
US-A- 5 235 237
US-B1- 6 336 365
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND



    [0001] Geophysical surveying (e.g., seismic, electromagnetic) is a technique where two-or three-dimensional "pictures" of the state of an underground formation are taken. Geophysical surveying takes place not only on land, but also in marine environments (e.g., ocean, large lakes). Marine geophysical survey systems use a plurality of sensor streamers (long cables), which contain one or more sensors to detect acoustic energy emitted by one or more sources and reflected from the underground formation. Detection and interpretation of the signals represented thereby can be attenuated by destructive interference with reflections of the energy from interfaces present in the marine environment, particularly the water-air interface at the surface.

    [0002] Discrimination against reflected signals may be provided by combining signals from multiple detector types sensitive to different physical characteristics of the acoustic signal. For example, when appropriately combined, the output from hydrophones sensitive to the pressure perturbation from the acoustic signal may be used in conjunction with the output of a detector sensitive to the velocity of a fluid particle for example, a geophone, may provide such discrimination. However, these detectors, particularly the geophone, typically are complex and concomitantly, costly to manufacture. Thus a low-cost device which may be used to provide similar capabilities would provide a competitive advantage in the marketplace.

    [0003] U.S. Pat. No. 6,336,365 to Blackadar et al. is directed to a low-cost accelerometer. The background section of Blackadar appears to describe an accelerometer comprising a pair of support members 102 holding a piezoceramic beam 104. Deflections of the beam 104 generate electrical signals responsive to the deflections.

    [0004] Published EP application EP 0 882 987 A1 to Matsushita Electric Industrial Co., Ltd. is directed to a piezoelectric acceleration sensor. In particular, Matsushita appears to describe an acceleration sensor where the piezoelectric element 100 is supported in the center by a support member 7a.

    [0005] Published EP Application EP 0 675 365 A2 to Matsushita Electric Industrial Co., Ltd. is directed to an acceleration sensor. In particular, Matsushita appears to describe a piezoelectric vibrator 100 comprising a rectangular piezoelectric element 301 centered-supported by metallic protrusions 303.

    [0006] U.S. Pat. No. 5,235,237 to Leonhardt is directed to an accelerometer. In particular, Leonhardt appears to describe an accelerometer 10 where the proximal end of the cantilever is held by the housing 14.

    [0007] U.S. Published Application No. 2011/0310698 to Maples et al. is directed to dual axis geophones for pressure/velocity sensing "triple component" streamers. In particular, Maples appears to describe towing streamers that contain hydrophones and acoustic particle detectors.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0008] For a detailed description of exemplary embodiments, reference will now be made to the accompanying drawings in which:

    Figure 1A shows, in an exploded view, an accelerometer in accordance with at least some embodiments;

    Figure 1B shows, in a perspective view an accelerometer in accordance with at least some embodiments;

    Figure 1C shows, in a top section view an accelerometer in accordance with at least some embodiments;

    Figure 2A shows in a perspective view, a housing in accordance with at least some embodiments;

    Figure 2B shows, in a top section view, a housing in accordance with at least some embodiments;

    Figure 3A shows, in a perspective view, a piezoelectric sensing element in accordance with at least some embodiments;

    Figure 3B shows, in a side elevation view, a piezoelectric sensing element in accordance with at least some embodiments;

    Figure 4A shows, in a perspective view, a mounting plate in accordance with at least some embodiments;

    Figure 4B shows, in a front elevation view, a mounting plate in accordance with at least some embodiments;

    Figure 5A shows, in a perspective view and front elevation an end plate in accordance with at least some embodiments;

    Figure 5B shows, in a front elevation view, an end plate in accordance with at least some embodiments;

    Figure 6A shows in a front elevation view, and side elevation a cap in accordance with at least some embodiments;

    Figure 6B shows in a side elevation view, a cap in accordance with at least some embodiments;

    Figure 7 shows a schematic front elevation of a piezoelectric sensing element in accordance with at least some embodiments;

    Figure 8 shows a transverse section view of an accelerometer in accordance with at least some embodiments; and

    Figure 9 shows an overhead view of a marine survey system in accordance with at least some embodiments;

    Figure 10 shows a flow diagram of a method in accordance with at least some embodiments.


    NOTATION AND NOMENCLATURE



    [0009] Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, different companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms "including" and "comprising" are used in an openended fashion, and thus should be interpreted to mean "including, but not limited to...." Also, the term "couple" or "couples" is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections.

    [0010] "Cable" shall mean a flexible, load carrying member that also comprises electrical conductors and/or optical conductors for carrying power and/or signals between components.

    [0011] "Marine environment" shall mean an underwater location regardless of the salinity of the water. Thus, even an underwater location in a body of fresh water shall be considered a marine environment.

    [0012] "Fluid particle" shall mean a small amount of fluid which may be identifiable while moving with a fluid flow; a fluid particle may also be referred to as a fluid element. In some embodiments, "fluid particle" may be specifically interpreted to mean any fluid parcel that is smaller than about one-tenth wavelength of sound in a medium in any direction, and, for example, in at least some embodiments may be less than 0.75m in any direction.

    [0013] "Transect" shall mean to subdivide or partition into separately identifiable portions, but not necessarily into physically disjoint portions.

    [0014] "Exemplary," as used herein, means serving as an example, instance, or illustration." An embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

    [0015] The terms "upper" and "lower" shall be considered relative locational terms in view of the local force of gravity and a particular orientation of a device, but shall not be read to require a particular operational orientation of the device.

    DETAILED DESCRIPTION



    [0016] The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure or the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure or the claims, is limited to that embodiment. The scope of the invention is solely defined by the appended claims.

    [0017] The various embodiments are directed to an accelerometer which may be used to detect fluid particle accelerations and thereby, by integration, fluid particle velocities in conjunction with marine geophysical survey systems. Although the developmental context may be marine geophysical survey, embodiments of the accelerometer in accordance with the principles disclosed herein are of general applicability and may be used in other applications where a determination of an acceleration of a body is desired. When used in the context of a marine geophysical survey, measurements of fluid particle velocity can be used to predict properties of formations below a body of water. In particular, measurements of fluid particle velocity may assist in identifying the location of hydrocarbon-bearing reservoirs in the formations.

    [0018] Figures 1A and 1B show perspective views of an accelerometer 100 in accordance with at least some embodiments. Turning first to Figure 1A, an exploded perspective view of an accelerometer 100 is shown. Accelerometer 100 includes a sensor 102. In at least some embodiments, sensor 102 comprises a piezoelectric sensing element 104 disposed within mounting plates 106. Together, piezoelectric sensing element 104 and mounting plates 106 comprise a centrally supported beam. Mounting plates 106 transect piezoelectric sensing element 104 into two cantilever portions 105 and a central portion 107 disposed between mounting plates 106. Mounting plates 106 abut an interior wall of housing 114. The embodiment of accelerometer 100 shown in Figure 1A includes a pair of mounting plates 106, however alternative embodiments may employ a single mounting plate 106. In such embodiments, a single mounting plate may transect piezoelectric sensing element 104 into two cantilever portions without a central portion. Piezoelectric sensing element 104 will be described in further detail in conjunction with Figure 3. As described further below in conjunction with Figures 3 and 7, the centrally supported beam architecture of the piezoelectric sensing element 104 and mounting plates 106 form a spring-mass system which may be responsive to accelerations of accelerometer 100.

    [0019] Mounting plates 106 may also be configured to provide electrical coupling of signals generated by piezoelectric sensing element 104 to external circuitry (not shown in Figure 1) via wires 108. Mounting plates 106 may be formed from printed circuit board material. An embodiment of a plate that may be used in conjunction with accelerometer 100 will be described in further detail in conjunction with Figure 4. Wires 108 may be bare conductors, or alternatively may comprise insulated conductors, for example. Wires 108 may couple to external circuitry via end plate 110 and external wires 112. External wires 112 may be comprised of insulated conductors. However, it would be understood by those skilled in the art that, to avoid the shorting of external wires 112, wires 112 may be comprised of bare conductors.

    [0020] Piezoelectric sensing element 104 may be disposed within housing 114. Housing 114 may comprise a circular cylinder forming openings 113A, 113B in corresponding ends 115A, 115B. Housing 114 further defines an internal volume 117 (partially obscured in Figure 1A) for receiving piezoelectric sensing element 104. Piezoelectric sensing element 104 may be received in internal volume 117 via opening 113A. Housing 114 may be any suitable material sufficient to protect piezoelectric sensing element 104 from damage when accelerometer 100 is deployed. Housing 114 may, for example, be comprised of a metal shell formed from materials as brass, copper or aluminum. An embodiment of housing 114 which may be used in conjunction with accelerometer 100 is shown in further detail in Figure 2. The housing 114 may be reconfigured with other cross-sectional shapes, such as rectangles, triangles, etc. Alternatively, in some examples that are not part of the claimed invention, the housing 114 may be omitted. End plate 110 may be fixedly attached to housing 114. In embodiments of housing 114 formed from a metal, attachment of end plate 110 to housing 114 may be by soldering. Alternatively, attachment may be effected by an adhesive. Housing 114 may be closed by cap 116 which may be received in opening 113B. Cap 116 may be comprised of the same or different material than housing 114 and may be fixedly attached thereto by soldering (in embodiments comprised of a solderable metal) or, alternatively, by an adhesive. Note that in some embodiments of accelerometer 100, cap 116 may be omitted, for example, in deployments wherein environmental exposure of accelerometer 100, and, in particular piezoelectric sensing element 104, is not of concern.

    [0021] Figure 1B shows a perspective view of an assembled accelerometer 100 in accordance with at least some embodiments. In Figure 1B, housing 114, external wires 112 and cap 116 are visible as in Figure 1A. Additionally, potting 118 may be disposed in the end of housing 114 proximal to the external wires thereby sealing such end and insulating the connections between external wires 112 and end plate 110 (not shown in Figure 1B). Potting 118 may comprise a potting compound such as HMP-85 from Chase Corporation, however, other potting compounds may also be employed.

    [0022] Refer now to Figure 1C. Figure 1C shows a cross sectional view of accelerometer 100 along the section 1C-1C in Figure 1B. Piezoelectric sensing element 104 may be disposed within interior volume 117 of housing 114. Potting 118 is shown in further detail and abutting end plate 110. As depicted in the illustrated embodiment of accelerometer 100, cap 116, housing 114 and potting 118 form a sealed enclosure for piezoelectric sensing element 104. Further, in an embodiment in which housing 114 comprises a metallic structure, the outside diameters or circumferences 120 of mounting plates 106 may also comprise a solderable material and circumferences 120 may be attached to an interior wall 122 of housing 114 by soldering thereto. Likewise, an outside diameter or circumference 124 of end plate 110 and a circumference 126 of cap 116 may also be attached to housing 114 by soldering.

    [0023] Figure 2 shows an embodiment of housing 114 in further detail, in two views: a perspective view, Figure 2A and a cross-sectional view along section 2B-2B in the perspective view, Figure 2B. The inside diameter or interior wall 122 of housing 114 bounds interior volume 117 and may include a counter bore 202 that defines an annular shoulder region 204. Openings 115A, 115B further define the extent of interior volume 117. Counter bore 202 forms shoulder region 204 where it abuts the remaining portion of interior wall 122. Shoulder region 204 may mate with circumference 124 of end plate 110 (not shown in Figure 2) thereto as illustrated in Figure 1C, and may be fixedly attached thereto by soldering, for example. A scribed score or similar marking such as an indentation or paint line (not shown on Figure 2) may be provided on the exterior of housing 114 parallel to its longitudinal axis and aligned with piezoelectric sensing element 104 to facilitate orienting the accelerometer.

    [0024] Refer now to Figure 3 showing, in perspective, Figure 3A and end view, Figure 3B, a piezoelectric sensing element 104 in accordance with at least some embodiments of the principles set forth herein. Piezoelectric sensing element 104 includes a pair of piezoelectric plates 302A and 302B, adhesive layers 304 disposed between piezoelectric plates 302A, 302B and conducting plate 306. In at least some embodiments, piezoelectric plates 302A and 302B may be substantially rectangular, although other geometries may also be used in alternative embodiments. Further, piezoelectric plates may be disposed having a substantially congruent relationship therebetween. Piezoelectric plates 302A and 302B may be comprised of a ceramic piezoelectric material, such as, for example, lead titanate zirconate (PZT). As would be understood by one of ordinary skill in the art with the benefit of this disclosure, piezoelectric materials exhibit an electric charge when subject to mechanical stress and, conversely, exhibit a mechanical strain when subject to an electric potential. Thus, a piezoelectric material subject to an acceleration and thereby a force in accordance with the laws of mechanics may exhibit an electric charge in response thereto. Piezoelectric plates 302A and 302B may be comprised of APC 850 material from APC International, Ltd., which is a PZT-based material. Other piezoelectric materials, for example, barium titanate (BaTiOs), lead titanate (PbTiOs), zinc oxide (ZnO), sodium potassium niobate ((K,Na)NbO3), bismuth ferrite (BiFeO3), sodium niobate (NaNbOs), bismuth titanate (Bi4Ti3O12), sodium bismuth titanate (Na0.5Bi0.5TiO3), berlinite (AlPO4), barium sodium niobate (Ba2NaNb5O15), lead potassium niobate (Pb2KNb5O15), quartz, Rochelle salt or plastic piezoelectric materials such as polyvinylidene fluoride (PVDF) may be used alternatively for the piezoelectric sensing element 104. Conducting plate 306 may be comprised of copper, brass, or other metallic material. Adhesive layers 304 may be comprised of an epoxy adhesive. An exemplary epoxy adhesive which may be used in an embodiment of piezoelectric sensing element 104 is LOCTITE® E-30CL epoxy structural adhesive from Henkel Corporation. Further, adhesive layers 304 may be omitted, conducting plate 306 may be omitted, or both adhesive layers 304 and conducting plate 306 may be omitted.

    [0025] Considering further piezoelectric plates 302A and 302B, piezoelectric plates 302A, 302B may have disposed on a face 308 thereof a conducting material to facilitate the attachment of mounting plates 106 as described in conjunction with Figure 1 above. For example, faces 308 may comprise silvered surfaces. Faces 308 may comprise other metals, for example electroless nickel, or gold. Further still, piezoelectric plates 302A and 302B may be polarized. For example, in an embodiment, piezoelectric plates 302A and 302B may have an electric polarization, P, in a direction substantially perpendicular to faces 308, shown as the y-direction in Figure 3. In at least some embodiments, piezoelectric plates 302A and 302B may be arranged such that the respective polarizations, P, are oppositely directed, whereby for example, in piezoelectric plate 302A, P may be substantially directed in the positive y-direction, and in piezoelectric plate 302B, P may be substantially directed in the negative-y direction. Such a disposition of plates 302A and 302B may be referred to a series mode operation. Series mode operation will be described further below in conjunction with Figure 7. Although the illustrated embodiment of piezoelectric sensing element 104 employs two piezoelectric plates, piezoelectric sensing element 104 may be comprised of a single plate, wherein faces 308 comprise opposite faces of the single plate.

    [0026] Refer now to Figure 4 showing in further detail an exemplary mounting plate 106 which may be used in conjunction with an embodiment of accelerometer 100. Figure 4 depicts mounting plate 106 in perspective, Figure 4A, and front elevation view, Figure 4B. Mounting plate 106 includes a slot 402 configured to receive piezoelectric sensing element 104 as described above in conjunction with Figures 1A-C, and conducting traces 404 which may serve to solderably attach to piezoelectric sensing element 104 via a portion 405 abutting slot 402. Thus, for example, a joint may be formed between portion 405 and a silvered face 308 of piezoelectric element 104 by the application of a eutectic composition of paste solder at the junction of portion 405 and face 308. The paste solder may be of the type used in surface-mount construction. The joint may then be formed by application of heat at a low temperature, e.g. just sufficient to melt the paste solder, using a soldering tool with large thermal mass such that the temperature of the tool is not materially reduced by the heat lost in melting the solder. In alternative embodiments, the joint may be formed using a conducting adhesive, and in yet other embodiments, an adhesive and embedded conducting wire may be used.

    [0027] Additionally, conducting traces 404 may also serve to electrically connect wires 108 to piezoelectric sensing element 104, via holes 407. Holes 407 may extend through a thickness of mounting plate 106 and may be plated through to form an electrical connection to conducting traces 404, and may be configured to receive ends of wires 108. Mounting plate 106 may further comprise conducting traces 406 disposed at an outside diameter thereof. In embodiments of housing 114 comprised of a metallic shell, conducting traces 406 may serve as solderable attachments thereto. In at least some embodiments, mounting plate 106 may be comprised of a circular disk, and further, a portion of a circular disk. Thus, the periphery of mounting plate 106 may include arcuate surfaces 408, which may be defined by circular arcs 409. Surfaces 408 may abut interior wall 122 of housing 114. Additionally, the periphery of mounting plate 106 may be additionally comprised of linear surfaces 410 which may be defined by chords 411. In at least some embodiments, mounting plate 106 may be fabricated of glass-reinforced epoxy laminate material, for example FR4 glass laminate printed circuit board material.

    [0028] Referring now to Figure 5, there is shown an end plate 110 which may be used in conjunction with accelerometer 100. Figure 5 shows a perspective, Figure 5A, and front elevation view, Figure 5B, of end plate 110. End plate 110 includes conductive traces 502. Holes 504A and 504B may extend through a thickness of end plate 110 and be configured to receive ends of wires 112 and 108, respectively. Holes 504A and 504B may comprise plated-through holes, and may further comprise solderable connections to wires 112 and 108. End plate 110 may also include conductive trace 506 disposed at the outside diameter of end plate 110. In embodiments of housing 114 comprised of a metallic shell, conducting trace 506 may serve as a solderable attachment thereto. In at least some embodiments, end plate 110 may have an outside diameter of about 14 mm. Further, in at least some embodiments, end plate 110 may be fabricated of a glass-reinforced epoxy laminate material, for example FR4 glass laminate printed circuit board material.

    [0029] Figure 6 shows an exemplary embodiment of a cap 116 which may be used in conjunction with accelerometer 100. Figure 6A shows a front elevation view and Figure 6B a side elevation view of cap 116. A diameter of periphery 602 of cap 116 may have a diameter sufficient to enclose an end of housing 114. Flange portion 604 may have a diameter sized to mate with an inside diameter of housing 114. In embodiments of housing 114 comprised of a metallic shell, the diameter of flange portion 604 may be further sized to form a solderable attachment to housing 114. In other embodiments, an adhesive may be used to form the attachment. As previously discussed, in at least some embodiments of accelerometer 100, cap 116 may be omitted as, for example, in deployments of accelerometer 100 in which sealing of piezoelectric sensing element 104 from exposure to foreign matter is not an issue. In at least some embodiments, periphery 602 may have a diameter of about 14.5 mm. Further, in at least some embodiments flange portion 604 may have a diameter of about 13.6 mm. The dimensions set forth herein are exemplary and other dimensions may be used in conjunction with embodiments of accelerometer 100 deployed in various applications. Cap 116 may be comprised of a metal, and in at least some embodiments may comprise, for example, brass or copper.

    [0030] To further understand the operation of an accelerometer in accordance with the principles of the disclosure refer now to Figure 7. Figure 7 schematically illustrates the displacement of piezoelectric sensing element 104 subject to an acceleration along the y-axis in the negative-y direction. In at least some embodiments of accelerometer 100, the y axis may be the desired axis of sensitivity, wherein the response of the accelerometer to components of an applied acceleration along, for example, axes mutually perpendicular to the y axis, is relatively small. For the purposes of illustration, the displacements are exaggerated in Figure 7. The flexural response of piezoelectric sensing element 104 to such acceleration comprises a compression of the upper portion thereof going into compression in the x direction and the lower portion of piezoelectric sensing element 104 going into tension in the x direction. In an embodiment of piezoelectric sensing element 104 configured for series mode operation, the opposite polarization of piezoelectric plates 302A and 302B, the complementary stresses can produce a net charge displacement which manifests itself as an output voltage signal proportional to the y component of the displacement of cantilever portions 105. In conjunction with its own mass, the flexural spring constant of piezoelectric sensing element 104 forms a "spring-mass system." As such, it may exhibit a resonant frequency in the flexural mode. At frequencies below such resonant frequency, the lateral stresses in the x-direction resulting from flexure of piezoelectric sensing element 304 may be proportional to the component of acceleration along the y axis. In an embodiment including two piezoelectric plates 302A, 302B comprising APC 850 each having exemplary dimensions of about 27 mm length (x-axis), by about 10mm width (z-axis) and 0.25 mm thickness (z-axis) and a conducting plate 306 comprised of brass disposed therebetween and having a thickness of 0.2 mm, the flexural mode resonant frequency may be about 2.3 kHz. Considering an embodiment deployed in a marine environment, such a resonant frequency is above the band of frequencies generated by seismic sources. The resonant frequency may be adjusted by, for example, the attachment of weights to cantilever portions 105 of piezoelectric sensing element 104. The dimensions set forth herein are exemplary and other dimensions may be used in conjunction with embodiments of accelerometer 100 deployed in various applications.

    [0031] Considering further a marine environment, accelerations induced by the seismic signal fluid particle motion are generated by an acoustic pressure wave. As would be understood by one of ordinary skill in the art with the benefit of this disclosure, the magnitude of the pressure wave relative to the magnitude of the acceleration of the fluid particle is inversely proportional to the frequency of the pressure wave. Generally, pressure is a scalar and acts isotropically over the surface of housing 114. Figure 8 shows a simplified transverse section through accelerometer 100 to illustrate the action of a pressure wave thereon. The pressure acting on accelerometer 100 is depicted by arrows 802. The pressure is supported in part by the hoop stiffness of housing 114. A slight decrease in the circumference of housing 114 may result therefrom producing stress in the y and z directions in piezoelectric sensing element 104. The electrical output of piezoelectric sensing element 104 may be a function of the amount of stress and its direction relative to the axis of polarization of the piezoelectric material comprising sensing element 104. As discussed above, in at least some embodiments, the polarization may be along the y axis. In such embodiments, a compressive stress along the z axis will produce a positive displacement of charge and a compressive stress along the y axis will produce a negative displacement of charge. However, because of the orthotropic nature of piezoelectric material, these counter-polarized displaced charges may not have the same amplitude and therefore may not cancel (algebraically sum to zero). In at least some embodiments, mounting plate 106 may, as described above in conjunction with Figure 4, have a perimeter comprising circular arcs 409 and chords 411. The stress distribution in the y-z plane may thereby be modified such that the ratio of the pressure-induced stresses in the y and z directions are scaled wherein the charges respectively displaced are both opposite in sign and substantially equal in magnitude. Consequently, in such embodiments, the counter-polarized charges may substantially cancel, and in such embodiments, the acoustic pressure sensitivity may be substantially reduced. Additionally, by way of example, considering the y axis to be the desired axis of sensitivity, the sensitivity of accelerometer 100 to rotations about the y axis may be further reduced in embodiments of accelerometer 100 comprising a pair of mounting plates 106. Such an exemplary embodiment has been described above in conjunction with Figure 1. As described in conjunction with Figure 7, flexural deflections of cantilever portions 105 may generate piezoelectric charge displacements to further provide an output signal from sensing element 104. It is further noted that a rotation of piezoelectric sensing element 104 about the z axis, which may be induced by a rotation of accelerometer 100, may produce an out-of-phase flexure of cantilever portions 105, that is, a flexure in which the displacements of the cantilever portions are oppositely directed (not shown in Figure 7). The resulting stresses may comprise a compressive stress in one of the cantilever portions 105 and a tensile stress in the other. The piezoelectric charge displacements may then be of opposite sign and may substantially cancel, thereby rendering accelerometer 100 substantially insensitive to such rotations about the z axis.

    [0032] Still considering a marine environment deployment, Figure 9 shows an overhead view of a marine survey system 900 in accordance with at least some embodiments. In particular, Figure 9 shows a survey vessel 902 having onboard equipment 904, such as navigation, energy source control, and data recording equipment. Survey vessel 902 is configured to tow one or more streamers 906A-F through the water. While Figure 9 illustratively shows six streamers 906, any number of streamers 906 may be used. The discussion continues with respect to streamers 906 being sensor streamers, but streamers 906 are illustrative of any towed geophysical survey cable, such as transmitter cables and source cables.

    [0033] The sensor streamers 906 are coupled to towing equipment that maintains the streamers 906 at selected depth and lateral positions with respect to each other and with respect to the survey vessel 902. The towing equipment may comprise two paravane tow lines 908A and 908B each coupled to the vessel 902 by way of winches 910A and 910B, respectively. The winches enable changing the deployed length of each paravane tow line 908. The second end of paravane tow line 908A is coupled to a paravane 912, and the second end of paravane tow line 908B is coupled to paravane 914. In each case, the tow lines 908A and 908B couple to their respective paravanes through respective sets of lines called a "bridle". The paravanes 912 and 914 are each configured to provide a lateral force component to the various elements of the survey system when the paravanes are towed in the water. The combined lateral forces of the paravanes 912 and 914 separate the paravanes from each other until the paravanes put one or more spreader lines 920, coupled between the paravanes 912 and 914, into tension. The paravanes 912 and 914 either couple directly to the spreader line 920, or as illustrated couple to the spreader line by way of spur lines 922A and 922B.

    [0034] The sensor streamers 906 are each coupled, at the ends nearest the vessel 902 (i.e., the proximal ends) to a respective lead-in cable termination 924A-F. The lead-in cable terminations 924 are coupled to or are associated with the spreader lines 920 so as to control the lateral positions of the streamers 906 with respect to each other and with respect to the vessel 902. Electrical and/or optical connections between the appropriate components in the recording system 904 and the sensors (e.g., 916A, 916B) in the streamers 906 may be made using inner lead-in cables 926A-F. Much like the tow lines 908 associated with respective winches 910, each of the lead-in cables 926 may be deployed by a respective winch or similar spooling device such that the deployed length of each lead-in cable 926 can be changed.

    [0035] Sensors 916A, 916B may include one or more instruments to detect seismic signals which may be generated by a source, such as an air gun or marine vibrator (not shown in Figure 9) and reflected by the sea floor and the geologic formations lying beneath. Such instruments may include an accelerometer 100 in accordance with at least some of the embodiments described herein sensitive to accelerations of the fluid particles induced by the acoustic seismic signal. In some embodiments, such instruments may also include a hydrophone sensitive to acoustic pressure fluctuations comprising the seismic signal. The component of velocity of such fluid particles along the axis of sensitivity of accelerometer 100 may be obtained by time integration of the output signals of the accelerometer. By suitably combining such velocity data with the output from the hydrophone, artifacts in the seismic signal from, for example, reflections of the signal from the sea surface may be substantially reduced.

    [0036] Figure 10 shows a flow chart of a method 1000 for measuring a motion of a body. In block 1002 a first cantilever portion of a sensing element is deflected in a direction opposite a first acceleration direction of the body. A second cantilever portion of the sensing element is deflected in the direction opposite the first acceleration direction of the body in block 1004. In block 1006 a first voltage is created having a first polarity, the first voltage being created across electrical leads in response to the deflecting of the cantilever portions. The first cantilever portion is deflected along a direction opposite a second acceleration direction of the body in block 1008, the second acceleration direction being opposite the first acceleration direction. In block 1010 the second cantilever portion is deflected along a direction opposite the second acceleration direction of the body, and in block 1012 a second voltage is created having a second polarity, the second polarity opposite the first polarity, the second voltage being created across leads responsive to the deflecting of the cantilever portions. Method 1000 ends at block 1014. It is noted that although the flow chart depicts the blocks of the method in serial fashion, some operations may be executed substantially simultaneously, and the serial depiction does not indicate that the described operations are necessarily to occur sequentially in time.

    [0037] A geophysical data product indicative of certain properties of the subsurface rock may be produced from the measuring motion of the body. The geophysical data product may include processed seismic or electromagnetic geophysical data and may be stored on a non-transitory, tangible computer-readable medium. The geophysical data product may be produced offshore (i.e. by equipment on a vessel) or onshore (i.e. at a facility on land) either within the United States or in another country. If the geophysical data product is produced offshore or in another country, it may be imported onshore to a facility in the United States. Once onshore in the United States, geophysical analysis, possibly including further data processing, may be performed on the data product.

    [0038] References to "one embodiment," "an embodiment," "a particular embodiment," and "some embodiments" indicate that a particular element or characteristic is included in at least one embodiment of the invention. Although the phrases "in one embodiment," "an embodiment," "a particular embodiment," and "some embodiments" may appear in various places, these do not necessarily refer to the same embodiment.

    [0039] The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, multiple accelerometers 100 may be deployed in embodiments in which the respective sensitivity axes are individually oriented to resolve different components of the applied acceleration.

    [0040] The scope of the invention is solely defined by the appended claims.


    Claims

    1. An accelerometer, comprising:

    a housing (114);

    a sensor (102) sealed within the housing (114), the sensor (102) comprising:

    a first piezoelectric element (302A) having a first polarization, the first piezoelectric element defines an upper surface;

    a second piezoelectric element (302B) having a second polarization, the second piezoelectric element defines a lower surface parallel to the upper surface of the first piezoelectric element, and the first polarization aligned with the second polarization;

    a first mounting plate (106) having a substrate of non-conductive material, the first mounting plate defines a first aperture (402);

    the first and second piezoelectric elements (302AB) extending through the first aperture (402) such that the first mounting plate (106) transects the first and second piezoelectric elements (302AB), the piezoelectric elements (302AB) define a first cantilever portion (105) on a first side of the first mounting plate (106), and the piezoelectric elements (302AB) define a second cantilever portion (105) on a second side of the first mounting plate (106) opposite the first side;

    wherein the first mounting plate (106) defines a periphery that abuts an interior wall (122) of the housing (114), the periphery being attached to the interior wall (122) of the housing (114).


     
    2. The accelerometer of claim 1, wherein the periphery of the first mounting plate (106) is attached to the interior wall (122) by solder.
     
    3. The accelerometer of claim 1 or 2, wherein the first mounting plate (106) further comprises a circular disk.
     
    4. The accelerometer of any of claims 1 to 3, further comprising conductive traces (406) disposed at the periphery of the first mounting plate (106), the conducting traces (406) soldered to the interior wall (122) of the housing (114).
     
    5. The accelerometer of any of the preceding claims:

    wherein the upper surface of the first piezoelectric element (302A) defines a first plane; and

    wherein the lower surface of the second piezoelectric element (302B) defines a second plane parallel to the first plane, wherein preferably the first mounting plate (106) defines a first surface that defines a third plane, and wherein the third plane is perpendicular to the first and second planes.


     
    6. The accelerometer of any of the preceding claims, further comprising:

    a second mounting plate (106) that defines a second aperture (402), the second mounting plate (106) spaced apart from the first mounting plate, and the second mounting plate (106) parallel to the first mounting plate (106);

    wherein the first and second piezoelectric elements (302AB) extend through the second aperture (402) such that the second mounting plate (106) transects the first and second piezoelectric elements (302); and

    wherein the first cantilever portion (105) is disposed distally to the first mounting plate (106) and the second cantilever portion (105) is disposed distally to the second mounting plate (106).


     
    7. The accelerometer of any of the preceding claims, wherein the first mounting plate (105) comprises a metallic member disposed (404) abutting the first piezoelectric element (302A), the first piezoelectric element (302A) bonded to the metallic member (404), and wherein the metallic member (404) and the first piezoelectric member (302A) are preferably bonded by soldering the metallic member (404) and a metallized layer on the upper surface of the first piezoelectric element.
     
    8. The accelerometer of any of the preceding claims, further comprising:

    a metallic member (306) comprising a sheet of conductive material, a surface of the metallic member defines a first rectangle;

    the first piezoelectric element (302A) coupled to a first side of the metallic member (306);

    the second piezoelectric element (302B) coupled to a second side of the metallic member (306), the second side opposite the first side;

    wherein the upper surface of the first piezoelectric element (302A) defines a second rectangle congruent to the first rectangle; and

    wherein the lower surface of the second piezoelectric element (302B) defines a third rectangle congruent to the first rectangle.


     
    9. The accelerometer of claim 8, further comprising:

    a second mounting plate (105) that defines a second aperture (402), the second mounting plate (105) spaced apart from the first mounting plate (105), and the second mounting plate (105) parallel to the first mounting plate (105);

    wherein the first and second piezoelectric elements (302AB) extend through the second aperture (402) such that the second mounting plate (105) transects the first and second piezoelectric elements (302AB);

    wherein the first cantilever portion (105) is disposed distally to the first mounting plate (106) and the second cantilever portion (105) is disposed distally to the second mounting plate (106); and

    wherein the first and second mounting plates (106) are constructed of a substrate of non-conductive material; and preferably

    wherein the housing (114) further defines a, first end, a second end opposite the first end, and an interior volume (117), and preferably further comprising:

    a cap (116) coupled to and occluding the first end of the housing (114);

    the mounting plates (106), piezoelectric elements (302), and metallic member disposed (306) within the interior volume (117);

    an end cap (110) coupled to and partially occluding the second end;

    a first electrical lead (112) that extends through the end cap (110), the first electrical lead (112) electrically coupled to the first piezoelectric element (302A); and

    a second electrical lead (112) that extends through the end cap (110), the second electrical lead (112) electrically coupled to the second piezoelectric element (302B).


     
    10. A streamer comprising:

    a cable (906);

    a hydrophone (916) coupled to the cable (906), the hydrophone (916) sensitive to acoustic pressure fluctuations; and

    an accelerometer (100, 916) according to any of the preceding claims coupled to the cable (906).


     
    11. An accelerometer (100) according to any of claims 1 to 9 or a streamer (906) according to claim 10, wherein the accelerometer (100) is configured to produce an electrical signal in response to an acceleration component in a direction of sensitivity perpendicular to the upper surface, and the accelerometer configured to produce substantially no electrical signal in response to pressure acting on the accelerometer.
     
    12. A method of using an accelerometer (100, 916) as claimed in claims 1 to 9, the method comprising:

    measuring motion of a body (1000) by deflecting (1002, 1004) the cantilever portions (105) of the piezoelectric elements (302AB) of the accelerometer (100, 916) and thereby creating a first voltage responsive to the deflecting (1006), the deflecting (1002, 1004) of the cantilever portions (105) along directions opposite directions of acceleration of the body (1000);

    conveying forces associated with increased ambient pressure through the first mounting plate (106) to the piezoelectric elements (302AB), wherein the mounting plate is configured such that counter-polarized charges of the piezoelectric elements (302AB) associated with the forces substantially cancel.


     
    13. The method of claim 12, wherein measuring the motion of the body and conveying forces further comprises supporting the sensing element by way of the mounting plate medially disposed on said sensing element.
     
    14. The method of claim 12 or 13, further comprising towing a streamer in a body of water, wherein the cantilever portions (1002, 1004) of piezoelectric elements (302AB) are disposed on the streamer, wherein the motion of the body comprises motion of a fluid particle, the method further comprising producing a geophysical data product from the measured motion of the fluid particle indicative of certain properties of subsurface rock below the body of water.
     


    Ansprüche

    1. Beschleunigungsmesser, der Folgendes umfasst:

    ein Gehäuse (114);

    einen Sensor (102), der innerhalb des Gehäuses (114) abgedichtet ist, wobei der Sensor (102) Folgendes umfasst:

    ein erstes piezoelektrisches Element (302A), das eine erste Polarisation aufweist, wobei das erste piezoelektrische Element eine obere Oberfläche definiert;

    ein zweites piezoelektrisches Element (302B), das eine zweite Polarisation aufweist, wobei das zweite piezoelektrische Element eine untere Oberfläche parallel zu der oberen Oberfläche des ersten piezoelektrischen Elements definiert und die erste Polarisation mit der zweiten Polarisation ausgerichtet ist;

    eine erste Montageplatte (106), die ein Substrat aus nicht leitendem Material aufweist, wobei die erste Montageplatte eine erste Öffnung (402) definiert;

    wobei sich das erste und das zweite piezoelektrische Element (302AB) durch die erste Öffnung (402) derart erstrecken, dass die erste Montageplatte (106) das erste und das zweite piezoelektrische Element (302AB) schneidet, wobei die piezoelektrischen Elemente (302AB) einen ersten Auslegerabschnitt (105) auf einer ersten Seite der ersten Montageplatte (106) definieren, und die piezoelektrischen Elemente (302AB) einen zweiten Auslegerabschnitt (105) auf einer der ersten Seite gegenüberliegenden zweiten Seite der ersten Montageplatte (106) definieren;

    wobei die erste Montageplatte (106) einen Umfang definiert, der an einer Innenwand (122) des Gehäuses (114) anliegt, wobei der Umfang an der Innenwand (122) des Gehäuses (114) befestigt ist.


     
    2. Beschleunigungsmesser nach Anspruch 1, wobei der Umfang der ersten Montageplatte (106) an der Innenwand (122) durch Löten befestigt ist.
     
    3. Beschleunigungsmesser nach Anspruch 1 oder 2, wobei die erste Montageplatte (106) ferner eine Kreisscheibe umfasst.
     
    4. Beschleunigungsmesser nach einem der Ansprüche 1 bis 3, der ferner Leiterbahnen (406) umfasst, die an dem Umfang der ersten Montageplatte (106) angeordnet sind, wobei die Leiterbahnen (406) mit der Innenwand (122) des Gehäuses (114) verlötet sind.
     
    5. Beschleunigungsmesser nach einem der vorhergehenden Ansprüche:

    wobei die obere Oberfläche des ersten piezoelektrischen Elements (302A) eine erste Ebene definiert; und

    wobei die untere Oberfläche des zweiten piezoelektrischen Elements (302B) eine zweite Ebene parallel zur ersten Ebene definiert, wobei vorzugsweise die erste Montageplatte (106) eine erste Oberfläche definiert, die eine dritte Ebene definiert, und wobei die dritte Ebene senkrecht zu der ersten und der zweiten Ebene ist.


     
    6. Beschleunigungsmesser nach einem der vorhergehenden Ansprüche, der ferner Folgendes umfasst:

    eine zweite Montageplatte (106), die eine zweite Öffnung (402) definiert, wobei die zweite Montageplatte (106) von der ersten Montageplatte beabstandet ist und die zweite Montageplatte (106) parallel zu der ersten Montageplatte (106) ist;

    wobei sich das erste und das zweite piezoelektrische Element (302AB) derart durch die zweite Öffnung (402) erstrecken, dass die zweite Montageplatte (106) das erste und das zweite piezoelektrische Element (302) schneidet; und

    wobei der erste Auslegerabschnitt (105) distal zu der ersten Montageplatte (106) angeordnet ist und der zweite Auslegerabschnitt (105) distal zu der zweiten Montageplatte (106) angeordnet ist.


     
    7. Beschleunigungsmesser nach einem der vorhergehenden Ansprüche, wobei die erste Montageplatte (105) ein metallisches Element umfasst, das angeordnet (404) ist, um an das erste piezoelektrische Element (302A) anzuliegen, wobei das erste piezoelektrische Element (302A) an das metallische Element (404) gebunden ist, und wobei das metallische Element (404) und das erste piezoelektrische Element (302A) vorzugsweise durch Verlöten des metallischen Elements (404) und einer metallisierten Schicht auf der oberen Oberfläche des ersten piezoelektrischen Elements verbunden werden.
     
    8. Beschleunigungsmesser nach einem der vorhergehenden Ansprüche, der ferner Folgendes umfasst:

    ein metallisches Element (306), das eine Bahn aus leitendem Material umfasst, wobei eine Oberfläche des metallischen Elements ein erstes Rechteck definiert;

    wobei das erste piezoelektrische Element (302A) mit einer ersten Seite des metallischen Elements (306) gekoppelt ist;

    wobei das zweite piezoelektrische Element (302B) mit einer zweiten Seite des metallischen Elements (306) gekoppelt ist, wobei die zweite Seite der ersten Seite gegenüberliegt;

    wobei die obere Oberfläche des ersten piezoelektrischen Elements (302A) ein zweites Rechteck definiert, das kongruent zu dem ersten Rechteck ist; und

    wobei die untere Oberfläche des zweiten piezoelektrischen Elements (302B) ein drittes Rechteck definiert, das kongruent zu dem ersten Rechteck ist.


     
    9. Beschleunigungsmesser nach Anspruch 8, der ferner Folgendes umfasst:

    eine zweite Montageplatte (105), die eine zweite Öffnung (402) definiert, wobei die zweite Montageplatte (105) von der ersten Montageplatte (105) beabstandet ist und die zweite Montageplatte (105) parallel zu der ersten Montageplatte (105) ist;

    wobei sich das erste und das zweite piezoelektrische Element (302AB) durch die zweite Öffnung (402) derart erstrecken, dass die zweite Montageplatte (105) das erste und das zweite piezoelektrische Element (302AB) schneidet;

    wobei der erste Auslegerabschnitt (105) distal zu der ersten Montageplatte (106) angeordnet ist und der zweite Auslegerabschnitt (105) distal zu der zweiten Montageplatte (106) angeordnet ist; und

    wobei die erste und die zweite Montageplatte (106) aus einem Substrat aus nicht leitendem Material hergestellt sind; und vorzugsweise

    wobei das Gehäuse (114) ferner ein erstes Ende, ein dem ersten Ende gegenüberliegendes zweites Ende und ein Innenvolumen (117) definiert und vorzugsweise ferner Folgendes umfasst:

    eine Kappe (116), die mit dem ersten Ende des Gehäuses (114) gekoppelt ist und dieses verdeckt;

    die Montageplatten (106), piezoelektrische Elemente (302) und das metallische Element (306), das innerhalb des Innenvolumens (117) angeordnet ist;

    eine Endkappe (110), die mit dem zweiten Ende gekoppelt ist und dieses teilweise verdeckt;

    eine erste elektrische Leitung (112), die sich durch die Endkappe (110) erstreckt, wobei die erste elektrische Leitung (112) mit dem ersten piezoelektrischen Element (302A) elektrisch gekoppelt ist; und

    eine zweite elektrische Leitung (112), die sich durch die Endkappe (110) erstreckt, wobei die zweite elektrische Leitung (112) mit dem zweiten piezoelektrischen Element (302B) elektrisch gekoppelt ist.


     
    10. Streamer, der Folgendes umfasst:

    ein Kabel (906);

    ein Hydrophon (916), das mit dem Kabel (906) gekoppelt ist, wobei das Hydrophon (916) gegenüber akustischen Druckschwankungen empfindlich ist; und

    einen Beschleunigungsmesser (100, 916) nach einem der vorhergehenden Ansprüche, der mit dem Kabel (906) gekoppelt ist.


     
    11. Beschleunigungsmesser (100) nach einem der Ansprüche 1 bis 9 oder ein Streamer (906) nach Anspruch 10, wobei der Beschleunigungsmesser (100) konfiguriert ist, um als Reaktion auf eine Beschleunigungskomponente in einer senkrecht zu der oberen Oberfläche liegenden Empfindlichkeitsrichtung ein elektrisches Signal zu erzeugen und der Beschleunigungsmesser konfiguriert sind, um im Wesentlichen kein elektrisches Signal als Reaktion auf den auf den Beschleunigungsmesser wirkenden Druck zu erzeugen.
     
    12. Verfahren zum Verwenden eines Beschleunigungsmessers (100, 916) nach den Ansprüchen 1 bis 9, wobei das Verfahren Folgendes umfasst:

    Messen einer Bewegung eines Körpers (1000) durch Ablenken (1002, 1004) der Auslegerabschnitte (105) der piezoelektrischen Elemente (302AB) des Beschleunigungsmessers (100, 916) und dadurch Erzeugen einer ersten Spannung, die auf das Ablenken (1006) reagiert, wobei das Ablenken (1002, 1004) der Auslegerabschnitte (105) entlang Richtungen ist, die Beschleunigungsrichtungen des Körpers (1000) entgegengesetzt sind;

    Fördern von Kräften, die erhöhtem Umgebungsdruck zugeordnet sind, durch die erste Montageplatte (106) zu den piezoelektrischen Elementen (302AB), wobei die Montageplatte derart konfiguriert ist, dass sich die gegenpolarisierten Ladungen der piezoelektrischen Elemente (302AB), die den Kräften zugeordnet sind, im Wesentlichen aufheben.


     
    13. Verfahren nach Anspruch 12, wobei das Messen der Bewegung des Körpers und der Förderkräfte ferner ein Stützen des Erfassungselements mittels der auf dem Erfassungselement medial angeordneten Montageplatte umfasst.
     
    14. Verfahren nach Anspruch 12 oder 13, das ferner ein Schleppen eines Streamers in einem Gewässer umfasst, wobei die Auslegerabschnitte (1002, 1004) von piezoelektrischen Elementen (302AB) auf dem Streamer angeordnet sind, wobei die Bewegung des Körpers die Bewegung eines Fluidpartikels umfasst, wobei das Verfahren ferner das Erzeugen eines geophysikalischen Datenprodukts aus der gemessenen Bewegung des Fluidpartikels umfasst, das bestimmte Eigenschaften von unterirdischem Gestein unter dem Gewässer anzeigt.
     


    Revendications

    1. Accéléromètre, comprenant :

    un boîtier (114) ;

    un capteur (102) scellé à l'intérieur du boîtier (114), le capteur (102) comprenant :

    un premier élément piézoélectrique (302A) ayant une première polarisation, le premier élément piézoélectrique définissant une surface supérieure ;

    un second élément piézoélectrique (302B) ayant une seconde polarisation, le second élément piézoélectrique définissant une surface inférieure parallèle à la surface supérieure du premier élément piézoélectrique, et la première polarisation étant alignée avec la seconde polarisation ;

    une première plaque de montage (106) ayant un substrat en matériau non conducteur, la première plaque de montage définissant une première ouverture (402) ;

    les premier et second éléments piézoélectriques (302AB) s'étendant à travers la première ouverture (402) de telle sorte que la première plaque de montage (106) coupe transversalement les premier et second éléments piézoélectriques (302AB), les éléments piézoélectriques (302AB) définissant une première partie en porte-à-faux (105) sur un premier côté de la première plaque de montage (106), et les éléments piézoélectriques (302AB) définissant une seconde partie en porte-à-faux (105) sur un second côté de la première plaque de montage (106) opposé au premier côté ;

    dans lequel la première plaque de montage (106) définit une périphérie qui vient en appui contre une paroi interne (122) du boîtier (114), la périphérie étant fixée à la paroi interne (122) du boîtier (114).


     
    2. Accéléromètre selon la revendication 1, dans lequel la périphérie de la première plaque de montage (106) est fixée à la paroi interne (122) par soudure.
     
    3. Accéléromètre selon la revendication 1 ou 2, dans lequel la première plaque de montage (106) comprend en outre un disque circulaire.
     
    4. Accéléromètre selon l'une quelconque des revendications 1 à 3, comprenant en outre des traces conductrices (406) disposées à la périphérie de la première plaque de montage (106), les traces conductrices (406) étant soudées à la paroi interne (122) du boîtier (114).
     
    5. Système selon l'une quelconque des revendications précédentes :

    dans lequel la surface supérieure du premier élément piézoélectrique (302A) définit un premier plan ; et

    dans lequel la surface inférieure du second élément piézoélectrique (302B) définit un deuxième plan parallèle au premier plan, dans lequel de préférence la première plaque de montage (106) définit une première surface qui définit un troisième plan, et dans lequel le troisième plan est perpendiculaire aux premier et deuxième plans.


     
    6. Accéléromètre selon l'une quelconque des revendications précédentes, comprenant en outre :

    une seconde plaque de montage (106) qui définit une seconde ouverture (402), la seconde plaque de montage (106) étant espacée de la première plaque de montage, et la seconde plaque de montage (106) étant parallèle à la première plaque de montage (106) ;

    dans lequel les premier et second éléments piézoélectriques (302AB) s'étendent à travers la seconde ouverture (402) de telle sorte que la seconde plaque de montage (106) coupe transversalement les premier et second éléments piézoélectriques (302) ; et

    dans lequel la première partie en porte-à-faux (105) est disposée distalement par rapport à la première plaque de montage (106) et la seconde partie en porte-à-faux (105) est disposée distalement par rapport à la seconde plaque de montage (106).


     
    7. Accéléromètre selon l'une quelconque des revendications précédentes, dans lequel la première plaque de montage (105) comprend un organe métallique disposé (404) en appui contre le premier élément piézoélectrique (302A), le premier élément piézoélectrique (302A) étant lié à l'organe métallique (404), et dans lequel l'organe métallique (404) et le premier élément piézoélectrique (302A) sont de préférence liés par brasage de l'organe métallique (404) et d'une couche métallisée sur la surface supérieure du premier élément piézoélectrique.
     
    8. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre :

    un organe métallique (306) comprenant une feuille de matériau conducteur, une surface de l'organe métallique définissant un premier rectangle ;

    le premier élément piézoélectrique (302A) accouplé à un premier côté de l'organe métallique (306) ;

    le second élément piézoélectrique (302B) accouplé à un second côté de l'organe métallique (306), le second côté étant opposé au premier côté ;

    dans lequel la surface supérieure du premier élément piézoélectrique (302A) définit un deuxième rectangle conforme au premier rectangle ; et

    dans lequel la surface inférieure du second élément piézoélectrique (302B) définit un troisième rectangle congru au premier rectangle.


     
    9. Procédé selon la revendication 8, comprenant en outre :

    une seconde plaque de montage (105) qui définit une seconde ouverture (402), la seconde plaque de montage (105) étant espacée de la première plaque de montage (105), et la seconde plaque de montage (105) étant parallèle à la première plaque de montage (105) ;

    dans lequel les premier et second éléments piézoélectriques (302AB) s'étendent à travers la seconde ouverture (402) de telle sorte que la seconde plaque de montage (105) coupe transversalement les premier et second éléments piézoélectriques (302AB) ;

    dans lequel la première partie en porte-à-faux (105) est disposée distalement par rapport à la première plaque de montage (106) et la seconde partie en porte-à-faux (105) est disposée distalement par rapport à la seconde plaque de montage (106) ; et

    dans lequel les première et seconde plaques de montage (106) sont construites d'un substrat en matériau non conducteur ; et de préférence

    dans lequel le boîtier (114) définit en outre une première extrémité, une seconde extrémité opposée à la première extrémité et un volume interne (117), et comprenant en outre de préférence :

    une coiffe (116) accouplée à et bouchant la première extrémité du boîtier (114) ;

    les plaques de montage (106), les éléments piézoélectriques (302) et l'organe métallique étant disposés (306) à l'intérieur du volume interne (117) ;

    une coiffe d'extrémité (110) accouplée à et bouchant partiellement la seconde extrémité ;

    un premier conducteur électrique (112) qui s'étend à travers la coiffe d'extrémité (110), le premier conducteur électrique (112) étant couplé électriquement au premier élément piézoélectrique (302A) ; et

    un second conducteur électrique (112) qui s'étend à travers la coiffe d'extrémité (110), le second fil électrique (112) étant couplé électriquement au second élément piézoélectrique (302B).


     
    10. Flûte comprenant :

    un câble (906) ;

    un hydrophone (916) accouplé au câble (906), l'hydrophone (916) étant sensible aux fluctuations de pression acoustique ; et

    un accéléromètre (100, 916) selon l'une quelconque des revendications précédentes accouplé au câble (906).


     
    11. Accéléromètre (100) selon l'une quelconque des revendications 1 à 9 ou flûte (906) selon la revendication 10, dans lequel l'accéléromètre (100) est configuré pour produire un signal électrique en réponse à une composante d'accélération dans une direction de sensibilité perpendiculaire à la surface supérieure, et l'accéléromètre étant configuré pour ne produire sensiblement aucun signal électrique en réponse à la pression agissant sur l'accéléromètre.
     
    12. Procédé d'utilisation d'un accéléromètre (100, 916) selon les revendications 1 à 9, le procédé comprenant :

    la mesure du mouvement d'un corps (1000) en déviant (1002, 1004) les parties en porte-à-faux (105) des éléments piézoélectriques (302AB) de l'accéléromètre (100, 916) et en créant ainsi une première tension en réponse à la déviation (1006), la déviation (1002, 1004) des parties en porte-à-faux (105) le long de directions opposées de directions d'accélération du corps (1000) ;

    le transport de forces associées à une pression ambiante accrue à travers la première plaque de montage (106) vers les éléments piézoélectriques (302AB), la plaque de montage étant conçue de telle sorte que les charges contre-polarisées des éléments piézoélectriques (302AB) associées aux forces s'annulent sensiblement.


     
    13. Procédé selon la revendication 12, dans lequel la mesure du mouvement du corps et des forces de transport comprend en outre le support de l'élément de détection au moyen de la plaque de montage disposée médialement sur ledit élément de détection.
     
    14. Procédé selon la revendication 12 ou 13, comprenant en outre le remorquage d'une flûte dans un plan d'eau, dans lequel les parties en porte-à-faux (1002, 1004) d'éléments piézoélectriques (302AB) sont disposées sur la flûte, dans lequel le mouvement du corps comprend le mouvement d'une particule de fluide, le procédé comprenant en outre la production d'un produit de données géophysiques à partir du mouvement mesuré de la particule de fluide indiquant certaines propriétés de la roche souterraine sous le plan d'eau.
     




    Drawing



































    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description