Built-in hydrophone in liquid conducting elements

Abstract

An embedded hydrophone sensor in a hydraulic body such as pipe, fitting, or flow meter (PIPE) that includes a thinned "pipe" wall membrane of radius R, that has a profile that provides sufficient flexural deflection under pressure with effective thickness t_pipe. A piezo-electric element connected to the pipe membrane using a glue or mechanical means, while the piezo membrane thickness should be less than pipe_membrane thickness multiplied by (maximum_strain_Piezo / maximum_strain_Pipe).

Description

BUILT-IN HYDROPHONE IN LIQUID CONDUCTING ELEMENTSBACKGROUND OF THE INVENTIONCross reference to other patent applications{0001 { The present invention claims priority to provisional US patent application No.63 / 760,920 filed on 20 February 2025, the entire content thereof being incorporated therein.Field Of The Invention

[0002] The present invention relates to built-in hydrophone in liquid conducting elements such as pipes and fittings. More precisely, the present invention relates to a hydrophone sensor in a hydraulic body, an assembly of a hydrophone sensor and of a hydraulic body to form an embedded hydrophone sensor, and to a method for manufacturing an embedded hydrophone.Brief Description Of The Related Art[0003 { Hydrophones are sensitive acoustic sensors designed to measure acoustic waves in liquids. Hydrophones are used for acoustic communication, measuring acoustic signals in the water to characterize the flow, turbulence and leak detection. Integrating hydrophones into liquid conducting elements such as pipes and fitting can be an effective way to add functionality to the existing instruments or piping elements. For example adding a hydrophone to ultrasonic water meters that use through the pipe flow measurement, or adding a hydrophone to any water conducting element.

[0004] One object of the present invention is to provide a solution for integrating hydrophone, without jeopardizing the sensitivity of the hydrophone.SUMMARY OF THE INVENTION0005^ In a preferred embodiment, the present invention is an embedded hydrophone sensor in a hydraulic body such as pipe, fitting, or flow meter (PIPE) according to claim 1. The hydraulic body includes a thinned wall membrane of radius R, that has a profile that provides sufficient flexural deflection under pressure with effective wall thickness. The hydrophone sensor has a piezo-electric element connectable to the pipe membrane using a glue or mechanical means.The piezo-electric element can be a piezo electric membrane having a piezo membrane thickness be less than wall membrane thickness multiplied by a ratio of a maximum strain the piezo electric membrane is capable to bear over a maximum strain the wall membrane is capable to bear.The piezo-electric membrane can be attached to the wall membrane with a glue that fills in the gaps between the piezo-electric membrane and the wall membrane, having sufficient strength to transmit the bending force from the wall membrane to the piezoelectric membrane.The maximum sensitivity is achieved by choosing the piezo membrane thickness equal to the wall membrane thickness multiplied by a ratio of a maximum strain the piezo electric membrane is capable to bear over a maximum strain the wall membrane is capable to bear, with sufficient safety coefficient to prevent the piezo cracking under strain.The present invention also proposes an hydrophone assembly comprising an hydrophone sensor and hydraulic body section, wherein the hydraulic body section comprises a housing formed in the hydraulic body section with a bottom wall, the bottom wall being a pipe wall membrane with a pipe wall membrane thickness.The hydrophone sensor comprises a piezo-electric element, wherein the piezoelectric element is a bending mode piezo electric element in form of a piezo electric membrane, and the piezo electric membrane is housed in the housing and connected to the pipe wall membrane using a piezo attachment, and the piezo electric membrane has a piezo electric membrane thickness less than or equal to the pipe wall membranethickness multiplied by a ratio of a maximum strain that the piezo electric membrane can bear before breaking over a maximum strain that the pipe wall membrane can bear before breaking.[GOH] In an aspect, the hydrophone assembly comprises an external shielding element covering the piezo electric membrane to shield the piezo electric membrane, wherein the external shielding element is connected to the hydraulic body.The hydrophone assembly can further comprise an internal shielding element interposed between the hydraulic body wall and the piezo electric membrane, wherein the internal shielding element is connected to the external shielding to the mesh from outside, in particular a shielding mesh in the piezo fixation element.The present disclosure also proposes a method of manufacturing an embedded hydrophone sensor in a hydraulic body section, comprising: providing a hydraulic body section with a housing having a bottom wall, wherein the bottom wall is a pipe wall membrane with a pipe wall membrane thickness, attaching a bending mode piezo electric element to the pipe wall membrane, wherein the bending mode piezo electric element is a piezo electric membrane with a piezo electric membrane thickness based on the pipe wall membrane thickness, and wherein the piezo electric membrane thickness is set less than or equal to the pipe wall membrane thickness multiplied by a ratio of a maximum strain that the piezo electric membrane can bear over a maximum strain that the pipe wall membrane can bear.GH] In an aspect, the piezo electric membrane is glued to the pipe wall membrane, and the piezo membrane thickness t2 is set less than or equal to the pipe wall membrane thickness multiplied by the ratio of the maximum strain that the piezo membrane can bear over the maximum strain that the pipe membrane can bear, multiplied by a factor k representing the deflection ratio between the piezo-membrane and the pipe wall membrane.In an aspect, the method further comprises the step of shielding the piezo electric membrane from electromagnetic fields, comprising covering the piezo electric membrane with an external shielding plate and connecting the hydraulic body to the external shielding plate.

[0014] An internal shielding element can be interposed between the hydraulic body wall and the piezo electric membrane, and the internal shielding element be connected to the external shielding element.

[0017] Shielding allows protecting form unwanted electromagnetic signals.

[0012] The method allows manufacturing an embedded hydrophone with high sensitivity of the hydrophone within relatively small sensor area.

[0019] Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a preferable embodiments and implementations. The present invention is also capable of other and different embodiments and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0929] For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description and the accompanying drawings, in which:

[0021] FIG. 1 illustrates pressure on a pipe element causing bending.

[0022] FIG. 2 illustrates an exploded assembly of a hydraulic body and a piezo element.

[0023] FIG. 3 illustrates an embedded hydrophone assembly with a metal hydraulic body element and a shielding configuration.

[0024] FIG. 4 illustrates an embedded hydrophone assembly with a plastic hydraulic body element and a shielding configuration.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The preferred embodiments of the inventions are described with reference to the drawings.

[0002] To create a sensitive hydrophone one needs a large area of the piezo-electric sensor or a significant strain of the piezo-electric element. Total electric charge Q is calculated as follows:Q=d*e(r) / A, withQ the total electric charge (Coulombs),d the piezoelectric charge coefficient (C / m2). For bending mode, the appropriate coefficient is used, eg. dsi or d33,e(r) strain at position r,A is the electrode area.

[0027] A first strategy to create a sensitive hydrophone is to increase the strain. The solution is to use a bending mode piezo-electric element coupled to a pipe element that can bend.

[0028] The challenge is to make a pipe element that is flexible and still strong enough to withstand the hydrostatic pressure that is required for the hydraulic body. The pressure waves cause the pipe element to bend locally and cause bending of the piezoelectric element coupled thereto and generate electric signal proportional to the pressure wave signal.

[0029] FIG. 1 illustrates a wall 10 of a pipe element with pressure on the pipe element causing bending of the pipe wall 10. The pipe wall is a pipe membrane has a profile that provides sufficient flexural deflection under pressure and has an effective pipe thickness tl.

[0030] The example of Fig. 1 is a pipe, but this is not limiting, and other hydraulic bodies in which hydrophones are to be built-in are also contemplated, such as fittings.

[0031] FIG. 2 illustrates modification of a hydraulic body section of a hydraulic body 1 for integration of a piezo element 20 within the hydraulic body 1.|0032] On FIG. 2, the hydraulic body section is a rectangular pipe section that is typical for ultrasonic water meter.§0033] However, the hydraulic body 1 can be of any shape, in flow meters it can be rectangular, or oval. In other cases, it can be round.§0034] To integrate the piezo element 20 into the hydraulic body 1, a housing 25 is the hydraulic body section comprises a housing 25 formed in the hydraulic body section with a bottom wall. The bottom wall is a pipe wall membrane 10 with a pipe membrane thickness.§0033] The piezo electric element is a bending mode piezo electric element 20, also called piezo electric membrane, attached to the pipe wall membrane 10.§0036] It is understood that the pipe wall membrane 10 requires an optimal profile for maximum flexibility and sufficient strength. The profile might not be the same as the profile of the piezo element 20.

[0037] The piezo electric element 20 can be attached to the pipe membrane 10 with a flexible adhesive 30 that fills in the gaps between the piezo electric membrane and the pipe membrane.0038] There is a need to apply flexible adhesive 30 that will transmit the strain from the pipe wall membrane 10 to the piezo electric element 20. This means that the flexible adhesive 30 should have sufficient strength to transmit the bending force from the pipe wall membrane to the piezo-electric membrane.039 The flexible adhesive 30 can be MS polymer or Polyurethane glue that are strong and flexible.0040] One challenge of the built-in hydrophone is to achieve high sensitivity of the hydrophone within relatively small sensor area. The piezo-electric membrane is glued to the thinned pipe wall section that have different elastic constant and different strain to break.10041] The pipe wall membrane 10 is a thinned pipe wall section and has a pipe membrane thickness tl . The piezo-electric element 20 is a bending mode piezo electric element, also referred to as a piezo electric membrane.In one example, the piezo electric element is a disc shaped membrane. The piezoelectric membrane has a piezo electric membrane thickness t2. The piezo electric membrane thickness t2 increases the electric charge generated by bending deflection of the membrane, but also increases the strain under bending.

[8043] There is a need to match the Piezo-electric membrane thickness t2 to the pipe wall membrane thickness tl to get high sensitivity and not to break the piezo electric membrane 20.

[8044] The proposed design enables optimal performance of the embedded hydrophone. The charge of the piezo electric membrane 20 generated under deflection is given by: Q=d31*s*A Equation 1.-Q - generated charge-d31 - piezo-electric constant-£ - strain- A areaf 0G4S| For a given membrane, the strain is a function of the thickness and radius of the membrane. In case of a flat membrane, the strain is given by:where: t = membrane thicknessX= deflection in the center of the membraneR= membrane radius[fW46] Typically the pipe wall membrane thickness tl is calculated and designed to withstand the maximum hydrostatic pressure that is required for the hydraulic body / pipe.[ 04'7] If, for the flexible adhesive 30, a thin layer of glue that does not stretch significantly under the bending is used, the deflection “X” is the same for pipe wall membrane 10 and for the Piezo electric membrane 20.[0048^ The maximum strain of the piezo electric membrane is about 0.1%, while the brass maximum strain of the pipe section in the elastic region is 0.3% and for Polyphenylene Sulfide PPS is 1%. Therefore, we can calculate a thickness t2 of the piezo-electric membrane 20 given the pipe wall membrane thickness tl and the maximum strain that each material can bear.

[0049] The piezo electric membrane thickness t2 should be less than the pipe wall membrane thickness tl multiplied by(maximum strain Piezo / maximum strain Pipe) Equation 3.where maximum strain Pipe is the maximum strain that the pipe membrane is designed for and maximum strain_piezo is the maximum strain that the piezo membrane can bear. The skilled person understands that the maximum strain that the piezo electric membrane / pipe membrane can bear means the maximum strain before breaking. For example, if the pipe is made of brass, the maximum strain before breaking is 0.3 %, and for a membrane made of PZT, the maximum strain before breaking is 0.1 %.[OOSO] If, for the flexible adhesive 30, a thick adhesive layer is used between the pipe wall membrane 10 and the piezo-electric membrane 20, as shown on Figure 2, the deflection of the piezo-electric membrane 20 will be smaller than deflection of the pipe wall membrane 10, as the adhesive layer 30 will stretch. In this case the equation 3 above is modified with a factor k that represents the deflection ratio between the piezo-membrane and the pipemembrane.f Slf It results that the piezo thickness t2 should be less than pipe wall membrane thickness tl multiplied by(k* maximum strain Piezo / maximum strain Pipe) Equation 4.

[0052] In case that the piezo-electric membrane 20 has a different cross section shape relative to the pipe-wall-membrane 10, such as for example a flat piezo -membrane and cylindrical pipe-wall membrane, the design criteria for the piezo-electric thickness will be guided by maximum strain that the piezo-electric membrane can bear under maximal pressure.

[8053] As piezo-electric elements are very sensitive to electric interference, it is very important to shield the piezo electric membrane 20, in particular to shield against electromagnetic fields.

[9054] In case of metal hydraulic bodies, such a metal pipe, the shielding can be configured as shown in FIG. 3. The piezo electric membrane 20 is isolated from the metal pipe with a shielding plate 50, while the shielding plate 50 is connected to the hydraulic body.

[8055] In other words, the shielding is an external shielding 50, and the hydraulic body and the external shielding plate creates a Faraday cage.

[8058] In case of a plastic hydraulic body, the shielding can be similar to the one described in FIG. 3, or having a shielding plate around the whole pipe circular shape.

[0057] In case of plastic hydraulic body, it is also proposed to add an internal electromagnetic shielding element 51 between the hydraulic body membrane and the piezo electric membrane, and to connect the external shielding to the mesh from outside. This is illustrated in Fig.4 showing an example of internal electromagnetic shielding element. In this case, the internal electromagnetic shielding element 51 is a shielding mesh in the piezo fixation such as the glue between the hydraulic body wall and the piezo electric membrane 20.

[8055] The embedded hydrophone can be connected to the external amplifier, preferable transimpedance charge-pump amplifier. Alternatively the amplifier can be installed near the piezo element under the shield. The hydrophone can be connected via piezo wires 58 from the piezo electric membrane 20. The piezo wires 58 are protected by a metal shield mesh 55, coupled to the shielding plate 50.

[0059] The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended thatthe scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.

Claims

CLAIMSWhat is claimed is:1 , An embedded hydrophone sensor in a hydraulic body section of a hydraulic body such as pipe, fitting, or flow meter (PIPE), the hydraulic body section including a pipe wall membrane having a pipe wall membrane thickness,wherein the hydrophone sensor comprises a piezo-electric element connectable to the pipe wall membrane using a piezo attachment, wherein the piezo-electric element is a bending mode piezo electric element in form of a piezo electric membrane, and wherein the piezo electric membrane has a piezo electric membrane thickness less than or equal to the pipe wall membrane thickness multiplied by a ratio of a maximum strain that the piezo electric membrane can bear over a maximum strain that the pipe wall membrane can bear.The embedded hydrophone sensor according to claim 1 , where the piezo attachment is a glue to fill in gaps between the piezoelectric membrane and the pipe wall membrane, having sufficient strength to transmit the bending force from the pipe wall membrane to the piezo-electric membrane.The embedded hydrophone sensor according to claim 1, where a maximum sensitivity is achieved by setting the piezo electric membrane thickness equal to the pipe wall membrane thickness multiplied by a ratio of a maximum strain that the piezo electric membrane can bear over a maximum strain that the pipe wall membrane can bear.4, An hydrophone assembly comprising an hydrophone sensor and hydraulic body section, wherein the hydraulic body section comprises a housing formed in the hydraulicbody section with a bottom wall, the bottom wall being a pipe wall membrane with a pipe wall membrane thickness,wherein the hydrophone sensor comprises a piezo-electric element, wherein the piezoelectric element is a bending mode piezo electric element in form of a piezo electric membrane, and the piezo electric membrane is housed in the housing and connected to the pipe wall membrane using a piezo attachment, andwherein the piezo electric membrane has a piezo electric membrane thickness less than or equal to the pipe wall membrane thickness multiplied by a ratio of a maximum strain that the piezo electric membrane can bear before breaking over a maximum strain that the pipe wall membrane can bear before breaking.The hydrophone assembly according to claim 4, comprising an external shielding element covering the piezo electric membrane to shield the piezo electric membrane, wherein the external shielding element is connected to the hydraulic body.A, The hydrophone assembly according to claim 5, further comprising an internal shielding element interposed between the hydraulic body wall and the piezo electric membrane, wherein the internal shielding element is connected to the external shielding to the mesh from outside, in particular a shielding mesh in the piezo fixation element.7.. A method of manufacturing an embedded hydrophone sensor in a hydraulic body section, comprising:providing a hydraulic body section with a housing having a bottom wall, wherein the bottom wall is a pipe wall membrane with a pipe wall membrane thickness, attaching a bending mode piezo electric element to the pipe wall membrane, wherein the bending mode piezo electric element is a piezo electric membrane with a piezo electric membrane thickness based on the pipe wall membrane thickness,wherein the piezo electric membrane thickness is set less than or equal to the pipe wall membrane thickness multiplied by a ratio of a maximum strain that the piezo electric membrane can bear over a maximum strain that the pipe wall membrane can bear.

8. The method according to claim 7, wherein the piezo electric membrane is glued to the pipe wall membrane, and the piezo membrane thickness t2 is set less than or equal to the pipe wall membrane thickness multiplied by the ratio of the maximum strain that the piezo membrane can bear over the maximum strain that the pipe membrane can bear, multiplied by a factor k representing the deflection ratio between the piezo-membrane and the pipe wall membrane.

9. The method according to claim 7 or 8, comprising the step of shielding the piezo electric membrane from electromagnetic fields, comprising covering the piezo electric membrane with an external shielding plate and connecting the hydraulic body to the external shielding plate.10.. The method according to claim 9, comprising the step of interposing an internal shielding element between the hydraulic body wall and the piezo electric membrane, and connecting the internal shielding element to the external shielding element.

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