Method for defining the geometry and arrangement of a plurality of electrodes for a piezoelectric device and associated piezoelectric device

Abstract

The present invention relates to a method (100) implemented by computer for defining a geometry and an arrangement of a plurality of electrodes (El-En) for a piezoelectric device (1) installable on an installation area (Z) of a surface (F), said method (100) comprising: obtaining (101) one or more images (Sl-Sn) of the spatial distribution of the wave field of an ultrasonic wave on said installation area (Z), wherein said ultrasonic wave originates from a point (P) on said surface (F) located at a distance (D) from said installation area (Z); comparing (102) the wave field value of the respective pixels of said one or more images (Sl-Sn) with an upper threshold (Thmax) or a lower threshold (Thmin); and defining (103) said geometry and said arrangement for each of said plurality of electrodes (El-En) of said piezoelectric device (1) based on said comparison.

Description

[0001] METHOD FOR DEFINING THE GEOMETRY AND ARRANGEMENT

[0002] OF A PLURALITY OF ELECTRODES FOR A PIEZOELECTRIC DEVICE

[0003] AND ASSOCIATED PIEZOELECTRIC DEVICE

[0004] The present invention relates to a method and computer product for defining the geometry and arrangement of a plurality of electrodes of a piezoelectric device.

[0005] More specifically, the method allows defining the geometry and arrangement of each of the electrodes based on a comparison between the value of the pixels of an image representative of the spatial distribution of the wave field on an installation area and respective threshold values.

[0006] The present invention further relates to a process for manufacturing a plurality of electrodes and to a piezoelectric device applicable / installable on an installation area of a surface that comprises a plurality of electrodes whose specific geometry and arrangement enable the generation of a focused ultrasonic wave at a predetermined point on the surface.

[0007] Hereinafter, the description will particularly address the field of monitoring structures made of metallic and composite materials used in aerospace, aircraft, railway, and automotive platforms, as well as in all fields in which structural integrity monitoring plays a critical role in ensuring the safety of users of such structures.

[0008] The description will also address the field of energy and data transfer via ultrasonic waves, such as guided elastic waves, to points that are not easily accessible or are inaccessible via wired or radio connections, for example due to shielding by walls made of conductive material.

[0009] It is, however, evident that this description should not be considered limited to the specific materials or objects mentioned herein. Background Art

[0010] The inspection and verification of structural integrity are of vital importance in modern aerospace, aircraft, railway, and automotive platforms, as well as in all sectors where structural integrity monitoring plays a crucial role in ensuring the safety of the users of such structures.

[0011] The general objective of structural health monitoring is to detect, locate, and quantify any damage to the structures under observation through sensor systems mounted on or permanently integrated into the structure.

[0012] Such systems should enable early damage detection and assessment of damage progression, as well as allow evaluation of the effectiveness of possible repair actions. Consequently, achieving these objectives would significantly improve the safety and reliability of the relevant structures, while drastically reducing maintenance and operational costs.

[0013] However, existing structural health monitoring systems based on guided ultrasonic waves, developed thus far and currently in use in this field, still suffer from several significant physical and / or technological limitations, such as: i) the lack of established design methodologies for application to various materials under different conditions of temperature, humidity, vibrations, pressure, etc.; ii) the need for bulky, heavy instrumentation with high power consumption; iii) the requirement to use sophisticated signal processing techniques that demand powerful computational platforms; iv) high wiring complexity between sensors and processing units, especially in dense transducer networks requiring a high number of sensors / actuators per unit area, resulting in unacceptable increases in weight and maintenance costs; v) the inability to steer the ultrasonic beam in a 360° direction.

[0014] A possible solution to these problems is offered by EP 3283876, which discloses a method for producing a piezoelectric device and electrodes for monitoring the structural integrity of a structure, comprising the steps of defining a directivity function D(kl,k2) that presents, in the wave number domain, a plurality of maxima arranged on different concentric circles centered at the origin of the axes; computing a spatial load distribution f(xl,x2) via the inverse Fourier transform of the directivity function D(kl,k2) defined in the wave number domain; producing the device and electrodes in which the directivity function D(kl,k2) is asymmetric; and fabricating the plurality of electrodes by collecting the values of the load distribution f(xl,x2) in the complex plane, defining at least two sectors of said plane each including at least one real and one imaginary value, wherein each electrode corresponds to the points of the load distribution f(xl,x2) lying within the same sector.

[0015] However, this solution allows focusing the beam in a specific direction but not at a specific point of the structure, as desired in some applications (so-called “hot-spot monitoring’"').

[0016] Therefore, there is a need for a process for manufacturing a plurality of electrodes for a piezoelectric device and an associated piezoelectric device for nonintrusive, continuous, active and passive monitoring of a specific point of a structure made of composite or metallic material, with negligible power consumption and minimal impact on the mechanical parameters (weight, stiffness) of the structure itself.

[0017] Object Of The Invention

[0018] An object of the present invention is to overcome the aforementioned drawbacks by providing a process for manufacturing a plurality of electrodes for a piezoelectric device and a piezoelectric device designed for non-intrusive, continuous, active and passive monitoring of a specific point on a structure made of composite and / or metallic material, characterized by negligible power consumption and minimal impact on the mechanical parameters (weight, stiffness) of the structure itself. A further object of the present invention is to enable energy and / or data transfer (so-called “wireless power transfer"" through the emission of guided ultrasonic waves to points that are not easily accessible or are inaccessible via wired or radio connections, for example due to shielding by walls made of conductive material.

[0019] Therefore, it is an object of the present invention a method as defined in claim 1, a manufacturing process as defined in claim 11, a piezoelectric device as defined in claim 12, a processing unit as defined in claim 15, a computer product as defined in claim 16 and a network of devices as defined in claim 17.

[0020] Additional preferred embodiments are described in the dependent claims.

[0021] List of Attached Figures

[0022] The present invention will now be described, by way of illustrative but nonlimiting example, according to one of its embodiments, with particular reference to the attached figures, in which:

[0023] Figure 1 shows a perspective view of a structure on whose surface a piezoelectric device is placed for monitoring a specific point of the structure itself, according to an embodiment of the present invention;

[0024] Figure 2 shows a block diagram of a process for manufacturing a plurality of electrodes for a piezoelectric device, according to an embodiment of the present invention.

[0025] Figure 3 shows a top view of the spatial distribution over the surface of the wave field of an isotropic ultrasonic wave originating at a specific point of the structure.

[0026] Figure 4 shows a first image of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 3 on an installation area of the surface.

[0027] Figure 5 shows a second image of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 3 on an installation area of the surface.

[0028] Figure 6 shows a top view of the geometry and arrangement of four electrodes of the piezoelectric device, according to a first embodiment of the present invention;

[0029] Figure 7 shows a top view of the structure on whose surface the piezoelectric device is placed, which includes electrodes having the geometry and arrangement shown in Figure 6. In Figure 7, the piezoelectric device is powered to generate a focused ultrasonic wave at the specific point of the structure; Figure 8 shows a top view of the spatial distribution over the surface of the wave field of an isotropic ultrasonic wave originating at a specific point of the structure.

[0030] Figure 9 shows a first image of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 8 on an installation area of the surface.

[0031] Figure 10 shows a second image of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 8 on an installation area of the surface.

[0032] Figure 11 shows a top view of the geometry and arrangement of four electrodes of the piezoelectric device, according to a second embodiment of the present invention;

[0033] Figure 12 shows a top view of the structure on whose surface the piezoelectric device is placed, which includes electrodes having the geometry and arrangement shown in Figure 11. In Figure 12, the piezoelectric device is powered to generate a focused ultrasonic wave at the specific point of the structure;

[0034] Figure 13 shows a top view of the spatial distribution over the surface of the wave field of an isotropic ultrasonic wave originating at a specific point of the structure.

[0035] Figure 14 shows a first image of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 13 on an installation area of the surface.

[0036] Figure 15 shows a second image of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 13 on an installation area of the surface.

[0037] Figure 16 shows a top view of the geometry and arrangement of four electrodes of the piezoelectric device, according to a third embodiment of the present invention;

[0038] Figure 17 shows a top view of the structure on whose surface the piezoelectric device is placed, which includes electrodes having the geometry and arrangement shown in Figure 16. In Figure 17, the piezoelectric device is powered to generate a focused ultrasonic wave at the specific point of the structure;

[0039] Figure 18 shows a schematic perspective view of the piezoelectric device, on whose piezoelectric substrate surface a plurality of electrodes are arranged, according to the third embodiment of the present invention;

[0040] Figure 19 shows a schematic perspective view of the piezoelectric device shown in Figure 18, on whose opposite surface of the piezoelectric substrate the common electrode is arranged;

[0041] Figure 20 shows a schematic side view of the piezoelectric device, according to the first, second, or third embodiment of the present invention.

[0042] Detailed Description of the Invention

[0043] In the various figures, similar parts will be indicated using the same reference numerals.

[0044] With reference to Figure 1, a perspective view is shown of a structure H, such as a structure H made of metallic and / or composite material, on the surface F of which a piezoelectric device 1 is installed for monitoring a point P of interest located at an arbitrary distance D from the installation area of the piezoelectric device 1, for example, a distance ranging between 5 cm and 200 cm from the installation area Z.

[0045] Such a structure H may form part of the load-bearing frame or the outer structure of a transport vehicle, such as an aircraft, automobile, or ship; a satellite, a container, or any other structure such as a pipe support or a thin plate. However, it is clear that the present invention should not be considered limited to any specific type of structure or particular field of application.

[0046] The piezoelectric device 1 comprises a piezoelectric substrate and a plurality of electrodes, the geometry and arrangement of which allow for non-intrusive, continuous, active and passive monitoring of a specific point P of the structure H and / or the transfer of energy and / or data via guided ultrasonic waves to the arbitrary point P of the structure H, for example, a point on the outer or inner surface of the structure H.

[0047] Figure 2 shows a block diagram of a process 200 for manufacturing a plurality of electrodes for the piezoelectric device 1.

[0048] The process 200 comprises a step 100 in which the geometry and arrangement of each electrode of a plurality of electrodes El-En for a piezoelectric device 1 is defined, and a step 201 in which each of the plurality of electrodes El-En is manufactured based on the geometry and arrangement obtained in step 100.

[0049] The definition of the geometry and arrangement of each of the electrodes El- En may be obtained by means of a processing unit configured to perform step 100 of process 200.

[0050] The processing unit may include a processor (e.g., a microprocessor, a programmable processor, one or more computers, etc.) and other auxiliary components such as random access memory (RAM) and read-only memory (ROM).

[0051] The processing unit is configured to execute one or more instructions which, when executed by the processing unit, cause the processing unit to perform method 100 (or step 100) as will be described below with reference to Figure 2

[0052] Such instructions may be part of a computer program and be tangibly embedded or stored in a computer product, for example, in a volatile or non-volatile storage device readable by the processing unit. Examples of storage devices include magnetic media, optical media, RAM, ROM, removable media, and other types of media.

[0053] Furthermore, the processing unit may be operatively connected to display means and / or a user interface configured to present information related to the arrangement and geometry of the electrodes El-En for the piezoelectric device 1.

[0054] With reference to Figure 2, method 100 comprises step 101, in which one or more images Sl-Sn are obtained representing the spatial distribution of the wave field (so-called "displacement wavefield") of an ultrasonic wave on the installation area Z of the surface F, on which the piezoelectric device 1 may be positioned.

[0055] Figure 3 shows a top view of the spatial distribution of the wave field of an isotropic ultrasonic wave originating at the specific point P of the structure, such as an elastic wave.

[0056] In Figure 3, point P is located at a distance of 20 cm from the installation area, and the ultrasonic wave is a periodic wave with a wavelength of 13.2 mm and a center frequency fc of 100 kHz. In the illustrated example, the installation area Z is square-shaped, measuring 80 mm x 80 mm.

[0057] The wave distribution is shown across the surface F, which includes the installation area Z.

[0058] The field of such an elastic ultrasonic wave may assume both positive and / or negative values. This wave field represents the propagation of small-amplitude perturbations imposed on the surface F by the elastic wave originating from point P and it may include displacement fields of the surface F and / or their derivatives, which may also have negative values.

[0059] Figure 4 shows a first image SI of the spatial distribution of the wave field of the ultrasonic wave illustrated in Figure 3 on the installation area Z of the surface F.

[0060] Figure 5 shows a second image S2 of the spatial distribution of the wave field of the ultrasonic wave shown in Figure 3 on the installation area Z of the surface F.

[0061] Since both images SI and S2 are obtained for the same installation area Z, there is a geometric correspondence between the pixels of image SI and the respective pixels of image S2. Thus, for each pixel pxi(x, y) of the first image SI, there exists a corresponding pixel px2(x, y) in the second image S2 with the same coordinates x, y.

[0062] In general, each of the images Sl-Sn, representing an image of the wave field over the same installation area Z, is captured at a capture instant ti-nwithin a time interval corresponding to the period of the ultrasonic wave, different with respect to the capture instant of each of the remaining images.

[0063] For example, the first image SI may be captured at a first capture instant ti, when the amplitude of the ultrasonic wave field reaches its maximum intensity within the installation area Z, as a result of excitation at point P. For example, this maximum may be identified by observing the variation in field intensity at different time instants.

[0064] The second image S2 may be captured at a second instant t2, corresponding to a quarter period of the ultrasonic wave after the first capture instant ti, thus the second instant t2 can be defined as: t2 = tl + (l / fc) / 4 where fc is the center frequency and 1 / fc is the period of the ultrasonic wave generated at point P on surface F. This center frequency fc may be an arbitrary frequency, for example any frequency comprised from 20 kHz to 1 MHz, such as a frequency equal to 100 kHz.

[0065] In some embodiments, images Sl-Sn may be obtained from a storage device accessible to the processing unit, such as a removable memory, a remote data server accessible via a communication network, or other memory media.

[0066] In other embodiments, the images Sl-Sn may be generated via a digital twin of structure H, which computes or predicts the spatial distribution, over the installation area Z, of the wave field of an ultrasonic wave generated at the focal point P of the ultrasonic wave.

[0067] In further embodiments, the images Sl-Sn may be obtained directly from an ultrasonic field acquisition device, such as a laser doppler vibrometer, configured to generate the image of the spatial distribution, over the installation area Z, of the wave field of an ultrasonic wave generated at the focal point P of the ultrasonic wave.

[0068] Referring again to Figure 2, method 100 comprises step 102, in which the wave field values of the respective pixels of the images Sl-Sn are compared with an upper threshold Thmax or a lower threshold Thmin.

[0069] This comparison may be carried out either by comparing the value of individual pixels of the image or by comparing the average value of a block of pixels within the image against the upper threshold Thmax or the lower threshold Thmin.

[0070] In step 103, the geometry and arrangement for each of the plurality of electrodes El-En of the piezoelectric device 1 are then defined based on the comparison performed in step 102.

[0071] For example, the definition of the electrodes El-En of the piezoelectric device 1 may be carried out using only a single image SI.

[0072] In this case, the geometry and arrangement for each of the plurality of electrodes El-En may be defined by executing the following sub-steps: i. selecting a first pixel pxi of a first image SI from the set of images Sl-Sn; ii. associating said first pixel pxi with a first electrode El if the value of the pixel pxi is greater than the upper threshold Thmax; and iii. associating said first pixel pxi with a second electrode E2 if the value of the pixel pxi is less than the lower threshold Thmin, wherein the lower threshold Thmin is less than the upper threshold Thmax.

[0073] These sub-steps may be repeated for each of the pixels of the first image SI, or for a selected group of pixels, in order to define the geometry and arrangement of the electrodes for the entire installation area Z, or a portion thereof.

[0074] In other embodiments, the definition of the electrodes El-En of the piezoelectric device 1 may be determined using both a first image SI and a second image S2.

[0075] In this case, it is possible to define the geometry and arrangement of four electrodes E1-E4, such as the geometry and arrangement illustrated in Figure 6.

[0076] In particular, Figure 6 shows the geometry and arrangement of the electrodes obtained using images SI and S2, as shown in Figures 4 and 5, respectively.

[0077] In this case, the definition of the geometry and arrangement of the four electrodes E1-E4 may be carried out by performing the following sub-steps: i. selecting 1021 a first pixel pxi from a first image SI of the set of images Sl-Sn; ii. comparing the value of the first pixel pxi of the first image SI with the value of a corresponding second pixel px2of a second image S2; iii. associating the first pixel pxi with a first electrode El if the value of the first pixel pxi is greater than the upper threshold Thmax and its absolute value is greater than the absolute value of the second pixel px2.

[0078] In this case, electrode El is defined by all pixels pxi that satisfy the following criterion:

[0079] El : |Sl(pxi)| > |S2(px2)| and Sl(pxi) > Thmax iv. associating the first pixel pxi with a second electrode E2 if the value of the first pixel pxi is less than the lower threshold Thmin and its absolute value is greater than the absolute value of the second pixel px2.

[0080] In this case, electrode E2 is defined by all pixels pxi that satisfy the following criterion:

[0081] E2: |S l(pxi)| > |S2(px2)| and Sl(pxi) < Thmin v. associating the second pixel px2with a third electrode E3 if the value of the second pixel px2is greater than the upper threshold Thmax and its greater than the first pixel pxi.

[0082] In this case, electrode E3 is defined by all pixels px2that satisfy the following criterion:

[0083] E3: |S2(px2)| > |Sl(pxi)| and S2(px2) > Thmax vi. associating the second pixel px2with a fourth electrode E4 if the value of the second pixel px2is less than the lower threshold Thmin and its absolute value is greater than the absolute value of the first pixel pxi, where the lower threshold Thmin is less than the upper threshold Th max.

[0084] In this case, electrode E4 is defined by all pixels px2that satisfy the following criterion:

[0085] E4: |S2(px2)| > |Sl(pxi)| and S2(px2) < Thmin

[0086] These sub-steps may be repeated for each pixel of the first image SI, or for a set of pixels, to define the geometry and arrangement of the electrodes for the entire installation area Z or a portion thereof.

[0087] Since both images S 1 and S2 are obtained for the same installation area Z, the position of the first pixel pxi in the first image SI corresponds to the position of the second pixel px2 in the second image S2.

[0088] By means of method 100, it is thus possible to define a geometry and arrangement of the electrodes El-En of the piezoelectric device 1 corresponding to a “fingerprint” of the wave field on the installation area Z of the ultrasonic wave generated at the focal point P of the ultrasonic wave, as a function of the characteristics of the particular wave generated, the location of point P, and the geometric and physical properties of structure H.

[0089] Once the geometry and arrangement of the electrodes El-En of the piezoelectric device 1 have been defined, it is possible to manufacture each of the plurality of electrodes El-En on a piezoelectric substrate 20, based on the geometry and arrangement obtained using method 100.

[0090] The resulting piezoelectric device 1 can then be installed on the installation area Z, such that when the piezoelectric device 1 is placed on the installation area Z of the surface F, and each electrode of the plurality El-En is powered by a respective electrical signal — so that a plurality of phase-shifted electrical signals with equal amplitude power the plurality of electrodes El-En — the piezoelectric device 1 generates a focused ultrasonic wave at point P.

[0091] It is, however, evident that this description should not be considered limited to the definition of the geometry and arrangement of the specific number of electrodes illustrated in the figures. Therefore, it is possible to define an arbitrary number of electrodes, using for example an arbitrary number of images Sl-Sn, without departing from the scope of protection as defined by the attached claims.

[0092] Figure 7 shows a top view of structure H, on the surface F of which the piezoelectric device 1 is positioned. The device includes electrodes whose geometry and arrangement are shown in Figure 6.

[0093] In Figure 7, the piezoelectric device 1 is powered to generate a focused ultrasonic wave at the specific point P of the structure, thus enabling energy and / or data transfer at point P by means of guided ultrasonic wave emission.

[0094] For example, the electrodes E1-E4 may be powered by electrical signals having the following waveform:

[0095] El — A*Sin(wt)

[0096] E2 -A*Sin(wt)

[0097] E3 — A*Cos(wt)

[0098] E4 —> -A*Cos(wt) whereby A represents the signal amplitude, arbitrarily chosen, for example V, w represents the pulsation 27t*fc, and t represents the time instant considered.

[0099] These voltage signals are referenced to the common electrode G of device 1, each signal may be provided by a respective voltage source connected to an electrode E1-E4 and to the common electrode G. Each of the voltage sources may be controlled by a control logic unit.

[0100] With reference to Figures 3-7, Figures 8-12 pertain to a second embodiment of the present invention.

[0101] Figures 8-12 differ from Figures 3-7 in that the point P is located at a different distance D from the installation area Z, in this specific case, the distance D is equal to 35 cm, consequently, in the second embodiment, the geometry and arrangement of electrodes E1-E4, obtained using images SI and S2 shown in Figures 9 and 10, correspond to that shown in Figure 11, and are therefore different from the geometry shown in Figure 6.

[0102] With reference to Figures 8-12, Figures 13-17 pertain to a third embodiment of the present invention.

[0103] Figures 13-17 differ from both Figures 3-7 and Figures 8-12 in that point P is located at yet another distance D from the installation area Z, in this case, the distance D is equal to 10 cm, consequently in the third embodiment, the geometry and arrangement of electrodes E1-E4, obtained using images SI and S2 shown in respective Figures 14 and 15, correspond to that illustrated in Figure 16, and therefore differ from the geometries shown in Figure 6 or Figure 11.

[0104] Figures 18 and 19 show a schematic perspective view of the piezoelectric device, as realized according to the third embodiment of the present invention.

[0105] Figure 18 show the geometry and arrangement of electrodes E1-E4 corresponding to that shown in Figure 16.

[0106] With reference to Figures 18 and 19, the piezoelectric device 1 has a rectangular shape with dimensions of 80 x 80 mm and a thickness of 0.5 mm. However, the piezoelectric substrate 20 may have an arbitrary shape, preferably rectangular or circular, and an arbitrary thickness. Therefore, it is evident that the piezoelectric device 1 of the present invention should not be considered limited to the particular shape or dimensions indicated here. On the opposite surface from that where electrodes E1-E4 are arranged, a common electrode G is provided, which may be a planar, non-pattemed electrode extending across the entire opposite surface.

[0107] Figure 20 shows a schematic side view of piezoelectric device 1, according to the first, second, or third embodiment of the present invention.

[0108] The piezoelectric device 1 is applicable on an installation area Z of a surface F for monitoring a point P on said surface F. The piezoelectric device 1 comprises a piezoelectric substrate 20, a common electrode G, and a plurality of electrodes El-En.

[0109] Specifically, the spatial arrangement and geometry of each electrode El-En on the piezoelectric substrate 20 are based on a representation of the spatial distribution on the installation area Z of the wave field of an ultrasonic wave originating at point P of the surface F, wherein said representation includes a plurality of wave field values lower than a lower threshold Thmin or greater than an upper threshold Th max.

[0110] In this way, when the piezoelectric device 1 is placed on the installation area Z of the surface F, and each electrode of the plurality El-En is powered by a respective electrical signal — such that a plurality of phase-shifted electrical signals with equal amplitude powers the plurality of electrodes El-En — the piezoelectric device 1 generates a focused ultrasonic wave at point P.

[0111] The devices 1 can also be connected in modular, scalable networks, and may either be adhered to the surface of structure H to be monitored, or permanently integrated. These devices 1 can be connected to form a network comprising a plurality of devices 1 as described with reference to Figure 20, wherein each device 1 is configured to transmit and / or receive an ultrasonic beam from / to one or more devices 1 of the network of devices.

[0112] Such a network of devices may also comprise a control logic unit communicatively coupled to at least one of the devices 1 to transmit / receive one or more electrical signals to / from the devices 1.

[0113] This configuration enables the installation of the devices 1 of the network directly on an existing structure H (so called “retrofitting”) by adhering the devices to the surface F of the structure H to monitor or permanently integrating them.

[0114] The control logic unit enables interpretation of the data acquired from the devices 1 in an automated manner, eliminating the costs associated with using specialized operators, making it possible to detect damage early and assessing its progression, and evaluate the effectiveness of potential repair actions.

[0115] Advantageously, by means of the process 200 for manufacturing a plurality of electrodes El-En for a piezoelectric device 1, object of the present invention, it is possible to overcome the physical and / or technological limitations of currently used solutions, providing a piezoelectric device 1 that: i) can be applied or integrated into structures H made of various materials (composite or non-composite); ii) features low power consumption, enabling both generation and reception of ultrasonic waves that propagate in programmable directions; iii) has reduced bulk and weight, with minimal impact on the mechanical parameters (weight, stiffness) of the same structure H; iv) reduces wiring complexity, thanks to the use of guided wave systems for combined transmission of data and power over the structure H; v) enables focusing of the ultrasonic wave at arbitrary points, for example so- called "hot-spots" within structures H made of composite or metallic materials, thus allowing continuous structural integrity monitoring of the structure H itself and reducing inspection time for detecting barely visible damage. A second advantage provided by the method for defining the geometry and arrangement of a plurality of electrodes El-En for a piezoelectric device 1, object of the present invention, lies in enabling the design of transducers based on the acquisition of wave propagation data and the measurement of the corresponding wave field.

[0116] A third advantage of the piezoelectric device 1 is its ability to perform inspection of areas that are difficult or impossible to access using wired or radio communication methods, for example due to electromagnetic shielding by conductive walls.

[0117] In the aerospace sector, for instance, the piezoelectric device 1 may serve as a diagnostic element for the early detection of impact-induced delaminations in composite structures. These delaminations represent a critical failure mode, as they may compromise the global structural H integrity and so the safety of the aerial transportation while remaining invisible or barely visible during visual inspection.

[0118] A fourth advantage obtained by means of the piezoelectric device 1, object of the present invention, is the possibility to power electronic devices, such as electronic receivers positioned in radiation shielded areas, but that can be reached by elastic waves.

[0119] For example, by simulating the placement of a piezoelectric receiver at point P, the use of device 1 enables more efficient energy transfer compared to existing solutions as can be seen by the result shown in the following table, whereby it is shown the estimated power transfer efficiency, calculated as the ratio between the electrical power input to the transducer and the electrical power received by a piezoelectric receiver positioned at point P. This efficiency is compared with that achieved using the device described in EP 3283876 and a commercial array of circular (non-shaped) piezoelectric transducers:

[0120] Such energy transfer can be useful, for example, in the oil and gas sector, where device 1 can be used to focus an ultrasonic beam on critical points P affected by corrosion, such as near pipe supports, allowing the monitoring of so-called hotspots or the filtering of specific propagation modes (for example, the so-called “torsional waves”), which are particularly useful for detecting defects in pipelines and are characterized by very low attenuation, thus enabling long-range inspections.

[0121] A fifth advantage provided by the piezoelectric device 1, subject of the present invention, is the ability to quickly, safely, and non-invasively detect the degradation that structures undergo throughout their service life by combining the use of device 1 with an electronic signal conditioning system and a dedicated inspection methodology.

[0122] A sixth advantage provided by the piezoelectric device 1, subject of the present invention, is its low power consumption, which makes it possible to install the device permanently on structures and to control it remotely, even when the available energy and computing resources are limited — for example, in the case of space probes or satellite devices.

[0123] The present invention has been described for illustrative but non-limiting purposes according to its preferred embodiments, and it is understood that variations and / or modifications may be made by experts in the field without departing from the corresponding scope of protection, as defined by the attached claims.

Claims

CLAIMS1. A computer-implemented method (100) for defining a geometry and an arrangement of a plurality of electrodes (El-En) for a piezoelectric device (1) installable on an installation area (Z) of a surface (F), said method (100) comprising the steps of: obtaining (101) one or more images (Sl-Sn) of the spatial distribution of the wave field of an ultrasonic wave on said installation area (Z), each of said one or more images (Sl-Sn) being captured at a capture instant (ti-n) of a time interval corresponding to the period of said ultrasonic wave, wherein said capture instant (ti-n) is different from the capture instant for each of the remaining images, wherein said ultrasonic wave is originated at a point (P) on said surface (F) located at a distance (D) from said installation area (Z); comparing (102) the wave field value of the respective pixels of said one or more images (Sl-Sn) with an upper threshold (Thmax) or a lower threshold (Thmin); and defining (103) said geometry and said arrangement for each of said plurality of electrodes (El-En) of said piezoelectric device (1) based on said comparison.

2. The method (100) according to the preceding claim, wherein comparing (102) the value of the respective pixels of an image comprises comparing thevalue of a pixel of said image or comparing the average value of a block of pixels of said image.

3. The method (100) according to claim 1 or 2, wherein defining (103) said geometry and said arrangement for each of said plurality of electrodes (El- En) comprises: i) selecting a first pixel (pxi) of a first image (SI) of said one or more images (Sl-Sn); ii) associating said first pixel (pxi) with a first electrode (El) if said value of said first pixel (pxi) is greater than said upper threshold (Thmax); and iii) associating said first pixel (pxi) with a second electrode (E2) if said value of said first pixel (pxi) is less than said lower threshold (Thmin), wherein said lower threshold (Thmin) is less than said upper threshold (Thmax).

4. The method (100) according to the preceding claim, comprising repeating steps (i)-(iii) for each of the pixels of said first image (SI).

5. The method (100) according to claim 1 or 2, wherein defining (103) said geometry and said arrangement for each of said plurality of electrodes (El-En) comprises:i) selecting (1021) a first pixel (pxi) of a first image (SI) of said one or more images (Sl-Sn); ii) comparing said value of said first pixel (pxi) of said first image (SI) with a value of a corresponding second pixel (px2) of a second image (S2) of said one or more images (Sl-Sn); iii) associating said first pixel (pxi) with a first electrode (El) if said value of said first pixel (pxi) is greater than said upper threshold (Thmax) and its absolute value is greater than the absolute value of said value of said second pixel (px2); iv) associating said first pixel (pxi) with a second electrode (E2) if said value of said first pixel (pxi) is less than said lower threshold (Thmin) and its absolute value is greater than the absolute value of said value of said second pixel (px2); v) associating said second pixel (px2) with a third electrode (E3) if said value of said second pixel (px2) is greater than said upper threshold (Thmax) and its absolute value is greater than the absolute value of said value of said first pixel (pxi); and vi) associating said second pixel (px2) with a fourth electrode (E4) if said value of said second pixel (px2) is less than said lower threshold (Thmin) and its absolute value is greater than the absolute value of said value of said firstpixel (pxi), wherein said lower threshold (Thmin) is less than said upper threshold (Th max).

6. The method (100) according to the preceding claim, comprising repeating steps (i)-(vi) for each of the pixels of said first image (SI).

7. The method (100) according to claim 5 or 6, wherein the position of said first pixel (pxi) in said first image (SI) corresponds to the position of said second pixel (px2) in said second image (S2).

8. The method (100) according to any of claims 5-7, wherein said first image (SI) is captured at a first capture instant (ti) when the amplitude of the wave field of said ultrasonic wave reaches its maximum, and wherein said second image (S2) is captured at a second capture instant (t2) corresponding to a quarter period of said ultrasonic wave after said first capture instant (ti).

9. The method (100) according to any of the preceding claims, wherein obtaining (101) one or more images (Sl-Sn) comprises:- obtaining said one or more images (Sl-Sn) from a storage device; or- generating said one or more images (Sl-Sn) using a digital twin that calculates or predicts said spatial distribution of the wave field of saidultrasonic wave on said installation area (Z) when said ultrasonic wave is generated at the focal point (P) of the ultrasonic wave; or- obtaining said one or more images (Sl-Sn) from an ultrasonic field acquisition device operating on said installation area (Z) when said ultrasonic wave is generated at the focal point (P) of the ultrasonic wave.

10. The method (100) according to any of the preceding claims, wherein said surface (F) is part of a structure (H), preferably wherein said structure (H) is a laminated structure made of metallic and / or composite material.

11. A process (200) for manufacturing a plurality of electrodes (El -En) for a piezoelectric device (1) installable on an installation area (Z) of a surface (F), said process comprising the step of: manufacturing (201) each of said plurality of electrodes (El-En) based on said geometry and said arrangement obtained by the method (100) according to any of the preceding claims.

12. A piezoelectric device (1) applicable to an installation area (Z) of a surface (F) for monitoring a point (P) on said surface (F), said piezoelectric device comprising:a piezoelectric substrate (20) comprising a first surface and a second surface opposite said first surface; a common electrode (G) disposed on said first surface; and a plurality of electrodes (El-En) disposed on said second surface, the spatial arrangement and geometry of each of said plurality of electrodes (El- En) on said piezoelectric substrate (20) being based on a representation of the spatial distribution on the installation area (Z) of the wave field of an ultrasonic wave originated at the point (P) on said surface (F), wherein said representation comprises a plurality of wave field values lower than a lower threshold (Thmin) or higher than an upper threshold (Thmax), such that, when said piezoelectric device (1) is placed on said installation area (Z) of the surface (F) and each electrode of said plurality of electrodes (El-En) is powered by a respective electrical signal such that a plurality of electrical signals power said plurality of electrodes (El-En), said electrical signals of said plurality of electrical signals being phased with equal amplitude, said piezoelectric device (1) generates a focused ultrasonic wave at said point (P).

13. The piezoelectric device (1) according to claim 12, wherein said piezoelectric substrate (20) is of rectangular or circular shape.

14. The piezoelectric device (1) according to claim 12 or 13, wherein said plurality of electrodes (El-En) comprises a first electrode (El), a second electrode (E2), a third electrode (E3), and a fourth electrode (E4).

15. A processing unit configured to perform the method (100) according to any of claims 1-10.

16. A computer product comprising instructions that, when executed by a processing unit, cause the processing unit to perform the method (100) according to any of claims 1-10.

17. A network of devices comprising: a plurality of devices (1) according to claim 12 or 13, wherein each device(1) is configured to receive / transmit an ultrasonic beam from / to one or more devices (1) of said network of devices; and a control logic unit communicatively coupled to at least one of said plurality of devices (1) to receive / transmit one or more electrical signals from / to said devices (1).

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