WO2025156052A1

WO2025156052A1 - Multi-element ultrasonic transducer

Info

Publication number: WO2025156052A1
Application number: PCT/CA2025/050095
Authority: WO
Inventors: Pierre Belanger; Aubin CHABOTY
Original assignee: Ecole de Technologie Superieure
Current assignee: Ecole de Technologie Superieure
Priority date: 2024-01-26
Filing date: 2025-01-24
Publication date: 2025-07-31
Anticipated expiration: 2026-07-26

Abstract

A multi-element ultrasonic transducer for examining an object comprises a piezoelectric layer comprising at least one emitting element configured to apply to the object input ultrasound waves having a center frequency lower than or equal to 500 kHz to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object, and a plurality of receiving elements spaced from the at least one emitting element, the plurality of receiving elements and the at least one emitting element arranged along the longitudinal axis, the plurality of receiving elements configured to acquire, from the object, acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves.

Description

MULTI-ELEMENT ULTRASONIC TRANSDUCER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of United States Provisional Patent Application No. 63/625,345 filed on January 26, 2024, the contents of which are hereby incorporated by reference.

FIELD

[0002] The improvements generally relate to the field of measurement devices and, more particularly, to multi-element ultrasonic transducers.

BACKGROUND

[0003] Ultrasound waves are used to examine objects in a variety of applications, including medical and industrial applications. For instance, in industrial applications, ultrasound waves may be used in non-destructive testing to enable rapid inspections over long distances. In medical applications, ultrasound waves may be used to diagnose various conditions such as osteoporosis. However, the lack of standardized quality control and the heterogeneity in results provided by existing ultrasound techniques limit their use. In addition, existing techniques have proven sensitive to intrinsic properties of biological objects such as soft tissue or bone but fail to access each parameter simultaneously which can result in incomplete diagnosis in medical applications.

[0004] Therefore, there is a need for improvement.

SUMMARY

[0005] In accordance with one aspect, there is provided a multi-element ultrasonic transducer for examining an object. The transducer comprises a piezoelectric layer comprising at least one emitting element configured to apply to the object input ultrasound waves having a center frequency lower than or equal to 500 kHz to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object, and a plurality of receiving elements spaced from the at least one emitting element, the plurality of receiving elements and the at least one emitting element arranged along the longitudinal axis, the plurality of receiving configured to acquire, from the object, acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves through the object.

[0006] In at least one embodiment in accordance with any previous/other embodiment described herein, the plurality of receiving elements are formed by cutting through at least part of a thickness of the piezoelectric layer at regular intervals along a length of the piezoelectric layer.

[0007] In at least one embodiment in accordance with any previous/other embodiment described herein, the plurality of receiving elements are formed by cutting through between about 90% and about 95% of the thickness of the piezoelectric layer.

[0008] In at least one embodiment in accordance with any previous/other embodiment described herein, the plurality of receiving elements are formed by cutting through an entirety of the thickness of the piezoelectric layer.

[0009] In at least one embodiment in accordance with any previous/other embodiment described herein, the at least one emitting element is configured to apply the input ultrasound waves along a direction perpendicular to the longitudinal axis.

[0010] In at least one embodiment in accordance with any previous/other embodiment described herein, the plurality of receiving elements is arranged in a linear array along the longitudinal axis.

[0011] In at least one embodiment in accordance with any previous/other embodiment described herein, the at least one emitting element is spaced from the plurality of receiving elements by a first distance, and further wherein adjacent ones of the plurality of receiving elements are spaced apart by a second distance, the first distance greater than the second distance.

[0012] In at least one embodiment in accordance with any previous/other embodiment described herein, the transducer further comprises an absorbing element positioned in a gap between the at least one emitting element and a first one of the plurality of receiving elements, the absorbing element configured to acoustically isolate the at least one emitting element from the plurality of receiving elements.

[0013] In at least one embodiment in accordance with any previous/other embodiment described herein, the transducer further comprises at least one matching layer interposed between the piezoelectric layer and the object, the at least one matching layer configured to provide impedance matching between the piezoelectric layer and the object.

[0014] In at least one embodiment in accordance with any previous/other embodiment described herein, the transducer further comprises a backing layer coupled to the piezoelectric layer, the backing layer configured to prevent parasitic reflection of the input ultrasound waves.

[0015] In at least one embodiment in accordance with any previous/other embodiment described herein, the transducer further comprises electrodes disposed on opposed surfaces of the piezoelectric layer, wherein the at least one emitting element is configured to apply the input ultrasound waves in response to an excitation voltage applied to the electrodes.

[0016] In at least one embodiment in accordance with any previous/other embodiment described herein, the transducer further comprises a casing configured to receive the matching layer, the piezoelectric layer, and the backing layer therein.

[0017] In accordance another aspect, there is provided a method for examining an object. The method comprises applying, using at least one emitting ultrasonic transducer element, input ultrasound waves to the object to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object, the input ultrasound waves having a center frequency lower than or equal to 500 kHz, acquiring, using a plurality of receiving ultrasonic transducer elements spaced from the at least one emitting ultrasonic transducer element and arranged therewith along the longitudinal axis, acoustic waves from the object, the acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves through the object, processing the acoustic waves to identify at least one characteristic of the object, and outputting an output signal indicative of the at least one characteristic of the object. [0018] In at least one embodiment in accordance with any previous/other embodiment described herein, the input ultrasound waves are applied along a direction perpendicular to the longitudinal axis.

[0019] In at least one embodiment in accordance with any previous/other embodiment described herein, processing the acoustic waves to identify the at least one characteristic of the object comprises generating a signal representation of the acoustic waves, and

[0020] comparing the signal representation of the acoustic waves to a plurality of reference signals to identify the at least one characteristic of the object.

[0021] In at least one embodiment in accordance with any previous/other embodiment described herein, generating the signal representation of the acoustic waves comprises applying a two-dimensional Fast-Fourier Transform to the acoustic waves.

[0022] In at least one embodiment in accordance with any previous/other embodiment described herein, comparing the signal representation of the acoustic waves to the plurality of reference signals comprises minimizing an error function having as inputs the signal representation of the acoustic waves and the plurality of reference signals, and selecting one of the plurality of reference signals based on the minimizing of the error function.

[0023] In at least one embodiment in accordance with any previous/other embodiment described herein, the object is a long bone, and further wherein the acoustic waves are processed to identify the at least one characteristic comprising at least one of a geometry, a degradation, and mechanical properties of the bone.

[0024] In at least one embodiment in accordance with any previous/other embodiment described herein, the object is a plate-like structure, and the acoustic waves are processed to identify the at least one characteristic comprising at least one quality parameter of the platelike structure.

[0025] In at least one embodiment in accordance with any previous/other embodiment described herein, the object is a bonded joint, and the acoustic waves are processed to identify the at least one characteristic comprising at least one property of the bonded joint. [0026] In accordance with yet another aspect, there is provided a system for examining an object. The system comprises a processing unit and a non-transitory computer-readable medium having stored thereon instructions executable by the processing unit for applying, using at least one emitting ultrasonic transducer element, input ultrasound waves to the object to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object, the input ultrasound waves having a center frequency lower than or equal to 500 kHz, acquiring, using a plurality of receiving ultrasonic transducer elements spaced from the at least one emitting ultrasonic transducer element and arranged therewith along the longitudinal axis, acoustic waves from the object, the acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves through the object, processing the acoustic waves to identify at least one characteristic of the object, and outputting an output signal indicative of the at least one characteristic of the object.

[0027] Many further features and combinations thereof concerning embodiments described herein will appear to those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE FIGURES

[0028] In the figures,

[0029] Fig. 1A is a schematic diagram of an example of a multi-element ultrasonic transducer, in accordance with one embodiment;

[0030] Fig. 1 B is an exploded view of the transducer of Fig. 1A, in accordance with one embodiment;

[0031] Figs. 2A, 2B, and 2C are perspective views of the piezoelectric layer of Fig. 1 B, in accordance with one embodiment;

[0032] Fig. 3 is a front view of the piezoelectric layer of Fig. 2B, in accordance with one embodiment;

[0033] Fig. 4 illustrates an example representation of acoustic waves acquired using the transducer of Fig. 1 A, in accordance with one embodiment; and [0034] Fig. 5 is a block diagram illustrating an example computing device, in accordance with one embodiment.

[0035] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

[0036] Fig. 1A and Fig. 1 B show an example of a multi-element ultrasonic transducer 100, in accordance with one embodiment. The configuration and orientation of the transducer 100 will be described and illustrated herein in the three-dimensional Euclidean space defined by perpendicular axes x, y, and z. In one embodiment, the transducer 100 is used in medical applications to examine an elongated object 101 of a biological nature, such as biological tissue. For example, the transducer 100 may be used to perform in-vivo measurements in axial transmission for early diagnosis of osteoporosis through bone quality assessment and fracture risk prediction. In another embodiment, the transducer 100 is used to inspect an object 101 in industrial applications (including, but not limited to in the energy and petrochemical industries). For example, the transducer 100 may be used in non-destructive testing applications, to assess properties of bonded plates or to evaluate the properties of a bonded joint. In this case, the object 101 under inspection may be made of any suitable material. Other embodiments may apply and it should be understood that the transducer 100 may be used for any suitable application.

[0037] As will be described further below, the transducer 100 is configured to emit ultrasound waves into the object 101 for the purpose of examining or inspecting the object 101 . The emitted ultrasound waves are referred to herein as “input ultrasound waves” or “input ultrasonic waves”, where the terms “ultrasound” and “ultrasonic” are used interchangeably herein. For this purpose, the transducer 100 is coupled to (e.g., positioned on) the object 101 and oriented along a longitudinal axis A thereof (which is parallel to the x axis). The transducer 100 may be coupled to the object 101 using any suitable coupling means (also referred to as a “coupling medium” or “couplant”) that enables transmission of the input ultrasound waves emitted from the transducer 100 to the object 101 and reception at the transducer 100 of acoustic waves acquired from the object 101 . The coupling means may include, but is not limited to, dry coupling (e.g., by the transducer 100 applying pressure on the object 101), liquid coupling (e.g., using fluid, gel, water, oil, cream, or the like), and solid coupling (e.g., using foil).

[0038] As illustrated in Fig. 1A and Fig. 1 B, the transducer 100 comprises an active layer 102 (also referred to herein as a “piezoelectric layer”), electrodes 103, a matching layer 104, an absorbing element 105, a backing layer 106, one or more wires 107, and a casing 108. The piezoelectric layer 102, matching layer 104, backing layer 106, and casing 108 are vertically arranged along a central axis B (parallel to the z axis) which is transverse to the longitudinal axis A. While reference is made herein to the transducer 100 being positioned on (i.e. over the object 101) such that the transducer elements (i.e. the piezoelectric layer 102, matching layer 104, backing layer 106, and casing 108) are vertically arranged one on top of the other in the configuration shown in Fig. 1A and Fig. 1 B, it should be understood that the orientation may be reversed. For example, in some applications, the transducer 100 may be positioned underneath the object 101 and ultrasound waves may be applied to the object 101 through a bottom surface (not shown) thereof rather than an upper surface thereof, as illustrated in Fig. 1A. Thus, the use of terms such as “over”, “on”, “overlie”, “underlie” herein should be understood to be for illustrative purposes as the orientation of the transducer elements may vary depending on the application.

[0039] The piezoelectric layer 102 and the matching layer 104 are substantially planar (in a plane defined by the x and y axes) and have an elongated shape, the piezoelectric layer 102 and the matching layer 104 extending along the axis A. In particular, the piezoelectric layer 102 has a top (or upper) face 110a and an opposed bottom surface 110b, and the matching layer 104 has a top (or upper) face 112a and an opposed bottom face 1 12b. Although the piezoelectric layer 102 and the matching layer 104 are illustrated and described herein as having a rectangular cross-section (when taken in a plane defined by the x and z axes), it should be understood that the transducer 100 may have any other suitable cross-section, such as square.

[0040] The matching layer 104 underlies the piezoelectric layer 102, with the upper face 112a of the matching layer 104 being positioned against the bottom face 110b of the piezoelectric layer 102. Since the acoustic impedance of the piezoelectric layer 102 is typically different from that of the object 101 , the matching layer 104 provides an impedance match between the piezoelectric layer 102 and the object 101. In turn, the matching layer 104 improves the efficiency of the transducer 100 to transmit input ultrasound waves into the object 101 and to receive acoustic waves from the object 101 .

[0041] In one embodiment, the acoustic impedance of the matching layer 104 is defined as follows:

[0042] where ZM is the acoustic impedance of the matching layer 104, Zpiezo is the acoustic impedance of the piezoelectric layer 102, and Zo is the acoustic impedance of the object 101. It should however be understood that the characteristics (e.g., acoustic impedance) of the matching layer 104 may be determined using any suitable technique.

[0043] The matching layer 104 may be made of any suitable material and may have any suitable shape. In the illustrated embodiment, the matching layer 104 is a rectangular slab (e.g., a rectangular parallelepiped) that is substantially planar and has a uniform thickness. In one embodiment, the matching layer 104 is made of epoxy, such as a silver-loaded epoxy. For example, the epoxy adhesive EPO-TEK® 301 may be used. While the transducer 100 is illustrated and described herein as having a single matching layer 104, it should be understood that the transducer 100 may comprise multiple matching layers as in 104 (e.g., stacked matching layers).

[0044] The backing layer 106 is coupled (e.g., overlies) the piezoelectric layer 102, such that the piezoelectric layer 102 is interposed between the matching layer 104 and the backing layer 106. The backing layer 106 is used to increase the amount of ultrasound waves radiated to the transducer 100 away from the object 101 . In particular, the backing layer 106 is configured to extract the ultrasound waves coming from the piezoelectric layer 102 (i.e. the input ultrasound waves) which do not propagate in the object 101 , and to absorb (or attenuate) these ultrasound waves so that they are not reflected back to the piezoelectric layer 102, thereby providing acoustic damping and preventing parasitic reflections of ultrasound waves. The backing layer’s wave attenuation property for a given frequency of use, which is defined by the acoustic attenuation coefficient of the backing layer 106, enables the backing layer 106 to absorb the ultrasound waves. The backing layer 106 further provides mechanical support to the transducer 100.

[0045] The backing layer 106 may be made of any suitable material and may have any suitable shape. It should however be understood that, in order for all the ultrasound waves which are not transmitted to the object 101 to be extracted, it is desirable for the backing layer 106 to be made of a material having the same acoustic impedance as the piezoelectric layer 102. In one embodiment, the backing layer 106 is made of powdered tungsten mixed with epoxy TC-1600 at the acoustic impedance matching volume ratio cured directly onto the piezoelectric layer 102. In the case presented herein, the acoustic impedance of the backing layer 106 is equal to 35 MRayl. Other embodiments may apply.

[0046] The piezoelectric layer 102, the matching layer 104, and the backing layer 106 are enclosed in the casing 108. As can be seen in Fig. 1 B, in one embodiment, the casing 108 comprises a supporting member 1 14a, an enclosure 1 14b, and a cap 114c which are configured to be arranged along the central axis B and secured to one another using any suitable means (e.g., an adhesive, screws, or the like). The supporting member 114a, enclosure 114b, and cap 114c may be made of any suitable material and manufactured using any suitable technique. In one embodiment, the casing 108 is made of polylactic acid (PLA) and manufactured using 3D printing. Other embodiments may apply.

[0047] The supporting member 1 14a has a substantially planar shape and is configured to be positioned over the piezoelectric layer 102 (and coupled thereto using any suitable means), with the matching layer 104 underlying the piezoelectric layer 102. In the illustrated embodiment, the supporting member 114a has a rectangular shape and has an aperture 116 formed therein. The aperture 116 is configured to receive the piezoelectric layer 102 therein. In order to ensure that the piezoelectric layer 102 can be snug-fitted in the aperture 116 and securely retained therein, the aperture is shaped and sized to match the shape and size of the piezoelectric layer 102. In this manner, when the supporting member 1 14a is placed over the piezoelectric layer 102, the top face 1 10a of the piezoelectric layer 102 is exposed through the aperture 1 16. [0048] The enclosure 114b is a hollow prism having a height 'IT and a cross-section (taken along the plane defined by the x and y axes) shaped and sized to substantially match the shape and size of the piezoelectric layer 102. In particular, the width and the length of the enclosure 114b substantially match the width and the length of the piezoelectric layer 102. As used herein, the term “length” refers to the dimension of a given transducer element along the x axis, the term “width” refers to the dimension of the given transducer element along the y axis, and the term “height” or “thickness” refers to the dimension of the given transducer element along the z axis. In the illustrated embodiment, the enclosure 114b is a prism having a rectangular base (i.e. a rectangular cross-section). The enclosure 1 14b has a first end face 117a and a second end face 117b opposite the first end face 117a. A central opening 118 is formed in the enclosure 1 14b and extends from the first end face 117a to the second end face 117b. The central opening 118 is illustratively rectangular and is shaped and sized to match the shape and size of the piezoelectric layer 102. The second end face 1 17b of the enclosure 114b is coupled (using any suitable means) to the support member 114a (along the central axis B) so that the top face 110a of the piezoelectric layer 102 is exposed through the central opening 118. The enclosure 114b (i.e., inner walls thereof, not shown, which delimit the central opening 118) further encapsulates the backing layer 106 which overlies the piezoelectric layer 102. In one embodiment, when so positioned, the enclosure 1 14b extends away from the piezoelectric layer 102 by a height ‘IT. The cap 114c is configured to be coupled to (e.g., positioned over) the first end face 117a of the enclosure 114b so as to close the opening 118. When the cap 114c is so coupled, the casing 108 allows for electrical insulation and protection of the components of the transducer 100.

[0049] Referring now to Figs. 2A, 2B, and 2C in addition to Fig. 1A and Fig. 1 B, the piezoelectric layer 102 may be made of any suitable material including, but not limited to, a ceramic material such as lead zirconate titanate (or PZT), lead magnesium niobate-lead titanate single crystal (or PMN-PT), piezoelectric polymer (e.g., Polyvinyliden fluoride or PVDF), piezoelectric compositions (e.g., lead-free ceramics), and composites. It should be understood that the choice of the material for the piezoelectric layer 102 defines, in part, the performance of the transducer 100. [0050] The piezoelectric layer 102 comprises a plurality of individual ultrasonic transducer components 120 (also referred to herein as “transducer elements”). In one embodiment, the piezoelectric layer 102 is plated on its top and bottom surfaces 1 10a, 1 10b with a conductive material forming the electrodes 103, such that a conductive electrode 103 is plated on each transducer element 120. In one embodiment, a positive electrode 103 is plated on one side (e.g., the top surface 1 10a) of the piezoelectric layer 102 and a negative electrode 103 is plated on the opposite side (e.g., the bottom surface 110b) of the piezoelectric layer 102. Any suitable process (including, but not limited to, a subtractive process, an additive process, etching, physical vapor deposition, etc.) may be used to plate the conductive electrodes 103 and any suitable material (e.g., platinum, chrome, gold) may be used. The electrodes 103 may have any suitable thickness. In one embodiment, the electrodes 103 have a thickness of about 100 nm. The transducer elements 120 are interconnected to enable the transducer 100 to interface with a driver circuit (not shown) through the wires 107. The wires 107 are illustratively bonded to the electrodes 103 using any suitable technique and may comprise coaxial cables, twisted pair cables, or the like. The driver circuit is then configured to apply (through the wires 107 and via the electrodes 103) electrical excitation signals (e.g., an excitation voltage) to each transducer element 120 to operate the latter.

[0051] The ultrasonic transducer elements 120 are disposed in a common plane (defined by the x and y axes of Fig. 2A, with the x axis being parallel to the longitudinal axis A and the y axis being transverse to the longitudinal axis A). In particular, the ultrasonic transducer elements 120 are arranged in a linear (or one-dimensional, 1 D) array, along the longitudinal axis A, as illustrated in Fig. 2A. The transducer elements 120 comprise an emitting element 120a and one or more receiving elements 120b spaced from the emitting element 120a. The emitting element 120a and the receiving elements 120b are positioned on the same side of the object 101. Any suitable number of receiving elements 120b may be used. It should be understood that the higher the number of receiving elements 120b, the more accurate the results produced by the transducer 100. However, the higherthe number of receiving elements 120b, the largerthe dimensions (e.g., the length) ofthe transducer 100. It is therefore desirable to select the number of receiving elements 120b to maximize accuracy while minimizing the dimensions (e.g., length) of the transducer 100. [0052] Although reference is made herein to the transducer 100 comprising a single emitting element 120a, it should be understood that, although not illustrated, the transducer 100 may comprise one or more emitting elements as in 120a in some embodiments. In this case, it is desirable for the emitting elements as in 120a to be properly separated from one another (i.e. spaced by a suitable distance that may vary depending on the application). In some embodiments, a first and a second emitting element as in 120a may be provided, with the first emitting element 120a being positioned adjacent one end of the array of receiving elements 120b and the second emitting element 120a being positioned adjacent the opposite end of the array of receiving elements 120b. This may enable measurement in two directions without requiring the transducer 100 to be moved.

[0053] The piezoelectric layer 102 may have any suitable dimensions, i.e. any suitable length T, thickness ‘t’, and width ‘w’, depending on the application. The length I is defined from the emitting element 120a to a last one of the receiving elements 120b (i.e. the receiving element 120b that is positioned furthest away from the emitting element 120a). A length ‘l_R’, which is lower than the length I, is defined from a first one of the receiving elements 120b (i.e. the receiving element 120b that is positioned closest to the emitting element 120a) to the receiving element 120b. The thickness t is defined from the top face 110a of the piezoelectric layer 102 to the bottom face 1 10b of the piezoelectric layer 102. The thickness t may be uniform along the length of the transducer 100. The width w is defined from an edge (or side) 122a of the piezoelectric layer 102 to the opposed edge (or side) 122b of the piezoelectric layer 102. The width w may be uniform such that the emitting element 120a and the receiving element(s) 120b have the same width. It may be desirable for the piezoelectric layer 102 to have a length I between about 30 mm and about 60 mm (for a number of receiving elements 120b between about 30 and 60), a width w between about 5 mm to about 10 mm, and a thickness t between about 0.5 mm to about 4 mm, depending on the application. In one embodiment, the piezoelectric layer 102 has a length I of about 60 mm, a width w of about 10 mm, and a thickness t of about 0.96 mm. Other embodiments may apply.

[0054] Each receiving element 120b has a width d_x (referred to herein as the “element width”), and every two adjacent receiving elements 120b are spaced apart by a distance (also referred to as the “pitch”) p (shown in Fig. 3), which is the distance between the center of two adjacent receiving elements 120b. The element width d_x and the pitch p may have any suitable value. In one embodiment, the element width d_x is between about 1 mm and 2 mm and the pitch p is about 2 mm or less (where the element width d_x is given by d_x = p - g, where g is the width of the gap 124 between adjacent receiving elements 120b, as discussed further below), for a piezoelectric layer having a length between 30 mm and 60 mm. In order to enable extraction of dispersion curves (e.g., by two-dimensional Fast-Fourier Transform (2D-FFT), as will be described further below, or any other suitable technique such as singular value decomposition or SVD), the pitch p is regular (i.e. the receiving elements 120b are spaced by a same distance) along the length of the piezoelectric layer 102. The emitting element 120a is in turn spaced from a first one of the receiving elements 120b (i.e. the receiving element 120b closest to the emitting element 120a) by a distance (or spacing) d, thereby creating a void (or gap) between the emitting elements 120a and the first one of the receiving elements 120b The value of the spacing d may be selected to be a multiple of the value of the element width d_x. The multiple is preferably an integer greater than one (1) such that the spacing d is greater than the element width d_x. As such, the emitting element 120a may be spaced form the first one of the receiving elements 120b by a distance d which is equal to the overall width of several adjacent receiving elements 120b. For example, the multiple may be equal to five (5) such that the spacing d is five (5) times the width d_x. For example, for an element width d_x of 1 mm, the spacing d may be 5 mm. Other embodiments may apply.

[0055] In one embodiment and as can be seen in Fig. 2C, an absorbing element 105 fills the void between the emitting element 120a and the first one of the receiving elements 120b. By separating the emitting element 120a from the receiving elements 120b, acoustic isolation between the transducer elements 120 can be achieved, thus preventing ultrasonic signals from propagating directly between the emitting element 120a and the receiving elements 120b.

[0056] As illustrated in Fig. 3, the receiving elements 120b may be formed by cutting the piezoelectric layer 102 at regular intervals (equal to the pitch p) along its thickness t (i.e. cutting the piezoelectric layer 102 in the transverse direction perpendicular to the longitudinal axis A) to create gaps 124 between adjacent receiving elements 120b. Each gap 124 has a non-zero width g, the value of the gap width g varying depending on the application and being defined by the width of the device used to form the receiving elements 120b (e.g., the blade cutting the piezoelectric layer 102). It is however desirable for the width g of the gaps 124 to not exceed 0.1 mm. The gaps 124 are formed in the piezo electric layer 102 to prevent mechanical cross-talk between the receiving elements 120b. Any suitable cutting technique including, but not limited to, laser cutting, die cutting, diamond cutting, or the like, may be used to form the receiving elements 120b. In one embodiment, the piezoelectric layer 102 is cut along part of its thickness t, such that the gaps 124 only extend partly through the thickness t by a depth t-i. In one embodiment, the depth ti of cut is between about 90% and about 95% of the overall thickness t of the piezoelectric layer 102. For example, for an overall thickness t of 1 mm, the depth ti of cut may be between 0.90 mm and 0.95 mm. Cutting the piezoelectric layer 102 along part of its thickness t may allow for a continuous electrode 103 to be provided on the bottom surface 110b of the piezoelectric layer 102, thus facilitating manufacturing of the transducer 100. It should however be understood that the piezoelectric layer 102 may alternatively be cut along the entirety of its thickness t such that the depth ti of cut is equal to the thickness t. It should however be understood that the receiving elements 120b may be formed without any cutting being used. Each receiving element 120b may indeed be separated from adjacent receiving elements 120b by positioning the receiving elements 120b such that they are equally spaced, thereby alleviating the need to cut the piezoelectric layer 102.

[0057] In operation, in response to the excitation voltage applied to the electrodes 103, the emitting element 120a is configured to emit input ultrasound waves for application to the object 101 through the matching layer 104 along the direction indicated by arrow C1 in Figs. 1A and 2C. In one embodiment, the direction C1 is substantially perpendicular to the longitudinal axis A. It should however be understood that the angle between the direction C1 and the longitudinal axis A of the object 101 may vary depending on the application. In biomedical applications, such as when the transducer 100 is used to examine a bone, the soft tissue surrounding the bone acts as a fluid, thus resulting in the input ultrasound waves being emitted at a ninety (90) degree angle (i.e. the direction C1 to be perpendicular to the longitudinal axis A of the bone) into the soft tissue for transmission to the bone. In other applications (e.g., industrial applications), the input ultrasound waves may be emitted in the (x, y) plane (i.e. along a direction C1 substantially parallel to either the x axis or the y axis) in order to generate a different type of wave in the object 101 under inspection. In addition, controlling (using any suitable means) the angle between the direction C1 and the longitudinal axis A of the object may allow to favor certain propagation mode associated with the ultrasound waves, thus allowing for additional mode selectivity.

[0058] The bandwidth of (i.e. the range of frequencies associated with) the transducer 100 is centered at a low frequency (also referred to as the “transmission center frequency”), which is a frequency lowerthan or equal to about 500 kHz. As used herein, the term “center frequency” or “central frequency”, when used with reference to an ultrasound wave (e.g., emitted by the transducer 100), refers to the frequency with the strongest amplitude inside the bandwidth of the transducer 100. If the amplitude is constant within the bandwidth, the center frequency corresponds to the frequency in the middle of the bandwidth. The emitting element 120a is thus configured for the application of the input ultrasound waves having a center frequency in the low frequency range, i.e. in a frequency range between bout 20 kHz and about 500 kHz. In this manner, it is possible to ensure that the input ultrasound waves penetrate deep into the object 101 for assessing the characteristics of the overall object 101 (rather than characteristics of a localized area of the object 101 as per existing techniques). It should be understood that the frequency range of the input ultrasound waves emitted by the emitting element 120a may vary and may be defined according to the properties and thickness of the object 101. In one embodiment, the input ultrasound waves have a frequency between about 50 kHz and about 500 kHz. It should however be understood that other frequencies are considered and any suitable frequency (lower than or equal to about 500 kHz) allowing ultrasonic guided waves to propagate longitudinally through the object 101 may be used. As used herein, the term “ultrasonic guided waves” (or UGW) refers to ultrasound waves which are confined by the boundaries of an elongated structure (e.g., a waveguide), allowing the waves to travel large distances with little loss in energy. Indeed and as understood by those skilled in the art, under the cutoff frequency of the first high order mode, ultrasonic guided waves have the ability to propagate over long distances with minimal attenuation.

[0059] The input ultrasound waves cause ultrasonic guided waves to propagate longitudinally in the object 101 , along a direction substantially parallel to the longitudinal axis A (indicated by arrow C2 in Figs. 1A and 2C), a phenomenon referred to herein as “axial transmission”. In other words, the ultrasonic guided waves propagate in a direction that is substantially perpendicular to the direction at which the input ultrasound waves are emitted. The ultrasonic guided waves propagate along the length of the object 101 by a given distance, while being guided by the object’s boundaries. This in turn causes acoustic waves to be generated. The one or more receiving elements 120b are used to acquire the acoustic waves from the object 101. In some embodiments, the receiving elements 120b are configured for acquiring the acoustic waves over any suitable period, as time-domain signals which are indicative of propagation properties of the ultrasonic guided waves propagating through the object 101 . In one embodiment, receiving elements 120b that are positioned further away from the emitting element 120a will receive an acoustic wave after receiving elements 120b that are positioned closer to the emitting element 120a.

[0060] The acoustic waves acquired by the receiving elements 120b are then processed, for instance via a processing system 121 communicatively coupled (using any suitable communications means) to the transducer 100. The processing system 121 may be implemented via any suitable computer or other computing device, as appropriate. The processing system 121 acquires from the transducer 100 information relating to the input ultrasound waves emitted by the emitting element 120a and to the acoustic waves acquired by the receiving elements 120b. The processing system 121 is configured for processing the information received from the transducer 100, for instance to assess various characteristics or properties of the object 101 , using the propagation properties of the ultrasonic guided waves propagating through the object 101. In particular, following acquisition, the acoustic waves may be processed by the processing system 121 so as to produce a signal representation of the object 101. Such processing may be performed using any suitable technique including, but not limited to, 2D-FFT.

[0061] In one embodiment, the signal representation of the object 101 may be shown as a dispersion curve, comprising a frequency (y-axis) expressed in MHz versus wavenumber (x- axis) expressed in reciprocal meters (1/m or nr¹), where the wavenumber is the spatial frequency of a wave, measured in cycles per unit distance or radians per unit distance. It should however be understood that such a signal representation is one embodiment for processing the acoustic waves acquired by the receiving elements 120b. Fig. 4 illustrates an example of a signal representation 400, which comprises information on the propagation properties of the ultrasonic guided waves propagating through the object 101. In particular, dispersion curve trajectories 402, which can be seen in Fig. 4, provide information relative to bone material properties and geometry (the object 101 being a bone). The signal representation 400 is thus indicative of various characteristics of the object 101 when compared to reference signals associated with objects of known characteristics (e.g., obtained from a look-up table), as described further below.

[0062] In medical applications, examples of characteristics of the object 101 include intrinsic biological properties of the object 101 . For example, the transducer 100 may be placed along a body part over an examined bone (e.g., a long bone such as the arm radius bone or the leg tibia bone) and in contact with the skin, with the emitting element 120a and the receiving elements 120b being positioned on the same side (e.g., anterior or posterior) of the bone. The signal representation 400 may then be indicative of properties of the bone (e.g., cortical thickness, bone shape and other geometrical properties, bone stiffness, bone density, bone elasticity, bone porosity, degradation in bone thickness, material properties, and/or mechanical properties) that allow for cortical bone characterization. In industrial applications, examples of characteristics of the object 101 include, but are not limited to, quality parameters such as component thickness and the presence of defects, or bonded joint properties.

[0063] In order to determine the characteristics of the object 101 , the processing system 121 may be configured to compare the signal representation as in 400 to multiple reference signals which may be obtained from experimental data, simulations, or any other suitable source. When a particular reference signal is found to match (e.g., within a given threshold) the signal representation as in 400 or is found to be the closest match of a group of reference signals, the characteristics that produced the particular reference signal can be attributed to the object 101 associated with the signal representation 400. In some embodiments, the processing system 121 implements an error function and minimization of the error function is sought to identify a closest match for the signal representation 400. For example, the processing system 121 may minimize an error function having as inputs the signal representation 400 and the reference signals, and select one of the reference signals based on the minimizing of the error function. Other embodiments may apply. To ensure the matching is based on dispersive properties of ultrasonic wave and their amplitude, the amplitude of the signal representation 400 is of importance. [0064] Referring now to Fig. 5, a method 500 for examining an object extending along a longitudinal axis using a multi-element ultrasonic transducer, such as the transducer 100 of Fig. 1A, will now be described in accordance with one embodiment. The method 500 may be performed using the processing system 121 of Fig. 1A, which may command or otherwise operate the transducer 100 to perform certain actions, as appropriate.

[0065] At step 502, the method 500 comprises applying input ultrasound waves to the object at low frequencies to cause a longitudinal propagation of ultrasonic guided waves through the object along the longitudinal axis. The input ultrasound waves may be applied using an emitting ultrasonic transducer element, such as the emitting element 120a of Fig. 2A. The input ultrasound waves applied at step 502 have a center frequency lower than or equal to 500 kHz. The input ultrasound waves may be applied at step 502 at an angle substantially perpendicular to the longitudinal axis of the object (e.g., axis A of Fig. 1A).

[0066] At step 504, the method 500 comprises acquiring acoustic waves produced by the propagation of the ultrasonic guided waves through the object. The acoustic waves may be acquired using one or more receiving ultrasonic transducer elements (such as the receiving elements 120b of Fig. 2A) which are spaced from the emitting ultrasonic transducer element and arranged therewith along the longitudinal axis.

[0067] At step 506, the method 500 comprises processing the acoustic waves to identify at least one characteristic of the object. In some embodiments, processing at step 506 comprises generating a signal representation of the acoustic waves and comparing the signal representation of the acoustic waves to a plurality of reference signals to identify the at least one characteristic of the object. The signal representation of the acoustic waves may be generated by applying a 2D-FFT to time-domain signals representative of the acoustic waves. The signal representation of the acoustic waves may be compared to the plurality of reference signals by minimizing an error function having as inputs the signal representation of the acoustic waves and the plurality of reference signals, and selecting one of the plurality of reference signals based on the minimizing of the error function.

[0068] At step 508, the method 500 comprises outputting an output signal indicative of the at least one characteristic of the object. As used herein, outputting of the output signal may comprise outputting to a display device or other suitable output device (e.g., associated with the processing system 121) or to another computing device and/or processing system, which may be local or remote to the processing system 121 . The output signal may be output by the processing system 121 for presentation to an operator on a display, for storage in a data store or other repository, or the like. In medical applications where the object is a long bone, the at least one characteristic comprises at least one of a geometry, a degradation, and mechanical properties of the bone. In industrial applications where the object is a plate-like structure, the at least one characteristic comprises at least one quality parameter (e.g., component thickness and/or presence of defects) of the plate-like structure.

[0069] Fig. 6 is a schematic diagram of a computing device 600, exemplary of an embodiment. As depicted, computing device 600 includes at least one processing unit (or processor) 602, memory 604 storing instructions 606, and at least one I/O interface (illustrated as ‘Inputs’ and ‘Outputs’). The computing device 600 may be used to implement the processing system 121 of Fig. 1A. For simplicity, only one computing device 600 is shown but more computing devices 600 operable to access remote network resources and exchange data may apply. The computing devices 600 may be the same or different types of devices. The elements of the computing device 600 may be connected in various ways including directly coupled, indirectly coupled via a network, and distributed over a wide geographic area and connected via a network (which may be referred to as “cloud computing”).

[0070] Each processing unit 602 may be, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), or any combination thereof.

[0071] Memory 604 may include a suitable combination of any type of computer memory that is located either internally or externally such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. [0072] The I/O interface enables the computing device 600 to interconnect with one or more input devices, such as a keyboard, mouse, camera, touch screen and a microphone, or with one or more output devices such as a display screen and a speaker. Additionally, the I/O interface may facilitate the exchange of information and/or commands between the processing system 121 , when implemented via the computing device 600, and the transducer 100.

[0073] In some embodiments, the computing device 600 includes one or more network interfaces to enable the computing device 600 to communicate with other components, to exchange data with other components, to access and connect to network resources, to serve applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, and others, including any combination of these.

[0074] Compared to existing techniques, the systems and methods described herein may, in some embodiments, allow to improve measurement accuracy and accordingly achieve more precise determination of the characteristics of the object under examination. In particular, in medical applications such as the diagnosis and prevention of osteoporosis, applying the input ultrasound waves for axial transmission at low frequencies (i.e. below 500 kHz) may allow for the ultrasound waves to penetrate deeper into the bone, thus allowing for various properties of the entire bone (e.g., geometry, degradation in bone thickness, and mechanical properties of the cortical region) to be assessed. In contrast, existing techniques typically apply input ultrasound waves at high frequencies (i.e. in the MHz range), which may only allow to assess properties (e.g., porosity and cortical geometry) of a localized area of the bone near the surface. This may in turn prove insufficient to assess the risk of fracture. In addition, the configuration of the proposed multi-element ultrasonic transducer allows for the device to be portable, which may result in facilitated use on the field. Furthermore, the costs associated with the overall measurement system can be reduced using the proposed ultrasonic transducer. [0075] Throughout the present discussion, numerous references may be made regarding servers, services, interfaces, portals, platforms, or other systems formed from computing devices. It should be appreciated that the use of such terms is deemed to represent one or more computing devices having at least one processor configured to execute software instructions stored on a computer readable tangible, non-transitory medium. For example, a server can include one or more computers operating as a web server, database server, or other type of computer server in a manner to fulfill described roles, responsibilities, or functions.

[0076] Various embodiments may be in the form of a software product. The software product may be stored in a non-volatile or non-transitory storage medium, which can be a compact disk read-only memory (CD-ROM), a USB flash disk, or a removable hard disk. The software product includes a number of instructions that enable a computer device (personal computer, server, or network device) to execute the methods provided by the embodiments.

[0077] The embodiments described herein are implemented by physical computer hardware, including computing devices, servers, receivers, transmitters, processors, memory, displays, and networks. The embodiments described herein provide useful physical machines and particularly configured computer hardware arrangements. The embodiments described herein are directed to electronic machines and methods implemented by electronic machines adapted for processing and transforming electromagnetic signals which represent various types of information. The embodiments described herein pervasively and integrally relate to machines, and their uses; and the embodiments described herein have no meaning or practical applicability outside their use with computer hardware, machines, and various hardware components. Substituting the physical hardware particularly configured to implement various acts for non-physical hardware, using mental steps for example, may substantially affect the way the embodiments work. Such computer hardware limitations are clearly essential elements of the embodiments described herein, and they cannot be omitted or substituted for mental means without having a material effect on the operation and structure of the embodiments described herein. The computer hardware is essential to implement the various embodiments described herein and is not merely used to perform steps expeditiously and in an efficient manner. [0078] For example, and without limitation, the computing device 500 may be a server, network appliance, embedded device, computer expansion module, personal computer, laptop, personal data assistant, cellular telephone, smartphone device, ultra-mobile personal computer (UMPC) tablets, video display terminal, gaming console, electronic reading device, and wireless hypermedia device or any other computing device capable of being configured to carry out the methods described herein

[0079] The present disclosure provides many example embodiments. Although each embodiment represents a single combination of inventive elements, other examples may include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, other remaining combinations of A, B, C, or D, may also be used.

[0080] The term “connected” or "coupled to" may include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0081] Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope as defined by the appended claims. It should be understood that the examples described above and illustrated herein are intended to be exemplary only.

[0082] Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. Additionally, the scope of the following claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the description as a whole.

Claims

WHAT IS CLAIMED IS:

1. A multi-element ultrasonic transducer for examining an object, the transducer comprising: a piezoelectric layer comprising: at least one emitting element configured to apply to the object input ultrasound waves having a center frequency lower than or equal to 500 kHz to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object; and a plurality of receiving elements spaced from the at least one emitting element, the plurality of receiving elements and the at least one emitting element arranged along the longitudinal axis, the plurality of receiving configured to acquire, from the object, acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves through the object.

2. The transducer of claim 1 , wherein the plurality of receiving elements are formed by cutting through at least part of a thickness of the piezoelectric layer at regular intervals along a length of the piezoelectric layer.

3. The transducer of claim 2, wherein the plurality of receiving elements are formed by cutting through between about 90% and about 95% of the thickness of the piezoelectric layer.

4. The transducer of claim 2, wherein the plurality of receiving elements are formed by cutting through an entirety of the thickness of the piezoelectric layer.

5. The transducer of any one of claims 1 to 4, wherein the at least one emitting element is configured to apply the input ultrasound waves along a direction perpendicular to the longitudinal axis.

6. The transducer of any one of claims 1 to 5, wherein the plurality of receiving elements is arranged in a linear array along the longitudinal axis.

7. The transducer of any one of claims 1 to 6, wherein the at least one emitting element is spaced from the plurality of receiving elements by a first distance, and further wherein adjacent ones of the plurality of receiving elements are spaced apart by a second distance, the first distance greater than the second distance.

8. The transducer of claim 7, further comprising an absorbing element positioned in a gap between the at least one emitting element and a first one of the plurality of receiving elements, the absorbing element configured to acoustically isolate the at least one emitting element from the plurality of receiving elements.

9. The transducer of any one of claims 1 to 8, further comprising at least one matching layer interposed between the piezoelectric layer and the object, the at least one matching layer configured to provide impedance matching between the piezoelectric layer and the object.

10. The transducer of any one of claims 1 to 9, further comprising a backing layer coupled to the piezoelectric layer, the backing layer configured to prevent parasitic reflection of the input ultrasound waves.

1 1 . The transducer of any one of claims 1 to 10, further comprising electrodes disposed on opposed surfaces of the piezoelectric layer, wherein the at least one emitting element is configured to apply the input ultrasound waves in response to an excitation voltage applied to the electrodes.

12. The transducer of any one of claims 1 to 11 , further comprising a casing configured to receive the matching layer, the piezoelectric layer, and the backing layer therein.

13. A method for examining an object, the method comprising: applying, using at least one emitting ultrasonic transducer element, input ultrasound waves to the object to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object, the input ultrasound waves having a center frequency lower than or equal to 500 kHz; acquiring, using a plurality of receiving ultrasonic transducer elements spaced from the at least one emitting ultrasonic transducer element and arranged therewith along the longitudinal axis, acoustic waves from the object, the acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves through the object; processing the acoustic waves to identify at least one characteristic of the object; and outputting an output signal indicative of the at least one characteristic of the object.

14. The method of claim 13, wherein the input ultrasound waves are applied along a direction perpendicular to the longitudinal axis.

15. The method of claim 13 or 14, wherein processing the acoustic waves to identify the at least one characteristic of the object comprises: generating a signal representation of the acoustic waves; and comparing the signal representation of the acoustic waves to a plurality of reference signals to identify the at least one characteristic of the object.

16. The method of claim 15, wherein generating the signal representation of the acoustic waves comprises applying a two-dimensional Fast-Fourier Transform to the acoustic waves.

17. The method of claim 15 or 16, wherein comparing the signal representation of the acoustic waves to the plurality of reference signals comprises minimizing an error function having as inputs the signal representation of the acoustic waves and the plurality of reference signals, and selecting one of the plurality of reference signals based on the minimizing of the error function.

18. The method of any one of claims 13 to 17, wherein the object is a long bone, and further wherein the acoustic waves are processed to identify the at least one characteristic comprising at least one of a geometry, a degradation, and mechanical properties of the bone.

19. The method of any one of claims 13 to 17, wherein the object is a plate-like structure, and further wherein the acoustic waves are processed to identify the at least one characteristic comprising at least one quality parameter of the plate-like structure.

20. The method of any one of claims 13 to 17, wherein the object is a bonded joint, and further wherein the acoustic waves are processed to identify the at least one characteristic comprising at least one property of the bonded joint.

21 . A system for examining an object, the system comprising: a processing unit; and a non-transitory computer-readable medium having stored thereon instructions executable by the processing unit for: applying, using at least one emitting ultrasonic transducer element, input ultrasound waves to the object to cause a longitudinal propagation of ultrasonic guided waves along a longitudinal axis of the object, the input ultrasound waves having a center frequency lower than or equal to 500 kHz; acquiring, using a plurality of receiving ultrasonic transducer elements spaced from the at least one emitting ultrasonic transducer element and arranged therewith along the longitudinal axis, acoustic waves from the object, the acoustic waves produced by the longitudinal propagation of the ultrasonic guided waves through the object; processing the acoustic waves to identify at least one characteristic of the object; and outputting an output signal indicative of the at least one characteristic of the object.