Ultrasonic Transducers

Abstract

An ultrasonic transducer for surgical applications is disclosed. The ultrasonic transducer includes a rear mass; a forward mass; an ultrasonic actuator portion held between the rear mass and the forward mass; and an ultrasonic horn portion forward of the forward mass. The rear mass, the ultrasonic actuator portion, the forward mass, and the ultrasonic horn portion are disposed along a longitudinal axis of the transducer. Vibrations generated by the ultrasonic actuator portion are transmitted along a vibrational energy transmission path to the forward mass and to the ultrasonic horn portion, where they are amplified in amplitude by the ultrasonic horn portion. One or more of the rear mass, the forward mass, and the ultrasonic horn portion include a plurality of openings that open toward the longitudinal axis, intersect the vibrational energy transmission path, and are configured to provide increased mechanical compliance in a direction along the vibrational energy transmission path.

Description

[Technical field]

[0001] This application claims priority to GB2110897.2, filed on July 29, 2021, the content and elements of which are incorporated herein by reference for all purposes.

[0002] ULTRASONIC TRANSDUCERS AND METHODS OF OPERATING ULTRASONIC TRANSDUCERS FIELD OF THE DISCLOSURE The present invention relates to ultrasonic transducers and methods of operating ultrasonic transducers that are particularly, though not necessarily exclusively, suited for surgical applications. [Background technology]

[0003] The design of modern ultrasonic surgical devices, either for hard or soft tissue, almost always resembles the configuration invented by Paul Langevin and Cirofsky in 1922 for underwater applications [1]. Generally, these devices employ ultrasonic vibrations to enhance the cutting performance and employ transducers mounted in handheld devices. For soft tissue cutting, some common features can be identified. Figure 1 shows the Harmonic® ACE® + Shears (Ethicon® Endosurgery, Johnson & Johnson, Cincinnati, Ohio, USA), where one can recognize the waveguide 10, the handpiece 12, and the Langevin transducer 14. The inset in Figure 1 also shows the vibration direction "Vib", which in this case is longitudinal (parallel to the longitudinal axis of the transducer and the waveguide), and the jaw blade mechanism with pivotable jaws 16 and vibrating blade 18.

[0004] SENHANCE TMThe Harmonic® ACE® + Shears together with Ultrasonic (BOWA® Medical, BOWA-electronic GmbH & Co. KG, Gomaringen, Germany) are the only two ultrasonic cutting devices compatible with robotic surgery platforms at the time of writing, which are the Da Vinci® Surgical System (Intuitive® Surgical Inc., Sunnyvale, CA, USA) and the SENHANCE Surgical System (Intuitive® Surgical Inc., Sunnyvale, CA, USA), respectively. TM Surgical System (BOWA® Medical, Gomaringen, Germany).

[0005] One of the most recent inventions in Da Vinci® energy devices is the EndoWrist® (Intuitive® Surgical Inc.). This articulated joint allows a range of motions at the end effector similar to that of the human wrist, replicating the experience of open surgery. Figure 2 shows a typical Da Vinci® end effector with EndoWrist® technology. The end effector 20 is attached to the end of a shaft 22 and has a first pivot joint 24 that allows flexion and extension (rotation about a first axis) and a second pivot joint 26 that allows adduction and abduction (rotation about a second axis that is (in this case) perpendicular to the first axis). A grasper 28 is located at the distal end of the end effector.

[0006] Several energy instruments with EndoWrist® technology available at the time of writing have a diameter of 5-10 mm, which allows them to be inserted through a laparoscopic port and manipulated inside the human body. To date, there are no ultrasonic cutting devices with EndoWrist® technology. Figure 2 shows the range of motion available with the EndoWrist® generic end effector [2]. Current ultrasonic cutting devices only allow axial and rotational motion because the transducer is too large to fit into a 5-10 mm trocar. The transducer is axially constrained to the robot arm, and the waveguide that transmits the ultrasonic vibrations from outside the human body to the end effector inside cannot bend. This is a significant disadvantage for surgical ultrasonic devices. Indeed, ultrasonic cutting has been shown to be more precise and effective than other energy instruments, with superior coagulation rates, but the latter are still chosen for their agility.

[0007] US Pat. No. 9,408,622 discloses a flexible waveguide that overcomes some of the problems discussed above, but still offers only limited dexterity.

[0008] Ultrasonic surgical instruments are an alternative to electrocautery instruments and have the potential to achieve similar results while avoiding some of the drawbacks of electrocautery instruments.

[0009] Harmonic® ACE + Shears is the only ultrasound device compatible with the Da Vinci® Surgical System. One of its main drawbacks is its incompatibility with the EndoWrist® and its lack of flexibility. The main reason for this is the size of the ultrasound transducer, which is too long and large to clamp onto the end of the wristed joint of the end effector and thread through a burr hole or laparoscopic port.

[0010] Long rigid waveguides are preferred for transmitting ultrasonic frequency vibrational energy from the outside to the inside of the human body, which necessarily limits ultrasonic energy devices to a few applications that do not require access to difficult sites.

[0011] Table 1 outlines the advantages and disadvantages of ultrasonic cutting instruments compared to monopolar and bipolar surgical instruments for minimally invasive surgery. Despite the numerous advantages presented in Table 5.1, the long straight waveguide and lack of an articulated joint at the blade tip make the device less flexible in terms of maneuverability, limiting its use to some procedures where only axial targets can be reached.

[0012] Table 1 : Advantages and disadvantages of ultrasonic energy instruments compared with monopolar and bipolar electrocautery instruments for minimally invasive surgery [6], [7]. TIFF2024528106000002.tif73149

[0013] Ultrasound technology has been employed in robotic laparoscopic surgery for the purpose of parenchymal (functional) tissue cutting, separating the parenchyma of an organ from the connective and supporting tissues. Ultrasound energy is also used in lobectomy for the removal of parts of an organ. Other common laparoscopic procedures in which ultrasonic energy is preferred, despite being a non-articulating instrument, include gastrectomy, adrenalectomy, splenectomy, and hepatectomy.[6] Summary of the Invention [Problem to be solved by the invention]

[0014] In view of the above, the present invention has been conceived. [Means for solving the problem]

[0015] With the current state of the art in Langevin transducer design, ultrasonic surgical instruments such as dissectors (dissectors) cannot be miniaturized while maintaining the functionality and performance of the device.

[0016] Accordingly, the inventors have addressed the problems identified above by examining in detail the effects of the mechanical compliance of transducer components along the transducer's vibrational energy transmission path.

[0017] This disclosure presents different "developments" of the invention, each with different optional aspects and further optional features, which are set out below as Development A and Development B.

[0018] Development A In a first aspect of development A, the present invention provides an ultrasonic transducer for surgical applications, the ultrasonic transducer comprising: rear mass; anterior mass; an ultrasonic actuator portion held between the rear mass and the front mass; An ultrasonic horn portion is provided in front of the front mass portion, The vibration generated by the ultrasonic actuator portion is transmitted to the front mass portion and the ultrasonic horn portion along a vibration energy transmission path, and the vibration is amplified by the ultrasonic horn portion, One or more of the rear mass, the front mass, and the ultrasonic horn include a plurality of apertures that are configured to intersect the vibrational energy transmission path and provide increased mechanical compliance in a direction along the vibrational energy transmission path.

[0019] In a second aspect of Development A, the present invention provides a surgical instrument comprising an ultrasonic transducer according to the first aspect.

[0020] In a third aspect of Development A, the present invention provides a method of operating an ultrasonic transducer, the ultrasonic transducer comprising: rear mass; anterior mass; an ultrasonic actuator portion held between the rear mass portion and the front mass portion; An ultrasonic horn portion is provided in front of the front mass portion, The method includes providing an electrical signal to the ultrasonic actuator portion, transmitting the electrical signal along a vibrational energy transmission path to the forward mass portion and the ultrasonic horn portion, and generating vibrations by the ultrasonic horn portion to an amplified amplitude; One or more of the rear mass, the front mass, and the ultrasonic horn include a plurality of apertures that are configured to intersect the vibrational energy transmission path and provide increased mechanical compliance in a direction along the vibrational energy transmission path.

[0021] In a fourth aspect of Development A, the present invention provides a method for cutting tissue by ultrasonic cutting with an ultrasonic blade, comprising operating an ultrasonic transducer as described in the third aspect and transmitting vibrational energy to the ultrasonic blade.

[0022] The transducer can be a Langevin type transducer, such as a bolt-on Langevin transducer, which is useful for surgical applications due to its low frequency and high power operating characteristics.

[0023] The ultrasonic actuator portion may comprise a piezoelectric material element, such as a piezoelectric ceramic element. A plurality of such elements may be provided. One or more associated electrodes may be provided for transmitting a drive signal to the piezoelectric material element(s). If the front and / or rear masses are made of a conductive material, such as a metal, the front and / or rear masses may provide ground electrical contact(s) for the piezoelectric material element(s).

[0024] The vibrational energy transmission path in the rear mass, the front mass and / or the ultrasonic horn may include an annulus. The annulus may take the form of, for example, a hollow cylinder, the wall of which extends along the vibrational energy transmission path, and along which the vibrational energy travels during operation. A number of openings intersecting the vibrational energy transmission path may thus be provided through the wall of the annulus. The openings are typically through holes. In principle it is possible to use blind holes, but it is expected that subsequent operation of the transducer would not be appropriate.

[0025] Each aperture may have a substantially uniform cross-section along its depth. When the depth direction of an aperture is considered to be a direction parallel to the walls of the aperture, the depth direction may be substantially perpendicular to the vibrational energy transmission path (e.g., locally at the transducer).

[0026] Each opening may have the same size (e.g., the same diameter if the openings have a circular cross-sectional shape, or other characteristic linear dimension(s) for other shapes). The openings may have the same cross-sectional area. Furthermore, the openings may have the same shape as each other, or may be selected from a limited number (e.g., two, three, or four) shapes.

[0027] The apertures may be arranged according to a repeating pattern, for example, the apertures may be arranged according to a regular lattice, such as a square lattice, a rectangular lattice, a triangular lattice, a hexagonal lattice, etc.

[0028] Alternatively, the apertures may be arranged substantially randomly, or may be randomly offset from a virtually regular repeating pattern.

[0029] There can be three or more apertures. For example, there can be 5 or more, 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, 45 or more, or 50 or more apertures. In some embodiments, there can be more apertures, but typically there are fewer than 500 apertures.

[0030] Suitable cross-sectional shapes for an aperture include circle, ellipse, oval, circle, triangle, square, rectangle, square, diamond, pentagon, hexagon, pentagon, octagon, etc. A combination of two or more such shapes may be used as an aperture. An aperture may have a randomly generated shape. An aperture typically has a closed perimeter.

[0031] The opening is, for example, at least 0.01 mm 2 , at least 0.05 mm 2 , at least 0.1 mm 2 , at least 0.2 mm 2 , at least 0.4 mm 2 , at least 0.6 mm 2 , at least 0.8 mm 2 , at least 1 mm 2 , at least 1.5 mm 2 , or at least 2 mm 2 There is no particular upper limit to the cross-sectional area of ​​the apertures, except that an appropriate number of apertures must be fitted to the overall size of the transducer to affect compliance of the associated components.

[0032] The openings can be formed by any suitable manufacturing technique, such as machining, cutting (e.g., laser cutting) or etching, or by manufacturing the part with a net shape or near net shape technique such as casting, additive manufacture, etc.

[0033] The openings may be filled with a filler material that may have a Young's modulus lower (e.g., at least a factor of 5 lower, at least a factor of 10 lower, at least a factor of 20 lower, or at least a factor of 50 lower) than the Young's modulus of the material in which the openings are formed. Suitable materials include epoxy or other resin-based materials.

[0034] Apertures may be formed in two or more of the rear mass, the front mass and the ultrasonic horn.

[0035] The operating frequency of the transducer may be, for example, at least 1 kHz, at least 5 kHz, at least 10 kHz, at least 20 kHz, or at least 30 kHz, or at least 40 kHz. The operating frequency of the transducer may be, for example, up to 200 kHz, up to 150 kHz, up to 100 kHz, or up to 90 kHz, up to 80 kHz, or up to 70 kHz. For example, a suitable operating frequency is about 55 kHz.

[0036] The displacement amplitude at the distal end of the horn can be in the range of 1 to 200 microns peak-to-peak at the operating frequency.

[0037] In the operating method, the ultrasonic transducer has a power of, for example, 10 to 1000 Wcm -2 The ultrasonic transducer may be operated at a power density in the range of, for example, 1 to 1000 W.

[0038] As mentioned above, the apertures are formed in one or more of the rear mass, the front mass and the ultrasonic horn. These are referred to herein as the vibrational energy transmission line components of the transducer. Each component may have a monolithic structure, i.e., formed from a single piece of material without heterointerfaces (grain boundaries are, of course, permitted). Thus, the requirement that the apertures provide increased mechanical compliance in a direction along the vibrational energy transmission line, with respect to the configuration of the embodiment of the invention, is intended to be compared to a reference configuration in which the ultrasonic transducer is identical except that the apertures are replaced by the material of the relevant component. Considering the operating frequency of the transducer according to the configuration of the embodiment of the invention compared to that of the reference configuration, the operating frequency of the configuration of the embodiment of the invention differs (e.g., is smaller) than the operating frequency of the reference configuration by at least 1 kHz (or at least 2 kHz, or at least 3 kHz, or at least 4 kHz, or at least 5 kHz, or at least 6 kHz, or at least 7 kHz, or at least 8 kHz, or at least 9 kHz, or at least 10 kHz). Thus, the configuration of the embodiment of the invention can have a more compact format than other reference configurations for the same operating frequency. This means that such a transducer is more practical to place for insertion into the body during surgery than placing the transducer outside the body and using a long waveguide. This means that the transducer can be placed distal to a flexible joint of the surgical instrument, allowing for easier positioning of the transducer.

[0039] The length of the transducer may be 40 mm or less (measured along the vibration energy transmission path from the proximal end of the rear mass to the distal end of the horn). The maximum diameter of the transducer (measured perpendicular to the length) may be 15 mm or less.

[0040] Furthermore, as discussed above, when considering a configuration of an embodiment of the present invention in comparison to a reference configuration, the configuration of an embodiment of the present invention may demonstrate one or more figures of merit that are the same as or better than the reference configuration. eff is the k of the reference configuration eff Additionally or alternatively, the Q of the configuration of the embodiment of the present invention may be the same as or better than m is the Q of the reference configuration m It may be the same as or better than.

[0041] Development B Following on from the work that led to Development A, the inventors have conducted further research and believe that their invention in the art may be further expressed as a further development, herein designated Development B. It is contemplated that any of the following aspects and / or further optional features may be combined, alone or in any combination, with any of the aspects or optional features described with respect to Development A.

[0042] In a general aspect of Development B, the present invention provides an ultrasonic transducer for surgical applications, the ultrasonic transducer comprising: rear mass; anterior mass; an ultrasonic actuator portion held between the rear mass portion and the front mass portion; An ultrasonic horn portion is provided in front of the front mass portion, the rear mass, the ultrasonic actuator portion, the front mass, and the ultrasonic horn portion are disposed along a longitudinal axis of the transducer; The vibration generated by the ultrasonic actuator portion is transmitted to the front mass portion and the ultrasonic horn portion along a vibration energy transmission path, and the vibration is amplified by the ultrasonic horn portion, One or more of the rear mass, the front mass, and the ultrasonic horn include a plurality of apertures that open toward the longitudinal axis and are configured to intersect the vibrational energy transmission path and provide increased mechanical compliance in a direction along the vibrational energy transmission path.

[0043] In a first aspect of development B, the present invention provides an ultrasonic transducer according to a general aspect together with one or more of the following features.

[0044] The transducer can be a Langevin type transducer, such as a bolt-on Langevin transducer, which is useful for surgical applications due to its low frequency and high power operating characteristics.

[0045] The ultrasonic actuator portion may comprise a piezoelectric material element, such as a piezoelectric ceramic element. A plurality of such elements may be provided. One or more associated electrodes may be provided for transmitting a drive signal to the piezoelectric material element(s). If the front and / or rear masses are made of a conductive material, such as a metal, the front and / or rear masses may provide ground electrical contact(s) for the piezoelectric material element(s).

[0046] The vibrational energy transmission path in the rear mass, the front mass and / or the ultrasonic horn may include an annulus. The annulus may take the form of, for example, a hollow cylinder, the walls of which surround the longitudinal axis and extend along the vibrational energy transmission path, along which the vibrational energy travels during operation. A number of openings intersecting the vibrational energy transmission path may thus be provided through the wall of the annulus. The openings are typically through holes. In principle it is possible to use blind holes, but it is expected that subsequent operation of the transducer would not be appropriate.

[0047] The apertures are positioned to increase mechanical compliance in a direction along the vibrational energy transmission path. In particular, the axial stiffness of the rear mass, the front mass and / or the ultrasonic horn can be adjusted by the presence of the apertures. The axial stiffness affects the resonant frequency at which longitudinal modes occur.

[0048] Longitudinal-torsional (LT) mode conversion can occur by changing from longitudinal to torsional modes or by coupling of longitudinal and torsional modes [see, for example, Ultrasonics 52 (2012) 950-988]. In operation, the apertures may provide substantially no longitudinal to torsional mode conversion. For example, the apertures may be provided in an achiral array. Additionally or alternatively, the apertures may be provided in a non-helical array. If a helical array is discernible in the array, preferably a mirror-symmetric helical array is also discernible in the array. Avoiding LT mode conversion preserves the longitudinal modes, which is desirable for cutting soft tissue.

[0049] The achiral nature of the array may be determined by the relative positions of the apertures, optionally in combination with the shape of each aperture. For example, the relative positions of each aperture and the shape of each aperture may be arranged such that the array of apertures is superimposable on its own mirror image. The mirror image may be defined with respect to a plane of reflection parallel to the longitudinal axis.

[0050] In some embodiments, the apertures are not provided in the ultrasonic horn. Thus, to the extent this specification suggests that apertures be provided in one or more of the rear mass, the front mass, and the ultrasonic horn, and the transducer optionally includes further features disclosed herein, it should be expressly understood that a modification of this disclosure would be for the apertures to be formed only in the rear mass and / or the front mass, and not in the ultrasonic horn.

[0051] The array of apertures may be defined relative to the geometric centre or centroid of each aperture. The geometric centre is the average position of all points along the edge of an aperture. The apertures (e.g. geometric centres) may be arranged in a reflective symmetrical array, where for at least a portion of the array there is at least one plane of reflective symmetry parallel to and coincident with the longitudinal axis. Alternatively or additionally, for at least a portion or portions of the array there may be at least one plane of reflective symmetry perpendicular to the longitudinal axis.

[0052] The apertures may be arranged according to a repeating pattern. For example, the apertures may be arranged according to a two-dimensional regular lattice mapped onto the surface of the front mass and / or the rear mass. The regular lattice may include a unit cell defined by lattice parameters a, b, and β, where a and b are the lengths of the respective edges of the unit cell and β is the angle between the edges. The regular lattice may include a unit cell where β is 90 degrees and / or where a is equal to b. Regular lattices such as square, rectangular, triangular, and hexagonal lattices may be suitable.

[0053] Alternatively, the apertures may be substantially randomly positioned, or may be randomly offset from a virtually regular repeating pattern.

[0054] There can be three or more apertures. For example, apertures can be formed in the front mass and / or the rear mass where there can be four or more, six or more, eight or more, ten or more, twelve or more, sixteen or more, twenty or more, twenty-four or more, thirty or more, forty or more, or fifty or more apertures. In some embodiments there can be more apertures, but typically there are fewer than 500 apertures.

[0055] The apertures may be longitudinally offset from one another along the longitudinal axis. This longitudinal arrangement may comprise two or more apertures. For example, three or more, four or more, five or more, eight or more, nine or more, or ten or more apertures may be longitudinally offset from one another.

[0056] The apertures may be disposed axially parallel to the longitudinal axis. The apertures may be formed in the forward mass and / or the aft mass, and for a plane parallel to and terminating in the longitudinal axis with a maximum total number of apertures intersecting the plane, the maximum total number of apertures intersecting the plane may be at least two apertures. For example, there may be at least three apertures, at least five apertures, at least six apertures, or at least eight apertures intersected by the plane. The plane may coincide with the apertures across their geometric centers.

[0057] Additionally or alternatively, the apertures may be circumferentially arranged. For example, the apertures may be formed in the forward and / or aft masses, and for a cross section taken perpendicular to the longitudinal axis at a location along the longitudinal axis where the total number of apertures intersecting the cross section is greatest, the maximum total number of apertures intersecting the cross section may be at least two apertures. For example, there may be four or more, six or more, eight or more, ten or more, twelve or more apertures intersected by the cross section. The cross sections may coincide with the apertures through their geometric centers.

[0058] Alternatively, or in addition, the apertures may be formed in the forward and / or aft masses, and for a cross section taken perpendicular to the longitudinal axis at a position along the longitudinal axis corresponding to the maximum total number of apertures intersecting that cross section, the apertures may occupy at least 10% of the circumference of the forward or aft mass, respectively. For example, the apertures may occupy at least 20%, at least 30%, at least 40%, at least 50%, or at least 60% of the circumference of the forward or aft mass, respectively.

[0059] Apertures may be formed in two or more of the rear mass, the front mass and the ultrasonic horn.

[0060] Each aperture may have a substantially uniform cross-section along its depth. When the depth direction of an aperture is considered to be a direction parallel to the walls of the aperture, the depth direction may be substantially perpendicular to the vibrational energy transmission path (e.g., locally at the transducer).

[0061] Suitable cross-sectional shapes for an aperture include circle, ellipse, oval, circle, triangle, square, rectangle, square, diamond, pentagon, hexagon, pentagon, octagon, etc. A combination of two or more such shapes may be used as an aperture. An aperture may have a randomly generated shape. An aperture typically has a closed perimeter.

[0062] Each opening may have the same size (e.g., the same diameter if the openings have a circular cross-sectional shape, or other characteristic linear dimension(s) for other shapes). The openings may have the same cross-sectional area. Furthermore, the openings may have the same shape as each other, or may be selected from a limited number (e.g., two, three, or four) shapes.

[0063] The opening is, for example, at least 0.01 mm 2 , at least 0.05 mm 2 , at least 0.1 mm 2 , at least 0.2 mm 2 , at least 0.4 mm 2 , at least 0.6 mm 2 , at least 0.8 mm 2 , at least 1 mm 2 , at least 1.5 mm 2 , or at least 2 mm 2 There is no particular upper limit to the cross-sectional area of ​​the apertures, except that an appropriate number of apertures must be fitted to the overall size of the transducer to affect the compliance of the associated components.

[0064] Apertures may be formed in the front mass and / or the rear mass, and each aperture may have a plane of reflective symmetry parallel to the longitudinal axis.

[0065] Each opening may have a longitudinal length parallel to the longitudinal axis and a circumferential width in a circumferential direction perpendicular to the longitudinal axis. The circumferential width may be greater than the longitudinal length. For example, the longitudinal length may be less than 95%, 90%, 80%, 60%, 50%, or 40% of the circumferential width.

[0066] The aperture may have an apex angle θ that is bisected by a transverse plane perpendicular to the longitudinal axis. Alternatively, or additionally, the aperture may have an apex angle θ that is bisected by a plane parallel to the longitudinal axis. In some embodiments, the lateral (e.g., circumferential) and longitudinal dimensions of the aperture are determined for a given cross-sectional area based on the magnitude of the apex angle θ.

[0067] The openings can be formed by any suitable manufacturing technique, such as machining, cutting (e.g., laser cutting) or etching, or by manufacturing the part with a net shape or near net shape technique such as casting, additive manufacture, etc.

[0068] The openings may be filled with a filler material that may have a Young's modulus lower (e.g., at least a factor of 5 lower, at least a factor of 10 lower, at least a factor of 20 lower, or at least a factor of 50 lower) than the Young's modulus of the material in which the openings are formed. Suitable materials include epoxy or other resin-based materials.

[0069] The front mass may include a proximal portion in contact with the ultrasonic actuator portion, a distal portion connected to the ultrasonic horn portion, and an intermediate portion disposed between the proximal portion and the distal portion. The aperture may be provided in the intermediate portion.

[0070] The proximal and intermediate portions may have substantially the same outer diameter. For example, the proximal and intermediate portions may be integrally formed with one another. The intermediate and proximal portions may have substantially the same outer diameter. For example, the front mass may have a substantially uniform cross-section. For example, the front and / or rear masses may be cylindrical with a substantially constant diameter. The uniform cross-section and constant diameter are considered as such without consideration of variations due solely to the presence or formation of apertures.

[0071] The apparent elastic modulus of the intermediate portion may be no more than 80% of the apparent elastic modulus of a supposed reference intermediate portion, the supposed reference intermediate portion being identical to the intermediate portion except for the absence of the apertures.

[0072] The length of the transducer (measured along the longitudinal axis from the proximal end of the rear mass to the distal end of the horn) may be 60 mm or less. For example, the length of the transducer may be 40 mm or less. The maximum diameter of the transducer (measured perpendicular to the length) may be 15 mm or less.

[0073] The operating frequency of the transducer may be, for example, at least 1 kHz, at least 5 kHz, at least 10 kHz, at least 20 kHz, or at least 30 kHz, or at least 40 kHz. The operating frequency of the transducer may be, for example, up to 200 kHz, up to 150 kHz, up to 100 kHz, or up to 90 kHz, up to 80 kHz, or up to 70 kHz. For example, a suitable operating frequency is about 55 kHz.

[0074] The displacement amplitude at the distal end of the horn can be in the range of 1 to 200 microns peak-to-peak at the operating frequency.

[0075] In the operating method, the ultrasonic transducer has a power of, for example, 10 to 1000 Wcm -2 It can be operated at a range of power.

[0076] As mentioned above, the apertures are formed in one or more of the rear mass, the front mass and the ultrasonic horn. These are referred to herein as the vibrational energy transmission line components of the transducer. Each component may have a monolithic structure, i.e., formed from a single piece of material without heterointerfaces (grain boundaries are, of course, permitted). Thus, the requirement that the apertures provide increased mechanical compliance in a direction along the vibrational energy transmission line, with respect to the configuration of the embodiment of the invention, is intended to be compared to a reference configuration in which the ultrasonic transducer is identical except that the apertures are replaced by the material of the relevant component. Considering the operating frequency of the transducer according to the configuration of the embodiment of the invention compared to that of the reference configuration, the operating frequency of the configuration of the embodiment of the invention differs (e.g., is smaller) than the operating frequency of the reference configuration by at least 1 kHz (or at least 2 kHz, or at least 3 kHz, or at least 4 kHz, or at least 5 kHz, or at least 6 kHz, or at least 7 kHz, or at least 8 kHz, or at least 9 kHz, or at least 10 kHz). Thus, the configuration of the embodiment of the invention can have a more compact format than other reference configurations for the same operating frequency. This means that such a transducer is more practical to place for insertion into the body during surgery than placing the transducer outside the body and using a long waveguide. This means that the transducer can be placed distal to a flexible joint of the surgical instrument, allowing for easier positioning of the transducer.

[0077] Furthermore, as discussed above, when considering a configuration of an embodiment of the present invention in comparison to a reference configuration, the configuration of an embodiment of the present invention may demonstrate one or more figures of merit that are the same as or better than the reference configuration. eff is the k of the reference configuration eff Additionally or alternatively, the Q of the configuration of the embodiment of the present invention may be the same as or better thanm is the Q of the reference configuration m It may be the same as or better than.

[0078] In a second aspect of development B, the present invention provides a surgical instrument including an ultrasonic transducer according to the first aspect of development B.

[0079] In a third aspect of Development B, the present invention provides a method of operating an ultrasonic transducer according to the first aspect of Development B, the method comprising applying an electrical signal to an ultrasonic actuator portion, transmitting the electrical signal along a vibrational energy transmission path to a forward mass portion and to an ultrasonic horn portion, and generating vibrations of an amplified amplitude by the ultrasonic horn portion.

[0080] In a fourth aspect of Development B, the present invention provides a method of cutting tissue by ultrasonic cutting with an ultrasonic blade, the method comprising operating an ultrasonic transducer as described in the third aspect and transmitting vibrational energy to the ultrasonic blade.

[0081] The present invention includes any combination of the aspects and optional features described herein, except where expressly stated that such combination is expressly prohibited or avoided. [Brief description of the drawings]

[0082] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments and experiments illustrating the principles of the present invention will now be described with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows Harmonic® ACE® + Shears (Ethicon® Endosurgery, Johnson & Johnson, Cincinnati, Ohio, USA). [Diagram 2] FIG. 2 shows a typical Da Vinci® end effector equipped with EndoWrist® technology. [Diagram 3] Figure 3 shows a typical surgical ultrasound system with its major components. [Figure 4] FIG. 4 shows a schematic cutaway perspective view of a classical d33 mode Langevin type ultrasonic transducer. [Figure 5A] Figure 5A is a schematic diagram of a symmetric Langevin transducer. [Figure 5B] Figure 5B is a schematic diagram of an asymmetric Langevin transducer. [Figure 6A] Figures 6A and 6B show the effect of the length and position of the piezoelectric ceramic stack on the efficiency of high-power ultrasound (Figure 6A). The figure is taken from reference

[15] . [Figure 6B] Figure 6B shows the effect of the length and position of the piezoelectric ceramic stack on the normalised figure of merit (Fig. 6B). This figure is taken from reference

[15] . [Figure 7] FIG. 7 shows serpentine electrodes and a schematic diagram showing how they can be arranged in a piezoelectric stack. [Figure 8] FIG. 8 shows a schematic diagram of the longitudinal vibration mode of a rod having the Poisson effect. [Figure 9] FIG. 9 shows diagrams of different hollow cylinders used to study the effect of different holes to modify the apparent Young's modulus. [Figure 10] Figure 10 shows the hole geometry and characteristic angle θ used for the sample shown in Figure 9. Note that the hole orientation in this figure is the same as in Figure 9, with the long axis perpendicular to the page. [Figure 11] Figure 11 shows the longitudinal mode frequency as a function of cylinder length for each hole configuration based on different values ​​of the angle θ. These graphs also show the apparent Young's modulus for the different cylinders modeled. [Figure 12] Figure 12 shows the longitudinal mode frequency as a function of cylinder length for each hole configuration based on different values ​​of the angle θ. These graphs also show the apparent Young's modulus of the different cylinders modeled. [Figure 13]Figure 13 shows the longitudinal mode frequency as a function of cylinder length for each hole configuration based on different values ​​of the angle θ. These graphs also show the apparent Young's modulus for the different cylinders modeled. [Figure 14] FIG. 14 shows a schematic perspective view of the BLT model investigated to evaluate the effect of hole shape and distribution in the forward mass. [Figure 15] FIG. 15 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of a 4f.pp HC-TSM transducer. [Figure 16] FIG. 16 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of a 4f.pp HC-TSM transducer. [Figure 17] FIG. 17 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of a 4f.pp HC-TSM transducer. [Figure 18] FIG. 18 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of a 4f.pp HC-TSM transducer. [Figure 19] FIG. 19 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of an 8 f.pp HC-TSM transducer. [Figure 20] FIG. 20 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of an 8 f.pp HC-TSM transducer. [Figure 21] FIG. 21 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of an 8 f.pp HC-TSM transducer. [Figure 22] FIG. 22 shows the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of an 8 f.pp HC-TSM transducer. [Diagram 23] FIG. 23 shows a comparison of the fitted curves for the standard and HC-TSM transducers, showing the relationship of L1fr and front mass (FM) to rear mass (BM) length. [Figure 24]FIG. 24 shows the magnitude of the electrical impedance and the phase of the electrical impedance for the standard and HC-TSM 55 kHz tuned transducers, respectively. [Diagram 25] FIG. 25 shows the magnitude of the electrical impedance and the phase of the electrical impedance for the standard and HC-TSM 55 kHz tuned transducers, respectively. [Figure 26] 26 is a perspective view of an exemplary ultrasound transducer according to an embodiment of the present invention. FIG 26 shows the transducer in a front perspective. [Figure 27] 27 is a perspective view of an exemplary ultrasound transducer according to an embodiment of the present invention, showing the transducer from a rear perspective. [Figure 28] 28 is a perspective view of an exemplary ultrasound transducer according to an embodiment of the present invention, showing the transducer in a longitudinal perspective cross section. [Figure 29]

[0023] Figure 29 is a perspective view of an exemplary ultrasound transducer in accordance with an embodiment of the present invention. Figure 29 shows the transducer in an exploded rear perspective view. [Diagram 30] 30 is a perspective view of an exemplary ultrasound transducer according to an embodiment of the present invention, showing the transducer in a front perspective view with the horn displaced. [Diagram 31] FIG. 31 shows velocity amplitude with respect to signal frequency for an exemplary ultrasonic transducer. [Diagram 32] FIG. 32 shows displacement amplitude with respect to signal frequency for an exemplary ultrasonic transducer. [Diagram 33] FIG. 33 is a side perspective view of another exemplary ultrasound transducer according to an embodiment of the present invention. [Diagram 34] FIG. 34 is a side perspective view of another exemplary ultrasound transducer according to an embodiment of the present invention. [Diagram 35]Figure 35 shows the dimensions of five different diamond shaped holes that were investigated to evaluate the effect of varying the axial angle θ. Note that in this and subsequent figures, the angle θ is measured at a different apex compared to the longitudinal axis, in contrast to, for example, Figure 10. [Figure 36A] FIG. 36A shows a schematic perspective view of the forward mass configurations investigated to evaluate the individual and combined effects of varying the axial angle, number of axially positioned holes, and number of circumferentially positioned holes. [Figure 36B] FIG. 36B shows a schematic perspective view of the forward mass configurations investigated to evaluate the individual and combined effects of varying the axial angle, number of axially positioned holes, and number of circumferentially positioned holes. [Figure 36C] FIG. 36C shows a schematic perspective view of the forward mass configurations investigated to evaluate the individual and combined effects of varying the axial angle, number of axially positioned holes, and number of circumferentially positioned holes. [Figure 37] FIG. 37 shows the effect of varying the number of axially positioned holes on the resonant frequency for different hole placements and sizes. [Figure 38] FIG. 38 shows the effect of varying the number of circumferentially spaced holes on the resonant frequency for different hole placements and sizes. [Figure 39] FIG. 39 shows the effect of changing the shaft angle θ on the resonant frequency for different arrangements of holes. [Diagram 40] FIG. 40 shows the effect of varying the number of axially and circumferentially arranged holes on the gain of the first longitudinal mode L1 of each transducer. [Diagram 41] FIG. 41 shows the effect on resonant frequency of varying the arrangement and dimensions of the holes in the fore mass compared to the resulting mass of each fore mass design. [Figure 42A] FIG. 42A shows a schematic side perspective view of a standard device model presented as CAD and Wireframe drawings, respectively. [Figure 42B]FIG. 42B shows a schematic side perspective view of the standard device model presented as CAD and Wireframe drawings, respectively. [Figure 42C] FIG. 42C shows side perspective views of the standard device model in the contracted and deployed configurations, respectively, of the L1 longitudinal mode. [Fig.42D] FIG. 42D shows a side perspective view of the standard device model in the contracted and deployed configurations, respectively, of the L1 longitudinal mode. [Figure 43A] FIG. 43A shows a schematic side perspective view of the folded front mass assembly model shown as CAD and wireframe drawings, respectively. [Figure 43B] FIG. 43B shows a schematic side perspective view of the folded front mass assembly model shown as CAD and wireframe drawings, respectively. [Figure 43C] FIG. 43C shows a side perspective view of the folded front mass assembly model in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Fig. 43D] FIG. 43D shows a side perspective view of the folded front mass assembly model in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Figure 44A] FIG. 44A shows a schematic side perspective view of an improved front mass assembly model according to an embodiment of the present invention presented as CAD and wireframe drawings, respectively. [Figure 44B] FIG. 44B shows a schematic side perspective view of an improved front mass assembly model according to an embodiment of the present invention presented as CAD and wireframe drawings, respectively. [Figure 44C] FIG. 44C shows a side perspective view of the modified forward mass device model in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Fig.44D] FIG. 44D shows a side perspective view of the modified forward mass device model in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Figure 45A] FIG. 45A shows schematic side perspective views of another improved front and rear mass arrangement model according to an embodiment of the present invention presented as CAD and wireframe drawings, respectively. [Figure 45B] FIG. 45B shows schematic side perspective views of another improved front and rear mass arrangement model according to an embodiment of the present invention presented as CAD and wireframe drawings, respectively. [Figure 45C] FIG. 45C shows a side perspective view of the improved front and rear mass device models in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Figure 45D] FIG. 45D shows a side perspective view of the improved front and rear mass device models in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Figure 46A] FIG. 46A shows schematic side perspective views of further improved front and rear mass arrangement models according to an embodiment of the present invention, presented as CAD and wireframe drawings, respectively. [Figure 46B] FIG. 46B shows schematic side perspective views of further improved front and rear mass assembly models according to an embodiment of the present invention, presented as CAD and wireframe drawings, respectively. [Figure 46C] FIG. 46C shows side perspective views of the second improved front and rear mass assembly model in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Figure 46D] FIG. 46D shows a side perspective view of the second improved front and rear mass assembly model in the contracted and deployed configurations of the L1 longitudinal mode, respectively. [Figure 47] FIG. 47 illustrates a front perspective view of a cylinder showing a preferred random arrangement of openings for incorporation into the front or rear mass structure in accordance with another exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] Further background to the invention, as well as aspects and embodiments of the invention, will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated by reference.

[0084] A typical surgical ultrasonic system with its main components is shown in FIG. 3. A high power signal generator 30 is connected to a power supply 32 and controls an ultrasonic transducer, principally designated by reference numeral 34. The ultrasonic transducer is the key element of the system that converts electrical energy into useful mechanical vibrations. Typical operating frequencies of the transducer are in the range of 20-100 kHz for surgical applications. The ultrasonic transducer is usually mounted within a casing 36 for safe handling. A probe (waveguide) 38 is attached to one end of the transducer to guide the wave motion towards the tissue. As shown diagrammatically in FIG. 3, the transducer includes a piezoelectric stack 40 sandwiched between a forward mass 42 and a rearward mass 44. A horn 46 is disposed between the forward mass 42 and the waveguide 38.

[0085] Each component of the system has its own role and importance, and the design of each part follows certain rules to achieve the desired frequency, characteristics and effect in the tissue.

[0086] Langevin transducer design guidelines are the result of many years of successful use. Numerous books, articles, and dissertations have reported on them extensively; see, for example, refs. 8, 9, 10. As a guide to design considerations, important design specifications are outlined below.

[0087] The classical d shown in Fig. 4 33 In the schematic perspective cross-sectional view of a -mode Langevin type ultrasound transducer, like reference numerals are used for corresponding features as in FIG.

[0088] In many known devices, ultrasonic transducers are inspired by the sandwich configuration proposed by Langevin and Cirovsky, first applied in 1918 to an underwater acoustic projector [1]. The Langevin design, also called "Tonpilz" in German as "singing mushroom", simply consists of a stack of piezoelectric rings (usually piezoelectric ceramic) with electrodes 52 interposed between them, which is prestressed between the rear mass 44 and the forward mass 46 by a prestressing bolt 50 [8]. This type of transducer is also known as a bolted Langevin transducer (BLT). In FIG. 4, the forward mass includes a flange 54 at the rear end of the forward mass and cooling holes 56 formed through the flange 54.

[0089] As a starting point for the design, we introduce some basic concepts by comparing the case of a thin rod, where the diameter d is much smaller than the length l (d << l), to the Langevin transducer. Assuming a thin rod, the length of the transducer is approximately half the wavelength, λ, as defined in Equation 1.

[0090] where c is the speed of sound in the rod and f is the desired operating frequency. The speed of sound in a particular material is defined in Equation 2: JPEG2024528106000004.jpg22161Here, E M is the Young's modulus and ρ is the density of the material. Equation 3 gives the natural frequency for the longitudinal vibration mode n (n= 1,2,3...) of the thin rod: Here's how TIFF2024528106000005.tif6150 is estimated. JPEG2024528106000006.jpg12161

[0091] FIG. 5A is a schematic diagram of a symmetric Langevin transducer. If the transducer can be divided down the center by a nodal plane, Each half of the transducer can be studied independently, corresponding to a length of 9150.

[0092] Figure 5B is a schematic diagram of an asymmetric Langevin transducer.

[0093] Resonant frequency ( Recall that the dimensions of the piezoelectric stack are JPEG2024528106000008.jpg6150), the relationship between the acoustic impedance, ζ, and length of both the piezoelectric stack and the end mass is given by Equation 4: JPEG2024528106000009.jpg21160 The subscripts p and m represent the piezoelectric and end mass (either the rear or front mass), respectively. JPEG2024528106000010.jpg6150 are the thickness of the piezoelectric ring and the length of the end mass, respectively. JPEG2024528106000011.jpg6150 is the acoustic impedance of the end mass, which is calculated from Equation 5. JPEG2024528106000012.jpg13160 and JPEG2024528106000013.jpg6150 is the acoustic impedance of the piezoelectric element calculated from Equation 6. JPEG2024528106000014.jpg11161where A is the cross-sectional area of ​​the component.

[0094] Equation 4 can be used to approximate the resonant frequency of a transducer with known dimensions, or to find unknown dimensions if the frequency and other parameters are known

[12] .

[0095] The piezoelectric stack 40 is generally 33 Mode Ring or d 31 For high power applications, "hard" piezoelectric ceramics such as PZT4 or PZT8 are used in an even number of rings to create a piezoelectric stack, placed between the front and rear masses with the electrodes in between.

[0096] The total length of the piezoelectric stack is chosen to be approximately one-quarter of l, although this choice is influenced by the available drive electronics: increasing the ceramic thickness requires a higher drive electric field, has higher electrical impedance, higher mechanical losses, and higher capacitance, resulting in higher overall cost

[13] .

[0097] The center of the stack is optimally located in the nodal plane, labeled "node" in Figure 5A, which is located at the center of the transducer for a symmetric design where distortion is highest. The stack location affects both the resonant frequency and vibration amplitude, and therefore its location is an important aspect of the design process

[14] .

[0098] Typically, the piezoelectric stack is placed away from the nodal position towards the rear mass in an asymmetric configuration, as shown in Figure 5B, to allow for placement of the support flange for casing attachment. In this configuration, the flange has minimal effect on the vibration modes. In an asymmetric design, each λ / 4 section can be analyzed independently, and considering one half of the transducer including the rear mass, the piezoelectric ceramic stack, and a portion of the front mass, l1, Equation 7 can be used to estimate either the frequency or the unknown dimensions of the transducer. JPEG2024528106000015.jpg27161

[0099] Lierke

[15] has shown that the maximum efficiency of a transducer is achieved when the piezoelectric ceramic stack is centrally located and its length is half the total length of the transducer. The greater the offset from the node, the greater the efficiency, as shown in Figure 6A. JPEG2024528106000016.jpg6150 will be lower. Considering the figure of merit normalized to the maximum value of 6150, we again find that the optimal location for the piezoelectric stack is at the center of the transducer. As shown in Figure 6B, L ピエゾ / L トランスデューサ When the ratio is between 0.2 and 0.5, the normalized figure of merit exceeds 90%

[15] .

[0100] The electrodes are typically chosen to have similar material properties (density, modulus, acoustic impedance) as the piezoelectric material to avoid unwanted stress concentrations. Note that "electrodes" are referred to herein as separate entities from the metallization that is formed on the piezoelectric material.

[0101] In a handheld transducer, serpentine electrodes 52a, 52b as shown in FIG. 7 may be used to provide electrical contacts on each side of an individual piezoelectric ring 58. Each piezoelectric ring takes the form of an apertured disk, with apertures 60 formed through the disk 58 along its major axis. In the left portion of FIG. 7, one electrode 52a and one piezoelectric ring 58 are shown separately. In the right portion of FIG. 7, two serpentine electrodes 52a, 52b and four piezoelectric rings R forming a piezoelectric stack are shown. 1 , R 2 , R 3 , R 4 Each serpentine electrode 52a, 52b has a spaced apart electrode ring portion facing the end face of each piezoelectric ring, and a connection between the electrode ring portions. Such serpentine electrodes are useful in that they have limited lateral projection and only a few terminating wires, and no soldering is required near the rings. The only soldering required is in the soldering area 62 shown. Cooling fins are also found in some applications

[16] .

[0102] The metallization on the piezoelectric element (ring) is usually formed by a 3-10 μm layer obtained by sputtering deposition, electroplating or special coating of Cr, Ni or Au or other combinations depending on the material supplier, which forms the interface between the piezoelectric element and the electrodes.

[0103] A prestressing bolt is used to apply and distribute the prestress within the stack. Titanium (or a titanium-based alloy) is the preferred material due to its high strength and ability to withstand repeated loading. The main reason for prestressing is to prevent the piezoelectric ceramic from being subjected to excessive tensile stress during vibration, as it is typically seven times weaker in tension than in compression. Furthermore, prestressing helps to stabilize both the resonant frequency and the magnitude of the impedance, plus ensures the persistence of electrical contact during high levels of vibration

[16] .

[0104] The basic properties required for a prestressing bolt are low stiffness, achieved by a long bolt, small shank diameter, and low Young's modulus, as well as high resistance to repeated loading. As the forward mass elongates, the bolt threads elongate, and the friction generated between the bolt and the forward mass can cause undesirable heating and subsequent thread failure (e.g. fatigue failure). The stiffness of the prestressing bolt can be equal to or less than the stiffness of the forward mass and less than the stiffness of the piezoelectric ceramic stack. However, long transmission bolts suffer more from mechanical failure

[17] .

[0105] In general, the necessary and optimal prestress to be applied is not prescribed and varies with each design and piezoelectric material used. Typical prestresses applied to hard piezoelectric ceramics are in the range of 25-50 MPa for PZT4 and 30-79 MPa for PZT8

[16] . It is important to note that the properties of piezoelectric ceramics deteriorate with increasing prestress, resulting in a decrease in the piezoelectric coefficient and a decrease in the maximum operating temperature; it can also cause depolarisation and increased mechanical losses in the piezoelectric material. All these parameters are also known to deteriorate more with age when prestressed.

[0106] Regarding the behavior of piezoelectric crystals under prestress conditions, it has been reported that uniaxial pressure in the range of 0–60 MPa adversely affects the electromechanical properties, with the same results as those highlighted for piezoelectric ceramics (see references

[18] –

[20] ). In addition, piezoelectric crystals can also undergo phase transitions under the simultaneous combination of a high-power electric field and uniaxial pressure

[21] .

[0107] The rear mass plays a major role as an inertial mass and distributes the prestress laterally across the piezoceramic ring. It is usually a solid cylinder, but a conical shape has been reported to be usable, increasing the bandwidth of the transducer

[22] . A rule of thumb for the steel rear mass indicates that its length should be at least 45% of the diameter of the piezoceramic stack, and its diameter should be at least equal to that of the piezoceramic stack. If other materials are used instead of steel, the Young's modulus can be used as a comparison, and the dimensions are adjusted inversely accordingly. For example, if a material with a Young's modulus half that of steel is used, the length of the rear mass should be doubled (see references [8]-

[10] and

[23] ).

[0108] The forward mass transfers the vibration energy to the horn and the probe / blade and often includes a flange that connects to the case. The flange sometimes includes holes for air cooling (see Figure 4). Often it is made of the same material so that it can be mated to the horn and they can be machined together, but when this is not possible, either spanner holes or wrench flats are provided and the forward mass and horn are connected by threads. For surgical instruments, wrench flats are preferred as they are more suitable for small diameter instruments. The material used for the forward mass is typically more compliant and less dense than the material used for the rear mass to better facilitate the transmission of ultrasonic vibrations

[24] .

[0109] The horn is a mechanical amplifier that increases the vibration amplitude from the forward mass: the vibrational energy passing through a constant cross-sectional area remains constant; however, as the cross-sectional area gradually decreases along the direction the vibrational energy travels, the vibrational energy density and amplitude increase.

[0110] As one skilled in the art will appreciate, different horn designs can be used, including stepped, linear, tapered, and exponential. Some horns use surface notches to convert the vibration from a longitudinal mode to a torsional or transverse mode. In some cases, multiple horns are linked together in a cascade, an amplifier called a "booster".

[24]

[25]

[0111] The case protects the user from the high voltages and currents required to excite the transducer, as well as from excessive heating. It is designed to clamp the device at its nodal plane, so that the fundamental vibration modes of the device are not affected.

[0112] The waveguide or probe is generally a rod-like structure that guides the waves to its tip. In devices for cutting soft tissue used in laparoscopic surgery, the tip is usually a blade at the end of a long waveguide. To handle the cyclic stresses of the ultrasonic vibrations and at the same time withstand any load, it is usually made of Ti6Al4V alloy (90% titanium, 6% aluminum, 4% vanadium, 0.25% iron and 0.2% oxygen). The length of the transmission rod is an integer number of half wavelengths at the operating resonant frequency of the device and is attached to the horn at an antinode

[26] .

[0113] The blade at the tip of the probe transmits the ultrasonic energy to the tissue and is shaped depending on the desired effect / application. Different blade designs are outlined below.

[0114] Suitable Blade Tip: (a) For soft tissue cutting and sealing: THUNDERBEAT® type S, Olympus® Medical [3]; (b) for ultrasonic aspiration: SONOPET® (Stryker®, Kalamazoo, MI, USA); (c) precision cutting of bone for reuse elsewhere in the body: SONOPET® Payner® 360 Bone Chip, (Stryker®

[27] )

[28] ; (d) For bone cutting: SONOPET® bent blade (Stryker®)

[29] .

[0115] As mentioned previously, an important aspect of the transducer design process is the selection of materials to be used, which depends on their properties and application requirements.

[0116] Young's Modulus E M quantifies the stiffness of an elastic material and is defined in Equation 8: JPEG2024528106000018.jpg21160 is the ratio of stress σ and strain ε, F is the force imparted to the material through the cross-sectional area A, and dl is the change in length along the axis, the initial length being l.

[0117] Elasticity describes how a material returns to its original shape after being distorted, with the force of recovery being proportional to the applied stress. Elasticity is described by Hooke's Law, Equation 9: JPEG2024528106000019.jpg14161Here, k indicates stiffness.

[0118] As is well known, Hooke's law is only valid in the elastic region of the stress-strain curve, which is the portion of the curve that leads to the yield strength. A typical material is subjected to a stress of: - Tensile stress when stretched vertically -Compressive stress when compressed vertically -Shear stress when a material is sheared in the plane of the stressed area.

[0119] Another important parameter in material selection is acoustic attenuation. As a longitudinal sound wave propagates through a medium, its intensity decreases from the source. Energy loss phenomena are due to scattering and absorption, which arise from wave motion in directions other than longitudinal and from heating due to friction. Materials with low acoustic attenuation are preferred; these include light alloys made from metals such as titanium, aluminum and magnesium; heavier materials such as brass and tungsten should be avoided if possible. A simple way to look at this is in the use of the speed of longitudinal sound: the faster the speed of sound in a material, the less energy is lost

[10] .

[0120] During cyclic tensile loading, the transducer components undergo dynamic deformation, experiencing high levels of both stress and strain depending on the geometry and material properties of the components, e.g., sharp corners and step shapes. These forces may concentrate and cause heating and failure, e.g., cracking. Typical design guides indicate that the ultimate tensile strength of each material should be 30% higher than the maximum stress the tool will be subjected to under service conditions

[30] .

[0121] The transducer components should also be acoustically matched: the speed of sound in a material depends on Em and ρ (Eq. 2), but when another material is present, some of the energy is transmitted forward, some of it is reflected back from the interface between the materials, and some of the energy may be converted to a different wave mode.

[0122] The amount of reflected energy is expressed as the reflection coefficient Rc in Equation 10: JPEG2024528106000020.jpg28160, where JPEG2024528106000021.jpg6150 are the acoustic impedances of the first and second media, respectively.

[0123] The closer the acoustic impedance of the materials, the more energy will be transferred through the interface, which is desirable for an efficient device. The rear and front masses should be made of different materials, with a "lower density" one being used for the front mass. This contributes to an increase in the vibration amplitude in front of the transducer. Thus, Equation 11: JPEG2024528106000022.jpg37160 must be respected in order to achieve maximum energy transmission between the piezo stack and the forward mass

[10] ,

[31] .

[0124] By applying ultrasonic energy to a medium, different vibration modes can be generated, the simplest of which is the longitudinal mode, shown in Figure 8, where continuous expansion and contraction is observed along the longitudinal axis of the transducer, along with simultaneous lateral motion caused by Poisson's ratio

[24] .

[0125] The longitudinal modes can also be used to generate other modes by modifying the waveguide and / or horn as described above. By adding transverse vibrations to the longitudinal motion through the use of asymmetric blades, asymmetric longitudinal motion can be achieved, allowing for a more efficient cutting process in certain applications, as described above for ultrasonic bone cutting surgical instruments.

[0126] The cutting mechanism and dynamics of action depend on the particular surgical task: cavitation is used in tissue preservation instruments, direct impact or "jackhammer effect" in bone cutting instruments, and thermal effects are employed in devices for soft tissue cutting and coagulation.

[0127] In ultrasonic cutting devices used on soft tissue, a thermal effect is desired and the tissue is heated to the point of denaturation. The tip of the device that produces this effect has a decoupled bifurcation, as shown in the inset of Figure 1, that allows the jaws to move and press the tissue against the ultrasonic vibrating blade. The clamping pressure required to close the jaws is applied by the surgeon's hand through a mechanical lever. Due to the induced friction, the tissue is heated, denatured, and cut in a matter of seconds without bleeding.

[0128] The interaction of ultrasound devices with soft tissue is complex and depends on the protein and water content of the tissue undergoing surgery. In general, tissues with a high water content are easier to cut, while tissues with a high protein content, such as blood vessels, nerves, and connective tissues, require more energy. Temperatures can exceed 100°C, which is enough to denature proteins, and if tissue is heated above the critical necrotic temperature, the damage becomes irreversible and cannot be repaired.

[0129] The cutting and hemostatic effects are not independent but occur simultaneously; however, depending on the blade frequency and vibration amplitude, one may dominate: lower frequency and higher vibration result in faster cutting and slower coagulation, whereas higher frequency and lower vibration result in slower cutting and faster coagulation

[25] ,

[26] .

[0130] The Da Vinci® Surgical System (Intuitive® Surgical, Inc.) was introduced with the EndoWrist® mentioned above. The Harmonic® ACE+Shears (Ethicon® Endo-Surgery) are the only ultrasonic surgical instruments compatible with the Da Vinci® to date. One drawback of this tool is its lack of maneuverability, which means it is not compatible with the EndoWrist® technology. This incompatibility is due to several interrelated reasons, which are discussed below.

[0131] First, consider the operating frequency and device configuration. Ultrasonic surgical devices with hemostatic incision function generally operate at about 55 kHz

[34] . The operating frequency of the BLT is related to the device length. Typically, the BLT is designed to operate mainly in the first longitudinal vibration mode, L1, which corresponds to half the wavelength. This places a constraint on the device length. In addition, the volume and position of the piezoelectric stack affect the efficiency and function of the device. This determines the number of piezoelectric ring elements in the stack and their diameter to achieve the required vibration amplitude performance. Under these conditions, it is not possible to miniaturize the device without compromising on the operating frequency and reducing performance; i.e., the longitudinal vibration amplitude of the blade (about 80 μm)

[35] .

[0132] Now consider the waveguide. From the above conditions, it becomes evident that the resulting ultrasonic transducer is in fact too long and too large to fit into the laparoscope port; therefore, an introduction waveguide is used to transfer the vibrations from the transducer outside the body to the end effector (blade) inside the body. As a result, this design limits the maneuverability of the blade in that the waveguide needs to be long enough to place the transducer outside the body. To improve the maneuverability of the blade, it is useful to include an integrated wristed joint in the end effector of the device. However, this creates an interface with an interruption, and therefore a discontinuity, in the waveguide. In this case, the ultrasound is reflected rather than transmitted to the blade, resulting in immobility of the blade.

[0133] The present inventors have investigated whether previous improvements in this field might be useful to aid in the miniaturization of ultrasound transducers useful in surgery.

[0134] For example, in

[36] , BLT optimization was performed to miniaturize an ultrasonic scalpel for vascular cutting and sealing, and the device was integrated into a multi-degree-of-freedom end effector for the Micro Hand® S robotic system (Tianjin University, China). A 55 kHz resonating device with a length of approximately 50 mm and a diameter of 10 mm was developed. The device was successfully integrated and implemented beyond the wrist-like joint, and blade displacements of over 100 μm were reported. In vitro experiments were performed with chicken tissue to demonstrate the functionality and potential of the device. However, in practice, the reported work does not present an innovative miniaturization strategy. The length of the fabricated device is approximately the same as expected for a 55 kHz resonator, which is too large for practical laparoscopic surgery.

[0135]

[37] and

[38] reported a folded horn transducer in which the horn length was reduced by a factor of two while maintaining the same operating frequency. This design shortens the overall length of the device but does not decouple it from the actual horn length.

[0136] Flextensional transducers are assembled by sandwiching a piezoelectric disk between two cymbal-shaped metal end caps. Some improvements to this design have been reported, including the introduction of bolts to prevent failure of the adhesive epoxy layer under high power driving. Flextensional transducers can have a relatively compact format. However, a drawback of this design is the possible asymmetry resulting from the epoxy adhesive layer, which can change the vibration mode of the device. In addition, the typical design utilizes the radial mode of the piezoelectric disk, which is not suitable for anisotropic piezoelectric crystals.

[0137] In

[42] and

[43] , a planar ultrasonic silicon scalpel was reported. This design used PZT piezoelectric ceramics and achieved a blade vibration amplitude of about 50 μm at 68 kHz. The device dimensions were length = 80 mm, thickness = 20 mm, and width = 22.5 mm, and the current configuration and material properties of Si do not lend themselves to miniaturization. This design has also been shown and demonstrated with a piezoelectric crystal

[23] .

[0138] d 31 Another use of the modes demonstrated the use of piezo crystals for the actuation of standard needles for anesthesia

[44] . This design is integrated into the rear and front masses and for this reason can be called a pseudo-Langevin device due to its similarity to the piezoelectric ring stack configuration. This design achieves a needle tip displacement of less than 10 μm at 70 VPP. Furthermore, the operating frequency of the device is about 80 kHz and the total length, without the needle, is more than 40 mm. This means that the total length of the device must be increased to achieve 55 kHz, making this design less suitable for miniaturization purposes. A further drawback of these designs is the presence of a bonding layer, in this case made of conductive epoxy, which can break under high vibration stresses. Another bonding-related problem with this design is due to the breakdown of the symmetry of the vibration modes, which creates stress concentration points that can cause device failure, i.e., delamination and cracking from the substrate, at high vibration stresses.

[0139] We next consider the needs of robotic surgery related to this disclosure. Many studies have reported that ultrasonic scalpels are superior in incision quality and sealing speed compared to standard electrocauteries, see, for example,

[45] . Interestingly, few studies have mentioned the generation of surgical smoke during surgery

[46] ,

[47] , which can reduce laparoscopic visibility and also delay the overall surgical time for endoscope cleaning.

[0140] In robotic surgery, ultrasonic dissectors are primarily used for dissection of parenchymal tissue to separate functional organ tissue from connective and supporting tissue, and for lobectomy to remove lobes or portions of organs [5], [6],

[48] . Common robotic procedures that include the use of ultrasonic dissectors to perform specific intra-operative tasks include hepatectomy, splenectomy, bowel resection, adrenalectomy, and thyroidectomy. A study on robotic-assisted thyroid surgery

[49] compared a wristed bipolar electrocautery (Vessel Sealer Extend, Intuitive® Surgical, Inc.) with an ultrasonic dissector (Harmonic® ACE + Shears, Ethicon® Endo-Surgery).

[0141] Direct comparisons have shown that the use of ultrasonic scalpels reduces intraoperative blood loss and improves incision margins and sealing speeds compared to standard electrocauteries. However, a high risk of patient injury, such as burns and inadvertent tissue perforation, has been observed with ultrasonic dissectors due to a combination of high waveguide temperatures and lack of maneuverability of the instrument. Thus, ultrasonic dissectors with flexible joints and mounted at the end of a robotic shaft beyond the wrist will address these issues.

[0142] The present invention addresses some of the design constraints identified above and provides a method for reducing the f _rThis is based on the realization that the stiffness of ultrasonic transducer components can be engineered to decouple the stiffness from the device length. In this disclosure, the term "metastructure" (similar to the concept of "metamaterial") refers to structures that are designed to exhibit different mechanical properties than the bulk material from which they are made.

[0143] Equation 3 shows the relationship between the longitudinal mode natural frequency y, the sound speed and the thin rod length. Considering n=1 and substituting c into the mathematical definition (Equation 2), Equation 12 is obtained: JPEG2024528106000023.jpg21160Young's modulus represents the stiffness of a material, and therefore E M A rod-like structure made of a material with low stiffness will vibrate longitudinally at a lower frequency than a material with low compliance (high stiffness). Therefore, in the context of the embodiments herein, we are interested in modifying (or tuning) the stiffness of a rod-like structure without changing its length, to make it resonate at a desired frequency.

[0144] A review of mechanical metamaterials

[50] presents several strategies to alter the mechanical properties of a structure by engineering the unit cells that form the overall lattice. In particular, the apparent Young’s modulus of the structure can be altered in one or more directions, typically leading to an increase in the anisotropy of the Young’s modulus of the structure.

[0145] To implement this concept in an ultrasound transducer, a study was conducted that showed that the cylindrical component of the transducer could be designed to change its apparent Young's modulus, and thus the frequency of the longitudinal modes, without changing the length of the transducer. Three different formats of hollow cylindrical components were considered in this study, each of which was suitable for use as the forward mass of a BLT transducer.

[0146] As shown in Figure 9, the hexagonal sample used a hexagonal array of through holes through the wall of a hollow cylinder, with a total number of holes of 54. The hole arrangement is based on a hexagonal lattice. Considering the centers of each hole, these centers are regularly spaced circumferentially around the cylinder, with each center aligned in a plane perpendicular to the major axis of the cylinder, with six centers per plane. In the drawings, the axial length of the cylinder was 12 mm, but this is for illustration purposes and in the modeling, the axial length of the cylinder was changed to show the effect of the hole arrangement on the stiffness. A force F was applied along the major axis of the cylinder.

[0147] The SpringNet sample shown in FIG. 9 was identical to the hexagonal sample except for the hole shape, which was diamond shaped.

[0148] The hole sample shown in FIG. 9 was identical to the hexagonal sample except for the hole shape, which was elliptical.

[0149] The hole geometry of each sample was modified based on Figure 10. For each hole, the angle θ was defined as the hole height of 1.5 mm measured in a direction parallel to the major axis of the cylinder. Note that in this part of the disclosure, the angle θ is defined as shown in Figure 10. In subsequent parts of the disclosure, the angle θ is defined differently.

[0150] 11, 12 and 13 show the longitudinal mode frequencies as a function of cylinder length for each hole shape based on different values ​​of the angle θ.

[0151] For the solid cylinder, E = 121 GPa (i.e., Young's modulus of the bulk material) and the frequency response is shown by the upper dashed line. For the hollow cylinder, the apparent Young's modulus is 42 GPa and the frequency response is shown by the lower dashed line. Each sample incorporating holes placed as described above has a lower resonant frequency for a particular length of cylinder compared to the hollow cylinder. Or stated differently, the addition of holes reduces the length of the cylinder required to achieve a particular resonant frequency. Furthermore, decreasing the angle θ for each type of hole leads to a lower resonant frequency. Note that the annular wall thickness of the hollow cylinder and the perforated samples are the same.

[0152] Based on the above studies, further research was done based on honeycomb (HC) shaped holes. This choice was made because HC showed great ability to lower the resonant frequency without introducing other vibration modes close to L1. TSM stands for Tuneable Stiffness Metastructure.

[0153] The HC-TSM angle θ and the number of HC-TSM features per plane (fpp) are the parameters that determine the apparent Young's modulus and therefore the f r All models investigated in this study are shown in Figure 14. The results of the HC-TSM design study are presented and discussed only for the L1 mode, as it represents the vibration mode of interest in ultrasound transducers for surgical applications.

[0154] Figures 15-18 show the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of a 4f.pp HC-TSM transducer. Figures 19-22 show the effect of changing the aperture angle on the magnitude and phase of the electrical impedance of an 8f.pp HC-TSM transducer.

[0155] Figures 15 and 17 show that changes are observed in the magnitude and phase of the electrical impedance, as well as the frequency location of the L1 mode, over a broader spectrum, from 0 to 300 kHz. Figures 16 and 18 show data near the L1 mode, which show that decreasing the aperture angle from 120° to 90° and 60° results in a decrease in the frequency of the L1 mode. The magnitude and phase of the electrical impedance of a standard transducer are also shown for reference.

[0156] Similarly, Figures 19 and 21 show that changes are observed in the magnitude and phase of the electrical impedance and the frequency location of the L1 mode over a broader spectrum, 0-300 kHz. Figures 20 and 22 show the dates near the L1 mode. They show that decreasing the aperture angle from 120° to 90° and 60° results in a decrease in the frequency of the L1 mode. The magnitude and phase of the electrical impedance of a standard transducer are also shown for reference.

[0157] Table 2 shows the effect of the introduction of the HC-TSM on the transducer parameters related to the L1 mode. The key point that emerged from this design study is that the L1 mode was changed without changing the transducer length. In addition, the f r Smaller but positive changes were also observed in other transducer properties, such as a reduction in the magnitude of electrical impedance at and an improvement in operating bandwidth.

[0158] Table 2 : Summary of L1 mode results for the design variables considered in the HC-TSM transducer. TIFF2024528106000024.tif57144

[0159] Therefore, a comparison can be made between a "standard" 55 kHz transducer and the exemplary HC-TSM transducer, where these transducers differ in the forward mass construction based on the above discussion. The most important initial comparison that can be made between the two transducer models is the ability of the HC-TSM device to resonate in the L1 mode at a lower frequency than the standard device, despite being of equal length and made of the same materials, as shown in Figure 23.

[0160] Figures 24 and 25 show the electrical impedance magnitude and electrical impedance phase of the standard and HC-TSM 55 kHz tuned transducers, respectively. The electrical impedance magnitude and phase spectra in Figures 24 and 25 show that the curve fitting correctly determined the FM-BM length for the 55 kHz resonator in both cases.

[0161] Table 3 compares the device parameters for the L1 mode of each device. The introduction of the HC-TSM enabled a transducer design with a length 20.5% shorter than the standard design at nearly the same fr. Furthermore, the HC-TSM transducer presented a 30% reduced electrical impedance at resonance and a 28% increased bandwidth compared to the standard design.

[0162] Table 3 : Device parameters extrapolated from the simulated electrical impedances of Figures 24 and 25 for a device tuned at 55 kHz for the L1 mode. TIFF2024528106000025.tif31132

[0163] Figures 26-30 show diagrams of an exemplary ultrasound transducer according to an embodiment of the present invention. Figure 26 shows the transducer in a front perspective view. Figure 27 shows the transducer in a rear perspective view. Figure 28 shows the transducer in a longitudinal cross-sectional perspective view.

[0164] Figure 29 shows the transducer in an exploded rear side perspective, and Figure 30 shows the transducer with the horn modified in a front perspective.

[0165] In each of Figures 26-30, the transducer has a rear mass 44 and a front mass 46 with a horn 48 positioned forward of the front mass. Two piezoelectric ceramic rings 58 of opposite polarity sandwich an electrode 52 to form a piezoelectric stack (ultrasonic actuator portion) which is held between the rear and front masses by prestressing bolts 50 and nuts 51. The front mass has an annular portion in the form of a cylindrical outer wall around a longitudinal axis A with an array of holes (in this case circular holes) formed therethrough. In operation, a drive signal is applied to the electrode 52 and the front and rear masses are grounded, causing vibration of the piezoelectric ring. The rear mass 44, the piezoelectric ceramic ring 58, the electrode 52, the front mass 46 and the horn 48 are positioned along the longitudinal axis of the transducer. Vibrations generated in the piezoelectric ceramic ring 58 are thereby transferred along the vibration energy transmission path to the front mass 46 and the horn 48. The vibrations are then amplified in amplitude by the horn 48. A circular hole open to the longitudinal axis intersects the vibrational energy transmission path, and this configuration provides increased mechanical compliance along the vibrational energy path and in the axial direction parallel to the longitudinal axis.

[0166] 29, the forward mass 46 includes a proximal portion 46a, an intermediate portion 46b, and a distal portion 46c. The proximal portion 46a is in contact with the actuator portion. The apertures are formed in the intermediate portion 46b. The distal portion 46c is in contact with the horn portion. The proximal portion 46a, the intermediate portion 46b, and the distal portion 46c of the forward mass 46 are integrally formed with one another and have substantially the same outer diameter, ignoring the effect on the outer diameter due to the presence of the aperture 70.

[0167] In operation, the arrangement of the apertures ensures that there is virtually no conversion from longitudinal to torsional modes, thereby preserving the longitudinal modes. This is achieved by the achiral array of holes, which can be superimposed on its own mirror image.

[0168] In this embodiment, there are a total of 24 holes, all formed in the foremass. The depth and cross-sectional area of ​​each hole are identical. The holes are arranged in a reflection-symmetric array (with respect to the geometric center of each hole) with a number of reflection-symmetric planes parallel to and coincident with the longitudinal axis. One such reflection-symmetric plane is shown in FIG. 28 as the plane in which the cross-section is taken. It is clear that there are also reflection-symmetric planes in the plane perpendicular to the longitudinal axis. The array consists of three rows of holes arranged axially (parallel to the longitudinal axis), with each row consisting of eight holes arranged circumferentially. The holes are arranged in a rectangular grid that is mapped onto the surface of the foremass. Thus, there is a reflection-symmetric plane perpendicular to the longitudinal axis that coincides with the second (central) row of holes.

[0169] For a plane that is parallel to and terminates at the longitudinal axis and that has the largest total number of holes intersecting the plane (e.g., plane R shown diagrammatically in FIG. 28), the maximum total number of holes intersecting the plane in the front mass in this embodiment is 3. Also, in a cross section taken orthogonal to the longitudinal axis at a position along the longitudinal axis where the total number of holes intersecting the cross section is the largest, the maximum total number of holes intersecting the cross section is 8.

[0170] The achievable vibration amplitudes of the standard and HC-TSM 55 kHz transducers were compared. The HC-TSM transducer demonstrated 33% higher displacement at the blade tip than the standard design with the same drive signal.

[0171] Figure 31 shows velocity amplitude with respect to signal frequency for an exemplary ultrasonic transducer. The legend shows a signal with 0.8V Vrms, but there are no data points for this. Instead, the lowest curve is at 3.5V Vrms and the curve ramps up to 73V Vrms.

[0172] 32 shows the displacement amplitude with respect to signal frequency for an exemplary ultrasonic transducer. The lowest curve is for a Vrms of 0.8V and the curve gradually increases up to a Vrms of 73V.

[0173] 33 illustrates a side perspective view of another exemplary ultrasound transducer in accordance with a different embodiment of the present invention. In this embodiment, the rear mass 64 and the front mass 46 each have a cylindrical outer wall with an array of circular holes formed therethrough.

[0174] 34 illustrates a side perspective view of another exemplary ultrasound transducer in accordance with another embodiment of the present invention, in which only the rear mass 64 has a cylindrical outer wall with an array of circular holes formed therethrough.

[0175] Further studies conducted to further explore the above insights proposed multiple foremasses with different arrays of apertures to evaluate the resulting resonant frequencies. The foremass structure was modelled with an array of holes formed in a hollow cylindrical foremass, with the foremass having an outer diameter of 10.00mm.

[0176] The general shape of each hole used in this further study is a diamond with two lines of symmetry (with rounded corners with an internal radius of curvature of 0.10 mm). Each hole is aligned with the longitudinal axis of the forward mass (and thus with the longitudinal axis of the transducer) with one line of symmetry parallel to the longitudinal axis and the other line of symmetry perpendicular to the longitudinal axis. In other words, a first set of opposing interior angles of the diamond are bisected by a plane parallel to and coincident with the longitudinal axis, and a second set of opposing interior angles are bisected by a plane perpendicular to the longitudinal axis. Each forward mass structure has one of five diamond-shaped holes of different dimensions. As shown in FIG. 35, each hole type has a side length of approximately 1.00 mm. Thus, the dimensions of a hole are determined by its interior angles, and are identified herein by the axial angles corresponding to the first set of opposing interior angles. The axial angles of the five types of holes are 150°, 120°, 90°, 60°, and 30°, respectively. Note that the definitions of the angles characterizing these holes are different from those used in Figure 10. The longitudinal and circumferential dimensions of the diamond-shaped openings are listed in Table 4.

[0177] Table 4 :Longitudinal and circumferential dimensions of diamond-shaped hole type TIFF2024528106000026.tif47139

[0178] Assuming that each side of the diamond-shaped hole has a length of 1.00 mm, the value of the longitudinal length as a percentage of the circumferential width is 57.73% for the hole with a 120° shaft angle and 26.79% for the hole with a 150° shaft angle.

[0179] Three parameters were varied between each forward mass: the axial angle of the holes, the number of holes in the axial direction (i.e., aligned parallel to the longitudinal axis), and the number of holes in the circumferential direction (i.e., aligned perpendicular to the longitudinal axis).

[0180] For simplicity in this further work, the hole arrangement is based solely on a rectangular grid superimposed on the cylindrical shape of the foremass.

[0181] The number of axial holes was varied between 1, 3 and 5. The number of circumferential holes was varied between 2, 4 and 8. Thus, a total of 45 new forward mass structures were investigated. Figures 36A-C show front perspective views of each forward mass structure. Figures 36A, 36B and 36C show sets of forward mass structures with 2, 4 and 8 circumferentially arranged holes, respectively.

[0182] To identify each forward mass configuration, the following nomenclature was developed: XA_YP_Z, where X, Y, and Z represent the axial hole number, circumferential hole number, and axial angle, respectively.

[0183] Each forward mass has a circumference of 31.42mm. Therefore, for a cross section taken perpendicular to the longitudinal axis at a position along the longitudinal axis corresponding to the maximum total number of holes intersecting that plane, the proportion of the circumference occupied by the maximum number of holes (or circumferential fill-factor) for each forward mass structure is given in Table 5 below.

[0184] Table 5 : For each forward mass structure, the maximum percentage of the perimeter occupied by holes intersecting a planar cross-section (circumferential filling factor). TIFF2024528106000027.tif119148

[0185] FIG. 37 shows the resonant frequency of the first longitudinal mode with varying number of axial holes. Note that the lines between the dots are shown for illustrative purposes only to demonstrate the decrease in resonant frequency with increasing number of axially arranged holes. For the data points in row 5A, the lowest curve corresponds to the _8P_150 structure, followed by _8P_120, _8P_90, _4P_150, _4P_120, _2P_150, _4P_90, _8P_60, _2P_120, _2P_90, _4P_60, _2P_60, _8P_30, _4P_30 and _2P_30, with the last one being the highest curve. The solid data points in row 0A correspond to the standard solid model of the front mass without holes. The horizontal dashed lines are there to clarify the divide between the increase and decrease in resonant frequency compared to the standard solid model. The other data point in row 0A corresponds to a hollow foremass with no hole.

[0186] When observing the change in resonant frequency between the devices with the largest axial angle, 150 1A_8P_150, 3A_8P_150, and 5A_8P_150, a decrease in resonant frequency of 5.5% was observed first, followed by a decrease of 4.5%. This trend is seen in each series of devices with a common angle; therefore, increasing the number of axial holes from 3 to 5 promotes a smaller decrease in resonant frequency compared to the change in resonant frequency after increasing the number from 1 to 3, implying that an inverse relationship exists between the resonant frequency and the number of axially arranged holes.

[0187] Therefore, further increasing the number of axial holes has a lesser effect on the resonant frequency. The number of axial holes is limited by the dimensions of the transducer, and further increasing the number of holes may degrade the structural integrity.

[0188] FIG. 38 shows the resonant frequency of the first longitudinal mode for varying the number of holes in the circumferential direction. Note that, as before, the data points in the 0P row correspond to the standard solid and hollow models of the forward mass without holes. The horizontal dashed lines are there to clarify the divide of the increase and decrease in resonant frequency compared to the standard solid model. For the data points in the 8P row, the lowest curve corresponds to the 5A_ _150 structure, followed by 5A_ _120, 3A_ _150, 3A_ _120, 5A_ _90, 1A_ _150, 3A_ _90, 1A_ _120, 5A_ _60, 3A_ _60, 1A_ _90, 1A_ _60, 5A_ _30, 3A_ _30 and 1A_ _30, the last of which is the highest curve.

[0189] Taking the 5A_X_150 class of device (where X is either 2P, 4P, or 8P), for example, increasing the number of holes from 2 to 4 and 4 to 8, there is a 2.2% decrease in resonant frequency followed by an 8.8% decrease. This trend is shown for each class of device; thus, increasing the number of circumferential holes from 2 to 4 produces a slight change in resonant frequency compared to increasing the number of holes from 4 to 8. Such a nonlinear relationship suggests that further increase in the number of perpendicular holes will continue to effectively decrease the resonant frequency. However, the number of holes is limited by the hole dimensions relative to the perimeter of the transducer. Similar to the number of axial holes, an increase in the number of holes degrades the structural integrity of the forward mass, and stress analysis is similarly useful in understanding the maximum number of holes possible in this direction without adversely affecting the stability of the forward mass.

[0190] FIG. 39 shows the resonant frequency of the first longitudinal mode for increasing axial angle of the hole. Note that, as before, the data points in the 0 column correspond to the standard solid and hollow models of the forward mass without the hole. The horizontal dashed lines are there to clarify the divide of the increase and decrease in resonant frequency compared to the standard solid model. For the data points in the 150° column, the lowest curve corresponds to the 5A_8P_ structure, followed by 3A_8P_, 5A_4P_, 1A_8P_, 3A_4P_, 5A_2P_, 3A_2P_, 1A_4P_ and 1A_2P_, the last of which is the highest curve.

[0191] The resonant frequency decreases as the hole angle increases. Devices with holes at angles less than 90 degrees show the expected increase in frequency as evident from the resolving dashed lines compared to the standard solid model. A decrease in resonant frequency is expected for devices with holes with axial angles greater than 90 degrees, with 11 of these 18 devices showing such a decrease. It can therefore be concluded that while increasing the hole axial angle is an effective strategy to reduce the resonant frequency of some devices employing hole arrays, it is with the combination of modification of the three parameters associated with the hole array that the greatest reduction in resonant frequency can be seen.

[0192] The results of this study show that increasing the circumferential number of holes has the greatest effect on resonant frequency, followed by the hole angle and axial number of holes, however changes to all three of these parameters are beneficial.

[0193] The largest decrease in resonant frequency was observed for the 5A_8P_150 device, where a 10.5% decrease in frequency was observed from the solid model resonant frequency, resulting in a resonant frequency of ~35 kHz. A comparison of this device with a commercial BLT

[51] (manufacturer part number: SMBLTD45F40H) with a resonant frequency of 40 kHz demonstrates that the designed device exhibits a lower frequency, despite being similar (5A_8P_150 = 53 mm, SMBLTD45F40H = 53.75 mm).

[0194] To ensure the modification of the forward mass structure as a viable strategy for the miniaturization of ultrasonic transducers, the degree of longitudinal or axial displacement of the modified device must be equal to or greater than that of the standard solid or hollow model. In particular, the transducer should have a suitable gain that is greater than the standard solid and hollow models. The gain is determined by the ratio of the maximum axial displacement of each end of the transducer, i.e., the front end (distal end) of the forward mass and the rear end (proximal end) of the rear mass. The axial displacement is the change in position of a portion of the ultrasonic transducer in a direction parallel to the longitudinal axis relative to its equilibrium position. Thus, the position where the displacement is equal to zero corresponds to the node of the device.

[0195] FIG. 40 shows the calculated gain for each transducer device corresponding to the first longitudinal mode L1 for each of the 45 modified forward mass configurations. The forward mass types on the x-axis are grouped by the number of axially arranged holes in common. It is clear that each forward mass configuration, regardless of the hole arrangement, results in a gain that is greater than that of the standard solid model represented by the leftmost data point. Despite this, FIG. 38 shows that an increase in the number of axially arranged holes has a relatively small effect on the gain. In contrast, an increase in the number of circumferentially arranged holes (i.e., an increase in the number of fpp) results in a larger increase in gain, and this effect is observed to a greater extent when increasing the number of fpp from 4 to 8. The increase in gain that occurs as a function of the increase in axial angle from 30° to 150° is more pronounced in devices using a greater number of circumferentially arranged holes.

[0196] The greatest increase in gain over the standard solid model occurred with the 5A_8P_150 forward mass type, providing an 82.4% increase in gain. This device also showed the greatest reduction in resonant frequency.

[0197] It is important to realize that the difference in resonant frequency is caused by the change in mass as well as the effect of the changed forward mass structure on mechanical compliance and wave propagation. Therefore, the effect of mass loss on the operation of the transducer was investigated by considering the volume of mass removed for each forward mass type to compare the resonant frequency of each forward mass type.

[0198] Figure 41 shows for each forward mass type the "cross" data point indicates the total mass of the forward mass, and the "circle" data point indicates the resonant frequency of the first longitudinal mode L1. The forward mass types are ordered on the x-axis first by shaft angle, then by number of axially arranged holes, then by number of circumferentially arranged holes. Groups of points connected by lines represent forward mass types that share a common shaft angle.

[0199] Comparing the mass and resonant frequency of 5A_8P_30 (40.2kHz) and 5A_8P_150 (35.3kHz), there is a difference of 4.9kHz in resonant frequency despite the same mass (6.54g), and a 0.0% decrease in mass corresponds to a 12.2% decrease in resonant frequency. Therefore, it is quite clear that the decrease in resonant frequency is caused by a change in the structure of the front mass, rather than a change in mass.

[0200] Further studies proposed three transducer models with different aperture arrangements for direct comparison with the "standard" solid model and the "folded" forward mass model. The standard solid model uses solid forward and rear masses, except for the required passage for the bolt passing through the rear and forward masses. All five models include a forward mass, a rear mass, two piezoelectric rings, two electrodes, and a bolt passing through the rear mass and connected to the forward mass. Each transducer has the same overall length equal to 67 mm and the same overall diameter equal to 15 mm. The material metal that constitutes each device, including the forward mass, rear mass, and bolt, is titanium (Ti), and the electrode material of each device is copper (Cu). Each device model uses the same piezoelectric type PZ26 (MEGGITT)

[52] .

[0201] Figures 42-46 show schematic diagrams of the models of each transducer device using separate CAD and wireframe drawings to show a side perspective view of each model. The contraction and expansion vibration phases at the resonant frequencies of the longitudinal modes are shown for each model.

[0202] Figures 42A-D show the standard model with no openings in the front and rear masses. The contracted shape shown in Figure 42C corresponds to a phase of ωt=0°, and the expanded shape shown in Figure 42D corresponds to a vibration phase of ωt=180°, where ω is the resonant frequency of the standard model in the longitudinal mode.

[0203] Figures 43A-D show a layered fore-mass model in which the fore- and aft-masses have no openings, but the fore-mass comprises a series of concentric inner folds. The series of folds are defined by separate, overlapping, inner and outer annular cavities. The inner annular cavity extends inwardly from the distal end of the fore-mass, and the outer annular cavity surrounds the inner annular cavity. The innermost fold comprises a solid cylinder (which appears to extend axially in Figure 43D) that extends axially toward the distal end of the fore-mass and conducts vibration forward of the fore-mass. The contracted shape shown in Figure 43C corresponds to a phase of ωt=0°, and the expanded shape shown in Figure 43D corresponds to a vibration phase of ωt=180°, where ω is the resonant frequency of the layered model in the longitudinal mode.

[0204] Figures 44A-D show a modified front mass model (FM-mod) with a solid rear mass and an array of elliptical holes formed in a hollow front mass. The array has nine axially arranged rows of holes, with each row having eight circumferentially arranged holes. The circumferential dimension of each hole is greater than the longitudinal dimension of each corresponding hole. There are 72 holes in total. The contracted shape shown in Figure 44C corresponds to a phase of ωt=0°, and the expanded shape shown in Figure 44D corresponds to a vibration phase of ωt=180°, where ω is the resonant frequency of the FM-mod model in the longitudinal mode.

[0205] FIG. 45A-D shows a first modified forward and aft mass model (FM&BM-mod) with an array of elliptical shaped holes formed in the hollow forward mass and hollow aft mass. The circumferential dimension of each hole is greater than the longitudinal dimension of each corresponding hole. There are 144 holes in total, with 72 holes in each of the forward and aft masses. The array has 18 axially arranged rows of holes, with 9 rows in each of the forward and aft masses, each with 8 circumferentially arranged holes. The holes are arranged in two rectangular grids mapped onto the surfaces of the forward and aft masses, respectively. Thus, for a plane that is parallel to and terminates on the longitudinal axis and has the greatest total number of holes intersecting the plane, the maximum total number of holes intersecting the plane in the forward mass is 9. The aft mass has the greatest total number of identical holes intersecting the plane. For a cross section taken perpendicular to the longitudinal axis at a location along the longitudinal axis where the total number of holes intersecting the cross section is maximum, the maximum total number of holes intersecting the cross section in the front and rear masses is 8. The contracted shape shown in FIG. 45C corresponds to a phase of ωt=0°, and the expanded shape shown in FIG. 45D corresponds to a vibration phase of ωt=180°, where ω is the resonant frequency of the FM&BM-mod model in the longitudinal mode.

[0206] FIG. 46A-D shows a second modified forward and aft mass model (FM&BM-mod2) with an array of elliptical shaped holes formed in the hollow forward mass and hollow aft mass. The circumferential dimension of each hole is greater than the longitudinal dimension of each corresponding hole. There are 104 holes in total, with 52 holes in each of the forward and aft masses. The array has 26 axially arranged rows of holes, with 13 rows in each of the forward and aft masses, each row having 4 holes. In this model, the holes are arranged in two triangular grids that are mapped onto the surfaces of the forward and aft masses, respectively. Thus, for a plane that is parallel to and terminates on the longitudinal axis and has the largest total number of holes intersecting the plane, the maximum total number of holes intersecting the plane in the forward mass is 7. The aft mass has the largest total number of identical holes intersecting the plane. For a cross section taken perpendicular to the longitudinal axis at a location along the longitudinal axis at which the total number of holes intersecting that cross section is greatest, the maximum total number of holes intersecting that cross section in the forward mass and aft mass is four.

[0207] Table 6 shows the L1 mode resonant frequency and gain from the center of the piezoelectric stack to the distal end of the front mass for each transducer device model. As shown by the design study above, the L1 mode frequency could be changed without changing the transducer length. Compared to the standard model, all three modified devices provide lower resonant frequencies and higher gains. The resonant frequency was reduced for the folded front mass model with respect to the standard model. Despite this, the FM-mod and FM&BM-mod2 models have lower resonant frequencies than the folded front mass model. This proves that the mechanical compliance of the transducer device can be reduced to a greater extent by having multiple openings instead of the folded front mass arrangement.

[0208] All three transducer models with an array of holes formed in the front and / or rear mass have greater gain than either the layered front mass model or the standard model. The FM&BM-mod2 transducer assembly model has the lowest resonant frequency among the five transducer models presented in Table 6.

[0209] Table 6 : Results of resonance frequency and gain of L1 mode in the proposed transducer model TIFF2024528106000028.tif47147

[0210] As an observation, note that the FM&BM-mod device model has a higher resonant frequency than the layered device model. Without wishing to be bound by theory, this is believed to be due to a combination of both higher modal density and the lattice itself dominating the vibrational response. This result is interesting given the substantial increase in gain compared to the folded horn structure, especially when the resonant frequencies are only <1kHz different.

[0211] 47 shows a front perspective view of a cylinder 90 showing a suitable random arrangement of apertures 70a to be incorporated into a front or rear mass structure according to another exemplary embodiment of the present disclosure. The holes are substantially randomly arranged, but are spaced apart by a minimum distance to maintain the structural integrity of the device. The array of holes is thus intended to provide a similar effect as the regular array of holes discussed above, and in particular, to not provide substantial longitudinal to torsional mode conversion.

[0212] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, whether expressed in their specific form, or in terms of means for performing a disclosed function, or in a method or process for obtaining a disclosed result, may be utilized to embody the invention in various of its forms, either separately or in any combination of such features as appropriate.

[0213] Although the present invention has been described in conjunction with the exemplary embodiments above, many equivalent modifications and variations will be apparent to those skilled in the art upon review of this disclosure. Accordingly, the exemplary embodiments of the present invention described above are considered to be illustrative and not limiting. Various changes can be made to the described embodiments without departing from the spirit and scope of the present invention.

[0214] For the avoidance of doubt, all theoretical explanations provided herein are provided for the purpose of enhancing the understanding of the reader and the inventors do not wish to be bound by these theoretical explanations.

[0215] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0216] Throughout this specification, including the following claims, unless the context otherwise requires, the words "comprise" and "include", and conjugations such as "comprises", "comprising" and "including" are to be understood as implying the inclusion of stated wholes or steps, or groups of wholes or steps, and not as implying the exclusion of other wholes, steps, or groups of wholes or steps.

[0217] It should be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. As used herein, ranges may be expressed as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, it will be understood that the particular value forms another embodiment by use of the antecedent "about." The term "about" with respect to numerical values ​​is arbitrary and may mean, for example, ±10%.

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Claims

1. 1. An ultrasonic transducer for surgical applications, comprising: Rear mass part; Front mass part; an ultrasonic actuator portion held between the rear mass portion and the front mass portion; an ultrasonic horn portion located forward of the front mass portion; the rear mass, the ultrasonic actuator portion, the front mass, and the ultrasonic horn portion are arranged along a longitudinal axis of the transducer; the vibration generated by the ultrasonic actuator portion is transmitted to the front mass portion and the ultrasonic horn portion along a vibration energy transmission path, and the vibration is amplified by the ultrasonic horn portion; an ultrasonic transducer, wherein one or more of the rear mass, the front mass, and the ultrasonic horn include a plurality of openings that open toward the longitudinal axis, intersect the vibrational energy transmission path, and are configured to provide increased mechanical compliance in directions along the vibrational energy transmission path.

2. The ultrasound transducer of claim 1 , wherein the transducer is a Langevin transducer.

3. 2. The ultrasonic transducer of claim 1, wherein the vibrational energy transmission path in the rear mass, the front mass, and / or the ultrasonic horn includes an annular portion, and the plurality of openings intersecting the vibrational energy transmission path are provided through a wall of the annular portion.

4. The ultrasonic transducer of claim 1 , wherein each opening has a substantially uniform cross-section along its depth.

5. The ultrasonic transducer of claim 1 , wherein each of the plurality of openings has the same size.

6. The ultrasonic transducer of claim 1 , wherein the plurality of apertures are arranged according to a repeating pattern.

7. The ultrasonic transducer of claim 1 , wherein three or more openings are provided.

8. 2. The ultrasonic transducer of claim 1, wherein the length of the transducer measured along the vibrational energy transmission path from the proximal end of the rear mass to the distal end of the horn is 40 mm or less.

9. 9. The ultrasonic transducer of claim 8, wherein the maximum diameter of the transducer measured perpendicular to the length is 15 mm or less.

10. 10. An ultrasonic transducer according to any one of claims 1 to 9, wherein in operation the plurality of apertures provide substantially no longitudinal to torsional mode conversion.

11. 10. The ultrasound transducer of claim 1, wherein the plurality of apertures are arranged in an achiral array.

12. The ultrasonic transducer according to claim 1 , wherein the plurality of openings are not provided in the ultrasonic horn portion.

13. 10. The ultrasound transducer of claim 1, wherein the plurality of apertures are arranged in a reflective symmetrical array.

14. The ultrasonic transducer of claim 1 , wherein the plurality of apertures are arranged in a repeating pattern.

15. 10. The ultrasonic transducer of claim 1, wherein the plurality of apertures are arranged substantially randomly or randomly offset from a virtually regular repeating pattern.

16. 10. An ultrasonic transducer according to any one of claims 1 to 9, wherein there are 20 or more apertures.

17. 10. The ultrasonic transducer of claim 1, wherein the plurality of openings occupy at least 10% of the perimeter of the front mass or the rear mass for a cross section taken perpendicular to the longitudinal axis at a position along the longitudinal axis corresponding to the maximum total number of openings intersecting that cross section.

18. 10. The ultrasonic transducer of claim 1, wherein the front mass includes a proximal portion in contact with the ultrasonic actuator portion, a distal portion connected to the ultrasonic horn portion, and an intermediate portion disposed between the proximal portion and the distal portion, and the plurality of openings are provided in the intermediate portion.

19. A surgical instrument comprising an ultrasonic transducer according to any one of claims 1 to 9.

20. 1. A method of operating an ultrasonic transducer, comprising: The ultrasonic transducer includes: Rear mass part; Front mass part; an ultrasonic actuator portion held between the rear mass portion and the front mass portion; an ultrasonic horn portion located forward of the front mass portion; the rear mass, the ultrasonic actuator portion, the front mass, and the ultrasonic horn portion are arranged along a longitudinal axis of the transducer; the vibration generated by the ultrasonic actuator portion is transmitted to the front mass portion and the ultrasonic horn portion along a vibration energy transmission path, and the vibration is amplified by the ultrasonic horn portion; wherein one or more of the rear mass, the front mass, and the ultrasonic horn include a plurality of openings that open toward the longitudinal axis, intersect the vibrational energy transmission path, and are configured to provide increased mechanical compliance in directions along the vibrational energy transmission path.

21. The method of claim 20, wherein the ultrasonic transducer operates at a power in the range of 1 to 1000 W.

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