Abstract:
An ultrasonic surgical tool has an elongate waveguide operatively connected or connectable to a source of ultrasonic vibrations. An operative element at a distal end of the waveguide has a diameter less than that of the waveguide. A connecting portion of intermediate diameter may connect the operative element and the waveguide. A proximal end of the operative element forms a first step junction, located at a nodal plane of ultrasonic vibrations in the waveguide and operative element, producing a velocity amplitude gain across the step junction. A second zero-gain step junction between the connecting portion and the waveguide is located at an anti-nodal plane. The operative element may include a curved distal cutting and welding element having a pair of elongate welding grooves defining a cutting edge. Alternatively, the operative element may include a welding element having a flat or slightly ridged operative face.

Description:
PRIORITY 
     This application is a US national stage patent application claiming priority under PCT Article 22(1) to a patent application entitled “Ultrasonic Tissue Dissector” having International Application No. PCT/GB2009/001278 filed on May 21, 2009 and International Publication Number WO 2009/141616 A1 published on Nov. 26, 2009. The present application is also a US national stage patent application claiming priority under PCT Article 22(1) to a patent application entitled “Ultrasonic Transducer System” having International Application No. PCT/GB2009/001281 filed on May 21, 2009 and International Publication Number WO 2009/141618 A2 published on Nov. 26, 2009. Both PCT applications claim priority to an application entitled “Improved Torsional Mode Tissue Dissector” filed in the UK Intellectual Property Office on May 21, 2008 and assigned Patent Application No. 0809243.9. The contents of the two PCT applications and the UK application are hereby incorporated by reference in their entirety. 
     RELATED APPLICATION 
     This application is related to a US national stage patent application filed on Nov. 22, 2010 entitled “Ultrasonic Transducer System” and also claiming priority to the two PCT applications and the UK application. The contents of that application are hereby incorporated by reference in their entirety. 
     BACKGROUND 
     1. Field of the Related Art 
     This disclosure relates to a surgical tool, and, more particularly, to a system and method for cutting tissue by utilizing ultrasonically vibrating blades of the surgical tool. 
     2. Description of the Related Art 
     In the past few decades, considerable interest has been directed toward the use of ultrasonically activated blades and shears for the dissection, cutting, and welding of soft tissue. 
     It is known to cut tissue by means of ultrasonically vibrated knives or scalpels. When a scalpel cuts tissue its effectiveness is indicated by the cutting force. This derives from the pressure required to separate the structure and from the frictional drag as the blade is drawn between the cut sections. Vibrating the blade can reduce friction and may also reduce the bond strength of the tissue. Both objectives could be achieved by applying vibrations to the cutting blade in either a longitudinal or a torsional mode. 
     Haemostatic cutting of individual vessels and well vasculated tissue has been taught by U.S. Pat. Nos. 3,636,943 and 3,862,630. In the &#39;943 and &#39;630 patents, the use of ultrasonic energy in the form of mechanical vibrations is transmitted by a tool member to close off small severed blood vessels, such as in humans, by the formation of closures at the terminal portions thereof, and stop what is referred to as “ooze,” that requires constant mopping or cleansing techniques during an operation. Such tool member may be in the form of a knife ultrasonically vibrated to simultaneously sever and close off respective terminal portions of the severed blood vessels while performing surgical procedures. The tool member, of a proper configuration, may also join together layers of tissue, including the walls of unsevered blood vessels, and with respect to the latter is foreseen as replacing the “tying off” of arteries and veins currently necessary in surgery. Thus, these patents use a longitudinal mode system to activate a blade, which has roughened surfaces in order to increase frictional energy transfer during the cutting of vascular tissue. 
     Additionally, U.S. Pat. Nos. 5,322,055 and 6,283,981 disclose oscillatory systems with the addition of hinged passive elements designed to press the target tissue against an energized blade so as to increase the frictional drag of tissue on the blade, and, thus, increase the heating effect necessary to ensure coagulation during the cutting process. 
     The &#39;055 patent relates to an ultrasonic surgical apparatus that includes a surgical instrument having a hand piece with a transducer for converting an electrical signal into longitudinal vibratory motion of a blade connected to the hand piece and an accessory releasably connected to the hand piece to enable clamping of tissue against the vibrating blade to afford improved coagulating and cutting of tissue. Scissors-like grips actuate a pivoted clamp jaw along one side of the ultrasonically vibrating blade to compress and bias tissue against the blade in a direction normal to the direction of longitudinal vibratory movement. The clamp jaw and blade are rotatable relative to one another to align a selected blade edge of a multi-edged blade with the clamp jaw for cutting and coagulating while clamping or circumferentially spacing a selected blade edge from the clamp jaw for cutting and coagulating without clamping. 
     The &#39;981 patent relates to a method of designing a balanced ultrasonic surgical instrument including an ultrasonic transmission rod and an asymmetric ultrasonically actuated blade attached to the distal end of the ultrasonic transmission rod. The ultrasonically actuated blade includes a treatment portion. The treatment portion has a functional feature such as, for example, a curved blade which makes the treatment portion asymmetric. In such method, a balance portion including at least a first asymmetric balance feature is designed and positioned between the ultrasonically actuated blade and the ultrasonic transmission rod to balance out any undesirable torque generated by the treatment portion. 
     All of the above-described systems share the common principle of frictionally generated heating, related to cyclic vector reversal at the friction interface, to ensure that coagulation occurs simultaneously with tissue separation. In such systems, the frictionally generated heating principle is described in terms of longitudinal excitation of the cutting blade. However, pure longitudinal excitation is not the most efficient manner to transfer vibrational energy into soft tissue. 
     Moreover, in U.S. Pat. No. 6,425,906 and GB 2,371,492, it is noted that Young and Young first disclosed the use of different vibrational modes specifically chosen to take advantage of direct compression wave transmission into target tissue with its unique capacity to generate cavitation as the main form of energy dissipation. Specifically, such patents were the first to disclose a system and method for using torsional excitation to transfer vibrational energy into soft tissue. 
     For example, the &#39;906 patent relates to a surgical tool for cutting and/or coagulating tissue that includes a piezo-electric driver to generate ultrasonic energy including torsional mode vibrations. The &#39;906 patent also relates to a distal torsional mode end effector, which creates focused energy transmission into target tissue trapped by a hinged jaw element against an activated waveguide. 
     In the GB 2,333,709 patent, the use of multi-wavelength torsional mode waveguides is disclosed in relation to minimally invasive general surgical procedures. In the &#39;709 patent, mechanisms of energy transfer are described that relate specifically to shear mode torsional systems and the conventional compression wave longitudinal equivalents. The &#39;709 patent further discloses that excitation of a waveguide having a length greater than 7 or 8 times the half wavelength for shear mode transmission creates issues, which are exaggerated relative to those experienced in similar compression wave systems. 
     Thus, while it is known to use torsional excitation to transfer vibrational energy into soft tissue, it is still desirable to produce further surgical tools that effectively manipulate torsional mode excitation. 
     SUMMARY 
     In an embodiment of the present disclosure, a waveguide is presented including a first end; a second end; and a plurality of nodal planes; wherein the plurality of nodal planes are disposed along a surface of the waveguide; and wherein selective positioning of the plurality of nodes or nodal planes along the surface of the waveguide allows for manipulation of one or more parameters related to the waveguide. 
     In another embodiment of the present disclosure, a method for isolating a waveguide is presented including positioning a plurality of nodal planes along a surface of the waveguide; wherein the waveguide has a first end and a second end; and wherein selective positioning of the plurality of nodes along the surface of the waveguide allows for manipulation of one or more parameters related to the waveguide. 
     In another embodiment of the present disclosure, a method for manufacturing a waveguide is presented including positioning a plurality of nodal planes along a surface of the waveguide; wherein the waveguide has a first end and a second end. 
     The present disclosure also provides a computer-readable medium which stores programmable instructions configured for being executed by at least one processor for performing the methods described herein according to the present disclosure. The computer-readable medium can include flash memory, CD-ROM, a hard drive, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present disclosure will be described herein below with reference to the figures wherein: 
         FIG. 1A  is a schematic diagram of a torsional mode transducer having an extended stack to facilitate frequency matching to a horn, in accordance with the present disclosure; 
         FIG. 1B  is a schematic diagram of a torsional mode transducer having an extended stack with a threaded spigot located in a tapered hole, in accordance with the present disclosure; 
         FIG. 1C  is a schematic diagram of a torsional mode transducer illustrating critical dimensions of the transducer with a circumscribed cylinder from which a major component is machined; 
         FIG. 2  is a schematic diagram of an axial view of a torsional mode transducer; 
         FIG. 3  is a schematic diagram of a geometric relationship between flexural stack displacement and torsional horn displacement, in accordance with the present disclosure; 
         FIG. 4  is a schematic diagram of a torsional mode transducer connected to a waveguide with an illustration of the displacement amplitude distribution, in accordance with the present disclosure; 
         FIG. 4A  is a schematic diagram illustrating a detail of the end effector of the torsional mode transducer of  FIG. 4 , in accordance with the present disclosure; 
         FIG. 5  is a schematic diagram of a longitudinal mode transducer connected to a waveguide with an illustration of the displacement amplitude distribution, in accordance with the present disclosure; 
         FIG. 6  is a schematic diagram of an axial view of a curved end effector in a torsional mode waveguide configuration, in accordance with the present disclosure; 
         FIG. 7  is an isometric schematic diagram of a curved end effector in a torsional mode waveguide configuration shown in  FIG. 6 , in accordance with the present disclosure; 
         FIG. 8A  is an isometric schematic diagram of a welder end effector in a torsional mode waveguide configuration, in accordance with the present disclosure; 
         FIG. 8B  is a detailed front view of the distal end of the end effector, in accordance with another exemplary embodiment of the present disclosure; 
         FIG. 9  is a schematic diagram of a waveguide, shroud, and hinged jaw of a torsional mode waveguide configuration, in accordance with the present disclosure; 
         FIGS. 10A ,  10 B, and  10 C are schematic diagrams of the jaw configuration, in accordance with the present disclosure; 
         FIG. 11  is a block diagram of a first embodiment of control and power circuits for a torsional mode ultrasonic generator, in accordance with the present disclosure; 
         FIG. 12  is a block diagram of a second embodiment of control and power circuits for a torsional mode ultrasonic generator, in accordance with the present disclosure; and 
         FIG. 13  is a schematic diagram of an alternative embodiment of a torsional mode transducer having an extended stack with two threaded spigots, one located at a proximal end and one located at a distal end of a threaded shaft, in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing figures, in which like references numerals identify identical or corresponding elements, a system and method for cutting tissue by using torsional mode excitation in accordance with the present disclosure will now be described in detail. 
     While embodiments of the present disclosure are susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the embodiments of the present disclosure to the specific form disclosed, but, on the contrary, the embodiments are intended to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the present disclosure as defined in the claims. 
     The present disclosure may be understood more readily by reference to the following detailed description of the disclosure taken in connection with the accompanying drawing figures, which form a part of this disclosure. It is to be understood that the disclosure herein is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed subject matter. 
     The present disclosure proposes utilizing torsional ultrasound for efficiently transferring vibrational energy into soft tissue. Unlike any other ultrasonic tools, the surgical tool of the exemplary embodiments directs powerful compression energy into the target tissue, resulting in secure coagulation and fast cutting. Away from these compression grooves, only relatively less efficient frictional energy is present. This is minimized further through a fine polishing process that reduces the risk of transferring unwanted energy into vital structures and significantly reduces the likelihood of fatigue failure with low gain. The surgical tools of the exemplary embodiments direct compression energy into the target tissue. Energy is transferred quickly, denaturing the tissue protein and rapidly forming a coagulum. At the same time the central blade cuts through the tissue as the jaw of the surgical tool is closed. The result is fast and efficient haemostatic cutting. 
     The present disclosure further proposes emphasizing the fundamental advantages of torsional mode systems over conventional longitudinal extensional devices. The present disclosure further addresses the characteristics of torsional dissector systems that introduce particular opening issues. 
     For instance, torsional mode transmission has several advantages over longitudinal mode transmission. These include, but are not limited to the following: the motional gain associated with cross sectional changes is greater in shear wave transmission than in equivalent compression wave transmission. Analysis of torsional mode concentrators reveals a gain dependence on moments of inertia associated with section changes along the transforming element. In contrast, compression wave transmission is related to linear force variation which changes with sectional area. This consideration leads to the motional gain expression for a longitudinal mode stepped transformer, defined as the square of the diameter ratio between input and output sections, and for the shear wave equivalent, the third power of the diameter ratio. This characteristic is consistent with increased Q and impedance transformation ratio for shear wave systems relative to compression wave equivalents. Thus, tuning to resonance requires more critically refined generator circuitry and tuning algorithms capable of differentiating between sharply defined resonance features. 
     Another distinguishing feature between longitudinal and torsional mode systems relates to transducer design. Transducer designs are specific to particular modes. The classic Langevin sandwich transducer is conventionally used to generate and sustain compression waves in a longitudinal mode system. In contrast, a mode converting horn with tangentially attached transducer stack is configured to generate a torsional output from the narrow end of the horn. The transducer stack is driven in a selected flexural mode to generate a torsional mode in the horn. Alternative flexural stack modes result in a substantially longitudinal output from the mode converter. As a result, in each case pure torsional or longitudinal modes depend on the design of the waveguide attached at the output of the horn. Operating frequencies generally result in overtone modes with waveguides spanning several wavelengths. The relationship between the horn and transducer stack renders the oscillatory system susceptible to complex transverse modes occurring in the horn and waveguide assembly. Careful and accurate control of the drive frequency is required to excite the correct mode and lock the correct mode by the generator frequency/mode control circuitry. The exemplary embodiments described below illustrate how to control a drive frequency to fine-tune resonance features and excite a desired mode for a surgical tool. 
     Embodiments will be described below while referencing the accompanying figures. The accompanying figures are merely examples and are not intended to limit the scope of the present disclosure. 
     Referring to  FIG. 1A , a schematic diagram of a torsional mode transducer having an extended stack to facilitate frequency matching to a horn, in accordance with the present disclosure is presented. 
     The torsional mode transducer  10  of  FIG. 1A  includes a horn  12 , a threaded element  14 , ceramic rings  16 , electrodes  18 , a back plate  20 , a first sensor  22 , and a second sensor  24 . The length, X, of the back plate  20  is designated as  26  and the length, Y, of the threaded element  14  is designated as  28 . 
     In an exemplary embodiment of the present disclosure, the transducer  10  permits the generation of either longitudinal vibrations or pure torsional waves. Transducer  10  includes a transducer stack, comprising a number of axially polarized PZT ceramic rings  16 , separated by silver or gold plated brass electrodes  18  and is compressively attached to a tangential face of the transducer  10  via spigoted back plate  20 , with threaded spigot  32  located in tapped hole  34  (as shown in  FIG. 1B ). 
     Moreover,  FIG. 1A  shows at least two piezo-electric sensors, a first sensor  22  and a second sensor  24  located on the horn  12 . The sensors  22  and  24  are located so that they respond selectively to torsional and longitudinal horn modes. In the former, the waveform from each piezo-electric sensor  22 ,  24  will be phase shifted according to the change in torsional displacement from the sensors of the horn where it is at a minimum, to the periphery where it is at a maximum. In the presence of a longitudinal mode, both sensors  22 ,  24  would experience the same extensional displacement of the horn proximal end face, producing in phase outputs from the piezo-electric sensors  22 ,  24 . The specific operation of sensors  22 ,  24  will be further described below with reference to  FIG. 11 . 
     Furthermore, threaded element  14  may be designed to be any length  28 . The length  28  of the threaded element  14  may be varied based on a plurality of factors, such as, but not limited to, the material of the horn  12  and the natural resonant frequencies of one or more components of the transducer  10  (e.g., horn  12 , stack assembly, and/or waveguide  56 ). The threaded element  14  may be varied between a few millimeters up to 20 mm depending on the desired application. The length  28  of the threaded element  14  affects the output of the horn  12 . In other words, by varying the length  28  of the threaded element  14  one skilled in the art may produce a desired vibration or wave (e.g., a torsional wave, a pure torsional wave, a longitudinal wave, a flexural mode wave or a combination of these waves). Additionally, the length  26  of the back plate  20  may be varied between a few millimeters up to 20 mm depending on the desired application and may also affect the type of wave produced by the horn  12 . Preferably, the smaller the length  28  of the threaded element  14 , the better the achievement of the desired excitation or mode. For example, the length  28  of the threaded element  14  may be in the range of 2-10 mm. 
     Once again, the insertion of the threaded element  14  enables an optimization of the realization of pure torsional mode as the output of the horn  12  and enables an accurate method of fine-tuning a surgical tool/device to a user&#39;s desired specifications. Also, threaded element  14  may be adjusted prior to assembly or after (subsequently) assembly of the transducer  10  to an external device (e.g., such as a waveguide  56  described below with reference to  FIGS. 4 and 5 ). Also, threaded element  14  may have a variety of different uniform or non-uniform shapes. The substantially cylindrical shape in the Figures is merely illustrative. 
     Thus, in accordance to  FIG. 1A , a drive frequency may be controlled to fine-tune resonance features and excite a desired mode for a surgical tool by adding a threaded element  14  between the horn  12  and the transducer stack of the transducer  10 . Additionally,  FIG. 1A  defines means for varying the stack assembly properties, which in turn define the modal characteristics of the horn  12 . The ability to optimize the torsional output from the transducer  10  is enhanced by providing or enabling this tuning facility at each end of the stack assembly. 
     Referring to  FIG. 1B , a schematic diagram of a torsional mode transducer having an extended stack with a threaded spigot located in a tapered hole, in accordance with the present disclosure is presented. 
     Torsional mode transducer  11  is substantially similar to torsional mode transducer  10  and thus will only be discussed further herein to the extent necessary to identify differences in construction and/or use. The torsional mode transducer  11  of  FIG. 1B  includes a horn  12 , a threaded element  14 , ceramic rings  16 , electrodes  18 , a back plate  20 , a first sensor  22 , and a second sensor  24 . Additionally, the transducer  11  includes a threaded spigot  32  located in a tapered hole  34 . 
     As shown in  FIG. 1A , the transducer stack/assembly includes a threaded element  14  inserted between the transducer stack and the horn  12 . As shown in  FIG. 1B , to facilitate attachment of the threaded element  14  to the horn  12 , spigot  32  is extended to accommodate attachment of threaded element  14 . This feature allows the resonant characteristics of the complete stack incorporating threaded element  14  to be tuned by adjusting the overall length of the transducer stack prior to attachment to the horn  12 . Threaded element  14  may be either parallel-sided or tapered in section towards its distal end. Preferably horn  12  is a tapered horn. 
     Referring to  FIG. 1C , a schematic diagram of a torsional mode transducer illustrating critical dimensions of the transducer with a circumscribed cylinder from which a major component is machined is presented. 
     The torsional mode transducer  13  includes a stack assembly  21  disposed between the back plate  20  and a cylindrical surface  31 . The stack assembly  21  abuts the cylindrical surface  31  via abutment member  37  mounted on one tangential face created by machining the shaded region of the circumscribing cylindrical surface  31  of  FIG. 1C .  FIG. 1C  and  FIG. 2  (described below) illustrate dimensional definitions transducers  13 ,  15 .  FIG. 1C  defines circumscribing surface  31  which sets a tangential mounting plane of the stack assembly  21 . A flexural rotation of the stack assembly  21  through angle, θ, (designated as element  44  in  FIG. 3 ), generates a torque about the horn axis ◯, thus driving the horn  12  into a torsional mode. 
     Referring to  FIG. 2 , a schematic diagram of an axial view of a torsional mode transducer is presented. 
     The torsional mode transducer  15  includes a threaded hole  34  for waveguide attachment. Additionally, the transducer  15  includes exponential tapering surfaces  36 , cylindrical extremity  38 , cylindrical isolating flange  33  located adjacent to the horn  12 , shaded area  35 , and the abutment member  37 . 
     Horn  12  is machined with exponential tapering surfaces  36  and interrupted by cylindrical isolating flange  33 , where the exponential tapering surfaces  36  are cut tangentially to circumscribing cylindrical surface  31  (see  FIG. 1C ). Moreover, stack assembly  21  (see  FIG. 1C ) is disposed adjacent to horn  12  so that&#39;s its cylindrical extremity  38  coincides with an outer extremity of a tangential face of the horn  12  and overlaps an inner extremity as indicated by the shaded area  35 . 
     Referring to  FIG. 3 , a schematic diagram of a geometric relationship between flexural stack displacement and torsional horn displacement, in accordance with the present disclosure is presented. 
     The geometric relationship  40  of  FIG. 3  illustrates stack displacement  42  and an angle, θ, designated as  44 . 
     Transducer  10  having the stack assembly is located on horn  12  so that its cylindrical extremity coincides with the outer extremity of a tangential face of the horn  12 . The relationship between the stack diameter, d′, the proximal horn effective diameter d, and the circumscribed diameter D are chosen critically in order to generate the required vibrational mode and resonant frequency. 
     Rotational movement of the proximal horn mass is initiated by a flexural mode displacement within the stack assembly as illustrated in  FIG. 3 . This mode is possible when d′&gt;d/ 2 , allowing for a more compact transducer design than employing a conventional axial mode stack where d′&lt;&lt;d/ 2 .  FIG. 3  illustrates the geometry which controls the transfer of stack displacement  42  to the horn  12 . The equation defining the resolved component of flexural displacement F T , at angle θ,  44 , to mounting plane, is given as: T=F T  cos θ. l=½ F T  cos (arctan ((d−d′)/d)). (d 2 +(d−d′) 2 ) 1/2 . 
     Critical selection of d′/D ratio for optimum compact transducer operation is defined as 0.45&lt;d′/D&lt;0.55; preferably, 0.482; and for normal (axial mode stack) operation, 0.3&lt;d′/D&lt;0.4; preferably 0.333. Torsional resonance is established in either case by critical selection of a length of the horn  12 , a diameter of connecting member  52  (shown in  FIGS. 4 and 5 ) and the dimensions of the waveguide  56  (shown in  FIGS. 4 and 5 ). 
     Referring to  FIG. 4 , a schematic diagram of a torsional mode transducer connected to a waveguide with an illustration of the displacement amplitude distribution, in accordance with the present disclosure is presented. 
     The transducer/waveguide configuration  50  includes torsional mode transducer  10  described above with reference to  FIG. 1A . The transducer/waveguide configuration  50  further includes connecting member  52 , a first nodal plane  54 , waveguide  56 , a second nodal plane  58 , shroud tube  60 , a third nodal plane  62 , a fourth nodal plane  64 , and an end effector  66 . The end effector  66  depicts a portion of the waveguide  68  and a distal tip  70 . Arrow  80  illustrates the torsional movement of the waveguide  56 . 
       FIG. 4  further depicts a graph  71  illustrating a transmission wave that is generated when the transducer/waveguide configuration  50  is activated. A half wavelength  72  is generated between the horn  12  and the connecting member  52 . A half wavelength  74  is generated between the first nodal plane  54  and the second nodal plane  58 . A half wavelength  74  is also generated between the last two distal nodes  64  and  62 . A quarter of a wavelength  76  is generated between the fourth nodal plane  64  and the distal tip  70  of the end effector  66 . Note that the mid-section of the waveguide is omitted to save repetition, but may be typically  7  or  8  wavelengths long.  FIG. 4  further depicts a graph  51  illustrating the effect of stack flexing (as described below). 
     Additionally, the waveguide  56  consists of an integral number of half wavelengths for shear wave propagation at the resonant frequency. Waveguide isolation is achieved by local increase in diameter coincident with nodal planes  54 ,  58 ,  62 ,  64 , which create space between the plastic lined shroud tube  60  and active regions of the waveguide  56 . 
     Moreover, the waveguide may be referred to as an elongated shaft having a proximal end and a distal end. In addition, the distal end may be separated into one or more sections. For example, with respect to  FIGS. 6-8B , the distal end may be separated into three sections. The first section may have a first width and a first length, the second section may have a second width and a second length, and the third section may have a third width and a third length, where the first, second, and third widths are the same or different from each other. The first section may refer to an end effector, the second section may refer to a connecting section, and the third section may refer to a tip portion/blade portion of the distal end of the elongated shaft. The end effector may be a curved blade having twin grooves as illustrated in  FIG. 4 , element  70 . 
     Referring to  FIG. 4A , a schematic diagram illustrating a detail of the end effector of the torsional mode transducer of  FIG. 4 , in accordance with the present disclosure is presented. The detailed view illustrates the shape of the distal tip  70 , which depicts a twin groove configuration. Of course, one skilled in the art could contemplate a plurality of different distal tip configurations to achieve either longitudinal and/or torsional excitation. 
     Referring to  FIG. 5 , a schematic diagram of a longitudinal mode transducer connected to a waveguide with an illustration of the displacement amplitude distribution, in accordance with the present disclosure is presented. 
     Transducer  90  is substantially similar to torsional mode transducer  50  and thus will only be discussed further herein to the extent necessary to identify differences in construction and/or use. Transducer  90  has a similar transmission wave graph to the transmission wave graph illustrated in  FIG. 4 . Graph  91  illustrates a transmission wave that is generated when the transducer/waveguide configuration  90  is activated. A half wavelength  92  is generated within the horn  12 . A half wavelength  94  is generated between the first nodal plane  54  and the second nodal plane  58 . A half wavelength  94  is also generated between the third nodal plane  62  and the fourth nodal plane  64 . A quarter of a wavelength  96  is generated between the fourth nodal plane  64  and the distal tip  70  of the end effector  66 .  FIG. 5  further depicts a graph  95  illustrating the effect of stack flexing (as described below). 
     In the alternative exemplary embodiment, as illustrated in  FIG. 5 , the transducer stack assembly is activated in a variant flexural mode such that end face  82  of the back plate  20  is deflected as indicated by arrow  84  in a longitudinal direction. This stack movement generates a longitudinal mode in the horn  12  at a frequency consistent with compression wave transmission in the horn  12  and attached waveguide  56 . The frequency for longitudinal resonance is related to the designed torsional mode frequency by the expression: F tor /F long =G/E, where, G, is the shear modulus and, E, is Young&#39;s modulus for the horn  12  and waveguide material. 
     These features (i.e., threaded element  14  incorporated in the transducer  10  and nodal planes  54 ,  58 ,  62 ,  64 ) allow a surgical tool system to be driven alternately in either longitudinal or torsional modes with the possibility of generating an increased distal length of effective displacement, with the advantage that there is no need for an additional transducer stack attached to the horn proximal end face to create the longitudinal displacement as taught in Young and Young, the dual mode application, issued as GB Patent No. 2,438,679. Moreover, nodal bosses or nodal planes  54 ,  58 ,  62 ,  64  machined on the waveguide  56  provide a simple means of acoustic isolation of the waveguide  56  from the mounting tube(s)  160 , which allow the torsional/longitudinal resonance to be deployed with a cooperative hinged jaw  182  (see  FIG. 9 ). 
     In both  FIGS. 4 and 5 , the transducer configurations  50 ,  90  can generate either longitudinal or torsional resonance in a tuned multi half wave rod system attached to the narrow end of the horn  12 .  FIGS. 4 and 5  illustrate the relative effects of two flexural stack modes in orthogonal planes, as shown in graphs  51 ,  71 ,  91 ,  95 . Specifically, graphs  51  and  95  illustrate the effect of the stack flexing in the YZ plane which generates a torsional mode in the horn  12  and the waveguide  56 . When excited at a different frequency, exciting flexure in the XY plane of  FIG. 5 , the output is longitudinal.  FIGS. 4 and 5  further illustrate the potential to generate two different modes alternately at different frequencies, which are selected to produce torsional and longitudinal wavelengths with a number of coincident nodal planes  54 ,  58 ,  62 ,  64 . The ability to tune the stack assembly allows one skilled in the art to optimize either longitudinal or torsional outputs and also to combine them with an appropriate switched, dual frequency electrical generator (as described below with reference to  FIGS. 11 and 12 ). 
     Essentially, the stack assembly and the horn  12  determine the mode of vibration and the waveguide  56  is tuned to resonate in a particular mode by adjusting its length to encompass a number of half wavelengths at one or more designated frequencies. Furthermore, graph  51  shows a stack mode which generates a rotational mode in the horn  12 , creating torsional resonance in the waveguide  56 , indicated by arrows  71  and  80 . The horn  12  always embodies a half wave length with antinodes at both ends. 
     Moreover, the nodal planes  54 ,  58 ,  62 ,  64  are established as part of the resonance displacement pattern and are used to provide mechanical isolation by incorporating local bosses on the waveguide  56 . These create gaps between the waveguide  56  and the plastic shroud liner (see  FIG. 9 ).  FIGS. 4 and 5  both serve to illustrate the relationship between the stack flexural mode (plane XY longitudinal and YZ torsional) and the waveguide mode.  FIG. 4  illustrates a torsional system, whereas  FIG. 5  illustrates a longitudinal system. The only difference in the waveguide  56  is that the compression half wave length is greater than the torsional since compression wave velocity is greater than shear velocity for a given material. 
     The prior art of Young and Young, GB 2423931, teaches the use of a torsional mode dissector with a curved distal end effector substantially tapered from the distal tip and with only relatively short focusing grooves towards the proximal blade end. This lack of distal focusing grooves reduces the coagulating efficiency of the tip of the curved blade although it permits some lateral tissue welding capability. 
     It is one objective of the exemplary embodiments illustrated in  FIGS. 6 and 7  to create a torsional mode curved end effector  100 ,  130  with a full distal focusing feature.  FIGS. 6 and 7  will be simultaneously described. 
       FIG. 6  illustrates curved end effector  100  in accordance with the present disclosure, which comprises three distal waveguide regions; a proximal first portion  102  of section Wo, which would attach to a torsional waveguide and transducer as defined in  FIG. 4 ; a half wavelength second distal section extending from nodal isolating boss  122 , through quarter wave anti-nodal step  124  to first distal nodal step  126  of section Ws; and a third distal quarter wavelength region extending from distal step  126  to torsional blade tip  128  of section Wl. The third section embodies a double grooved focusing region  114 , similar to that illustrated in  FIG. 4A  and defining the extent of the distal blade. 
     The end effector waveform is shown schematically as  101  in  FIG. 6 , where the second effector region of length Z,  120 , is shown to be a half wavelength, with initial length X,  116 , terminating in anti-nodal step  124 . 
     The anti-nodal step has a zero amplitude gain characteristic, which in conjunction with nodal gain step  126 , permits control of the critical torsional displacement amplitude within curved blade region  114 . 
     It is another objective of the exemplary embodiments of the present disclosure, to minimize transverse modes created by the inertial effect of the axially offset mass associated with the curved effector blade, which in  FIG. 6  is offset from the waveguide axis by a distance  112 . Clearly, by reducing the diameter of the distal blade section  114 , relative to the input section Wo,  102 , the inertial moment which generates unwanted transverse modes, is reduced. 
     The limits satisfying this criterion are expressed by the inequality: 1.5&lt;Wo/Wl&lt;3.0. Inclusion of the zero gain anti-nodal step  124  allows one skilled in the art to limit the peak distal blade amplitude to 200 microns by relying on the amplitude gain at  126 . The nodal torsional gain is found from the expression: Gain, K=(Ws/Wl) 3 . The above consideration permits blade curvature and peak displacement amplitude to meet operating criteria for acceptable haemostatic tissue dissection. Blade curvature is controlled so that the distal tip is constrained to lie within the cylindrical envelope defined by section Wo at  106 . 
     The magnitude of the waveguide section steps at  124 ,  126  and any non-linear variation in the section along Y,  118 , in  FIG. 6 , can clearly be varied independently to control the output characteristics of the waveguide, thus allowing high rotational amplitudes with minimum harmful transverse modes. It is noted that the above expressions serve as an exemplary definition only and do not limit scope for wider application of the present disclosure. 
       FIGS. 8A and 8B  are schematic illustrations of a further aspect of the present disclosure intended to optimize the use and effectiveness of the torsional mode transducer, waveguide, and end effector system referred to throughout the present disclosure, in a particular surgical process which involves tissue welding as an end point objective. In this function, the elements of the end effector structure, which focus energy into the target tissue, for example, a specific large blood vessel, are emphasized whilst at the same time changing the detail of features which encourage tissue separation in order to delay or prevent that process. 
       FIG. 8A  shows a welder end effector  140  attached to waveguide  142  at nodal step plane  134 . The section change at the nodal step creates sufficient torsional amplitude gain, according to the principles described earlier, to enable the tissue contacting face  136  to direct energy into the target vascular tissue.  FIG. 8B  shows profile of end effector blade  136  which is essentially flat but may be raised centrally as shown, creating angled faces  148   a  and  148   b  which meet at ridge feature  145 . Surface  36  may be close to the diametral plane of the end effector, defined by waveguide axis  146  in  FIG. 8B . 
     The displacement amplitude of the torsional mode activation in faces  148   a  and  148   b  is maximum at the periphery and small along the central ridge  145 . This characteristic generates focused ultrasound transmission into contacting tissue on either side of the ridge, thus creating a strong weld. The low energy associated with ridge  145  produces only a slow tissue separation effect delaying cutting and ensuring a fully haemostatic tissue bond in the target vessel adjacent to facets  148   a  and  148   b.    
     Cutting is further slowed by employing a pulse mode electrical drive to the torsional transducers. Additionally, according to the present disclosure, and especially when using an end effector having a flat operative face, or one with a very shallow longitudinal ridge, which acts to delay or de-emphasize cutting in favor of welding or coagulating the tissue(s) with which the end effector is in contact with, the end effector can be activated with pulsed ultrasonic vibrations. Therefore, this results in pulsing the ultrasonic activation of the tool or end effector driven by the transducer. The generator is described with reference to  FIGS. 11 and 12  below. The operation of ultrasonically activated dissectors and welders such as described above is greatly enhanced by the provision of a hinged cooperative jaw attached to a protective shroud which also houses a jaw articulation system. This is more fully illustrated by reference to  FIGS. 9 and 10  below. 
     Referring to  FIG. 9 , a schematic diagram of a waveguide, shroud, and hinged jaw of a torsional mode waveguide configuration, in accordance with the present disclosure is presented. 
     The torsional mode waveguide configuration  150  includes one or more liners  152 , a separating member  154 , a waveguide axis  156 , a waveguide  158 , a concentric tube  160 , a locking member  162 , an axial view of spigot(s)  164 , a socket balls  166 , an outer surface  168 , a tube edge  170 , a gap  172 , a top portion  174  of jaw  182 , a clamping feature  176 , a first inner portion  178  of jaw  182 , and a second inner portion  180  of jaw  182 . 
     In another exemplary embodiment of the present disclosure, shown in  FIGS. 9 ,  10 A,  10 B, and  10 C, a torsional mode dissector head incorporating a waveguide, a co-operative jaw, a protective outer casing and an acoustic isolation system is described. 
       FIG. 9  depicts a distal portion of an ultrasonic tissue dissector. Jaw  182  is attached permanently to the socket balls  166  and the clamping feature  176 , thus allowing the jaw  182  to rotate in a plane which is parallel to the waveguide axis  156 . The present disclosure permits jaw  182  to be removably mounted to the socket balls  166 , being supported on spigots  164 , which engage in the locking member  162 . Attachment of the jaw  182  is achieved by expanding gap  172  until the separation of the spigots  164  is sufficient to allow them to engage in the locking member  162  having socket balls  166 . 
     Thus, a further advantage of the torsional mode waveguide configuration  150  over traditional art is the method of acoustic isolation of the waveguide  158  from the passive elements of the system, represented by concentric tube  160  and one or more liners  152 . 
     Referring to  FIGS. 10A ,  10 B, and  10 C, schematic diagrams of the jaw configuration, in accordance with the present disclosure are presented. 
     Jaw configuration  200  is substantially similar to the jaw portion  184  of  FIG. 9  and thus will only be discussed further herein to the extent necessary to identify differences in construction and/or use. Jaw configuration  200  further includes a pair of pivot members  202  and a pair of receiving members  204 . 
       FIG. 10A  merely illustrate how the pivot members  202  fasten to the receiving members  204  of  FIG. 10B .  FIG. 10C  merely illustrates how the gap  172  separates the ends of the jaw configuration  200  in order to provide a linking mechanism between the spigot  164 , the socket balls  166  and the locking member  162 . 
     Referring to  FIG. 11 , a block diagram of a first embodiment of control and power circuits for a torsional mode ultrasonic generator, in accordance with the present disclosure is presented. 
     The block diagram  220  includes first isolation blocks module  222 , signal conditioning module  224 , digitization module  226 , software algorithms module  228 , DDS signal generator module  230 , power amplifier module  232 , second isolation blocks module  234 , current sensor module  250 , power sensor module  260 , and amplitude sensor module  270 . The current sensor module  250 , the power sensor module  260 , and the amplitude sensor module  270  may be collectively referred to as an output transducer  240 . 
     In general, an electrical generator has the capability of driving torsional mode systems, such as the ones described in  FIGS. 1-8 . For example, a processor controlled DDS (direct digital synthesis) chip  230  may drive a switch mode power amplifier  232  coupled to a torsional mode transducer  240  through transformer and impedance matching inductors  250 ,  260 ,  270 . The matching circuit, incorporating current and voltage monitoring components and including appropriate isolating circuitry  222 ,  234 , is shown in  FIG. 11 . 
     To ensure correct mode selection, the output signals from the current and displacement monitoring circuits  250 ,  260 ,  270  are compared during a broad frequency scan. Transducer displacement amplitude  270  is monitored using piezo ceramic sensors  5  and  6  mounted on the horn  12 , as shown in  FIGS. 1 and 2 . The signal from sensor  22 , positioned on the horn axis, uniquely gives a minimum output when the transducer is a torsional resonance. The output from sensor  24  is a maximum at torsional resonance. By contrast the outputs from each sensor  22 ,  24  would be at a maximum when the horn  12  is at a longitudinal resonance. 
     Referring to  FIG. 12 , a block diagram of a second embodiment of control and power circuits for a torsional mode ultrasonic generator, in accordance with the present disclosure is presented. 
     The block diagram  300  includes an output transducer  302 , a sensor  304 , a current sensor  310 , a power sensor  320 , an amplitude sensor  330 , algorithms  340 , a first output  342 , a second output  344 , and a drive power signal  346 . 
     The main significance of this second embodiment of the control and power circuits for the torsional mode ultrasonic generator  300  is that it mirrors the transducer current variation as the generator frequency passes through torsional resonance. By comparing these traces it is therefore possible to detect torsional resonance with absolute certainty. Clearly, either current amplitude signals can be used as a means of effecting resonance control. However, a more useful result is obtained by using instantaneous load current and voltage to compute instantaneous power. Additionally, a tuning algorithm may then be written to select resonance coincident with maximum power and control loop algorithms may be written for coarse and fine tuning characteristics. 
     Referring to  FIG. 13 , a schematic diagram of an alternative embodiment of a torsional mode transducer having an extended stack with two threaded spigots, one located at a proximal end and one located at a distal end of a threaded shaft, in accordance with the present disclosure is presented. 
     Torsional mode transducer  400  is substantially similar to torsional mode transducer  11  of  FIG. 2  and thus will only be discussed further herein to the extent necessary to identify differences in construction and/or use. The torsional mode transducer  400  of  FIG. 13  includes a horn  12 , a threaded element  14 , ceramic rings  16 , electrodes  18 , a back plate  20 , a first sensor  22 , and a second sensor  24 . The transducer  400  further includes a threaded spigot  32  located in a tapered hole  34 . Additionally, and in contrast to  FIG. 2 , the transducer  400  includes a second threaded spigot  410  on the distal end of the threaded shaft  420 . 
     In this exemplary alternative embodiment, the threaded shaft  420  is provided with tightenable spigots  32 ,  410  (or nuts) at both its proximal and its distal end. This allows the stack assembly to be compressed further while still mounted to the horn  12 . Also, one may use exchangeable spigots/nuts  32 ,  410  at the free end of the stack assembly, having different sizes and masses, the variation in mass allowing one to tune the resonant frequency produced by the stack assembly. In existing stacks, one merely builds a stack, and then checks what frequency it happens to produce and tuning can be carried out by exchanging the spigot/nut  32 , but this is less convenient because one needs to separate the stack assembly from the horn  12  to access the nut  32 . In contrast, having a threaded shaft  420  with opposing spigots  32 ,  410  allows for more versatility in assembly and manufacturing. 
     In conclusion, fine-tuning resonance requires more critically refined generator circuitry and tuning algorithms capable of differentiating between sharply defined resonance features. The exemplary embodiments provide for efficient fine-tuning of resonance characteristics of one or more components of a surgical tool in order to selectively provide for pure torsional vibrations/waves and/or longitudinal vibrations/waves and/or flexural vibrations/waves. 
     It is to be understood that the illustrated embodiments are for the purpose of example, and that numerous other configurations of transducer/waveguide assemblies exist. Accordingly, the illustrated and described embodiments are not intended to limit the scope of the inventive subject matter only to those embodiments. 
     It should also be understood that the transducer/waveguide arrangements described herein can be used in connection in a wide variety of applications outside the implementations described herein. For example the transducer/waveguide arrangements described herein can be used in cooperation with other known transducer/waveguide arrangements. The transducer/waveguide arrangements described herein can also be useful for non-human applications. 
     The present disclosure also includes as an additional embodiment a computer-readable medium which stores programmable instructions configured for being executed by at least one processor for performing the methods described herein according to the present disclosure. The computer-readable medium can include flash memory, CD-ROM, a hard drive, etc. 
     It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. The claims can encompass embodiments in hardware, software, or a combination thereof 
     Although the illustrative embodiments of the present disclosure have been described herein with reference to the accompanying drawings, it is to be understood that the disclosure is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the disclosure. 
     Those skilled in the art, having the benefit of the teachings of the present disclosure as herein and above set forth, may effect modifications thereto. Such modifications are to be construed as lying within the scope of the present disclosure, as defined by the appended claims.