Abstract:
Ultrasonic devices having transducer assembly including a stack of alternating electrodes and piezoelectric elements. A mounting device having a first and second end is adapted to receive ultrasonic vibration from the stack and transmit it from the first to the second end. A bolt including a head and shaft is configured to threadedly engaged the mounting device. The transducer assembly includes a deformable pressure element having a central opening that permits insertion of the shaft therethrough, and has a convex side facing the bolt head and a concave side facing the stack in a non-deformed state, but, in a deformed state, applies compression forces to the stack based on the deformation. The deformable pressure element may alternately include a surface area, in its deformed state, substantially equivalent to the surface area of a piezoelectric element and/or a first and second beveled surface defining the concave side.

Description:
This application claims the benefit of Provisional Patent Application Ser. No. 60/661,739, filed on Mar. 15, 2005, to which priority is claimed pursuant to 35 U.S.C. §119(e) and which is hereby incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   (a) Field of the Invention 
   The present invention relates generally to ultrasonic transducer assemblies and, more particularly, to transducer assemblies of the composite or sandwich type incorporating a deformable pressure element. 
   (b) Description of the Prior Art 
   Ultrasonic transmission devices are well known for use in a variety of applications such as, for example, surgical operations and procedures. Ultrasonic transmission devices usually include a transducer that converts electrical energy into vibrational motion at ultrasonic frequencies. The vibrational motion is transmitted to vibrate a distal end of a surgical instrument. Such uses are disclosed in representative U.S. Pat. Nos. 3,636,943 and 5,746,756, both incorporated herein by reference. 
   High-intensity ultrasonic transducers of the composite or sandwich type typically include front and rear mass members with alternating annular piezoelectric transducers and electrodes stacked therebetween. Most such high-intensity transducers are of the pre-stressed type. They employ a compression bolt that extends axially through the stack to place a static bias of about one-half of the compressive force that the piezoelectric (PZT) transducers can tolerate. Sandwich transducers utilizing a bolted stack transducer tuned to a resonant frequency and designed to a half wavelength of the resonant frequency are described in United Kingdom Patent No. 868,784. When the transducers operate they are designed to always remain in compression, swinging from a minimum compression of nominally zero to a maximum peak of no greater than the maximum compression strength of the material. 
   As shown in  FIG. 1 , an acoustic or transmission assembly  80  of an ultrasonic device generally includes a transducer stack or assembly  82  and a transmission component or working member. The transmission component may include a mounting device  84 , a transmission rod or waveguide  86 , and an end effector or applicator  88 . 
   The transducer assembly  82  of the acoustic assembly  80  converts the electrical signal from a generator (not shown) into mechanical energy that results in longitudinal vibratory motion of the end effector  88  at ultrasonic frequencies. When the acoustic assembly  80  is energized, a vibratory motion standing wave is generated through the acoustic assembly  80 . The amplitude of the vibratory motion at any point along the acoustic assembly  80  depends on the location along the acoustic assembly  80  at which the vibratory motion is measured. The transducer assembly  82 , which is known as a “Langevin stack”, generally includes a transduction portion  90 , a first resonator or aft end bell  92 , and a second resonator or fore end bell  94 . The transducer assembly  82  is preferably an integral number of one-half system wavelengths (nλ/2) in length. 
   The distal end of the first resonator  92  is connected to the proximal end of transduction section  90 , and the proximal end of the second resonator  94  is connected to the distal end of transduction portion  90 . The first and second resonators  92  and  94  have a length determined by a number of variables, including the thickness of the transduction section  90 , the density and modulus of elasticity of material used in the resonators  92  and  94 , and the fundamental frequency of the transducer assembly  82 . 
   The transduction portion  90  of the transducer assembly  82  may include a piezoelectric section (“PZTs”) of alternating positive electrodes  96  and negative electrodes  98 , with piezoelectric elements  70  alternating between the electrodes  96  and  98 . The piezoelectric elements  70  may be fabricated from any suitable material, such as, for example, lead zirconate-titanate, lead meta-niobate, lead titanate, or ceramic piezoelectric crystal material. Each of the positive electrodes  96 , negative electrodes  98 , and piezoelectric elements  70  have a bore extending through the center. The positive and negative electrodes  96  and  98  are electrically coupled to wires  72  and  74 , respectfully. The wires  72  and  74  transmit the electrical signal from the generator to electrodes  96  and  98 . 
   The piezoelectric elements  70  are energized in response to the electrical signal supplied from the generator to produce an acoustic standing wave in the acoustic assembly  80 . The electrical signal causes disturbances in the piezoelectric elements  70  in the form of repeated small displacements resulting in large compression forces within the material. The repeated small displacements cause the piezoelectric elements  70  to expand and contract in a continuous manner along the axis of the voltage gradient, producing high frequency longitudinal waves of ultrasonic energy. The ultrasonic energy is transmitted through the acoustic assembly  80  to the end effector  88 . 
   The piezoelectric elements  70  are conventionally held in compression between the first and second resonators  92  and  94  by a bolt and washer combination  106 . The bolt  106  preferably has a head, a shank, and a threaded distal end. The bolt  106  is inserted from the proximal end of the first resonator  92  through the bores of the first resonator  92 , the electrodes  96  and  98 , and piezoelectric elements  70 . The threaded distal end of the bolt  106  is screwed into a threaded bore in the proximal end of second resonator  94 . 
   Other embodiments of the prior art utilize a stud that is threadedly engaged with both the first and second resonators  92  and  94  to provide compressive forces to the PZT stack. Threaded studs are also known in the prior art for attaching and detaching transmission components to the transducer assembly. See, for example, U.S. Pat. Nos. 5,324,299 and 5,746,756. Such bolts and studs are utilized to maintain acoustic coupling between elements of the sandwich type transducer or any attached acoustic assembly. Coupling is important to maintain tuning of the assembly, allowing the assembly to be driven in resonance. 
   In previous designs, the compression means may be inadequate and may be unable to provide a uniform pressure across the inside diameter to the outside diameter of each PZT and through the entire PZT stack, the “r” and “z” axes as shown in  FIG. 1  and graphically illustrated in  FIG. 2 . A Finite Element analysis shows that the ratio of the pressure in the R axis is of the order of 4:1. 
   U.S. Pat. No. 5,798,599 discloses an ultrasonic transducer assembly which includes soft, aluminum foil washers disposed between facing surfaces of adjacent members of the PZT stack. The washers deform under compressive loading to follow the microscopic surface irregularities of the adjacent member surfaces. However, such washers are used primarily to address local stresses and do not address the macroscopic stress gradients present in loaded ultrasonic instruments. 
   Current designs, such as those disclosed in U.S. Pat. No. 6,491,708 to Madan, et al. attempt to provide a more uniform distribution across individual PZTs and through the PZT stack. One such disclosed embodiment includes providing a bolt head that is substantially equal to the diameters of the individual PZTs. A second disclosed embodiment provides for an aft end bell having a first contact surface and a second contact surface, where the contact area of the second contact surface is less than the surface area of the first contact surface. Rather than applying pressure to the PZT stack at the central bore of the bolt hole, as has been provided in previous devices, the disclosed embodiment transfers the applied pressure to a location offset from the central bore. The Madan patent discloses an improvement in Finite Element Analysis ( FIG. 3 ) over prior designs, such as, for example, the pressure distribution illustrated in  FIG. 2 , yet may require the use of non-standard components. 
     FIG. 2  illustrates a prior art plane  10  defined by points  12 ,  14 ,  16 , and  18  illustrating an example of a Finite Element Analysis for conventional transducer designs.  FIG. 2   a  illustrates that plane  10  is a plane extending radially from the central axis of transducer assembly  82 , excepting the bore, and extends longitudinally from the most proximal surface of the transduction portion  90  to the most distal surface of the transduction portion  90 .  FIG. 3  illustrates a Finite Element Analysis of U.S. Pat. No. 6,491,708 to Madan, et al. showing an improved uniform pressure distribution over a transduction portion plane  20 . Transduction portion plane  20  corresponds to plane  10  and illustrates an improved uniform pressure distribution across the proximal surface of the transduction portion as is shown between points  22  and  24 . 
   Non-uniform pressure across the r and z axes may reduce transducer efficiency and may lead to high heat generation. This limitation becomes acutely critical in temperature-limited applications. In temperature-limited applications, the reduced efficiency translates into higher heat generation in the transducer and reduced maximum output. Further, non-uniform pressure limits the magnitude of compression and therefore limits the power capability of the transducer. 
   There is a need, therefore, for an ultrasonic transducer provided with standard components that exhibits substantially uniform compressive stresses across each PZT and throughout the PZT stack to reduce heat generation and increase power output efficiency. 
   SUMMARY OF THE INVENTION 
   Embodiments in accordance with the present invention are directed to ultrasonic transducer assemblies and, more particularly, to transducer assemblies of the composite or sandwich type incorporating a deformable pressure element. Embodiments of the present invention are directed to ultrasonic devices having a transducer assembly adapted to vibrate at an ultrasonic frequency in response to electrical energy. The transducer assembly includes a stack of alternating positive and negative electrodes and piezoelectric elements in an alternating relationship with the electrodes. A mounting device having a first end and a second end is adapted to receive ultrasonic vibration from the stack and to transmit the ultrasonic vibration from the first end to the second end of the mounting device. A bolt including a head and a shaft is configured to threadedly engaged with the mounting device. The transducer assembly further includes a deformable pressure element having a substantially central opening larger than the shaft, the opening configured to permit insertion of the shaft therethrough, the deformable pressure element having a convex side facing the bolt head and a concave side facing the stack in a non-deformed state, the deformable pressure element, in a deformed state, applying compression forces to the stack based on the deformation. 
   In other embodiments, the deformable pressure element includes a surface area, in its deformed state, substantially equivalent to the surface area of an individual piezoelectric element. In other embodiments the deformable pressure element includes a first and second beveled surface defining the concave side. In other embodiments the deformable pressure element is annular in shape. 
   Further embodiments of the present invention are directed to ultrasonic surgical devices including a transducer assembly adapted to vibrate at an ultrasonic frequency in response to electrical energy. The transducer assembly includes alternating annular positive and negative electrodes and annular piezoelectric elements in alternating relationship with the electrodes to form a stack having a longitudinal axis. A mounting device includes a first end and a second end, the mounting device adapted to receive ultrasonic vibration from the stack and to transmit the ultrasonic vibration form the first end to the second end of the mounting device. A bolt having a head and a shaft is threadedly engaged with the mounting device. A deformable pressure element includes a substantially central opening larger than the shaft, the opening configured to permit insertion of the shaft therethrough, the deformable pressure element having a convex side facing the bolt head and a concave side facing the stack in a non-deformed state, the deformable pressure element, in a deformed state, applying compression forces to the stack based on the deformation. The ultrasonic surgical device includes a transmission rod having a first end and a second end, the transmission rod adapted to receive ultrasonic vibration form the transducer assembly and to transmit the ultrasonic vibration from the first end to the second end of the transmission rod. An end effector having a first end and a second end is adapted to receive the ultrasonic vibration from the transmission rod and to transmit the ultrasonic vibration from the first end to the second end of the end effector. 
   The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the invention may be set forth with particularity in the appended claims. The invention itself, however, both as to organization and methods of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a side view of an acoustic or transmission assembly for conventional transducer designs; 
       FIG. 2  is a graph of a prior art plane illustrating an example of a Finite Element Analysis for conventional transducer designs; 
       FIG. 2   a  is a perspective view of a plane extending radially from the central axis of a transducer assembly; 
       FIG. 3  is a graph of the Finite Element Analysis of U.S. Pat. No. 6,491,708 to Madan, et al. showing an improved uniform pressure distribution over a transduction portion plane; 
       FIG. 4  is a perspective view of one embodiment of a deformable pressure element in accordance with embodiments of the present invention; 
       FIG. 5  is a side view of one embodiment of the deformable pressure element incorporated with a transducer assembly shown in initial assembled form in accordance with embodiments of the present invention; 
       FIG. 6 , is a side view illustrating threading the distal portion of the bolt into the corresponding threaded portion of the second resonator to compress the deformable pressure element in accordance with embodiments of the present invention; 
       FIG. 7  is a graph of a Finite Element Analysis in accordance with embodiments of the present invention; 
       FIG. 7   a  is a perspective view of an embodiment having the plane extending radially from the central axis in accordance with embodiments of the present invention; 
       FIG. 8  is a side view of another embodiment of the deformable pressure element in accordance with embodiments of the present invention, where the outer perimeter has a smaller diameter, with respect to the central axis, than the outer diameter of first resonator; 
       FIG. 9  is a side view of a further embodiment of the deformable pressure element in accordance with embodiments of the present invention, where the outer perimeter has substantially the same diameter; 
       FIG. 10  is a side view of another embodiment of the deformable pressure element in accordance with embodiments of the present invention, where the diameter of the outer perimeter is substantially equal to the diameter of the outer perimeter of the first resonator; 
       FIG. 11  is a perspective view of a further embodiment of a deformable pressure element in accordance with embodiments of the present invention having a first contact surface and a second contact surface; 
       FIG. 12  is a side view of a further embodiment of a deformable pressure element in accordance with embodiments of the present invention having a first contact surface and a second contact surface; and 
       FIG. 13  is a side view of a further embodiment of a deformable pressure element in accordance with embodiments of the present invention that may apply pressure to the proximal surface of first resonator at three points. 
   

   While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail below. It is to be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Before explaining the present invention in detail, it should be noted that the invention is not limited in its application or use to the details of construction and arrangement of parts illustrated in the accompanying drawings and description. Rather, the illustrative embodiments of the invention may be implemented or incorporated in other embodiments, variations, and modifications, and may be practiced or carried out in various ways. Furthermore, unless otherwise indicated, the terms and expressions employed herein have been chosen for the purpose of describing the illustrative embodiments of the present invention for the convenience of the reader and are not for the purpose of limiting the invention. 
     FIG. 4  illustrates one embodiment of a deformable pressure element  100  in accordance with the present invention. Deformable pressure element  100  may be, for example, a deformable concave disk having a first contact surface  102 , a second contact surface  104 , an outer perimeter  110 , and an inner perimeter  112 . Deformable pressure element  100  may further include a central bore  108  which may be adapted to receive a bolt. 
     FIG. 5  illustrates one embodiment of the deformable pressure element  100  incorporated with a transducer assembly  182  shown in initial assembled form. Transducer assembly  182  may include, for example, a first resonator or aft end bell  192 , a transduction portion  190 , and a second resonator or fore end bell  194 . The transducer assembly may be, for example, an integral number of one-half system wavelengths (Nλ/2) in length. 
   The distal end of the first resonator  192  may be connected to the proximal end of transduction portion  190 . The first and second resonators  192  and  194  may be, for example, constructed from any suitable material including, but not limited to, titanium, aluminum, or steel. The first and second resonators  192  and  194  may have a length determined by a number of variables, including the thickness of the transduction portion  190 , the density and modulus of elasticity of material used in the resonators  192  and  194 , and the fundamental frequency of the transducer assembly  182 . 
   The transduction portion  190  of the transducer assembly  182  may include a piezoelectric section (PZTs) of alternating positive electrodes  196  and negative electrodes  198 , with piezoelectric elements  199  alternating between the electrodes  196  and  198 . The piezoelectric elements  199  may be fabricated from any suitable material, such as, for example, lead zirconate-titanate, lead meta-niobate, lead titanate, or ceramic piezoelectric crystal material. Each of the positive electrodes  196 , negative electrodes  198 , and piezoelectric elements  199  may have a bore extending through the center. The positive and negative electrodes are electrically coupled to wires (not shown). The wires may transmit signals from a generator (not shown) to the electrodes  196  and  198  as is commonly known in the art. 
   The piezoelectric elements  199  may be energized in response to the electrical signal supplied from the generator to produce an acoustic standing wave in the acoustic assembly, such as, for example, the acoustic assembly  80  of  FIG. 1 . The electrical signal causes disturbances in the piezoelectric elements  199  in the form of repeated small displacements resulting in large compression forces within the material. The repeated small displacements cause the piezoelectric elements  199  to expand and contract in a continuous manner along the axis of the voltage gradient, producing high frequency longitudinal waves of ultrasonic energy. The ultrasonic energy is then generally transmitted through the acoustic assembly to an end effector. 
   The piezoelectric elements  199  may be held in compression between the first and second resonators  192  and  194  by a compression element or bolt  106 . The bolt  106  may have, for example, a head, a shank, and a threaded distal end. The bolt  106  may be inserted through the bore  106  of the deformable pressure element  100 , through the proximal end of the first resonator  192  through the bores of first resonator  192 , the electrodes  196  and  198 , and the piezoelectric elements  199 . The threaded distal end of the bolt  106  may be screwed into a threaded bore in the proximal end of second resonator  194 . 
   In one embodiment of the present invention, the bolt  106  may be a standard bolt characteristically used in transducer assemblies. However, any suitable compression means may be used in accordance with the present invention. The distal surface of the head of the bolt  106  may contact the second contact surface  104  of the deformable pressure element  100 . The first contact surface  102  may be placed in contact with the distal surface of the first resonator  192 . Shown in  FIG. 5  in the initial assembled form, the outer perimeter  110  of the deformable pressure element  100  may contact the proximal surface of the first resonator  192 . The inner perimeter  112  of the deformable pressure element  100 , at about the central bore  108 , may contact the distal surface of the bolt  106 . 
   In one embodiment, as depicted in  FIG. 6 , threading the distal portion of the bolt  106  into the corresponding threaded portion of the second resonator  194  may compress the deformable pressure element  100  thereby, for example, driving the deformable pressure element  100  substantially parallel to the proximal surface of the first resonator  192 . When bolt  106  is loaded, pressure may be applied to the proximal surface of the first resonator  192  in multiple locations including for example, at the outer perimeter and at the inner perimeter of the deformable pressure element  100 . By applying pressure to multiple locations along the proximal surface of first resonator  192 , pressure variations within the PZT stack may be reduced. Additionally, applying pressure at multiple locations may allow the pressure variations applied to the PZT stack to be tuned depending on the configuration and placement of the outer perimeter and the inner perimeter of the deformable pressure element  100 . Furthermore, the present invention may reduce the pressure variation in the PZT stack by incorporating standard components, such as an off-the-shelf bolt  106 , washer  100 , or first end resonator  192 , which may reduce the cost of providing highly efficient medical devices. 
   The embodiment disclosed in  FIG. 5  may, for example, display a plane  200  (as shown in  FIG. 7 ) illustrating, for example, a Finite Element Analysis in accordance with the present invention.  FIG. 7   a  illustrates one embodiment of the plane  200  extending radially from the central axis, excepting the bore, and extending longitudinally from the proximal surface of transduction portion  190  to the distal surface of the transduction portion  190 . Plane  200  includes points  202  and  204 , representing the planar proximal surface of the transduction portion  190 . Referring to  FIGS. 5 ,  7 , and  7   a , by incorporating the deformable pressure element  100  into an existing transducer assembly having a standard bolt  106  and first resonator  192 , the present invention may reduce the amount of pressure variation across the proximal surface of the transduction portion  190  as compared to conventional transducer assemblies. By combining a reduction of pressure variation, as compared to many conventional instruments, with the low cost associated with the use of standard components, the present invention may provide users with a cost-effective and efficient medical device. 
   As will be readily apparent to one of ordinary skill in the art from the teachings herein, the deformable pressure element  100  may be dimensioned with any suitable outer perimeter  110  and inner perimeter  112 . For example,  FIGS. 8 ,  9 , and  10  disclose embodiments of deformable pressure element  100  depicted in the loaded form.  FIG. 8  discloses one embodiment of the deformable pressure element  100 , where the outer perimeter  210  has a smaller diameter, with respect to the central axis, than the outer diameter of first resonator  292 , and the inner perimeter has a larger diameter than the diameter of the bore.  FIG. 9  discloses one embodiment of the deformable pressure element  100 , where the outer perimeter  210  has substantially the same diameter, measured from the from the central axis, as the outer diameter of the first resonator  292 , and the inner perimeter  212  has a smaller diameter than the bore of first resonator  292 .  FIG. 10  discloses one embodiment of the deformable pressure element  100 , where the diameter of the outer perimeter  210  is substantially equal to the diameter of the outer perimeter of the first resonator  292 , measured from the central axis, and the inner diameter  210  is larger than the diameter of the bore of the first resonator  292 . The illustrated embodiments are disclosed by way of example only and are not intended to limit the scope of the invention. The present invention includes the configuration of deformable pressure element  100  to contact at least two points on the proximal surface of first resonator  192  at any suitable location for reducing pressure variation. 
     FIG. 11  illustrates a further embodiment of a deformable pressure element  300  having a first contact surface  302  and a second contact surface  304 . The deformable pressure element  300  may also be provided with an outer perimeter  310 , an inner perimeter  312 , and a bore  308 . In one embodiment, the deformable pressure element  300  is crenelated and may include multiple projections  314 . The multiple projections  314  may reduce the stiffness of the deformable pressure element  300  that may be preferable in certain medical devices. The present invention includes using any suitable deformable material, with any suitable spring coefficient, configured in any suitable shape, to provide users with a desirable level of pressure uniformity and spring coefficient. For example, the deformable pressure element  300  may be titanium, steel, or any other suitable material. The deformable pressure element  300  may also be any suitable shape. In further embodiments of the present invention, at least two deformable pressure elements  300  may be stacked between the bolt  106  and the first resonator  292 , at least one deformable pressure element  300  may be placed between second resonator  294  and the distal end of the transducer portion  290 , and/or at least one deformable pressure element may be placed between the piezoelectric elements  199 . 
     FIG. 12  illustrates a further embodiment of a deformable pressure element  400  having a first contact surface  402  and a second contact surface  404 . The deformable pressure element  400  may also be provided with an outer perimeter  410  and an inner perimeter  412 . Second contact surface  404  may contact the bolt  406 . In one embodiment of the present invention, first contact surface  402  may contact at least two points on the first resonator  492  by providing the first resonator  492  with a concave proximal surface  440  into which first contact surface  402  is driven. In one embodiment, when unloaded, the deformable pressure element  400  may be planar in configuration where, upon loading, the deformable pressure element  400  may be driven parallel to the concave proximal surface  440 . Applying pressure to deformable pressure element  400  may drive the deformable pressure element  400  into the convex proximal surface  440 , thereby applying pressure at, for example, the outer perimeter  410  and the inner perimeter  412 . Applying pressure to at least two points on the proximal surface of the first resonator  492  may reduce the pressure variation within the PZT and may increase the efficiency of instruments constructed in accordance with the present invention. 
     FIG. 13  illustrates a further embodiment of a deformable pressure element  500  that may apply pressure to the proximal surface of first resonator  592  at three points. Applying pressure at multiple points may further decrease pressure variation across the Langevin Stack. For example deformable pressure element  500  may include a first contact surface  502  and a second contact surface  504 . The deformable pressure element  500  may also include an outer perimeter  510 , an inner perimeter  512  and, when unloaded, a concave portion  520 . Second contact surface  504  may contact the bolt  506 . When pressure is applied to the second contact surface  502  by tightening the bolt  506 , the first contact surface  502  of the deformable pressure element  500  may be driven against the proximal surface of the first resonator  592 . Tightening the bolt  506  may apply pressure to the first resonator at the outer perimeter  510  and the inner perimeter  512  of deformable pressure element  500 . Additionally, applying pressure may compress the concave portion  520  of the deformable pressure element  500 , thereby providing a third contact point at the nadir, or deepest portion of the concavity. Providing multiple contact points may increase pressure uniformity throughout the Langevin stack. The illustrated embodiments are illustrated by way of example only and are not intended to limit the scope of the invention. For example, a deformable pressure element may be provided with multiple concavities permitting pressure to be applied at any suitable number of points. 
   Thus, the described embodiments are to be considered in all aspects only as illustrative and not restrictive, and the scope of the invention is, therefore, indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.