Abstract:
A tubular piezoelectric transducer comprising a tube of piezoelectric material and having a plurality of external electrodes for inducing in a first end of the tube at least one movement of a plurality of possible movements; at least two spokes attached to and extending radially inwardly of the tube for movement with the first end; a hub at an inner end of the at least two spokes and being located on the longitudinal axis of the tube, the hub being attached to the at least two spokes for movement therewith; the hub being for receiving therein a probe for movement of the probe with the hub. A phaco-probe incorporating the transducer is also disclosed.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to our two earlier U.S. patent application Ser. No. 10/611,401 (published as 2004/0118686) filed Jul. 1, 2003 for the invention titled “Piezoelectric Tubes” and Ser. No. 10/611,306 (published as 2005/0017603) filed Jul. 1, 2003 for the invention entitled “Pump” (our “earlier applications”), the contents of which are hereby incorporated by reference as if disclosed herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to an ultrasonic mechanical emulsifier and relates more particularly, though not exclusively, to an ultrasonic mechanical emulsifier using piezoelectric material. 
       BACKGROUND TO THE INVENTION 
       [0003]    One of the most important areas in minimally invasive surgery is phacoemulsification surgery, which has revolutionized cataract surgery in the recent years. In phacoemulsification surgery, an ultrasound probe is inserted into the eye. Ultrasound energy is applied to the crystalline lens of the eye to emulsify it. The emulsified material is then removed from the eye using vacuum. The capsular bag is left behind for the implantation of an artificial intraocular lens replacing the cataractous crystalline lens. 
         [0004]    Phacoemulsification allows the relatively large cataract to be removed via a small incision. However, the ultrasound energy used may damage the cornea, which is the transparent ‘cover’ of the eye, causing the loss of the endothelial cell layer. Significant loss of endothelial cells may lead to a later complication known as bullous keratopathy requiring corneal transplant. Bullous keratopathy is now the commonest indication of corneal transplant in many parts of the world. 
         [0005]    One of the good surgical techniques which helped to reduce endothelial cell loss is the use of mechanical forces emanating from a phaco probe tip. These forces are better localised than ultrasound energy. Mechanical forces used include techniques known as phaco-chop, and using a second instrument to manually break up small pieces of lens material and the removal of these fragments using high vacuum. The lower the mechanical breaking force, the higher the vacuum force will be required. However, high vacuum has its dangers. It can suck in the posterior capsule thereby rupturing it. Rupture of the posterior capsule can lead to serious complications such as retinal detachment and intraocular lens displacement. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with a first preferred aspect there is provided a tubular piezoelectric transducer comprising a tube of piezoelectric material and having a plurality of external electrodes for inducing in a first end of the tube at least one movement of a plurality of possible movements; a hub having its centre located on the longitudinal axis of the tube, the hub being for movement with the first end; the hub being for receiving therein a probe for movement of the probe with the hub. 
         [0007]    According to a second preferred aspect there is provided a phaco-probe comprising a tubular piezoelectric transducer including a tube of piezoelectric material and having a plurality of external electrodes for inducing in a first end of the tube at least one movement of a plurality of possible movements; a hub having its centre located on the longitudinal axis of the tube, the hub being for movement with the first end; the hub being for receiving therein a probe for movement of the probe with the hub. 
         [0008]    For both aspects the plurality of external electrodes may extend longitudinally of the tube and may be on an external surface of the tube. The plurality of external electrodes may comprise four electrodes arranged as equal quadrants extending longitudinally of the tube. There may be at least two spokes attached to and extending radially inwardly of the tube for movement with the first end. There may be four equally-spaced spokes. The at least two spokes may be at the first end or adjacent the first end. The hub may be of a form selected from: integral with the spokes, formed by the spokes, securely attached to the spokes, formed by the tube, and integral with the tube. The at least two spokes and the hub may be relatively rigid so all motion of the first end is transmitted to the probe through the at least two spokes and hub. The probe may be attachable to the hub by one of: a friction fit, a snap fit, a bayonet fitting, and a screw-thread connection. The plurality of possible movements may be selected from: reciprocating motion of the first end in the direction of the longitudinal axial of the tube, rotational motion of the first end about the longitudinal axis of the tube; vertical oscillation of the first end, horizontal oscillation of the first end; and arcuate oscillation of the first end about the longitudinal axis of the tube. The probe may comprise a head end extending axially outwardly from the first end. The head end may have at its outer end a probe tip. 
         [0009]    The probe may be located within a funnel-shaped housing, the tip extending beyond the housing. The funnel-shaped housing and the head end may conduct ultrasonic vibrations able to be produced by the tubular piezoelectric transducer to the probe tip for radiating the ultrasonic vibrations from a phace-probe tip. The phaco-probe tip may comprise a tip of the funnel-shaped housing, and the probe tip. The phaco-probe may further comprise a stack of piezoelectric actuators capable of reciprocal movement in the direction of the longitudinal axis of the tubular piezoelectric transducer. The stack of piezoelectric actuators and the tubular piezoelectric transducer may be able to be operated independently of each other. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In order than the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only preferred embodiments of the present invention, the description being with reference to the accompanying illustrative drawings. 
           [0011]    In the drawings: 
           [0012]      FIG. 1  is a representation of a preferred embodiment of a tubular piezoelectric transducer; 
           [0013]      FIG. 2  illustrates the bending and longitudinal deformation of the tubular piezoelectric transducer of  FIG. 1  at the resonant frequency with (a) being the bending mode and (b) being the longitudinal mode; 
           [0014]      FIG. 3  illustrates the sequential bending of the tubular piezoelectric transducer; 
           [0015]      FIG. 4  illustrates the rotational motion of the tubular piezoelectric transducer; 
           [0016]      FIG. 5  is a perspective view of the tubular piezoelectric transducer with probe fitted; 
           [0017]      FIG. 6  shows an assembled phaco-probe with the tubular piezoelectric transducer; 
           [0018]      FIG. 7  is a partial longitudinal, vertical cross-sectional view of the phaco-probe of  FIG. 6 ; 
           [0019]      FIG. 8  shows the phaco-probe of  FIG. 6  with PZT stacks; 
           [0020]      FIG. 9  is a partial longitudinal, vertical cross-sectional view of a first variant of the phaco-probe of  FIG. 8 ; 
           [0021]      FIG. 10  is a partial longitudinal, vertical cross-sectional view of a second variant of the phaco-probe of  FIG. 8 ; 
           [0022]      FIG. 11  is a partial longitudinal, vertical cross-sectional view of a variant of the phaco-probe of  FIG. 10 ; and 
           [0023]      FIG. 12  is an illustration of an alternative form of the tubular piezoelectric transducer. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    To refer to  FIG. 1  there is shown a tubular piezoelectric transducer  10  made of a formulated piezoelectric material and consists of a hollow, radially-poled piezoelectric tube  12  in accordance with our earlier applications. The tube  12  is coated with outer electrodes  14  on its outer curved surface  16  and may have inner electrodes  24  on its inner curved surface  26 . The electrode configuration may be varied according to requirements. For example, there may be any number of electrodes: two, three, four, eight, and so forth; or they may extend circumferentially; depending on requirements for each application. For example, in  FIG. 1 , there are four electrodes  14  on the outer surface in equal, longitudinally-extending quadrants  18  with small gaps  20  between them. The quadrants  18  of the electrodes  14  extend longitudinally of the tube  12 . 
         [0025]    With this configuration, the transducer  10  is able to perform bending or longitudinal deformations by extension and contraction of that part of the tube  12  having an electrode quadrant  18  to which has been applied an electric field. 
         [0026]    The tubular piezoelectric transducer  10  offers a number of advantages: good structural rigidity, easy calibration and high resonant frequency. It can be used in both off-resonance and resonance conditions. The transducer  10  is able to deform in three dimensions, and may do so with a sub-nanometer resolution. 
         [0027]    Due to a large mechanical output at resonant frequencies, the use of the transducer  10  at resonant frequencies is of advantage. For the preferred embodiment, the advantage is the ability to combine ultrasonic energy and the induced mechanical energy when the transducer  10  is working at its resonant frequency. 
         [0028]      FIGS. 2 and 3  show the bending and longitudinal vibration mode of the transducer  10 . The longitudinal vibration or reciprocating motion mode can be obtained by connecting the outer electrodes  14  and applying an electric signal on the outer electrodes  14  and inner electrodes  24  of the transducer  10 . The deformation of the transducer  10  reaches its maximum at the resonant frequency of the transducer  10 . Due to the large-amplitude harmonic elongation or contraction, an ultrasonic wave will be generated that travels along the longitudinal direction of the transducer  10 . The operational frequency may be in the range of KHz to MHz for the transducer  10 . The tubular piezoelectric transducer  10  converts electric energy to elastic mechanical vibrations, where the vibration energy generated will then radiate to the processed medium. 
         [0029]    The bending mode is formed by applying an electric field on a pair of diagonally-opposite outer electrodes  14 . The bending mode can be sequential and provide twisting and/or rotational actions, as shown in  FIG. 3 . The motion will be of a first end  28  of the tube  12 . If another electric field is applied to the other diagonally-opposite pair of outer electrodes  14 , with the electric fields applied to the two pairs of outer electrodes  14  having a phase difference of 90 degrees, a rotational mode can be obtained as seen in  FIG. 4 . The tubular piezoelectric transducer  10  may rotate clockwise or counter clockwise depending on the excitations of the applied electric fields. As such the rotational motion is a sequential movement as shown in  FIGS. 3 and 4 :
       (a) in  FIGS. 3(   a ) and  4 ( a ), the first end  28  of the transducer  10  is bent downwardly;   (b) in  FIGS. 3(   b ) and  4 ( b ) the first end  28  of the transducer  10  is bent sideways to the right;   (c) in  FIGS. 3(   c ) and  4 ( c ) the first end  28  of the transducer  10  is bent upwardly; and   (d) in  FIGS. 3(   d ) and  4 ( d ) the first end  28  of the transducer  10  is bent sideways to the left.       
 
         [0034]    By following this sequence, an anti-clockwise rotational movement of the first end  28  is obtained. Other combinations of movements may be used. For example, a sequential combination of (a) and (c) will provide a vertical oscillation; a sequential combination of (b) and (d) will provide a horizontal oscillation; a sequential combination of (a) with (b) and/or (d) will provide an lower arcuate oscillation; a sequential combination of (c) with (b) and/or (d) will provide an upper arcuate oscillation; a sequential combination of (d) with (a) and/or (c) will provide a left-hand arcuate oscillation; and a sequential combination of (b) with (a) and/or (c) will provide a right-hand arcuate oscillation. 
         [0035]    As such the motions may any one of, or any combination of two or more of:
       reciprocating motion in the direction of the longitudinal axial of the tube  12 ;   rotational motion about the longitudinal axis of the tube  12 ;   vertical oscillation;   horizontal oscillation; and   arcuate oscillation.       
 
         [0041]    To assist the output of the rotational motion of the first end  28 , the transducer  10  may have radially-directed spokes  30  and a central hub  32  at or adjacent the first end  28 . The spokes  30  and hub  32  may be integral with the tube  12 , or may be formed separately and subsequently attached to the tube  12 . The number of spokes  30  may be as required or desired. As shown there are four spokes  30 . It has been found that if there are four outer electrodes  14  a relatively smooth rotational movement can be achieved. However, there is no direct relationship between the number of electrodes  14  and the number of spokes  30 . The hub  32  may be integral with the spokes  30 , be formed by the spokes  30 , or be securely attached to the spokes  30 . The spokes  30  and hub  32  may be of any suitable material, including a non-piezoelectric material. The centre of the hub  32  is located on the central, longitudinal axis of the tube  12 . The spokes  30  and the hub  32  are preferably relatively rigid so all motion of the first end  28  is transmitted to an object through the spokes  30  and/or hub  32 . 
         [0042]    The rotational motion is a functional motion of the transducer  10 . Due to this motion, an object that engages the hub  32  will be forced to move with the hub  32  due to the frictional interaction at the contact area within the hub  32 . This allows the transducer  10  to be a larger piezo-tube, and the working motion be induced via the radially-directed spokes  30  and the central hub  32 . 
         [0043]    The tube  12  may be produced by an extrusion process, and the spokes  30  and hub  32  added subsequently. Alternatively, the tube  12 , spokes  30  and hub  32  may be integrally formed. 
         [0044]    When the applied electric fields to the electrodes  14 ,  24  are synchronized, the extension and contraction of the transducer  10  is in the direction of the longitudinal axis of the tube  12 . This provides a linear motion. It also provides a second mode of mechanical force, and will enable the emission of ultrasonic energy at a designed focus point when at the resonant frequency. 
         [0045]    In this embodiment, a probe  40  is connected to the tubular piezoelectric transducer  10  either directly or by the spokes  30  and hub  32 . The probe  40  has two main functions: to provide a small tip for micro-surgical procedures, and to focus and amplify the vibration energy. The probe  40  concentrates the vibration energy at its tip, and radiates the resultant ultrasonic energy in a focused manner. The length of the probe  40  depends on the frequency applied. For example, the optimal length is inversely proportional to the frequency of operation of the tubular piezoelectric transducer  10 . 
         [0046]      FIG. 5  shows the transducer  10  with the probe  40  attached thereto by engagement with the hub  32 . The probe  40  may pass through the transducer  10  from the first end. 
         [0047]    The probe has a head end  42  extending axially outwardly from the first end  28 . Extending axially outwardly from the rear end  34  of the tube  12  is a rear sleeve  44 . Rear sleeve  44  may pass to the transducer  10 . The attachment of the probe  40 , or the head end  42  of the probe  40 , to the hub  32  may be: a friction fit; a snap fit; use a bayonet fitting; a screw-thread connection; or otherwise as required or desired. Power supply for the electrodes  14  may be through the rear sleeve  44 . 
         [0048]      FIGS. 6 and 7  show a phaco probe  70  of standard and known construction to which a tubular piezoelectric transducer  10  has been fitted. The tubular piezoelectric transducer  10  includes the probe  40  the head end  42  of the probe  40  being located in a funnel-shaped housing  72 . The phaco probe  70  has a tip  46 . The tip  46  comprises the tip  72   a  of the housing  72  and the tip  40   a  of the probe  40 . The tip  42   a  extends from the head end  42  and may be a separate component, or may be integral with the head end  42 . The entire assembly (apart from the tip  46  and part of the rear sleeve  44 ) is contained within a housing body  74 . The tip  46  is capable of the various movements described above. The housing  72  and the head end  42  of probe  40  conduct the ultrasonic vibration energy produced by the tubular piezoelectric transducer  10  to the tip  46  so that the ultrasonic vibration generated by the tubular piezoelectric transducer  10  radiates outwardly from the tip  46 . 
         [0049]    The housing  72  is connected to the tubular piezoelectric transducer  10  such that the longitudinal motion translates to the tip  72   a  of the housing  72 . The main function of the tip  46  is to concentrate and radiate the ultrasonic energy as well as providing the rotational, vertical and horizontal motion. 
         [0050]    As shown in  FIGS. 9 to 11 , the tubular piezoelectric transducer  10  can be combined with a stack  50  of piezoelectric actuators of known design and construction and only being capable of reciprocal movement in the direction of the longitudinal axis of the stack  50  and/or tubular piezoelectric transducer  10 . The combination of the tubular piezoelectric transducer  10  with the PZT stack may be in any one or more of various configurations. The stack  50  can be located and connected in series at either end of the tubular piezoelectric transducer  10 . The first configuration of  FIG. 8  has the stack  50  at the end of the tubular piezoelectric transducer  10  remote from the tip  46 . As shown in  FIGS. 9 and 10 , the stack  50  is at the end of the tubular piezoelectric transducer  10  adjacent the tip  46 . In  FIG. 9  the stack  50  is attached to the end of the tubular piezoelectric transducer  10  whereas in  FIG. 10  the stack  50  is apart from the end of the tubular piezoelectric transducer  10 . The stack  50  may be able to be operated independently of the tubular piezoelectric transducer  10 , and the tubular piezoelectric transducer  10  may be able to be operated independently of the stack  50 , to allow a surgeon to have more control over the extent of the motion. 
         [0051]    The function of the PZT stack  50  is to increase the magnitude of the longitudinal motion of the housing  72 . The tip  72   a  of the housing  72  provides most of the longitudinal mechanical motion. The magnitude of the longitudinal motion is the combination of the longitudinal motion of the tubular piezoelectric transducer  10  and the PZT stack  50 . The housing  72  will transmit the ultrasonic energy from the PZT stack  50  and the tubular piezoelectric transducer  10 . 
         [0052]    The tip  40   a  of the probe  40  also transmits ultrasonic energy. In addition, the tubular piezoelectric transducer  10  enables the rotational, vertical and horizontal motion of the probe  40  that is amplified at the tip  46  due to the length of the probe  40 . 
         [0053]    As shown in  FIG. 11 , the probe  40  may be hollow such that one end is connected to a vacuum suction pump. In this way, the broken lens can be extracted from the eye. 
         [0054]    In  FIG. 12  the tubular piezoelectric transducer  10  is solid at least at the first end  28  and forms the hub  30  so there is no need for spokes  30  where the piezoelectric transducer is solid. This is at the first end  28  as illustrated. The hub  30  is formed by and/or is integral with the tube  12 . 
         [0055]    The performance of the transducer  10  may be adjusted over a wide range. Rotational speeds of up to 8,000 rpm have been achieved with up to 10 mNm of torque. Less than 1 W output power was required. 
         [0056]    The embodiments described include a device that is able to provide mechanical energy coupled with ultrasonic energy for the emulsification function. The micro actuator uses a tubular piezoelectric transducer that provides a mechanical force to a probe to enable the probe to break the lens into small pieces, where the driven tip will provide faster disrupting force than manual chopping forces. It will also provide a more controlled and contained force delivery compared to an ultrasonic or laser phaco-tip, leading to safer surgery with improved results. Most importantly, the actuation combines mechanical and ultrasonic functions into one micro-surgical tool. This allows a minimal incision, and interruption, for the cataract procedure. 
         [0057]    The apparatus may also be used for other medical and non-medical applications such as, for example:
       (a) dissolving or disintegrating of foreign deposits of material from vessels including cholesterol in blood vessels, and blood clots;   (b) dissolving or disintegrating materials; or   (c) micro-positioning.       
 
         [0061]    Whilst there has been described in the foregoing description preferred embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations in details of design, construction and/or operation may be made without departing from the present invention.