Classifications

• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/18—Methods or devices for transmitting, conducting or directing sound
  • G10K11/20—Reflecting arrangements
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting-in contact lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/00736—Instruments for removal of intra-ocular material or intra-ocular injection, e.g. cataract instruments
  • A61F9/00745—Instruments for removal of intra-ocular material or intra-ocular injection, e.g. cataract instruments using mechanical vibrations, e.g. ultrasonic
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/18—Methods or devices for transmitting, conducting or directing sound
  • G10K11/24—Methods or devices for transmitting, conducting or directing sound for conducting sound through solid bodies, e.g. wires

Definitions

• the invention concerns a device which vibrates a hollow needle at ultrasonic frequencies.
• the invention can be used in the medical treatment of cataracts, wherein the vibrating needle shatters the cataract, and the shattered debris is withdrawn through the hollow part of the needle.
• FIG. 1 illustrates a piezoelectric transducer 3 which can be used to set up a standing ultrasonic wave in tube 6.
• the transducer comprises two piezoelectric crystals 9 and 12 separated by an electrode 15.
• the crystals When the crystals are excited by an alternating current signal applied to surfaces 21A and 21B, the crystals expand and contract at the frequency of the signal. That is, the crystals cycle between the expanded size indicated by phantom lines 18 and the smaller size indicated by surfaces 21A and 21B.
• This cyclic expansion and contraction applies mechanical pulses to tube 6. If the pulsing frequency equals the resonant frequency of the tube 6, a standing wave is established.
• the standing wave causes a needle 24 to oscillate between phantom position 24A and solid position 24.
• the oscillating needle can be used to fracture hard materials, such as cataracts in the human eye.
• One type of prior art device uses an electrode 15 manufactured of a beryllium-copper alloy.
• an electrode suffers from the cyclic compression and relaxation imposed by the vibration of the crystals 9 and 12; over time, the electrode 15 becomes extruded, as illustrated in grossly exaggerated form in Figure 2.
• This extrusion causes at least three effects. First, it causes minute air gaps to appear, as illustrated by gap 28. These air gaps degrade the acoustic coupling between surfaces 30 and 33, thus reducing the efficiency of transmission of ultrasonic energy into tube 6. Second, the air gaps degrade the electrical contact between electrode 15 and crystals 9 and 12. Good electrical contact is necessary in order to deposit the electrical charge which induces the piezoelectric movement of the crystals 9 and 12.
• the extrusion unloads the mechanical pressure which was originally applied to the crystals 9 and 12. That is, the crystals are preloaded in compression by mechanical forces illustrated by arrows 36 and 39 in Figure 1.
• the electrode 15 reacts the forces 36 and 39.
• the change in thickness of the electrode caused by the extrusion reduces the reaction, decreasing the compression, thus causing the crystals 9 and 12 to become unloaded and to operate under nonoptimal conditions.
• a second feature of the probe in Figure 1 is that significant acoustic energy, indicated by waves 40, radiates away from, and not into, tube 6. Waves 40 do not impart energy to the needle 24; their energy is lost.
• a piezoelectric crystal transducer sandwich is located between a high acoustic impedance medium, called a reflector, and a low acoustic impedance medium, called a resonator.
• the resonator impedance is matched to the acoustic load thereby transferring maximum power from the transducer to the load.
• the high impedance reflector recovers acoustic energy which would be otherwise lost and redirects it through the resonator acoustic path towards the load. The result is a higher efficiency energy transfer compared to prior art mechanisms.
• Automatic frequency and load tracking capability is provided electronically by a phacoemulsification control circuit.
• An optimum, nearly constant mechanical stress environment is maintained for the piezoelectric transducers over a specified operational temperature range by a unique flexible clamping mechanism.
• An optimum mechanical stress environment is maintained for the needle support by the resonator which is an acoustic horn and tube combination having a shape that closely approximates the ideal catenoidal horn assembly.
• Figure 1 illustrates a phacoemulsification probe as used in the prior art.
• Figure 2 illustrates the extrusion which can occur in electrode 15 in Figure 1.
• FIGS 3 and 4 illustrate one form of the invention.
• Figure 5 illustrates reflection of acoustic waves by reflector 43 in Figure 4.
• Figure 6 illustrates schematically the compression of transducer 3 of Figure 3.
• Figure 7 illustrates schematically the expansion of rod 66B, which represents rod 66 in Figure 3, which occurs in order to maintain constant pressure upon transducer 3B in Figure 7.
• Figure 8 illustrates a circuit which provides a signal to a transducer which is of the same frequency as the resonant frequency of a load on the transducer.
• an ultrasonic transducer 3 is located between a reflector 43 and a resonator 46.
• the transducer comprises an electrode 50, constructed of unhardened #01 carbon steel, and two piezoelectric crystals 53 and 56, constructed of a modified lead zirconate titanate ceramic material, formed into rings, silver coated for electrical conductivity, and marketed under the trade name PXE by the Electronic Components and Materials Division of North American Phillips Corporation.
• a lug 59 fastened to the electrode, allows connection to a power supply.
• An insulating tube 61 fits within a bore 63 within transducer 3.
• the reflector 43 is fastened to the resonator 46 by a hollow threaded tube 66, which mates with threaded regions 68 and 70 in the reflector and resonator. Both the hollow tube 66 and the resonator 46 are constructed of 6AL-4V titanium. Reflector 43 is constructed of #17 tungsten. Insulating sleeve 61 is constructed of Teflon, Teflon being a trademark of the DuPont Chemical Corporation.
• threaded tube 66 is first threaded into resonator 46 until an end 72 in Figure 3 becomes seated against shoulder 75. Then, reflector 43 is threaded onto threaded tube 66, in order to compress the transducer 3. The amount of compression is determined by the following method.
• a two microfarad capacitor 77 is connected across piezoelectric crystal 56, as indicated in Figure 3. This connection places capacitor 77 in parallel with crystals 53 and 56. This parallel arrangement exists because the threaded tube 66 electrically connects reflector 43 with resonator 46, thus placing resonator 43 and reflector 46 at the same electrical potential. (That is, surfaces 79 and 80 of the crystals are both electrically connected to lead 83 of the capacitor 77, while surfaces 85 and 86 are connected with lead 89.)
• reflector 43 After placement of capacitor 77 in parallel with crystals 53 and 56, reflector 43 is advanced toward resonator 46 by rotation upon threaded tube 66 until the piezoelectric crystals are compressed to the extent that the voltage across capacitor 77 reaches 0.75 volts. At this time, advancement of reflector 43 is stopped, and the piezoelectric crystals 53 and 56 are now properly compressed.
• a phacoemulsification needle 94 known in the art, such as Model Number IA-145, available from Storz Instrument Company, located in St. Louis, Missouri, is screwed into threaded end 96 of resonator 46.
• the needle vibrates in a longitudinal mode by alternately compressing to solid position 94 and expanding to phantom position 98.
• the vibrational displacement, indicated by dimension 101, is about 5/1000ths of an inch.
• the vibration of the needle occurs at the oscillation frequency of the piezoelectric crystals 53 and 56, which are coupled to the needle 94 through resonator 46.
• Curved region 104 of the resonator 46 acts as a horn in order to impedance-match crystal 56 with needle 94, in order to maximize energy flow toward the needle 94.
• Resonator 46 functions as a 1/4 wavelength transmission line (at the crystal frequency) on which needle 94 acts as a load.
• Crystals 53 and 56 in Figure 3 are driven by a signal applied to electrode 50 and reflector 43.
• the application of an alternating current signal to the crystals 53 and 56 causes them to cyclically expand to the phantom position 107, shown in exaggerated form in Figure 4, and then contract to the solid position shown.
• This cyclic expansion and contraction applies mechanical pulses to the resonator 46, at the signal frequency.
• the signal frequency which drives electrode 50 and reflector 43 is preferably 28.0 to 29.0 kilohertz.
• One system for applying such a driving signal to crystals 53 and 56 is described in U.S. patent application entitled “Control System For Ophthalmic Surgical Instruments," Serial No. 928,170, filed November 6, 1986, in which the inventors are Gregg Scheller, et al., and which is assigned to the assignee of the present invention. This application is hereby incorporated by reference.
• One embodiment of such a system is available from Storz Instrument Company, St. Louis, Missouri, under the product name of "DAISY.”
• One type of circuit that is utilized in the DAISY system to apply an electrical signal to drive the transducer at its resonant frequency is shown in the block diagram of Figure 8.
• the transducer 3 is modeled as an RLC series resonant network in parallel with a capacitance when operating under load and near the transducer's resonant frequency. This model of the transducer is not shown in
• the driving circuit Being a closed loop system, the driving circuit is essentially an oscillator which fulfills the Barkhausen criteria for oscillation: zero phase shift and unity loop gain.
• the design frequency of the oscillator is 28,500 + - 500 hertz.
• the feedback portion of the loop consists of an injection oscillator 203, a band pass active filter 205, a low pass active filter 207, and a variable gain amplifier 209.
• the injection oscillator 203 provides an initial voltage signal at a frequency near the transducer resonant frequency. That signal will be disengaged from the feedback loop path once the driving circuit provides a signal strong enough to maintain the transducer oscillations.
• the band pass and low pass filters provide the appropriate frequency selectivity and phase shift characteristics to maintain the strength of the transducer feedback signal while the transducer phase characteristics vary over a normal operating range.
• the signal fed back from the transducer is derived over a compensation network 213 which provides additional frequency selectivity and phase shift stability.
• the variable gain amplifier 209 establishes the loop gain during initial calibration of the filter circuits, and remains essentially fixed after the filter circuit calibration is complete.
• the power amplifier and transformer 215 provide a maximum driving voltage of about 380 volts rms with a maximum current of about 10 milliamps rms.
• a gain control network 218 provides a stable voltage signal output by comparing the driving voltage, on line 221, with a voltage command reference level, provided by a user on line 223, ' and then compensating for any differences by adjusting the gain of the power amplifier 215.
• Vibration of the needle 94 in Figure 3 can be used in the medical treatment of hardened objects, such as cataracts in the human eye.
• the vibrating needle 94 when brought near a cataract, causes the cataract to shatter, and the shattered debris is withdrawn through channel 110, under the influence of a vacuum source 115 attached to nipple 117.
• reflector 43 is constructed of tungsten.
• Tungsten has a very high acoustic impedance, of the order of 90 x 10 6 kg/(m 2 -sec) to 105 x 10 6 kg/(m 2 - sec) . Consequently, the acoustic energy reflected at the interface 79 in Figure 3 is reflected (1) in phase, with
• the reflection coefficient which is a complex number having both real and imaginary parts (both being possibly nonzero) , describes the amount of the incident wave energy which is reflected at the boundary between the different materials. It also describes the phase relationship between the incident and reflected waves, that relationship being either in phase (zero degrees phase shift) or out of phase (by up to 180 degrees) .
• the principal design methods employed for the transducer assembly used an initial assumption that the transmission media for the acoustic waves are lossless. This assumption provides the benefit that the mathematical manipulations required to implement an acoustic transmission design are far more manageable, and incur little cost in terms of accuracy of the final result.
• the reflection coefficient is calculated. In its most general form, that calculation is simply a ratio of (1) the differences between two acoustic impedances and (2) the sum of those same two impedances. A potentially confusing situation arises when trying to assign numerical values to each impedance before the ratio is computed.
• the calculation for the reflection coefficient, R is the following:
• Z L represents the specific acoustic impedance presented to the acoustic wave as it travels from a medium having a characteristic acoustic impedance Z 0 into a medium having a characteristic acoustic impedance Z x .
• the numerical value of the specific acoustic impedance is a function of the characteristic acoustic impedance, the length of the material from the incident wave interface to the acoustic termination of that material section, and the numerical value (possibly complex) of the specific acoustic impedance presented to the transmitted wave when it reaches the termination.
• Also important, in the most general sense, are the attenuation properties of the material. However, as stated earlier, those properties are ignored for the purposes of this design because it is felt that sufficient dimensional constraints have been placed on the component parts so that the no loss assumption remains valid.
• the wavelength of the acoustic wave as it passes through the ceramic crystal material is the wavelength of the acoustic wave as it passes through the ceramic crystal material.
• its length must be close to 1/4 wavelength with a low acoustic impedance backing, that is, with a backing which is nearly an acoustic short circuit over the operating frequency range of the transducer assembly.
• the acoustic impedance of air is usually considered to be an acoustic short circuit.
• the specific acoustic impedance presented to the transmitted acoustic wave at the tungsten reflector termination is nearly zero. Therefore, the specific acoustic impedance presented to the incident acoustic wave at the interface between the ceramic crystal and the tungsten reflector is nearly infinite.
• the numerical value of Z L is very large compared with Z 0 , and the reflection coefficient, defining the pressure amplitude and phase shift of the incident acoustic wave occurring upon reflection, will nearly equal unity.
• the actual length of the reflector section is less than 1/4 wavelength.
• the no loss assumption results in a pure imaginary number representing the specific acoustic impedance presented by the reflector.
• the net result is that the magnitude of the reflection coefficient will always be 1, even for reflector lengths other than 1/4 wavelength.
• the noticeable difference in the reflected wave will be the phase relation between it and the incident wave. Varying the length of the reflector will change that phase relationship. For the present configuration, that phase shift should be less than 30 degrees over the normal operating frequency range of the transducer.
• Z x is approximately 100 x 10 6 kg/(m 2 -sec) and Z 0 is approximately 30 x 10 6 kg/(m 2 -sec). Both of these numbers are real, that is, complex numbers with a zero imaginary part.
• Z L is approximately 130 x 10 6 kg/(m 2 -sec) . This number is imaginary, that is, a complex number with a zero real part.
• Z L is derived from standard distributed transmission line methods which incorporate the length, acoustic velocity and attenuation characteristics of the material, as well as the characteristics of the acoustic load making contact with the material.
• ⁇ is the phase shift constant
• 1 is the material length
• j is the square root of -1.
• threaded tube 66 in Figures 3 and 4 is constructed of 6AL-4V titanium.
• This alloy of titanium has a small modulus of elasticity. Modulus of elasticity is commonly defined as the ratio of unit stress to unit strain, or tensile force per square inch divided by elongation per unit length. Stated another way, with a low modulus, a small tensile force causes a large elongation of the threaded tube 66. In oversimplified terms, the titanium threaded tube 66 stretches easily. The small modulus of elasticity is important because thermal expansion and contraction of the threaded tube 66, which hold together reflector 43 and resonator 46
• the force applied by a spring 137 is proportional to its percentage change in elongation, but, however, it may be assumed that, for small elongations (of the size involved in thermal expansions) the force is relatively constant. Therefore, if thermal expansion of the transducer 3 tends to drive wall 134 into phantom position 134A with respect to wall 132, springs 137 stretch, maintaining a relatively constant opposing force, which compresses transducer 3. Threaded rod 66 in Figure 3, in acting like spring 137, maintains the pressure upon crystals 53 and 56 at a relatively constant value.
• Rod 66 in Figure 3 has an outer diameter of 0.164 inches, an inner diameter of 0.0625 inches, and has a length between threaded junctions (i.e., dimension 130, representing the distance between junctions 68 and 70) of 0.580 inches. These dimensions of rod 66 give it an approximate modulus of elasticity of 16.5 x 10 6 psi, which is considered appropriate for the diameter of transducer 3, which is 0.394 inches, and for temperature excursions from 60 degrees Fahrenheit to 270 degrees Fahrenheit.
• Rod 66 has been described as a spring which experiences a small extension, in response to thermal expansion of transducer 3, thus applying only a small change in pressure to crystals 53 and 56. It will now be shown that the particular configuration of the invention in Figure 3 causes an even smaller change in pressure, as compared with the schematic configuration of Figure 6.
• the stretching region of rod 66 were coextensive with transducer 3 (i.e., threaded junction 68 ended at point 135, so that the stretching region of rod 66 is as long as transducer 3) , and if the stretching region of rod 66 were 1 inch long, then the percentage change of rod 66 is 0.001/1.0 or 0.1 percent.
• Figure 3 provides a change in spring force which is three times smaller than when the stretching region of rod 66 is coextensive with transducer 3 (i.e., 0.033 v. 0.1).
• One reason for this * reduction in change is that the length of spring involved (length 130) is longer than transducer 3, whose thermal expansion, if unaccommodated, tends to increase pressure on crystals 53 and 56.
• transducer 3B expands from dimension 140 to dimension 144
• rod 66B expands from dimension 146 to dimension 148.
• the absolute expansion of transducer equals the absolute expansion of rod 66 (dimension 152)
• the percentage expansion of rod 66B is less than the percentage expansion of transducer 3 (dimension 150/dimension 140) . Consequently, the change in spring force applied by rod 66 is less than if the percentage change in length of rod 66 were equal to that of transducer 3.
• threaded rod 66 in region 130 in Figure 3 is not significantly elongated at the acoustic frequency of about 29 kilohertz by the acoustic pulses.

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• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Multimedia (AREA)
• Ophthalmology & Optometry (AREA)
• Acoustics & Sound (AREA)
• Biomedical Technology (AREA)
• Heart & Thoracic Surgery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Vascular Medicine (AREA)
• Surgery (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Transducers For Ultrasonic Waves (AREA)
• Ultra Sonic Daignosis Equipment (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Surgical Instruments (AREA)
• Apparatuses For Generation Of Mechanical Vibrations (AREA)

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• 1989
  • 1989-09-28 JP JP51067989A patent/JPH03502540A/ja active Pending
  • 1989-09-28 NL NL8921049A patent/NL8921049A/nl not_active Application Discontinuation
  • 1989-09-28 CH CH198390A patent/CH678700A5/de not_active IP Right Cessation
  • 1989-09-28 EP EP19890911502 patent/EP0389615A4/en not_active Withdrawn
  • 1989-09-28 WO PCT/US1989/004207 patent/WO1990003150A1/en not_active Application Discontinuation
• 1990
  • 1990-05-21 GB GB9011289A patent/GB2229924B/en not_active Expired - Lifetime
  • 1990-05-29 SE SE9001916A patent/SE468197B/sv not_active IP Right Cessation

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