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WO2007008428A2 - Transducteur ultrasonore a faible contrainte - Google Patents

Transducteur ultrasonore a faible contrainte Download PDF

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Publication number
WO2007008428A2
WO2007008428A2 PCT/US2006/025253 US2006025253W WO2007008428A2 WO 2007008428 A2 WO2007008428 A2 WO 2007008428A2 US 2006025253 W US2006025253 W US 2006025253W WO 2007008428 A2 WO2007008428 A2 WO 2007008428A2
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WO
WIPO (PCT)
Prior art keywords
driven
active elements
stimulating signal
resonator assembly
transducer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2006/025253
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English (en)
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WO2007008428A3 (fr
Inventor
Benjaman R. Johnson
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Blackstone Ney Ultrasonics Inc
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Blackstone Ney Ultrasonics Inc
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Publication of WO2007008428A2 publication Critical patent/WO2007008428A2/fr
Anticipated expiration legal-status Critical
Publication of WO2007008428A3 publication Critical patent/WO2007008428A3/fr
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0607—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements
    • B06B1/0611—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements in a pile
    • B06B1/0618—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements in a pile of piezo- and non-piezoelectric elements, e.g. 'Tonpilz'

Definitions

  • the present invention relates to ultrasound systems, and more particularly, to systems for generating high power ultrasonics energy and introducing the ultrasonics energy into fluid media for the purpose of cleaning and/or liquid processing.
  • Prior art ultrasound transducers include resonator components that are typically constructed of materials such as polarized piezoelectrics, ceramics, or magnetostrictives (aluminum and iron alloys or nickel and iron alloys). These resonator components are also referred to herein as active elements because they spatially oscillate at the frequency of an applied stimulating signal.
  • the transducers are mechanically coupled to a tank containing a liquid that is formulated to clean or process the object of interest.
  • the amount of liquid is adjusted to partially or completely cover the object in the tank, depending upon the particular application.
  • the transducers When the transducers are stimulated to spatially oscillate, they transmit ultrasound into the liquid, and hence to the object. The interaction between the ultrasound-energized liquid and the object create the desired cleaning or processing action.
  • one type of prior art ultrasound transducer includes one or more resonator components compressed between a front plate and a back plate, with the compression typically established by a nut and bolt assembly, with the bolt extending from the back plate, through the back plate, resonator components and the front plate and terminated by the nut adjacent to the front plate or terminated by a threaded bore in the front plate, which functions as a nut.
  • FIG. IA shows a cross-sectional exploded view when the transducer is in a resting state
  • FIG. 1B shows a cross-sectional view of the transducer when the resonator components are driven by the stimulating signal to increase in thickness
  • FIG.1C shows a cross- sectional view of the transducer when the resonator components are passing through the resting state position
  • FIG. ID shows a cross-sectional view of the transducer when the resonator components are driven by the stimulating signal to decrease in thickness.
  • State of the art sandwich type transducers also known as Langevin type transducers, operate in the manner shown in FIGS IA to ID. That is, the driven active elements, typically polarized piezoelectric ceramics, are driven to increase in thickness during one half cycle and driven to decrease in thickness during the next half cycle, resulting in the losses described above.
  • These state of the art sandwich type transducers will be referred to herein as “resonant transducers” or “half wave resonant transducers” when used at their fundamental frequency and will be referred to as “harmonic transducers” when used at overtone frequencies.
  • one or more ultrasound generators drive one or more ultrasound transducers or arrays of transducers, in accordance with the embodiments described herein, coupled to a liquid to clean and/or process a part or parts, or to produce a processing effect on the liquid.
  • the liquid is preferably contained within a tank, and the one or more ultrasound transducers mount on or within the tank to impart ultrasound into the liquid.
  • “ultrasound”, “ultrasonic” and “ultrasonics” generally refer to acoustic disturbances in a frequency range above about eighteen kilohertz (khz) and which extend upwards to over five megahertz (Mhz).
  • ultrasonic will generally refer to acoustic disturbances in a frequency range above about eighteen kilohertz and extending up to about 99khz.
  • Ultrasound and ultrasonics will be used to mean the complete range of acoustic disturbances from about 18khz to 5Mhz, except when they are use with terms such as “lower frequency” ultrasound, “low frequency” ultrasound, “lower frequency” ultrasonics, or “low frequency” ultrasonics, then they will mean ultrasound between about 18khz and 99khz.
  • “Megasonics” or “megasonic” refer to acoustic disturbances between about 351khz and 5Mhz.
  • the prior art has manufactured "low frequency” and "megasonic" ultrasound systems.
  • Typical prior art low frequency systems for example, operate at 25khz, 40khz, and as high as 90khz.
  • Typical prior art megasonic systems operate between 600khz and 2Mhz.
  • Certain aspects of the invention apply to low frequency ultrasound and to megasonics. However, certain aspects of the invention apply to ultrasound in the 100khz to 350khz region, a frequency range which is sometimes denoted herein as “microsome” or “microsomes.” The upper end of the microsome frequency range from about 300khz to 350khz is called herein "higher microsomes" or "higher frequency microsome".
  • resonant transducer means a transducer operated at a frequency or in a range of frequencies that correspond to a one-half wavelength (lambda) of sound in the transducer stack.
  • Harmonic transducer means a transducer operated at a frequency or in a range of frequencies that correspond to 1 lambda, 1.5 lambda, 2 lambda or 2.5 lambda of sound, and so on, in the transducer stack.
  • the harmonics of a practical physical structure are often not exact integer multiples of the fundamental frequency, the literature sometimes refer to these non- integer harmonics as overtones.
  • harmonics will mean resonances higher in frequency than the fundamental resonant frequency.
  • “Bandwidth” means the range of frequencies in a resonant or harmonic region of a transducer over which the acoustic power output of a transducer remains between 50% and 100% of the maximum value.
  • low-stress ultrasound transducer means a transducer constructed or driven such that the active elements that are driven by a stimulating signal are not all driven to increase in thickness during one segment of time and are not all driven to decrease in thickness during some other segment of time.
  • the active elements that are driven by a stimulating signal will hereinafter be called “driven active elements”, note, a transducer may have active elements that are not driven during part or all of the time that a stimulating signal is applied to the transducer, these active elements during times that they are not driven will be called active elements or insulators.
  • polarized piezoelectric ceramic will often be used herein interchangeably with driven active element, resonator, resonator component, resonator disc and disc resonators.
  • This operation of the driven active elements within a low-stress ultrasound transducer typically causes a canceling or suppression effect at a frequency or in a range of frequencies that correspond to one-half wavelength of sound in the transducer stack. Therefore, when referring to a low-stress ultrasound transducer, fundamental frequency will mean the lowest frequency at which the assembly will resonate and harmonics, harmonic frequencies or overtones will mean resonances higher in frequency than the fundamental frequency.
  • Bandwidth means the range of frequencies in the fundamental or a harmonic region of a low-stress ultrasound transducer over which the acoustic power output of the low-stress ultrasound transducer remains between 50% and 100% of the maximum value.
  • hz refers to hertz which is cycles per second
  • khz refers to kilohertz and a frequency magnitude of one thousand hertz
  • Mhz refers to megahertz and a frequency magnitude of one million hertz.
  • stimulating signal is generally an AC voltage at a frequency or in a range of frequencies that correspond to the bandwidth surrounding a fundamental or overtone frequency.
  • a stimulating signal may be a fixed frequency, or it may sweep frequency. Sweeping frequency stimulating signals are typically obtained at the output of sweeping frequency generators.
  • the simplest stimulating signal is single phase, that is, two wires or two connections supplying a single frequency voltage or sweeping frequency voltage.
  • This invention uses single phase stimulating signals, but also uses multiple phase stimulating signals.
  • a split phase stimulating signal has two voltages that are 180 degrees out of phase and that are typically supplied on three wires or three connections. This split phase stimulating signal is often obtained at the output of a center tapped transformer.
  • n phase stimulating signals that are three voltages 120 degrees out of phase with each other are also used herein.
  • an n phase stimulating signal where n is an integer is applicable to this invention.
  • This n phase stimulating signal has n voltages that are 360 divided by n degrees out of phase with each other.
  • Sweeping frequency generators change their output frequency through successive frequencies in a bandwidth, e.g., sweeping from the lowest frequency in a chosen bandwidth through the bandwidth to the highest frequency in the chosen bandwidth, then sweeping from this highest frequency through the bandwidth back to the lowest frequency.
  • the function of time for these frequency changes is typically linear, but other functions of time, such as part of an exponential, are possible.
  • “sweep frequency” refers to the reciprocal of the time that it takes for successive frequencies to make a round trip, for example, change from one frequency through the other frequencies and back to the original frequency.
  • sweep rate might technically be interpreted as the rate of change from one successive frequency to the next, the more common usage for sweep rate will be used herein; that is, “sweep rate” means the same as sweep frequency. It is generally undesirable to operate an ultrasound transducer at a fixed, single frequency because of the resonances created at that frequency. Therefore, an ultrasound generator can sweep the operational frequency through some or all of the available frequencies within the transducer's bandwidth at a "sweep rate.” Accordingly, particular frequencies have only short duration during the sweep cycle (i.e., the time period for sweeping the ultrasound frequency up and down through a range of frequencies within the bandwidth).
  • the “resonator or resonator assembly” refers to the central components compressed between the front mass and the back mass in a sandwich type transducer. These central components typically include two or more driven active elements and one or more electrodes.
  • the central components may also include one or more insulators (some of which may be non driven active elements), one or more masses, one or more heatsinking elements or electrodes that also can be used as heatsinking elements or masses.
  • the present invention concerns the applied uses of ultrasound energy, and in particular the application and control of ultrasonics to clean and/or process parts within a liquid, or to impart a processing effect on the liquid.
  • one or more ultrasound generators drive one or more ultrasound transducers, or arrays of transducers, coupled to a liquid to clean and/or process the part.
  • the liquid is preferably held within a tank; and the transducers mount on or within the tank to impart ultrasound into the liquid.
  • the transducer includes a resonator assembly having a first surface and a second surface on opposite sides thereof, a front mass having a surface adjacent to the first surface of the resonator assembly, a back mass having a surface adjacent to the second surface of the resonator assembly, and a compression assembly mounted on the front mass and the back mass.
  • the compression assembly is adapted to fasten the front and back masses, biasing those masses toward each other and thereby effecting compression across the resonator assembly, hi one preferred form, at least one of the components of the resonator assembly that is a driven active element is reversed in polarity compared to known sandwich type transducers such that at least one of the components that is a driven active element is driven to decrease in thickness while other of the components that are driven active elements are driven to increase in thickness.
  • the resonator assembly components are wired to a switching device such as a relay which allows them to act as in a known sandwich type half wave resonant transducer during one state of the relay, i.e., the driven active elements all are driven to increase in thickness during one half cycle and all are driven to decrease in thickness during the next half cycle, and to act in the inventive way in the other state of the relay, i.e., at least one of the components that is a driven active element is driven to decrease in thickness while other of the components that are driven active elements are driven to increase in thickness during one half cycle and at least one of the components that is a driven active element is driven to increase in thickness while at least one other of the components that are driven active elements are driven to decrease in thickness during the next half cycle.
  • a switching device such as a relay which allows them to act as in a known sandwich type half wave resonant transducer during one state of the relay
  • the driven active elements all are driven to increase in thickness during one half cycle and all are driven to decrease in thickness during the next
  • this electrode Electrical contact is made to this electrode from the first wire from the stimulating signal and the second wire from the stimulating signal is connected to either the front mass or the back mass, or in the case that the radiating diaphragm is in electrical contact with the front mass, this second wire from the stimulating signal can be connected to the radiating diaphragm.
  • Configuration two has a center electrode between the two driven active elements and a second electrode between the front mass and the surface of the driven active element that is adjacent to the front mass.
  • the stimulating signal wires are connected to these two electrodes.
  • Contact to the driven active element surface adjacent to the back mass is made by the electrical contact from the front mass, through the compression assembly, to the back mass which contacts the driven active element surface adjacent to the back mass.
  • Configuration three has a center electrode between the two driven active elements and a second electrode between the back mass and the surface of the driven active element that is adjacent to the back mass.
  • the stimulating signal wires are connected to these two electrodes.
  • Contact to the driven active element surface adjacent to the front mass is made by the electrical contact from the back mass, through the compression assembly, to the front mass which contacts the driven active element surface adjacent to the front mass.
  • Configuration four has a center electrode between the two driven active elements, a second electrode between the back mass and the surface of the driven active element that is adjacent to the back mass, and a third electrode between the front mass and the surface of the driven active element that is adjacent to the front mass.
  • Electrodes two and three Since electrode configurations are well known to those skilled in the art and since there are many variations of electrode configurations that accomplish the same function, in this specification and in the claims of this invention the electrode configuration will sometimes be eliminated or partially defined where clarity results. It should be understood that the needed electrodes that are not detailed could be any of the many configurations known to those skilled in the art.
  • Various aspects of the low-stress ultrasound transducer can be implemented without the use of a center electrode.
  • One example of this aspect of the invention has two driven active elements, one stacked on top of the other, with electrodes at the opposite ends of the stack.
  • An insulator is typically needed at one end of this electrode and active element stack to prevent the back mass, compression assembly and front mass from shorting out the electrodes.
  • the driven active elements are oriented such that when the electrodes are driven by a stimulating signal, one of the driven active elements is driven to increase in thickness while the other driven active element is driven to decrease in thickness.
  • the capacitance of driven active elements is in series, making the total transducer capacitance substantially one quarter the value of the value that results with one of the other four electrode configurations.
  • the tank bottom or other radiating surface is also used as the front plate or front mass of the transducer assembly, therefore, the compression assembly is mounted on the radiating surface and the back mass.
  • the two or more driven active elements within the resonator assembly operate in the inventive way, i.e., at least one of the driven active elements are driven to decrease in thickness while the other driven active elements are driven to increase in thickness.
  • the resonator assembly includes at least two driven active elements. According to another preferred embodiment, the resonator assembly includes three or more driven active elements placed one on top of the other. [0023] According to another preferred embodiment, the compression assembly is mounted on central regions of the front and back masses. Ih one preferred form, the compression assembly includes a bias bolt and nut assembly, and the front mass, the resonator assembly, and the back mass define a bore extending along a central axis of the front mass, the resonator assembly, and the back mass for receiving the bolt.
  • the bolt is adapted to pass through the central bore of the stacked back mass, resonator assembly and front mass, and the nut is a discrete element, which is screwed onto a lead end of the bias bolt.
  • the bore defined in the front mass includes threads on an inner surface of said bores, and the lead end of the bias bolt is screwed into the threaded bore in the front mass, so that the front mass acts as the "nut".
  • the bolt can extend from the front mass to a nut in or adjacent to the back mass or it can extend from the back mass to a nut adjacent to or within the front mass.
  • the compression assembly is mounted on peripheral regions of the front mass and the back mass.
  • the compression assembly includes at least two bolt and nut assemblies, and the front mass and the back mass define at least two bores at peripheral regions extending along axes parallel to a central axis of the front mass and the back mass for receiving the at least two bolts.
  • the nut can be a discrete element that is adapted to be screwed on a lead end of a corresponding bolt, or alternatively, the bore in the front mass includes threads on an inner surface for engaging the threads on the lead end of the bolt, such that the front mass functions as the "nut".
  • the bias bolts adjustably engage the back mass and the front mass so as to compress the two or more polarized piezoelectric ceramics between the back mass and the front mass.
  • the transducer may further include insulators disposed between the bolt and the resonator assembly, and electrodes connected to the resonator assembly.
  • the sandwich type ultrasonic transducer preferably has a low-density back mass (i.e., aluminum, magnesium, etc.) and is used to produce a device with an especially wide bandwidth.
  • This large bandwidth allows effective sweeping over a dramatically larger range of frequencies.
  • This sweeping can be conventional linear sweep or one of the non constant sweeps known as double sweeping, dual sweep, random sweep, or chaotic sweep.
  • a low-density back mass provides a larger surface area compared to that of a prior art steel back mass of the same acoustic length. This increased surface area also allows higher heat dissipation per transducer that in turn allows a higher overall power output at the overtone frequencies.
  • the resonators are made from ceramic, preferably non-silvered polarized piezoelectric ceramic. Elimination of the oft-applied silver to the faces of the polarized piezoelectric ceramic is accomplished through a lapping process that ensures extreme flatness of the polarized piezoelectric ceramics. These flat non- silvered surfaces optimize utilization for high power applications.
  • a transducer characterized by an especially high bandwidth may or may not contain non-silvered polarized piezoelectric ceramics.
  • An example of another improvement is the incorporation of multiple concentric ceramic polarized piezoelectric elements in place of the solid ceramic polarized piezoelectric discs often used.
  • these concentric cylindrical shells are tailored to ensure that the radial resonant frequencies of the polarized piezoelectric ceramics do coincide with that of the transducer assembly for maximized output at that frequency.
  • these concentric rings are tailored to ensure that the radial resonant frequencies of the polarized piezoelectric ceramics do not coincide with that of the transducer assembly to minimize strain at those frequencies.
  • These polarized piezoelectric ceramics can be silvered or lapped free of silver.
  • another improvement of the transducer is a deviation from cylindrical symmetry on any of the components for the reason of • yielding a device of extreme bandwidth as well as the manipulation/elimination of radial resonant frequencies.
  • An example of this deviation from cylindrical symmetry includes slots on the sides of the front mass or elliptical masses. If properly implemented, deviation from cylindrical symmetry, including the addition of flats or slots on the sides of the high power ultrasonic transducer front mass, can result in a device with exceptionally large bandwidth. In a similar way to concentric ceramics, it can also result in a transducer having radial resonance frequencies that are tailored with respect to the rest of the frequency spectrum, specifically the longitudinal resonance.
  • This transducer is designed specifically to have as flat an impedance verses frequency curve as possible in the region of said transducer's resonance at its overtones. This design feature is intended to maximize the benefits obtained from the sweeping of frequencies within some bandwidth about some center frequency.
  • another configuration of the transducer is a resonator assembly where there is a mass between two driven active elements. While one driven active element is driven to decrease in thickness, the other is driven to increase in thickness. This moves the mass toward the driven active element that is driven to decrease in thickness during one half cycle. During the next half cycle, the driven active elements undergo the opposite change and the mass is driven in the other direction. This produces a sound wave that is propagated from the center portion of the transducer without causing a gross movement of the front mass, back mass or bias bolt.
  • another configuration of the transducer is a resonator assembly where there is a mass between four driven active elements. While one pair of driven active elements is driven to decrease in thickness, the other pair is driven to increase in thickness. This moves the mass toward the driven element pair that is driven to decrease in thickness during one half cycle. During the next half cycle, the other driven active element pair undergoes a decrease in thickness and the mass is driven in their direction. This produces a sound wave that is propagated from the center portion of the transducer without causing a gross movement of the front mass, back mass or bias bolt.
  • One skilled in the art will recognize that there are two ways to realize this aspect of the present invention.
  • One way is to construct the transducer such that one pair of driven active elements on one side of the mass have their positive polarity surfaces next to each other and the second pair of driven active elements on the other side of the mass have their negative polarity surfaces next to each other. With this construction, a single phase stimulating drive signal can be used to get the inventive operation.
  • the other way to realize the inventive operation is to construct the transducer such that like polarity surfaces are next to each other in both pairs of driven active elements, and to use out of phase stimulating signals to drive the driven active elements so they operate in the inventive way, i.e., when one pair of driven active elements is driven to decrease in thickness, the other pair is driven to increase in thickness.
  • another configuration of the transducer is a resonator assembly where there is a mass between four driven active elements.
  • the electrodes of the four driven active elements are wired to a switching device such as a relay which allows them to act as in a known sandwich type half wave resonant transducer during one state of the relay, i.e., the driven active elements all increase in thickness during one half cycle and all decrease in thickness during the next half cycle, and to act in the inventive way in the other state of the relay, i.e., a first pair of driven active elements are driven to decrease in thickness while the second pair of driven active elements are driven to increase in thickness during one half cycle and the first pair of driven active elements are driven to increase in thickness while second pair of driven active elements are driven to decrease in thickness during the next half cycle.
  • another configuration of the transducer is a resonator assembly where there is an insulating mass between two driven active elements.
  • These driven active elements have an orientation typical of prior state of the art sandwich type transducers, however, the driven active elements are independently driven by signals that are out of phase such that while one driven active element is driven to decrease in thickness, the other is driven to increase in thickness. This moves the insulating mass toward the driven element that is driven to decrease in thickness during one half cycle. During the next half cycle, the driven active elements undergo the opposite change and the insulating mass is driven in the other direction. This produces a sound wave that is propagated from the center portion of the transducer without causing a gross movement of the front mass, back mass or bias bolt.
  • a preferred way to produce the out of phase signals is with a center-tapped transformer.
  • another configuration of the transducer is a resonator assembly containing three driven active elements that are properly insulated and each is driven by one of three stimulating signals that are each 120 degrees out of phase with each other. During any point in time, while at least one of said three driven active elements are driven to increase in thickness, at least one of the other driven active elements is driven to decrease in thickness. The net displacement of the resonator assembly is zero for any time period, however, a sound wave at the frequency of the stimulating signal is generated.
  • a preferred aspect of the present invention is a resonator assembly for use in a sandwich type transducer driven by at least one stimulating signal has at least two driven active elements and proper electrodes to couple the at least one stimulating signal to the at least two driven active elements, wherein at a point in time, at least one of the at least two driven active elements is driven to decrease in thickness while at least one of the other of the at least two driven active elements is driven to increase in thickness when the resonator assembly is installed in a sandwich type transducer and is driven by at least one stimulating signal.
  • a resonator assembly for use in a sandwich type transducer driven by at least one stimulating signal has a first polarized piezoelectric ceramic and a second polarized piezoelectric ceramic.
  • the first polarized piezoelectric ceramic has a positive polarity surface and a negative polarity surface on opposite sides and the second polarized piezoelectric ceramic has a positive polarity surface and a negative polarity surface on opposite sides.
  • the two polarized piezoelectric ceramics are arranged with the positive polarity surface of the first polarized piezoelectric ceramic adjacent to the negative polarity surface of the second polarized piezoelectric ceramic.
  • a resonator assembly has two modes of operation for use in a sandwich type transducer assembly.
  • the resonator assembly consists of a first polarized piezoelectric ceramic with a positive polarity on one side and a negative polarity on the other side and a second polarized piezoelectric ceramic with a positive polarity on one side and a negative polarity on the other side; and it has a center electrode with one side adjacent to the positive polarity side of the first polarized piezoelectric ceramic and with the other side of the center electrode adjacent to the positive polarity side of the second polarized piezoelectric ceramic.
  • a second electrode adjacent to the negative polarity side of the first polarized piezoelectric ceramic and a third electrode adjacent to the negative polarity side of the second polarized piezoelectric ceramic plus an insulating means to prevent the sandwich type transducer assembly from electrically shorting the second electrode to the third electrode completes the resonator assembly.
  • a series mode of the resonator assembly is formed when a first electrical connection is made to the second electrode and when a second electrical connection is made to the third electrode to realize one set of frequency ranges; and, a parallel mode of the resonator assembly is formed when a first electrical connection is made to the center electrode and a second electrical connection is made to both the second and third electrodes to realize a second set of frequency ranges.
  • a resonator assembly with two modes of operation for use in a sandwich type transducer assembly and a two state switching system driven by a stimulating signal consists of a stimulating signal delivered between lead one and lead two; a first polarized piezoelectric ceramic with a positive polarity on one side and a negative polarity on the other side; a second polarized piezoelectric ceramic with a positive polarity on one side and a negative polarity on the other side; a center electrode with one side adjacent to the positive polarity side of the first polarized piezoelectric ceramic and with the other side of the center electrode adjacent to the positive polarity side of the second polarized piezoelectric ceramic; a second electrode adjacent to the negative polarity side of the first polarized piezoelectric ceramic; a third electrode adjacent to the negative polarity side of the second polarized piezoelectric ceramic; an insulating means to prevent the sandwich type transducer assembly from electrically shorting the second electrode to
  • a resonator assembly with two modes of operation for use in a sandwich type transducer and driven by at least one stimulating signal consists of at least two driven active elements; and electrodes to couple the at least one stimulating signal to the at least two driven active elements.
  • the resonator assembly in the first mode has at least one of the at least two driven active elements driven to decrease in thickness while at least one of the other of the at least two driven active elements is driven to increase in thickness when the resonator assembly is installed in the sandwich type transducer and is driven by the at least one stimulating signal
  • the resonator assembly in the second mode has all of the at least two driven active elements driven to decrease in thickness simultaneously or driven to increase in thickness simultaneously when the resonator assembly is installed in the sandwich type transducer and is driven by the at least one stimulating signal.
  • a series resonator assembly for use in a sandwich type transducer driven by a stimulating signal consists of at least two driven active elements, each stacked on top of one another; and electrodes at the opposite ends of the driven active elements stack to couple the stimulating signal to the driven active elements stack.
  • at least one of the at least two driven active elements is driven to decrease in thickness while at least one of the other of the at least two driven active elements is driven to increase in thickness when the resonator assembly is installed in the sandwich type transducer and is driven by the at least one stimulating signal.
  • a series resonator assembly for use in a sandwich type transducer driven by a stimulating signal consists of a first polarized piezoelectric ceramic and a second polarized piezoelectric ceramic stacked one on top of the other; and two electrodes at the opposite ends of the polarized piezoelectric stack to couple the stimulating signal to the polarized piezoelectric stack.
  • first polarized piezoelectric ceramic has a positive polarity surface and a negative polarity surface on opposite sides thereof
  • second polarized piezoelectric ceramic has a positive polarity surface and a negative polarity surface on opposite sides thereof
  • the two polarized piezoelectric ceramics are arranged with the positive polarity surface of the first polarized piezoelectric ceramic adjacent to and in electrical contact with the positive polarity surface of the second polarized piezoelectric ceramic forming a series connection of the two polarized piezoelectric ceramics.
  • a series resonator assembly for use in a sandwich type transducer driven by a stimulating signal consisting of a first polarized piezoelectric ceramic and a second polarized piezoelectric ceramic stacked one on top of the other; and two electrodes at the opposite ends of the polarized piezoelectric stack to couple the stimulating signal to the polarized piezoelectric stack.
  • first polarized piezoelectric ceramic has a positive polarity surface and a negative polarity surface on opposite sides thereof
  • second polarized piezoelectric ceramic has a positive polarity surface and a negative polarity surface on opposite sides thereof
  • the two polarized piezoelectric ceramics are arranged with the negative polarity surface of the first polarized piezoelectric ceramic adjacent to and in electrical contact with the negative polarity surface of the second polarized piezoelectric ceramic forming a series connection of the two polarized piezoelectric ceramics.
  • a resonator assembly with two modes of operation for use in a sandwich type transducer assembly consisting of a first polarized piezoelectric ceramic with a positive polarity on one side and a negative polarity on the other side; a second polarized piezoelectric ceramic with a positive polarity on one side and a negative polarity on the other side; a center electrode with one side adjacent to the negative polarity side of the first polarized piezoelectric ceramic and with the other side of the center electrode adjacent to the negative polarity side of the second polarized piezoelectric ceramic; a second electrode adjacent to the positive polarity side of the first polarized piezoelectric ceramic; a third electrode adjacent to the positive polarity side of the first polarized piezoelectric ceramic; a third electrode adjacent to the positive polarity
  • a series mode of the resonator assembly is formed when a first electrical connection is made to the second electrode and when a second electrical connection is made to the third electrode to realize one set of frequency ranges; and, wherein a parallel mode of the resonator assembly is formed when a first electrical connection is made to the center electrode and a second electrical connection is made to both of the second and third electrodes to realize a second set of frequency ranges.
  • a method for producing sound energy with a sandwich type transducer consists of a stimulating signal for driving the driven active elements of the transducer, whereby the stimulating signal causes at least one of the driven active elements to decrease in thickness while the other driven active elements are driven to increase in thickness, thereby producing sound energy at frequencies above those of half wave resonant transducers and with lower energy loss.
  • a method for producing sound energy with a sandwich type transducer and switching system that can be driven in two states.
  • At least one stimulating signal is supplied for driving the driven active elements of the transducer.
  • the at least one stimulating signal causes at least one of the driven active elements to decrease in thickness while the other driven active elements are driven to increase in thickness during state one of the switching system, and whereby the at least one stimulating signal causes all of the driven active elements to decrease in thickness simultaneously or to increase in thickness simultaneously during state two of the switching system, thereby producing sound energy at a larger number of frequency bands than those of half wave resonant transducers.
  • the number of driven active elements can be odd and the effects of a reversed drive voltage configuration realized with phase shifting of the stimulating voltages.
  • This aspect of the present invention is applicable to any number of phase shifted stimulating signals greater than one and a like number times any integer of driven active elements.
  • This condition of the displacement of the driven active elements adding up to zero for all times with phase shifted stimulating signals will be referred to herein as a "zero displacement phase shifted drive voltages configuration".
  • This zero displacement phase shifted drive voltages configuration suppresses the half wave resonant frequency of the sandwich structure and results in low loss and frequencies above the half wave resonant frequency of the sandwich structure.
  • a sandwich type ultrasound transducer is driven by n stimulating signals where n is any integer greater than 3, consisting of a resonator assembly having a first surface and a second surface on opposite sides thereof and containing n driven active elements and n-1 insulators, the insulators between alternate driven active elements such that no driven active elements are adjacent to each other; a front mass having a surface adjacent to the first surface of the resonator assembly; a back mass having a surface adjacent to the second surface of the resonator assembly; electrodes to couple the n stimulating signals to the n driven active elements; a compression assembly coupling the front mass and the back mass, and adapted to effect a compression across the resonator assembly, wherein each of the n stimulating signals are substantially equal in frequency and magnitude, but substantially 360 divided by n degrees phase shifted from each other, wherein at a point in time, at least one of the n driven active elements is driven to decrease in thickness while at least one of the other of the n driven
  • a sandwich type ultrasound transducer driven by at least one stimulating signal comprises a resonator assembly having a first surface and a second surface on opposite sides thereof and containing at least two driven active elements; a front mass having a surface adjacent to the first surface of the resonator assembly; a back mass having a surface adjacent to the second surface of the resonator assembly; electrodes to couple the at least one stimulating signal to the at least two driven active elements; a compression assembly coupling the front mass and the back mass, and adapted to effect a compression across the resonator assembly.
  • Each of the driven active elements has a positive polarity on one surface, wherein at a point in time, at least one of the at least two driven active elements is driven with a positive voltage on the surface with a positive polarity while at least one of the other of the at least two driven active elements is driven with a negative voltage on the surface with a positive polarity when the ultrasound transducer is driven by the at least one stimulating signal.
  • this new form of transducer operation can be realized by polarity placement of the driven active elements or by phasing of the stimulating signals.
  • Two stimulating signals 180 degrees out of phase, three stimulating signals 120 degrees out of phase and four stimulating signals 90 degrees out of phase are preferred aspects of the invention, however, the invention is not limited to these numbers or ideal phases.
  • the invention encompasses any configuration of at least two driven active elements where the net motion in the transducer assembly or the resonator assembly is reduced by causing at least one of the driven active elements to increase in thickness while at that point in time at least one of the other driven active elements is driven to decrease in thickness. This reduction of net motion reduces losses in the transducer assembly allowing operation at high frequency overtones due to the emergence of an under damped condition at these frequencies and it also provides more efficient and reliable operation at the lower overtone frequencies.
  • FIG. IA shows a cross-sectional view of a prior art transducer in a resting state
  • FIG. IB shows a cross-sectional view of the prior art transducer in FIG. IA when the transducer is driven to 90 degrees of the stimulating signal
  • FIG.1C shows a cross-sectional view of the prior art transducer in FIG. IA when the transducer is driven to 180 degrees of the stimulating signal;
  • FIG. ID shows a cross-sectional view of the prior art transducer in FIG. IA when the transducer is driven to 270 degrees of the stimulating signal;
  • FIG.2A shows a cross-sectional view of a transducer according to one preferred embodiment of the present invention.
  • FIG.2B shows a cross-sectional view of the transducer in FIG.2A when the transducer is driven to 90 degrees of the stimulating signal
  • FIG.2C shows a cross-sectional view of the transducer in FIG.2A when the transducer is driven to 180 degrees of the stimulating signal;
  • FIG.2D shows a cross-sectional view of the transducer in FIG.2A when the transducer is driven to 270 degrees of the stimulating signal
  • FIG.3A shows a cross-sectional view of a transducer with two driven active elements and a center mass according to a preferred embodiment of the present invention.
  • FIG.3B shows a cross-sectional view of the transducer in FIG.3A when the transducer is driven to 90 degrees of the stimulating signal
  • FIG.3C shows a cross-sectional view of the transducer in FIG.3A when the transducer is driven to 180 degrees of the stimulating signal
  • FIG.3D shows a cross-sectional view of the transducer in FIG.3A when the transducer is driven to 270 degrees of the stimulating signal;
  • FIG.4A shows a cross-sectional view of a transducer with four driven active elements and a center mass according to a preferred embodiment of the present invention.
  • FIG.4B shows a cross-sectional view of the transducer in FIG.4A when the transducer is driven to 90 degrees of the stimulating signal
  • FIG.4C shows a cross-sectional view of the transducer in FIG.4A when the transducer is driven to 180 degrees of the stimulating signal
  • FIG.4D shows a cross-sectional view of the transducer in FIG.4A when the transducer is driven to 270 degrees of the stimulating signal
  • FIG.5 schematically shows a series and parallel resonator assembly with a switching device to obtain two modes of operation
  • FIG.6 schematically shows a conventional resonator assembly driven by out of phase stimulating signals to suppress a half wave fundamental resonant frequency
  • FIG.7 schematically shows a resonator assembly with three driven active elements and a three phase stimulating signal with each voltage 120 degrees out of phase with each other.
  • FIG. 2A shows a cross-sectional view of a transducer 500 according to one preferred embodiment of the present invention.
  • FIG. 2B shows a cross-sectional view of transducer 500 when transducer 500 is driven to 90 degrees of the stimulating signal.
  • FIG. 2C shows a cross- sectional view of transducer 500 when transducer 500 is driven to 180 degrees of the stimulating signal.
  • FIG. 2D shows a cross-sectional view of transducer 500 when transducer 500 is driven to 270 degrees of the stimulating signal.
  • the transducer 500 employs a Langevin architecture, also known in the art as a sandwich transducer. According to one embodiment of the invention, the transducer 500 as shown in FIG.
  • the 2A includes a back mass 502, a front mass 504, a resonator assembly including a first polarized piezoelectric ceramic 506 with a positive polarity indicated by a dot 536 near its bottom surface and a second polarized piezoelectric ceramic 508 with a positive polarity indicated by a dot 538 near its bottom surface, and a compression assembly including a central bias bolt 516.
  • the transducer may further include an insulator, which is not shown in the drawings, disposed between the bolt 516 and the polarized piezoelectric ceramics 506 and 508, and electrodes (not shown) in any of four known configurations and connected to the polarized piezoelectric ceramics 506 and 508.
  • spaces are drawn between individual parts, for example, between 502 and 506, between 506 and 508, between 508 and 504 and between the head of bolt 516 and its mating surface in the back mass 502.
  • These spaces are drawn for clarity, in the actual compressed sandwich transducer assembly the respective surfaces are pressed together by the force of the compression assembly. This force is typically in the range of 500 to 10,000 pounds, insuring contact of the surfaces and compression of the polarized piezoelectric ceramics.
  • the back mass 502, front mass 504, first polarized piezoelectric ceramic 506 and second polarized piezoelectric ceramic 508 are each characterized by a substantially annular shape extending about a central axis AY with the positive polarity surfaces indicated by dots 536 and 538 each oriented toward the front mass 504.
  • a two wire stimulating signal is applied to transducer 500 with the first wire connected to the center junction where the positive polarity surface of polarized piezoelectric ceramic 536 is adjacent to the negative polarity surface of polarized piezoelectric ceramic 538.
  • the second wire supplying the stimulating signal is connected to the two remaining surfaces of polarized piezoelectric ceramics 506 and 508.
  • the bore of the front mass 504 does not extend completely through the front mass 504 along the axis AY.
  • Other embodiments may include an inner bore of the front mass 504 that extends completely through the front mass 504.
  • the front mass 504 further includes threads on the walls of the inner bore. In one preferred embodiment, the threads are machined into the inner bore, although other techniques known in the art may also be used to create threads in the inner bore.
  • the back mass 502, front mass 504, first polarized piezoelectric ceramic 506 and second polarized piezoelectric ceramic 508 are stacked so as to be adjacent and disposed along the common central axis AY, as shown in FIGS. 2A to 2D.
  • the first polarized piezoelectric ceramic 506 and the second polarized piezoelectric ceramic 508 are "sandwiched" between the back mass 502 and the front mass 504.
  • the bias bolt 516 is preferably symmetrically disposed about the common axis AY, and includes a first end 526 and a second end 528.
  • the outer radius near first end 526 is characterized by an abrupt change, forming a shelf 530.
  • the second end 528 includes threads along the outer surface for mating with the threads on the walls of the inner bore of the front mass 504.
  • the transducer 500 is assembled by passing the bias bolt 516 through the bore of the back mass 502, the bore of the first polarized piezoelectric ceramic 506, the bore of the second polarized piezoelectric ceramic 508, and into the bore of the front mass 504.
  • the threads on the bias bolt 516 engage the threads in the bore of the front mass 504.
  • the bias bolt 516 is tightened, the bias bolt 516 is drawn into the bore of the front mass 504, and the shelf 530 on the bias bolt 516 contacts the shelf 524 on the back mass 502, thereby applying a force to the back mass 102 along the axis AY toward the front mass 504.
  • bias bolt 516 compresses the first polarized piezoelectric ceramic 506 and the second polarized piezoelectric ceramic 508 between the front mass 504 and the back mass 502.
  • the bias bolt 516 can be tightened or loosened to adjust the amount of compression on the polarized piezoelectric ceramics 506 and 508.
  • Electrodes connected to the polarized piezoelectric ceramics 506 and 508 provide input ports to the polarized piezoelectric ceramics for a stimulating signal from an ultrasonic signal generator.
  • the polarized piezoelectric ceramics may receive the stimulating signal via an electrically conducting front mass and/or an electrically conducting back mass, instead of or in addition to the electrodes.
  • the polarized piezoelectric ceramic components within the transducer 500 spatially oscillate in one or more modes associated with the frequency of the applied stimulating signal.
  • the transducer 500 transmits the spatial oscillations via the front mass as ultrasound, to (for example) a tank that contains a cleaning solution and an object to be cleaned.
  • FIG. 3 A shows another embodiment of the invention where a sandwich type transducer 600 is similar to the construction and operation of transducer 500 in FIG. 2 A, except that transducer 600 has a central mass 601 between the polarized piezoelectric ceramics 506 and 508.
  • transducer 600 has a central mass 601 between the polarized piezoelectric ceramics 506 and 508.
  • polarized piezoelectric ceramic 506 is driven to increase in thickness
  • polarized piezoelectric ceramic 508 is driven to decrease in thickness causing the central mass 601, to move toward the front mass 504.
  • FIG. 3B shows the transducer 600 at the middle of this first half cycle, i.e., at 90 degrees.
  • FIG. 3B shows the transducer 600 at the middle of this first half cycle, i.e., at 90 degrees.
  • FIG. 3C shows transducer 600 at the end of the first half cycle or at 180 degrees where the condition is the same as in FIG. 3 A.
  • the opposite effect occurs where the central mass 601 is moved toward the backmass 502 as shown in FIG. 3D at 270 degrees.
  • electrodes and the compression bolt are not shown and spaces between the components were inserted for clarity.
  • FIGs. 4A to 4D show another aspect of the invention where a transducer 650 containing central mass 601 has the mass driven by two pairs of polarized piezoelectric ceramics.
  • FIG. 5 shows another embodiment of the invention where a resonator assembly 907 and a relay 910 are configured for two modes of operation.
  • the resonator assembly 907 is constructed with a stack of five components in the following order and orientation, bottom electrode 901 is adjacent to the negative polarized surface of polarized piezoelectric ceramic 902 which has its positive polarized surface adjacent to the center electrode 903, which is adjacent to the positive polarized surface of polarized piezoelectric ceramic 904, which has its negative polarized surface adjacent to the top electrode 905.
  • This resonator assembly 907 is configured for use in a sandwich type transducer by use of a relay 910.
  • the relay 910 When the relay 910 is in the deenergized condition, it is said to be in a first state. When relay 910 is energized, it is said to be in a second state.
  • This embodiment of the invention provides two modes of operation. In a first mode, where the relay is in the first state, a sandwich type transdu ⁇ er using this resonator assembly can be operated at the low loss high frequencies made possible by the present invention. In a second mode, where the relay is in the second state, a sandwich type transducer using this resonator assembly can be operated at the half wave fundamental resonant frequency of a conventional transducer.
  • Another advantage to the embodiment of the invention shown in FIG. 5 is the series and parallel connections of the polarized piezoelectric ceramics.
  • the polarized piezoelectric ceramics are in series which causes the capacitance of the resonator assembly to be one-half of that of a single polarized piezoelectric ceramic.
  • This low capacitance has an advantage at high frequencies because corresponding inductive components within a generator producing a high frequency stimulating signal 911 are of a practical size and value.
  • Another advantage is that the currents needed to drive the resonator assembly are reduced by the lower capacitance.
  • the polarized piezoelectric ceramics are in parallel which provides a lower impedance and lower drive voltages at these lower frequencies.
  • other switching devices can be used in place of relay 910 in FIG. 5.
  • triacs can be used to switch the stimulating signals to the proper electrodes in resonator assembly 907.
  • FIG. 6 shows yet another embodiment of the invention where resonator assembly 907 from FIG. 5 is now driven by two stimulating signals that are 180 degrees out of phase.
  • the resonator assembly in FIG. 6 is constructed with three electrodes 901, 903, and 905 and with two polarized piezoelectric ceramics 902 and 904, but this time the stimulating signal 911 is transformed with transformer 912 so that it is split into two stimulating signals 913 and 914 that are 180 degrees out of phase with each other.
  • the first stimulating signal 913 is connected to electrodes 903 and 907 and the second stimulating signal 913 is connected to electrodes 901 and 903.
  • the polarity of the polarized piezoelectric ceramics 902 and 904 and the orientation of the stimulating signals 913 and 914 cause one polarized piezoelectric ceramic to increase in thickness, say polarized piezoelectric ceramic 914, while the other polarized piezoelectric ceramic 913 is driven to decrease in thickness.
  • this driven apparatus 900 in FIG. 6 is used in conjunction with a sandwich type transducer assembly, the half wave fundamental resonant frequency is suppressed and the resultant low loss provides for the high frequencies of the present invention.
  • FIG. 7 shows another embodiment of the invention where a resonator assembly 730 consisting of three driven active elements 702, 706 and 710 are each driven by stimulating signals 742, 746 and 750 respectively that are 120 degrees out of phase with each other. Insulators 704 and 706 separate the driven active elements and electrodes 701, 703, 705, 707, 709 and 711 supply the stimulating signals 742, 746 and 750 to the driven active elements 702, 706, and 710.
  • This first stimulating signal 742 is connected to the first driven active element 702 at electrodes 701 and 703 with Vl at the positive polarity side of the first driven active element 702.
  • This second stimulating signal 746 is connected to the second driven active element 706 at electrodes 705 and 707 with V2 at the positive polarity side of the second driven active element 706.
  • This third stimulating signal 750 is connected to the third driven active element 710 at electrodes 709 and 711 with V3 at the positive polarity side of the third driven active element 710.
  • This connection results in the driven active elements seeing a voltage equal to the sum of Vl, V2, and V3 at any point in time. Since this sum is always zero, the net displacement of this resonator assembly 730 is substantially zero when driven by stimulating sources 740 and therefore the half wave fundamental frequency of any sandwich type transducer in which it is installed will be suppressed.
  • the lead end of the bias bolt is screwed into a threaded bore in the front mass for tightening the transducer assembly, so that the front mass acts as a "nut".
  • the bore may extend through the front mass and a nut, which is a discrete element, is screwed onto the lead end of the bias bolt to tighten the transducer assembly.
  • the back mass 502 is fabricated from a low-density material (with respect to prior art back mass components) such as aluminum, magnesium, beryllium, titanium, or other similar materials known in the art, including alloys and other mixed composition materials.
  • a low-density material describes a material with a density of less than 6.0 grams per cubic centimeter (g/cc).
  • the back mass 502 is made of type 7075-T651 aluminum, although other similar materials may also be used.
  • the front mass 504 is made of type 2024 aluminum, although other similar materials may also be used.
  • the back mass 502 and front mass 504 being made from different materials contributes to the ultrabroad bandwidth of the transducer 500.
  • a low density back mass 504 results in a physically longer back mass, or a larger surface area as compared to a higher density back mass of the same acoustic length.
  • the increased length (or larger surface area) further contributes to the multiple center frequencies of operation, and the ultrabroad bandwidth at each of the center frequencies.
  • the polarized piezoelectric ceramics 506 and 508 are fabricated from a ceramic material that has been polarized via techniques well know in the art to imbue a piezoelectric effect.
  • the resonators may include other piezoelectric materials known in the art, such as natural piezoelectrics (e.g., quartz) or magnetostrictives.
  • the embodiment of FIGS. 2 A to 7 includes two or four polarized piezoelectric ceramics, other embodiments of the transducer may include multiple resonators including odd numbers.
  • the transducer 500 can be operated at a dedicated single frequency, or it can be excited at multiple frequencies, i.e., at any of its higher frequency overtones.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)

Abstract

La présente invention se rapporte un transducteur qui comprend un ensemble résonateur possédant des première et seconde surfaces sur ses côtés opposés, une masse avant possédant une surface adjacente à la première surface de l'ensemble résonateur, une masse arrière possédant une surface adjacente à la seconde surface de l'ensemble résonateur, et un ensemble de compression monté sur la masse avant et la masse arrière. L'ensemble de compression est adapté pour exercer une compression à travers l'ensemble résonateur. L'ensemble résonateur contient au moins deux éléments actifs entraînés, de façon que, lorsqu'au moins l'un des éléments actifs entraînés est entraîné pour augmenter d'épaisseur, au moins l'un des autres éléments actifs entraînés soit entraîné pour diminuer d'épaisseur.
PCT/US2006/025253 2005-07-08 2006-06-28 Transducteur ultrasonore a faible contrainte Ceased WO2007008428A2 (fr)

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US6016821A (en) * 1996-09-24 2000-01-25 Puskas; William L. Systems and methods for ultrasonically processing delicate parts
DE19933361C1 (de) * 1999-07-16 2001-02-15 Sebastian Preis Vorrichtung zur Aufnahme von Haustierkot
US6673016B1 (en) * 2002-02-14 2004-01-06 Siemens Medical Solutions Usa, Inc. Ultrasound selectable frequency response system and method for multi-layer transducers

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