EP0351416B1 - Ultrasonic instrument - Google Patents

Ultrasonic instrument Download PDF

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Publication number
EP0351416B1
EP0351416B1 EP88902977A EP88902977A EP0351416B1 EP 0351416 B1 EP0351416 B1 EP 0351416B1 EP 88902977 A EP88902977 A EP 88902977A EP 88902977 A EP88902977 A EP 88902977A EP 0351416 B1 EP0351416 B1 EP 0351416B1
Authority
EP
European Patent Office
Prior art keywords
vessel
transducer
ultrasonic
contact surface
liquid
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.)
Expired
Application number
EP88902977A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0351416A1 (en
Inventor
Douglas Mcqueen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
McQueen Douglas
Original Assignee
Individual
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to AT88902977T priority Critical patent/ATE82530T1/de
Publication of EP0351416A1 publication Critical patent/EP0351416A1/en
Application granted granted Critical
Publication of EP0351416B1 publication Critical patent/EP0351416B1/en
Expired legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
    • B08B3/04—Cleaning involving contact with liquid
    • B08B3/10—Cleaning involving contact with liquid with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration
    • B08B3/12—Cleaning involving contact with liquid with additional treatment of the liquid or of the object being cleaned, e.g. by heat, by electricity or by vibration by sonic or ultrasonic vibrations
    • 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
    • B06B3/00—Methods or apparatus specially adapted for transmitting mechanical vibrations of infrasonic, sonic, or ultrasonic frequency

Definitions

  • the present invention concerns an apparatus for exciting motion in a liquid contained in a vessel by means of ultrasonics for cleaning and/or penetration of an object at least partially submerged in the liquid, and including at least one ultrasound transducer in physical contact with the vessel.
  • a transducer In known ultrasonic apparatus a transducer is used whose contact surface against the bottom of the vessel is as large or larger than the active element, which is often a piezoelectric ceramic. This means that the whole contact surface moves up and down in time with ultrasound to generate sound in the bath. Such a surface, wich is a number of sound wavelengths in size, radiates efficiently into the bath, that is, the radiation coefficient is near unity. This also means that all the energy that enters the bath penetrates exactly that limited area. In a bath with a volume of one liter one usually wants about 50 watts of input acoustic power.
  • the contact surface is about 5 x 5 cm one gets 2 watts/cm2 input power, which is complemented by power reflected from the limiting surfaces of the bath, and which further increases the intensity by a factor of two or more. In this way the subharmonic regime is reached, and the apparatus is clearly audible. The situation is even worse when working with larger baths and higher power from a small number of transducers.
  • the bath's or vessel's other limiting surfaces also radiate sound to the bath, but that radiation is rather ineffective.
  • the vessel is made of thin metal, usually stainless steel, with a thickness of 0.4 mm, and the ultrasonic vibrations are transmitted in the form of bending waves (for stainless steel of thickness 0.4 mm and at 40 kHz the wavelength of the bending waves is 10 mm).
  • These bending waves radiate poorly.
  • the radiation efficiency is about 0.01. Therefore it is very difficult to obtain a high radiation intensity from such a surface, whose contribiution to the total radiation is insignificant. Rather, the radiation is concentrated to the contact surface of the transducer, where the intensity is high.
  • the transducer generates strong audible subharmonics. Their production is connected with the way the ultrasonic transducer (normally containing one or more piezoelectric ceramics) is made, and its attachment to the vessel. The subharmonics are therefore not produced by the electrical power supply per se, but rather have an acoustic cause.
  • the total thickness is 40 mm, and the transducer has a working frequency of 40 kHz, corresponding to a vibration resonance in the transducer.
  • the front piece is desiginated positively coned.
  • This transducer can transmit maximally about 50 watts of ultrasound to the bath, according to the manufacturer.
  • the probable reason for this limit is that the ultrasound must be transmitted through a limited area (diameter 45 mm) to the bath, whence the intensity is high. When this intensity becomes too high, a cavitation pillow in the liquid outside the transducer is formed which effectively limits power transmission (see for example Theodor F Hueter & Richard H Bolt, Sonics , Wiley, New York, 1955, page 232). If more ultrasonic power is needed in the bath more transducers must be used.
  • the other type of transducer is disc-shaped and contains a piezoelectric ceramic in the form of a plate which is attached to the vessel with its plane side as contact surface.
  • a transducer has a diameter of about 40 mm.
  • Such transducers are very simple, but they are relatively inefficient, and they are therefore used mainly in applications where the desired ultrasonic power is low.
  • the acoustic bending wave wavelength in these vessels is about 10 mm for frequencies around 40 kHz.
  • the contact surfaces of the above transducers are therefore several bending wave wavelengths in size, and about as large as a wavelength in water at these frequencies.
  • This means that the ultrasound that is generated in the transducer is radiated out into the fluid through exactly that surface so that the intensity of the ultrasound is approximately the ultrasound power divided by the contact surface.
  • This also means that a "shadow angle" is formed, so that only that part of the bath volume that is within a calculable angle from the normal (usually between 45 and 60 degrees) is irradiated directly with ultrasound.
  • the intensity in the fluid outside the transducer must be high.
  • the purpose of the present invention is to achieve a simple and inexpensive instrument for silent ultrasonic treatment, and which can transmit high ultrasonic powers to fluids. These goals have been realized by making the diameter or diagonal of the ultrasonic transducer's contact surface against the vessel smaller than or equal in size to a bending wave wavelength in the vessel material and to a sound wave wavelength in the liquid.
  • the transducer can be used at several different frequencies, either one at a time or in combination.
  • the ultrasonic power in a fluid in a vessel can be kept high while at the same time the ultrasonic intensity at the limiting surfaces of the vessel remains relatively low. This means that subharmonics are absent and that ultrasonic irradiation of an object in the fluid comes from many different directions simultaneously.
  • Fig. 1 shows a section through an instrument for ultrasonic generation according to the invention.
  • Fig. 2 shows a perspective view of a transducer according to the invention.
  • Fig. 3 is a diagram of measurement results from comparison tests.
  • the invention consists of the ultrasonic tranducer's contact surface's being limited to a very small area.
  • small is meant an area whose diameter is smaller than or of the same order of magnitude as the bending wave wavelength is the vessel's walls, and whose diameter is simultaneously also smaller than a sound wavelength in the liquid that is in the bath.
  • the sound wavelength is about 35 mm.
  • the ultrasonic energy must still be transmitted to the liquid in the bath. This takes place through the above mentioned bending waves in the vessel, which is assumed to be made of a thin material, for example 0.4 mm stainless steel.
  • the whole vessel vibrates, which means that there is a radiating surface of about 500 cm2 for one liter of liquid. With a radiation intensity of only 0.1 watt/cm2 there is still 50 watts of ultrasound in the bath. This radiation intensity is less than 5 % of the intensity that is reached in today's ultrasonic apparatus, not counting reflections, in spite of the fact that the ultrasonic energy in the bath is the same, 50 watts/liter.
  • the invention further allows generation of the desired ultrasonic energy in a bath without concentrating the intensity to the contact surface of the transducer.
  • Ultrasonic powers of over 100 watts in one liter baths have been achieved without detectable subharmonics. Further, four such transducers have been applied to a larger bath (12 liters) and generated over 300 watts of ultrasonic power in that bath without audible subharmonics. At the same time it has been possible to measure the same cleaning efficiency in the one liter bath according to the invention as in conventional ultrasonic baths of the same size. Using hydrophones it has been possible to show the presence of cavitation in both cases.
  • the instrument according to the invention consists of a housing 7 in which there is a vessel 8, for example made of stainless steel.
  • a generator is designated 10.
  • the transducer according to the invention is shown one embodiment in figure 2.
  • a transducer 1 can for example consist of a front piece 3, one end of which is shaped as a truncated cone 2 with a concave surface 2a.
  • the top surface of the cone or its contact surface 2b against the vessel has an appropriate diameter of 7 mm.
  • the front piece 3 made of aluminium, which for a metal has a relatively low acoustic impedance, and has a total length of 25 mm.
  • the conical part 2 of the front piece has a length of 11 mm.
  • the conical shape should show a continual transition between the front piece's base diameter (25 mm) and the contact surface 2b (7 mm).
  • the back piece 6 of the transducer is made of steel, which for a metal has a relatively high acoustic impedance. It is 24.9 mm long. Between the front piece and the back piece there is a piezoelectric ceramic 5 (thickness about 2 mm) and an electrode 4. For safety reasons there is a thin ceramic disc placed between the electrode and the front piece, in order to insulate it electrically. Electrical current with the desired frequency is coupled to the transducer via the electrode 4 and the back piece 6. It is also possible to have a transducer with two piezoelectric ceramics stacked on each other and two additional electrodes.
  • the whole transducer is glued together with heat cured epoxy glue, in contrast with most conventional transducers which are held together by central bolts.
  • the contact surface 2b of the transducer is glued to the steel vessel which can have a wall thickness of 0.4 mm.
  • the three lowest vibration resonances of the transducer are about 45 kHz, about 100 hKz, and about 170 kHz.
  • One and the same transducer can be used for any of these frequencies, and it can deliver at least 100 watts of acoustic power to a water bath in the vessel 8.
  • the transducer can have other dimenesions, depending on which frequencies are desired to be generated and what powers are required.
  • the transducer does not need to be glued together either, but rather it can be bolted together. Furthur it is possible to replace the different materials (aluminum and steel) with other materials if such is desirable in a certain application. It is not necessary to use a piezoelectric material, and magnetostrictive materials or other materials can be used. The important thing is that the transducer's contact surface 2b is smaller than or of the same order of magnitude as the bending wave wavelength in the vessel and the sound wavelength in the fluid that is to be excited by the ultra sound.
  • a 0.6 mm thick ceramic disc is placed between the front piece and the electrode to insulate the front and vessel electrically from the electrical system.
  • Naturally materials other than ceramics can be used, and other thicknesses.
  • mechanical contacts with the ultrasonic transducer should be avoided as they can disturb the resonanse picture and take away ultrasound in an undesirable manner.
  • a way of achieving a mechanical contact which does not have these deficiencies is to attach the mechanical support at or near a velocity node on the transducer.
  • the ceramic disc is near such a node and can therefore be used as a support point without disturbing the transducer's function.
  • Today's ultrasonic transducers for cleaning purposes can transmit only 50 watts of ultrasound to the bath from each transducer. This has to do with the design of the transducer.
  • the ultrasonic transducer according to the invention is not affected by the same limit, but rather it has been shown to be able to transmit more than 100 watts of ultrasound to a corresponding bath. Further it is possible to measure how fast contaminants are removed from an object in an ultrasonic bath. This cleaning is quicker in an ultrasonic instrument according to the invention.
  • the other curves have been obtained with silent ultrasonic instuments according to the invention.
  • the curve marked “b” is for 45 kHz; the curve marked “c” is for 100 kHz; the curve marked “d” is for 170 kHz.
  • the highest curve, marked “e”, is for a combination of 45 kHz ultrasound (half the power) and 170 kHz ultrasound (half the power), with a total ultrasonic power equal to the ultrasonic power that was used for the three other measurments according to the invention.
  • Similar curves have been obtained for industrial grinding paste instead of fingerprints. The process is quicker when higher temperatures and better solvents are used.
  • the reason that conventional apparatus show poorer cleaning efficiency is that the ultrasound is radiated into the bath from a limited surface defined by the transducer's contact surface, and a shadow angle is formed.
  • the object to be cleaned is irradiated mainly from a single direction.
  • the other curves, for the instrument according to the invention, show the increasing cleaning efficiency. As the frequency is increased faster cleaning is achieved, in accordance with the theory that was presented by McQueen (Ultrasonics 24 , 273 (1986)).
  • the highest curve which is a combination of low and high ultrasonic frequencies, should give a result corresponding to an average of those two frequencies. That is not the case, and instead an unexpected higher result is obtained. The same good result is obtained with industrial grinding paste on titanium surface.
  • the transducer according to the invention is especially well suited to make use of this positive result, as it can be used at two or more frequencies at the same time.
  • the frequencies be different, for examle one frequency should be at least fifty percent higher than the other. This does not necessarily exclude chosing 20 kHz and 30 kHz, but it is clear from figure 3 that it is better to use one frequency between about 30 kHz and 50 kHz and the other frequency over about 100 kHz. It should be remembered that higher frequencies can be more efficient at cleaning, and that higher frequencies can penetrate into tight spaces, in precision mechanical devises, for example, better than lower frequencies can.
  • the transducer according to the invention is equipped with a front piece which has more than one narrowed part and also several contact surfaces.
  • the transducer that has been described above has only one narrowed part toward the vessel.
  • the limited, small contact surface can be a mechanically weak point, because it is relatively easy to break the transducer away from the vessel at that point. If one and the same transducer is provided with two or three or more such contact points the whole transducer will be more stable mechanically.
  • each point must have a contact surface which is less than a water wavelength and a bending wave wavelength in size.
  • the invention is not limited to the examples above, but can be varied within the frame of the principles that have been mentioned. Further, the application of the invention is not restricted to cleaning solid objects in a liquid bath, for instance precision mechanical devices, electrical and electronic components (circuit boards,ceramic substrates, silicon wafers, integrated circuits, etc), optical components (lenses, filters, fiber optics, etc), even if ultrasound has been shown to be excellent for cleaning surface mounted circuits.
  • the invention can advantageously be used in process industries, for example electrochemical processes such as electroplating, biochemical processes such as cell growing, catalytic processes such as sewerage cleaning, separation processes such as ultrafiltration and chromatography, leaching processes, etc.
  • the frequency regime which is intended here is not restricted either toward lower or toward higher frequencies.
  • the transducer's power can be increased to several hundred watts or reduced to a few watts, for example by changing its diameter.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Cleaning By Liquid Or Steam (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Surgical Instruments (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)
  • Ultra Sonic Daignosis Equipment (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
EP88902977A 1987-03-18 1988-03-18 Ultrasonic instrument Expired EP0351416B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT88902977T ATE82530T1 (de) 1987-03-18 1988-03-18 Ultraschallinstrument.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE8701117 1987-03-18
SE8701117A SE456971B (sv) 1987-03-18 1987-03-18 Ultraljudsinstrument

Publications (2)

Publication Number Publication Date
EP0351416A1 EP0351416A1 (en) 1990-01-24
EP0351416B1 true EP0351416B1 (en) 1992-11-19

Family

ID=20367904

Family Applications (1)

Application Number Title Priority Date Filing Date
EP88902977A Expired EP0351416B1 (en) 1987-03-18 1988-03-18 Ultrasonic instrument

Country Status (5)

Country Link
EP (1) EP0351416B1 (sv)
AT (1) ATE82530T1 (sv)
DE (1) DE3876093D1 (sv)
SE (1) SE456971B (sv)
WO (1) WO1988006927A1 (sv)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6853794B2 (en) * 2002-07-02 2005-02-08 Lightel Technologies Inc. Apparatus for cleaning optical fiber connectors and fiber optic parts

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4136897C1 (sv) * 1991-11-09 1992-09-03 Martin Walter Ultraschalltechnik Gmbh, 7541 Straubenhardt, De
DE60126857T2 (de) * 2000-04-28 2007-10-31 Kao Corp. Horn für eine Vorrichtung zur Ultraschallreinigung
GB2425974A (en) * 2005-05-09 2006-11-15 Orion Diagnostica Oy Sonication of a medium
AU2013204792B2 (en) 2012-10-08 2014-09-18 Liquitab Systems Limited Apparatus method and system for disintegration of a solid
FR3057667B1 (fr) * 2016-10-13 2018-11-30 Centre National De La Recherche Scientifique Transducteur piezoelectrique, procede de fabrication s'y rapportant, et dispositif de spectroscopie par resonance ultrasonore

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4074152A (en) * 1974-09-30 1978-02-14 Kabushiki Kaisha Toyota Chuo Kenkyusho Ultrasonic wave generator
FR2580198B1 (fr) * 1985-04-16 1988-09-09 Omega Formation Dispositif de nettoyage de pieces mecaniques par ultrasons

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6853794B2 (en) * 2002-07-02 2005-02-08 Lightel Technologies Inc. Apparatus for cleaning optical fiber connectors and fiber optic parts

Also Published As

Publication number Publication date
ATE82530T1 (de) 1992-12-15
SE8701117L (sv) 1988-09-19
SE456971B (sv) 1988-11-21
DE3876093D1 (de) 1992-12-24
EP0351416A1 (en) 1990-01-24
SE8701117D0 (sv) 1987-03-18
WO1988006927A1 (en) 1988-09-22

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