US3687219A - Ultrasonic beam expander - Google Patents
Ultrasonic beam expander Download PDFInfo
- Publication number
- US3687219A US3687219A US831402A US3687219DA US3687219A US 3687219 A US3687219 A US 3687219A US 831402 A US831402 A US 831402A US 3687219D A US3687219D A US 3687219DA US 3687219 A US3687219 A US 3687219A
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- Prior art keywords
- lens
- ultrasonic
- ultrasonic energy
- generating
- incident
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- 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
- G10K11/26—Sound-focusing or directing, e.g. scanning
- G10K11/30—Sound-focusing or directing, e.g. scanning using refraction, e.g. acoustic lenses
Definitions
- This invention relates generally to ultrasonic generators and more specifically to those types of generators which include means for controlling the wavefront curvature of the output beam.
- Ultrasonic energy is used for many purposes, such as for examination of various types of objects for hidden flaws therein.
- the usual source of ultrasonic energy is a piezoelectric transducer driven by an electronic oscillator at an appropriate frequency.
- Such transducers can be manufactured from a wide variety of materials. Quartz transducers are often preferred for high quality wavefronts. Unaided by other'elements, an ultrasonic energy beam of large cross-sectional area is obtained by a transducer of substantially the same large area. Transducers, especially those made of quartz, are very expensive and cost an amount which varies in proportion to their area. Therefore, it is desirable to use as small a transducer as possible and somehow expand the small ultrasonic energy beam emitted therefrom into a beam having a larger cross-sectional area without degrading the wavefront quality.
- an ultrasonic energy generator which includes a transducer and a single element solid ultrasonic lens, both supported by a housing which contains a liquid for coupling ultrasonic energy therebetween.
- the transducer is preferably flat X-cut quartz which emits a collimated ultrasonic beam which strikes the lens at an incident surface thereof.
- the radius of curvature of the incident lens surface is chosen to substantially increase the divergence of the incident beam.
- the divergence of the beam passing through the lens element and the thickness of the lens determine the cross-sectional dimension of the ultrasonic beam emitted through an exit surface of the lens.
- the exit surface has a radius of curvature chosen to converge to some degree the diverging beam passing through the ultrasonic lens and thereby produce an output ultrasonic beam having a predetermined wavefront curvature and cross-sectional area.
- the output beam is, therefore, substantially larger in cross-sectional area than the incident ultrasonic beam generated by the quartz transducer alone.
- Such an ultrasonic energy generator will most commonly be used in a liquid such as ordinary water or a liquid having a velocity of sound therein that is close to that of water. Therefore, the lens element should have the characteristic that sound travels therein much faster than it does in water so that the radii of curvature of the lens surfaces may be kept large to avoid generation of unwanted shear waves.
- the coupling liquid within the housing may have a speed of sound lower than that of water so that the radius of curvature of the incident lens surface may be kept large. With materials characterized by these relative speeds of sound therein, the incident lens surface is convex and the exit lens surface is concave.
- a preferred combination of materials satisfying these criteria is aluminum or an alloy with high aluminum content for the lens element and a halogenated hydrocarbon such as trichlorotrifluoroethane (commercially available as Freon 1 13) or carbon tetrachloride for the coupling liquid within the generators housing.
- a halogenated hydrocarbon such as trichlorotrifluoroethane (commercially available as Freon 1 13) or carbon tetrachloride for the coupling liquid within the generators housing.
- the normally high reflection loses at the boundaries of an aluminum lens may be substantially reduced by applying thereto a coating of graphite having a thickness at any point along the surfaces of the lens equal to an odd number of quarter wavelengths of ultrasonic energy in the graphite.
- a thickness of graphite that is equal to a quarter wavelength at the fundamental frequency is applied to both sides thereof.
- FIG. 1 illustrates in one form a beam expanding ultrasonic generator according to the present invention
- FIG. 2 is a cross-sectional view of the ultrasonic generator of FIG. 1 cut in half along a plane passing through section 2-2;
- FIG. 3 illustrates a modification of the ultrasonic generator shown in cross section in FIG. 2.
- ultrasonic energy herein is not to be taken as a limitation upon the frequency range in which a beam expanding ultrasonic generator according to the present invention may operate.
- the techniques of the present invention apply to generating and controlling compressional wave energy of any useable frequency.
- the higher sonic frequencies i.e. those considerably above the audible range
- the term ultrasonic energy will be utilized in describing the present invention. This should, however, in no way limit the scope of the invention.
- a beam expanding lens 1 1 is attached to a transducer containing housing 13 and generates a collimated ultrasonic beam through an exit surface 15 of the lens 11.
- FIG. 2 shows an enlarged cross-sectional view of the ultrasonic generator and beam expander of FIG. 1.
- a flat X-cut quartz piezoelectric transducer 17 is physically attached to the housing 13 in some appropriate liquid-tight manner.
- the transducer 17 is electrically connected to an electronic oscillator (not shown) for generating a collimated beam 19 having a cross-sectional area substantially corresponding to the area of the transducer 17.
- the collimated beam 19 having a radius h strikes the lens element 11 at an incident surface 21 thereof.
- the incident surface 21 is convex with a radius of curvature r appropriate for the particular materials used to diverge the rays of the collimated beam 19 into a diverging ultrasonic energy beam 23.
- the lens 11 has a thickness d along its center line.
- the exit lens surface 15 has a radius of curvature r appropriate for the particular materials used to converge the diverging beam 23 into a collimated output beam 25 having a radius h".
- a useful beam expander for a wide variety of testing applications is one utilizing a readily available and economical 2 inch quartz crystal 17 (h 1 inch) which emits a 6 inch output beam 25 (n" 3 inches).
- the housing 13 contains an ultrasonic coupling liquid 27 to efficiently transfer energy from the transducer to the lens.
- Use of a liquid coupling medium instead of a solid medium provides flexibility in chosing the shapes of the transducer 17 and of the incident lens surface 21.
- the beam expanding ultrasonic generator In order to keep the beam expanding ultrasonic generator as compact as possible, care is chosen in selecting the materials of the coupling liquid 27 and of the solid lens 11. It is assumed for purposes of describing herein a specific embodiment of the invention that the beam expanding ultrasonic generator will be used in a water medium (n" 1.0). Aluminum is a preferred material for the solid lens 11 since it has a low index of refraction relative to water, n 0.235 (defined as the ratio of velocity of sound in water to the velocity of sound in aluminum).
- the coupling liquid 27 is chosen from among those which have index of fraction much greater than that of water, and thus one that is useful in combination with an alumunum lens.
- Such a liquid is trichloro-trifluoroethane (commercially available as Freon 113), with an index of refraction of n 2.066.
- Freon 113 trichloro-trifluoroethane
- the large difference between the indexes of refraction of aluminum and Freon, and between the indexes of refraction of aluminum and water allows the radius of curvature of the lens surfaces to be kept large as well as allowing the thickness of the lens to remain small for a given beam expansion.
- Certain well known optical principles may be applied in the design of a specific ultrasonic beam expander. Applicable optical principles are discussed in a number of texts, such as Fundamentals of Optics by Jenkins and White, third edition, especially Chapter 8 thereof. Referring to FIG. 2, a method of design may be illustrated by tracing an extreme ultrasonic ray 20 from the transducer 17, through the lens 11 and into the output ultrasonic beam 25.
- the ray 20 strikes the incident lens surface 21 at an angle 0 with a line normal to the surface.
- the ray 20 emerges from that surface at an angle 0 with the normal.
- K is some safety factor less than unity.
- K could be chosen to be 0.75 but its particular value will depend upon the lens material used and the amount of losses that can be tolerated.
- the next step in designing a beam expander according to the present invention is to determine the thickness of the lens 11 required to produce a collimated output beam 25 of the desired diameter.
- a graphical method is satisfactory.
- the angle 0' can be calculated from equation (2). This establishes the path of the extreme ray 20 through the lens, and also establishes the path of an extreme ray 22. Ray 22 follows a path which is the mirror image of the path of ray 20. These two extreme rays are graphically extended until they are separated by an amount 2h", the desired output beam diameter. This separation is shown in F IG. 2 between points 23a and 23b on the extreme rays. Two points of the lens exit surface 15 are then established to be points 23a and 23b.
- the next step is to determine a radius of curvature r of the lens exit surface 15 which will cause the extreme ray 20 to leave the lens substantially parallel with the center line, thereby to produce the collimated ultrasonic beam 25.
- the ray 20 strikes the exit surface 15 at an angle 0" with a line normal to the surface 15.
- the ray 20 leaves the exit surface 15 at an angle 0 with the normal.
- transducer-lens assembly illustrated herein is insensitive to wavelength.
- the beam emitted by the transducer will be expanded the same amount regardless of the ultrasonic frequency emitted by the transducer.
- acoustic impedance of a material is defined as the product of its density and the speed of sound therein.
- a mismatch of impedances of two materials creates large energy reflections at an interface between the two materials, as is well known. in the configuration described with respect to FIG. 2, reflective losses at the two interfaces total about 78 percent of the ultrasonic energy striking the incident lens surface 21.
- each surface of the lens 11 is coated with a thin layer of material having an impedance which is nearly a geometric mean between the impedances of the two materials joined. It has been found that graphite has an impedance which is substantially the geometric mean between the impedances of the alu' minum lens and the fluids that contact the lens on either side thereof. High density graphite is preferred, having a density in the neighborhood of 1.8 grams per cubic centimeter. The lower density graphite is also satisfactory but is not preferred because of its higher absorption losses. As shown in FIG. 3, the incident lens surface 21 may be coated with a thin layer of high density graphite 31 to substantially reduce reflection losses water interface. The reflective losses of such a lens are.
- the graphite layers 31 and 33 should have a thickness which is substantially an odd number of onefourth wavelengths within graphite in order to prevent rather substantial losses therein. Also, since the ab-. solute thickness of the graphite layers should be as small as possible to reduce absorption, it has been found preferable that the layers have a one-fourth wavelength thickness. it should be noted that the thickness of these layers may vary depending on position along a surface of the lens since the thickness must be measured along a sound ray'passing thereth ro ugh which does not necessarily make the same. angle with the surfaces of the layer at all positions. Equations for determining graphite thickness as a function of position along'the lens surface are given in the book Waves in Layered Media, L. M. Brekhovskikh, Academic Press (1960). Equation 5.26 at page 50 is especially useful here.
- a one-fourth wavelength thickness has a further advantage in situations where the transducer may be operated at either its fundamental or an odd harmonic since a layer having a one-fourth wavelength thickness at the transducer fundamental frequency will have a thickness equal to an odd number of one-fourth wavelengths at any of the transducers odd harmonics.
- the typical fundamental frequencyfor object flaw examination is one megacycle, with the possibility of the same transducer emitting odd harmonics thereof upon adjusting the driving oscillator to 3, 5, or 7, etc. megacycles.
- An ultrasonic lens comprising,
- a solid metal member including aluminum having surfaces shaped to provide desired refraction of ultrasonic wave energy
- Apparatus for generating a controlled beam of ultrasonic energy comprising,
- a solid ultrasonic lens having a convex incident surface and a concave exit surface on opposite sides thereof, said concave exit lens surface being shaped to form a substantially collimated output beam when said exit surface contacts water,
- means for generating an ultrasonic energy beam including a flat transducer which generates a collimated beam
- a housing joining said generating means and said lens in a fixed spatial relationship in a manner to direct 7 8 said ultrasonic energy beam to strike said lens intrasonic energy comprising, cident surface, and a solid ultrasonic lens constructed of a material ina coupling liquid sealed in said housing, whereby said eluding aluminum and having a convex incident liquid transmits said ultrasonic energy from said rfa a d a concave exit surface on opposite transducer to said incident ultrasonic lens surface.
- Irasomc gy comprising, a housing joining said generating means and said lens a solid ultrasonic lens having a convex incident surin a fi d i l l i hi i a manner to di face and a concave exit Surface on opposite Sides said ultrasonic energy beam to strike said lens inthereof, said solid ultrasonic lens being con- 10 cident Surface, and StruFted of a material which characterized by a coupling liquid sealed in said housing, whereby said having a Speed of Sound therem at least twlce that liquid transmits said ultrasonic energy from said of water transducer to said incident ultrasonic lens surface.
- said a housing joining said generating means and said lens in a fixed spatial relationship in a manner to direct said ultrasonic energy beam to strike said
- a coupling liquid sealed in said housing said coupling liquid being characterized by having a speed of sound therein which is significantly less than that of water, whereby said liquid transmits said ultrasonic energy from said transducer to said incident ultrasonic lens surface.
- Apparatus for generating a controlled beam of ulcoupling liquid includes a halogenated hydrocarbon.
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Transducers For Ultrasonic Waves (AREA)
Abstract
Description
Claims (8)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US83140269A | 1969-06-09 | 1969-06-09 |
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US3687219A true US3687219A (en) | 1972-08-29 |
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US831402A Expired - Lifetime US3687219A (en) | 1969-06-09 | 1969-06-09 | Ultrasonic beam expander |
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Cited By (25)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3968459A (en) * | 1975-01-29 | 1976-07-06 | Sperry Rand Corporation | Ultrasonic driver transducer |
US4011747A (en) * | 1975-06-20 | 1977-03-15 | The Board Of Trustees Of The Leland Stanford University | Method and apparatus for acoustic scanning using waves scattered by an acoustic grating |
US4028933A (en) * | 1974-02-15 | 1977-06-14 | The Board Of Trustees Of Leland Stanford Junior University | Acoustic microscope |
US4137779A (en) * | 1972-12-08 | 1979-02-06 | Kraftwerk Union Aktiengesellschaft | Methods and arrangement for the determination of crack-depths in ultrasonic non destructive testing |
US4143554A (en) * | 1977-03-14 | 1979-03-13 | Second Foundation | Ultrasonic scanner |
US4183249A (en) * | 1975-03-07 | 1980-01-15 | Varian Associates, Inc. | Lens system for acoustical imaging |
US4197921A (en) * | 1978-04-06 | 1980-04-15 | Rca Corporation | Anti-reflective acoustic wavefront refraction element |
US4205686A (en) * | 1977-09-09 | 1980-06-03 | Picker Corporation | Ultrasonic transducer and examination method |
US4281661A (en) * | 1977-11-23 | 1981-08-04 | C. G. R.-Ultrasonic | Medical echo sounding apparatus with a wide sector scanning angle |
US4387720A (en) * | 1980-12-29 | 1983-06-14 | Hewlett-Packard Company | Transducer acoustic lens |
US4391281A (en) * | 1977-01-06 | 1983-07-05 | Sri International | Ultrasonic transducer system and method |
US4450542A (en) * | 1982-03-05 | 1984-05-22 | Sperry Corporation | Multiple beam lens transducer for sonar systems |
US4700575A (en) * | 1985-12-31 | 1987-10-20 | The Boeing Company | Ultrasonic transducer with shaped beam intensity profile |
US4799177A (en) * | 1985-12-31 | 1989-01-17 | The Boeing Company | Ultrasonic instrumentation for examination of variable-thickness objects |
US4881618A (en) * | 1986-06-06 | 1989-11-21 | Olympus Optical Co., Ltd. | Acoustic lens for use in acoustic microscope |
US4967873A (en) * | 1988-07-27 | 1990-11-06 | Olympus Optical Co., Ltd. | Acoustic lens apparatus |
US5235553A (en) * | 1991-11-22 | 1993-08-10 | Advanced Imaging Systems | Solid ultrasonic lens |
US5365024A (en) * | 1989-03-31 | 1994-11-15 | Olympus Optical Co., Ltd. | Acoustic lens system |
US5948985A (en) * | 1996-05-31 | 1999-09-07 | Ormet Corporation | Method and apparatus for ultrasonic testing of aluminum billet |
US6229562B1 (en) | 1997-07-08 | 2001-05-08 | Stanley H. Kremen | System and apparatus for the recording and projection of images in substantially 3-dimensional format |
US20090025474A1 (en) * | 2007-07-23 | 2009-01-29 | Peter Lagergren | Ultrasonic fuel level monitoring system incorporating an acoustic lens |
US20100242593A1 (en) * | 2009-03-25 | 2010-09-30 | Lagergren Peter J | Ultrasonic liquid level monitoring system |
US8412473B2 (en) | 2011-04-11 | 2013-04-02 | Schmitt Industries, Inc. | Event monitoring and detection in liquid level monitoring system |
US9411040B2 (en) * | 2014-06-23 | 2016-08-09 | Goodrich Corporation | Systems and methods for acoustic windows |
US11141130B2 (en) * | 2015-07-01 | 2021-10-12 | Centre National De La Recherche Scientifique (Cnrs) | Insonification method for obtaining a predetermined field of ultrasonic waves and production method for making an ultrasonic lens for these purposes |
Citations (3)
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US2565159A (en) * | 1949-04-21 | 1951-08-21 | Brush Dev Co | Focused electromechanical device |
US3168659A (en) * | 1960-01-11 | 1965-02-02 | Gen Motors Corp | Variable focus transducer |
US3239801A (en) * | 1964-12-18 | 1966-03-08 | Automation Ind Inc | Liquid lens ultrasonic beam controlling device |
-
1969
- 1969-06-09 US US831402A patent/US3687219A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2565159A (en) * | 1949-04-21 | 1951-08-21 | Brush Dev Co | Focused electromechanical device |
US3168659A (en) * | 1960-01-11 | 1965-02-02 | Gen Motors Corp | Variable focus transducer |
US3239801A (en) * | 1964-12-18 | 1966-03-08 | Automation Ind Inc | Liquid lens ultrasonic beam controlling device |
Cited By (31)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4137779A (en) * | 1972-12-08 | 1979-02-06 | Kraftwerk Union Aktiengesellschaft | Methods and arrangement for the determination of crack-depths in ultrasonic non destructive testing |
US4028933A (en) * | 1974-02-15 | 1977-06-14 | The Board Of Trustees Of Leland Stanford Junior University | Acoustic microscope |
US3968459A (en) * | 1975-01-29 | 1976-07-06 | Sperry Rand Corporation | Ultrasonic driver transducer |
US4183249A (en) * | 1975-03-07 | 1980-01-15 | Varian Associates, Inc. | Lens system for acoustical imaging |
US4011747A (en) * | 1975-06-20 | 1977-03-15 | The Board Of Trustees Of The Leland Stanford University | Method and apparatus for acoustic scanning using waves scattered by an acoustic grating |
US4391281A (en) * | 1977-01-06 | 1983-07-05 | Sri International | Ultrasonic transducer system and method |
US4143554A (en) * | 1977-03-14 | 1979-03-13 | Second Foundation | Ultrasonic scanner |
US4205686A (en) * | 1977-09-09 | 1980-06-03 | Picker Corporation | Ultrasonic transducer and examination method |
US4281661A (en) * | 1977-11-23 | 1981-08-04 | C. G. R.-Ultrasonic | Medical echo sounding apparatus with a wide sector scanning angle |
US4197921A (en) * | 1978-04-06 | 1980-04-15 | Rca Corporation | Anti-reflective acoustic wavefront refraction element |
US4387720A (en) * | 1980-12-29 | 1983-06-14 | Hewlett-Packard Company | Transducer acoustic lens |
US4450542A (en) * | 1982-03-05 | 1984-05-22 | Sperry Corporation | Multiple beam lens transducer for sonar systems |
US4700575A (en) * | 1985-12-31 | 1987-10-20 | The Boeing Company | Ultrasonic transducer with shaped beam intensity profile |
US4799177A (en) * | 1985-12-31 | 1989-01-17 | The Boeing Company | Ultrasonic instrumentation for examination of variable-thickness objects |
US4881618A (en) * | 1986-06-06 | 1989-11-21 | Olympus Optical Co., Ltd. | Acoustic lens for use in acoustic microscope |
US4967873A (en) * | 1988-07-27 | 1990-11-06 | Olympus Optical Co., Ltd. | Acoustic lens apparatus |
US5365024A (en) * | 1989-03-31 | 1994-11-15 | Olympus Optical Co., Ltd. | Acoustic lens system |
US5235553A (en) * | 1991-11-22 | 1993-08-10 | Advanced Imaging Systems | Solid ultrasonic lens |
US5948985A (en) * | 1996-05-31 | 1999-09-07 | Ormet Corporation | Method and apparatus for ultrasonic testing of aluminum billet |
US6229562B1 (en) | 1997-07-08 | 2001-05-08 | Stanley H. Kremen | System and apparatus for the recording and projection of images in substantially 3-dimensional format |
US20030160864A1 (en) * | 1997-07-08 | 2003-08-28 | Kremen Stanley H. | System and apparatus for recording and projecting 3-dimensional images |
US7142232B2 (en) | 1997-07-08 | 2006-11-28 | Kremen Stanley H | System and apparatus for recording and projecting 3-dimensional images |
EP2171409A1 (en) * | 2007-07-23 | 2010-04-07 | Schmitt Measurement Systems, INC. | Ultrasonic fuel level monitoring system incorporating an acoustic lens |
US20090025474A1 (en) * | 2007-07-23 | 2009-01-29 | Peter Lagergren | Ultrasonic fuel level monitoring system incorporating an acoustic lens |
US7905143B2 (en) * | 2007-07-23 | 2011-03-15 | Schmitt Measurement Systems, Inc. | Ultrasonic fuel level monitoring system incorporating an acoustic lens |
EP2171409A4 (en) * | 2007-07-23 | 2013-05-29 | Schmitt Measurement Systems Inc | Ultrasonic fuel level monitoring system incorporating an acoustic lens |
US20100242593A1 (en) * | 2009-03-25 | 2010-09-30 | Lagergren Peter J | Ultrasonic liquid level monitoring system |
US8104341B2 (en) * | 2009-03-25 | 2012-01-31 | Schmitt Measurement Systems, Inc. | Ultrasonic liquid level monitoring system |
US8412473B2 (en) | 2011-04-11 | 2013-04-02 | Schmitt Industries, Inc. | Event monitoring and detection in liquid level monitoring system |
US9411040B2 (en) * | 2014-06-23 | 2016-08-09 | Goodrich Corporation | Systems and methods for acoustic windows |
US11141130B2 (en) * | 2015-07-01 | 2021-10-12 | Centre National De La Recherche Scientifique (Cnrs) | Insonification method for obtaining a predetermined field of ultrasonic waves and production method for making an ultrasonic lens for these purposes |
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