US2589375A - Ultrasonic generator - Google Patents

Description

March 18, 1952 E. H. HARRIS 2,589,375

ULTRASONIC GENERATOR Filed Sept. 28, 1949 I 4 Sheets-Sheet l INVENTOR E1501? Hunfinyton Harri/ 5 BY ATTORNEYS March 18, 1952 E. H. HARRIS ULTRASONIC GENERATOR 4 Sheets-Sheet 2 Filed Sept. 28, 1949 Q mm mm Ii n m m Wm m A WI #9 A g m g w 1 PM. hu "WNW w I... NQ\ NM.

- I ww II R N vm 6% @w is r $2 m I L I m9 w u uhx.h.h....

INVENTOR Eliot Hwzzrzyon Harris ATTO R N EYS March 18, 1952 'E HARRIS 2,589,375

ULTRASONIC GENERATOR Filed Sept. 28, 1949 4 Sheets-Sheet 4 FIG. 9.

Q Q Q Q Q E Q v INVENTOR EAL/07' HUNT/1V6 7'0/V HARRIS ATTORNEYS Patented Mar. 18, 1952 UNITED STATES PATENT, OFFICE ULTRASONIC GENERATOR Eliot Huntington Harris, New York, N. Y.

Application September 28, 1949, Serial No. 118,323 12 Claims. (01. 177-7) This invention relates to the generation of compressional waves or vibrations having a frequency above the highest frequency of response for the human car. More particularly, it relates to improved apparatus for generating such ultrasonic waves.

One of the objects of this invention is to provide an improved generator of ultrasonic waves which is simple, practical and durable in operation. Another object is to provide apparatus of the above character which may be manufactured from readily available inexpensive materials without excessive labor costs. A further object is to provide apparatus of the above character capable of generating compression waves with high efficiency and a wide range of displacement amplitudes. It is another object to provide apparatus of the above character capable of generating such waves over a wide range of frequencies without critical or complicated adjustment of the apparatus. Another object is to provide such apparatus in which the frequency of the waves may be varied during operation. Other objects will be in part obvious and in part pointed out hereinafter. l

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts, as will be exemplified in the structure to be hereinafter described, and the scope of the application which will be indicated in the following claims.

Pressure waves created in air, within a particular range of frequencies, are audible to the human ear. However, as the frequency of these waves is increased, the human ear becomes less responsive to the waves, and, accordingly, above 15 or 20 thousand cycles per second, the waves become inaudible. higher in frequency can be generated, and their existence can be detected by thermal means, striation methods, piezoelectric pick-up and other physical devices. Such longitudinal waves of frequency above the audible hearing range are called ultrasonic Waves.

It has been found that such high frequency waves in either gas or liquid medium are useful for many purposes, both in production and in research. However, generation in air of ultrasonants having appreciable energy and with variable frequency over wide frequency bands has been a very difficult laboratory problem and has hampered the advancement of scientific knowledge of the effects produced by such wave motions.

Experiments, starting as early as 1833, utiliz- However, sound waves much I ing specially designed whistles, minute tuning forks, spark discharges, or various other laboratory mechanisms indicated that these waves had unusual and interesting characteristics, and that such waves might well be useful for certain commercial applications if satisfactory generating equipment could be constructed. Some of the fields in which experiments have been conducted relate to emulsification, cavitation, coagulation, and underwater object detection.

Other fields, still to be explored but in which promising indications have :been obtained, include the effects on crystallization and grain formation, degassing operations, fog clearance, dispersion of metals in liquids, biological studies, including the treatment of viable cells, sterilization, destruction of enzymes, killing of insects, dispersion of paint pigments, polymerization and depolymerization, catalyzation, therapy, and many others.

It has been found that particular effects can be achieved with high efiiciency if certain critical frequencies are employed. These critical frequencies may depend on environmental conditions and may shift during a particular process, making it necessary to change the frequency of these generated waves in order to successfully complete the desired process. In some applications, a certain minimum power is required to achieve the desired result and below this power level no substantial effects may be observed.

Accordingly, there have been many attempts to produce apparatus capable of generating such ultrasonic Waves. Many kinds and. varieties of generators have been developed, but none would produce all frequencies over a band that extended into the higher reaches of the sonic spectrum.

For example, piezoelectric crystals, such as quartz, have the property of converting electrical vibrations into mechanical vibrations. There are several disadvantages of such a crystal arrangement, for example, such crystals are relatively expensive, and the size may be prohibitive at the lower frequencies. Moreover, the efficiency of operation. is relatively low and the amount of power which may be applied to the crystal is definitely limited, and if the power should exceed this value, the crystal may be fractured. In many instances, the most important disadvantage is that the frequency range over which the crystal may be operated efficiently is very narrow, so that such a device is relatively unsuitable for applications which require variations in frequency.

Other devices, such as magnetostriction units,

' that described above.

3 sirens, whistles, are limited in range to frequencies below those most desirable for many applications,

In the accompanying drawings, in which is shown one of the various possible embodiments of this invention:

Figure 1 is an elevational view of an ultrasonic generator constructed in accordance with the present invention;

Figure 2 is an enlarged sectional view taken on the line 2-2 of Figure 1;

Figure 3 is an enlarged the line 33 of Figure 1;

Figure 4 is an enlarged sectional view taken on the line 3- of Figure 1;

Figure 5 is an enlarged partial section taken on the line 5-5 of Figure 1;

Figure 6 is a sectional view taken on the line 6-6 of Figure 1;

Figure '7 is a sectionalview- E-i of Figure 1;

Figure 8 is a sectionalview taken on the line 8-8 of Figure 1; and

Figure 9 is a schematic diagram representing apparatus suitable to the ultrasonic generator.

Similar reference characters refer to similar parts throughout the several views of the drawings.

sectional view taken on taken on the line As shown in the drawings, a piston 2 of mag-' netic material (Figures 1 and 8) is mounted between a pair of driving coils and ii. The piston 2 is in the shape of a disc, or may have any other desired configuration, and may be formed, for example, of an alloy of nickel, silicon, and iron so that it has desirable magnetic properties, and, in order that it may respond to the desired frequency range, is of relatively small dimensions; for example, it may have a diameter of one centimeter and a thickness of -three ten-thousandthsof an inch.

In order that the piston 2 may vibrate as freely as possible, and that it may operate efficiently over a wide frequencyrange without serious resonance eifects, it is mounted on a non-magnetic sheet or net 8 of material having suitable resilient or. flexing characteristics and which is non-elastic within the amplitude of movement when in oscillation. For example, 'goodresults have been obtained using a net formed of nylon thread, such as is used for the manufactureof ladies hairnets, or it may be formed of' nylon cloth. The sheet 8 is clamped along two opposite edges (Figure 4) and is maintained under suitable tension'by a spring arrangement described below.

One edge of the-sheet 8 is secured to a beveled surface of a tensioning member l2 (Figure 4) by an adjacent beveled surface of a clamping piece l2- (Figure 3), which fits within-tension member i2 and is secured thereto by screws 16 which pass through clamping piece IQ into the tensioning member I2. The sheetB thus is secured atone end along its entire length so that even'tensioning may be applied to the entire edge of the sheet. The opposite edge of sheet 8 is secured in a similar manner to frame member 18 (Figures 1 and 4) between the opposing beveled faces of frame member is and a clamping piece 22 by screws 25 in substantially the same manner as The other two edges 26 and 28 (Figure 1) of themembrane 8 are'unsupported and are free along their entire length from the surroundingstructure.

In order that the desired tension may be mainfor applying electrical energy springs 54 and 513 are mounted on rods tained upon the membrane 8, the tensioning member I2 is slidably supported on two rods, generally indicated at 32 and 3 which extend between frame member IB and a second frame member 36, to which they are secured, respectively, by nuts 38 and 42 and lock nuts M and 45, respectively. Rods 32 and 3d are provided with threaded portions i8 and 52, respectively, which pass through clearance openings near the ends of tensioning member i2. In order to provide the desired tension on sheet 5, compression 32 and 34, respectively, and abut against tensioning member l2- and are held in compression by a pair of knurled thumb nuts 58 and 62 which are in threaded engagement with rods 32 and 3 respectively.

Itis apparent that as the thumb nuts 53 and 52, the pressure exerted by springs 56 and 56 increases and, thus, the sheet 8 is placed under increasing tension. It is also apparent that these thumb nuts 58 and 62 may be adjusted individually so that uniform tension may be applied throughout the membrane 8.

In order that the tensioning adjustments may be approximately reset if the structureis dismantled, a pair of scales 6 and'66 are provided, which are secured to tensioning member 12 by screws 68 and extend outwardly over thumb screws fiaand 52, respectively. Suitable-calibrations are inscribed on the members.

It is to beunderstood that thesheet 8 is for the purpose of supporting the piston 2 between the coils i and 6, and that, desirably, the movement of piston 2 is not restrained elasticallyby the supporting sheet 8, so that resonant-efiects are substantiallyeliminated over the operating range.

In order to vibrate the piston (Figure 8) over the entire range of frequencies, the coils t and 5 are'arranged to alternately attract the piston 2 in opposite direction; The coil 3 comprises a coilform'or spool 12 which supports awinding Hi. The coil form 12 is constructed ofinsulating material as, for example, ceramic or similar material, and the Winding H5 is a low impedance winding;- the-- axis of which extendsthrough the piston 2.

The coil t, mounted on the opposite side of the piston 2, comprises a spool 'Z'dformed of similar material and a winding it. The spool 16 is similar to coil form 12 except that an opening 82 is always provided centrally therethrough. The winding l8 is-similar in all respects to the winding M.

With this arrangement, when alternating currents having the-proper phase-relationship are caused to flow through windings M and. '18, a magnetic fieldis created whichtendsto urge piston 2' first in one direction and then in the opposite direction. The movement of piston 2 creates-theultrasonic vibrations; The vibrations are transmitted to the desired area through the opening 82 in the spool H5.

The coil form 12 is supported on apreferably non-metallic bridge. 8 which is supported at each end by U-shaped non-magnetic members 85 and 85A, by means of screws 83 which extend through slots 90.

Coil form 16 is supported on a bridge. member 92 which is provided with a circular opening 9 coincident with the opening 82 in coil form 16. Thebridge member 92 is supported atthe ends by means of U-shaped members 95 and 96A to which it'issecured by bolts 98.

In order that the generation of the ultrasonic waves can be accomplished efficiently, it is important that the coil forms I2 and I6 be placed as close to the piston 2 as is possible without the sheet 8 or the piston 2 making contact with the coil forms during any part of the vibratory energization.

In order to accomplish this, the members 86 and 96 are supported adjustably at their outer ends on two screw members I02 and I04, respectively (Figure 5). The member 86 is in threaded engagement with screw I02, which is supported rotatably in a U-shaped yoke I 06, and which is provided with a knurled adjustment knob I08. The support 96 is in threaded engagement with screw member I04, which is supported rotatably in the opposite end of yoke I06, and which is provided with a similar knurled adjustment knob I I2. The innermost portions I I6 and I I8 of screw members I 02 and I04 are of reduced diameter and are seated rotatably in suitable recessed openings in opposite sides of an abutment member I22.

In order to anchor screw members I02 and I04 in place, snap rings I24 and I26 are provided in suitable grooves in screws I02 and I 04, respectively.

Thus, by rotation of knob I08, the support 36 and the coil 4 may be moved laterally with respect to the piston 2 so that the desired close spacing may be achieved readily. The outer end of member 06A is supported in a similar manner so that the opposite end of the structure which supports coil 4 may be moved in a similar manner by adjustment of a knob I08A (Figures 1 and 2), and the structure which supports coil 6 may be adjusted by knobs H2 and I I2A. In order to facilitate these adjustments, a mirror I32 (Figure 1) can be mounted, for example, on rod 32 by means of a bracket I34 (Figure 7) which is fitted advantageously with a swivel connection I36 so that the angular direction of the mirror face may be adjusted readily. A similar mirror (not shown) may be attached to rod 34 in a diagonal position so that, by placing a small light source directed downward on the second mirror on the opposite side of the coils 4 and, 6, the spacing between the coils may be adjusted readily by observing in the mirror I32 the passage of light between coil form I2 and the piston 2 and between the spool 16 and the opposite side of the piston 2.

For the purpose of centering the coils 4 and 6 over and under the piston 2, slots 90 are provided in the bridge members 84 and 92, whereby the bridge members 84 and 92 may be moved laterally with respect to the U-shaped members 86, 80A, 95 and 95A when screws 88 and 98 are loosened (Figure 8).

Longitudinal adjustment of the coils 4 and 6 may be obtained for the purpose of further centering over and under piston 2 by loosening screws H4 (Figure 5) and moving them within the limits of the holes H5, thus obtaining longitudinal adjustment by the movement of yoke I06.

It is desirable that the coils 4 and 6 be coaxial and centered with respect to piston 2. It is advantageous to adjust coil 4 so that the space between piston 2 and the near face of coil 4 is a multiple of half wave lengths. This adjustment may be easily located byobserving the output intensity on any indicating device, such as the sensitive flame, or a metering device if greatest eificiency is desired. If coil 4 is provided withcenter hole similar to coil 6, then it is sufficient that the clearances between coils 4 and 6 and the piston 2 be small. It is further advantageous for the sheets 8 to be adjusted with sufiicient tension to hold the piston 2 in position but also loose enough so that the tension does not exercise a restoring force on the piston within its displacement amplitude.

In order to energize windings I4 and I8, a source of oscillating electrical energy is used. The preferred arrangement is to provide alternations to windings I4 and I8 such that thereis a lead or lag in the phase relationship of the oscillations between the two windings. Thus, there is produced four peak impulses to move .piston 2 during each cycle of the driving current. These will occur from alternate directions and cause the piston 2 to complete two cycles for each cycle of the driving current. Other arrangements may be'employed. A square wave form in which one half of the wave is suppressed in winding I4 and a similar condition established in the winding 18 with the additional requirement that the suppression in one winding corresponds to the peak in the other will produce an excellent force diagram for movement of the piston 2. In this case, one cycle of the driving current produces one cycle of the piston movement. However, for a variable frequency, such a circuit as last described becomes extremely complex. The simplest circuit provides a sinusoidal wave form of the same phase to the two windings I4 and I8. In this case, it is necessary to have the direction of winding in one driving coil opposite to the winding of the other. It is also necessary to magnetize the piston 2 in the direction of its thickness. Thus, due to the polarity of the piston 2, there is a simultaneous repulsive-attractive force acting on the piston in one direction and then in the other direction as the current reverses. This produces one cycle of the piston for one cycle of the current. The residual magnetism of piston 2, when polarized in the direction of its thickness, which is the axial direction, is low and the rate of decay is too high for long usage. Maintaining an electrical charge on the piston introduces the additional inertia of the conductor and offers the danger of a spark which might ignite combustible gases present in certain applications. For these and other obvious reasons, the preferred arrangement calls for a 90 phase relationship between the oscillations in the windings 14 and 18.

In order to obtain a variable frequency oscillating current in the windings I4 and I8, any one of the availabletypes of circuits may be used. For example, the circuit diagrammatically indicated in Figure 9 has been found suitable. Alternating house service at A and B (Figure 9) serves the power pack I40. The incident high frequency can be conveniently supplied by a commercial signal generator I38. The signal is then amplified by the wide band amplifier I42. The output is coupled with the power transformer I44. The secondary I45 is preferably at reduced voltage, as, for example, 25 volts with a primary potential of 2800 volts. In this way, a small number of turns will be called for in the windings I4 and I8.

In order to obtain the 90 phase shift between the driving coils I4 and I8, a phasing network may be placed in the driving circuit parallel to the windings I4 and I8 and consisting of a resistance I52 and a condenser I48 in series. It is advisable to center tap this circuit to a connection between windings I4 and 18.

The location of this phasing network is not example, may be a square other wave form.

. sides of said piston for, vibrating said pi essential in the preferred circuit. For example,

xtheflphase shift m ybe lo a ed at ...9l Pl :from the variabiezf eq enc scncr tqr li an the. amplifiers l 42 ;willbe- -designed for; paraiiel amplification of the two sircuit e Qu nn will.,be;.coupled to, power transformer 14;} and a twin (not shown) 1 The second nected directly with their respe e will. e sen- .W ni E 4 and T8. This-arrangement is more -econornical s n h a phfier "is; .1 ne, 'e i i:.:l e power.v vHowever, it is mu ei fills tii fi t9 12 2 156 inv frequ ncy: .Both ar angement es r bed 7.

q re h changes he made in e va ue 9 t -components; particularly the phasing:- network, 1 aszthe, frequency isich fii 11. 9 a n emen .shown inFigure; 9-;p1oved suitable-over small bands; such as 5Q lie, to 50 k c.-, wi thqut changes.

Convenient switches are therefore fql diei il t allowqfor difielient frequency bands. still anotherarrangement would call f or a center tap in the secondary I46 With junction between the :two windings M and J8. In this case resistance I52 is placed in the lead from secondary 146B to winding 18 and condenser M8 is placed in the lead from secondary 146A to winding-l t.

, VWith this arrangement, the wave form at the windings .is apt; to be affectedby every small change inpfrequency; {This would call for a rebalance of the systern; after each small frequency change. is w v 1:

117,15 to be understood that the wave form applied to the coils 4 and 6 may. be varied in accordance with a particular application and; for Wave, a sawtooth, or

.VIt is'seen readily that a highlyeificient generator ofsupersonants has been provided which V, is operable overan extremely widefrequency range and which may beconstructed' easily and economically. It is to be understood that various Vmodifications maybe madefio adapt the structune to, various applications and uses and that certain features of ,the; inventionrnay sometimes be util ze w h t. a ic respendi u e. 9.? ot features, all withinthe spiritand scope ofthe present invention asset forth in the following claims. 1 ,5:

, Lelaim:

1;"In apparatus for generating ultrasonic vibrations, a translating device comprising. a supportingframe,aw piston of,magneti material, a

sheet of resilient non-magneticmaterial supported by saidframe, said piston being secured to and supported by said sheet ior free transverse movement therewith, i-firstand secondcoil with axial opening for egress of the ultrasonic vibrations. supported by; said frame cm oppositena positioned so that, the axes of said ceils p ass through said piston, and a source gf first and second periodic out-of-phase currents; connected to said coils ;for;causing said piston to rnove alternately toward said first and; second coils thereby to generate ultrasonic: vibrations.

2. Apparatus, asdescribed in ciaizn 1 wherein said first and second currents are substantially ninety degreesout-of -phasc v: 3:

3. In apparatus for generating ultrasonic vibrations, a translating device comprising a supporting frame, a piston-of magnetic substance,

, non-metallicv non-:nragnetic supporting material secured to said frame, said piston being secured .to and supported by said material ;so -as to be free for limited elastically ;=unrestrained, transverse movement, a firstand; a secQnd, oil having an axial opening for;.the ultrasonic vibrations supported by saidlframe on opposite sides of said piston for vibrating vsaid pistoh'yand a source of. first i and second periodic outoi-phase' cu;- rents. connected respectively, to saidfirst and second Icoils, 'for' causing said piston 'to' move as a 7 unit in a. transverse ,direction alternately "toward said first and second coils thereby to generate ultrasonic vibrations,

i. In apparatus for generating ultrasonic vibrations, a translating device comprising a supporting frame. a piston of magneticmaterial, a

meter flexible non-magnetic material supported by said frame, said piston being secured to and supportediby said 'net' for limitedfree transverse movementtherewith, a first and a ,secondcoil supported by, saidfframe on oppositesides of said piston forfvibrating said'piston,,one of saidcoils having an axial opening substantially the area of said piston,fa source ofialternating current, a phaseshifting network connected to said source and to said coils for causing alternating current 1 to flow in each of said coils, the current through said first coil lagging by substantially ninety degrees the current inlsaid second coil.

- 5. In apparatus for generating untrasonic vibrations, a translating, device'comprising a supporting frames, piston or magnetic material, a sheet of, resilient non-magnetic, material supported by said. frame, said piston being supported for limited free transverse movement by said sheet, a first and secondlcoil supported by said frame adjacent said piston and on opposite sides of said sheet for vibrating said piston, said second coil having a longitudinal opening therethrough in alignment with said piston for transmitting the ultrasonic vibrations and a source of first i and second periodic out-of-phase currents con-- nected respectively to said first and second coils for causing said piston to'generate ultrasonic vibrationsl '62 Apparatus as described in claim 5 including manual screwv adjustments for regulating the position of said coils relative ,to' said, piston.

.7. In appa'ratusfor generating ultra-sonic vibrations, a translating, device comprising a supporting frame, alpist'onflof magnetic material,

7 a isl ieet'Tof flexible non-magnetic material sup- 1 ported by'saidlframe'fsaid piston being supported "i by saidsheetgand positionedthereon at a point substantially .removedfrorn points at which said 1; sheet issuppcrtedfa first and second coil supported'by said frame "adjacent said piston and positioned on oppositelsides of, said, sheet for .vibrating"said piston, said second coilfhaving a longitudinal opening theretlirough in alignment with said piston for transmitting the ultrasonic vibrations, and afsource of first and second periodic out-0f phase currents connectedrespectively to said first and second coils for causing said being supported by said sheet for substantially free transversernovement, first and second 0ppositely disposed coils mounted adjacent said piston for vibrating said piston as a unit relativeto said coils, at least one of said coils having a longitudinal opening for egress of the ultrasonic wave motion and a source of first and second alternating out-of-phase currents connected respectively to said first and second coils for producing periodically varying magnetic fields to which said piston is responsive.

9. Apparatus as claimed in claim 8 including adjustment screws for adjusting individually the positions of said coils relative to said piston.

10. In apparatus for generating ultrasonic vibrations, a translating device comprising a supporting frame, a small thin disc of magnetic material, a fixed and a movable clamp secured to said frame, screw adjusting means for varying the position of said movable clamp, a strip of flexible non-magnetic open mesh supported at one end by said movable clamp and at the opposite end by said fixed clamp, said disc being supported by said mesh for substantially free transverse movement, first and second coils with axial openings mounted adjacent said disc for vibrating said disc as a unit relative to said coils, separate screw adjustments for varying the position of said coils with respect to said disc and a source of first and second periodic outof-phase currents connected respectively to said first and second coils for producing periodic magnetic fields to which said disc is responsive.

11. In apparatus for generating ultrasonic vibrations, a translating device comprising a supporting frame, a piston of magnetic material, a strip of resilient non-magnetic material supported by said frame, said piston being supported by said strip for free transverse movement therewith, first and second supporting bridges adjustably supported by said frame on opposite sides of said strip, first and second oppositely disposed coils supported respectively by said first and second bridges adjacent said piston, said coils having longitudinal openings for passage of the wave motion, and a source of periodic out-ofphase currents of ultrasonic frequency connected to said coils for causing said piston to vibrate transversely as a unit, thereby to generate ultrasonic vibrations.

12. In apparatus for generating ultrasonic vibrations, a translating device comprising a supporting frame, a piston of magnetic material, a fixed and a movable clamp secured to said frame, screw adjusting means for varying the position of said movable clamp, a strip of resilient non-magnetic material supported at one end by said movable clamp and at the opposite end by said fixed clamp, said piston being supported by said strip for substantially free transverse movement, first and second supporting bridges adjustably supported by said frame on opposite sides of said strip, first and second oppositely disposed coils supported respectively by said first and second bridges adjacent said piston for vibrating said piston, at least one of said coils having an axial opening for egress of the wave motion and a source of first and second alternating out-of-phase currents connected respectively to said first and second coils for producing periodically varying magnetic fields to which said piston is responsive.

ELIOT HUNTINGTON HARRIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,042,881 Critchfield June 2, 1936 2,064,048 White Dec. 15, 1936 2,069,583 Lewis Feb. 2, 1937 2,135,328 Critchfield Nov. 1, 1938 2,216,380 Von .Voigtlander Oct. 1, 1940

Images