US3105124A - Inertialess transducer - Google Patents

Description

' sept. 24, 1963 Filed Feb. 27. 1961 w. R. ToRN INERTIAL-Ess TRANsnucER 2 Sheets-Sheet 1 sept. 24, 1963 w. R. TORN 3,105,124

INERTIALESS TRANSDUCER Filed Feb. 27. l1961 2 Sheets-Sheet 2 NEW BIT USED FOR FINE FINISHING, THEN USED FOR ROUGH FINISH ON NEXTJOB JOZ United States Patent C 3,105,124 WERTEALESS TRANSDUCER Wiliiarn R. Tern, St. Charles, lli., assigner to Duitane Corporation, St. Charles, lll., a corporation of Delaware Fiied Feb. 2'7, 196i, Ser. No. 92,069 lill Claims. (Cl. 1791l3) This invention relates to an inertialess transducer and more particularly to a device which can convert electrical energy into radiant energy and is an improvement upon the construction discltosed and claimed in United States Patent No. 2,768,246, issued on October 23, 1956 to Siegflied Klein. The construction disclosed in said patent generally comprises a means for generating a gaseous discharge within a small cell exposed to atmosphere. This discharge is created and maintained by high frequency electric currents which can be modulated by suitable signal currents. The discharge emits a wide spectrum of electromagnetic radiation ranging from infra-red through visible light to ultraviolet. This radiant energy, when generated within a cell forming part of a horn such as disclosed in the patent referred to above, is emitted in the form of a iine pencil.

In addition to the emitted rays, it is believed that the temperature of the gas or air yat the discharge region is also varied in a rapid manner by the modulations. Such temperature variations appear to be responsible for pressure variations in the gas. By providing sufficient coupling between the discharge region and the atmosphere, it is possible to generate pressure waves in the atmosphere corresponding to the modulating waves. There does not appear to be any definite top or bottom limits to the frequency range `of such pressure waves. In practice, waves below about 3,000 cycles per second require an undesirably long coupling horn between the discharge region and atmosphere, so that devices of this type for converting electrical energy into sound waves are most conveniently designed for operation at frequencies above 3,000 or 3,500 cycles per second. It is understood, however, that such devices can operate with lower frequencies insofar as sound is concerned, if the size and expense of a coupling horn are disregarded. `It is, of course, understood that the cell containing the discharge region must be of electrically insulating material. The high temperatures existing at the discharge region require that the envelope be of refractory material. For long life, quartz has been found to be best.

The manufacture of quartz parts, without subsequent i grinding operations, lcan not be accomplished to close dimensional tolerances comparable to metal working. In fact, it has been found that dimensional variations of the order of as little as .020 in a quartz cell result in large variations in the electrical and acoustic characteristics of a transducer. This has reacted upon the electrical accessories, as the oscillator for' example, and has required custom adjustments. The same has been true of the acoustic portions, as the horn.

While the present invention in general relates to an improved transducer and 4the manufacture thereof in quantity, there are a number of facets to the overall invention. First and foremost is a practical and economical method of manufacturing quartz cells to close tolerances. Second is the structure of a transducer which has desirable and predetermined operating characteristics. Such characteristics include the generation and maintenance of a stable gaseous discharge within the cell, these at generally predetermined potentials. Furthermore, the transducer structure is quite efficient in that leakage of Vibratory energy is reduced to a minimum. Whether the transducer is used for acoustic purposes or as a generator of high frequency electro-magnetic waves (infra-red or light as two examples) the present invention makes possible economical production as well as reliable use of what may be termed van ionic inertialess transducer.

The more general as well as specific aspects of the present invention will be more readily appreciated and understood when presented in connection with a description of the invention and reference to the drawings.

FIGURE 1 is a perspective view of the new transducer.

FIGURE 2 is a section on line 2-2 of FIGURE l.

FIGURE 3 is a section detail on line 3 3 of FIG- URE 2.

FIGURE 4 is enlarged sectional detail of the inner electrode and its relation to the cell.

`FIGURE 5 is a view illustrating apparatus for drilling the quartz, this figure showing the bit for shaping the discharge chamber within the cell. f

FIGURE 6 is a view generally similar to FIGURE 5 but showing the bit and cell enlarged.

FIGURES 7 and 8 show the bits used in connection with other drilling operations on a quartz cell blank.

The transducer unit proper consists of cell 10 of refractory insulating material, inner or center electrode 11 and outer electrode 12. The transducer unit has coupling member 14 of insulating material for coupling the transducer to a horn, not shown. This horn, as pointed out in the Klein patent referred to, may taper to provide acoustic coupling to atmosphere or any shape may be used simply to provide a path to atmosphere of the radiant energy generated by the discharge. As the invention is not concerned with the horn, no further description is necessary.

As is described in the Klein patent, a radio-frequency oscillator applies potentials to the two electrodes and generates and maintains a gaseous discharge within the cell. The RF. applied to the electrodes can be modulated at lower frequencies and cause the arc intensity to vary at modulating frequencies. The variation in intensity of the discharge results in the generation of waves in the gas, usually air, within the cell and such waves can be transmitted to atmosphere.

insofar as manufacture to close tolerances is concerned, the problem is focused on cell 10i. This cell is made of quartz to a high purity. Bcause of the hardness of quartz and close tolerances of concave surfaces, conventional grinding technique was too expensive for quantity production. The actual method of manufacture of the cell will be described later.

Cell 10 has outer cylindrical surface 18, front (horn) end 1.9 and rear end 20. It has been found that at high audio frequencies (over 10,000 cps.) and ultra audio frequencies, undesired leakage of vibratory energy at joints can easily occur. Accordingly, end faces 19 and 2@ must be accurately iitted to the remaining parts of the unit. This is most easily accomplished in quantity production by having end faces 19 and 20 flat -and perpendicuiar to the axis of cell i0. For transducers for handling frequencies up to 20,000 c.p.s. or more, it is preferred to have end face 19 :true to about 2. Such a tolerance will reduce leakage of vibratory energy to an inconsequential level. Outside surface I3 of cell 10 should also be accurate, since it determines the ygeometry of outer electrode 12.

Cell l0 has coaxial chambers v23 and 24 extending from end faces 19 and 20 toward each other. Chambers 23 and 24 are joined together by passage 25. Passage 25 is cylindrical and has circular ends 26 and 27. The diameter of passage 25 is less than the transverse dimensions of chambers 23 and 24 near the ends of the cell. Chamber 24 has a cylindrical shape, `although this is not essential. Chamber `2li has `annular end wall 30 at end annales 27 of passage 25 :and hm cylindrical wall 31 extending to rear end face 2.0.

Chamber 23 conta-ins the ygaseous discharge and must therefore be made quite accurately. For use `as a trans- 23 has tapered portion 33 extending from end 25 of passage 2S. f

The :taper is about 30 although this value is not critical. However it should not be greater than 45 and no less than if desirable reproduction isto be provided. Portion 34 of chamber 23 extends from circular region 35 to end face 19. Portion 34 of chamber 23 may also taper generally linearly. This taper is smaller than for portion 233` and may be about TO3-20. The axial length of chamber portion 34 Will depend in some measure upon the ease with which a horn can Ihave its small end accurately shaped. IIn practice, portion 34 may have an axial length equal to the maximum diameter of the cham- Y ber at end face 19. Discharge chamber portion 33 may have the end diameters in the ratio of about 2 to '1. Passage may have a length equal to or greater than its diameter. The dimensions or proportions of chamber 31 are not important. In general, the surfaces defining passage 25 and chamber 2?` should be accurate to about .1002. The overall length of cell 1li and its outside diameter are not important, `but what is important is the accuracy of these dimensions.

Referring now to inner electrode 11, this consists of head all' supported on neck 41 extending from shoulder 42 carried by a relatively massive body portion. Except 'for head 4d, the remainder of electrode 11 may be made of any metal or material which can conduct electricity.

Thus neck 41 or shoulder'42 or the body portion or all A of the Vthree may be 'made of material like iron, copper or brass. electrical resistance .is unimportant since the amount of current carried is relatively low. It is also possible to make neck 41 asia thermistor and design it so that the change of resistance, with respect to temperature will be sufficient to provide a current control action'. The tolerances on head 4@ and the massive body portion of the electrode 'will be determined generally by the cell tolerances.

Head 40, during a discharge, is maintained at a high temperature. The material of head must be capable of Awithstanding a high temperature and for transducer use 'should be .free of sputtering. Sputtering of :the head metal results in generation of noise. In addition, the material should be easy to machine or shape. 'Ilhe material used for cigarette lighters in automobiles or as electrodes in auto engine spark plugs can be use-d. Such metals as kanthal and itopheta A can be used. These metals generally are alloys of iron and chromium and can Withstand temperatures of labout lO'OO" C. in air. The remainder of the electrode 'is conveniently of the same metal, although any metal may be used.

Head 49 has the shape of a truncated cone with sharp edges and `46 at the front and rear of the head re- For most metals and'alloys, ythe variation of vtained in production to about .002.

, Y '4 Abody portion 51 smoothly merges into cylindrical terminal portion S4. Body portions 49 and 51 must be able to enter chamber 24 and the electrode is preferably long enough to extendV beyond end face 2li of cell 1t);

ltwill be noted that in the assembled transducer circular edge 4d should be disposed within passage 25 while edge 45 should be forwardly of end26 of the passage. The clearance between yedgeV 46 and the wall of passage 25 should be several thousandths of an inch. `Both edges 41S and 46 are sharp. The taper of head 40 can be about 3d, although this is not critical. However, a tapered head is important. y

lt has been found that a discharge will start easily along kan edge of the head. lf a flat head with no taper is provided, then the discharge is unstable and tends to wander along the surface of the head. The cone shaped head stabilizes the discharge and tendsk to keep it in one position. 'Ille sharp edges make it easier to initiate a discharge. Y

. The relative mass ofhead 40* and neck 41 will determine how quickly the head will heat and temperature at which it will stabilize itself. The heat dissipation characteristics will depend upon the geometry of the electrode, availability of kcirculating air to the electrode and also the amountof RF. energy fed into the system. It will be understood that inner electrode 11 is pressed firmly into position. It need not be cemented.

Outer electrode V12-is of any metal, as spring brass, copper or stainless steel. Guter electrode 12 is in the shape of a split cylinder having slot all extending longitudinally thereof. It is Yimportant to have the inside edges of electrode 12 free of burrs. This will permit electrode 12 to lay snugly against outer surface 18 ofcell 10'. It is important to avoid air pockets between the cell and electrode, since such pockets may have arcs'and result in noise as well as damage. Preferably outer electrode 12 is so disposed that its rear edge A62 will be offset rearwardly of edge 46 of inner electrode 11 for maximum efficiency. The amount of offset is not critical, but should be mainl The location of forward edge 63 is not critical and this can be flush with end face 19 of cell 10.

The slit in the outer electrode permits of expansion of the metal during operation without cracking coupling insulator sleeve 14. Coupling sleeve `1.4 has rear face 66 provided with chamber 67 dimensioned to accommodate outer electrode Y12. The outer electrode is preferably cemented into coupling sleeve 14. 'The edge of the material at chamber 67 at face 66 is cut away for countersinking. Chamber 67 has bottom wall 68 flat and this must be as accurate as front face 19 of cell 1G'. Any radial Y path yalong face 19 will permit energy to escape.

spectively. The diameter of edge 46 is a bit less than Coupling sleeve 14 has tapered axial passage 7d extendingfrom wall 68 to front face 71 of the sleeve. Passage 70 at small end 73 registers with and is alined with chamber 23 of cell 1l). The front portion of sleeve 14 is shouldered at '75y for accommodating metal or plastic horn '76'. Sleeve 14 may be of ceramic, glass, plastic, or any insulating material. MetalV support plate 77 is disposed around a portion of the horn for supporting the entire transducer.

The accuracy of the electrodes, cell 1lil and sleeve 14 Y is directed toward providing smooth, snug fits with minimum tendency of cooking of any parts. By maintaining good alinement, uniform field distribution is obtained. In -the -assembly so far described, cell 10 and inner electrode 11 are readily separated from each other and' from outer electrode 12. It is therefore important to provide means for maintaining the parts in alined relation during operation.

The transducer parts are maintained in operative posiv tion by the following. Metal cap 80 iits over portion 54 of inner electrode 11. Cap 80l has wire 81 attached thereto as one terminal. Wire 82 attached kto electrode 12 is the other terminal of the transducer. Cap 80 has shoulder 84 providing reduced portion 85. Insulator bar 86 is apertured to accommodate reduced cap portion 85 and is urged forwardly (toward the horn end) by springs 38 and 89 having ends attached to the ends of bar 86 and flanges 90 and 91 of metal plate 92 rigidly attached to plate 77. It is understood that plates 77 and 92 are tight enough on horn part 76 to withstand the pull of the springs. If desired, a three point support for cap 80 may be provided instead of two points. Thus a three legged spider with legs symmetrically disposed may be used with springs to provide a balanced force on cap 80 axially of the cell. The arrangement shown is convenient and permits easy replacement of the cell or other parts. Bar 86 can be pulled away from the cap and swung out of the way.

As has been previously indicated, the economical manufacture ofA quartz cells to close tolerances of the order of .00 for interior surfaces presented serious problems. For example, in a practical device, passage 25 has a diameter of .060 with a tolerance of plus or minus .0012". The maximum diameter of chamber 23 is .150 plus or minus the same tolerance. Making the quartz cell to close tolerance insofar as length and outside diameter are concerned presented no particularly serious problems. However, manufacturing the quartz cell to the desired internal tolerances presented serious production problems. The only practical method for drilling involved the use of ultrasonic equipment. As is well known, this equipment involves the phenomenon of magnetostriction. Thus certain ferromagnetic materials such as certain nickel-iron alloys are particularly for this purpose. When a rod of this material is subjected to a magnetic field Whose intensity varies at a suitable frequency, such as for example, 30,000 c.p.s., the length of the rod will vary by -a small amount.

It is well known in ultra-sonic drilling that the drill bit must be muchI softer than the work. Bits of soft metal such as soft steel or iron or brass are frequently used and it is customary to braze a bit to the end of the magnetostrictive rod. The bit Working with a slurry of finely divided abrasive in water or oil is used to operate on the work.

In prior ultra-sonic drilling, it is customary to use the bit to operate upon a substantial number of pieces of material-constituting the work. When the Wear on the bit was sufficient, it was necessary to remove the bit and braze a new bit in position.

In -the application of ultra-sonic drilling and grinding to quartz for the manufacture of cells to desired tolerances, it was found that this procedure of using the same bit for a substantial number of quartz pieces of work was not dependable. It was dicult to manufacture cells to the required tolerances and the drilling costs including time were very high."

Replacing brazed bits at frequent intervals to improve tolerances of the finished product resulted in extensive time for brazing new bits into position. Trying to save brazing time results in excessive drilling time with poor control yover the quality of the finished work.

In accordance with the present invention, both problems were simultaneously solved by making an expendable bit which could be quickly and easily replaced. It was found that if a certain operational procedure with regard to drilling the cells was adopted that the problems of quality control of the work as well as quick replacement of the bit were solved. This was accomplished generally by designing the bit as a screw machine product which could be automatically manufactured in large quantities and having a screw coupling as the attaching means for the bit to the magnetostrictive rod.

Screw couplings for bits in ultra-sonic dril-ling have not previously been considered practical. This is because the combination of temperature changes and vibration tend to loosen the bit and thus reduce the efficiency of grinding to the vanishing point. In accordance with the present invention, however, theprevious Vdisadvantage regarding frequent bit replacement is utilized to render the use of a screw coupling for the bit practical. This however, was only possible by utilizing a novel drilling technique. This techniques consists in utilizing a new but expendable bit purely to finish a previously roughed cell to final dimensions. The roughing for the discharge chamber of the quartz blank may consist in drilling to within about .004 inch of the desired dimensions. Thus a brand new bit is only used to cut out about this amount of quartz. Thereafter, the partly used bit Wil-l be applied to rough out a different quartz blank, after which the bit can be discarded.

It is clear, therefore, that a bit designed for screw machine manufacture and susceptible to being quickly screwed on or off greatly reduces the drilling time and the time for changing bits, as Well as providing a close control over tolerances in the finished product. It is understood that this technique has these advantages only because of the extreme hardness of quartz.

The various steps in the procedure of manufacturing a cell are illustrated in FIGURES 5 to 8 inclusive, of the drawings. It is understood that the quartz cell blank consists of a cylindrical member, the ouside of which has been ground to size, both with regard to diameter and length. For convenience, FIGURES 5 and 6 show the cell having the discharge region ground out. Thus, magnetostrictive rod is disposed within winding 96. The winding is connected to a current source of ultra-sonic frequencies, these ranging anywhere from about 20,000 cps. to as much as 100,000 c.p.s. The actual frequency used is determined by such factors as the size of the work and the character of the grinding operation.

Rod 95 has tapering portion 98 terminating at face 99. End 99 of the rod is provided with a threaded recess l0() axially of the rod. Disposed in recess 100 is a drill bit of the shape desired. In FIGURES 5 and 6, the active portion of the drill bit is shaped as illustrated, Drill bit 101 has a threaded bolt portion which fits into threaded recess 100. The drill bit also has flange portion 02 which rests against flat face 99 and body portion 103. The active portions of the drill bit will depend upon the nature of the operation. A slurry of finely divided abrasive in water or oil as previously specified can be directed on the work by means of hose 105 and nozzle 106.

Thus referring to FIGURES 7 and 8, two drill bits are shown for respectively drilling an axial passage through a quartz cylinder blank and then drilling or grinding chamber 31 in the blank. The initial axial passage illustrated in FIGURE 7 Will ultimately form passage 25 in the finished cell and will therefore be dimensioned accordingly. During the grinding or drilling, it is important that the work be rotated slowly around the drill axis. This will prevent unevenness in the finished work. The rotation of the work or oscillation back and forth may be accomplished manually by turning the chuck 108 into which the work is mounted by the ring handle or by turning the entire magnetostrictive rod.

When chamber 23 of the cell is to be drilled and ground, a bit which has been previously used for finishing is used for roughing out purposes. After the chamber is roughed out to within about .002" to about .004, then a brand new bit is substituted. This brand new bit is then used for finishing chamber 23 to size and this bit is now used for roughing out chamber 23 in a succeeding quartz blank.

Insofar as passage 25 or chamber 31 are concerned, a bit may be used on one or two blanks depending upon the amount of wear. It appears that these two steps, grinding passage 25 and chamber 31, do not appear to be as demanding as operating on the cell for producing chamber 23. Thus, with either passage 25 or chamber 311, there is no necessity for always using a new bit for a finishing operation. This is particularly true of chamber 31 whose tolerances may be as much as .004. However,

tionship along the cell axis.l

the depth of chamber 3-1 is important and must be accurately controlled. This is principally due to the desired relationship'betweenthe over-lapping edges of the outer and inner electrodes as previously set forth. Y l lt is possible to have the threaded bolt portion at the end of'the magnetostrictive rod and have a threaded recess in the bit.

j What is claimed is: f Y

1. A transducer comprising a cell of refractory electrically insulating material, said cell having a bore extending along the length thereof with the. ends of the bore enlarged .to `form front and rear chambers, an inner electrode disposed within the rear chamber and having an active electrode portion projecting through the bore' and into thel front chamber, an outer electrode disposed around the cell at the front portion of the cell, said outer electrode enclosing'the portion of theV cell defining the frontjcharnber, said outer electrode being in the form of a split metal sleeve and an insulating member disposed around said outer electrode, said cell, outer electrode and insulating member being snug, said outer electrode having room for expansion and means for maintaining said cell and electrodes in predetermined relation.

"bore and Van enlarged head portion extendingl from the front portion of the bore toward the second chamber, said head portion having the shape of a truncated cone with the free endof said head constituting the :small end, the base of the cone extending laterally beyond the neck of the electrode and lying within the bore, an :outer electrode in the form of a metal member disposed around the cell, a second Vmember of electrically insulating lnaterial disposed around the frontrportion of the outer electrode and Vhaving a chamber therethrough communicating with the cell chamber.

7. The construction according to claim 6 wherein said outer electrode is in the'forrn of a metallic sleeve having 2. The transducer accordingV to claim l wherein said Y means for maintaining said electrodes in predetermined relation include means for impressing a spring bias on said inner electrode to urgesaid inner electrode forwardly and maintain the transducer intact.

3. The construction according tc claim 2 wherein said means for creating said spring bias includes an insulating member pressing against the rear endof said inner electrode and springs engaging said insulating member to urge the same forwardly of the transducer.

4. A transducer comprising a cell of refractoryv elec- I trically insulating material, said cell having a generally cylindrical bore passingthrough the length thereofy withk enlarged chambers at the front vand rear portions of said cell, an inner electrode having a body portionvdisposed in said rear chamber and having an active electrode portion extending forwardly through the bore and into said front chamber, said active electrode portion including an electrode' head having the shape of a truncated cone with the head partly in the bore and partly'in the front cham-VV ber, the forward end of the head having a` smaller `diam,- eter than the rear endof the head, an :outer electrode disposed around the front portion of the cell, said outer electrode having the general shape of a sleeve with the rear end of the electrode overlapping the active head portion of the` inner electroder and the outer electrode extending forwardly around the front portion of the cell in which the frontchamber lies.

5. rThe construction according to claim 4 wherein said inner `electrode has a shoulder engaging the cell material at the forward' endj of the onechamber to define Vthe position of said electrode andV wherein means'are provided for maintaining said electrodes Vcell in aligned vrelaa slot longitudinally to permit expansion thereof within the second insulating member.

8. The construction according to claim 6 wherein means are provided for spring pressing said inner electrode for# wardly of the transducer and axiallyof the cell.

9. The construction according to claim 6 wherein said cell is of quartz and has the forward end thereof disposed against a portion of the second insulating member, the meeting surfaces thereof being accurately ground to minimize the escape of vibratory energy which may be generated by the transducer in the other chamber and wherein saidY second lchamber has a conical portion with the cone angle being between about 20 and about 45 for desirable'reproduction of audio frequencies'. f

10. A transducer comprising a quartz-cell having af bore terminating in chambers at the two ends of said cell,

'an inner electrode having a bodypportion within one -1,000 C without sputtering and an outer electrode consisting' of a metal member disposed around the cell.

lil. The transducer according to claim l() wherein saidl inner electrode' is an alloy containing chromium.

References Cited in thefile of this patent UNITED STATES PATENTS Levy Sept. 9,

Claims (1)

10. A TRANSDUCER COMPRISING A QUARTZ CELL HAVING A BORE TERMINATING IN CHAMBERS AT THE TWO ENDS OF SAID CELL, AN INNER ELECTRODE HAVING A BODY PORTION WITHIN ONE CHAMBER AND A PORTION IN SAID BORE AND TERMINATING IN AN ACTIVE HEAD PORTION EXTENDING INTO SAID OTHER CHAMBER, SAID HEAD PORTION HAVING THE GENERAL SHAPE OF A TRUNCATED CONE AND CONSISTING OF A METALLIC MATERIAL WHICH CAN WITHSTAND TEMPERATURES IN AIR OF THE ORDER OF ABOUT 1,000*C. WITHOUT SPUTTERING AND AN OUTER ELECTRODE CONSISTING OF A METAL MEMBER DISPOSED AROUND THE CELL.

Images