Ultrasonic transducers

[57] ABSTRACT

Ultrasonic transducers which are constructed to have an outer shell surrounding a portion of the acoustic transformer of the transducer to serve as a vibration damper and also as part of the transducer structure. The shell is attached at a region near the node of the transformer to control the quantity of energy transmitted thereto. In many of the embodiments, the outer shell is attached without the necessity of a resilient support, he transducer is also constituted to accept a housing and form a sealing relationship therewith to fluid, in some embodiments a portion of the sealing means being located on the outer shell, and in other embodiments on another portion of the transformer.

Claims, 15 Drawing Figures

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U.S. Patent Dec. 30,1975

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ULTR ASONIC TRANSDUCERS RELATED APPLICATION:

This application is a continuation of my prior copending application Ser. No. 153,380, filed June 15, 1971.

Ultrasonic transducers are well known devices for converting electrical energy into vibrational motion at ultrasonic frequencies, broadly considered to be in the range from 1 khz to 100 khz. Many of these transducers use a stack of magnetostructive elements for producing the desired energy conversion.

The present invention relates to improvements in ultrasonic transducers. More specifically, the transducers of the invention are of the magnetostructive type and include a stack of elements of magnetostructive material, a workpiece or tool, and an acoustic transformer between the stack and the workpiece for transmitting energy from the stack to the workpiece. The transformers are of a type which include an outer shell which is attached near or at a node point of an internal part of the transformer. The shell serves as a support by which the transducer can be held and/or a housing attached. The shell forms a part of the resonating structure and its characteristics can be changed to alter the resonant frequency of the transducer. It is preferred that the outer shell have a portion of relatively heavy mass which will serve as a vibration damper.

In the preferred embodiments of the invention, the outer shell is attached to the other part of the transformer without the use of a resilient support. This means that the entire instrument can be sterilized, such as by autoclaving, without any risk of damaging it.

Also, in accordance with preferred embodiments of the invention, the transducers are constructed in a manner such that a housing can be provided in which a fluid can be circulated to cool the stack members. The structures are such that the housings can be fastened to the outer shell or another part of the transducer transformer. In many cases, this can be done without the need of any resilient sealing members. In some of the embodiments, a screw thread is used as the fastening means. This prevents the insert (stack, transformer and workpiece) from being pulled axially out of the housing.

Also in accordance with the invention, novel transducer structures are disclosed which can support high stress loads and which have a large stroke of motion of the workpiece.

It is therefore an object of the invention to provide novel ultrasonic transducer structures having an outer shell which is used as a support member.

A further object is to provide ultrasonic transducers which are made entirely of metal material.

Another object is to provide novel ultrasonic transducers having arrangements for attaching a fluid containing a housing thereto without the need of a sealing element.

Yet another object is to provide novel ultrasonic transducer structures which are constructed with a flange member adjacent to an outer shell, the flange serving as one sealing surface for a fluid containing housing.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings, in which,

FIGS. lAand IB when taken together, show partially in cross-section a one embodiment of a transducer in accordance with the invention in cross-section;

FIG. 2 is a diagram showing the longitudinal motion of the vibrational energy of the transducer of FIG. 1;

FIG. 3 is a front view of the transducer of FIG. 1;

FIG. 4 is a cross-sectional view of the transducer of FIG. 1 taken along the lines 4—4 of FIG. 1;

FIG. 5 is a fragmentary view of a front portion of a transducer, taken in cross-section, of another embodiment of the invention;

FIG. 6 is a cross-sectional view of the front portion of yet another embodiment of transducer;

FIG. 7 is a diagram showing the longitudinal component of motion of the vibrational energy of the transducer of FIG. 6;

FIG. 8 is a view in cross-section of the front portion of still another transducer;

FIG. 9 is a view partially in cross-section of a further embodiment of a housing for a transducer; and

FIGS. 10-14 are views partly in cross-section of portions of still further embodiments of transducers.

FIGS. 1A, IB and 2-4 depict one embodiment of the invention and the general operational aspects thereof. The insert or transducer T includes a stack of laminations 10 of a suitable magnetostrictive material, for example, nickel or a nickel alloy. The left end of the stack laminations are shown brazed or welded together at 11. An acoustical impedance transformer 14 has one end connected, such as by brazing, to the other end of the stack at 18. A workpiece or tool 12 is connected to be part of the transformer 14. This connection also can be made by brazing or made as part of the central section of the transformer.

The acoustical impedance transformer 14 is shown as having a central section formed by pieces 14a, 14b and 14c. It also includes the tool 12 and the inner and outer shells 30a and 30b of a resonant elastic support member 30. Each of these sections is in a general tubular shape, except for the tool, and the cross-sectional area of the central portions 14a, 14b and 14c decreases between the end 18 of the stack 10 and the work tool 12. Thus, the mass of respective sections decrease toward the tool. The central section of the transformer including the tool 12 can be made of one solid piece of material which has been suitably machined and bent to form the tool shape or of separate pieces of material joined together. The tool 12 can be of any suitable shape which will operate with the transducer. A fluid flow passage 23 is formed through the entire length of the central portion of transformer 14.

The main function of the acoustical impedance transformer 14 is transporting energy from the stack of magnetostrictive material 10 to the work tool 12. The transformeer 14 is designed to have its resonant frequency (when attached to the tool 12) substantially equal to the resonant frequency of the stack 10 so that the junction 18 between the two is at or close to the loop (end) of the longitudinal component of vibration of the stack. At this point the stress produced by the component of longitudinal vibration is lower and the losses of energy due to the reflection of standing waves is negligible.

The acoustical transformer 14 also serves the function of increasing or decreasing the stroke of vibration of the tool 12 in a desired manner when the stack is vibrating with a given stroke of motion. For the particular transformer construction shown in FIG. 1, the distri3,930,173 bution of the longitudinal motion of mass particles in a given cross-section is shown directly below in FIG. 2. The end of the stack 10 which is connected to the transformer section 14a at point 18 imposes a longitudinal component of vibration upon the section 14α of a magnitude corresponding to the amplitude A„. This is a loop of the longitudinal component of motion whose amplitude changes in a cosine function from the end 11 toward the end 18. The amplitude of motion decreases from A_o at point 18 as it progresses toward the junction 15 of the two transformer sections 14a and 14b. Junction 15 is substantially one-quarter wavelength or 90°, at the resonant frequency of the transformer, from the loop 18. It is, therefore, close to the nodal point where the amplitude of longitudinal vibration is zero. From loop point 18, the amplitude of longitudinal vibration of a transformer section 14α at any point X is given as Aj. = A_o cos x and decreases to zero at node point 15.

The maximum velocity (v_mnj.) of mass particles at the loop point 18 is given by the following formula:

⁼ 2irfA₀ (1) where f is the resonant frequency of the transducer. The maximum acceleration (+_m/lx) of mass particles at the same loop point 18 is given by the following formula:

⁼ &lt;O²A_D (2)

From the node point 15, toward the tool, the amplitude of the longitudinal motion begins to increase at a faster rate in transformer section 14b than the increase on the other side of the node for a corresponding distance of the transformer section 14α. The reason that the rate of increase is greater is because of the smaller mass per unit acoustical length of the transformer section 14b than for section 14α.

Transformer 14 is a resonant vibrator having four loops of longitudinal vibration, at points 18 and 21, 32 and 39 and two nodes at points 15 and 36. Its acoustical length is X/2 = 180° = ir radians. Masses on each side of the nodes 15 and 36 are moving longitudinally in opposite directions. The node is a region of substantially no longitudinal motion. Therefore, points can be found on both sides of the node where the kinetic energies are in substantial equilibrium.

As explained previously, the masses on each side of the nodes are different. By suitably selecting the masses on each side of the nodes 15 and 36, a desired magnification factor M can be obtained for the transducer. In a simple vibrator, considering a mass and velocity m₀and v„ on the left side of a node and a mass and velocity m, and v, on the right side at any point where an equilibrium holds the following will apply:

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The magnification factor M for this case is as follows:

v.’ v. A,

M= -4-= -¹— = -7-= v. A„ m,

A greater stroke of motion is obtained at the end of the acoustical transformer with the smallest cross-section since it has the smallest mass. This explains the more rapid increase in the amplitude of motion due to the longitudinal component of vibration from node 15 to point 17, where section 14b joins section 14α, and the still more rapid increase where the mass of transformer section 14c is even smaller from point 17 to 21. There is also a magnification from point 21 to the free end 22 (tip) of the tool 12 since the latter has a smaller mass per unit length than the transformer section 14c. If the tool tip 12 were substantially straight, then in FIG. 2, A, would represent the amplitude of the component of longitudinal vibration at the output end point 22 of the transformer. The actual stroke length at 22 is equal to 2A, since the end of the transformer vibrates longitudinally in both directions for a distance A! about the point shown. As explained below, the curved workpiece 22 shown in FIG. 1 also exhibits flexural motion, i.e. motion transverse to the longitudinal axis of the insert.

Due to variances in the physical tolerances of the parts of the insert encountered during manufacturing, as well as a changing load which is encountered at the working end of the tool 12, the resonant frequency of similarly designed inserts made on a production basis and operating under different load conditions will differ. Variations are also encountered in the acoustical length and the position of the node point for the same reasons. This length should be 360° for the entire vibrator structure from the end of the stack to the end of the working tip, regardless of the actual physical length of the transducer and the influence of the load. Both these factors combine to create a working frequency for the transducer which can be different from the designed resonant frequency at which maximum efficiency will be obtained.

Since, because of manufacturing tolerances and different working conditions, it is not possible to design a transducer structure which will always oscillate at a particular frequency and the position of the node point cannot be accurately predicted. Also, as pointed out above, the node position changes with changing load. The present invention provides a transducer having an elastic support for the outer shell in which the support can be attached to the central tubular section within a fairly wide region at an around the node point. The elastic support controls the flow of energy. Its mass becomes, to some extent, an integral part of the vibrating structure. If the support is attached at the output side of the node, it can serve as a dampener of vibrations at the output end of the support. If it is attached at the input side to the node it can serve as an amplifier. If it is attached directly at the node it will not adversely affect the operations of the transducer. It should be understood, however, that the mass of the support makes it an energy accumulator and the vibrating energy will be converted into heat. In the embodiment shown in FIG. 1, the majority of the heat is produced on the inner shell section 30α of the support. Some of this is transported to the outer shell section 30i and to the surrounding medium, such as water, if used.

The support is constructed in such a manner that it permits the transducer to be held by the outer shell portion 30ά with little vibration being transmitted thereto. The amount of ultrasonic vibratory energy transmitted to the outer support shell 30h depends on many factors, one of which is the ability of the shell to absorb or transmit the energy. In the embodiment of FIG. 1, the front portion 38 of the outer shell section 30/&gt; is designed to function as an energy damper by being of a relatively large mass. The large mass section 38 dissipates a large portion of the energy wh h passes through the nodal region of outer section 3lj. It also

3,930 5 has a low amplitude of motion and transmits some of the vibrational energy to the surrounding medium, air or fluid, in which the transducer is used. The resonant support 30 is part of the entire vibrating structure and it effects the performance and behavior of the trans- ³ducer as a whole.

The resonant support 30, and particularly the outer section 30&amp;, provides a means by which a cover or housing can be fastened to the transducer. Further, it shields the central section 14a, 14&amp;, 14c of the internal ¹⁰section which is capable of radiating high energy loads. This is also desirable.

In several of the embodiments of the invention to be described, an outer shell is provided with a type of fastening means which can form a water tight seal with- ¹⁵out the use of an O-ring or other similar sealing member. This greatly simplifies the transducer construction where it is to be used with a cooling fluid. Further, as previously described, by suitably shaping the outer shell or modifying the mass of one or more of its sec- ²θ tions, the transducer can be “tuned”, within limits, to a desired resonant frequency and output stroke of motion after it'has been manufactured.

As seen in FIG. 1, an elastic support 30α is used to attach the outer shell 30&amp; to the transducer. Elastic ²⁵support 30ά is attached at its end 31 to the central section bf the transformer at node point 15 or in the region therearotind. This region around the node has a given amplitude of vibration on each side of the actual node. The amplitude of this vibration can be small and ³⁰will be substantially zero at the node. This small, or zero, amplitude vibration is transmitted to the outer shell 30. The elastic support 30α is relatively thin to reduce the transmission of energy to the outer shell 30ά. 35

The outer shell is attached to the end 32 of the elastic support 30α which is remote from the end 31. Section 30h extends over and is coaxial with the elastic support 30α and projects toward the nodal region of the outer shell. ⁴⁰

The first portion of outer shell 30i&gt; which is attached to the elastic support 30α, has a relatively small wall thickness as has the elastic support 30α for. restricted transmission of ultrasonic energy toward the nodal region of the outer shell 30i&gt;. ⁴⁵

In the proximity of its nodal region, the wall of ‘the outer shell is formed with a screw thread 35. and a flange 36 which is to be used for attaching a housing 40. Beyond the flange there is. a thinned down wall portion 37 which also serves to reduce, the quantity of ⁵⁰energy transmitted through the support. The portion 38 of heavier mass than any other portion of sections 30α or 30b, terminates the shell at its free end 39. Portion 38 serves as a vibration damper as previously explained. ⁵⁵

While point of attachment 31 is a loop for the elastic support 30α, the amplitude of the longitudinal compo-, nent of vibration is reduced going to the left toward the junction 32 of sections 30ά and 30b. Since elastic support section 30α and the thin walled portion of section ⁶⁰30b which is substantially coaxial with elastic support 30α have substantially a λ/4 acoustical length and relatively thin cross-section, they present a high resistance to the transmission of ultrasonic energy.

The elastic support section 30α together with the ⁶³shell, including piece 38 of heavy mass, are acoustical sections which together are close to λ/2 long. Whatever motion is imposed on the outer shell at point 32, its ,173 amplitude decreases toward the node point where the flange 36 islocated. Finally, because of the large mass of the portion 38 beyond the flange, there is relatively little vibration of the shell to the right of the nodal point because, as previously described, this greater mass moves with a lower stroke.

The transducer structure is well suited for accepting and retaining the tubular housing 40 -through which there is fluid-flow communication in a chamber 66. As seen in FIG. 1, a through passage 23 is formed throughout the entire length of the transformer 14. This passage opens at the end 21 of section 14c so that fluid will be directed by a groove onto the inner surface of the tool 12. Another passage 24 is formed through the wall of the transformer so that there will be fluid communication between the housing chamber 66 and the passage 23.

The inner end of housing 40 is threaded at end 42 to mate with the thread 35 on the support 30. The inner surface of flange 36 tapers inwardly to mate with an outward taper on the end 43 of the housing. When fastened tightly, the end 43 of the housing butts against the wall of the flange 36 to form a fluid-tight seal against the fluid in the housing. The two opposite tapers on the flange and housing prevent flowing of the housing material.

The housing 40 can be made of plastic or any other similar suitable electrically non-conductive material. The portion of the housing immediately to the left of the threads 42 can be shaped as desired to provide a suitable grip for the fingers of the operator using the transducer. This gripping section can extend for any desired length consistent with the total overall length of the transducer and is shown as terminating the small tapered section 44. To the left of section 44 the housing is formed with a widened section 46. A groove 48 is cut in section 46 to accept and hold an O-ring 50 to prevent penetration of moisture to the energizing coil 58. The wall thickness of the housing is then reduced to provide an area between a pair of upstanding ring bosses 54, 56 on which is wound the coil 58. The coil 58 is-in close proximity to the stack elements 10 to supply the necessary energizing force to the stack so that it will exhibit a magnetostrictive effect. A circuit for supplying the current is disclosed in the copending application of Gabriel Popescu entitled “Generator For Producing Ultrasonic Energy,” Ser. No. 152,947 filed June 14, 1971, which is assigned to the assignee of the subject invention.

The housing 40 terminates in a threaded section 59 (FIG. IB) which has a groove 60 which accepts and holds another O-ring 62 which holds the leads supplying current to the coil 58 in place. End section 59 has a passage 64 formed through it which communicates with the chamber 66 of housing 40.

A cover 70, which also can be of plastic or any other suitable material, fits over the end of housing 40 and that portion on which the coil 58 is located. A tight engaging fit is made between the inner surface of the cover 70 and the O-rings 50 on one end and the thread and O-ring 62 on the other so that the cover will not slide or unscrew off. The end of the cover 70 has an internal thread 74. An end cap 76, which is also of an insulating material, is pressed against the housing 40 when the cover is screwed oh. A pair of leads 69 for supplying current to the coil 58 pass through end cap 76 as well as a conduit 80 for supplying water or other similar cooling fluid to the· housing chamber 66. The

3,930,173 end of the conduit 80 fits into the passage 64 at the end of the housing 40. The portions of the leads 69 and conduit 80 outside of housing 40 are normally contained within a.common sleeve (not shown) or other suitable member.

The cooling fluid coming in conduit 80 into the chamber 66 completely surrounds the stack 10 and its laminations. This fluid passes from chamber 66 into the opening 24 in the transformer (FIG, 1A) and through the passage 23 to exit onto the tool 12. It should be noted that the fluid in chamber 66 never comes into contact with the current carrying coil 58. This is a decided advantage from the point of view of safety since the possibility of any short circuits occurring between the electrical current and the water.

As should also be noted, the housing 40 is attached to the transducer in the area (35 and 36) of the node of the outer shell 30b. This reduces or substantially eliminates the vibration which is transmitted to the housing 40. This is also advantageous since it makes it easier for the operator to use the transducer.

The transducer of FIGS. 1-4 has several advantages. It is simple in construction while still being efficient in the transmission and utilization of energy. No complicated tubes or other arrangements are necessary for directing fluid onto the tool. Further, no resilient support members are used, such as O-rings, as in the case with other prior art transducers. In addition, the threaded engagement between the housing 40 and the transducer insert (stack, transformer and tool) prevents separation of the two which might more easily take place if a sliding or press-fit were used between the two.

It should be understood that the transducer of FIG. 1 also operates the curved tool tip 12 to have a flexural component of motion at its end 22. This is in addition to the longitudinal component of the vibrational energy which was discussed previously. In the case of the curved tip, the amplitude of the longitudinal vibration component decreases from point 21 substantially to zero at the tip end 22 rather than increases as in the case of a straight tip. The curved tip 12 of FIG. 1A has a maximum amplitude of flexural vibration at its end 22 as it moves back and forth transverse to the insert longitudinal axis on each side thereof. The flexural component also has a mode point located at the mode point 15 previously described for the longitudinal component. This node point for the flexural vibration is, however, more than one wavelength away as measured in terms of the standing wave of the flexural component of motion. The flexural component is produced due to the curved portion of the tool tip which lies off center of the longitudinal axis of the other portions of the transformer, that is, the tip provides an asymmetric mass to the compressional waves in the structure which produce the longitudinal motion. When a curved tip is used, the structure acts to convert compressional energy, normally producing longitudinal motion, to flexural motion at the tool tip 22.

FlG. 5 shows another embodiment of transducer which is similar to that shown in FIG. 1. The main difference here being that the portion of the internal section of the acoustical transformer between the node point 15 at which the connection of the elastic support 30&lt;z is made, and the. end .21 of the internal section of the transformer is formed by a conical tapering section 69 instead of using the two tubular sections 14α and 14c as in FIG. 1. This arrangement operates satisfacto rily. However, the magnification factor obtained by the use of a transformer with a conical section is not as great as with al! cylindrical sections. As in the case of FIG. 1, the construction of housing 40 can be the same.

FIG. 6 shows another embodiment of the invention which in many respects is similar to that of FIG. 1. Here, the support 130 is made slightly different in that the portion 132 which joins the elastic support 130α and the outer shell section 130b is relatively thick. This thickened portion 132 is also formed with a groove 139 in which is located a resilient O-ring 141. Outer section 130b is also formed with a thickened annular rib 135 which serves as both a damper for the resonant support and a stop for the end of a housing 140. The end section 138 is tubular and of relatively large mass to also serve as a damper. The housing 140 is somewhat different from that of FIG. 1 in that it is held to the insert by a press-fit over the O-ring 141. The O-ring provides the seal for the fluid in chamber 66.

With the foregoing exceptions, the construction of the transducer of FIG. 6 is similar to that of FIG. 1. It should again be noted that the outer shell is connected to the central portion of the transducer in a manner to reduce the vibrations present on the outer shell. Also, no resilient mountings are needed.

FIG. 7 shows the pattern of the longitudinal component of the vibrational motion for the stack and central region of the transducer. The operation of this transducer is similar to that of FIG. 1. That is, if the tool tip is substantially straight the amplitude of the longitudinal motion increases between the start of the tip and its end 22. If the tool tip is curved, the amplitude of the longitudinal motion decreases and, instead, the amplitude of the flexural component of motion increased to maximum at the end of the tip.

FIG. 8 shows another embodiment of the invention which is similar to that of FIG. 6. Here, however, the O-ring for holding the housing is located on the housing itself instead of on the resonator support. A groove 151 is formed on the inner wall adjacent the end of the housing 150 and an O-ring 152 is located therein. This provides a seal for the fluid within the chamber 66 of the housing. The elastic support 130α and portion of the outer shell 130b have substantially the same wall thickness and the thickened section 132 of FIG. 6 is eliminated. The operation of the transducer of FIG. 8 is similar to that of FIG. 6.

In some applications it is desired to have an increased stroke length for the tool of the transducer. Stroke length is limited by the strength of the material forming the acoustical transformer and the tool itself. The stess produced by the longitudinal component of motion is given by the following formula:

i,— 2irf»CiA« sin X (*&gt;

where:

f “ the resonant frequency of the transducer p = the density of the transducer material C_t = the velocity of sound For a given frequency and stroke length, the stress in a given cross-section of a chosen shape is directly proportional tb the density of the metal used:

It has been found that titanium is a suitable metal which can support a high stress. Titanium also has another advantage in that it is inert. This renders it particularly useful for some applications such as, for example, where the instrument is to be sterilized. However, titanium has disadvantages tn that it cannot be

3,930,173 readily brazed either to itself or to other metals as in the case of the more common materials, such as stainless steel, which are normally used for acoustical impedance transformers and tools.

In accordance with the invention, various forms of transducers are disclosed which can be made of titanium and which also are constructed in a way such that these transducers can be manufactured fairly easily. As in the case of the transducers previously described, a support member is also used for the same purposes mentioned previously.

In FIG. 10, a transducer is shown having the usual stack of laminations 10. To the end 18 of the stack adjacent the acoustical impedance transformer, a stud 170 is fastened, such as by welding or other suitable technique. The stud 170, which can be of Monel, has a threaded bolt 172 on the end thereof.

The acoustical impedance transformer 214, which is preferably made of titanium, has a threaded blind bore 182 formed in its end of the first internal section 214α adjacent the stack so that the transformer can be connected to the stack by the bolt 172 and energy transmitted to the transformer. This eliminates the need to weld the transformer to the stack. The transformer 214 is substantially one-half wavelength long between its ^:input end point 173 adjacent the stack and its output end 174. The stack 10 is also one half wavelength long so that the total length of the transducer is one wavelength. The tool is preferably formed of the same piece of material which forms the transformer 214 For exam- pie, after the end of the piece of material forming the transformer is made to size, the tool end is bent to the curved shape shown.

The node of the internal section of transformer 214 is at point 183. Between the input end 173 and the node point 183, the transformer section 214a is of generally cylindrical shape and is substantially one-quarter wavelength long. There is a conical taper in the internal section 214b between the node point 183 and the output end 174. The tapered section is substantially a quarter wavelength long. As in the case of the transducers previously described, points 173 and 174 are loops of the longitudinal vibration of tool 176. The magnification factor between the output end 18 of the stack and point 174 is determined by the mass of the transformer sections on each side of the node point 183. Since the mass to the right of the node point is smaller and gradually decreases, a positive magnification factor is obtained.

As previously described, it is difficult to manufacture transducers on a basis such that a precise resonant frequency and node can always be obtained. Therefore, the transducer of FIG. 10 is also provided with an outer shell support 190 for the same reasons as previously described. The support is also made of titanium and is attached to the transformer 215 at the node point 183. The support 190 can be made of a separate piece and attached to the transformer by suitable techniques such as, for example, welding. The first portion 191 of the support adjacent the transformer node 183 is made relatively thin to reduce the amount of energy transmitted to the remainder of the support. The outer wall of portion 191 is threaded at 193 to accept the mating screw threads 42 of housing 40.

A flange 194 is formed on the support adjacent the ¹threads 193. The wall of the flange tapers inwardly to form a tight fit with the outwardly tapering end 43α of the housing to provide a fluid tight seal for the fluid in the housing chamber 66. From the flange 914 the flange terminates in a cylindrical section 197 of heavier mass than the first section 191. Section 197 serves as a dampener for the vibrations.

The support 190 forms part of the vibrating structure. It is substantially one quarter wavelength long. Its left end is connected to the node 183 of the central section of the transformer and its right end is of a loop. Further, the thinned wall section 191 chokes energy transmission. Because of these factors, the support member 190 vibrates very little. Also, the housing 40 is attached to the support by thread 193 adjacent the node 183 so it also receives relatively little energy.

FIG. 11 shows another form of transducer which is similar to that of FIG. 10. The main difference is that the threads 202 which mate with threads 42 on housing 40 are located on the first internal section 214a of the acoustical transformer instead of on the resonant support member, as in FIG. 10. The threads 202 are in the general location of the node of the transformer. Therefore, there is very little energy transmitted to the housing 40. The wall of the heavier mass dampening portion of the resonant support 209 is thinned out at 210, to the right of the transformer node, to reduce the quantity of energy transmitted to the portion 209.

FIG. 12 shows still another embodiment of transducer which can be made of titanium and which is in some respects similar to that of FIG. 11. This is the preferred embodiment of transducer. Here, the threads 202 to hold housing 40 are located on the outer wall of the first internal transformer section 214a to the left of the node point. The end 43b of the housing 40 forms a fluid-tight seal against a flange 219 which is the beginning of the outer shell of support 230. The connection of the support 230 to the transformer section 214α is at or in the region of the node point of the internal transformer section and is made by the flange 219 and a thin wall section 232. Wall section 232 is generally perpendicular to the flange 219 and its reduced thickness ¹ reduces the amount of energy transmitted to the main portion 234 of the resonant support.

The outer shell is a portion of the transd··-. . structure and determines its resonant frequency. The thick wall portion 234 of the outer shell serves as a damper, as in the supports of the embodiments previously described. However, unlike the support of the other embodiments, the inner wall of portion 234 of the resonant support lies generally parallel to and is concentric with the conical outer surface of the second internal section 2146 of the transformer. Because of the heavy mass of portion 234 and also because of its concentricity with transformer section 2146, the vibrations are damped and also there is good shielding of any vibrations radiated from the conical transformer section.

The front end of the support 230 is stepped down at 236 to a generally tubular shape. The shape of the front end member 236 is used to “tune the resonant frequency of the transducer. The generally concave shape of the center section 234 is also advantageous since it provides a gripping surface for the thumb and finger of the user of the transducer. The shape can also be useful in tuning the transducer.

FIG. 13 shows still a further embodiment of transducer which is also suited to be manufactured from a high stress metal, such as titanium. Here, the first internal section 214α of the transformer is formed with a flange 250 at the node point. A resilient O ring 252 is backed up against the flange. The outer shell support

3,930,173

260 is in this case formed by front and rear pieces 261 and 262. Front piece 261 has a tubular front section of heavy mass adjacent the tool which is used as a damper. The rear portion of piece 261 is formed eith a flange 264 having screw threads 265 on a reduced diameter shoulder 266 behind the flange.

The rear piece 262 extends toward the rear of the transducer. A generally L-shaped ring flange 267 is formed on the front end of piece 262. Screw threads 268 are formed on the front end of flange 267 to mate with the threads 265 of the first outer shell piece 261.

These two pieces 261 and 262 are fastened together to form the complete support structure. The shoulder 266 of front piece 261 engages the transformer flange 250. The shoulder of the ring flange 267 of the rear piece 262 engages the O-ring 252 which in turn engages the transformer flange 250. The two pieces are tightened together by the mating threads 265 and 268.

The point of joining the two pieces of the support is at the flange 250, which is a node. The front piece 261 serves as a damper. As should be apparent, the outer shell support 260 is held to the transformer by the resilient O-ring 252. This is the only embodiment of the invention where such an arrangement is used. The rear piece 262 of the support serves as a damper and for the purpose of dissipating heat. Screw threads 271 are formed on the outer surface of the piece 262 in order to accept and hold the end of the housing 40. The fluidtight seal to chamber 66 is made by the O-ring 252.

FIG. 14 shows still a further embodiment of the invention which is in some respects similar to that of FIG. 13. Here, the O-ring 252 is eliminated and the threaded portions 265 and 268 of the respective pieces 261 and 162 are sized so that shoulders of the two pieces will engage the flange member 250, located at the node ³⁵point of the internal section of the transformer. This is essentially a press-type fit for the resonator structure.

In each of the embodiments of FIGS. 1-8 and 10-14, a fluid-flow passage 23 is shown extending the entire length of the transformer so that fluid can be directed ⁴⁰onto the tool. An opening 24 is also shown in the transformer to provide communication between the fluid in the housing chamber 66 and passage 23. It should be understood that in some cases, the transducers can be used without a fluid. In other cases, a fluid can be used only for the purpose of cooling the stack of laminations.

FIG. 9 shows a housing arrangement for the latter purpose. This housing can be used with any of the transducers previously described or with any other compatible type of transducer.

In FIG. 9, housing 340 has internal threads 342 at one end to mate with the threads 35 on the transducer and form a fluid-tight seal up against the flange 36. A pair of spacers 346, 348 are formed on the barrel of the housing to locate the current carrying coil 58. The other end of housing 340 is thinned down and is threaded at 350 and fits within a cap 354 which also has threads 356 to receive the threads 350.

A tubular sleeve 360 fits within the housing 340 and is of a size to define an annular space 362 which forms a outflow passage for the fluid. The interior portion of sleeve 360 defines a chamber 366 which surrounds the stack 10. The left end of sleeve 360 is formed with a cylindrical section 370 which fits within a correspondingly shaped bore 372 in the cap 354. An O-ring 374 located in a ring depression on the section 370 provides a fluid seal between the sleeve 360 and cap 354.

¹²

The cover sleeve 70 is internally threaded at 380 to mate with threads 382 on the left end of cap 354. A hollow end cap 385 has a reduced diameter section which is located within the rear opening 384 of the ⁵ cover sleeve 70. End cap 385 is held against the left end of cap 354 as the cover sleeve is threaded onto the cap 354. The current carrying leads 59 for the coil 58 pass through the opening in the end cap.

A fluid inlet conduit 390 passes through a bore in the ¹⁰ cylindrical section 370 of sleeve 360 to supply fluid to chamber 366. The fluid exits from chamber 366 through passage 367 on the other end of inner sleeve 360. The fluid, which has been heated by the stack, flows back out through the annular passage 362 into a ¹³ bore 357 through cap 354 in which is located an outlet conduit 359.

As seen, the housing structure of FIG. 9 provides both an inlet and an outlet for the fluid. As in the case of the housing of FIG. 6, the current-carrying coil is not ²⁰ in contact with the cooling fluid. In both of the housing structures of FIGS. 6 and 9, the transducer insert can be readily separated from the housing. There is no physical electrical connection between the insert and the housing. Further, in the case of FIG. 6, no addi²³ tional tubes are needed to supply fluid from the chamber to the workpiece.