Title of Invention	AN ULTRASONIC ROD TRANSDUCER FOR PRODUCING ULTRASOUND IN LIQUIDS
Abstract	An ultrasonic rod transducer has a heat transfer element that is thermally well coupled to the piezoelectric transducer. It provides for the thermal resistance to the surrounding atmosphere or to the housing, and thus to the bath in the case of immersed rod transducers, to be reduced.

Full Text

1 Ultrasonic Rod Transducer To improve the cleaning effect of cleaning baths the liquid in the baths is excited with ultrasound. The so called rod transducers, which are either completely immersed or only with the resonator portion extending into the bath, are used for ultrasonic excitation. The ultrasonic rod transducer has a resonator, to which an ultrasonic head is affixed at at least one end and acts as a radiator. The head forms a housing in which the piezoelectric ultrasonic transducer is accommodated. The electrical transducer consists of a number of piezoelectric ceramic wafers. The Curie temperature of the ceramic wafers is about 300°C. If the ceramic wafers are heated to this temperature or higher, the piezoelectric effect vanishes irreversibly. If the piezoelectric transducers are intended to be used in permanent operation, a distinct margin away safety from the Curie temperature must be maintained. Usually, the temperature at the surface of the ceramic transducer must not exceed about 1500C. Thus, if the bath temperature is about 130°C a permissible temperature overage of only 20°C remains. The piezoelectric transducers make of ceramic are highly efficient. Still, the supplied electrical energy is not completely converted to ultrasonic energy, but rather in part also results in heating of the transducer. The ultrasonic energy to be generated with the transducer is thus limited by the overtemperature of the transducer. In the known devices the piezoelectric transducer is cooled essentially only by the mechanically coupled resonator, which consists of titanium. Titanium is a poor conductor of heat. There is practically no other cooling, since for reasons of ultrasonic technology the housing of the head is filled with air, which forms an extremely poor conductor of heat, so that the heat is in practical terms not removed through the wall of the housing. Based on this, a task of the invention is to create an ultrasonic transducer that can generate greater ultrasonic energy. This task in accordance with the invention is an ultrasonic rod transducer having the characteristics of Claim 1 or of Claim 20. The ultrasonic rod transducer in accordance with the invention has a resonator to which the piezoelectric transducer is ultrasonically coupled via a coupling element. The coupling element in part at the same forms a part of the wall of the housing. The attachment of the housing or the housing wall is situated at an oscillation node, so that the ultrasonic energy is exclusively input into the resonator, while the housing itself remains practically free of ultrasound. The piezoelectric transducer, together with the attachment device, has a link at the coupling device of about l/4 and thus is too compact to be able to give off significant heat. 2 In accordance with the invention, therefore, a heat transfer element is coupled to the piezoelectric transducer. According to one solution the heat transfer element is designed so that it form a forms a very narrow air gap together with the inner wall of the housing. The narrower the air gap is, the smaller the thermal resistance of this air layer will be, i.e., the more heat that can be transferred from the piezoelectric transducer to the housing and thus to the bath. According to the other solution a heat transfer element that acts as a cooling element in the case of an aerated housing is created. The latter arrangement is a possibility if the transducer is situated outside of the bath anyway. This is a solution that occasionally comes up. The length of the heat transfer element in the area that is a part of the acoustic path is chosen so that the acoustic conditions are not disrupted by it. For example, the transfer element can have a length of l/2, where it is immediately then connected to a front face of the piezoelectric transducer. In this design the heat transfer element can have a cylindrical shape or can also have a prismatic shape, where the cross section is expediently star-shaped in order to obtain a surface that is as large as possible, through which heat can be given up to the housing and thus to the bath. Another possibility is to use a cup as a heat transfer element. For example, in the case of said cup the bottom is formed from the usual polished steel disk, which lies between the central nut and the piezoelectric transducer, to connect them mechanically. The heat transfer element does not have to be arranged only at the end of the piezoelectric transducer that is away from the coupling section. It turned out that the piezoelectric transducer does not reach its maximum temperature immediately in the area of the end away from the resonator but rather at a smaller distance from it. For this reason it is advantageous to fit the heat transfer element into the piezoelectric transducer. For this the heat transfer element again has a length of l/2. The individual measures with regard to surface design, insertion or cup shaped design or through-design can be confirmed with each other in diverse ways. In the case of a housing for the resonator head through which air can pass it is advantageous if the heat transfer element has a large surface area, and the surface that serves for cooling is expediently directed so that it lies parallel to the air flow path because of the effect of convection. Otherwise, further developments of the invention are the object of the dependent claims. In a thorough reading of the description of the figures it will become clear that a number of modifications that result from the relevant requirements are possible. In addition, a number of combinations of the disclosed characteristics are possible. To describe every conceivable combination would unnecessarily increase the size of the description of the figures. The description of the figures is therefore limited to a few basic variants. 3 Embodiment examples of the object of the invention are represented in the drawings; here: Figure 1 shows an ultrasonic rod transducer, in a simplified perspective view; Figure 2 shows the head of the rod transducer as in Figure 1 in a side view with opened housing; Figure 3 shows the head of the rod transducer in a view similar to Figure 2 with a different positioning of the heat transfer element; Figure 4 shows the head of the rod transducer as in Figure 1, a similar view as in Figure 2 with a cup-shaped heat transfer element; Figure 5 shows a cross section through the head of a rod transducer with star-shaped heat transfer element and a housing matched thereto, and Figure 6 shows the head of a rod transducer in a view similar to Figure 2 using a heat transfer element with cooling fins. Figure 1 shows an ultrasonic rod transducer 1 in a perspective view (not to scale). The ultrasonic rod transducer 1 has a resonator 2 and a head 3 connected to the resonator 2. The resonator 2 is cylindrical over its length with constant diameter. At the end away from head 3 there is a conical tip 4. The head 3 is provided with a threaded tubular stem 5 through which passes an electrical cable 6, via which electrical energy is supplied to head 3. The structure of the head is shown in Figure 2. Head 3 includes a connecting element 7, a piezoelectric transducer 8, a heat transfer element 9 and a cup-shaped housing cap 10. The connecting element 7 is a one-piece body of titanium with a cylindrical extension 11, the outside diameter which corresponds to the diameter of resonator 2. In the cylindrical extension 11 there is a coaxial pocket drilling 12 with inside threads. The resonator 2 is affixed to the connection element by means of the pocket boring 12. At the contact with extension 11 the connection element 7 forms a flange, which becomes a threaded extension 14 via an offset section and is a part of the housing of head 3. The threaded extension 14 is tubular and surrounds a stem 15, which is mechanically solidly affixed to the cylindrical extension 11. A sort of membrane is formed between stem 15 and threaded piece 14 in order to decouple flange 13 or threads 14 maximally from the oscillations that are fed to the extension 11 from the piezoelectric transducer 8. The connecting element 7 is a titanium piece machined from a solid blank and is thus one-piece. 4 Stem 15 which is coaxial to extension 11 forms a planar surface 16 on which the piezoelectric transducer 8 lies. In the embodiment example shown the piezoelectric transducer 8 is composed of a total of 6 piezoelectric ceramic wafers 7, between which electrodes 18 are inserted. Electrodes 18 are each provided on one side with terminal 19 to which conductors 20 are connected. In the embodiment example that is shown three of the terminals 19 point upward and three point downward (Figure 2). The terminals 19 that are on the same side in each case are connected electrically in parallel, so that from the electrical standpoint a dipole is formed, to which the feed or excitation A.C. voltage is fed at a frequency of usually greater than 25 kHz. Both the ceramic wafers 17 and the wafer shaped electrodes 18 are wafer shaped rings with planar face surfaces. Electrode 18 lying furthest to the right in Figure 3 forms the right face end of the piezoelectric transducer 8, while the ceramic disk 17 lying furthest to the left, which lies directly against stem 16, is the left face end. As can be seen, the piezoelectric transducer 8 is essentially cylindrical with plane face surfaces. The heat transfer element 9 is designed as a cylindrical tube with plane face ends 22 and 23. The outer surface 24 is cylindrical. On the side of the heat transfer element 9 that is farther from the piezoelectric transducer 8 there is a friction-reducing steel disk 25, which is pressed against piezoelectric transducer 8 by a nut 26. Nut 26 is screwed onto a threaded stem 27, indicated by dashed lines, which is anchored at the other end in stem 16 of connecting element 7. Both threaded stem 27 and nut 26 are made of titanium, while the heat transfer element 9 is made of aluminum. As a consequence of this arrangement the electrode 18 that is furthest to the right is an electrode that at the same time also feeds the ceramic wafer 17 that is farthest to the left. Between its two face surfaces 22 and 23 the heat transfer element 9 has an acoustic length ofl/2. The length of the piezoelectric transducer 8, including disk 25, nut 26 and stem 16, which goes up to the wall of the housing, has a length of l/4. The right end face of nut 26 thus lies at an antinode at resonance frequency. Housing cap 10 is, as shown, cup-shaped and is composed of a collar 28 and a cup bottom 29, from which the threaded stem 25 projects. At its free end collar 28 is provided with inside threads 31, which are screwed together with threads 14 in the assembled state. Collar 28 forms a cylindrical inner wall 32 of the housing. The diameter defined by the inner housing wall 32 is slightly greater than the outer diameter of the outer circumferential surface 24 of heat transfer 9. In assembled state the inner wall 32 of the housing is in a position as illustrated in Figure 2 by the dashed lines 33. Thus together with the outer circumferential surface 24, the inner wall 32 forms a narrow cylindrical gap 34 with a thickness between 0.5 and 5 5 mm and the length of the transfer element 9. Through this the thermal resistance to the outside of housing 10 is greatly reduced. As can also be seen from the figure, the maximum outer diameter of piezoelectric transducer 8, including the projecting terminals 19 is less than the outer diameter of heat transfer element 9 or the inner diameter of the inner space 32. In order to lead the electrical conduits past the heat transfer element 9, it contains two lengthwise slots, which cannot be seen because of the view of the drawing. The connecting cable 6 passes through the tubular threaded stem 5. When the ultrasonic rod oscillator 1 that is outfitted with head 3 as in Figure 2 is in operation, heat arises in the piezoelectric transducer 8. This heat is in part dissipated via the stem 16 and the resonator 2 that is connected to the extension 11 into the bath. In this way the left end of the piezoelectric transducer 8 receives a certain amount of cooling. The right end gives up its heat to the heat transfer element 9. The heat transfer element 9 in the form of the aluminum tube transports the heat through the narrow air gap 34 to the collar 28 of the housing cup 10 and from there into the bath. Therefore the right end of the piezoelectric transducer 8 experiences considerably better cooling than with the prior art. With the prior art the right end would be cooled only to the extent that the poorly heat conducting titanium bolts 27 could remove heat in the direction of the resonator 2. Through the use of the heat transfer element 9, the housing cup 10 is additionally employed to transfer the heat from the piezoelectric transducer 8 into the bath. The ceramic wafers 17 are not good heat conductors. The arrangement as in Figure 2 will consequently show maximum overtemperature in a region lying between the two face ends of the piezoelectric transducer; it is advantageous if heat transfer element 9 is inserted into piezoelectric transducer 8 as in Figure 3. As can be seen from the figure, a total of four ceramic disks 17 are arranged between heat transfer element 9 and connecting element 7, while two ceramic disks 17 are arranged between heat transfer element 9 and spacer disk 25. Through this the right face end of the piezoelectric transducer 8 is cooled via nut 26 and bolt 27, the intermediate part is cooled with the help of heat transfer element 9 in the direction toward housing 10 and the left end of the piezoelectric transducer 8 is cooled via the connection element 7 to the resonator 2. In the case of the embodiment examples as in Figures 2 and 3 the thermal resistance is determined by the area of the annular gap 34 and its thickness. The thermal resistance is inversely proportional to the area and inversely [sic] proportional to the thickness. The thickness of the gap cannot be reduced below a certain technical dimension for reasons of manufacturing technology without the danger that the heat transfer element 9 will contact inner side 32. This effect must absolutely be avoided, since otherwise ultrasonic energy will be coupled into housing 6 10 through this. There are also limits with regard to the area of the gap, because one cannot increase the size of the head to just any diameter. An increase of the cooling area can be achieved with the embodiment as in Figure 4. In the embodiment as in Figure 4 the heat transfer element 9 has the shape of a cup with a bottom 36 and collar 37. The collar of the cup points away from piezoelectric transducer 8, i.e., to the right in Figure 4. The bottom 36 lies between the right end of piezoelectric transducer 8 and the central securing nut 26. Bottom 36 replaces steel disk 26, i.e., cup 37 consists of the polished steel disk preferably at least in the region of bottom 36. In this embodiment there is not a compulsory need to make the heat transfer element 9, bottom 36 and collar 37 in a single piece. It is sufficient if it is ensured that the thermal resistance at the transition from bottom 36 to cup collar 37 is small by comparison with the thermal resistance that the heat transfer element 9 exhibits toward housing 10. Collar 37 is cylindrical both outside and inside, i.e., it bounds a cylindrical space. To obtain the desired large heat transfer area, the housing cup, in a departure from the previous embodiment example, is provided with an inward projecting cylindrical stem 38. Stem 38 is designed as a hollow structure, so that the bath liquid can circulate within it. In assembled state collar 28 of housing cup 10 forms cylindrical gap 34 with a small gap as in the embodiment example in Figures 2 and 3. Another cylinder gap with a similarly small gap width arises between the cylindrical inner wall of the cup 37 and stem 38. With that the cup shaped heat transfer element 9 is capable of removing heat from the housing cup 10 and from there into the bath both at the outside and at the inside of collar 37. Another possibility for increasing the area of the air gap between the heat transfer element 9 and the cup shaped housing 10 is illustrated in Figure 5. While in the previous embodiment examples the heat transfer element 9, apart from the slots for electrical connections, is largely rotationally symmetrical, heat transfer element 9 as in Figure 5 has a star-shaped structure in cross section. Figure 5 shows a section through head 3 at a right angle to the lengthwise axis or parallel to the axis along which the ultrasonic waves propagate, specifically through the heat transfer 9. One can see the central tightening bolt 27 and the star-shaped heat transfer element 9. It can be imagined as being formed of an annular ring with triangular points projecting from the ring. The collar 28 of housing 10 has an inner wall 32 that is made with a complementary star shape. Such a structure can be produced, for example, by machining or by stamping from the appropriate sheets. Instead of being screwed together via threads 14 and threads 31 a connection is made via connecting rods that pass through drillings 41. Drillings 41, which line up with each other, are provided both on a projecting shoulder of the bottom 29 of housing 10 and in flange 13. The 7 embodiment examples as in Figures 2-5 concern ultrasonic rod transducers that can be completely immersed. In the case of these rod transducers the head 3 is also situated in the bath. Figure 6 shows an embodiment of an ultrasonic rod transducer 1, the head 3 of which is situated outside of the bath. Head 3 is affixed to the container wall by flange 13. Housing 10 is situated in the free atmosphere. The further description can be limited to the differences with the previous embodiments. In order to achieve a good cooling effect, the collar 27 of the housing cup 10 is provided with a number of air holes 42, through which the outside atmosphere can circulate. To cool the piezoelectric transducer 8 better, a heat transfer element 9 that has a number of cooling fins 43 on its outside is used. In this embodiment it is not important for the gap between the heat transfer element and the housing 10 to be as small as possible. Rather the point is to dissipate as much heat as possible via the cooling fins 43 to the air circulating through air holes 42. The heat transfer element 9 in Figure 6 is arranged in the same way as in the embodiment example in Figure 1. It can also be centrally positioned in the piezoelectric transducer 8, in correspondence with Figure 2. The length of the heat transfer element 9 in the axial direction is again chosen so that the antinode of the standing wave is situated at the end of the tightening nut 26, while the transfer position through the wall that is formed in the connecting element 7 lies at the position of the oscillation node. The cooling fins in Figure 6 are only schematically represented in Figure 6. It is understood that the cross sectional design and diameter of the cooling fins 43 are also dimensioned according to acoustic technology in order to avoid breakage due to the induced acoustic oscillations. An ultrasonic rod transducer has a heat transfer element that is thermally well coupled to the piezoelectric transducer. It provides for the thermal resistance to the surrounding atmosphere or to the housing and thus to the bath to be reduced in the case of immersed rod transducers. 8 Claims 1. An ultrasonic rod transducer (1) for generation of ultrasound in liquids, with a housing (10, 11), that bounds in inner space and that has at least one outer wall (28, 29), whose inner side (32) is turned toward the inner space, with a piezoelectric transducer device (8), which has two end faces and which is accommodated in housing (10), with a resonator (2) that is situated outside of the housing (10, 13), with a connecting element (7), via which the transducer device (8) is connected to the resonator (2) and that projects at least partially from an outer wall (13) of the housing (10, 13), the heat transfer element (9) that is thermally connected to the piezoelectric transducer (8) and that has at least one surface (24) that runs next to the inner side (32) of an outer wall (28) to form a gap (34) in order to transfer the waste heat of the piezoelectric transducer (8) to the outer wall (28). 2. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the inner space has a cylindrical cross section. 3. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the heat transfer element (9) is cylindrical on its outer side. 4. An ultrasonic rod transducer as in Claim 2, characterized by the fact that the heat transfer element (9) has a prismatic shape that departs from the cylindrical shape, preferably a star shape. 5. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the inner space has a non-cylindrical prismatic cross section, where the face surface of the prism is at least approximately star-shaped. 6. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the star- shaped base area can be seen as consisting of a central area and arms projecting from this central area. 7. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the arms have like shapes. 8. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the arms, seen in cross section, are approximately triangular. 9. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the housing (10) has a cylindrical outer surface (28). 10. An ultrasonic rod transducer as in Claim 1, characterized by the fact that a housing part (10) essentially has the shape of a cylindrical cup (28, 29). 11. An ultrasonic rod transducer as in Claim 10, characterized by the fact that the housing part (10) contains, in the cylindrical cup (28, 29), an insert that bounds a prismatic inner space. 9 12. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the width of the gap (34) is between 0.5 mm and 3 mm. 13. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the connecting element (7) has a shoulder (13, 14), whose outer diameter is greater than the clear width of the inner space. 14. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the piezoelectric transducer device (8) is formed of a number of adjacently lying piezoelectric wafers (17), between which electrodes (18) are inserted. 15. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the piezoelectric transducer device (8) had two face ends and that heat transfer element (9) is arranged at a face end. 16. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the piezoelectric transducer device (8) has two segments, which are acoustically connected in succession and that the heat transfer element (9) is inserted between the two sections. 17. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the heat transfer element (9) has a length of l/2 in the direction parallel to the axis of oscillation. 18. An ultrasonic rod transducer as in Claim 1, characterized by the fact that the heat transfer element (9) has the shape of a cup, where the bottom (36) of the cup-shaped heat transfer element (9) is acoustically and thermally coupled to a face side of the piezoelectric device (8). 19. An ultrasonic rod transducer as in Claim 18, characterized by the fact that the housing (10, 13) has a recess (38) that fits into the inner space of the cup-shaped heat transfer element (9) to form a narrow gap. 20. An ultrasonic rod transducer (1) for generation of ultrasound in liquids, with a piezoelectric transducer device (8) that has two face ends, with a resonator (2), with a connection element (7) for connecting the transducer device (8) to the resonator (2) with a heat transfer element (9) that is thermally connected to the piezoelectric transducer (8) and that has at least one area that form a lower thermal resistance to the surrounding atmosphere than the piezoelectric device (8). 21. An ultrasonic rod transducer as in Claim 20, characterized by the fact that [it has] a housing (10) that is aerated. 22. An ultrasonic rod transducer as in Claim 20, characterized by the fact that the housing (2) contains aeration holes (42) for aeration. 23. An ultrasonic rod transducer as in Claim 20, characterized by the fact that the heat transfer element (9) has a divided surface as a kind of cooling body. 10 24. An ultrasonic rod transducer as in Claim 20, characterized by the fact that the piezoelectric converted device (8) has a stack ofindividual piezoelectric wafers (17), between which electrodes (18) are arranged. 25. An ultrasonic rod transducer as in Claim 20, characterized by the fact that the heat transfer element (9) is inserted in the piezoelectric transducer device (8). 26. An ultrasonic rod transducer as in Claim 1 or 20, characterized by the fact that the connecting device (7) is in part situated outside of the housing (10, 13). An ultrasonic rod transducer has a heat transfer element that is thermally well coupled to the piezoelectric transducer. It provides for the thermal resistance to the surrounding atmosphere or to the housing, and thus to the bath in the case of immersed rod transducers, to be reduced.

Documents:

02880-kolnp-2007-abstract.pdf

02880-kolnp-2007-claims.pdf

02880-kolnp-2007-correspondence others 1.1.pdf

02880-kolnp-2007-correspondence others.pdf

02880-kolnp-2007-description complete.pdf

02880-kolnp-2007-drawings.pdf

02880-kolnp-2007-form 1.pdf

02880-kolnp-2007-form 2.pdf

02880-kolnp-2007-form 3.pdf

02880-kolnp-2007-form 5.pdf

02880-kolnp-2007-gpa.pdf

02880-kolnp-2007-international publication.pdf

02880-kolnp-2007-international search report.pdf

02880-kolnp-2007-others.pdf

02880-kolnp-2007-pct request form.pdf

02880-kolnp-2007-priority document.pdf

2880-KOLNP-2007-CORRESPONDENCE OTHERS 1.2.pdf

2880-KOLNP-2007-CORRESPONDENCE.pdf

2880-KOLNP-2007-OTHERS 1.1.pdf

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