Ultrasonic transducer and ultrasonic flow measuring device

Abstract

Ultrasonic transducer (1) comprising a coupling element (3) and a piezo element (2), wherein a metal disk (4) is arranged between the coupling element (3) and the piezo element (2), wherein the metal disk (4) is connected with the piezo element (2) or with the coupling element (3) by means of an adhesive layer (5 or 6), characterized in that the adhesive layer (5 or 6) is producible, at least in certain regions, by means of a photochemically curable adhesive.

Claims

1. An ultrasonic transducer, comprising: a coupling element; a metal disk; and a piezo element, wherein: between said coupling element and said piezo element said metal disk is arranged; said metal disk is connected with said piezo element or with said coupling element by means of an adhesive layer; and said adhesive layer is enriched, at least in certain regions, with a component, which is heatable inductively under the action of LF-fields.

2. The ultrasonic transducer as claimed in claim 1, wherein: said adhesive layer has residues of an LF-field absorbing component.

3. The ultrasonic transducer as claimed in claim 1, wherein: said metal plate has an area facing said piezo element with a geometric center of gravity; said adhesive layer comprises a polymer; and the degree of crosslinking of the polymer decreases toward this center of gravity.

4. The ultrasonic transducer as claimed in claim 1, wherein: said adhesive layer is produced from a 2-component adhesive, wherein at least one component is surrounded by a micro encapsulation.

5. The ultrasonic transducer as claimed in claim 1, wherein: said adhesive layer is arranged both between said piezo element and said metal disk, as well as also between said metal disk and said coupling element; and said adhesive layer between said metal disk and said coupling element has the same chemical composition as the adhesive layer between said metal disk and said piezo element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter of the invention will now be explained in greater detail based on a number of examples of embodiments in the appended drawing, the figures of which show as follows:

(2) FIG. 1 is an exploded view of a first ultrasonic transducer of the invention;

(3) FIG. 2 is a sectional view of the first ultrasonic transducer;

(4) FIG. 3 is a detail view of the ultrasonic transducer of the invention;

(5) FIG. 4 is a detail view of a second ultrasonic transducer of the invention;

(6) FIG. 5 is a sectional view of a third ultrasonic transducer of the invention;

(7) FIG. 6 is a detail view of the third ultrasonic transducer of the invention;

(8) FIG. 7 is a detail view of a fourth ultrasonic transducer of the invention; and

(9) FIG. 8 is a detail view of a fifth ultrasonic transducer of the invention.

DETAILED DISCUSSION IN CONJUNCTION WITH THE DRAWINGS

(10) FIG. 1 shows an ultrasonic transducer 1 of the invention including a coupling element 3.

(11) The ultrasonic transducer 1 comprises an arrangement of a piezo element 2, a metal disk 4 and a coupling element 3. Arranged between the piezo element 2 and the metal disk is a first adhesive layer 5. Arranged between the metal disk 4 and the coupling element 3 is a second adhesive layer 6.

(12) Coupling element 3 is often also called a coupling body. Very often, coupling elements are embodied to have a wedge shape, so that those skilled in the art also speak of a coupling wedge.

(13) In the present example of an embodiment, the coupling element 3 is embodied as a coupling wedge. The basic form of the coupling element is cylindrical with a lateral surface 3.1 and two main surfaces 3.2 and 3.3. In such case, one of the two main surfaces 3.2 is tilted relative to the other main surface 3.3, so that a normal vector X of the main surface 3.2 is at an angle to the normal vector Y of the main surface 3.3. The normal vector X of the main surface 3.2 is, in such case, the same as the normal vector at least of the piezo element 2 and/or the metal disk 4. Main surface 3.3 serves as coupling surface and leads an ultrasonic, wanted signal in the case of a clamp-on ultrasonic, flow measuring device into the tube wall of a media conveying tube. In the case of a so-called in-line flow measuring device, thus a device with a fixedly installed measuring tube, the ultrasonic, wanted signal can also be introduced directly into the medium.

(14) The coupling element 3 shown in FIG. 1 has a special cavity 7 in the form of an inclined bore, in which the piezo element 2 and the metal disk 4 are securable.

(15) Cavity 7 in the coupling element 3 in the present example of an embodiment is a cylindrical recess containing the circularly shaped, main surface 3.2. Depending on shape of the piezo element 2, however, also other geometric forms are conceivable. Thus, the main surface 3.2 in cavity 7 can be square or rectangular, for example.

(16) At the main surface 3.2, the greater part, thus greater than 50%, of the ultrasonic signal produced by the piezo element is introduced into the coupling element 3. At the same time, the angular deviation of the main surface 3.2 from a parallel orientation to the main surface 3.3 defines the angle of incidence of the ultrasonic signal into the measured medium.

(17) Introduced into the cavity is an adhesive for adherring the coupling element 3 with the metal disk 4. This forms, after its curing, the second adhesive layer 6. The terminology, adhesive, in the sense of the invention means any substance, which is curable and in this cured state provides an affixing between two elements, here the metal disk 4 and the coupling element 3 or the metal disk 4 and the piezo element 2.

(18) The adhesive layers have especially a thickness of up to a maximum of 1 mm thick, preferably, however, a maximum of 0.5 mm thick. Alternatively, the bonding between the metal disk 4 and the coupling element 3 can occur through use of a potting compound of thickness equaling a multiple of lambda/4.

(19) Four variants of the invention can be used for forming the adhesive layer. In each case, the object of a fast fixing of the individual components at lesser temperature loading is solved in a different manner.

(20) For forming the first and/or second adhesive layer 5, 6 according to a first variant of the invention, a photochemically curable adhesive can be utilized.

(21) To the corresponding photochemical adhesives belong, among other things, the UV adhesives, which can be obtained e.g. from the the firm, Loctite.

(22) One option is that a one-component or multi-component adhesive is activated upon UV irradiation and forms bonds. This is the case, for example, for photo initiated curing acrylates. Alternatively, also a so called photo activator can be utilized, which is first of all activated by exposure to UV-light, for example, with radical formation, and then these radicals excite other components of the adhesive for chain reaction/cross-linking.

(23) Suitable fundamental systems for adhesive components are e.g. acrylates, polyurethanes or epoxide resins. The curing can be enabled, for example, using an LED curing lamp, e.g. a Delolux 80 lamp. The temperature rise, is, in such case, significantly less than with a conventional discharge lamp. The light wavelength is preferably in the range, 300 to 480 nm.

(24) For forming the first and/or second adhesive layer 5, 6 according to a second variant of the invention, an adhesive can be used, which contains at least one micro-encapsulated polymerization activating component, which is releasable under the action of microwaves.

(25) Micro-encapsulations are known per se and are applied extensively e.g. in the foods industry. Also, micro-encapsulated adhesives are known per se (see Kleben-Grundlagen, Technologien, Anwendungen (Adhesive BondingFundamentals, Technologies, Applications); sixth updated edition, pages 238-240). Such adhesives are applied e.g. in the case of the adherring of screws, where the micro-capsules are destroyed by the shearing. Such adhering, thread pre-coats are used e.g. in products of the firm, PreLok. Micro encapsulations with enclosed adhesive components are producible, for example, by the so-called drop method. In such case, at least one component is present in the micro-encapsulation, for, in given cases, together with additional components, triggering a polymeric chain reaction. Such component can be, for example, a hardener. In the case of epoxides, the hardener can be, for example, a multiple amine (e.g. diethylenetriamine). Alternatively, also a component of the adhesive, e.g. a polyol, can be enclosed in the micro-encapsulation.

(26) High energy microwave radiation enables a bursting of the micro-encapsulations. In this way, polymerization occurs and/or cross-linking of already existing polymer chains.

(27) Additionally, the micro-encapsulation, the encapsulated components and/or the unencapsulated components can advantageously include other ingredients, which strongly heat up under microwave irradiation or by induction and thereby pointwise develop heat, which supports the polymerization- and/or cross-linking reaction. A greater external heat input, which burdens the other components, e.g. the coupling body or the piezo element, is, consequently, not necessary or at least only necessary to a lesser degree. These other ingredients are heat absorbing particles, thus e.g. metal particles.

(28) For forming the first and/or second adhesive layer 5, 6 according to a third variant of the invention, an adhesive can be used, which contains at least one micro-encapsulated polymerization activating component, which is releasable under the action of ultrasonic waves.

(29) Such a technology is applied e.g. in the medical field, in order to release ultrasonic, contrast means by way of ultrasonic action. A corresponding technology and the micro-encapsulations are described in EP 0 977 594 B1, to which comprehensive reference is taken.

(30) In contrast to the technology there, the micro-encapsulation in the present case is utilized for enclosing an adhesive component. The micro-encapsulations can be made to burst by the ultrasonic waves of the piezo element 2 of the ultrasonic transducer 1. In this way, the arrangement provided for measuring is also utilized for its manufacture. For this, the piezo element can be supplied with an excitation energy during the manufacturing process, which is higher than the usual excitation energy for the measuring mode.

(31) Also, in the present case, the micro-encapsulation, the encapsulated and/or the unencapsulated component can contain ingredients, which strongly heat up under microwave irradiation or by induction and thereby provide pointwise hot spots, which support the polymerization- and/or cross-linking reaction. Also here, the heat absorbing particles can be e.g. metal particles.

(32) For forming the first and/or second adhesive layer 5, 6 according to a fourth variant of the invention, an adhesive can be utilized, which is enriched at least in certain regions with a component, which is heatable inductively under the action of LF- or HF-fields

(33) Such components can be e.g. ferromagnetic alloys or metals, such as nickel-iron. These components are also detectable in the adhesive layer after the curing. The adhesive layer contains, consequently, also in the cured state, residues of an LF- or HF-field absorbing component.

(34) A special advantage of heating with microwaves, induction or also of the micro-encapsulation is the locally limited effect and, thus, a polymerization, which protects surrounding materials. In such case, the heat input for this polymerization is very small.

(35) After started polymerization, the adhesive layer can be only pre-affixed or else completely cured in one process step. In the case of a pre-affixing, a heat treatment can follow for bringing about a complete polymerization. In such case, the heat input can advantageously be selected smaller, so that also in this case, a heat protecting manufacture for the residual components is possible (thus protecting e.g. the material of the piezo element or the material of the coupling element).

(36) Known concepts for securement of a bearing plate are designed to connect the bearing plate immediately with the piezo element or the coupling body. Application of the aforementioned adhesives permit a stepped curing of the adhesive.

(37) In the case of application of a photochemically curable adhesive and with irradiation as shown in FIGS. 2 and 3, the irradiation e.g. with ultrasonic waves and/or microwaves effects a lateral affixing of the metal disk 4 to the coupling element 3. This is understood as a type of pre-affixing, or tacking. This lateral affixing respectively between coupling element and metal disk and between metal disk and piezo element protects these elements against slipping before a final curing occurs.

(38) After transpired pre-affixing, depending on intensity of the irradiation, a fine adjustment, respectively fine orientation, of the individual components of the ultrasonic transducer arrangement can still occur.

(39) A final curing and therewith an affixing can occur, for example, right after the pre-affixing, in a furnace or alternatively by full surface irradiation of the coupling element 3, to the extent that coupling element 3 is transparent relative to the polymerization promoting radiation, e.g. UV radiation.

(40) In a third ultrasonic transducer arrangement of the invention, the applied adhesive can contain a micro-encapsulated, polymerization activating component, which is releasable under the action of ultrasonic waves.

(41) A special advantage of this variant is that the ultrasonic waves of the ultrasonic transducer can burst the micro-encapsulations. In a first frequency, which corresponds to the resonant frequency of the micro-capsules, thus, the capsules are caused to burst. Ultrasonic waves are transmitted as measurement signals with a second frequency. A user can determine a percentage of capsules it would like to burst as a function of the duration of the frequency. Thus, it is possible to pre-affix, to orient and, finally, to affix the metal disk.

(42) The aforementioned securement methods hold preferably both for forming the first as well as also the second adhesive layer.

(43) The irradiation of the lateral regions of the metal disk, respectively the adhesive layers, for pre-affixing can be achieved by positioning a radiation source in this lateral region.

(44) It is, however, also possible to embody the coupling element 3 in such a manner that a free space 8 is present between the edge of the metal disk 4 and the edge of the piezo element and the inner surface of the cavity 7. An ultrasonic transducer with such a coupling element 3 is shown in FIGS. 2 and 3.

(45) The radiation S from the radiation source, thus e.g. from the ultrasonic, microwave- or UV radiator, enters the free space 8 of the coupling element 3 and travels straight to a redirecting surface 9, where the radiation is redirected a. The redirecting surface 9 can be provided with a radiation reflecting layer or an ultrasonic wave reflecting layer. This occurs in FIG. 2 with an angle of 90. In this way, the radiation is directed parallel or essentially parallel to the first and/or second adhesive layer 5, 6 and enables an edge curing for pre-affixing the components, respectively the piezo element 2, the metal disk 4 and the coupling element 3, on top of one another.

(46) Then, a fine orientation of the metal disk or of the piezo element can occur, or a transport step can occur within a manufacturing plant.

(47) Finally, a curing can occur by irradiating centrally located adhesive through the coupling element or by thermally curing the adhesive. In such case, preferably a smaller energy can be expended than in the case of a usual thermal cross-linking without previous photochemical curing.

(48) FIG. 4 shows another advantageous variant, which can be used e.g. for a photochemical curing, an ultrasonic wave- or a microwave activated curing. In such case, the coupling body includes a focusing surface 9. This can be milled into the coupling body and then coated with a layer, e.g. a metal layer, which turns and focuses incoming radiation or ultrasonic waves in the direction of the adhesive layers 5, 6.

(49) FIGS. 5 and 6 show a variant, in the case of which radiation or ultrasonic waves passing through the coupling body 3 are reflected on a redirecting surface 10 laterally in the direction of the adhesive layers 5 and 6. In this version, the redirecting surface is coated with a reflecting layer, which provides a reflecting surface.

(50) FIGS. 7 and 8 show respective variants of the focusing, which supplementally focus the incoming radiation or ultrasonic waves and thereby steer such with targeting onto the lateral region of the adhesive layer.

(51) In FIG. 7, this occurs on a focusing surface 10, which is a reflecting layer applied on the coupling element 3. The contour, respectively bulge, of the focusing surface 10 can be integrally worked into the coupling body 3.

(52) In FIG. 8, the focusing occurs with the aid of a special focusing element 11, which protrudes inwardly into the free space 8. This focusing element 11 provides a focusing surface 10, on which the turning and focusing of radiation or ultrasonic waves occurs. Focusing element 11 can be arranged releasably on the coupling element 3, so that it can be reused in the production process.

(53) Of course, a corresponding focusing element can also be arranged in FIG. 4 in place of the focusing surface 9 there.

(54) In an additional variant (not shown) of the invention, the adhesive layer can be provided with energy conductors, thus e.g. light conductors or sound conductors. These enable the energy- and/or radiation to be input exactly to the position to be adhered.