Ultrasonic transducer for generating and detecting ultrasonic waves in a metallic test object
Patent Information
- Application Number
- AE202603061
- Authority / Receiving Office
- AE · AE
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-03-14
- Filing Date
- 2025-03-12
Smart Images
Figure ABST_ABST
Abstract
Description
Ultrasonic transducer for generating and detecting ultrasonic waves in a metallic test object The present invention relates to an ultrasonic transducer for generating ultrasonic waves in a metallic test object, having at least one magnet and having four sets of conductor track sections, each comprising at least one rectilinear conductor track section extending over a pole of the magnet in a bottom view, wherein the sets of conductor track sections differ in operation due to the direction of the current flow and the conductor track sections extend over the pole at an angle to a longitudinal direction of the pole in the bottom view, and having a control unit for energizing the conductor track sections. Furthermore, the invention relates to an ultrasonic transducer for detecting ultrasonic waves in a metallic test object, having at least one magnet and having four sets of conductor track sections, each comprising at least one rectilinear conductor track section extending over a pole of the magnet in a bottom view, wherein the sets of conductor track sections differ in operation due to the direction of the current flow and the conductor track sections extend over the pole at an angle to a longitudinal direction of the pole in the bottom view, and having a control unit for picking up the signals induced in the conductor track sections. The publication "A new chevron electromagnetic acoustic transducer design for generating shear horizontal guided wave" by Gautham et al, Ultrasonics, Vol. 135, December 2023, presents an ultrasonic transducer arrangement, specifically, an EMAT arrangement, which can be used with a strip-shaped permanent magnet array and a chevron-shaped meander coil for guided SH waves (horizontally polarized shear waves). The track wavelength is not defined by periodically changing magnetic poles, but rather by conductor pieces of the chevron-shaped coil lying obliquely above the magnetic strip or strips. The oblique conductor pieces can excite Lorentz forces in the test object which have both longitudinal and transverse components that cancel each other out in parts, so that the above-mentioned transverse waves result in the far field. In particular, pipelines or flat metal objects such as tank bottoms or semifinished products in the form of metal sheets are used as metallic test objects. In the past, several methods for determining the residual wall thickness at inaccessible points have been described in the literature and / or implemented for industrial use. However, they all have some physical limitations that limit the practical application and the ability for detection and size determination. In the ultrasonic methods for this application, a distinction is made between those which use guided waves and those which use angled volume waves. The "gold standard" for a reliable and quantitative estimation of the residual wall thickness is the normally incident ultrasonic time of flight measurement in a narrow grid. However, this method is very time-consuming and can only be used with appropriate accessibility. Guided waves have the advantage that they propagate over greater distances with little damping. This means that flat test objects such as pipe walls or tank bottoms can be tested relatively quickly and completely without a fine-mesh grid having to be scanned point by point. In addition, inaccessible areas can also be examined. In addition to the classic pulse echo method, the frequency-thickness dependence (dispersion) of the guided wave modes can be used in order to detect the corrosion or erosion thinning of structures using guided waves in a more sophisticated manner. In particular, at least three types of features can be taken into consideration during the inspection: transmission and reflection amplitudes phase and group speed changes (phase shift and time delay) the cutoff phenomena of the guided wavesAll of these features can be applied as a single mode or in a multi-mode approach or in a combination. The sensitivity and the ability to quantify the defect can be significantly increased if, on the one hand, multiple modes are deliberately excited in succession in a sequential test procedure and the components of the same mode reflected and transmitted at an inhomogeneity in the sound path are analyzed and evaluated. On the other hand, the signals which are mode-converted at the defect (both in transmission and in reflection) can also be deliberately analyzed. It has been found that higher-order modes are suitable for surface corrosion in thin sheets, and the same mode displays different sensitivity to corrosion detection at different phase speeds. SH waves are strongly influenced by factors such as surface quality, coating type and thickness, and defect morphology. On the other hand, Lamb waves are additionally influenced by liquid loads on one or both surfaces due to leakage waves. It is an object of the present invention to design an ultrasonic transducer, in particular an EMAT transducer in a more variable manner for the inspection of metallic test objects. The object is achieved by subject matter as claimed in claim 1 and by subject matter as claimed in claim 2. The object is furthermore achieved by a method as claimed in claims 13 and 14 and by subject matter as claimed in claim 15. Advantageous designs of the invention can be found in the dependent claims that refer back to these claims and in the following description. According to the invention, it is provided that in each case two sets of conductor track sections form a first and a second meandering coil, which can be driven via the control unit of the ultrasonic transducer, wherein the control unit is designed to drive the coils in phase or in opposite phase to generate Rayleigh or Lamb waves and in opposite phase or in phase to generate guided SH waves. Furthermore, the object is achieved according to the invention by an above-mentioned ultrasonic transducer for detecting ultrasonic waves, which is distinguished in that two sets of conductor track sections each form a first and a second meandering coil, wherein the control unit is designed to add or subtract the signals to detect Rayleigh or Lamb waves and to subtract or add them to detect guided SH waves. The control unit thus picks up the signals. The control unit can be constructed in multiple parts, such that, for example, the signals are received in a first part of the control unit and are possibly processed later in a second part of the control unit, for example, in an EDP unit separate from the first part of the control unit. Two such ultrasonic transducers according to the invention can be used as a pair of transducers for inspecting metallic test objects, in particular pipelines or metal sheets, wherein one transducer is provided for generating ultrasonic waves and one for detecting ultrasonic waves. However, a corresponding control unit can also be a single ultrasonic transducer which, in terms of circuitry, is designed on the one hand to energize the conductor track sections and subsequently to detect and pick up the signals induced in the conductor track sections. Again, the ultrasonic transducers of the same transducer pair can be used alternately and mutually for generating and detecting ultrasonic waves. Accordingly, an inspection device according to the invention for inspecting pipelines and / or other test objects, which can be regarded as flat bodies for generating the ultrasonic waves, can have one or more such transducers. In the context of the invention, a meandering coil is understood to mean a coil whose rectilinear conductor track sections relevant for the generation of Lorentz forces in the test object extend parallel to one another or in a direction parallel to one another, and wherein parallel conductor track sections of the same coil which are directly adjacent to one another, which, in the bottom view, extend over the pole or poles, are provided with opposite current directions. If multiple poles are used, in particular rectilinear conductor track sections located adjacent to one another with the same current directions in particular also extend overall over multiple poles. Multiple rectilinear conductor track sections of the same current flow direction can thus be arranged on one another, so that a section of the same current direction of the respective coil which is then longer and also covers multiple poles of magnets located adjacent to one another results. In this case, the magnet or magnets are aligned such that, during operation, the magnetic field lines can be assumed to be extending perpendicular to the conductor track sections and in the direction of the test object. In particular, a conductor track section has multiple parallel-extending parts of a conductor track of the respective coil, that is to say a respective coil can have multiple correspondingly meandering windings. The bottom view of the pole is that view in which the respective pole is viewed from the direction of the metallic test object being tested. During operation, the conductor tracks of the coils are located between the pole and the surface of the test object. They extend or run over the pole in this view. The control unit is provided with conventional electronic means for driving the coils and can each apply an alternating current, in particular an operating frequency f, between 100 kHz inclusive and 2 MHz inclusive, to the coils. In particular, the control unit is designed to be able to use different frequencies, such that it is possible to focus on the wall thickness of the object to be tested. The longitudinal direction of the pole relates to the bottom view of the pole and corresponds in the bottom view to a direction in which the length of the pole is measured, in particular wherein the length is greater than the width to be observed transversely thereto. When multiple poles of the same polarity are lined up, for example, bar magnets of polygonal or round cross section, the longitudinal direction taken is that direction in which the length of the identical poles directly lined up is measured, again in the bottom view. When multiple poles having opposite polarities located adjacent to one another in the bottom view are lined up, the longitudinal direction in the bottom view extends parallel to the interface between individual magnets located adjacent to one another. Rayleigh or Lamb waves are generated by the ultrasonic transducer according to the invention by driving in phase or in opposite phase with respect to a straight line extending parallel to the longitudinal direction of the pole in the bottom view if the conductor track sections of the two coils, which are located at the same height with respect to this straight line and on the same pole, have a current direction during operation which points in a different direction in the projection onto this straight line. Then, in the far field in the test object, the transverse components of the Lorentz forces add up in such a way that the longitudinal components of the Lorentz forces remain along the longitudinal direction of the pole in each case. In a coil setup in which the energizing in the projection onto said straight line in a different direction results when these are driven in opposite phase, the forces induced in the far field, i.e. in the test object, add up so that Rayleigh or Lamb waves are then correspondingly generated upon driving in opposite phase, in particular shifted by 180°. Correspondingly, it is the inverse in the generation of guided SH waves. In this case, with regard to the projection of the current directions onto the straight lines extending parallel to the longitudinal direction of the pole, the SH waves are generated when the conductor track sections of the two coils are energized at identical level and via identical poles in identical directions, depending on the setup with in-phase or opposite-phase driving. The same applies to the detection of Rayleigh or Lamb waves. If the projection of the induced current directions of the conductor track sections of the two coils at the same level of the above-described straight lines and above the same pole point in different directions, wherein in-phase signals result, these are added up for the detection of Rayleigh or Lamb waves or subtracted in the case of opposite-phase signals. This is dependent on the setup of the coils and the associated course of the conductor track sections. Insofar as the induced currents of the two conductor track sections of the two coils point in the same direction during projection and opposite-phase signals result, these are to be subtracted for the detection of SH waves. However, if in-phase signals result with an opposing set up, these are to be added up for the detection of SH waves. The invention thus makes it possible to generate both Rayleigh and Lamb waves using the same setup, which with the frequencies to be used enables quasi-instantaneous generation and detection of different wave types at the same location of the object to be tested, and allows a further inspection run or a further measurement setup to be saved. According to the invention, two meandering coils are thus combined and in the bottom view used above the pole of the at least one magnet. In a further embodiment of the invention, the ultrasonic transducer according to the invention is refined in such a way that at least two magnets which are adjacent to one another and are preferably strip-shaped and / or rod-shaped are present, the poles of which, in the bottom view, have alternating polarity in a transverse direction which extends transversely to the longitudinal direction of the pole, wherein the one or more conductor track sections of the sets of conductor track sections located adjacent to one another extend over at least two poles arranged adjacent to one another in the bottom view. Two meandering coils can thus be used above a magnet array, in particular designed as a permanent magnet array, so that, on the one hand, the desired waves can be generated well and a sufficiently clean signal having a good signal-to-noise ratio results for the detection. It is obvious that an enclosure or housing and any fastening means for the coils and magnets can also be added to the device according to the invention. For example, the coils can be covered on the side directed towards the test object with a slide protection, for example, a ceramic layer, which is part of a housing of the ultrasonic transducer. The control unit may have a separate housing. These means are to be selected depending on the setup and are known by the person skilled in the art. The first and the second coil are arranged on the same side of the at least one magnet or of the magnet array, such that the energy introduced into the coil can be transferred deliberately in the direction of the test object to be inspected. This is thus the side which is directed toward the wall in the operating case. Due to the local Lorentz forces acting in the test object with in-phase or opposite-phase driving of the two meandering coils, particle shifts in the longitudinal direction, in particular in the longitudinal direction of the poles, which are used to excite Rayleigh or Lamb waves, result analogously to the preceding and following conditions with respect to the projection of the current directions during operation in the superposition. The local, transverse force components of the Lorentz forces induced in the test object are oriented antiparallel and therefore mutually cancel out. The longitudinal components point in the same direction and are thus amplified, which results in the formation of the longitudinal wave. In contrast, guided SH waves can be generated when one of the two current directions is interchanged due to opposite-phase driving. For the purpose of more precise definition of the forces induced in the test object and to pick up a signal having an improved signal-to-noise ratio, in the bottom view, according to a refinement of the invention, deflections of the conductor track arranged between parallel conductor track sections of the same coil extend outside the at least one pole or on the edge of the at least one magnet. The conductor track sections are thus removed from the area of the greatest magnetic field line density and can be left out when observing the induction for the generation and detection of the ultrasonic waves. In particular, the ultrasonic transducer according to the invention is designed in such a way that conductor track sections of the two coils are assigned to one another in pairs, in particular wherein the conductor track sections of a respective pair intersect or cross in the bottom view. From this, very good formations of the waves to be induced or of the signals to be picked up from these waves can be achieved in the bottom view via the preferably strip-shaped magnet or magnets, in particular via a magnet array comprising at least four, six, or eight permanent magnets. By means of the assignment in pair of the conductor track sections of the two coils, which are located above the same pole and which cross one another, elementary cells can be formed in the bottom view, in which the force effects in the test object advantageous for the generation and detection can be clearly defined and structured. The conductor track sections extend in particular at an angle between 20° and 70° in relation to the longitudinal direction, more preferably at an angle of 30° to 60°, and even more preferably, they are each formed at an angle of 45° in relation to the longitudinal direction, such that ideal Lorentz forces are formed for respective and in particular for both wave types. This again refers to the bottom view. Only the number of degrees is considered, independently of whether the angle is measured in the mathematically positive or negative sense. In particular, the conductor track sections of the two coils are in this case each arranged at an angle of 90° to one another, such that symmetrical forces result both for the longitudinal waves and for the transverse waves. In this case, the conductor track sections of the two coils are aligned in relation to one another in particular in mirror symmetry in relation to a straight line lying parallel to or on the longitudinal axis. In order to be able to generate waves directed in an optimum manner, in particular in the case of pipelines, the conductor track sections are arranged in a surface with a possible curvature which is provided for adaptation to a surface of the test object. According to a refinement of the invention, which is advantageous in particular for sheet metal testing, the conductor track sections of the same coil lie in one plane, notwithstanding any deflections in the area of the intersection of the two coils, wherein this plane is to be aligned in particular perpendicularly to the surface normal of the test object during operation. The setup of an ultrasonic transducer according to the invention is particularly good for pipelines and sheet metal tests if the magnets have a length of three to six track wavelengths in the bottom view. The track wavelength ʎS is the spatial period length of the excited guided ultrasonic mode in the plate and corresponds to the distance between two conductor track sections of the respective coil arranged adjacent to one another and parallel with the same current direction, but with respect to the longitudinal direction. For the purposes of the invention, a plurality of strip-shaped magnets having alternating polarities is preferably arranged adjacent to one another, wherein it is preferably an even plurality. In the bottom view, the magnets have a width of one to six track wavelengths, wherein a strip-shaped magnet having a width that is less than the length of the magnet, based on the bottom view, is preferred. The object stated at the outset is likewise achieved by a method for generating ultrasonic waves, in which an ultrasonic transducer described above or below is provided with meandering coils, which are driven in phase or in opposite phase via a control unit of the ultrasonic transducer to generate Rayleigh or Lamb waves and in opposite phase or in phase to generate guided SH waves. Analogously, for a method according to the invention for detecting ultrasonic waves, the signals of the meandering coils of one of the ultrasonic transducers described above or below are added or subtracted in the control unit of the ultrasonic transducer for detecting Rayleigh or Lamb waves and subtracted or added for detecting guided SH waves. As described above, the control unit can be of single-part or multi-part design. In particular, the parts of the control unit can be a first part of the control unit in the form of electronic means for storing the signals and a second part of the control unit, which receives the data recorded by the first part separately from the first part and which processes the signals according to the invention. The control unit thus represents a one-part or multi-part data recording and evaluation device. Finally, the object stated at the outset is achieved by an inspection device which is designed for inspecting pipelines or for sheet metal testing and which has one or more transducers described above or below. This also has the corresponding advantages. For the relationships with respect to the phases of the signals induced in the coils, reference is made to the statements above and below. Further advantages and details of the invention can be inferred from the following description of the figures. In the schematic figures: Figure 1ashows a diagram of an inspection device according to the invention in a pipeline, Figure 1bshows an ultrasonic transducer according to the invention, Figure 1c shows a first meandering coil, Figure 1d shows a second meandering coil, Figure 2 shows a bottom view of the magnet array from figure 1b in the direction U, Figure 3 shows a part of the subject matter from figure 1b in the bottom view and with forces arising during operation, Figure 4 shows a part of the subject matter from figure 1b with forces arising during operation, Figure 5 shows a bottom view of the magnet array from figure 1b, Figure 6 shows a bottom view of the magnet array from figure 1b having meandering coils with in-phase driving of the two coils, Figure 7 shows the subject matter from figure 5 with opposite-phase driving of the two coils, Figure 8 shows a dispersion diagram for guided SH waves in a 2 mm steel plate, Figure 9 shows a dispersion diagram for Lamb waves in a 2 mm steel plate, Figure 10 shows signal recording and evaluation with an incident Lamb wave by means of a subject matter according to the invention, Figure 11shows signal recording and evaluation with an incident guided SH wave with a subject matter according to the invention, Figure 12 toFigure 15show parts of further subjects according to the invention in a bottom view. Individual technical features of the exemplary embodiments described below may also be combined, in combination with above-described exemplary embodiments and the features of one of the independent claims and any further claims, to form subjects according to the invention. Where appropriate, at least partially functionally identical elements have been provided with identical reference numerals. According to figure 1a, an inspection device 2 according to the invention is designed as an inspection pig for a test object 4 in the form of a pipeline. Propulsion means 6 in the form of cups or discs are arranged on a central body 5 of the inspection pig. In this way, the inspection pig is passively entrained with the flow by the medium located in the pipeline. A plurality of ultrasonic transducers 10 according to the invention is arranged in the circumferential direction around the central body via spring-loaded arms 8, these ultrasonic transducers being provided for generating ultrasonic waves in the pipeline wall and only two of which are shown. Further ultrasonic transducers 12 according to the invention are provided for detecting the ultrasonic waves generated in the pipeline wall and are likewise arranged again in the circumferential direction. A control unit 14 is used to energize the coils present in the ultrasonic transducers 10. In addition, the same control unit 14 or else a further control unit can be designed to pick up the signals induced in the coils of the ultrasonic transducers 12 and to evaluate them. Alternatively, the control unit 14 can also be provided only for picking up the signals and storing them, so that the evaluation itself is carried out in a further part of the control unit, which may not be physically connected to the illustrated part of the control unit. The ultrasonic transducers 10 and 12 according to the invention comprise a plurality of magnets in the form of a magnet array of strip-shaped magnets 18 designed as permanent magnets, which directly abut one another with alternating polarities (figure 1b). During operation, the magnets 18 are generally to be oriented having their north-south orientation perpendicular to the pipeline surface or to the surface of the object to be tested. A longitudinal direction L of the pole of the magnets 18 extends perpendicularly to the north-south orientation A in the direction of the longitudinal extension of the magnets 18. On the side of the ultrasonic transducer to be directed towards the pipeline wall, there are two coils 20 and 22 which are located directly one above the other and which are each designed as meandering or meander-shaped (figures 1c and 1d). With respect to these coils, in-phase driving means in each case a current flow with respect to the view of figures 1c and 1d from the connection point 21 of the coil 20 and from the connection point 23 of the coil 22 above the magnets 18 downward to the connection points 25 and 27. The coils are connected to the control unit via these connection points or connections. The first meandering coil according to figure 1c has conductor track sections 24 which, during operation and in the bottom view U from figure 1b, have the same current direction and which are each constructed from shorter conductor track sections lying one behind another and likewise denoted by 24 below. The current directions are generally indicated by the closed arrow tips of the conductor track sections (figures 3, 4, 6, and 7). Moreover, the coil 20 comprises further conductor track sections 26, which likewise extend over the pole in the bottom view and which differ from the conductor track sections 24 in operation due to an opposite current direction. These conductor track sections 26 can also be subdivided into multiple conductor track sections 26 lying one behind another. Correspondingly, the conductor track sections 24 and 26 form two sets of conductor track sections of the coil 20. This applies analogously to the conductor track sections 28 and 30 of the coil 22. The deflection sections or deflections 32 of the coils 20 and 22 have a length which corresponds to half the track wavelength ʎS. In the bottom view U, they lie outside the pole and are not taken into consideration with regard to any force effects. The conductor track sections 24, 26, 28, and 30 of the sets of conductor track sections of a respective coil 20, 22 each extend parallel or in mutually parallel directions. The conductor track sections 24 or 26 and 28 or 30 can be divided into a series of smaller conductor track sections 24 or 26 and 28 or 30, respectively, which abut one another, but which each have the same current direction. A corresponding division is shown in figures 3 and 4. Via this division of the coils, the elementary cells 34 shown in Figure 2 can be defined, which are used in each case for the subsequent observation of the forces and which generally have a length equal to half the track wavelength ʎS in the longitudinal direction. These elementary cells illustrate the force effect in the test object 4. During operation, the illustrated forces in the pipeline wall arise in these cells and with respect to the respective conductor track sections 24, wherein FL is the Lorentz force acting in the pipeline wall, FL,l is the longitudinal component, and FL,t is the transverse component of the Lorentz force. In general, the poles shown without shading in figure 2 et seq. are north poles and the dotted poles are south poles. In the pipeline wall, the force effects due to the coil 20 shown in figure 3 thus result on the particles present there. The force effects shown in figure 4 are those which result in the pipeline wall on the particles present there due to the coil 22. This takes place in the case of in-phase driving via the connection points 21 and 23. The forces shown in figures 3 and 4 and resulting in the test object 4 are superimposed in the respective elementary cells 34 depending on the driving of the coils 20 and 22, with the result that the effects which are advantageous for generating ultrasonic waves are obtained. Figure 5 shows how the conductor track sections of the two coils 20 and 22 intersect at a 90° angle in the bottom view U in the respective elementary cells 34. In this case, the coils 20 and 22 are arranged on the same side of the magnet array and moreover also close to one another or, as much as possible, in the same plane in order to keep the forces induced in the pipeline wall equal in dimension. It is obvious that the coils are insulated from one another and the deflections of the coils at the intersection point are not considered for the plane formation. The conductor track sections of the coils 20 and 22 are assigned to one another in pairs in the elementary cells 34. They are perpendicular to one another and cross one another. Thus, for example, in the left upper elementary cell 34 from figure 4, a conductor track section 24 is arranged perpendicular to a conductor track section 30. A conductor track section 26 is arranged perpendicular to a conductor track section 28 in the elementary cell 34 lying adjacent to it to the right. When the two meander coils 20 and 22 are driven in-phase, a resulting force is produced in the pipeline wall according to figure 6 on the particles present there in the direction of the double arrow 36, and thus a longitudinal or Lamb wave extending in the propagation direction 38 is generated. For the case that one of the two coils is driven at its opposite end, the same result would accordingly be produced with opposite-phase driving. Corresponding to the above, a resulting Lorentz force in the test object 4 is then obtained with opposite-phase driving of the meander coils depending on the elementary cell 34, which Lorentz force results in a particle displacement in the pipeline wall in the direction transverse to the propagation direction 38 according to the double arrow 40. The particle displacement in the pipeline wall is thus transverse to the propagation direction of the ultrasonic wave, by which an SH wave can be generated. In the bottom view from figures 5 to 7, it can be seen that the magnet array composed of the four strip-shaped magnets 18 located adjacent to one another has a width of 2 track wavelengths ʎS and a length of 3 track wavelengths ʎS. The propagation direction 38 is parallel to the longitudinal direction L of a pole in the bottom view U from figure 1b. With the exception of the crossing points, the conductor track sections of a respective coil 20, 22 lie in one plane. There is a mathematical-physical relationship between the operating frequency f of the different plate wave modes, the thickness d of the test object 4 (wall thickness), and the track wavelength λs, which results from the solution of the wave equation under the special boundary conditions of a plate-shaped waveguide. These solutions are usually represented in the form of dispersion diagrams. By means of the ultrasonic transducers according to the invention, guided SH waves depicted by way of example in the dispersion diagram from figure 8 can be generated in a 2 mm steel plate, wherein the speed in mm / µs is plotted on the y-axis and the frequency in MHz is plotted on the x-axis. The lines 42, 44 and 46 represent the phase speeds of the AS1 mode, the SS1 mode, and the AS2 mode. The dashed lines 48, 50, 52, and 54 correspond to the group speeds for the SS0 mode, the AS1 mode, the SS1 mode, and the AS2 mode. The phase speed of the SS0 mode corresponds to the group speed for the SS0 mode. The exemplary dispersion diagram for Lamb waves in a 2 mm steel plate is shown in figure 9, wherein the lines 56, 58, 60, and 62 represent the phase speeds for the A0 mode, the S0 mode, the A1 mode, and the S1 mode, while the dashed lines 64, 66, 68, and 70 each indicate the group speeds for the corresponding modes in the same order (A0, S0, A1, and S1 modes). The operating frequencies f can be read from these diagrams if a zero-point straight line is drawn having the slope of the track wavelength. The points of intersection with the mode curves then result in the operating points by way of frequency and phase velocity. The operating points of the lowest 4 SH and Lamb wave modes in a 2 mm steel plate at 4 mm track wavelength are shown below with f=operating frequency, cp=phase speed, and cg=group velocity.guided SH waveLamb wavemodefcpcgmodefcpcg[kHz][mm / µs][mm / µs][kHz][mm / µs][mm / µs]SS0 8003.203.20A0 6202.473.22AS111304.532.27S011304.532.26SS117907.161.43A115206.103.73AS2253010.121.01S115806.323.79 Figures 10 and 11 show the signals resulting in the meandering coils 20 and 22 for an ultrasonic transducer 12 designed for detecting ultrasonic waves. Figure 10 shows the signals in the case of a Lamb wave, wherein the coils are arranged in accordance with figure 5. In the top left diagram of figure 10, the received signal of the meandering coil 20 is shown, in the diagram at the bottom left, that of the coil 22 is shown. At the top right, in the case of a Lamb wave, a sum signal to be clearly detected results due to the in-phase induction of the signals, while the difference signal disappears. Conversely, in the case of an incident guided SH wave, in which opposite-phase signals are induced in the meander coil, shown in the two left diagrams of figure 11, these then disappear in the addition and are clearly recognizable in the subtraction as a difference signal (right diagrams of figure 11). Instead of a setup of the invention from figure 5, the same effect can already be produced in individual applications in a construction from figure 12 using only a single magnet 18 and a single coil. In this case, the ultrasonic transducer forms only two elementary cells 34 and also has a correspondingly small dimensioning of only half a track wavelength transverse to its longitudinal direction and a length of only one track wavelength. Instead of an exactly right-angled arrangement, the ultrasonic transducers can also be provided with meandering coils which are not perpendicular to one another in the elementary cells but are angled at an angle between 20° and 70° in relation to the longitudinal direction. In the variants of figures 13 and 14, only one coil is shown in each case for the sake of better clarity. At an angle ɑ of approximately 63°, a longitudinal force component of approximately 90% results, while the transverse force component results at 44.7% in relation to a conductor track which otherwise extends at a 45° angle in relation to the longitudinal direction L. As a result, the longitudinal force component can thus be increased, which can have advantages for the generation of a corresponding Lamb wave. With a steeper arrangement of the conductor track at an angle ɑ of approximately only 26° (figure 14), the transverse force component increases, so that this can be advantageous for the generation of guided SH waves. However, an alignment of the conductor track sections at an angle of 45° with respect to the longitudinal direction L is particularly preferred, such that guided Lamb and SH waves are generated equally well, independently of the fact that they can have different amplitudes. An array of bar magnets of round cross section, which lie adjacent to one another with alternating polarities in the transverse direction to the longitudinal direction L, but are located adjacent to one another with the same polarity in the longitudinal direction L, thus results in an array of magnets 18 of the same polarity, which are likewise strip-shaped again (figure 15). Both longitudinal waves and transverse waves are also generated here, wherein the elementary cells are then formed only over the surface of the poles according to the view in figure 15 and are parts of the conductor track sections outside the elementary cells 34.
Claims
1. An ultrasonic transducer for generating ultrasonic waves in a metallic test object (4), having at least one magnet (18) and having four sets of conductor track sections, each comprising at least one rectilinear conductor track section (24, 26, 28, 30) extending in a bottom view over a pole of the magnet (18), wherein the sets of conductor track sections differ during operation due to the direction of the current flow and the conductor track sections (24, 26, 28, 30) in the bottom view (U) extend at an angle to a longitudinal direction (L) of the at least one pole over the latter, and having a control unit for energizing the conductor track sections (24, 26, 28, 30), characterized in that two sets of conductor track sections each form a first and a second meandering coil (20, 22), which are drivable via the control unit (14) of the ultrasonic transducer, wherein the control unit (14) is designed to drive the coils (20, 22) in an in-phase or opposite-phase manner to generate Rayleigh or Lamb waves and to drive them in an opposite-phase or in-phase manner to generate guided SH waves. 2.An ultrasonic transducer for detecting ultrasonic waves in a metallic test object (4), having at least one magnet (18) and having four sets of conductor track sections, each comprising at least one rectilinear conductor track section (24, 26, 28, 30) extending in a bottom view (U) over a pole of the magnet (18), wherein the sets of conductor track sections differ during operation due to the direction of the current flow and the conductor track sections (24, 26, 28, 30) in the bottom view extend at an angle to a longitudinal direction of the at least one pole over the latter, and having a control unit (14) for picking up the signals induced in the conductor track sections (24, 26, 28, 30), characterized in that two sets of conductor track sections each form a first and a second meandering coil (20, 22), wherein the control unit (14) is designed to add or subtract the signals to detect Rayleigh or lamb waves and to subtract or add them to detect guided SH waves. 3.The ultrasonic transducer as claimed in one of the preceding claims, characterized by at least two magnets (18) which are located adjacent to one another and are preferably strip-shaped and / or rod-shaped, the poles of which have alternating polarity in the bottom view (U) in a transverse direction which extends transversely to the longitudinal direction (L) of the pole, wherein the conductor track sections (24, 26, 28, 30) of the set of conductor track sections in the bottom view (U) extend over at least two poles arranged adjacent to one another.4.The ultrasonic transducer as claimed in any one of the preceding claims, characterized in that the first and second coils (20, 22) are arranged on the same side of the at least one magnet (18). 5.The ultrasonic transducer as claimed in any one of the preceding claims, characterized in that, in the bottom view, deflections (32) arranged between conductor track sections (24, 26, 28, 30) of the same coil (20, 22) extend outside the at least one pole or on the edge of the at least one magnet (18).6.The ultrasonic transducer as claimed in any one of the preceding claims, characterized in that conductor track sections (24, 26, 28, 30) of the two coils (20, 22) are assigned to one another in pairs, in particular wherein the conductor track sections (24, 26, 28, 30) of a respective pair intersect in the bottom view (U).7.The ultrasonic transducer as claimed in claim 6, characterized in that the conductor track sections (24, 26, 28, 30) are angled at an angle between 20° and 70° in relation to the longitudinal direction (L), in particular are at an angle of 45° in relation to the longitudinal direction (L).8.The ultrasonic transducer as claimed in claim 6 or 7, characterized in that the conductor track sections (24, 26, 38, 30) of the two coils (20, 22) intersect at an angle of 90°. 9.The ultrasonic transducer as claimed in any one of the preceding claims, characterized in that the conductor track sections (24, 26, 28, 30) extend in a surface having any curvature that is provided for adaptation to a surface of the test object (4). 10.The ultrasonic transducer as claimed in claim 9, characterized in that the conductor track sections (24, 26, 28, 30) of the same coil (20, 22) lie in one plane. 11.The ultrasonic transducer as claimed in claim 10, characterized in that the magnets (18) have a length of 3 to 6 track wavelengths in the bottom view.
12. The ultrasonic transducer as claimed in claim 11, characterized in that the magnets have a width of 1 to 6 track wavelengths in the bottom view.13.A method for generating ultrasonic waves in a metallic test object, using an ultrasonic transducer as claimed in any one of the preceding claims comprising claim 1, characterized in that the meandering coils are driven in an in-phase or opposite-phase manner via a control unit (14) of the ultrasonic transducer to generate Rayleigh or lamb waves and in an opposite-phase or in-phase manner to generate guided SH waves. 14.A method for detecting ultrasonic waves in a metallic test object, using an ultrasonic transducer as claimed in any one of the preceding claims comprising claim 2, characterized in that the signals of the meandering coils are added or subtracted in the control unit (14) of the ultrasonic transducer to detect Rayleigh or lamb waves and subtracted or added to detect guided SH waves. 15.An inspection device for inspecting pipelines or for sheet metal testing, characterized by one or more ultrasonic transducers as claimed in any one of claims 1 to 12.