Ultrasonic transducer for generating and detecting ultrasonic waves in a metallic test object

Abstract

The invention relates to an ultrasonic transducer for generating ultrasonic waves in a metallic test object, having at least one magnet and having four conductor track portion sets, each comprising at least one rectilinear conductor track portion extending over a pole of the magnet in a bottom view, wherein the conductor track portion sets differ during operation in terms of the current flow direction, and the conductor track portions extend over the at least one pole at an angle to a longitudinal direction of said at least one pole in the bottom view, and having a control unit for supplying current to the conductor track portions, wherein in each case two conductor track portion sets form a first and a second meandering coil which can be controlled via the control unit of the ultrasonic transducer, wherein the control unit is designed to control the coils in phase or in phase opposition in order to generate Rayleigh or Lamb waves and in phase opposition or in phase in order to generate guided SH waves. The invention furthermore relates to a method for generating ultrasonic waves in a metallic test object using an ultrasonic transducer and to an inspection device for inspecting pipelines or for sheet metal testing.

Description

[0001] Ultrasonic transducer for generating and detecting ultrasonic waves in a metallic test object

[0002] The present invention relates to an ultrasonic transducer for generating ultrasonic waves in a metallic test object, having at least one magnet and four sets of conductor track sections, each comprising at least one rectilinear conductor track section running over a pole of the magnet in a bottom view, wherein the sets of conductor track sections differ in operation by the direction of the current flow and the conductor track sections run over the pole in the bottom view at an angle to a longitudinal direction of the pole, as well as having a control unit for supplying current to 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 four sets of conductor track sections, each comprising at least one rectilinear conductor track section running over a pole of the magnet in a bottom view, wherein the sets of conductor track sections differ in operation by the direction of the current flow and the conductor track sections run over the pole in the bottom view at an angle to the longitudinal direction of the pole, as well as having a control unit for receiving the signals induced in the conductor track sections.

[0003] The publication "A new chevron electromagnetic acoustic transducer design for generating shear horizontal guided waves" by Gautham et al., Ultrasoncis, Vol. 135, December 2023, presents an ultrasonic transducer arrangement, namely an EMAT arrangement, which can be used for guided SH waves (horizontally polarized shear waves) with a strip-shaped permanent magnet array and a chevron-shaped meander coil. The track wavelength is not defined by periodically alternating magnetic poles, but by conductor sections of the chevron-shaped coil arranged diagonally above the magnetic strip(s). The diagonal conductor sections can excite Lorentz forces in the test object that have both longitudinal and transverse components, which partially cancel each other out, resulting in the aforementioned transverse waves in the far field.

[0004] The metallic test objects used are, in particular, pipelines or flat metal objects such as tank bottoms or semi-finished products in the form of sheet metal.

[0005] In the past, several methods for determining residual wall thickness in inaccessible locations have been described in the literature and / or implemented for technical applications. However, they all have some physical limitations that restrict their practical application and their ability to detect and sizing.

[0006] Ultrasound methods for this application are divided into those that use guided waves and those that use angled bulk waves.

[0007] The "gold standard" for a reliable and quantitative estimate of the residual wall thickness is normally incident ultrasonic transit time measurement in a narrow grid. However, this method is very time-consuming and can only be used where appropriate accessibility is available.

[0008] Guided waves have the advantage of propagating over longer distances with low attenuation. This means that flat specimens such as pipe walls or tank bottoms can be inspected relatively quickly and completely without the need to scan a fine-mesh grid point by point. Furthermore, even inaccessible areas can be examined. In addition to the classic pulse-echo method, the frequency-thickness dependence (dispersion) of the guided wave modes can be used to more sophisticatedly detect corrosion or erosion thinning of structures using guided waves. In particular, at least three types of features can be considered during inspection:

[0009] • Transmission and reflection amplitudes

[0010] • Phase and group velocity changes (phase shift and time delay)

[0011] • the cutoff phenomena of the guided waves

[0012] All of these features can be applied as a single mode, in a multimode approach, or in combination. The sensitivity and ability to quantify the defect can be significantly increased if, on the one hand, several modes are specifically excited one after the other in a sequential test procedure and the reflected and transmitted components of the same mode at an inhomogeneity in the sound path are analyzed and evaluated. On the other hand, the mode-converted signals (both in transmission and reflection) at the defect can also be specifically analyzed. Higher-order modes have been found to be suitable for superficial corrosion in thin sheets, and at different phase velocities, the same mode exhibits different sensitivity for corrosion detection.

[0013] SH waves are strongly influenced by factors such as surface texture, coating type and thickness, and defect morphology. On the other hand, Lamb waves are additionally influenced by fluid loading on one or both surfaces due to leakage waves.

[0014] It is an object of the present invention to make an ultrasonic transducer, in particular an EMAT transducer, more variable for the inspection of metallic test objects.

[0015] The object is achieved by an object according to claim 1 and by an object according to claim 2. Furthermore, the object is achieved by a method according to claims 13 and 14 and by an object according to claim 15. Advantageous embodiments of the invention can be found in the subclaims that refer back to these claims and in the following description. According to the invention, two sets of conductor track sections each form a first and a second meandering coil that can be controlled via the control unit of the ultrasonic transducer, wherein the control unit is designed to control the coils in phase or antiphase to generate Rayleigh or Lamb waves and in phase or antiphase to generate guided SH waves.

[0016] Furthermore, the object is achieved according to the invention by an ultrasonic transducer for detecting ultrasonic waves as described above, which is characterized 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 for detecting Rayleigh or Lamb waves and to subtract or add them for detecting guided SH waves. The control unit thus receives the signals. The control unit can be constructed in several parts, so that, for example, the signals are received in a first part of the control unit and, if necessary, later processed in a second part of the control unit, for example in an IT unit separate from the first part of the control unit.

[0017] Two such ultrasonic transducers according to the invention can be used as a transducer pair for the inspection of metallic test objects, in particular pipelines or sheet metal, with one transducer being provided for generating and one for detecting ultrasonic waves. However, with an appropriate control unit, this can also be a single ultrasonic transducer, which is circuit-wise configured to supply current to the conductor track sections and subsequently to detect and record the signals induced in the conductor track sections. Again, the ultrasonic transducers of the same transducer pair can be used alternately and reciprocally for generating and detecting ultrasonic waves.

[0018] 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 comprise one or more such transducers.

[0019] For the purposes of the invention, a meandering coil is understood to be one whose straight conductor track sections relevant for generating Lorentz forces in the test object run parallel to one another or in a parallel direction, and wherein directly adjacent, parallel conductor track sections of the same coil, which run over the pole(s) when viewed from below, are provided with opposite current directions. When multiple poles are used, in particular adjacent straight conductor track sections with the same current directions extend overall, in particular over multiple poles. Multiple straight conductor track sections with the same current flow direction can thus be arranged next to one another, resulting in a longer section of the same current direction for the respective coil, which also covers multiple poles of adjacent magnets.The magnet(s) are aligned in such a way that during operation the magnetic field lines can be assumed to be perpendicular to the conductor track sections and in the direction of the test object.

[0020] In particular, a conductor track section has several parallel parts of a conductor track of the respective coil, ie a respective coil can have several windings formed in a corresponding meandering shape.

[0021] The bottom view of the pole is the view from the direction of the metallic test object being tested. During operation, the coil conductors are located between the pole and the surface of the test object. In this view, they run or extend over the pole.

[0022] The control unit is equipped with conventional electronic means for controlling the coils and can supply them with an alternating current, in particular with an operating frequency f between 100 kHz and 2 MHz. In particular, the control unit is designed to be able to use different frequencies, allowing adjustment to the wall thickness of the object to be tested.

[0023] The longitudinal direction of the pole refers to the bottom view of the pole and corresponds to a direction in which the length of the pole is measured in the bottom view, in particular where the length is greater than the width viewed perpendicular to it. When several poles of the same polarity are arranged in a row, for example in the cross-section of square or round bar magnets, the longitudinal direction is taken to be the direction in which the length of the identical poles directly next to one another is measured, again in the bottom view. When several poles are arranged in a row with opposite polarities next to one another in the bottom view, the longitudinal direction in the bottom view runs parallel to the interface between individual, adjacent magnets.

[0024] With respect to a straight line running parallel to the longitudinal direction of the pole when viewed from below, the ultrasonic transducer according to the invention generates Rayleigh or Lamb waves via in-phase or anti-phase control 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 that points in a different direction when projected onto this straight line. Then, in the far field in the test object, the transverse components of the Lorentz forces add up such that the longitudinal components of the Lorentz forces remain along the longitudinal direction of the pole.

[0025] In a coil setup where the current is applied in different directions when projected onto the straight line in question, when the coils are driven in antiphase, the forces induced in the far field, i.e. in the test object, add up in such a way that Rayleigh or Lamb waves are generated when the drive is in antiphase, in particular when shifted by 180°. The opposite is true when generating guided SH waves. With regard to the projection of the current directions onto the straight lines running parallel to the longitudinal direction of the pole, the SH waves are generated when the conductor track sections of the two coils of identical height and over identical poles are energized in identical directions, depending on the setup, with in-phase or antiphase drive.

[0026] The same applies to the detection of Rayleigh or Lamb waves. If the projection of the induced current directions of the conductor sections of the two coils at the same height of the above-described straight line and above the same pole point in different directions, resulting in in-phase signals, these are added together to detect Rayleigh or Lamb waves, or subtracted in the case of out-of-phase signals. This depends on the setup of the coils and the associated course of the conductor sections.

[0027] If the induced currents of the two conductor sections of the two coils point in the same direction during projection and result in antiphase signals, these must be subtracted to detect SH waves. However, if in-phase signals result from an opposite setup, they must be added together to detect SH waves. The invention thus makes it possible to generate both Rayleigh and Lamb waves with one and the same setup. This allows for the quasi-instantaneous generation and detection of different wave types at the same location on the object under test at the frequencies used, eliminating the need for an additional inspection run or measurement setup.

[0028] According to the invention, two meandering coils are thus combined and inserted above the pole of the at least one magnet in the bottom view. In a further embodiment of the invention, the ultrasonic transducer according to the invention is further developed such that at least two adjacent and preferably strip- and / or rod-shaped magnets are present, the poles of which have alternating polarity in a transverse direction running transversely to the longitudinal direction of the pole in the bottom view, wherein the one or more adjacent conductor track sections of the sets of conductor track sections run over at least two adjacent poles in the bottom view.Two meander-shaped coils can thus be used over 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 on the other hand a sufficiently clean signal with a good signal-to-noise ratio is obtained for detection.

[0029] It is understood that the device according to the invention may also include a housing or casing, as well as any fastening means for the coils and magnets. For example, the coils can be covered on the side facing the test object with a slip protection, such as a ceramic layer, which is part of a housing for the ultrasonic transducer. The control unit may have a separate housing. These means can be selected by a person skilled in the art depending on the setup and are known.

[0030] The first and second coils are arranged on the same side of the at least one magnet or the magnet array, so that the energy introduced into the coil can be directed in a targeted manner toward the test object to be inspected. This is the side facing the wall during operation.

[0031] Due to the local Lorentz forces acting in the test object when the two meandering coils are driven in phase or in phase opposition, the superposition of the two coils results in particle displacements in the longitudinal direction, particularly in the longitudinal direction of the poles, analogous to the above and below conditions regarding the projection of the current directions during operation. These displacements serve to excite Rayleigh or Lamb waves. The local, transverse force components of the Lorentz forces induced in the test object are aligned antiparallel and therefore cancel each other out. The longitudinal components point in the same direction and thus reinforce each other, leading to the formation of the longitudinal wave. However, if one of the two current directions is reversed due to antiphase control, guided SH waves can be generated.

[0032] For the purpose of more precisely defining the forces induced in the test object and for recording a signal with an improved signal-to-noise ratio, according to a further development of the invention, deflections of the conductor track arranged between parallel conductor track sections of the same coil run outside of the at least one pole or on the edge of the at least one magnet in the bottom view. The conductor track sections are thus removed from the area of ​​greatest magnetic field line density and can be ignored when considering the induction for the generation and detection of ultrasonic waves.

[0033] In particular, the ultrasonic transducer according to the invention is designed such that conductor track sections of the two coils are assigned to each other in pairs, in particular with the conductor track sections of a respective pair intersecting or crossing each other in the bottom view. This allows for very good formation of the waves to be induced or the signals to be recorded in the bottom view via the preferably strip-shaped magnet(s), in particular via a magnet array comprising at least four, six, or eight permanent magnets.

[0034] By assigning the conductor track sections of the two coils, which are located over the same pole and which cross each other, in pairs, unit cells can be formed in the bottom view in which the force effects in the test object that are advantageous for the generation and detection can be clearly defined and structured.

[0035] The conductor track sections run in particular at an angle between 20° and 70° 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° to the longitudinal direction, so that ideal Lorentz forces are formed for each and in particular for both wave types. This again refers to the bottom view. Only the number of degrees is taken into account, regardless of whether the angle is measured in the mathematically positive or negative sense. In particular, the conductor track sections of the two coils are each arranged at an angle of 90° to one another, so that symmetrical forces result for both the longitudinal and the transverse waves. The conductor track sections of the two coils are aligned in particular mirror-symmetrical to one another with respect to a straight line lying parallel to or on the longitudinal axis.

[0036] In order to be able to generate optimally directed waves, especially in pipelines, the conductor track sections are arranged in a surface with a possible curvature, which is intended to adapt to a surface of the test object.

[0037] According to a further development of the invention, which is particularly advantageous for sheet metal testing, the conductor track sections of the same coil lie in one plane, regardless of any deflections in the area of ​​the intersection of the two coils, which plane is to be aligned in particular perpendicular to the surface normal of the test object during operation.

[0038] The setup of an ultrasonic transducer according to the invention is particularly suitable for pipeline and sheet metal inspections when the magnets have a length of three to six track wavelengths when viewed from below. The track wavelength Δs is the spatial period length of the excited guided ultrasonic mode in the plate and corresponds to the distance between two adjacent and parallel conductor track sections of the respective coil with the same current direction, but relative to the longitudinal direction.

[0039] For the purposes of the invention, a plurality of strip-shaped magnets with alternating polarities are preferably arranged side by side, preferably in an even number. The magnets have a width of one to six track wavelengths when viewed from below, with a strip-shaped magnet having a width that is less than the length of the magnet, as viewed from below, being preferred.

[0040] The object posed at the outset is also achieved by a method for generating ultrasonic waves, in which a previously or subsequently described ultrasonic transducer is provided with meander-shaped coils, which are controlled via a control unit of the ultrasonic transducer in phase or antiphase to generate Rayleigh or Lamb waves, and in phase or antiphase to generate guided SH waves. Analogously, for a method according to the invention for detecting ultrasonic waves, the signals of the meander-shaped coils of one of the previously or subsequently described ultrasonic transducers are added or subtracted in the control unit of the ultrasonic transducer to detect Rayleigh or Lamb waves, and subtracted or added to detect guided SH waves. The control unit can be designed as a single-part or multi-part unit, as described above.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, as well as 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 single- or multi-part data recording and evaluation device.

[0041] Finally, the problem posed at the beginning is solved with an inspection device designed for inspecting pipelines or sheet metal and featuring one or more of the transducers described above or below. This device also offers the corresponding advantages.

[0042] For the relationships regarding the phases of the signals induced in the coils, reference is made to the above and the following.

[0043] Further advantages and details of the invention can be found in the following description of the figures. Schematically shown:

[0044] Fig. 1a is a schematic diagram of an inspection device according to the invention in a pipeline,

[0045] Fig. 1 b shows an ultrasonic transducer according to the invention,

[0046] Fig. 1c a first meander-shaped coil, Fig. 1d a second meander-shaped coil,

[0047] Fig. 2 is a bottom view of the magnet array according to Fig. 1 b in direction U,

[0048] Fig. 3 shows a part of the article according to Fig. 1 b in a bottom view and with forces arising during operation,

[0049] Fig. 4 shows a part of the object according to Fig. 1 b with forces arising during operation,

[0050] Fig. 5 is a bottom view of the magnet array according to Fig. 1 b,

[0051] Fig. 6 a bottom view of the magnet array according to Fig. 1 b with meandering

[0052] Coils with in-phase control of both coils,

[0053] Fig. 7 shows the object according to Fig. 5 with antiphase control of the two coils,

[0054] Fig. 8 a dispersion diagram for guided SH waves in a 2 mm steel plate,

[0055] Fig. 9 shows a dispersion diagram for Lamb waves in a 2 mm steel plate, Fig. 10 shows signal recording and evaluation of an incident Lamb wave using an article according to the invention,

[0056] Fig. 11 Signal recording and evaluation of an incident guided SH wave in an object according to the invention,

[0057] Fig. 12 to

[0058] Fig. 15 Parts of further objects according to the invention in a bottom view.

[0059] Individual technical features of the exemplary embodiments described below can also be combined with previously described exemplary embodiments as well as the features of one of the independent claims and any further claims to form subject matter according to the invention. Where appropriate, elements that are at least partially functionally equivalent are provided with identical reference numerals.

[0060] 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, as shown in Fig. 1a. Propulsion means 6 in the form of cups or discs are arranged on a central body 5 of the inspection pig. The inspection pig, along with the medium in the pipeline, is passively carried along with the flow by means of these. A plurality of ultrasonic transducers 10 according to the invention are arranged circumferentially around the central body via spring-loaded arms 8. These transducers are 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 also arranged circumferentially.

[0061] A control unit 14 serves to apply power to the coils present in the ultrasonic transducers 10. Furthermore, the same control unit 14 or a further control unit can be configured to receive the signals induced in the coils of the ultrasonic transducers 12 and evaluate them. Alternatively, the control unit 14 can also be provided solely for receiving the signals and storing them, so that the evaluation itself can be performed in a further part of the control unit, which may not be physically connected to the part of the control unit shown.

[0062] 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 lie directly next to one another with alternating polarities (Fig. 1b). During operation, the magnets 18 are to be aligned with their north-south orientation generally perpendicular to the pipeline surface or the surface of the object to be tested. A longitudinal direction L of the pole of the magnets 18 runs perpendicular to the north-south orientation A in the direction of the longitudinal extent of the magnets 18. On the side of the ultrasonic transducer facing the pipeline wall, there are two coils 20 and 22 arranged directly above one another, each of which has a meandering or meander-shaped design (Figs. 1c and 1d). With regard to these coils, in-phase control means a current flow with respect to the view in Fig.1c and 1d from connection point 21 of coil 20 and from connection point 23 of coil 22 above magnets 18 downwards to connection points 25 and 27. The coils are connected to the control unit via these connection points or connections.

[0063] The first meandering coil according to Fig. 1c has conductor track sections 24 which, during operation and in the bottom view U according to Fig. 1b, have the same current direction and which are each made up of shorter conductor track sections arranged one behind the other, also designated 24 below. The current directions are generally indicated by the closed arrowheads of the conductor track sections (Figs. 3, 4, 6 and 7). In addition, the coil 20 comprises further conductor track sections 26 which, in the bottom view, also run over the pole and which, during operation, differ from the conductor track sections 24 in that they have an opposite current direction. These conductor track sections 26 can also be divided into several conductor track sections 26 arranged one behind the other. Accordingly, the conductor track sections 24 and 26 form two sets of conductor track sections of the coil 20. The same applies to the conductor track sections 28 and 30, respectively, of the coil 22. The deflection sections orDeflectors 32 of coils 20 and 22 have a length corresponding to half the coil length wave length Δs. They are located outside the pole in the bottom view U and are not considered with regard to any force effects. The conductor track sections 24, 26, 28, and 30 of the conductor track section sets of a respective coil 20, 22 each run parallel or in mutually parallel directions.

[0064] The conductor track sections 24 or 26 and 28 or 30 can be divided into a series of adjacent smaller conductor track sections 24 or 26 and 28 or 30, each of which, however, has the same current direction. A corresponding division is shown in Figs. 3 and 4. This division of the coils allows the definition of the unit cells 34 shown in Fig. 2. These cells are used for the subsequent analysis of the forces and generally have a length in the longitudinal direction equal to half the track wavelength Δs. These unit cells illustrate the force effect in test object 4.

[0065] During operation, the forces shown in the pipe wall arise in these cells and in relation to the respective conductor track sections 24, where FL is the Lorentz force acting in the pipe wall, FL,I is the longitudinal component, and Fi,t is the transverse component of the Lorentz force. In general, in Figures 2ff, the poles shown without hatching are north poles and the dotted poles are south poles.

[0066] In the pipe wall, the forces shown in Fig. 3 therefore arise on the particles present there due to the coil 20. The forces shown in Fig. 4 are those that arise in the pipe wall on the particles present there due to the coil 22. This occurs with in-phase control via the connection points 21 and 23. The forces shown in Figs. 3 and 4 and resulting in the test object 4 are superimposed in the respective elementary cells 34 depending on the control of the coils 20 and 22, so that the advantageous effects for generating ultrasonic waves arise.

[0067] Fig. 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 unit cells 34. Coils 20 and 22 are arranged on the same side of the magnet array and, moreover, close to one another or as close as possible to the same plane in order to keep the forces induced in the pipeline wall constant. It is understood 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.

[0068] In the unit cells 34, the conductor track sections of the coils 20 and 22 are assigned to one another in pairs. They are perpendicular to one another and intersect. For example, in the upper left unit cell 34 according to Fig. 4, a conductor track section 24 is arranged perpendicular to a conductor track section 30. In the unit cell 34 adjacent to it on the right, a conductor track section 26 is arranged perpendicular to a conductor track section 28. When the two meander coils 20 and 22 are controlled in phase, a resultant force on the particles present in the pipe wall in the direction of the double arrow 36 is produced, as shown in Fig. 6, and thus a longitudinal or Lamb wave traveling in the propagation direction 38 is generated. If one of the two coils is controlled at its opposite end, the same result would occur with antiphase control.

[0069] According to the above, when the meander coils are driven in antiphase, depending on the unit cell 34, a resulting Lorentz force is generated in the test object 4, which leads to a particle displacement in the pipe wall in a direction transverse to the propagation direction 38 according to the double arrow 40. The particle displacement in the pipe wall is thus transverse to the propagation direction of the ultrasonic wave, which can generate an SH wave.

[0070] In the bottom view according to Figs. 5 to 7, it can be seen that the magnet array consisting of the four adjacent strip-shaped magnets 18 has a width of 2 track wavelengths Δs and a length of 3 track wavelengths Δs. The propagation direction 38 is parallel to the longitudinal direction L of a pole in the bottom view U according to Fig. 1 b. With the exception of the intersection points, the conductor track sections of a respective coil 20, 22 lie in one plane.

[0071] 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 As, which results from the solution of the wave equation under the special boundary conditions of a plate-shaped waveguide. These solutions are usually presented in the form of dispersion diagrams. Using the ultrasonic transducers according to the invention, guided SH waves can be generated in a 2 mm steel plate, as shown by way of example in the dispersion diagram in Fig. 8, with the velocity in mm / ps being plotted on the y-axis and the frequency in MHz on the x-axis. Lines 42, 44, and 46 represent the phase velocities of the AS1 mode, the SS1 mode, and the AS2 mode, respectively. The dashed lines 48, 50, 52, and 54 correspond to the group velocities for the SSO mode, the AS1 mode, the SS1 mode, and the AS2 mode, respectively.The phase velocity of the SSO mode corresponds to the group velocity for the SSO mode.

[0072] The exemplary dispersion diagram for Lamb waves in a 2 mm steel plate is shown in Fig. 9, where lines 56, 58, 60 and 62 represent the phase velocities for the A0 mode, the SO mode, the A1 mode and the S1 mode, while the dashed lines 64, 66, 68 and 70 each indicate the group velocities for the corresponding modes in the same order (AO, SO, A1 and S1 mode).

[0073] The operating frequencies f can be read from these diagrams by plotting a zero-point line with the slope of the track wavelength. The intersection points with the mode curves then yield the operating points through frequency and phase velocity. The operating points of the lowest four SH and Lamb wave modes in a 2 mm steel plate at a 4 mm track wavelength are shown below, where f = operating frequency, c = P =phase velocity and c g =Group velocity.

[0074] 10 and 11 show the signals resulting from the meandering coils 20 and 22 for an ultrasonic transducer 12 designed to detect ultrasonic waves. Fig. 10 shows the signals in the case of a Lamb wave, with the coils arranged as in Fig. 5. The upper left diagram of Fig. 10 shows the received signal of the meandering coil 20, and the lower left diagram shows that of coil 22. In the case of a Lamb wave, in the upper right, due to the in-phase induction of the signals, a clearly detectable sum signal results, while the difference signal disappears. The opposite is true in the case of an incident, guided SH wave, in which anti-phase signals are induced in the meandering coil, shown in the two left-hand diagrams of Fig. 11, these then disappear in the addition and are clearly recognizable as a difference signal in the subtraction (right-hand diagrams of Fig. 11).

[0075] Instead of a setup of the invention according to Fig. 5, the same effect can be generated even in individual applications with a structure according to Fig. 12 with just a single magnet 18 and a simple coil. In this case, the ultrasonic transducer forms only two unit cells 34 and also has correspondingly small dimensions of only half a track wavelength transverse to its longitudinal direction and only a length of one track wavelength. Instead of an exactly right-angled arrangement, the ultrasonic transducers can also be provided with meander-shaped coils that are not perpendicular to one another in the unit cells, but are angled at an angle of between 20° and 70° to the longitudinal direction. In the variants in Figs. 13 and 14, only one coil is shown for the sake of clarity.With an angle o of around 63°, a longitudinal force component of around 90% results, while the transverse force component is 44.7% based on a conductor track that otherwise runs at a 45° angle to the longitudinal direction L. This allows the longitudinal force component to be increased, which can have advantages for the generation of a corresponding Lamb wave. With a steeper arrangement of the conductor track with an angle o of only approximately 26° (Fig. 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 a 45° angle to the longitudinal direction L is particularly preferred, so that guided Lamb and SH waves are generated equally well, regardless of the fact that they may have different amplitudes.

[0076] An array of bar magnets with a round cross-section, which are arranged next to each other in the transverse direction to the longitudinal direction L with alternating polarities, but are arranged next to each other in the longitudinal direction L with the same polarity, thus results in an array of magnets 18 which are also strip-shaped and have the same polarity (Fig. 15).

[0077] Here, too, both longitudinal waves and transverse waves are generated, the unit cells then being formed only over the surface of the poles as shown in Fig. 15 and parts of the conductor track sections being outside the unit cells 34.

Claims

Claims 1 . Ultrasonic transducer for generating ultrasonic waves in a metallic test object (4), with at least one magnet (18) and with four sets of conductor track sections, each comprising at least one rectilinear conductor track section (24, 26, 28, 30) running over a pole of the magnet (18) in a bottom view, wherein the sets of conductor track sections differ in operation by the direction of the current flow and the conductor track sections (24, 26, 28, 30) run over the at least one pole in the bottom view (U) at an angle to a longitudinal direction (L) of the latter, and with 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 can be controlled via the control unit (14) of the ultrasonic transducer, wherein the control unit (14) is designed to control the coils (20,22) to generate Rayleigh or Lamb waves in phase or antiphase and to generate guided SH waves in phase or antiphase.

2. Ultrasonic transducer for detecting ultrasonic waves in a metallic test object (4), with at least one magnet (18) and with four conductor track section sets, each comprising at least one rectilinear conductor track section (24, 26, 28, 30) running over a pole of the magnet (18) in a bottom view (U), wherein the conductor track section sets differ in operation by the direction of the current flow and the conductor track sections (24, 26, 28, 30) in the un- view angled to the longitudinal direction of the at least one pole over the latter, and with a control unit (14) for receiving the signals induced in the conductor track sections (24, 26, 28, 30), characterized in that two conductor track section sets each form a first and a second meandering coil (20, 22), wherein the control unit (14) is designed to add or subtract the signals for detecting Rayleigh or Lamb waves and to subtract or add them for detecting guided SH waves.

3. Ultrasonic transducer according to one of the preceding claims, characterized by at least two adjacent and preferably strip- and / or rod-shaped magnets (18), the poles of which have alternating polarity in the bottom view (U) in a transverse direction which runs transversely to the longitudinal direction (L) of the pole, wherein the conductor track sections (24, 26, 28, 30) of the conductor track section sets run over at least two adjacently arranged poles in the bottom view (U).

4. Ultrasonic transducer according to 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. Ultrasonic transducer according to 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) run outside the at least one pole or on the edge of the at least one magnet (18).

6. Ultrasonic transducer according to 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. Ultrasonic transducer according to claim 6, characterized in that the conductor track sections (24, 26, 28, 30) are angled at an angle between 20° and 70° to the longitudinal direction (L), in particular at an angle of 45° to the longitudinal direction (L).

8. Ultrasonic transducer according to 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. Ultrasonic transducer according to one of the preceding claims, characterized in that the conductor track sections (24, 26, 28, 30) run in a surface with a possible curvature which is provided for adaptation to a surface of the test object (4).

10. Ultrasonic transducer according to claim 9, characterized in that the conductor track sections (24, 26, 28, 30) of the same coil (20, 22) lie in one plane.

11. Ultrasonic transducer according to claim 10, characterized in that the magnets (18) have a length of 3 to 6 track wavelengths in the bottom view.

12. Ultrasonic transducer according to 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, with an ultrasonic transducer according to one of the preceding claims comprising claim 1, characterized in that the meander-shaped coils are controlled via a control unit (14) of the ultrasonic transducer in phase or antiphase to generate Rayleigh or Lamb waves and in phase or antiphase to generate guided SH waves.

14. Method for detecting ultrasonic waves in a metallic test object, with an ultrasonic transducer according to one of the preceding claims, comprising claim 2, characterized in that the signals of the meander-shaped coils in the control unit (14) of the ultrasonic transducer are added or subtracted for the detection of Rayleigh or Lamb waves and subtracted or added for the detection of guided SH waves.

15. Inspection device for inspecting pipelines or for sheet metal testing, characterized by one or more ultrasonic transducers according to one of claims 1 to 12.

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