Eddy current sensor and eddy current measurement method

Abstract

An eddy current sensor (100) and a method (200) for eddy current measurement are disclosed, wherein the eddy current sensor (100) comprises: a first coil (102) for generating a first alternating electromagnetic field; and a second coil (104) for generating a second alternating electromagnetic field, wherein the second coil (104) is arranged concentrically to the first coil (102).

Description

[0001] Various embodiments relate to an eddy current sensor and a method for eddy current measurement.

[0002] In general, eddy current sensors can be used to measure displacement, distance, and / or position for numerous applications in various technical fields. This measurement can be non-destructive, wear-free, and / or contactless. Eddy current sensors can generally be used to analyze electrically conductive materials.

[0003] An eddy current sensor can have a coil by means of which an alternating electromagnetic field (e.g. an alternating magnetic field) is generated during an eddy current measurement. This alternating electromagnetic field can induce eddy currents in an object to be analyzed (e.g. examined). These eddy currents can lead to a change in the alternating electromagnetic field (e.g. vibration damping). Data can be recorded that represents this change in the alternating electromagnetic field, such as a change in amplitude, a phase shift, etc. The change in the alternating electromagnetic field can depend on the local electrical conductivity of a material of the object, a magnetic permeability of the material of the object, and the distance between the eddy current sensor and a local position in the object (e.g. a depth in the object).Therefore, eddy current measurement can be used to determine, for example, the layer thickness of electrically conductive layers of the object (e.g. a layer stack), material properties of the layers, and / or defects (e.g. voids, cracks, etc.).

[0004] The depth within the object to which the eddy currents are essentially generated (also known as the penetration depth) depends on the frequency of the alternating electromagnetic field (also known as the excitation frequency) and the impedance. For depth resolution, this excitation frequency can be varied in eddy current measurements to obtain data for different penetration depths.

[0005] However, the excitation frequency may be limited to a predefined measurement range (e.g., from approximately 100 kHz to approximately 1 MHz), since outside this range, the measurement sensitivity is significantly reduced. Consequently, the depth resolution of an eddy current measurement may be limited by the predefined measurement range of the eddy current sensor. For example, the measurement range may be limited by the electronics unit (e.g., its capacitances and / or resonances).

[0006] According to various aspects, an eddy current sensor is provided which enables a significantly increased depth resolution of an eddy current measurement. This is achieved by arranging a plurality of coils (e.g., two or more than two) concentrically to one another (e.g., concentrically within one another). Due to the concentric arrangement, each coil of the plurality of coils of the eddy current sensor can generate associated eddy currents at the same position of the object, but with different penetration depths, using a respective alternating electromagnetic field. In this way, each coil of the plurality of coils can be used to analyze a respective section in the depth direction within the object with increased depth resolution.

[0007] The concentric arrangement of the multiple coils allows an eddy current measurement (viewed in the lateral direction) to be performed simultaneously at the same position using each of the multiple coils. This not only ensures the same position for the measurement, but the simultaneous measurement also ensures the same environmental influences (such as temperature). This further increases the measurement accuracy (in addition to the increased depth resolution).

[0008] It shows Fig. 1A to 1G each illustrate aspects of an eddy current sensor according to various embodiments; Fig. 2 a method for eddy current measurement according to various embodiments; and Fig. 3 a system with two eddy current sensors according to different embodiments.

[0009] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced.

[0010] Fig. 1A to Fig. 1G each show aspects of an eddy current sensor 100 according to various embodiments.

[0011] Eddy current sensor 100 may generally comprise a plurality of coils (e.g., two or more than two) arranged concentrically with one another (e.g., inside one another). Each coil of the plurality of coils may be part of an oscillating circuit.

[0012] Clearly, the eddy current sensor 100 can be configured according to various aspects for sensor multiplexing in eddy current measurement.

[0013] Fig. 1A to Fig. 1D each show, for illustrative purposes, aspects of the eddy current sensor 100 with two coils arranged concentrically to one another (e.g., one inside the other) (namely a first coil 102 and a second coil 104). Fig. 1E to Fig. 1G each show aspects of the eddy current sensor 100 with three coils arranged concentrically with one another (e.g., one inside the other) (namely, the first coil 102, the second coil 104, and a third coil 106). It is understood that this is for illustrative purposes and that the eddy current sensor 100 may also have more than three coils arranged concentrically with one another (e.g., one inside the other).

[0014] A concentric arrangement of two (or more than two) coils can be understood to mean that they have (essentially) the same center point 110 when viewed in cross-section. The two coils can be rotationally symmetrical along their longitudinal axis. The coils can have the same shape. For example, each coil can be a cylindrical coil. However, the coils can also have a different shape (e.g., a rectangular (e.g., square)) in plan view. For illustration purposes, the figures show cylindrical coils. It is understood that this is an example and that the plurality of coils can also have a different shape.

[0015] Fig. 1A shows the first coil 102 and the second coil 104 in a schematic side view and Fig. 1B shows a schematic top view according to various aspects. Various aspects of the first coil 102 and the second coil 104 are described below. It is understood that the description may apply accordingly to other coils of the plurality of coils.

[0016] As shown, the first coil 102 (e.g., a first cylinder coil) and the second coil 104 (e.g., a second cylinder coil) may be arranged concentrically to one another and at least partially within one another.

[0017] The first coil 102 can be configured to generate a first alternating electromagnetic field. The second coil 104 can be configured to generate a second alternating electromagnetic field. An alternating electromagnetic field can also be referred to as an alternating magnetic field. According to various aspects, a magnetic field sensor (e.g., based on giant magnetoresistance, GMR) can be used instead of a receiving coil.

[0018] It is understood that when a coil is arranged concentrically with (e.g., at least partially within) another coil, the diameter (perpendicular to the longitudinal extent) of the coil differs from the diameter of the other coil. As a result, the alternating electromagnetic field generated by the first coil can generate eddy currents at a different depth in the object than the alternating electromagnetic field generated by the second coil.

[0019] Optionally, coils (e.g., the first coil 102 and the second coil 104) of the plurality of coils may differ with respect to one or more other parameters (also referred to as coil parameters). For example, the first coil 102 may have a first number of turns (short: number of turns) and the second coil 104 may have a second number of turns different from the first number. For example, the first coil 102 may have a first diameter of a conductor (e.g., wire) of the first coil 102 and the second coil 104 may have a second diameter of a conductor (e.g., wire) of the second coil 104 different from the first diameter. For example, the first coil 102 and the second coil 104 may have a different pitch (as the average pitch of the turns) from one another.It is understood that these are exemplary parameters and that the coils may additionally or alternatively differ with respect to other parameters (as long as they are arranged concentrically to each other). These parameters may define the electrical impedance of the coil, which in turn may define the resonant frequency of the eddy current sensor 100 and thus the measurement frequency.

[0020] Illustratively, the first coil 102 may have a first electrical coil impedance, and the second coil 104 may have a second electrical coil impedance different from the first electrical coil impedance. The first coil 102 may have a first magnetic field sensitivity, and the second coil 104 may have a second magnetic field sensitivity different from the first magnetic field sensitivity.

[0021] According to various aspects, the plurality of coils (e.g., the first coil 102 and the second coil 104 (and optionally the third coil 106)) may be transmit coils (also referred to as excitation coils, sensing coils, and / or measuring coils). The eddy current sensor 100 may include a plurality of receive coils.

[0022] For example, the eddy current sensor 100 can have exactly one receiving coil for each transmitting coil. According to various aspects, the multiple receiving coils (as described herein for the transmitting coils) can be arranged concentrically with one another (e.g., at least partially within one another). According to various aspects, the change in the alternating electromagnetic field due to the eddy current losses can be detected by means of the receiving coil assigned to a respective transmitting coil. Alternatively, the multiple coils (e.g., the first coil 102, the second coil 104, and, if present, the third coil) can serve both as transmitting coils and as receiving coils.

[0023] According to various aspects, the first coil 102 and the second coil 104 can be configured (as transmitting coils) such that the respectively generated (first and second) alternating electromagnetic fields exit the eddy current sensor 100 so that they can penetrate into an object to be analyzed and generate eddy currents therein.

[0024] According to various aspects, a frequency of the first alternating electromagnetic field may be smaller than a frequency of the second alternating electromagnetic field.

[0025] Fig. 1C shows, by way of example, the first eddy currents 112 induced in an object 108 in response to the first alternating electromagnetic field (generated by the first coil 102) and the second eddy currents 114 induced in the object 108 in response to the second alternating electromagnetic field (generated by the second coil 104). The different penetration depths of the alternating electromagnetic fields can be clearly seen from the different depths to which eddy currents are induced in the object 108. This can ensure increased depth resolution, since, for example, focusing at different depths is improved. For example, as in Fig. 1D, the object 108 may be a layer stack comprising the first layer 108(1), the second layer 108(2), and the third layer 108(3). For illustration purposes, the first alternating electromagnetic field may, for example, generate eddy currents in all three layers 108(1), 108(2), and 108(3), and the second alternating electromagnetic field may, for example, generate eddy currents substantially in the second layer 108(2) and the third layer 108(3). This depth to which the described eddy currents are substantially generated may also be referred to as the penetration depth. This penetration depth may be the depth at which the eddy current density has decreased to approximately 1 / e. By combining the measurement results, the depth resolution of the eddy current measurement for the second layer 108(2) and the third layer 108(3) can be increased.This is because the change in the second alternating electromagnetic field can provide more precise information with respect to the second layer 108(2) and the third layer 108(3) compared to the change in the first alternating electromagnetic field.

[0026] As described herein, the plurality of coils (e.g., the plurality of transmitting coils and / or receiving coils) may also comprise more than two coils. For illustrative purposes, FG.1E to Fig. 1G each has an eddy current sensor 100 of the three coils (with the third coil 106). As in Fig. As shown in Figure 1G, an alternating electromagnetic field generated by the third coil can have an even smaller penetration depth than the first alternating electromagnetic field and the second alternating electromagnetic field. For example, the third alternating electromagnetic field can generate eddy currents 116 substantially in the third layer 108(3). By combining the measurement results for the third alternating electromagnetic field with those of the other two alternating electromagnetic fields, the depth resolution of the eddy current measurement for the third layer 108(3) can be further increased. This is because the change in the third alternating electromagnetic field can provide even more precise information regarding the third layer 108(3) compared to the change in the second alternating electromagnetic field.

[0027] It is understood that the described layers 108(1), 108(2) and 108(3) serve to illustrate the penetration depths and can be any portions within the object 108.

[0028] In various aspects, it has been recognized that conventional eddy current sensors, for example, are not capable of characterizing layer stacks with a symmetrical structure (e.g., with respect to their respective thickness and / or material) with sufficient depth resolution. The eddy current sensor 100 described herein enables such characterization. For example, the eddy current sensor 100 enables a depth analysis of an object comprising a (e.g., carbon) fiber-reinforced material (e.g., plastic or textile). For example, the eddy current sensor 100 can be used for the depth analysis of a multiaxial fabric (non-crimp fabric, NCF) and / or a carbon fiber-reinforced plastic (CFRP, also referred to as carbon fiber-reinforced plastic).

[0029] It is understood that these are exemplary uses. In general, the eddy current sensor 100 described herein can be used particularly advantageously for multilayer material systems that have (relatively thin) layers of different electrical conductivity (e.g., CFRP-metal hybrids). The eddy current sensor 100 described herein enables, for example, electrically conductive components and dielectric components of the object 108 (e.g., the multilayer material system) to be characterized with increased accuracy. For example, the eddy current sensor 100 enables the characterization of fiber orientations and / or monitoring of the drying of battery foils.

[0030] To generate an alternating electromagnetic field, a high-frequency signal can be fed into a coil. For this purpose, the eddy current sensor 100 can, in some embodiments, comprise an electronics unit. In this case, the eddy current sensor 100 can, for example, comprise a sensor head in which the first coil 102 and the second coil 104 (and optionally also the third coil 106) are arranged. In other embodiments, the eddy current sensor 100 can comprise an interface configured to be coupled to an electronics unit (e.g., via a high-frequency cable). Illustratively, the interface can be configured to transmit (at least) a high-frequency signal from an electronics unit (e.g., via a high-frequency cable) to the eddy current sensor 100.

[0031] The electronics unit can, for example, be an eddy current converter.

[0032] Illustratively, according to various aspects, the eddy current sensor 100 may include or be a multi-coil sensor head for eddy current measurement. For example, the eddy current sensor 100 may include a housing in which the first coil 102 and the second coil 104 are arranged (thus forming the sensor head).

[0033] According to various aspects, the electronics unit may be configured to supply the first coil 102 and the second coil 104 each with a high-frequency signal (e.g., a high-frequency alternating current) to generate the first alternating electromagnetic field 112 and the second alternating electromagnetic field 114 (and optionally further the third alternating electromagnetic field 116).

[0034] The electronics unit can be configured to obtain the signals detected by means of the plurality of receiving coils (as measurement signals) and optionally to process them.

[0035] Optionally, the eddy current sensor 100 may include (at least) one temperature sensor for detecting a temperature value (which represents a temperature in an environment of the eddy current sensor 100). The electronics unit or another electronic unit may be configured to process the measurement signals to analyze the properties of the object 108. For example, the electronics unit may output an analog current or voltage signal, and the other electronic unit may process it. In some embodiments, the electronics unit may be an intelligent electronics unit configured to perform at least part of the processing and output a digital signal.

[0036] According to various aspects, the electronics unit can be configured to interconnect the coils described herein. For example, the coils configured as transmitting coils can be interconnected by means of the electronics unit. For example, the coils configured as receiving coils can be interconnected by means of the electronics unit. By interconnecting two or more coils, a coil with a different impedance (and thus a different frequency range) can be created. This can achieve additional depth discrimination. Information regarding such interconnection of coils can be found, for example, in DE 10 2010 048 917 A1.

[0037] Clearly, each individual coil and each combination of two or more than two coils generates a respective frequency range for eddy current measurement.

[0038] Illustratively, two coils (e.g., the first coil 102 and the second coil 104) result in three frequency ranges: the first coil 102 alone, the second coil 104 alone, and the interconnection of the first coil 102 and the second coil 104.

[0039] Illustratively, three coils (e.g. the first coil 102, the second coil 104 and the third coil 106) result in seven frequency ranges: the first coil 102 alone, the second coil 104 alone, the third coil 106 alone, the interconnection of the first coil 102 and the second coil 104, the interconnection of the first coil 102 and the third coil 106, the interconnection of the third coil 106 and the second coil 104, and the interconnection of the first coil 102, the second coil 104 and the third coil 106.

[0040] Consequently, the number of frequency ranges (and thus, for example, depth discrimination) can be significantly increased.

[0041] As described herein, the coils may be configured as transmit coils and / or as receive coils.

[0042] According to various aspects, processing described herein may be performed using the temperature value. As described herein, the eddy current sensor 100 described herein enables simultaneous measurement, so that the influence of temperature on the eddy current measurements is substantially equal across the multiple coils.

[0043] As described herein, at least two of the coils 102, 104, 106 may have different coil parameters from each other (in addition to the different diameters of all coils from each other). According to various aspects: - the second number of turns (number of turns) of the second coil 104 is greater than the first number of turns (number of turns) of the first coil 102, and / or - the second diameter of the conductor (e.g. wire diameter) of the second coil 104 is smaller than the first diameter of the conductor (e.g. wire diameter) of the first coil 102 such that an ohmic resistance and / or an inductive resistance of the first coil 102 and the second coil 104 is substantially equal.

[0044] If the eddy current sensor has the third coil 106 then: - a third number of turns (number of turns) of the third coil 106 is greater than the second number of turns (number of turns) of the second coil 104, and / or - a third diameter of the conductor (e.g. wire diameter) of the third coil 106 is smaller than the second diameter of the conductor (e.g. wire diameter) of the second coil 104 such that the ohmic resistance and / or the inductive resistance of the third coil 106 substantially corresponds to that of the first coil 102 and the second coil 104.

[0045] Clearly, the larger ohmic and inductive resistance (due to the longer conductor length (e.g. wire length)) of an outer coil can be compensated by adjusting the number of turns and / or the wire diameter of the inner coil(s).

[0046] In this way, all coils of the eddy current sensor 100 can have essentially the same impedance and thus the same operating range. This results in a versatile sensor, with the gain being constant for each coil.

[0047] In other aspects, the second number of turns (number of turns) of the second coil 104 may be smaller than the first number of turns (number of turns) of the first coil 102 such that the first coil 102 and the second coil 104 have substantially the same peak value of the alternating magnetic field strength. Similarly, the third number of turns (number of turns) of the third coil 106 may be smaller than the second number of turns (number of turns) of the second coil 104 such that the third coil 102 and the second coil 104 have substantially the same peak value of the alternating magnetic field strength.

[0048] Clearly, the larger coil diameter of the outer coil can reduce the peak value of the alternating magnetic field strength and this can be compensated (e.g. balanced) by the larger number of turns of the outer coil (compared to the concentric inner coils).

[0049] In this way, all coils of the eddy current sensor 100 can generate essentially the same peak value of the alternating magnetic field strength. As a result, all coils can exhibit essentially the same sensitivity to changes in the test specimen (e.g., cracks, conductivity changes, etc.).

[0050] Fig. 3 shows a system 300 which has (at least) two eddy current sensors 100 (e.g. a first eddy current sensor 100(1) and a second eddy current sensor 100(2)).

[0051] According to various aspects, the first eddy current sensor 100(1) and the second eddy current sensor 100(2) may be arranged in semi-transmission to each other.

[0052] In such a semi-transmission arrangement, the first eddy current sensor 100(1) and the second eddy current sensor 100(2) can be arranged at a defined distance from each other.

[0053] This allows the detection of direction-dependent eddy current propagation. This can be particularly advantageous in anisotropic materials and / or composite materials (e.g., carbon fiber composites and / or carbon fiber composite textiles).

[0054] Fig. 2 shows a flowchart of a method 200 for eddy current measurement according to various aspects.

[0055] The method 200 may include (in 202) inducing eddy currents in an object by (e.g., simultaneously) generating a first alternating electromagnetic field by means of a first coil and a second alternating electromagnetic field by means of a second coil arranged concentrically to the first coil.

[0056] The method 200 may include (in 204) collecting data representing eddy current losses due to the (induced) eddy currents.

[0057] Furthermore, the method 200 may optionally (in 206) comprise determining one or more pieces of information (e.g., depth discrimination of defects) regarding the object using the (acquired) data.

[0058] As explained herein, the first coil 102 and the second coil 104 (and optionally further the third coil 106) may be transmit coils according to various aspects. In this case, these coils 102, 104, 106 may also be configured as receive coils, or the eddy current sensor 100 may additionally comprise one or more receive coils.

[0059] According to various aspects, the first coil 102 and the second coil 104 (and optionally further the third coil 106) can be receiving coils. In this case, these coils 102, 104, 106 can also be configured as transmitting coils, or the eddy current sensor 100 can additionally have one or more transmitting coils.

[0060] According to various aspects, the first coil 102 and the second coil 104 (and optionally also the third coil 106, if present) may have the same winding direction. The winding direction of a coil may also be referred to as the winding orientation, winding sense, and / or winding direction. This winding direction may, for example, determine the (north pole-south pole) orientation of the generated magnetic field.

[0061] Fig. 4 shows a flow diagram of a method 400 for eddy current measurement according to various aspects.

[0062] The method 400 may include (in 402) inducing eddy currents in an object by generating (at least) one alternating electromagnetic field by means of at least one transmitting coil.

[0063] Method 400 may include (at 404) detecting, using a first receiving coil, a first change in the alternating electromagnetic field. The first change may represent eddy current losses due to the eddy currents.

[0064] Method 400 may include (at 406) detecting, using a second receiving coil, a second change in the alternating electromagnetic field. The second change may represent eddy current losses due to the eddy currents.

[0065] The second receiving coil and the first receiving coil can be arranged concentrically with each other (e.g., at least partially within each other). The second receiving coil and the first receiving coil can have the same winding direction.

[0066] Furthermore, the method 400 may optionally include determining one or more pieces of information (e.g., depth discrimination of defects) regarding the object using the first change and the second change.

[0067] Various examples are provided below that describe one or more aspects of the eddy current sensor 100 and the methods 200, 400. It is understood that aspects described with respect to the eddy current sensor 100 may also apply to the methods, and vice versa. For example, aspects described with respect to the eddy current sensor 100 may be correspondingly implemented in one of the methods.

[0068] Example 1 is an eddy current sensor comprising: a first coil (e.g., a first transmitting coil) for generating a first alternating electromagnetic field; a second coil (e.g., a second transmitting coil) for generating a second alternating electromagnetic field, wherein the second coil is arranged concentrically to the first coil.

[0069] It is understood that the eddy current sensor may also comprise more than two (transmitting) coils arranged concentrically with one another. For example, an eddy current sensor according to Example 1 may comprise two or more (transmitting) coils, wherein each (transmitting) coil of the two or more (transmitting) coils is configured to generate a respective alternating electromagnetic field, and wherein the two or more (transmitting) coils are arranged concentrically with one another (e.g., at least partially concentrically within one another).

[0070] Example 2 is configured according to Example 1, wherein the first coil is a (first) cylindrical coil; and / or wherein the second coil is a (second) cylindrical coil.

[0071] Example 3 is configured according to example 1 or 2, wherein the first coil and the second coil differ with respect to at least one (e.g., exactly one or more than one) of the following parameters: a number of turns (in short: number of turns), a diameter of a conductor (e.g., wire) of the coil, a pitch (as an average pitch of the turns).

[0072] Example 4 is configured according to any one of examples 1 to 3, wherein the first coil is configured such that at least a portion of the first alternating electromagnetic field, when generated, exits the sensor head in the direction of an object (to be analyzed); and / or wherein the second coil is configured such that at least a portion of the second alternating electromagnetic field, when generated, exits the sensor head in the direction of the object (to be analyzed).

[0073] Example 5 is configured according to any one of Examples 1 to 4, wherein the eddy current sensor further comprises: an electronics unit configured to supply (e.g. feed) the first coil and the second coil (e.g. simultaneously) with a (e.g. respective) high-frequency signal (e.g. a high-frequency alternating current) in order to generate the first alternating electromagnetic field and the second alternating electromagnetic field (e.g. simultaneously); or an interface for transmitting (at least) one high-frequency signal from an electronics unit (e.g. by means of a high-frequency cable) to the eddy current sensor in order to generate the first alternating electromagnetic field and the second alternating electromagnetic field (e.g. simultaneously).

[0074] Example 6 is configured according to example 5, wherein the electronic unit is configured to generate the first alternating electromagnetic field and the second alternating electromagnetic field such that a frequency of the first alternating electromagnetic field is lower than a frequency of the second alternating electromagnetic field.

[0075] Example 7 is configured according to any one of examples 1 to 6, wherein the second coil is arranged concentrically within the first coil; wherein the first coil comprises a first conductor having a first diameter and a first number of turns; wherein the second coil comprises a second conductor having a second diameter and a second number of turns; wherein the second number of turns is greater than the first number of turns and / or the second diameter is smaller than the first diameter such that an ohmic resistance and / or an inductive resistance of the first coil and the second coil are the same.

[0076] Example 8 is configured according to any one of examples 1 to 6, wherein the second coil is arranged concentrically within the first coil; wherein the first coil has a first number of turns; wherein the second coil has a second number of turns; wherein the second number of turns is smaller than the first number of turns such that a peak value of the alternating magnetic field strength of the first coil and the second coil is the same.

[0077] Example 9 is a method for eddy current measurement, the method comprising: inducing eddy currents in an object (e.g., having multiple layers) by (e.g., simultaneously) generating a first alternating electromagnetic field by means of a first coil and a second alternating electromagnetic field by means of a second coil arranged concentrically to the first coil (e.g., in an eddy current sensor); and acquiring data representing eddy current losses due to the (induced) eddy currents.

[0078] Example 10 is configured according to Example 9, the method further comprising: determining one or more pieces of information (e.g., a depth discrimination of defects) regarding the object (e.g., regarding one or more layers of the multiple layers of the object) using the (acquired) data.

[0079] Example 11 is an eddy current sensor comprising: at least one (e.g., one or more than one) transmitting coil for generating an alternating electromagnetic field; a first receiving coil for detecting a first change in the alternating electromagnetic field (due to eddy current losses); and a second receiving coil for detecting a second change in the alternating electromagnetic field (due to the eddy current losses); wherein the second receiving coil is arranged concentrically to the first receiving coil; and wherein the first receiving coil and the second receiving coil have the same winding direction.

[0080] As described herein, eddy current sensor 100 may include coils that can function as both transmitting coils and receiving coils. In this case, eddy current sensor 100 may, for example, include at least three coils (e.g., first coil 102, second coil 104, and third coil 106), such that one of these coils may serve as a transmitting coil and the other two may serve as receiving coils. It is understood that in this case, eddy current sensor 100 may include one or more additional transmitting coils and one or more additional receiving coils.

[0081] As described herein, the eddy current sensor 100 may comprise separate transmit coils and receive coils. In this case, the transmit coils and / or the receive coils may comprise two coils arranged concentrically to one another (e.g., with the same winding direction). For example, the eddy current sensor 100 may comprise two or more than two concentrically arranged transmit coils and / or two or more than two concentrically arranged receive coils.

[0082] Therefore, it is understood that the at least one transmitting coil and / or the receiving coils of the eddy current sensor according to Example 11, where applicable, may be configured as described in any of Examples 1 to 8.

[0083] Example 12 is a method for eddy current measurement, the method comprising: inducing eddy currents in an object (e.g., having multiple layers) by generating an alternating electromagnetic field by means of at least one transmitting coil; detecting, by means of a first receiving coil, a first change in the alternating electromagnetic field, wherein the first change represents eddy current losses due to the eddy currents; and detecting, by means of a second receiving coil, a second change in the alternating electromagnetic field, wherein the second change represents eddy current losses due to the eddy currents; wherein the second receiving coil is arranged concentrically to the first receiving coil; and wherein the first receiving coil and the second receiving coil have the same winding direction.

[0084] Example 13 is using a sensor having several (e.g. two or more than two) concentrically arranged coils for eddy current measurement.

[0085] Example 14 is configured according to Example 13, wherein the eddy current measurement is an eddy current measurement for depth analysis of an object comprising a (e.g., carbon) fiber reinforced material (e.g., plastic or textile).

[0086] Example 15 is configured according to example 13 or 14, wherein the object comprises a plurality of layers arranged one above the other in one direction (e.g., direction 13), wherein a structure of the plurality of layers is symmetrical with respect to the respective thickness and / or the respective material with respect to a plane perpendicular to the direction (e.g., plane 11-15).

[0087] Example 16 is a system comprising: a first eddy current sensor (100) according to any one of examples 1 to 8 or 11; and a second eddy current sensor (100) according to any one of examples 1 to 8 or 11; wherein the first eddy current sensor (100) and the second eddy current sensor (100) are arranged in semi-transmission to each other.

[0088] The expression that an element, a parameter, etc. "represents" another element, another parameter, etc. can be understood to mean that these are linked to each other, e.g. the element and / or the parameter is a (e.g. unique, e.g. one-to-one) function of the other element and / or parameter. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2010 048 917 A1

[0036]

Claims

[1] Eddy current sensor (100), comprising: • a first coil (102) for generating a first alternating electromagnetic field; • a second coil (104) for generating a second alternating electromagnetic field, wherein the second coil (104) is arranged concentrically to the first coil (102). [2] Eddy current sensor (100) according to claim 1, wherein the first coil (102) is a cylindrical coil; and / or wherein the second coil (104) is a cylindrical coil. [3] Eddy current sensor (100) according to claim 1 or 2, wherein the first coil (102) and the second coil (104) differ with respect to at least one of the following parameters: a number of turns, a diameter of a conductor of the coil, a pitch. [4] Eddy current sensor (100) according to one of claims 1 to 3, wherein the first coil (102) is arranged such that at least a part of the first alternating electromagnetic field, when generated, exits the sensor head in the direction of an object; and / or wherein the second coil (104) is arranged such that at least a part of the second alternating electromagnetic field, when generated, exits the sensor head in the direction of the object. [5] Eddy current sensor (100) according to one of claims 1 to 4, further comprising: • an electronic unit configured to supply the first coil (102) and the second coil (104) with a high-frequency signal to generate the first alternating electromagnetic field and the second alternating electromagnetic field; or • an interface for transmitting a high-frequency signal from an electronic unit to the eddy current sensor (100) in order to generate the first alternating electromagnetic field and the second alternating electromagnetic field. [6] Eddy current sensor (100) according to claim 5, wherein the electronic unit is configured to generate the first alternating electromagnetic field and the second alternating electromagnetic field such that a frequency of the first alternating electromagnetic field is lower than a frequency of the second alternating electromagnetic field. [7] Eddy current sensor (100) according to one of claims 1 to 6, wherein the second coil (104) is arranged concentrically within the first coil (102); wherein the first coil (102) comprises a first conductor having a first diameter and a first number of turns; wherein the second coil (104) comprises a second conductor having a second diameter and a second number of turns; wherein the second number of turns is greater than the first number of turns and / or the second diameter is smaller than the first diameter such that an ohmic resistance and / or an inductive resistance of the first coil (102) and the second coil (104) are the same. [8] Eddy current sensor (100) according to one of claims 1 to 6, wherein the second coil (104) is arranged concentrically within the first coil (102); wherein the first coil (102) has a first number of turns; wherein the second coil (104) has a second number of turns; wherein the second number of turns is smaller than the first number of turns such that a peak value of the alternating magnetic field strength of the first coil (102) and the second coil (104) is the same. [9] Method (200) for eddy current measurement, the method (200) comprising: • Inducing (202) eddy currents in an object (108) by generating a first alternating electromagnetic field by means of a first coil (102) and a second alternating electromagnetic field by means of a second coil (104) arranged concentrically to the first coil (102); and • Collecting (204) data representing eddy current losses due to the eddy currents. [10] The method (200) of claim 9, further comprising: • Determine one or more pieces of information about the object using the data. [11] Eddy current sensor (100), comprising: • at least one transmitting coil for generating an alternating electromagnetic field; • a first receiving coil (102) for detecting a first change in the alternating electromagnetic field; and • a second receiving coil (104) for detecting a second change in the alternating electromagnetic field; • wherein the second receiving coil (104) is arranged concentrically to the first receiving coil (102); • wherein the first receiving coil (102) and the second receiving coil (104) have the same winding direction. [12] Method (400) for eddy current measurement, the method (400) comprising: • Inducing (402) eddy currents in an object (108) by generating an alternating electromagnetic field by means of at least one transmitting coil; • detecting (404), by means of a first receiving coil (102), a first change in the alternating electromagnetic field, the first change representing eddy current losses due to the eddy currents; • detecting (406), by means of a second receiving coil (104), a second change in the alternating electromagnetic field, the second change representing eddy current losses due to the eddy currents; • wherein the second receiving coil (104) is arranged concentrically to the first receiving coil (102); and • wherein the first receiving coil (102) and the second receiving coil (104) have the same winding direction. [13] Using a sensor having a plurality of concentrically arranged coils for eddy current measurement; wherein preferably the eddy current measurement is an eddy current measurement for depth analysis of an object having a fiber-reinforced material. [14] Use of the sensor according to claim 13, wherein the object comprises a plurality of layers arranged one above the other in one direction, wherein a structure of the plurality of layers is symmetrical with respect to the respective thickness and / or the respective material with respect to a plane perpendicular to the direction. [15] System (300), comprising: • a first eddy current sensor (100) according to one of claims 1 to 8 or 11; and • a second eddy current sensor (100) according to one of claims 1 to 8 or 11; • wherein the first eddy current sensor (100) and the second eddy current sensor (100) are arranged in semi-transmission to one another.

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