FLEXIBLE EDDY CURRENT ARRAY PROBE

Abstract

The present subject matter may include a flexible eddy current array probe arrangement (ECA probe arrangement) capable of adapting its shape to complex profiles of structures under test without damaging the probe arrangement. Examples include structures with curved sections extending in two orthogonal directions (e.g., where the structure under investigation may exhibit complex surface curvature along an index axis and a scanning axis). The ECA probe arrangement may include slotted structures extending through a flexible printed circuit board (PCB) or other substrate, facilitating bending or curvature.

Description

STATE OF THE ART Technical field This document relates generally, but not limited to, devices and techniques for non-destructive testing, such as facilitating eddy current testing, and in particular devices and techniques which include a flexible eddy current array sensor arrangement (ECA sensor arrangement) that can adapt to curved or otherwise complex surface contours. Description of the state of the art Non-destructive testing (NDT) can refer to the application of one or more different techniques to examine regions on or within an object, for example, to determine whether faults or defects are present, or to otherwise characterize the object under investigation. One class of non-destructive testing may include the application of an eddy current testing approach, in which electromagnetic energy is applied to the object and resulting induced currents on or within the object are detected. The values ​​of a detected current (or associated impedance) provide an indication of the structure of the object under test, for example, to indicate the presence of a crack, cavity, porosity, or other inhomogeneity.In general, an eddy current sensor (EC sensor) comprises one or more sensing elements, such as inductive coils, that can be excited by an alternating current (AC) source. Such coils (or other electromagnetic sensing elements, such as Hall sensors) can be used to receive a signal indicating an induced eddy current on or within the structure. SUMMARY In one aspect, the present disclosure provides a circuit device for use with an eddy current array probe (ECA probe). The device can include a substrate, an array of coils, and conductive traces. The substrate can include a sensing region at a first end section of the substrate, a conduction region at a second end section of the substrate opposite the first end section, and an intermediate region extending between the sensing region and the conduction region. The array of coils can be defined in the sensing region and arranged laterally along it. The conductive traces can be defined in the intermediate region and the conduction region and extend longitudinally along them to connect the array of coils to a probe connector of the ECA probe.In the intermediate region of the substrate between at least some of the conductor tracks, longitudinal slots can be defined to mechanically decouple a bending of the detection region from the conductor guidance region. In one aspect, the present disclosure provides an eddy current array sensor arrangement (ECA sensing arrangement). The ECA sensing arrangement can include a probe and an acquisition device. The probe can include a printed circuit board with an array of coils and an elastic support structure that can be positioned against a surface of the printed circuit board. The acquisition device can be operationally connected to the array of coils to implement a specific time-controlled coil stimulation sequence and acquire corresponding eddy current signals. The printed circuit board can further include a substrate and conductive traces. The substrate can include a sensing region at a first end section of the substrate, and the array of coils can be defined in the sensing region and arranged laterally along it.The substrate can further include a conductor guidance region at a second end section of the substrate opposite the first end section and an intermediate region extending between the sensing region and the conductor guidance region. Conductors can be defined in the intermediate region and the conductor guidance region and extend longitudinally along them to connect the array of coils to the acquisition device. Longitudinal slots can be defined in the intermediate region of the substrate between at least some of the conductors. The elastic support structure can flex the sensing region of the substrate to conform to the contour of a test object when the probe is pressed against the test object. The longitudinal slots can mechanically decouple flexion of the sensing region from that of the conductor guidance region. In one aspect, the present disclosure provides a circuit device for use with an eddy current array probe (ECA probe). The device can include a substrate, an array of coils, and conductive traces. The substrate can include a sensing region at a first end section of the substrate, a conduction region at a second end section of the substrate opposite the first end section, and an intermediate region extending between the sensing region and the conduction region. The array of coils can be defined in the sensing region. The conductive traces can be defined in the intermediate region and the conduction region and extend along them to connect the array of coils to a probe connector of the ECA probe. Elongated slots can be defined in the intermediate region of the substrate.An elastic support structure of the ECA probe can bend the sensing region of the substrate to conform to the contour of a test object (e.g., when the ECA probe is pressed against the test object). The longitudinal slots can mechanically decouple bending of the sensing region from the conductor guide region. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a test object with a surface curved along several directions, according to at least one embodiment of the present disclosure. Fig. 2 is a top view of a circuit device for use with an eddy current array probe (ECA probe) according to at least one embodiment of the present disclosure. Fig. 3 is a detailed view of a section of the detection region of the circuit device of Fig. 2 according to at least one embodiment of the present disclosure. Fig. 4 is a circuit device for use with an eddy current array probe (ECA probe) comprising four substrate layers, according to at least one embodiment of the present disclosure. Fig. 5 is a first layer of the circuit device of Fig. 4 according to at least one embodiment of the present disclosure. Fig. 6 is a second layer of the circuit device of Fig. 4.4 according to at least one embodiment of the present disclosure. Fig. 7 is a third layer of the circuit device of Fig. 4 according to at least one embodiment of the present disclosure. Fig. 8 is a fourth layer of the circuit device of Fig. 4 according to at least one embodiment of the present disclosure. Fig. 9 shows an impedance plane representation and imaging showing a fault indication that can be obtained using an ECA detection arrangement according to at least one embodiment of the present disclosure. Fig. 10 is a schematic diagram of an ECA detection arrangement according to at least one embodiment of the present disclosure. Fig. 11 is a perspective view of an ECA probe arrangement according to at least one embodiment of the present disclosure.Figure 12 is an image showing a printed circuit board of an ECA probe that adapts to a complex surface of a test object, according to at least one embodiment of the present disclosure. DESCRIPTION Eddy current array (ECA) probes can be fabricated using flexible printed circuit board (PCB) materials. Such a flexible array can adapt to various surface shapes of structures under investigation. However, commonly available probes, even when fabricated using flexible PCB materials, can be relatively rigid and generally not stretchable (e.g., such ECA sensors may not be capable of stretching). For example, a commonly available ECA sensor might enclose a band (e.g., approximately 2.54 centimeters or about 1 inch wide), and such a configuration can limit the ECA probe's ability to adapt to some surfaces.For example, commonly available flexible probes may not be able to adapt to complex profiles that are concave along a scanning axis, or to profiles that have curvatures in two directions at the same time (e.g., a turbine blade root surface). Fig. 1 shows a test object 100 with a surface 102 having a profile with curvature in a first direction 104 and a second direction 106. Commonly available ECA probes may have difficulty conforming to a profile that has curvature in both directions. For example, flexible printed circuit boards (PCBs) can be bent sufficiently to conform to curvature in either direction separately. However, the flexible PCB may have difficulty bending sufficiently along the curvature in both directions simultaneously, resulting in sections of the detection region (e.g., the region of the substrate enclosing the ECA) of the flexible PCB lifting off the surface of the test object.This lifting of the detection region from the test object can lead to reduced coupling between the coils and the test object surface, which can degrade the sensitivity and accuracy of the eddy current measurements. In particular, areas of the detection region that are not in close contact with the test object can experience an increased lifting effect, resulting in reduced signal strength, increased noise, and unreliable detection of defects or anomalies. Furthermore, uneven contact across the detection region can cause fluctuations in the acquired data, making the interpretation of test results difficult and potentially allowing defects to go undetected. The present disclosure provides various devices and methods for ECA testing that can overcome challenges associated with examining different surfaces of a test object. For example, the present disclosure includes a flexible ECA probe arrangement that is able to better adapt to complex profiles extending in two orthogonal directions without damaging the probe arrangement (where, for example, the structure under investigation may have complex surface curvature in an index axis and in a scanning axis). According to various embodiments, the present disclosure provides a circuit device for use with an eddy current array probe (ECA probe). The circuit device can be implemented as a printed circuit board (PCB), for example, as a flexible PCB. Structural aspects of the circuit device can enable it to adapt to complex surfaces of a test object, as discussed further herein. The circuitry can include an array of coils for generating and detecting eddy currents and conductive traces for electrically connecting the coil array to a probe connector of an ECA probe and / or to a multiplexer unit integrated into the probe. Connecting the coil array to the probe connector allows the probe and / or an acquisition device to excite the coil array for generating and detecting eddy currents. During operation, the acquisition device can selectively power the coils and acquire non-destructive testing (NDT) data from the test object. The circuit device can enclose a substrate. The substrate can be made of flexible materials such as polyimide, which can provide both electrical insulation and mechanical flexibility. Other materials suitable for the substrate include polyester (PET), polyethylene naphthalate (PEN), liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), and aramid fibers (Nomex). The coils and conductor tracks can be defined in the substrate using copper or other conductive materials, which are structured by photolithography and etching. Other conductive materials suitable for defining the coils and conductor tracks can include aluminum, silver, gold, nickel, and conductive alloys such as copper-clad steel. The substrate can comprise multiple layers, with coils and conductor tracks defined in different layers to optimize electrical performance characteristics and mechanical flexibility. Vias can be used to electrically connect conductor tracks and coils between layers. The substrate can include a sensing region located at a first end section of the substrate. The array of coils can be defined within the sensing region and arranged laterally along it. In this context, a coil can be defined by a structured conductor track forming one or more loops or a spiral within the substrate, extending over one or more layers. The lateral arrangement of the coils can mean that the coils are positioned side by side and, in some embodiments, at least partially overlapping, extending along a length of the sensing region (e.g., along SRL, as shown in the embodiment of Fig. 2, along an edge at the first end section of the substrate).In comparison to arrangements where coils are offset longitudinally, the lateral and partially overlapping arrangement can allow the sensing region to maintain a relatively small width (e.g., a narrower SRw, as shown in the embodiment of Fig. 2) compared to the length of the sensing region (e.g., SRL) and the total lateral width of the substrate (e.g., the width of the substrate defined along the edge of the substrate at the first end section), thereby concentrating the sensing elements on a compact area. By arranging the coils in a relatively narrow sensing region, the circuit device can more easily bend simultaneously in a first direction along a longitudinal axis of the substrate (e.g., parallel to a scanning direction) and in a second direction orthogonal to the substrate's longitudinal axis. For example, a narrow sensing region, in combination with longitudinal slots defined in the substrate, as further discussed herein, can make the sensing region less resistant to simultaneous bending along multiple transverse axes, thus enabling the sensing region to conform to surfaces that are curved in multiple directions. This flexibility can provide adaptability to complex test object surfaces and can allow the sensing region enclosing the coil array to be consistently positioned closer to the test object surface (e.g.,is positioned against these) to achieve improved examination coverage and improved sensitivity. In some embodiments, the array of coils can include an alternating arrangement of first coils and second coils, with sections of the first coils overlapping with sections of the second coils. This arrangement can be achieved by placing a section of a first coil on one or more layers of the substrate and an overlapping section of a second coil on one or more other layers. For example, the coils can be configured as coil traces, with the coil traces of the first coils defined in a first subgroup of the sensing region layers and the coil traces of the second coils defined in a second subgroup of the sensing region layers. In some embodiments, the first and second coils can be aligned collinearly along the detection region. For example, the array of coils comprising the first coils can be arranged in a straight line or substantially a straight line, and the second coils can be arranged along the same straight line or substantially a straight line as those of the first coils. This linear arrangement maximizes coil coverage within the detection region while maintaining a narrow width (e.g., compared to nonlinear arrangements such as staggered or offset patterns, which require a wider detection region and can reduce flexibility). In some implementations, a first subgroup of the acquisition region layers can comprise two layers, and a second subgroup of the acquisition region layers can comprise two layers positioned between the two layers of the first subgroup. For example, first coils can be formed in a first and a fourth layer (e.g., an upper and a lower layer) of the acquisition region, while second coils can be formed in a second and a third layer (e.g., intermediate layers). This vertical offset can allow the first and second coils in the acquisition region to overlap without increasing the overall width of the acquisition region. Furthermore, placing the first coils in the first and fourth layers and the second coils in the second and third layers can compensate for the mean lift of each coil, resulting in more uniform sensitivity across the array.Thus, this overlapping arrangement can increase coil density and sensitivity while maintaining a compact sensing region. In addition to the sensing region, the substrate can include a conduction region at a second end section opposite the first end section and an intermediate region extending between the sensing and conduction regions. Conductors can be defined in the intermediate region and the conduction region and extend longitudinally along them to electrically connect the array of coils to the probe connector of the ECA probe. The conductors can be structured conductive traces routed along the substrate, with each coil connected to the probe connector via a dedicated pair of conductors. Vias can be used to connect conductors and / or coils between layers. Longitudinal slots can be defined in the intermediate region of the substrate between at least some of the conductor tracks. These slots can mechanically decouple a bend in the sensing region from the conductor routing region. The slots can be elongated openings extending parallel to the length of the substrate and can be arranged laterally across the intermediate region in a repeating pattern. In some embodiments, the slots can extend through all substrate layers, forming continuous gaps that pass completely through the thickness of the substrate. In other embodiments, the slots can extend only through a subset of the substrate layers.The shape of the slots can include elongated sections with curved ends, where the curved ends are wider than the intermediate sections, which helps to distribute mechanical stresses and prevent tearing at the slot boundaries. The introduction of these longitudinal slots allows the substrate to be divided into mechanically independent sections, enabling the sensing region to bend more freely without transferring mechanical stress to the conductor region. This mechanical decoupling means that when the sensing region is pressed against a contoured test object, the conductor region minimally inhibits or restricts the sensing region's bending. As a result, the sensing region can maintain close contact with complex surfaces while the conductor region remains relatively unaffected by deformation, thus reducing the risk of damage and improving the reliability of the circuit device during testing. The substrate can be elongated, with its width (in the lateral direction) being less than its length (in the longitudinal direction). The sensing region can be positioned at the first end section, the conduction region at the second end section, and the intermediate region extending between them. This geometry allows the sensing region to be concentrated toward the edge of the circuit device, while the conduction region provides space for electrical connections and integration with the probe connector. The detection region can have a width extending lengthwise from the edge of the first end of the substrate to the intermediate region, and a length extending along the edge of the first end. In some embodiments, the length of the detection region is at least five times greater than the width of the detection region, for example, at least eight times greater, at least twelve times greater, at least sixteen times greater, or at least thirty-two times greater. The aspect ratio of the width of the detection region to its length can be in a range of 1:5 to 1:32, for example, in a range of 1:8 to 1:32. For example, the detection region can be in a range of 1 to 5 mm in width and 5 to 25 mm in length (e.g., 1 mm wide and 5 mm long, 3 mm wide and 15 mm long, 5 mm wide and 25 mm long). A detection region width that is less than its length can allow for better bending in multiple orthogonal dimensions.The intermediate region can have a width similar to or equal to the length of the longitudinal slots and can extend longitudinally from the detection region to the conductor routing region. In certain embodiments, the width of the intermediate region is greater than one-third of the length of the detection region (e.g., IRw > SRL / 3). For example, if the detection region has a length in the range of 5 to 25 mm, the width of the intermediate region can be in the range of 2 to 10 mm (e.g., a detection region length of 5 mm and an intermediate region width of 2 mm, a detection region length of 18 mm and an intermediate region width of 10 mm, or a detection region length of 25 mm and an intermediate region width of 10 mm). The longitudinal slots can have a length greater than one-third of the length of the detection region (e.g., slot length > SRL / 3).For example, if the detection region has a length in the range of 5 to 25 mm, the longitudinal slots can have a length in the range of approximately 2 to 10 mm (e.g., a detection region length of 5 mm and a longitudinal slot length of 2 mm, a detection region length of 18 mm and a longitudinal slot length of 10 mm, or a detection region length of 25 mm and a longitudinal slot length of 10 mm). In certain embodiments, the width of the intermediate region is at least three times greater than the width of the detection region. For example, if the width of the detection region is in the range of 1 to 5 mm, the width of the intermediate region can be in the range of 3 to 15 mm (e.g., 1 mm wide detection region and 3 mm wide intermediate region, 3 mm wide detection region and 10 mm wide intermediate region, 5 mm wide detection region and 15 mm wide intermediate region). The longitudinal slots can have a length that is at least three times greater than the width of the detection region. For example, if the width of the detection region is in the range of 1 to 5 mm, the slots can have a length in the range of 3 to 15 mm (e.g., 1 mm wide detection region and 3 mm long slots, 3 mm wide detection region and 10 mm long slots, 5 mm wide detection region and 15 mm long slots). In some embodiments, the substrate can include a structure in which the sensing region is positioned at or near a longitudinal center point of the substrate, with intermediate regions extending outward from opposite sides of the sensing region (e.g., in a mirror-image or near-mirror-image arrangement). Each intermediate region can include a corresponding group of conductor tracks and longitudinal slots, such that the mechanical decoupling and flexing properties described herein are provided on both sides of the sensing region. This arrangement can allow the circuit device to flex or adapt in shape in both lateral directions with similar stiffness and deformation response (e.g., for applications requiring bidirectional scanning or where the probe orientation relative to the test object may vary).The width and length of the detection region and the geometry of the longitudinal slots and / or the length of each intermediate region may resemble the dimensions discussed further herein. In some embodiments, the intermediate region of the substrate may comprise fewer layers than the sensing region. For example, the sensing region may have four layers to accommodate the overlapping coils, while the intermediate region may have only two layers to increase flexibility and reduce material consumption. Pairs of conductors corresponding to each coil may run along respective layers of a two-layer intermediate region to and from the coils. The transition in the number of layers between the intermediate and sensing regions can be achieved using fabrication techniques such as selective lamination, where the sensing region is built up with additional layers, or by down-step routing. In some embodiments, each coil of the array can be connected to a pair of conductors, with the conductors of each pair extending along adjacent layers of the intermediate region in an overlapping arrangement. For example, transmit and return traces for a given coil can be routed on two adjacent layers, directly above and below each other, to minimize the loop area and reduce electromagnetic interference. Minimizing the loop area reduces the generation of unwanted eddy currents and interference between channels. In some embodiments, no more than two conductor pairs can be arranged between adjacent longitudinal slots. The conductors can be arranged between the longitudinal slots, with each longitudinal slot providing mechanical separation. Having a longitudinal slot between each conductor pair improves mechanical decoupling. However, adding more longitudinal slots can increase manufacturing effort and complexity. Limiting the number of conductor pairs between longitudinal slots to no more than two can provide sufficient mechanical decoupling while maintaining adequate electrical connectivity. In some embodiments, only one conductor pair can be routed between each longitudinal slot, further improving flexibility.In some embodiments, more than two pairs of conductor tracks can be routed between each longitudinal slot. In some embodiments, the circuit device can be manufactured using sophisticated printed circuit board (PCB) manufacturing processes, such as photolithography, chemical etching, or plasma etching and multilayer lamination. The substrate can be built up layer by layer, with each layer being patterned to define the desired coil and conductor geometries. Conductive materials can be deposited by techniques such as electroplating or sputtering, followed by etching to create intricate coil and conductor patterns. Longitudinal slots can be formed by high-precision laser cutting and / or mechanical punching. The slots can be formed after lamination to ensure they extend through the required number of substrate layers.Additional steps such as drilling and plating can be applied to create vias for electrical connections between the layers. The circuitry can be integrated into an ECA probe assembly, with the sensing region positioned at a probe tip and the lead-in region connected to a probe connector. An elastic support structure, such as a foam or elastomeric material, can be provided to press the sensing region against the test object and ensure a form-fitting contact. The elastic support structure can be designed to distribute pressure evenly along the length and / or width of the sensing region when pressed against a surface under investigation, so that the sensing region conforms closely to the shape of the surface under investigation, even if the surface includes curvatures in multiple directions.The elastic support structure can be made from materials such as silicone, polyurethane, or other elastomers, selected for their ability to deform under pressure and return to their original shape. This elastic deformation and recovery allows the support structure to maintain consistent contact forces across the sensing region during use, thereby reducing lift-off fluctuations and improving the reliability of the investigation. The support structure can be positioned directly behind the sensing region within the probe assembly and can be bonded or mechanically attached to the substrate or probe housing. During operation, an acquisition device connected to the circuit device via the probe can implement a timed coil stimulation sequence, selectively energizing the coils and acquiring corresponding eddy current signals. A multiplexer (MUX) can be used to select which coils are energized and read at any given time. The MUX can be integrated into the circuit device itself, for example, in the conductor routing region at the second end section of the circuit device, or, in other embodiments, it can be integrated into the probe assembly. The acquired data can be processed by the acquisition device to detect defects, cracks, or other anomalies in the test object. The flexible, decoupled design of the circuit device enables reliable examination of surfaces with complex geometries. Fig. 2 shows a circuit device 200 for use with an ECA probe, and Fig. 3 is a detailed view of a section of the circuit device of Fig. 2. Aspects of the circuit device of Fig. 2 and Fig. 3 can be implemented in any embodiment of the circuit device and / or the ECA probes described herein, and vice versa. The circuit device can enclose a substrate 206, which can extend longitudinally from a first end section 202 to a second end section 204. The first end section can be positioned near an edge of the substrate, and the second end section can be positioned near an opposite edge of the substrate. The substrate can be elongated, with a length greater than its width, and can provide both an electrical and a mechanical support structure for the components of the circuit device. At the first end section, the substrate can include a sensing region 208. At the second end section, the substrate can include a conductor guidance region 210. An intermediate region 212 can extend longitudinally between the sensing region and the conductor guidance region. An array of coils 214 can be arranged laterally along the detection region. The coils can be formed by structured conductive material within the substrate, with the respective coils positioned side by side and partially overlapping with at least one adjacent coil. The coils can be defined on one or more layers of the substrate to achieve a compact arrangement. In some embodiments, the array of coils can include alternating first coils 220 and second coils 222, with sections of the first coils overlapping with sections of the second coils. This overlapping arrangement can be realized by forming the first coils on one subset of substrate layers and the second coils on another subset of the substrate layers (e.g.,(by forming the first coils on one subset of the detection region layers and the second coils on another subset of the detection region layers). Such a configuration can increase coil density and sensitivity while maintaining the narrow width of the detection region. Traces 216 can extend longitudinally along the intermediate region and the conduction region. These traces can electrically connect each coil in the array to a probe connector and / or a probe multiplexer, enabling signal transmission between the coils and external electronics. A pair of traces can correspond to a specific coil to electrically connect the coil to the probe, and the respective traces within the pair can be routed on adjacent layers of the substrate and can overlap vertically to minimize the loop area, thereby reducing electromagnetic interference and superposition. In this context, the “loop area” refers to the effective electromagnetic loop area created by the transmit and return traces associated with each coil, rather than the physical coil windings themselves.The loop area can represent the size of the current-carrying loop formed by the conductor pair. A larger loop area can increase the coupling of the magnetic flux with external fields and therefore increase the susceptibility to induced noise, parasitic eddy currents, and crosstalk. By routing the conductors on adjacent layers so that they overlap vertically, the effective loop area of ​​each conductor pair can be reduced, thereby improving signal integrity and reducing electromagnetic interference. To improve mechanical flexibility, longitudinal slots 218 can be defined in the intermediate region, positioned between at least some of the conductor tracks. The slots can extend parallel to the length of the substrate and can mechanically decouple bending of the sensing region from the conductor-guiding region. This decoupling allows the sensing region to bend independently of the conductor-guiding region, thereby reducing the transmission of mechanical stress and minimizing the risk of damage during use on complex surfaces. The slots can include curved edges 228 at their end sections, which can be wider than the elongated intermediate sections of the slots. This geometry can help distribute mechanical stress and prevent cracking or breakage of the substrate at the slot ends. The edge 224 of the substrate can define the boundary of the first end section adjacent to the sensing region. Vias 226 can be used throughout the substrate to electrically connect conductors and coils between different layers. This can enable complex routing and the realization of overlapping coil arrangements without increasing the overall width of the sensing region. The width of the intermediate region IRw can be greater than the width of the detection region SRw, for example, at least three times wider, at least four times wider, or at least five times wider. The width SRw of the detection region can be relatively small compared to the length of the detection region SRL, which can extend along the edge of the first end section. For example, the length of the detection region SRL can be at least five times longer, at least six times longer, or at least seven times longer. In some embodiments, the width of the intermediate region IRw can be greater than one-third of the length of the detection region SRL (e.g., IRw > SRL / 3). Fig. 3 provides a detailed view of a section of the circuit device, focusing on the sensing region and the arrangement of the coil array. The lateral arrangement of the coils is shown in Fig. 3, with first and second coils positioned alternately collinearly along the sensing region. The vias for interlayer connections are also shown. In various embodiments of the circuit device of Figures 2 and 3, a narrow (e.g., 1.6 millimeters (mm) wide) active area (e.g., sensing region) comprises overlapping eddy current coils fabricated using a multilayer PCB structure. In this example, a first coil can be formed using conductors on layers 2 and 3 of the substrate, while a second coil can be formed using conductors on layers 1 and 4 of the substrate. A series of cuts, such as slits, holes, slots, or notches (in this example with a 14 mm extension), can be included in the flexible PCB array (e.g., longitudinal slots), which separate the bending of the sensitive coil area (e.g., the sensing region) from the bulk of the remaining flexible circuit array (e.g., the sensing region).decouple the region (of the conductor routing region), particularly from a region distal to the sensitive coil area located at the opposite end of the circuit assembly. The regions at the ends of the respective sections may be curved to reduce any potential concentration of mechanical stress at these points under deformation. Such features can inhibit or prevent tearing, delamination, or other mechanical damage to the sensor assembly. Fig. 4 is a circuit device 400 for use with an eddy current array probe (ECA probe) comprising four substrate layers. Fig. 4 shows the four substrate layers arranged one above the other, and each of Figs. 5, 6, 7 to 8 shows a different one of the four layers. Fig. 4 is similar in many aspects to the circuit device of Fig. 2. Any aspect disclosed with respect to the circuit device of Fig. 4 may be included in the embodiment of the circuit device of Fig. 2, and vice versa. The circuit device of Fig. 4 includes a sensing region 408, an intermediate region 412, and an array of coils 414. The array includes first coils 420 and second coils 422. The circuit device also includes conductor tracks 416 and longitudinal slots 418. Vias 426 are included to connect coil sections and / or conductor tracks between layers.Although a four-layer arrangement is shown in the non-restrictive embodiment of Fig. 4, this configuration is not intended to be restrictive. In other embodiments, a larger or smaller number of substrate layers may be used. For example, a two-layer or three-layer substrate may be used in simpler designs, or a five-layer, six-layer, or higher-layer substrate may be used in embodiments requiring additional conductor density, shielding, or mechanical tuning. The specific number of layers used may vary depending on the design requirements and is not restrictive unless expressly stated. Fig. 5 shows a first layer 432 of the circuit device of Fig. 4. As shown in Fig. 5, several turns of the first coils are defined in the first layer. Vias are used to connect turns of the first coils in the first layer to turns of the first coils in the fourth layer, as shown in Fig. 8. Conductor traces are defined in the first layer and connected to turns of the first coils defined in the first layer. Conductor traces in the first layer also extend to vias for connection to turns of the second coils defined in the third layer, as shown in Fig. 7. Fig. 6 shows a second layer 434 of the circuit device of Fig. 4. As shown in Fig. 6, several turns of the second coils are defined in the second layer. Vias are used to connect turns of the second coils in the second layer to turns of the second coils in the third layer, as shown in Fig. 7. Conductor traces are defined in the second layer and connected to turns of the second coils defined in the second layer. Conductor traces in the second layer also extend to vias for connection to turns of the first coils defined in the fourth layer, as shown in Fig. 8. Fig. 7 is a third layer 436 of the circuit device of Fig. 4. As shown in Fig. 7, several turns of the second coils are defined in the third layer. The turns of the second coils defined in the third layer are connected via vias to corresponding turns of the second coils defined in the second layer. The other ends of the turns of the second coils defined in the third layer are connected via vias to conductor tracks in the first layer. Fig. 8 is a fourth layer 438 of the circuit device of Fig. 4. As shown in Fig. 8, several turns of the first coils are defined in the fourth layer. The turns of the second coils defined in the fourth layer are connected via vias to corresponding turns of the first coils defined in the first layer. The other ends of the turns of the first coils defined in the fourth layer are connected via vias to conductor tracks in the second layer. Thus, as shown in Figs. 4, 5, 6, 7 to 8, the first coils are defined in the first and fourth layers, and conductor tracks for connecting the first coils to a probe are defined in the first and second layers. Furthermore, the conductor tracks of each pair corresponding to the first coils overlap as they run along their respective first and second layers of the substrate. The second coils are defined in the second and third layers, and conductor tracks for connecting the second coils to a probe are defined in the first and second layers. Furthermore, the conductor tracks of each pair corresponding to the second coils overlap as they run along their respective first and second layers of the substrate. Fig. 9 shows experimental test data 900, including an impedance plane 902 and corresponding imaging 904, which illustrates a defect indication 906 obtained using an ECA sensing arrangement according to an embodiment of the present disclosure. In this example, the test object is a turbine blade with a surface profile exhibiting curvature in multiple directions, which presents a challenging investigation scenario for conventional probes. The impedance plane displays the response of the ECA probe when scanning the test object, with the defect indication appearing as a distinct deviation or feature in the impedance data. The corresponding imaging provides a spatial representation of the location and size of the defect on the test object. The fault indication shown in Fig. 9 demonstrates the improved sensitivity and coverage that can be provided by the described ECA detection arrangement. In contrast, conventional eddy current array devices can have difficulty maintaining adequate contact with surfaces that exhibit curvature in multiple directions, causing areas of the detection region to lift off the surface and resulting in a corresponding loss of sensitivity. Consequently, faults such as the one shown in Fig. 9 can go undetected with conventional probes. Fig. 10 is a schematic diagram of an ECA sensing arrangement 1000. The sensing arrangement may include a test device 1040 (e.g., an acquisition device), such as a handheld or portable arrangement. The test device may be electrically connected to a probe arrangement 1050, for example, using a multi-wire connection 1030. The probe arrangement may include one or more transducers, such as an eddy current transducer array (EC transducer array) 1052, which includes respective EC sensors 1054A to 1054N. The transducer array may follow a linear or curved contour or may include an array of elements extending in multiple axes. In some embodiments, the probe arrangement may include or otherwise be connected to embodiments of the circuit devices disclosed herein (e.g., including an array of coils as the EC sensors). A modular probe array can be used, for example, to allow a test instrument to be used with different probe arrays. Generally, the transducer array can include EC coils, such as those mounted on or embedded in a substrate. The EC coils are electromagnetically connected to a target (e.g., a test specimen or "test object"). The test instrument can include digital and analog circuitry, such as a front-end circuit that includes one or more transmit signal chains, receive signal chains, or switching circuits (e.g., transmit / receive switching circuits). The transmit signal chain can include amplifier and filter circuitry, such as for providing transmit pulses for transmission through a connection to a probe array.A 1060 error associated with the target can be detected, for example, by monitoring an impedance or other electrical property associated with respective sensors in the converter array. While Fig. 1 shows a single probe assembly and a single transducer array, other configurations can be used, such as multiple probe assemblies connected to a single test device, or multiple transducer arrays used with a single probe assembly. Similarly, a test protocol can be carried out in coordination between multiple test devices, such as in response to an overall test scheme created by a particular test device or by another remotely located system, such as a data processing unit 1008 or a universal data processing device such as a laptop 1032, a tablet, a smartphone, a desktop computer, or the like. The front-end circuit 1022 can be connected to and controlled by one or more processor circuits, such as a processor circuit 1002 included as part of the test instrument. The processor circuit can be connected to a memory circuit 1004, for example, to execute instructions that cause the test instrument to perform one or more EC tests, process or store data relating to an EC investigation, or otherwise execute techniques as shown and described herein. The test instrument can be communicatively connected to other parts of the system, for example, using a wired or wireless communication interface 1020. The test device may include a display 1010, such as for displaying configuration information or results, and an input device 1012, such as one or more from a keyboard, trackball, function keys or screen keys, a mouse interface, a touchscreen, a stylus or the like, for receiving operator commands, configuration information or answers to queries. Fig. 11 shows an ECA probe arrangement 1100. The probe arrangement can include a circuit device 1102 connected to a probe 1104. The probe can include a connector 1106 for electrically connecting the probe to a receiving device. The probe can further include an elastic support structure 1108. The circuit device can represent any of the embodiments disclosed herein, including variations in substrate materials, coil arrangements, conductor routing, and slot configurations. Figure 11 shows the elastic support structure with a cylindrical shape, which is attached to an object-facing surface of the probe. This cylindrical shape of the support structure allows the circuit device, such as the sensing region, to bend laterally, enabling the sensing region to conform to the contour of the object under test. The elastic support structure can also allow the circuit device to bend longitudinally to adapt its shape to test object surfaces with curvature in multiple directions. In other embodiments, the elastic support structure can have various shapes, such as an arc, a saddle, a wedge, a dome, a crescent, a ring, or a segmented structure, depending on the desired contact profile and flexibility.The support structure can be made from materials such as silicone, polyurethane, foam or other elastomers, which are selected for their ability to deform and regain their shape while applying pressure against the circuit device to conform to the surfaces of a test object. In some embodiments, the elastic support structure cannot be positioned directly beneath the probe, as shown in Fig. 11. For example, the support structure can extend from the probe, together with the circuitry, allowing the circuitry to move more freely and be pressed into the contour of a test object along with the support structure. This arrangement can offer adaptability for examining surfaces with complex or irregular geometries, as the circuitry and support structure can be handled together to achieve optimal contact and coverage during non-destructive testing. Fig. 12 is a figure 1200 showing a printed circuit board of an ECA probe being pressed and bent by a person's hand into a complex surface of a test object. The figure shows that the printed circuit board, which represents an embodiment of the circuit device disclosed herein, is able to closely conform its shape to the surface of the test object, which has curvatures in multiple directions. This ability to adapt and maintain contact with complex, curved surfaces underscores the effectiveness of the flexible design of the circuit device for non-destructive testing applications. The arrangement configurations and accompanying drawings presented and described in this document can be used to facilitate the non-destructive testing of structures with curved contours or shapes, such as sharp curvatures in two directions simultaneously. Examples of structures with such a shape may include turbine blades, such as a sheathing region near the root of a high-pressure turbine blade used in a gas turbine engine. Each of the foregoing or non-restrictive aspects shown in the accompanying figures can stand alone or can be combined in various exchanges or combinations with one or more of the other aspects or other items described in this document. The above detailed description includes references to the accompanying drawings, which form part of the detailed description. The drawings show exemplary specific embodiments in which the invention can be carried out. These embodiments are also generally referred to as "examples." Such examples may include elements in addition to those shown or described. However, the inventor of the present invention also considers examples in which only those elements that are shown or described are provided.Furthermore, the present inventor also considers examples using any combination or interchange of those elements that are shown or described (or one or more aspects thereof), either in relation to a particular example (or one or more aspects thereof) or in relation to other examples shown or described herein (or one or more aspects thereof). In case of conflicting usages between this document and documents incorporated by reference, the usage in this document shall prevail. In this document, the terms "a" or "an" are used, as is customary in patent documents, to encompass one or more than one, irrespective of other instances or uses of "at least one" or "one or more". In this document, the term "or" is used to denote a non-exclusive "or", such that "A or B" includes "A but not B", "B but not A", and "A and B", unless otherwise specified. In this document, the terms "include" and "whereby" are used as common-language equivalents of "comprise" and "whereby", respectively.Furthermore, in the following aspects, the terms "including" and "comprehensive" are to be understood openly, meaning that a system, device, article, composition, formulation, or method that includes elements in addition to those listed in a claim after such a term will nevertheless be considered to fall within the scope of protection of that claim. Moreover, in the following aspects, the terms "first," "second," and "third," etc., are used merely as designations and are not intended to establish any numerical requirements for their objects. The above description is to be understood as illustrative and not as limiting. For example, the examples described above (or one or more aspects thereof) may be used in combination with one another. Other embodiments may be used, for example, by a person skilled in the art after reviewing the above description. The summary is provided to enable the reader to quickly grasp the nature of the technical disclosure. It is submitted with the understanding that it is not to be used for the interpretation or limitation of the scope of protection or the meaning of the claims. Furthermore, various features may be summarized in the above detailed description in order to streamline the disclosure. This should not be interpreted as meaning that an unclaimed disclosed feature is essential to any claim.Rather, the inventive element may lie in fewer than all features of a particular disclosed embodiment. Therefore, the following aspects are hereby included in the detailed description as examples or embodiments, each aspect constituting a separate embodiment, and it is intended that such embodiments may be combined with one another in various combinations or interchanges.

Claims

Circuit device for use with an eddy current array probe (ECA probe), the device comprising: a substrate comprising: a sensing region at a first end section of the substrate; a conduction region at a second end section of the substrate opposite the first end section; and an intermediate region extending between the sensing region and the conduction region; an array of coils defined in the sensing region and arranged laterally along the sensing region; conductive traces defined in the intermediate region and the conduction region and extending longitudinally along the latter to connect the array of coils to a probe connector of the ECA probe; and longitudinal slots defined in the intermediate region of the substrate between at least some of the conductive traces to mechanically decouple bending of the sensing region from the conduction region. Device according to claim 1, wherein the array of coils comprises an alternating arrangement of first coils and second coils, wherein sections of the first coils overlap with sections of the second coils. Device according to claim 2, wherein the longitudinal slots and the conductor tracks are defined in an alternating arrangement laterally over the intermediate region. Device according to claim 2, wherein the first coils and second coils are collinearly aligned. Device according to claim 2, wherein the detection region of the substrate comprises several detection region layers, wherein the coils comprise coil conductor tracks; the coil conductor tracks of the first coils are defined in a first subgroup of the detection region layers; and the coil conductor tracks of the second coils are defined in a second subgroup of the detection region layers. Device according to claim 5, wherein the first subgroup of the detection region layers comprises two layers and the second subgroup of the detection region layers comprises two layers positioned between the two layers of the first subgroup. Device according to claim 5, wherein the intermediate region of the substrate comprises fewer layers than the detection region. Device according to claim 1, wherein each coil of the array is connected to a pair of conductors and the conductors of the pair extend along adjacent layers of the intermediate region in an overlapping arrangement. Device according to claim 8, wherein no more than two pairs of conductor tracks are positioned between adjacent longitudinal slots. Device according to claim 1, wherein the detection region comprises: a width of the detection region extending longitudinally from an edge of the first end of the substrate to the intermediate region; and a length of the detection region extending along the edge of the first end of the substrate, and the length of the detection region is at least 5 times greater than the width of the detection region. Device according to claim 1, wherein the intermediate region comprises an intermediate width equal to a length of the longitudinal slots and extends longitudinally from the detection region to the conductor guidance region, wherein the width of the intermediate region is at least 3 times greater than the width of the detection region. Device according to claim 1, wherein the longitudinal slots comprise: curved end sections; and elongated sections between the curved end sections, and the curved end sections are wider than the elongated intermediate sections. Eddy current array detection arrangement (ECA detection arrangement), comprising: a probe, comprising: a printed circuit board comprising an array of coils; and an elastic support structure that can be positioned against a surface of the printed circuit board; and an acquisition device that can be operatively connected to the array of coils to realize a specific time-controlled coil stimulation sequence and to acquire corresponding eddy current signals, wherein the printed circuit board further comprises: a substrate, comprising: a detection region at a first end section of the substrate, wherein the array of coils is defined in the detection region and arranged laterally along it; a conduction region at a second end section of the substrate opposite the first end section; and an intermediate region extending between the detection region and the conduction region;Conductive traces defined in the intermediate region and the conduction region, extending longitudinally along these to connect the array of coils to the acquisition device; and longitudinal slots defined in the intermediate region of the substrate between at least some of the conductive traces, wherein the elastic support structure is configured to bend the sensing region of the substrate to conform to the shape of a test object's contour. ECA detection arrangement according to claim 13, wherein the array of coils comprises an alternating arrangement of first coils and second coils, wherein sections of the first coils overlap with sections of the second coils and the first coils and the second coils are collinearly aligned. ECA detection arrangement according to claim 14, wherein the longitudinal slots and the conductor tracks are defined in an alternating arrangement laterally over the intermediate region. ECA detection arrangement according to claim 13, wherein: the detection region of the substrate comprises multiple detection region layers; the coils comprise coil conductor tracks, wherein the coil conductor tracks of the first coils are defined in a first subgroup of the detection region layers; and the coil conductor tracks of the second coils are defined in a second subgroup of the detection region layers. ECA detection arrangement according to claim 16, wherein the first subgroup of detection region layers comprises two layers and the second subgroup of detection region layers comprises two layers positioned between the two layers of the first subgroup. ECA detection arrangement according to claim 16, wherein the intermediate region of the substrate comprises fewer layers than the detection region. ECA detection arrangement according to claim 13, wherein each coil of the array is connected to a pair of conductor tracks and the conductor tracks of the pair extend along adjacent layers of the intermediate region in an overlapping arrangement. ECA detection arrangement according to claim 13, wherein the detection region comprises: a width of the detection region extending longitudinally from an edge of the first end of the substrate to the intermediate region; and a length of the detection region extending along the edge of the first end of the substrate, wherein the intermediate region has an intermediate width equal to a length of the longitudinal slots and extending longitudinally from the detection region to the conductor guidance region, and the width of the intermediate region is greater than one-third of the length of the detection region. Circuit device for use with an eddy current array probe (ECA probe), the device comprising: a substrate comprising: a sensing region at a first end section of the substrate; a conduction region at a second end section of the substrate opposite the first end section; and an intermediate region extending between the sensing region and the conduction region; an array of coils defined in the sensing region; conductive traces defined in the intermediate region and the conduction region extending along them to connect the array of coils to a probe connector of the ECA probe; and longitudinal slots defined in the intermediate region of the substrate, wherein an elastic support structure of the ECA probe is configured to bend the sensing region of the substrate to conform to the shape of a test object's contour.

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