EP3458852A1

EP3458852A1 - Method for measuring by eddy currents and device for measuring by eddy currents

Info

Publication number: EP3458852A1
Application number: EP17742493.4A
Authority: EP
Inventors: Frédéric NOZAIS; Jean-Marc Decitre
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2016-06-27
Filing date: 2017-06-26
Publication date: 2019-03-27
Also published as: WO2018002503A1; FR3053120A1; US20190323991A1; FR3053120B1

Abstract

A method for measuring by eddy currents, comprising the following steps: A) providing at least one magnetic field sensor (110); B) providing at least one first magnetic inductor (120) for generating a first magnetic field (B1) which, at the magnetic field sensor (110), is orientated in a first direction of the detection axis (111); C) providing at least one second magnetic inductor (130) configured to generate a second magnetic field (B2) which, at the magnetic field sensor (110), is orientated in a second direction of the detection axis (111); D) providing a current supply system (140) (11, 12); E) modifying the configuration of the first and second magnetic inductors (120, 130) with respect to the magnetic field sensor (110) and/or the current supply system (140) in such a way that the sum of the first and second magnetic fields (B1+B2) at the magnetic field sensor (110) is zero, and F) measuring the eddy currents of a sample.

Description

FOUCAULT CURRENT MEASUREMENT METHOD AND MEASURING DEVICE THEREFOR

CURRENTS OF FOUCAULT

DESCRIPTION

TECHNICAL AREA

The invention relates to the field of non-destructive measurements and more particularly relates to non-destructive measurements by eddy currents.

The invention thus relates to an eddy current measurement method and an eddy current measurement device.

STATE OF THE PRIOR ART

The use of eddy current measurements makes it possible to detect the presence of possible defects on the surface of a metal object, this over a depth of 10 to 15 mm. It is thus possible to detect non-destructively the presence of any notches, cracks or other traces of corrosion on metal objects not necessarily planar. This type of measurement is thus particularly used in the aeronautical industry to control the structural elements of the aircraft that constitute the fuselage and the wings.

A measurement method generally comprises, and with reference to FIG. 1, the following steps:

A) providing at least one magnetic field sensor 110 having a detection axis 111 in which the magnetic field sensor 110 is sensitive to the magnetic field,

B) providing at least a first magnetic inductor 120 configured to generate a magnetic field B1 at a measurement zone 210,

D) providing a power supply system 140 for applying to the first magnetic inductor 120 a first periodic current 11 having a given period, F) non-destructive eddy current measurement of a given sample 200, the measurement zone 210 having at least a surface portion 201 of said sample 200.

It should be noted that, of course and according to the principle of eddy current measurement, if in step F) the measurement zone 210 comprises at least a part of the surface 201 of the sample, this measurement zone 210 s extends beyond the surface 201 and includes a portion of the sample under the surface 201 of the sample 200. Thus, such an eddy current measurement also makes it possible to detect a part of the buried defects.

The measuring step F) consists of applying the first periodic current 11 to the first magnetic inductor 120 by the magnetic supply system 140 so as to generate a periodic magnetic field at the measurement zone 210. This periodic magnetic field generates, in the sample and close to its surface, an induced electric current, said Foucault, which generates in return a magnetic field at the magnetic field sensor 110. However, the slightest defect, disturbing the path of the eddy currents causes a variation of the magnetic field perceived by the magnetic field sensor 110.

In order to optimize the measurement of the magnetic field generated by the eddy currents perceived by the magnetic field sensor 110 and to facilitate the analysis of the eddy current measurements, it is known to use the configuration of the first magnetic inductor 120 illustrated. in this configuration, the first magnetic inductor 120 generates, in a given current condition, a magnetic field B1 which is, at the level of the magnetic field sensor 110, oriented in a first direction of the detection axis 111, and at a measurement zone 210, oriented in a second direction of the detection axis 111 opposite to the first direction of the detection axis 111.

It will be noted that with such a configuration, the magnetic field generated by the eddy currents is directed along the detection axis 111. The measurement variation by eddy currents is thus reinforced. Moreover, this variation for a defect occurs, in such a configuration, according to a simple form called monopolar, that is, close to a Dirac distribution. The detection is thus simplified and it is easy to interpret the measurement by eddy currents to determine the location, or even the dimensioning of the identified defects.

While this configuration is particularly optimized for eddy current measurement, it has major disadvantages. Indeed, in such a configuration, the magnetic field sensor is subjected along its detection axis 111 to the sum of the magnetic field generated by the first magnetic inductor 120 and that generated by the eddy currents. However, the sensitivity of a magnetic field sensor 110, whatever its type, is generally limited and, in this configuration, the magnetic field sensor 110 is mainly used for measuring a known magnetic field, that generated by the first magnetic inductor 120. Moreover, in such a configuration, the intensity of the current supplying the first magnetic inductor 120 must be limited so that the magnetic field that it induces does not saturate the magnetic field sensor 110. The generated eddy currents, and hence the measured signal, are also limited.

In order to overcome these drawbacks, it is known from document WO2015 / 177341 to arrange this first magnetic inductor 120 in a configuration in which it generates a magnetic field perpendicular to the detection axis 111. In this way the magnetic field generated by the first Magnetic inductor 120 is not detected by the magnetic field sensor and does not disturb the measurement of the magnetic field generated by the eddy currents.

Nevertheless, as previously indicated, such a configuration is not optimized to provide a magnetic field generated by eddy currents along the detection axis and the eddy current measurements are more difficult to interpret.

Note that it is also known from WO2015 / 177341 to provide a second magnetic inductor to facilitate the adjustment of the magnetic field at the detection axis and thus obtain at the magnetic field sensor a sum of the magnetic fields. generated by the first and second magnetic inductor which is substantially perpendicular to the detection axis. This possibility has the same disadvantages mentioned above for the configuration of the document WO2015 / 177341 employing only one magnetic inductor.

Thus, in the prior art, there are no eddy current measurement methods making it possible to optimize the sensitivity of the measurement of the magnetic field generated by the eddy currents and which has a configuration facilitating the interpretation of the measurement by eddy currents.

STATEMENT OF THE INVENTION

The aim of the invention is to overcome this drawback and thus aims at providing an eddy current measurement method making it possible to optimize the sensitivity of the magnetic field measurement generated by eddy currents while facilitating the interpretation of the measurements obtained.

To this end, the invention relates to a method for measuring eddy currents comprising the following steps:

A) providing at least one magnetic field sensor having a detection axis according to which the magnetic field sensor is sensitive to the magnetic field,

B) providing at least a first magnetic inductor configured to generate, in a given current condition, a first magnetic field which is, at the magnetic field sensor, oriented in a first direction of the detection axis, and at a measurement zone, oriented in a second direction of the detection axis opposite to the first direction of the detection axis,

D) providing a power supply system for applying to the first magnetic inductor a first periodic current having a given period.

The method further comprising the steps of:

C) providing at least a second magnetic inductor configured to generate, in the same current condition as the first magnetic inductor, a second magnetic field at the magnetic field sensor which is, at the level of the magnetic field sensor and at the measuring zone oriented along the second direction of the detection axis,

the power supply system supplied in step D) being further configured to apply to the second magnetic inductor a second periodic current having the given period,

E) modifying the configuration of the first and second magnetic inductors vis-à-vis the magnetic field sensor and / or the current supply system so that in application of the first and second current the sum of the first and the second magnetic field at the magnetic field sensor is substantially zero,

F) non-destructive measurement by eddy currents of a given sample, the sample being positioned so that the measurement zone comprises at least a surface portion of said sample, the configuration of the first and second magnetic inductor modified to step E) being kept throughout the measurement.

By "sum of the first and second magnetic field at the magnetic field sensor" it should be understood, above and in the rest of this document, the vector sum of the first and second magnetic field at the field sensor magnetic. Thus, with such a substantially zero sum, the first and second magnetic fields are, at the level of the magnetic field sensor, each along the detection axis with a direction opposite to one another and a substantially equal amplitude. In general, when a sum of magnetic fields is mentioned, this sum is, unless otherwise specified, a vector sum.

In the same way, the measurement method according to the invention remaining an eddy current measurement method, the measuring zone comprising at least a part of the surface of the sample, this measuring zone of course extends to surface and includes part of the sample below the surface of the sample. Thus, such an eddy current measuring method according to the invention also makes it possible to detect part of the buried faults. Such an eddy current measurement method makes it possible to reduce at the level of the magnetic field sensor the relative portion of the magnetic field generated by the magnetic inductor (s) with respect to the magnetic field generated by the eddy currents. Indeed, the use of the second inductor combined with the modification of the configuration of the first and second magnetic inductor allows compensation, at least partially, of the magnetic field generated by the first magnetic inductor by means of the magnetic field generated by the second inductor . This compensation is accompanied by a strengthening of the magnetic field generated at the measurement zone, the magnetic fields generated by the first and the second magnetic inductor being added in a constructive manner. The eddy currents resulting at the measurement zone are therefore themselves reinforced.

Moreover, since this sum of field is oriented at the measurement zone along the detection axis of the magnetic field sensor, it follows that the magnetic field generated by the eddy currents at the measurement zone is also oriented along the detection axis. The detection of the magnetic field generated by the eddy currents is optimized and the interpretation of the eddy current measurements is facilitated.

It therefore follows from such a measurement method that the sum of magnetic fields induced by the first and the second magnetic inductor at the level of the magnetic field sensor is small, or even zero, whereas the magnetic field generated by the eddy currents is it is particularly optimized while allowing an easy interpretation of the measurements.

Note that such a method is beneficial regardless of the type of magnetic field sensor provided in step A). Indeed, in the case where the magnetic field sensor is a sensor of the inductive type, that is to say based on a coil, only the useful signal, that is to say the magnetic field generated by the currents of Foucault and more particularly by the modification of these eddy currents in the presence of a defect, is amplified. On the one hand amplification of the signal from the coil can be increased without risking saturating the amplification stage, on the other hand it is possible to increase the currents in the inductors. The signal-to-noise ratio is improved by one and / or the other of these actions. In the case where the magnetic field sensor is a magnetic type sensor, that is to say a sensor using a physical principle such as magnetoresistance, giant magnetoresistance, giant magnetoimpedance or the hall effect, the sensitivity The magnetic field sensor is used essentially for the useful signal, ie the magnetic field generated by the eddy currents. It is therefore possible to use the entire sensitivity range of the magnetic field sensor by limiting the saturation risks associated with the magnetic fields induced by the magnetic inductors.

Step E) of modifying the configuration of the first and second magnetic inductor can be performed at least partially in the absence of sample.

With such a step E) of modifying the configuration of the first and the second magnetic inductor, it is possible to have a relatively sensitive eddy current measurement regardless of the sample. Indeed, if the sample can, due to the gap effect (defined in this document as the distance between an inductor and the sample) that it creates, modify the sum of the first and second magnetic field at level of the magnetic field sensor, this modification will remain contained. The sum of the first and the second magnetic field at the magnetic field sensor remains contained and the sensitivity relatively optimized vis-à-vis methods of the prior art, this regardless of the sample.

The step E) of modifying the configuration of the first and second magnetic inductor can be performed at least partially in the presence of the sample with at least a portion of the surface of the sample which coincides with the measurement zone, the measurement area remaining at the surface of the sample during the implementation of step F).

With such a step E) of modifying the configuration of the first and second magnetic inductors, the eddy current measurement is particularly optimized. Indeed, the presence of the sample during step E) makes it possible to correct the air gap effect that it is likely to create. Thus during measurement step F), the sum of the first and second magnetic fields at the sensor magnetic field is substantially zero and therefore does not affect little or not the sensitivity of the eddy current measurement.

During step D) of supplying the second magnetic inductor, the second magnetic inductor may be substantially identical to the first magnetic inductor.

Step E) of modifying the configuration of the first and the second magnetic inductor may comprise the following sub-steps:

El) configuration of the power supply system so that the first and the second periodic current are substantially identical,

E2) modifying the relative placement of the second magnetic inductor to position it symmetrically to the first magnetic inductor with respect to the detection axis.

The combination of a use of a first and a second substantially identical inductor and a placement of the first and second inductor symmetrically to each other with respect to the detection axis allows to obtain simply, this by applying a first and a second current identical, a sum of the first and second magnetic field substantially zero at the magnetic field sensor.

E'1) configuration of the power supply system for applying the first and the second periodic current,

E'2) moving the second magnetic inductor so as to cancel the sum of the first and the second magnetic field at the magnetic field sensor.

E "1) configuring the power supply system to apply the first and the second periodic current, E "2) moving the magnetic field sensor with respect to the first and second magnetic inductors so as to cancel the sum of the first and second magnetic fields at the magnetic field sensor.

Such steps of modifying the configuration of the first and second magnetic inductors allow, by a simple modification of the relative placement of one of the second magnetic inductor and the magnetic field sensor, to cancel the sum of the first and the second inductor. second magnetic field at the magnetic field sensor.

E3) configuring the power supply system to apply the first and the second periodic current,

E4) modifying the second periodic current so as to cancel the sum of the first and second magnetic fields at the magnetic field sensor.

With a step of modifying the first and the second magnetic inductor, the cancellation of the sum of the first and the second magnetic field at the magnetic field sensor can be done by a simple configuration of the power supply system.

The invention further relates to an eddy current measuring device, the measuring device comprising:

at least one magnetic field sensor having a detection axis in which the magnetic field sensor is sensitive to the magnetic field, at least a first magnetic inductor configured to generate, in a given current condition, a first magnetic field which is, at level of the magnetic field sensor, oriented in a first direction of the detection axis, and at a measurement zone, oriented in a second direction of the detection axis opposite to the first direction of the axis of detection. detection,

at least one power supply system for applying to the first a first periodic current having a given period, the measuring device further comprising at least a second magnetic inductor configured to generate, under the same current conditions as the first magnetic inductor, a second magnetic field which is, at the level of the magnetic field sensor and at the level of the magnetic field, measurement oriented along the second direction of the detection axis,

the current supply system being configured to apply to the second magnetic inductor a second periodic current of the given period, and wherein the first and second magnetic inductors have at least one configuration vis-à-vis the magnetic field sensor and of the current supply system as in application of the first and second current, the sum of the magnetic field induced by respectively the first and the second magnetic inductor at the magnetic field sensor is substantially zero.

Such a device allows the implementation of a measurement method according to the invention and therefore benefits from this same measurement method.

The first and second magnetic inductors may be substantially identical.

The power supply system may be configured to power the first and second inductors with a first and a second substantially identical current.

With these configurations of the first and the second magnetic inductor and the power supply system, the sum of the first and the second magnetic field at the magnetic field sensor can be easily canceled.

The second magnetic inductor may be movably mounted relative to the first magnetic inductor and the magnetic field sensor.

In this way the cancellation of the sum of the first and the second magnetic field at the magnetic field sensor can be done by moving the second magnetic inductor vis-à-vis the first magnetic inductor and the magnetic field sensor. The magnetic field sensor may be movably mounted relative to the first and second magnetic inductors.

In this way the cancellation of the sum of the first and second magnetic fields at the magnetic field sensor can be done by moving the magnetic field sensor towards the first and second magnetic inductors.

The power supply system may be configured to apply a second periodic current to the second magnetic inductor different from the first periodic current to obtain the configuration of the first and second magnetic inductors vis-à-vis the magnetic field sensor. and the current supply system in which, in application of the first and second periodic currents, the sum of the magnetic field induced by the first and second magnetic inductors respectively at the magnetic field sensor is substantially zero.

In this way, the cancellation of the sum of the first and second magnetic fields at the magnetic field sensor can be done by adjusting the second current with respect to the first current.

The first and second magnetic inductors are respectively provided by a first and a second coil inscribed on the first and second faces respectively of a flexible dielectric support,

and wherein the magnetic field sensor is included in the flexible dielectric support.

Such a flexible dielectric support allows the device according to the invention to match the surface of the sample to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments, given purely by way of indication and in no way limiting, with reference to the appended drawings in which: FIG. 1 is a schematic view of an eddy current measuring device of the prior art which allows simplified detection of defects,

FIG. 2 is a schematic view of an eddy current measuring device according to a first embodiment of the invention,

FIG. 3 is a flow chart of the main steps of an eddy current measurement method according to the invention,

FIGS. 4A and 4B respectively illustrate a measuring device according to a second embodiment in which the first and second magnetic inductors are provided by two layers, and a configuration of this same measuring device illustrating the positioning of the first magnetic inductor a sample with a defect in order to simulate an eddy current measurement,

FIGS. 5A to 5C parallel the simulated magnetic field variation in the configuration of FIGS. 4A and 4B for an eddy current measuring device according to the prior art having only one magnetic inductor and that simulated by a device in FIGS. 5A a graph showing the magnetic field measured in the complex plane along the sample, in FIG. 5B a graph showing the amplitude variation of the magnetic field measured along FIG. the sample and with in FIG. 5C a graph showing the variation of the magnetic field measured in the complex plane along the sample,

FIG. 6 illustrates an arrangement of two magnetic field sensors, two first inductors and a second magnetic inductor according to a third embodiment of the invention,

Figure 7 illustrates an arrangement of a plurality of magnetic field sensors associated with a first and second second magnetic inductors according to a fourth embodiment of the invention. DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

FIG. 2 illustrates an eddy current measuring device 100 according to the invention when it is implemented in the context of an eddy current measurement on a sample 200.

Such a measuring device comprises:

a magnetic field sensor 110 having a detection axis 111 in which the magnetic field sensor 110 is sensitive to the magnetic field,

a first magnetic inductor 120 configured to generate, in a given current condition, a first magnetic field B1 which is, at the level of the magnetic field sensor 110, oriented in a first direction of the detection axis 111, and at the level of a measuring zone 210, oriented along a second direction of the detection axis 111 opposite to the first direction of the detection axis 111,

a second magnetic inductor 130 configured to generate, under the same conditions as the first magnetic inductor 120, a second magnetic field B2 which is, at the level of the magnetic field sensor 110 and at the measurement zone 210 oriented according to the second direction of the detection axis 210,

a power supply system 140 for applying to the first and second magnetic inductors 120, 130 respectively a first and a second periodic current 11, 12 having a given period.

The first magnetic field sensor 110 is illustrated in FIG. 2 only by its detection axis 111. The first magnetic field sensor may be any type of magnetic field sensor adapted to detect the magnetic field generated by the eddy currents during measurement. Thus, the first magnetic field sensor 110 may be either of the inductive type, such as a conventional coil or a flat coil on a flexible support, or of the magnetic type, such as the sensors based on the magnetoresistance, the sensors based on the giant magnetoresistance. , sensors based on the giant magnetoimpedance or the hall effect sensors. The first and second magnetic inductors 120, 130, according to this first embodiment, are both wire inductors for generating each a circular magnetic field, that is to say a magnetic field which is in all respects a circle centered around the tangentially oriented wire with respect to this same circle. The first and second magnetic inductors 120, 130 are substantially identical. The first and second magnetic inductors 120, 130 are arranged on either side of the magnetic field sensor 110 symmetrically with respect to the detection axis 111.

With such a configuration, when the current supply system applies to the first and second magnetic inductors 120, 130 of the first and second identical currents 11, 12, the first and second magnetic fields are, at the level of the magnetic field sensor 110, oriented along the detection axis in opposite directions to each other. Thus, the first and second magnetic inductors 120, 130 being substantially identical and the first and second currents 11, 12 applied to them being identical, the amplitudes of the magnetic fields induced by the first and second inductors 120, 130 magnetic sensor 111 are equal. As a result, the sum of the first and second magnetic fields B1 + B2 at the magnetic sensor is substantially zero.

In addition, outside the area between the first and second inductors, the magnetic fields generated by the first and second magnetic inductor 120, 130 are oriented in the same direction and their amplitudes add up. Thus, with a measurement zone 210 for which the induced magnetic fields are directed along the detection axis 111, as is the case in FIG. 2, it is possible to obtain for this measurement zone 210 a measurement by Foucault currents optimized and easy to analyze.

It will nevertheless be noted that, for such a configuration in which the first and second magnetic inductors 120, 130 are substantially identical and for which the first and the second currents 11, 12 are identical, the sample to be measured may disturb the compensation of the first magnetic field B1 by the second magnetic field B2. Indeed, because of its metallic character, the electromagnetic interaction between the sample and each of the first and second inductors 120, 130 is different (insofar as the gaps are different) and disturbs differently the first and second magnetic fields B1, B2 and thus the compensation of the latter at the level of the sensor. magnetic field 110.

Thus, according to a possibility of this first embodiment, it can also be provided an additional sub-step of modifying the second periodic current so as to cancel the sum of the first and second magnetic field B1 + B2 at the field sensor magnetic 110 after placement of the sample.

Such a measurement device 100 allows the implementation of an eddy current measurement method comprising, with reference to the flow chart of FIG. 3, the following steps:

A) supply of the magnetic field sensor 110,

B) providing the first magnetic inductor 120 configured to generate, in a given current condition, a first magnetic field B1 which is, at the level of the magnetic field sensor 110, oriented in a first direction of the detection axis 111, and at the measuring zone 210, oriented in a second direction of the detection axis 111 opposite to the first direction of the detection axis 111,

C) supplying the second magnetic inductor 130 configured to generate, in the same current condition as the first magnetic inductor 120, a second magnetic field B2 at the magnetic field sensor 110 which is, at the level of the magnetic field sensor 110 and at the measurement zone 210 oriented along the second direction of the detection axis 111,

D) providing a power supply system 140 for applying to the first magnetic inductor 120 and the second magnetic inductor 130 respectively the first and the second periodic current 11, 12 having the given period,

E) modifying the configuration of the first and the second magnetic inductor 120, 130 with respect to the magnetic field sensor 110 and the system current supply 140 such that in application of the first and the second current 11, 12 the sum of the first and second magnetic field B1 + B2 at the magnetic field sensor 110 is substantially zero, this modification being obtained in this first embodiment by a modification of the relative placement of the second magnetic inductor 130 in order to position it symmetrically to the first magnetic inductor 120 with respect to the detection axis 111,

F) non-destructive measurement by eddy currents of the given sample 200, the sample 200 being positioned so that the measuring zone 210) comprises at least one surface portion 201 of said sample 200, the configuration of the first and second magnetic inductor 120, 130 modified in step E), that is to say their placement symmetrical vis-à-vis the detection axis, being kept throughout the measurement.

It will be noted that in this first embodiment step E) comprises the following sub-steps:

El) configuration of the power supply system 140 so that the first and the second periodic current are substantially identical,

E2) placing the second magnetic inductor 130 symmetrically with the first magnetic inductor 120 with respect to the detection axis 111.

In addition, according to the possibility that there is provided a further sub-step of modifying the second periodic current 12, step E) further comprises the following substeps:

E3) placing the sample 200 with at least one surface portion 201 coinciding with the measurement zone 210,

E4) modifying the second periodic current 12 so as to cancel the sum of the first and the second magnetic field B1 + B2 at the magnetic field sensor 110.

The modification of the second periodic current 12 can consist in modifying at least one of the parameters of the second periodic current 12 among the amplitude and the phase shift with respect to the first periodic current 11. Of course, if this adjustment is preferably done with current, it is also possible without it is beyond the scope of the invention for the power supply system to be configured to change the voltage applied to the second magnetic inductor 130 to adjust the second periodic current 12 flowing therethrough.

Of course, as an alternative to such a step E4) it is also conceivable, without departing from the scope of the invention, to provide for a modification of the first periodic current 11, the characteristics of the second periodic current 12 remaining unchanged.

According to another variant of the invention, it is also conceivable that the step E) of modifying the configuration of the first and second magnetic inductors 120, 130 vis-à-vis the magnetic field sensor 110 and the magnetic field system. current supply 140 is made only by a modification of the second periodic current 12. According to this variant of the invention, step E) comprises only sub-steps E3) and E4).

With this step E) of modifying the configuration of the first and second magnetic inductors 120, 130, whether in the first embodiment or according to the variants of the invention, it is possible to perform an eddy current measurement. which, with such a measuring method, has an increased sensitivity. FIGS. 4A to 5B illustrate such increased sensitivity in the context of a second embodiment of the invention in which the first and second magnetic inductors 120, 130 are each in the form of a sheet.

A measuring device 100 according to this second embodiment differs from the first embodiment by the shape of each of the first and second magnetic inductors 120, 130, these being provided by plies instead of son.

Thus, as illustrated in FIG. 4A, which shows the arrangement of the first and second magnetic inductors and the magnetic field sensor with respect to the sample, each of the first and second magnetic inductors 120, 130 is in the form of a ply 0.57 mm wide and 10 μιη thick, and having 6 son (turns) of copper. Similarly to the first embodiment, the magnetic field sensor 110 is disposed between the first and the second magnetic inductor 120, 130. The magnetic field sensor 110 is formed by a coil etched on a flexible film and has its axis of rotation. detection 111 which is included in the plane in which the plies forming the first and the second magnetic inductor 120, 130 extend and which is perpendicular to the direction of the first and second currents 11, 12. This coil forming the field sensor magnetic 110 is a rectangular coil (winding in the thickness of the kapton film) and dimensions 0.6 mm wide, 2 mm deep and 0.08 mm thick.

With such an arrangement of the magnetic field sensor, the first and second magnetic fields B1, B2 are, at the level of the magnetic field sensor 110, respectively a first and a second direction of the detection axis 111.

The sample 200 is arranged facing the first magnetic inductor 120 opposite the second magnetic inductor 130 with a surface of the sample 201 which extends parallel to the plane along which the first and the second magnetic inductor 120 extend. , 130.

FIG. 4B illustrates more precisely the configuration of the first magnetic inductor 120 vis-à-vis the surface 201 of the sample 200. It will be noted that in this FIG. 4B is illustrated the connection wiring 125 of the first magnetic inductor 120. This configuration of the first magnetic inductor 120 has also been used to simulate the eddy current magnetic field measured by a magnetic field sensor 110 for the configuration according to this second embodiment and for a configuration of the prior art in which it is not possible. no second magnetic inductor 130 is provided. It can thus be seen from this FIG. 4B that a sample surface defect 220 has been introduced opposite the first magnetic inductor 120. FIG. 4B also shows the location of the magnetic inductor 130. measurement 210 above which the magnetic field sensor 110 is disposed and the direction 211 that the sensor is moved in the framework of these simulations to measure the variation of the magnetic field generated by the eddy currents. The measured magnetic field with such a configuration has been simulated by the CIVA ^® software for respectively a device according to the first embodiment and thus includes a second magnetic inductor 130 and a prior art device having no second inductor 130. Figures 5A to 5C show the results of such a simulation.

For these simulations, the measurement conditions are as follows:

the first periodic current 11 has an amplitude of 100 mA for a frequency of 100 kHz,

the second periodic current 12 has an amplitude of 150 mA and a frequency of 100 kHz, and is shifted by 345 ° with respect to the first periodic current 11,

the surface of the sample is arranged at 80 μιη of the first inductor, the first and the second magnetic inductor 120, 130 are each disposed at a distance of 55 μιη from the magnetic field sensor.

Thus, FIG. 5A shows the result in the complex plane of the measurement obtained by the magnetic field sensor 110 for a displacement in the direction 211 illustrated in FIG. 4B, this for, under the reference 301, the configuration according to this second embodiment of FIG. realization and for, under the reference 302, the configuration according to the prior art.

It can thus be seen in FIG. 5A that step E) of modifying the configuration of the first and second magnetic inductors 120, 130 with respect to the magnetic field sensor 110 and the current supply system 140 allows for the measure 301 according to the invention, to have a measurement which remains around the origin. For the measurement 302 according to the prior art, the magnetic field sensor 110 being subjected both to the magnetic field generated by the first magnetic inductor 120 and to that generated by the eddy currents, the measurement shows that, even at a distance from the 220, the magnetic field measured by the magnetic field sensor is relatively large. In this configuration of the prior art, the amplification of the measured magnetic field is limited by the saturation of the amplifier due to the strong magnetic field produced by the first inductor. In the configuration of measure 301 according to the invention, only the magnetic field created by the disturbance of eddy currents in the presence of a fault is amplified. The field variation due to the disturbance of the eddy currents, lower than the field created by the first magnetic inductor 120, can be amplified much more significantly. The sensitivity of the measurement after amplification 301 for the same defect is therefore significantly improved compared with the measurement of the prior art.

Figures 5B and 5C illustrate another advantage of the configuration according to the invention. Indeed, FIG. 5B shows the variation of the amplitude of the simulated magnetic field 303 for the configuration of the invention in which the second magnetic inductor 130 is provided, and that simulated 304 for the configuration according to the prior art in which a second inductor is not provided, this during the displacement of the magnetic field sensor in the direction 211. It can thus be seen that the amplitude increases significantly since we obtain a signal gain of 7.3 dB. Since the amplification conditions are identical for these two simulations, this gain is solely related to the addition, at the level of the measurement zone, of the magnetic field generated by the first and second magnetic inductors 120, 130.

This phenomenon is also illustrated in FIG. 5C, which shows the variations 305, 306 in the complex plane of the magnetic field measured by the magnetic field sensor 110 for the configuration according to the invention 305 and for the configuration according to the prior art 306 respectively. when moving the magnetic field sensor 110 in the direction 211. Only the variations related to the presence of the defect being shown in Figure 5C, the two representative signals 305, 306 of these variations start from the origin of the axes. It can thus be seen in this FIG. 5C that the variation 305 observed for the configuration according to the invention is much greater than that 306 observed for the configuration of the prior art.

Thus, the measurement method according to the invention benefits from the cumulative gain obtained by the low, or even the absence, of influence of the first magnetic inductor 120 on the magnetic field sensor 110, which makes it possible to optimize the amplification without degradation of the the sensitivity of the magnetic field sensor 110, and by the addition of the magnetic fields induced by the first and the second magnetic inductor 120, 130 at the level of the measurement zone 210. Thus, the measuring method according to the invention makes it possible to increase the magnetic field variation produced by the eddy currents and their amplification. The signal ratio (that is to say the variation of the magnetic field produced by the eddy currents, largely amplified) on noise is thus improved.

It may be noted that if in the first and second embodiments described above, the modification in step E) of the configuration of the first and the second magnetic inductor 120, 130 is provided mainly by a modification of the relative placement of the second magnetic inductor 130 relative to the first magnetic inductor 120, it is also possible to obtain such a modification otherwise.

Thus, step E) can alternatively or in addition comprise the following sub-steps:

E'1) configuration of the power supply system for applying the first and second currents 11, 12 respectively to the first and second magnetic inductors 120, 130,

E'2) modifying the placement of the second magnetic inductor 130 with respect to the first magnetic inductor 120 and the detection axis 120 so that the sum of the first and second magnetic field B1 + B2 at the magnetic field sensor 110 is substantially zero.

It may be noted that these sub-steps E'1) and E'2) can be implemented in the absence of the sample 200, in order to obtain a configuration that can be used with any sample that makes it possible to limit the influence of the magnetic field of the first magnetic inductor 120 without completely removing it due to an "air gap" effect caused by the presence of the sample. They can also be implemented in the presence of the sample 200 to take into account this "gap" effect. According to this second possibility, it may be envisaged to carry out the step of modifying the configuration of the first and second magnetic inductors in two stages. In a first step in the absence of the sample, by performing, for example, the substeps El) to E2) described in connection with the first embodiment of the invention. In the second step, after setting up the sample, for example by performing substeps E'1) and E'2).

Of course, the measuring device 100 according to this variant of the invention has, in order to allow such a configuration change, a second magnetic inductor 130 mounted movable relative to the first inductor 120.

As a variant, step E) may comprise the following sub-steps:

E "1) configuration of the power supply system 140 to apply the first and the second periodic current,

E "2) modifying the placement of the magnetic field sensor 110 with respect to the first and second magnetic inductors 120, 130 so as to cancel the sum of the first and second magnetic fields B1, B2 at the magnetic field sensor 110.

In the same way as the previous variant of the invention, the measuring device 100 according to this variant of the invention has, in order to allow such a configuration change, a magnetic field sensor 110 movably mounted relative to the first inductor magnetic 120.

FIG. 6 illustrates a measuring device 100 according to a third embodiment in which two first magnetic inductors 121, 122 and a single second magnetic inductor 130 are provided, each of these three magnetic inductors 121, 122, 130 being provided by a coil. respective plate inscribed on one of the faces of a flexible dielectric support. A measuring device 100 according to this second embodiment differs from a measuring device 100 according to the first embodiment in that there are provided two first magnetic inductors 121, 122 each formed by a respective flat coil, in that that the second magnetic inductor is also provided by a flat coil and that two magnetic field sensors 112, 113 are provided.

It is also conceivable, without departing from the scope of the invention, to provide more than two magnetic field sensors arranged regularly at equal distances, in continuity with the first two by adding the inductors (first and / or second inductor). ) required. So we can see in Figure 6 that the first two Magnetic inductors 121, 122 are each obtained by writing a respective flat coil on a first face of the dielectric support and the second magnetic inductor 130 is obtained by writing a flat coil on a second face of the flexible dielectric support. Such an inscription on a flexible dielectric support, such as a flexible printed circuit formed either in a polyimide or in a PEEK film, makes it possible to obtain a measuring device the shape of which can be adapted to the surface curvature of the sample to be measured. measure.

Of course, the support may also be, alternatively, rigid or semi-rigid, without departing from the scope of the invention and thus be formed, for example, in an epoxy resin, such as an epoxy resin of type FR-4 (abbreviation of "Flame Resistant-4", that is to say, in French, "flame resistant -4").

The coil forming the second magnetic inductor 120 is placed between the two coils respectively forming the first and the second first magnetic inductor 121, 122. In this way, it is possible to compensate with the second magnetic inductor 130, at each of the sensors. magnetic field 110, the magnetic field induced by the first and the second first magnetic inductor 121, 122.

The magnetic field sensors 112, 113 are included in the flexible dielectric support and have their detection axes 111 in the plane of the flexible dielectric support 150. The use of two magnetic field sensors 112, 113 allows, as illustrated in FIG. 6 to be able to measure by currents of

Foucault in two measurement zones 212, 213 simultaneously.

With such an arrangement of the magnetic field sensors 112, 113 included in a flexible dielectric support, the modification of the configuration of the first magnetic inductors 121, 122 and the second magnetic inductor 130 can be done by modifying the power supply system, in particular the current supplying the second magnetic inductor 130.

FIG. 7 illustrates a configuration of an eddy current measuring device 100 according to a fourth embodiment in which there is provided a first magnetic inductor 120, two second magnetic inductors 131, 132 and a plurality of magnetic field sensors 112, 113, 114. A measuring device 100 according to this fourth embodiment differs from a measuring device according to the first embodiment in that two second magnetic inductors 131 are provided. , 132 and a plurality of magnetic field sensors 112, 113, 114.

The second two magnetic inductors 131, 132 extend parallel to the first magnetic inductor 120 and symmetrically to each other with respect to a plane containing the first inductor and the field sensors 112, 113, 114.

The magnetic field sensors 112, 113, 114 are arranged between the first and second second magnetic inductors 120, 131, 132 aligned in a direction parallel to the first magnetic inductor 120. The detection axes 111, 111 ', 111 "of the sensors magnetic fields are parallel to each other and substantially perpendicular to the first and the second two magnetic inductors.

With such an arrangement of the measuring device 100 by eddy currents, the arrangement of the two second magnetic inductors 131 gives access to the magnetic field sensors 112, 113, 114. Thus the modification of the configuration of the first magnetic inductor 120 and the two seconds magnetic inductors 131, 132 may be made by changing the relative placement of the magnetic field sensors 112, 113, 114 vis-à-vis the first and second second magnetic inductors 120, 131, 132. It can indeed be seen in the figure 7 that it is possible to perform the eddy current measurement according to measurement zones 212, 213, 214 along the first magnetic inductor 120.

With such a measuring device, because of the plurality of magnetic field sensors 112, 113, 114, the eddy current measurement can be done by a simple lateral displacement of all the magnetic field sensors 112, 113, 114 and first and second second magnetic inductors 120, 131, 132.

Thus, as shown in this third and fourth embodiment, if in the first and second embodiments described above there is provided a single first inductor, a single second inductor and a single magnetic field sensor, other configurations. are also conceivable without departing from the scope of the invention. In the same way, it is also conceivable, without departing from the scope of the invention, to provide in a configuration such as those defined in the first and second embodiments, a multiple number of field sensor assemblies. magnetic and first and second magnetic inductor, each set taking the configuration of said first or second embodiment. Thus, it is possible to align at equal distance each of its sets so as to define a measurement line similar to that described above in the context of the fourth embodiment.

Claims

An eddy current measurement method comprising the following steps:

A) providing at least one magnetic field sensor (110) having a detection axis (111) in which the magnetic field capacitor (110) is sensitive to the magnetic field,

B) providing at least a first magnetic inductor (120) configured and arranged to generate, in a given current condition, a first magnetic field (B1) which is, at the level of the magnetic field sensor (110), oriented in a first direction of the detection axis (111), and at a measurement zone (210) oriented in a second direction of the detection axis (111) opposite to the first direction of the axis detection (111),

D) providing a power supply system (140) for applying to the first magnetic inductor (120) a first periodic current (11) having a given period,

the method being characterized in that it further comprises the following steps:

C) providing at least one second magnetic inductor (130) configured and arranged to generate, in the same current condition as the first magnetic inductor (120), a second magnetic field (B2) which is at the sensor magnetic field (110) and at the measurement zone (210) oriented along the second direction of the detection axis (111),

the power supply system (140) provided in step D) being further configured to apply to the second magnetic inductor (130) a second periodic current (12) having the given period,

E) modifying the configuration of the first and second magnetic inductors (120, 130) with respect to the magnetic field sensor (110) and / or the power supply system (140) in such a way that in application of the first and second current the sum of the first and second magnetic field (B1 + B2) at the magnetic field sensor (110) is substantially zero,

F) non-destructive eddy current measurement of a given sample (200), the sample (200) being positioned so that the measurement area (210) has at least a surface portion (201) of said sample (200), the configuration of the first and second magnetic inductor (120, 130) modified in step E) being maintained throughout the measurement.

The measuring method according to claim 1, wherein, step E) of modifying the configuration of the first and second magnetic inductors (110,

120) is performed at least partially in the absence of sample (200).

3. Measuring method according to claim 1 or 2, wherein the step E) of modifying the configuration of the first and second magnetic inductor (110, 120) is performed at least partially in the presence of the sample (200). the sample (200) being positioned so that the measuring area (210) has at least a surface portion (201) of said sample (200), the measurement area remaining at the surface (201) of the sample (200) during the implementation of step F).

4. Measuring method according to any one of claims 1 to 3, wherein during step C) of supplying the second magnetic inductor (130), the second magnetic inductor (130) is substantially identical to the first magnetic inductor ( 120).

5. Measuring method according to one of claims 4, wherein the step E) of modifying the configuration of the first and the second magnetic inductor (120, 130) comprises the following sub-steps:

El) configuring the power supply system (140) so that the first and second periodic currents (11, 12) are substantially identical, E2) modifying the relative placement of the second magnetic inductor (130) to position it symmetrically to the first magnetic inductor (120) with respect to the detection axis (111).

The measuring method according to any one of claims 1 to 5, wherein the step E) of modifying the configuration of the first and the second magnetic inductor (120, 130) comprises the following sub-steps:

E'1) configuring the power supply system (140) to apply the first and second periodic current (12),

- E'2) displacement of the second magnetic inductor (130) so as to cancel the sum of the first and the second magnetic field (B1 + B2) at the magnetic field sensor (110).

Measuring method according to any one of claims 1 to 5, wherein the step E) of modifying the configuration of the first and the second magnetic inductor (120, 130) comprises the following substeps :

E "1) configuring the power supply system (140) to apply the first and the second periodic current (11, 12),

E "2) moving the magnetic field sensor (110) relative to the first and second magnetic inductors (120, 130) to cancel the sum of the first and second magnetic fields (B1, B2) at the magnetic field (110).

The measurement method according to any one of claims 1 to 7, wherein the step E) of modifying the configuration of the first and second magnetic inductors (120, 130) comprises the following sub-steps:

E3) configuring the power supply system (140) to apply the first and the second periodic current, E4) modifying the second periodic current so as to cancel the sum of the first and second magnetic fields (B1 + B2) at the magnetic field sensor (110).

9. Measuring device (100) by eddy currents, the measuring device (100) comprising:

at least one magnetic field sensor (110) having a detection axis (111) in which the magnetic field sensor (110) is sensitive to the magnetic field,

at least one first magnetic inductor (120) configured and arranged to generate, in a given current condition, a first magnetic field (B1) which is, at the level of the magnetic field sensor (110), oriented in a first direction of the detection axis (111), and at a measurement zone (210), oriented in a second direction of the detection axis (111) opposite to the first direction of the detection axis (111) ,

at least one power supply system (140) for applying to the first a first periodic current (11) having a given period,

the measuring device (100) being characterized in that it further comprises at least one second magnetic inductor (130) configured and arranged to generate, under the same current conditions as the first magnetic inductor (120), a second field magnetic field (B2) which is, at the level of the magnetic field sensor (110) and at the measurement zone (210) oriented along the second direction of the detection axis (210),

the power supply system (140) being configured to apply to the second magnetic inductor (130) a second periodic current (12) of the given period,

and wherein the first and second magnetic inductors (120, 130) have at least one configuration vis-à-vis the magnetic field sensor (110) and the power supply system (140) such as in accordance with first and second currents, the sum of the magnetic field (Bl + B2) induced by the first and second magnetic inductor (120, 130) at the magnetic field sensor (110) is substantially zero.

The measuring device (100) according to claim 9, wherein the first and second magnetic inductors (120, 130) are substantially identical.

The measuring device (100) according to claim 9 or 10, wherein the power supply system (140) is configured to power the first and second inductors (120, 130) with a first and a second current ( 11, 12) substantially identical.

12. Measuring device (100) according to any one of claims 10 to 11, wherein the second magnetic inductor (130) is movably mounted relative to the first magnetic inductor (120) and the magnetic field sensor (110).

The measuring device (100) according to any one of claims 10 to 12, wherein the magnetic field sensor (110) is displaceably mounted relative to the first and second magnetic inductors (120, 130).

The measuring device (100) according to any one of claims 10 to 13, wherein the power supply system (140) is configured to apply a second periodic current (12) to the second magnetic inductor (130) different of the first periodic current (11) to obtain the configuration of the first and second magnetic inductors (120, 130) with respect to the magnetic field sensor (110) and the power supply system (140). in which, in application of the first and second periodic currents (11, 12), the sum of the magnetic field (B1 + B2) induced by the first and second magnetic inductors (120, 130) respectively at the magnetic field sensor (110) is substantially zero.

The measuring device (100) according to claim 10 or 11, taken or not in combination with claim 14, wherein the first and second magnetic inductors (120, 130) are respectively provided by a first and a second coil inscribed on respectively the first and the second face of a dielectric support (150),

and wherein the magnetic field sensor (110) is included in the dielectric medium (150).