1. A differential magneto-electric eddy current testing sensor is characterized in that: including magnetoelectric magnetic field sensor, exciting coil (1), permanent magnet (2), coil winding pipe (3) outside winding has exciting coil (1), magnetoelectric magnetic field sensor permanent magnet (2) are installed coil winding pipe (3) are inside, magnetoelectric magnetic field sensor includes first magnetoelectric magnetic field sensor (4), second magnetoelectric magnetic field sensor (5), permanent magnet (2) are located first magnetoelectric magnetic field sensor (4) between second magnetoelectric magnetic field sensor (5).

2. The differential magnetoelectric eddy current sensor according to claim 1, characterized in that: magnetoelectric magnetic field sensor includes two magnetostrictive layer (6) and piezoelectric layer (7), it has to accompany between magnetostrictive layer (6) piezoelectric layer (7).

3. The differential magnetoelectric eddy current test sensor according to claim 2, characterized in that: the magnetostrictive layer (6) is composed of a plurality of layers of iron-based soft magnetic amorphous alloy films made of epoxy resin.

4. The differential magnetoelectric eddy current test sensor according to claim 3, characterized in that: magnetostrictive layer (6) is formed by five layers of iron-based soft magnetism for amorphous alloy film epoxy resin glue bonding, every layer the thickness of iron-based soft magnetism amorphous alloy film is 25um, every layer epoxy resin glue thickness is 1um, magnetostrictive layer (6) gross thickness equals 0.129 mm.

5. The differential magnetoelectric eddy current test sensor according to claim 2, characterized in that: the piezoelectric layer is made of piezoelectric ceramics, and the size of the piezoelectric layer is 20mmx in length, 6mmx in width and 0.5mm in thickness; the magnetostrictive layer (6) has the size of 20mmx in length, 6mmx in width and 0.129mm in thickness.

6. The differential magnetoelectric eddy current test sensor according to claim 1, wherein: the distance d from the center of the first magnetoelectric magnetic field sensor (4) to the center of the second magnetoelectric magnetic field sensor (5) is 38 mm; the distance d/2 from the center of the permanent magnet (2) to the center of the first magnetoelectric magnetic field sensor (4) and the center of the second magnetoelectric magnetic field sensor (5) is 19 mm.

7. The differential magnetoelectric eddy current test sensor according to claim 1, wherein: the permanent magnet (2) is a circular permanent magnet and is made of a rubidium iron boron rare earth permanent magnet.

8. The differential magnetoelectric eddy current test sensor according to claim 1, wherein: the diameter of the permanent magnet (2) is 5mm, and the thickness is 3 mm.

9. The differential magnetoelectric eddy current test sensor according to claim 1, wherein: coil winding pipe (3) are made by PVC plastics or aluminium material or copper material, exciting coil (1) winding is in on coil winding pipe (3), exciting coil (1) winding number of turns is 470 circles, exciting coil (1) diameter is 10 mm.

10. The differential magnetoelectric eddy current test sensor according to claim 1, wherein: this difference magnetoelectric eddy current sensor still includes mounting (8), mounting (8) are installed inside coil winding pipe (3), first magnetoelectric magnetic field sensor (4) second magnetoelectric magnetic field sensor (5) permanent magnet (2) are installed on mounting (8).

Background

Eddy current inspection techniques are widely used to inspect conductive materials for defects. For example, for detecting whether oil and gas pipelines have lost their leaks; the device is used for detecting the internal stress change of the high-speed rail; the method is used for detecting whether cracks exist in high-precision parts of airplanes and rockets. Obviously, the eddy current detection technology has important value in production practice and military industry, and the defect of metal can be detected in advance to prevent occurrence of major accidents. However, the conventional eddy current inspection probe cannot identify fine defects or cracks due to the defects of low sensitivity and weak noise resistance. Therefore, it is imperative to improve the sensitivity of the detection probe.

Disclosure of Invention

The invention provides a differential magnetoelectric eddy current detection sensor which comprises a magnetoelectric magnetic field sensor, an exciting coil, a permanent magnet and a coil winding pipe, wherein the exciting coil is wound outside the coil winding pipe, the magnetoelectric magnetic field sensor and the permanent magnet are arranged inside the coil winding pipe, the magnetoelectric magnetic field sensor comprises a first magnetoelectric magnetic field sensor and a second magnetoelectric magnetic field sensor, and the permanent magnet is positioned between the first magnetoelectric magnetic field sensor and the second magnetoelectric magnetic field sensor.

As a further improvement of the present invention, the magnetoelectric magnetic field sensor includes two magnetostrictive layers and a piezoelectric layer, the piezoelectric layer being sandwiched between the magnetostrictive layers.

As a further improvement of the invention, the magnetostrictive layer is formed by epoxy resin glue used for the multilayer iron-based soft magnetic amorphous alloy film.

As a further improvement of the invention, the magnetostrictive layer is formed by bonding five layers of iron-based soft magnetic amorphous alloy films by using epoxy resin glue, the thickness of each layer of iron-based soft magnetic amorphous alloy film is 25 micrometers, the thickness of each layer of epoxy resin glue is 1 micrometer, and the total thickness of the magnetostrictive layer is equal to 0.129 mm.

As a further improvement of the invention, the piezoelectric layer is made of piezoelectric ceramics, and the size of the piezoelectric layer is 20mmx in length, 6mmx in thickness and 0.5 mm; the magnetostrictive layer has dimensions of 20mmx length, 6mmx width and 0.129mm thickness.

As a further improvement of the present invention, the distance d from the center of the first magnetoelectric magnetic field sensor to the center of the second magnetoelectric magnetic field sensor is 38 mm; the distance from the center of the permanent magnet to the center of the first magnetoelectric magnetic field sensor and the center of the second magnetoelectric magnetic field sensor is d/2-19 mm.

As a further improvement of the invention, the permanent magnet is a circular permanent magnet, and the material is a rubidium iron boron rare earth permanent magnet.

As a further improvement of the invention, the diameter of the permanent magnet is 5mm, and the thickness of the permanent magnet is 3 mm.

As a further improvement of the present invention, the coil winding tube may be made of PVC plastic or aluminum material or copper material, the exciting coil is wound on the coil winding tube, the number of winding turns of the exciting coil is 470 turns, and the diameter of the exciting coil is 10 mm.

As a further improvement of the present invention, the differential magnetoelectric eddy current sensor further includes a fixing member, the fixing member is installed inside the coil winding tube, and the first magnetoelectric magnetic field sensor, the second magnetoelectric magnetic field sensor, and the permanent magnet are installed on the fixing member.

The invention has the beneficial effects that: the differential magnetoelectric eddy current sensor adopts the outputs of the two magnetoelectric sensors for carrying out the differential, and the differential output is taken as the output of the detection probe, thereby reducing the interference of the noise of the differential magnetoelectric eddy current sensor and greatly improving the detection precision.

Drawings

FIG. 1 is a block diagram of an eddy current testing system of the present invention;

FIG. 2 is a block diagram of a magnetoelectric magnetic field sensor of the present invention;

FIG. 3 is a block diagram of a differential magnetoelectric eddy current test sensor according to the present invention;

FIG. 4 is a cross-sectional view of a differential magnetoelectric eddy current test sensor of the present invention;

FIG. 5 is a graph comparing the ability of a differential magnetoelectric eddy current test sensor of the present invention to detect defects with a single magnetoelectric eddy current sensor;

FIG. 6(a) is a graph of the output voltage versus crack depth for a differential magnetoelectric eddy current test sensor in accordance with the present invention;

fig. 6(b) is a graph showing the relationship between the output voltage and the crack length of the differential magnetoelectric eddy current sensor according to the present invention.

Detailed Description

As shown in fig. 3 to 4, the present invention discloses a differential magnetoelectric eddy current detection sensor, which includes a magnetoelectric magnetic field sensor, an excitation coil 1, a permanent magnet 2, and a coil winding tube 3, wherein the excitation coil 1 is wound outside the coil winding tube 3, the magnetoelectric magnetic field sensor and the permanent magnet 2 are installed inside the coil winding tube 3, the magnetoelectric magnetic field sensor includes a first magnetoelectric magnetic field sensor 4 and a second magnetoelectric magnetic field sensor 5, and the permanent magnet 2 is located between the first magnetoelectric magnetic field sensor 4 and the second magnetoelectric magnetic field sensor 5. The magnetoelectric magnetic field sensor has the advantages of high sensitivity, low power consumption, small size and low noise. The magnetoelectric magnetic field sensor is used for replacing the traditional detection coil, so that the sensitivity of eddy current detection can be greatly improved, and particularly, the defects of millimeter level can be detected.

The differential magnetoelectric eddy current detection sensor provided by the invention replaces the traditional detection coil as a detection probe to detect the change of the magnetic field, and can greatly improve the detection precision to detect smaller defects or cracks. The diagram of an eddy current testing system based on our differential magnetoelectric eddy current probe is shown in fig. 1:

when an excitation signal is introduced into the excitation coil 1, a primary alternating current magnetic field is generated, eddy current is generated under the detected body due to conductivity, a secondary magnetic field is generated, the first magnetoelectric magnetic field sensor 4 and the second magnetoelectric magnetic field sensor 5 detect the superposed magnetic field signal, the superposed magnetic field signal is converted into a voltage signal and then is differentiated, a differential voltage signal is output, and the position of the defect 10 is identified through the change of the differential voltage signal.

The details of the structure and the operation of the magnetoelectric magnetic field sensor will be described in detail below. Fig. 2 is a structural view of a single magnetoelectric sensor, which is fabricated from a three-layer structure, i.e., two magnetostrictive layers 6 sandwiching a piezoelectric layer 7. Wherein the magnetostrictive layer 6 is formed by bonding five layers (each layer is 25um) of iron-based soft magnetic amorphous alloy (Metglas) thin films by using epoxy resin glue, so that the total thickness of the magnetostrictive layer 6 is equal to 0.129 mm. The piezoelectric layer 7 is made of piezoelectric ceramic (PZT-8) and has a thickness of 0.5 mm. The thickness of the whole magnetoelectric magnetic field sensor is 0.76mm, and the length l is 20 mm. The size of the whole magnetoelectric sensor is 20mm multiplied by 6mm multiplied by 0.76 mm.

The working principle is as follows: when an alternating magnetic field exists, the magnetostrictive layer 6 is magnetized to vibrate so as to drive the piezoelectric layer 7 to vibrate, and a voltage signal is output in the thickness direction of the piezoelectric layer 7. The conversion from the magnetic field signal to the voltage signal is realized in the whole process. The invention provides a theoretical basis that the magnetoelectric magnetic field sensor can detect the change of the magnetic field. When the frequency of an alternating current magnetic field is at the resonant frequency of the magnetoelectric sensor, a huge magnetoelectric effect can be achieved, and the frequency is as high as 7V/Oe. The invention also provides a reason that the magnetoelectric magnetic field sensor replaces the traditional monitoring coil and is used as a detection probe, and the sensitivity of the magnetoelectric magnetic field sensor is far higher than that of the traditional detection coil. Of course, the magnetoelectric magnetic field sensor has noise of its own, and the detection precision is also influenced by external noise. Therefore, a differential magnetoelectric sensor is provided, and two magnetoelectric magnetic field sensors are used for carrying out differential, so that self noise can be offset, and the detection precision is improved. Fig. 3 is a detailed structural view of the differential magnetoelectric eddy current sensor.

In fig. 3 we can see that the outside of the differential magnetoelectric eddy current sensor is a coil winding tube 3 made of PVC plastic or aluminum material or copper material, on which an exciting coil 1 is wound with 470 turns and the coil diameter is 10 mm. Because a direct-current bias magnetic field is added beside the magnetoelectric magnetic field sensor, the sensitivity of the magnetoelectric magnetic field sensor can be increased, a simulation circular permanent magnet is arranged between the first magnetoelectric magnetic field sensor 4 and the second magnetoelectric magnetic field sensor 5, the simulation circular permanent magnet is made of rubidium, iron, boron and rare earth permanent magnet, the diameter of the simulation circular permanent magnet is 5mm, and the thickness of the simulation circular permanent magnet is 3 mm. Table 1 below is a specific parameter of the differential magnetoelectric eddy current sensor.

Fig. 4 is a cross-sectional view of a differential magnetoelectric eddy current sensor, which more clearly shows the structure of the sensor, and the distance d between the centers of two magnetoelectric magnetic field sensors is 38mm, and the distance d/2 between each magnetoelectric magnetic field sensor and the center of the permanent magnet 2 is 19 mm.

The specific structure and the working principle of the differential magnetoelectric eddy current detection sensor disclosed by the invention are described above. In the following we compare the ability of a differential magnetoelectric eddy current test sensor to identify defects with a single magnetoelectric eddy current sensor. A copper plate 9 with a length of 200mm, a width of 100mm and a depth of 4mm was examined using the test system of our FIG. 1, and a defect 10 with a length of 10mm, a width of 5mm and a depth of 2mm was located in the middle of the copper plate 9 and examined along the length d. The lift-off values are all 6mm, namely the distance between the differential magnetoelectric eddy current sensor and the detected body in the vertical direction is 6mm, the excitation current is 70mA, the detection direction is along the length d direction, and the position of the defect 10 in the length direction is 60mm-70 mm. The results are shown in FIG. 5.

In FIG. 5, dual-sensor represents a differential magnetoelectric eddy current test sensor and single sensor represents a single magnetoelectric eddy current sensor. We have found that there is a drop in the relative output value of the magnetoelectric eddy current sensor at the position of the defect 10, i.e., d 60mm to 70 mm. This is due to the reduction of eddy current effects at the defect 10, which results in a smaller secondary magnetic field against the primary magnetic field and thus a reduced output relative value. It can be clearly seen that the output relative value of the differential magnetoelectric eddy current detection sensor at the defect 10 is reduced by a larger amount, and the capability of the differential magnetoelectric eddy current detection sensor for detecting the defect 10 is proved to be stronger compared with that of a single magnetoelectric eddy current sensor. That is, the detection accuracy is better.

In fig. 6, L represents the fracture length and D represents the fracture depth. The differential magnetoelectric eddy current detecting sensor output voltage has a rapid rise in the vicinity of the defect 10, and the peak value is related to the length (L) and the depth (d) of the crack (the crack width is small), so that quantitative evaluation of the crack can be achieved using the differential magnetoelectric eddy current detecting sensor. Fig. 6(a) shows the relationship between the output voltage of the differential magnetoelectric eddy current test sensor and the crack depth, where the constant L is 30mm and the variable D is 2,4,6 mm. The middle point of the crack in the length direction is located at the middle point of the d coordinate axis in the figure, and the middle point of the crack in subsequent experiments is located at the center of the d coordinate axis. We can see that keeping L the same, the larger D, the larger the output voltage, the peak of the output voltage being in the middle of the defect 10. Fig. 6(b) shows the output voltage of the differential magnetoelectric eddy current test sensor as a function of the crack length. At constant D3 mm, the variable crack length L was 20,30,40 mm. We can see that keeping D the same, the larger L, the larger the output voltage, the peak of the output voltage in the middle of the defect 10 and jumping on the slope of the voltage rise at the edge of the defect 10. We can predict the length of the defect 10 by two symmetrical jump positions. It is worth noting that the maximum and minimum output voltages V are closely related to the length L and depth D of the crack. Thus a differential magnetoelectric eddy current test sensor may be used to determine the length and depth of the crack.

The invention has the beneficial effects that: the differential magnetoelectric eddy current sensor adopts the outputs of the two magnetoelectric sensors for carrying out the differential, and the differential output is taken as the output of the detection probe, thereby reducing the interference of the noise of the differential magnetoelectric eddy current sensor and greatly improving the detection precision.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.