Flexible fractal eddy-current sensor for Koch difference measurement plane and detection system of flexible fractal eddy-current sensor

Abstract

The invention relates to a Koch difference measurement plane flexible fractal eddy current sensor and a detection system thereof, and belongs to the technical field of nondestructive testing. The detection system for nondestructive detection of the sensor can be used for detecting surface and internal defects of a component, and various material defects can be detected through a non-contact detection method; the detection system is provided with a flexible eddy current sensor so that the flexible eddy current sensor can adapt to component surfaces of different shapes and sizes, and the sensor senses eddy current generated by an alternating magnetic field in a conductor, so that the detection of component surface and internal defects is realized. The non-contact detection method has the characteristics of high sensitivity and high resolution, and tiny defects can be effectively detected. The sensor can be adaptively adjusted according to the curvature and shape of the surface of the component, and good contact between the sensor and the surface of the component is ensured, so that the accuracy and reliability of detection are improved.

Description

Technical Field

[0001] The invention relates to a Koch difference measurement plane flexible fractal eddy current sensor and a detection system thereof, belonging to the technical field of non-destructive detection. Background Art

[0002] Eddy current detection technology based on the principle of electromagnetic induction is one of the commonly used technical means for non-destructive detection of surface and near-surface defects of conductive components such as metals due to its advantages such as rapidity, non-contact, no need for coupling agents, and safety. In recent years, the design of flexible sensors for non-destructive testing of metals with complex surfaces has become one of the research hotspots in the field of eddy current sensors. Due to its bendable characteristics, flexible sensors can be customized, contour-customized, or adaptively passively deformed according to the morphology of the component being tested.

[0003] The smallest crack that a flexible planar eddy current sensor can detect is one of the key indicators of its performance, and the shorter the crack that is discovered in time, the more important it is for guiding maintenance. In addition, sensor coil structure design and optimization is one of the effective ways to improve its sensitivity and resolution. However, multi-layer flexible circuit boards have lower flexibility and higher processing costs than flexible circuit boards with fewer layers. The Koch difference measurement planar flexible fractal eddy current sensor uses a more sophisticated coil structure design, which reduces the number of circuit board layers and improves the sensitivity of the sensor. The four-layer circuit board increases flexibility and reduces manufacturing costs while ensuring sensor sensitivity. Summary of the invention

[0004] The technical problem solved by the invention is: to overcome the deficiencies of the prior art and to provide a Koch difference measurement plane flexible fractal eddy current sensor and a detection system thereof.

[0005] The technical solution of the present invention is:

[0006] A Koch difference measurement planar flexible fractal eddy current sensor, the sensor comprising two layers of excitation coils, two layers of pickup coils and an instrument amplifier located on a flexible circuit board;

[0007] The two layers of excitation coils are respectively the first excitation coil and the second excitation coil, and the two layers of pickup coils are respectively the first pickup coil and the second pickup coil;

[0008] The first excitation coil is a two-turn third-order Koch curve with a circumscribed circle diameter of 5 mm, and is connected in series with each other. The first excitation coil is wound clockwise from the outside to the inside;

[0009] The second excitation coil is a two-turn third-order Koch curve with a circumscribed circle diameter of 5 mm, and is connected in series with each other. The second excitation coil is wound clockwise from the inside to the outside;

[0010] The drawing method of each layer of pickup coils is: divide the third-order Koch curve into two equal parts, then deflect the upper part inward twice and perform forward winding to obtain the three-turn Koch curve of the upper part, and deflect the lower part inward twice and perform reverse winding to obtain the three-turn Koch curve of the lower part; wherein the offset amount each time is 0.13mm; the two layers of pickup coils are connected in series;

[0011] The signal flow direction in the pickup coil is as follows: the signal on the upper part of the first pickup coil flows counterclockwise from outside to inside, enters the second pickup coil through the uppermost through hole, then flows counterclockwise from the upper half coil to the lower half coil, and finally enters the first pickup coil through the lowermost through hole. The input and output ends of the signal are both located on the layer where the first pickup coil is located;

[0012] The first excitation coil is located above the first pickup coil, the first pickup coil is located above the second excitation coil, and the second excitation coil is located above the second pickup coil.

[0013] It can also be:

[0014] The first pickup coil is located above the first excitation coil, the first excitation coil is located above the second pickup coil, and the second pickup coil is located above the second excitation coil.

[0015] The third-order Koch curve may also be a second-order Koch curve or a fourth-order Koch curve;

[0016] The instrument amplifier is used to amplify the signal picked up by the pickup coil;

[0017] The instrument amplifier is preferably an AD8421 instrument amplifier, and the gain is selected to be 20;

[0018] Pin 1 of the AD8421 instrument amplifier is connected to the input end of the pickup coil, pin 4 of the AD8421 instrument amplifier is connected to the output end of the pickup coil, pins 2 and 3 of the AD8421 instrument amplifier are connected to the gain resistor, the AD8421 instrument amplifier adjusts the gain of the amplifier by changing the resistance value, pins 5 and 8 of the AD8421 instrument amplifier are connected to the power supply voltage, pin 7 of the AD8421 instrument amplifier is the output end, and pin 8 of the AD8421 instrument amplifier is the reference voltage source;

[0019] The flexible circuit board is designed with two through holes for excitation signals, which are welded to the corresponding two-core aviation plugs; the flexible circuit board is designed with five through holes for pickup signals, which are welded to the corresponding five-core aviation plugs.

[0020] An application of a Koch difference measurement planar flexible fractal eddy current sensor, which is applied to a detection system for non-destructive testing;

[0021] The detection system includes a lock-in amplifier (OE1300), a power amplifier (ATA-101B), an acquisition card (NIUSB-6001) and a probe, and the sensor is installed in the probe;

[0022] The method for nondestructive testing is as follows: fix the sensor on a three-dimensional scanning table, and control its movement through a stepper motor. The control signal is sent by the host computer through serial communication. The host computer program-controlled module phase-locked amplifier generates a sinusoidal signal with adjustable frequency and amplitude and a reference signal corresponding to the sinusoidal signal, and outputs the sinusoidal signal to the power amplifier, which is amplified by the power amplifier and output to the probe as the excitation signal of the probe; the probe inputs the crack signal of the block to be tested picked up by the sensor as a differential signal to the input port of the module phase-locked amplifier. At this time, the reference signal channel of the module phase-locked amplifier is set to the internal reference mode, and the module phase-locked amplifier performs signal conditioning on the picked-up voltage signal and the reference signal, collects the signal processed by the phase-locked amplifier through the acquisition card, and then connects to the host computer through the USB interface for signal storage.

[0023] In the absence of defects, since the pickup coils are reversely wound, the induced voltages will cancel each other, resulting in a total voltage close to zero;

[0024] In the presence of defects, due to the uneven distribution of eddy currents, the induced voltages of the two parts of the pickup coils that are wound in opposite directions are no longer completely equal, resulting in a change in the differential signal. By amplifying and measuring the differential signal, defects in the material can be detected.

[0025] Beneficial Effects

[0026] The detection system of the sensor of the present invention for non-destructive testing can be used to detect surface and internal defects of components, and can detect various material defects through non-contact detection methods; the detection system is equipped with a flexible eddy current sensor so that it can adapt to the surfaces of components of different shapes and sizes, and the sensor can detect surface and internal defects of components by inducing eddy currents generated in the conductor by the alternating magnetic field. This non-contact detection method has the characteristics of high sensitivity and high resolution, and can effectively detect tiny defects. The sensor can be adaptively adjusted according to the curvature and shape of the component surface to ensure good contact between the sensor and the component surface, thereby improving the accuracy and reliability of detection.

[0027] The Koch difference measurement plane flexible fractal eddy current sensor adopts a more sophisticated coil structure, reducing the number of layers of the circuit board from ten to four, which not only improves the detection rate of short cracks, but also improves the sensitivity and flexibility of sensor detection, giving full play to the advantages of flexible sensors and reducing the manufacturing cost of sensors. The AD8421 instrument amplifier is arranged on the sensor to amplify the output signal of the pickup coil, improve the sensitivity, reliability and stability of the sensor, and provide a reliable basis for subsequent signal processing and analysis. The eddy current detection system equipped with a flexible eddy current sensor can be used to detect surface defects and sub-surface defects of irregular metal components. The minimum crack size of the high-temperature nickel-based alloy test block that can be detected by the sensor using the flexible fractal eddy current sensing system is 0.5mm×0.1mm×0.1mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The first exciting coil of the planar flexible fractal eddy current sensor for Koch difference measurement;

[0029] Figure 2 The first pick-up coil of the planar flexible fractal eddy current sensor for Koch difference measurement;

[0030] Figure 3 The second exciting coil of the planar flexible fractal eddy current sensor for Koch difference measurement;

[0031] Figure 4 The second pick-up coil of the planar flexible fractal eddy current sensor for Koch difference measurement;

[0032] Figure 5 The actual picture of the Koch difference measurement plane flexible fractal eddy current sensor after processing;

[0033] Figure 6 This is the corresponding relationship diagram between the 5-core aviation plug and the through hole;

[0034] Figure 7 This is the schematic diagram of the detection system;

[0035] Figure 8 This is the output signal diagram of the Koch difference measurement planar flexible fractal eddy current sensor (400kHz);

[0036] Fig. 9 Output signal cloud diagram of the planar flexible fractal eddy current sensor measured by Koch difference (400kHz);

[0037] Fig.10 The real part signal cloud diagram of the minimum crack measured by the Koch difference measurement planar flexible fractal eddy current sensor (400kHz). DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0039] Example

[0040] A Koch difference measurement planar flexible fractal eddy current sensor, the sensor includes two layers of excitation coils, two layers of pickup coils and an instrument amplifier located on a four-layer flexible circuit board. The processed sensor is shown in the figure below. Figure 5 As shown;

[0041] The two layers of excitation coils are respectively the first excitation coil and the second excitation coil, and the two layers of pickup coils are respectively the first pickup coil and the second pickup coil;

[0042] The first excitation coil is a two-turn third-order Koch curve with an outer circle diameter of 5 mm and connected in series. The first excitation coil is wound clockwise from the outside to the inside. The first excitation coil of the Koch difference measurement plane flexible fractal eddy current sensor is as follows: Figure 1 As shown;

[0043] The second excitation coil is a two-turn third-order Koch curve with an outer circle diameter of 5 mm and connected in series. The second excitation coil is wound clockwise from the inside to the outside. The second excitation coil of the Koch difference measurement plane flexible fractal eddy current sensor is as follows Figure 3 As shown;

[0044] The drawing method of the first pickup coil is: divide the third-order Koch curve into two equal parts, then deflect the upper part inward twice for forward winding to obtain the three-turn Koch curve of the upper part, deflect the lower part inward twice for reverse winding to obtain the three-turn Koch curve of the lower part, and the signal enters the first pickup coil through two lead-in wires on the right side of the coil; wherein the offset amount each time is 0.13mm, and the first pickup coil of the Koch difference measurement plane flexible fractal eddy current sensor is as follows Figure 2 As shown;

[0045] The drawing method of the second pickup coil is: divide the third-order Koch curve into two equal parts, then deflect the upper part inward twice for forward winding to obtain the three-turn Koch curve of the upper part, and deflect the lower part inward twice for reverse winding to obtain the three-turn Koch curve of the lower part; wherein the offset amount each time is 0.13mm, and the second pickup coil of the Koch difference measurement plane flexible fractal eddy current sensor is as follows Figure 4 As shown;

[0046] The two layers of pickup coils are connected in series;

[0047] The signal flow direction in the pickup coil is as follows: the signal on the upper part of the first pickup coil flows counterclockwise from outside to inside, enters the second pickup coil through the uppermost through hole, then flows counterclockwise from the upper half coil to the lower half coil, and finally enters the first pickup coil through the lowermost through hole. The input and output ends of the signal are both located on the layer where the first pickup coil is located;

[0048] wherein the first excitation coil is located above the first pickup coil, the first pickup coil is located above the second excitation coil, and the second excitation coil is located above the second pickup coil;

[0049] Alternatively, the first pickup coil is located above the first excitation coil, the first excitation coil is located above the second pickup coil, and the second pickup coil is located above the second excitation coil;

[0050] The third-order Koch curve may also be a second-order Koch curve or a fourth-order Koch curve;

[0051] The instrument amplifier is used to amplify the signal picked up by the pickup coil;

[0052] The instrument amplifier is preferably an AD8421 instrument amplifier, and the gain is selected to be 20;

[0053] Pin 1 of the AD8421 instrument amplifier is connected to the input end of the pickup coil, pin 4 of the AD8421 instrument amplifier is connected to the output end of the pickup coil, pins 2 and 3 of the AD8421 instrument amplifier are connected to the gain resistor, the AD8421 instrument amplifier adjusts the gain of the amplifier by changing the resistance value, pins 5 and 8 of the AD8421 instrument amplifier are connected to the power supply voltage, pin 7 of the AD8421 instrument amplifier is the output end, and pin 8 of the AD8421 instrument amplifier is the reference voltage source;

[0054] The flexible circuit board is designed with two through holes for excitation signals, which are welded to the corresponding 2-core aviation plugs. The flexible circuit board is designed with five through holes for pickup signals, which are welded to the corresponding 5-core aviation plugs. The corresponding relationship between the 5-core aviation plug and the through holes is shown in the figure. Figure 6 shown.

[0055] An application of a Koch difference measurement plane flexible fractal eddy current sensor, which is applied to the detection system for non-destructive testing. The principle diagram of the detection system is shown in Figure 7 As shown;

[0056] The detection system includes a lock-in amplifier (OE1300), a power amplifier (ATA-101B), an acquisition card (NIUSB-6001) and a probe, and the sensor is installed in the probe;

[0057] The method for nondestructive testing is as follows: fix the sensor on a three-dimensional scanning table, and control its movement through a stepper motor. The control signal is sent by the host computer through serial communication. The host computer program-controlled module phase-locked amplifier generates a sinusoidal signal with adjustable frequency and amplitude and a reference signal corresponding to the sinusoidal signal, and outputs the sinusoidal signal to the power amplifier, which is amplified by the power amplifier and output to the probe as the excitation signal of the probe; the probe inputs the crack signal of the block to be tested picked up by the sensor as a differential signal to the input port of the module phase-locked amplifier. At this time, the reference signal channel of the module phase-locked amplifier is set to the internal reference mode, and the module phase-locked amplifier performs signal conditioning on the picked-up voltage signal and the reference signal, collects the signal processed by the phase-locked amplifier through the acquisition card, and then connects to the host computer through the USB interface for signal storage.

[0058] In the absence of defects, since the pickup coils are reversely wound, the induced voltages will cancel each other, resulting in a total voltage close to zero;

[0059] In the presence of defects, due to the uneven distribution of eddy currents, the induced voltages of the two parts of the pickup coils that are wound in opposite directions are no longer completely equal, resulting in a change in the differential signal. By amplifying and measuring the differential signal, defects in the material can be detected.

[0060] The sensor's excitation coil uses a multi-turn Koch curve. The superposition of multiple turns of coils can generate a relatively strong magnetic field. Due to its strong excitation ability, it usually has a faster response speed and can capture the changes in eddy current signals more timely, so it has a higher sensitivity.

[0061] An instrumentation amplifier (AD8421) is arranged on the flexible sensor to amplify the output signal of the pickup coil; a housing matching the sensor is designed and assembled with the sensor to form a probe to improve the stability of the defect detection process;

[0062] When designing the power module for the AD8421 instrumentation amplifier, the key point is to convert the input voltage of 12V into a 5V output voltage and ensure the output voltage is stable through proper circuit design and component selection.

[0063] The eddy current detection system is combined with a three-dimensional scanning platform and equipped with a new Koch difference measurement plane fractal eddy current sensor to perform C-scan detection on a high-temperature nickel-based alloy test block with a size of 100mm×100mm×10mm. Figure 8 and Fig. 9The output signal diagram and output signal cloud diagram of the Koch difference measurement planar flexible fractal eddy current sensor when the excitation frequency is 400kHz. The sensor measured the minimum crack size of 0.5mm×0.1mm×0.1mm (length×width×depth). The Koch difference measurement planar flexible fractal eddy current sensor measured the minimum crack real part signal cloud diagram as shown in the figure. Fig.10 shown.

[0064] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Koch difference measurement planar flexible fractal eddy current sensor, characterized in that: The sensor includes two layers of excitation coils, two layers of pickup coils, and an instrumentation amplifier on a four-layer flexible circuit board; The two layers of excitation coils are respectively the first excitation coil and the second excitation coil, and the two layers of pickup coils are respectively the first pickup coil and the second pickup coil; The first excitation coil is a two-turn third-order Koch curve with a circumscribed circle diameter of 5 mm, and is connected in series with each other. The first excitation coil is wound clockwise from the outside to the inside; The second excitation coil is a two-turn third-order Koch curve with a circumscribed circle diameter of 5 mm, and is connected in series with each other. The second excitation coil is wound clockwise from the inside to the outside.

2. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 1, characterized in that: The drawing method of each layer of pickup coil is: divide the third-order Koch curve into two equal parts, then shift the upper part inward twice and perform forward winding to obtain the three-turn Koch curve of the upper part, and shift the lower part inward twice and perform reverse winding to obtain the three-turn Koch curve of the lower part; the two layers of pickup coils are connected in series.

3. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 2, characterized in that: The offset is 0.13 mm each time.

4. A Koch difference measurement plane flexible fractal eddy current sensor according to claim 2 or 3, characterized in that: The flow direction of the signal in the pickup coil is: the signal in the upper part of the first pickup coil flows counterclockwise from the outside to the inside, and enters the second pickup coil through the top through-hole. Then, the signal flows counterclockwise from the upper half of the coil to the lower half of the coil, and finally, enters the first pickup coil through the bottom through-hole. The input and output ends of the signal are both located on the layer where the first pickup coil is located.

5. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 4, characterized in that: The first excitation coil is located above the first pickup coil, the first pickup coil is located above the second excitation coil, and the second excitation coil is located above the second pickup coil.

6. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 4, characterized in that: Alternatively, the first pickup coil may be located above the first excitation coil, the first excitation coil may be located above the second pickup coil, and the second pickup coil may be located above the second excitation coil.

7. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 1, characterized in that: The third-order Koch curve may also be a second-order Koch curve or a fourth-order Koch curve.

8. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 1, characterized in that: The instrument amplifier is used to amplify the crack signal picked up by the pickup coil; The instrument amplifier is an AD8421 instrument amplifier, and the gain is selected as 20; Pin 1 of the AD8421 instrument amplifier is connected to the input end of the pickup coil, pin 4 of the AD8421 instrument amplifier is connected to the output end of the pickup coil, pins 2 and 3 of the AD8421 instrument amplifier are connected to the gain resistor, the AD8421 instrument amplifier adjusts the gain of the amplifier by changing the resistance value, pins 5 and 8 of the AD8421 instrument amplifier are connected to the power supply voltage, pin 7 of the AD8421 instrument amplifier is the output end, and pin 8 of the AD8421 instrument amplifier is the reference voltage source.

9. The Koch difference measurement plane flexible fractal eddy current sensor according to claim 1, characterized in that: The flexible circuit board is designed with two through holes for excitation signals, which are welded to the corresponding two-core aviation plugs; the flexible circuit board is designed with five through holes for pickup signals, which are welded to the corresponding five-core aviation plugs.

10. An application of a Koch difference measurement planar flexible fractal eddy current sensor, characterized in that The sensor is applied to the detection system for nondestructive testing; The detection system includes a module lock-in amplifier, a power amplifier, an acquisition card and a probe; The sensor is installed in the probe; The method for nondestructive testing is as follows: fix the sensor on a three-dimensional scanning table, and control its movement through a stepper motor. The control signal is sent by the host computer through serial communication. The host computer program-controlled module phase-locked amplifier generates a sinusoidal signal with adjustable frequency and amplitude and a reference signal corresponding to the sinusoidal signal, and outputs the sinusoidal signal to the power amplifier, which is amplified by the power amplifier and output to the probe as the excitation signal of the probe; the probe inputs the crack signal of the block to be tested picked up by the sensor as a differential signal to the input port of the module phase-locked amplifier. At this time, the reference signal channel of the module phase-locked amplifier is set to the internal reference mode, and the module phase-locked amplifier performs signal conditioning on the picked-up voltage signal and the reference signal, collects the signal processed by the phase-locked amplifier through the acquisition card, and then connects to the host computer through the USB interface for signal storage.

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