Novel Koch difference measurement plane fractal eddy current sensor and detection system thereof

Abstract

The invention relates to a novel Koch difference measurement plane fractal eddy current sensor and a detection system thereof, and belongs to the technical field of nondestructive testing. According to the novel Koch difference measurement plane fractal eddy current sensor, a fractal geometric design sensor coil structure is adopted, and a pick-up coil and an excitation coil both adopt Koch curves to condition eddy current vectors in more directions in a local area so as to improve the probability that eddy current is disturbed by cracks in different directions; according to the novel Koch difference measurement plane fractal eddy current sensor, the number of turns of a pickup coil and the number of layers arranged on a circuit board are large, induced voltage is increased by increasing the number of turns of the pickup coil, so that the detection sensitivity of the sensor is enhanced, and the detection sensitivity of the sensor to short cracks is improved.

Description

Technical Field

[0001] The invention relates to a novel Koch difference measurement plane 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 planar flexible 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, the design and optimization of the sensor coil structure is one of the effective methods to improve its sensitivity and resolution. The planar flexible Koch fractal eddy current sensor described in the document "Research on Crack Detection Performance of Planar Eddy Current Sensor Based on Koch Difference Measurement" shows high consistency in detecting short cracks in all directions. Since the sensor adopts the idea of ​​fractal geometry, the sensor coil structure uses the Koch curve to adjust the eddy current distribution, so that it improves the sensor's detection rate for cracks in special directions, but there is still a problem of weak signal caused by the small number of coil turns. Summary of the invention

[0004] The technical solution of the present invention is: to overcome the shortcomings of the prior art, propose a new Koch difference measurement plane fractal eddy current sensor and its detection system, and use flexible circuit board technology to solve this problem. By increasing the number of turns of the pickup coil, the induced voltage is increased to enhance its detection sensitivity, thereby improving the sensor's detection sensitivity to short cracks.

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

[0006] A novel planar fractal eddy current sensor for Koch difference measurement, the sensor comprising nine layers of pickup coils and one layer of excitation coil on a flexible circuit board;

[0007] The excitation coil is a single-turn third-order Koch curve with a circumscribed circle diameter of 10 mm;

[0008] The nine layers of pickup coils are connected in series in sequence;

[0009] The method for drawing the first-layer pickup coil is as follows: the third-order Koch curve is divided into two equal parts, and then the upper part is shifted inward five times and wound forward to obtain the six-turn Koch curve of the upper part, and the lower part is shifted inward five times and wound backward to obtain the six-turn Koch curve of the lower part;

[0010] The drawing method of the second-layer pickup coil is as follows: the third-order Koch curve is divided into two equal parts, and then the upper part is shifted inward five times and reversely wound to obtain the six-turn Koch curve of the upper part, and the lower part is shifted inward five times and forwardly wound to obtain the six-turn Koch curve of the lower part;

[0011] The drawing method of the third layer pickup coil, the fifth layer pickup coil, the seventh layer pickup coil, and the ninth layer pickup coil is the same as that of the first layer pickup coil;

[0012] The drawing method of the fourth layer pickup coil, the sixth layer pickup coil, and the eighth layer pickup coil is the same as that of the second layer pickup coil;

[0013] When the inward displacement is performed five times, the displacement distance each time is the same, and the displacement distance is 0.13 mm;

[0014] The diameter of the circumscribed circle of each layer of pickup coil is 10mm;

[0015] The excitation coil is located above the first layer of pickup coils.

[0016] Application of a new type of Koch difference measurement plane fractal eddy current sensor, which is applied to the detection system to detect defects on the test block;

[0017] The detection system is used to detect surface and internal defects of components, and includes a function generator (RLGOL-DG832), a power amplifier (RLGOL-PA1011), a digital multimeter (RLGOL-DM3058), a three-dimensional scanning platform, a stepper motor (SC100), a lock-in amplifier (SINE-OE2031), an industrial computer (IPC-610L) and a probe, wherein the sensor is installed in the probe;

[0018] Methods for non-destructive testing:

[0019] The scanning mechanism of the eddy current probe is based on the principle of electromagnetic induction. The probe is fixed on a three-dimensional scanning table controlled by a stepper motor. The function generator outputs a sinusoidal excitation signal and a reference signal. The sinusoidal excitation signal is amplified by a power amplifier. The effective value of the excitation current is monitored in real time by a digital multimeter. The pickup coil of the probe obtains the crack signal and inputs it into the phase-locked amplifier for processing. Finally, the crack signal data is transmitted to the industrial computer through the host computer software. The scanning path of the probe is preset by the host computer to ensure that the entire detection area is covered. The probe moves along the set path through the three-dimensional scanning table and the stepper motor. The detected magnetic field change signal is converted into an electrical signal and transmitted to the host computer. The host computer processes these signals and generates a C-scan image, which shows the signal strength. In the absence of defects, due to the reverse winding of the pickup coil, the induced voltages will cancel each other, resulting in a total voltage close to zero;

[0020] 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;

[0021] 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.

[0022] Beneficial Effects

[0023] The novel Koch difference measurement plane fractal eddy current sensor of the present invention adopts fractal geometry to design the sensor coil structure. The pick-up coil and the excitation coil both adopt Koch curves to adjust the eddy current vector in more directions in the local area, so as to increase the probability that the eddy current is disturbed by cracks in different directions.

[0024] The number of turns of the pickup coil of the new Koch difference measurement plane fractal eddy current sensor and the number of layers arranged on the circuit board are large. By increasing the number of turns of the pickup coil, the induced voltage is increased to enhance its detection sensitivity, thereby improving the sensor's detection sensitivity to short cracks;

[0025] The pickup coil of the new Koch difference measurement planar fractal eddy current sensor adopts a differential measurement design, which makes the sensor have a self-zeroing characteristic and can suppress lift-off noise and differential mode interference;

[0026] The new Koch difference measurement planar fractal eddy current sensor adopts a receiving-transmitting coil structure design, which can reduce the impact of electromagnetic interference from the external environment on the sensor performance, thereby effectively enhancing the sensitivity of the sensor.

[0027] A variety of material defects can be detected through non-contact detection methods. The detection system can be equipped with flexible eddy current sensors to adapt to the surfaces of components of different shapes and sizes. The sensor detects 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. In addition, 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The schematic diagram of the coil structure of the new Koch difference measurement planar fractal eddy current sensor;

[0029] Figure 2 It is the schematic diagram of the excitation coil;

[0030] Figure 3Schematic diagram of the pickup coils for the 2nd, 4th, 6th and 8th layers;

[0031] Figure 4 Schematic diagram of the pickup coils for the 3rd, 5th, 7th and 9th layers;

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

[0033] Figure 6 This is the schematic diagram of the detection system;

[0034] Figure 7 The cloud diagram of the minimum crack real part signal (200kHz) measured by the new Koch difference measurement planar fractal eddy current sensor. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] Example

[0037] A novel planar fractal eddy current sensor for Koch difference measurement is provided. The sensor comprises nine layers of pickup coils and one layer of excitation coil on a flexible circuit board. Figure 1 As shown, 1 is the excitation coil and 2 is the pickup coil;

[0038] The excitation coil is a single-turn third-order Koch curve with a circumscribed circle diameter of 10 mm. Figure 2 As shown;

[0039] The nine layers of pickup coils are connected in series in sequence;

[0040] The method for drawing the first layer of pickup coil is: divide the third-order Koch curve into two equal parts, then deflect the upper part inward five times and perform forward winding to obtain the six-turn Koch curve of the upper part, and deflect the lower part inward five times and perform reverse winding to obtain the six-turn Koch curve of the lower part, as shown in the attached figure. Figure 3 As shown;

[0041] The method for drawing the second layer pickup coil is: divide the third-order Koch curve into two equal parts, then shift the upper part inward five times and reversely wind it to obtain the six-turn Koch curve of the upper part, and shift the lower part inward five times and forwardly wind it to obtain the six-turn Koch curve of the lower part, as shown in the attached figure. Figure 4 As shown;

[0042] The drawing method of the third layer pickup coil, the fifth layer pickup coil, the seventh layer pickup coil, and the ninth layer pickup coil is the same as that of the first layer pickup coil;

[0043] The drawing method of the fourth layer pickup coil, the sixth layer pickup coil, and the eighth layer pickup coil is the same as that of the second layer pickup coil;

[0044] When the inward displacement is performed five times, the displacement distance each time is the same, and the displacement distance is 0.13 mm;

[0045] The diameter of the circumscribed circle of each layer of pickup coil is 10mm;

[0046] The excitation coil is located above the first layer of pickup coils.

[0047] The actual picture of the sensor after processing is shown in the attached Figure 5 As shown;

[0048] A new type of Koch difference measurement plane fractal eddy current sensor is used. The sensor is applied to the detection system to detect defects in the test block. The principle diagram of the detection system is shown in the attached figure. Figure 6 As shown;

[0049] The detection system includes a function generator (RLGOL-DG832), a power amplifier (RLGOL-PA1011), a digital multimeter (RLGOL-DM3058), a three-dimensional scanning platform, a stepper motor (SC100), a lock-in amplifier (SINE-OE2031), an industrial computer (IPC-610L) and a probe, and the sensor is installed in the probe;

[0050] Methods for non-destructive testing:

[0051] The probe is fixed on a three-dimensional scanning table controlled by a stepper motor. The function generator outputs a sinusoidal excitation signal and a reference signal. The sinusoidal excitation signal is amplified by a power amplifier. The effective value of the excitation current is monitored in real time by a digital multimeter. The pickup coil of the probe obtains the crack signal and inputs it into the phase-locked amplifier for processing. Finally, the crack signal data is transmitted to the industrial computer through the host computer software. The scanning path of the probe is preset by the host computer to ensure that the entire detection area is covered. The probe moves along the set path through the three-dimensional scanning table and the stepper motor. The detected magnetic field change signal is converted into an electrical signal and transmitted to the host computer. The host computer processes these signals and generates a C-scan image to show the signal strength.

[0052] 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;

[0053] In the presence of defects, due to the uneven distribution of eddy currents, the induced voltages in the reversely wound parts of the pickup coils 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.

[0054] Since the shape of the eddy current field is similar to that of the excitation source, the shape of the crack signal detected by the sensor is similar to the shape of the excitation coil structure, both of which are Koch snowflake shapes. When the excitation coil of the eddy current sensor generates an electromagnetic field, the eddy currents on the metal surface being measured will be affected by the shape of the excitation coil. Excitation coils of different shapes will result in eddy currents of different shapes and distributions, which will form a complex electromagnetic field distribution on the metal surface.

[0055] The test results show that the smallest crack size of the 5083 aluminum test block that the sensor can detect is 0.5mm×0.15mm×1mm; the smallest crack size of the high-temperature nickel-based alloy GH4169 test block is 3mm×0.15mm×1mm; and the smallest crack size of the Q235 steel test block is 1mm×0.15mm×1mm.

[0056] The eddy current detection system is equipped with a new Koch difference measurement plane fractal eddy current sensor to perform C-scan detection on a 5083 aluminum test block with a prefabricated crack. The test results show that the new Koch difference measurement plane fractal eddy current sensor can detect the smallest crack size on the 5083 aluminum test block as 0.5mm×0.15mm×1mm. The C-scan signal of the prefabricated crack of 0.5mm×0.15mm×1mm in the 5083 aluminum test block detected by the new Koch difference measurement plane fractal eddy current sensor is shown in the attached figure. Figure 7 shown.

[0057] Koch coils preferably use third-order curves, but second-order, fourth-order, and fifth-order coil structures can be designed;

[0058] The offset distance of the pickup coil is preferably 0.13 mm, but other offset distances are acceptable;

[0059] The excitation coil of the present invention preferably has one layer (one coil turn), and the pickup coil preferably has nine layers (each layer includes six coil turns), but any other number of layers and coil turns that meet the processing conditions are acceptable.

[0060] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel Koch difference measurement planar fractal eddy current sensor, characterized in that: The sensor includes nine layers of pickup coils and one layer of excitation coil on a flexible circuit board; The excitation coil is a single-turn third-order Koch curve with a circumscribed circle diameter of 10 mm; The nine layers of pickup coils are connected in series in sequence.

2. The novel Koch difference measurement plane fractal eddy current sensor according to claim 1 is characterized in that: The drawing method of the first layer pickup coil is: divide the third-order Koch curve into two equal parts, then shift the upper part inward five times and perform forward winding to obtain the six-turn Koch curve of the upper part, and shift the lower part inward five times and perform reverse winding to obtain the six-turn Koch curve of the lower part.

3. The novel Koch difference measurement plane fractal eddy current sensor according to claim 2 is characterized in that: The drawing method of the second-layer pickup coil is: divide the third-order Koch curve into two equal parts, then shift the upper part inward five times and reversely wind it to obtain the six-turn Koch curve of the upper part, and shift the lower part inward five times and forwardly wind it to obtain the six-turn Koch curve of the lower part.

4. The novel Koch difference measurement plane fractal eddy current sensor according to claim 3 is characterized in that: The drawing method of the third layer pickup coil, the fifth layer pickup coil, the seventh layer pickup coil, and the ninth layer pickup coil is the same as that of the first layer pickup coil.

5. The novel Koch difference measurement plane fractal eddy current sensor according to claim 4 is characterized in that: The drawing method of the fourth layer pickup coil, the sixth layer pickup coil and the eighth layer pickup coil is the same as that of the second layer pickup coil.

6. The novel Koch difference measurement plane fractal eddy current sensor according to claim 5 is characterized in that: When the inward displacement is performed five times, the displacement distance each time is the same, and the displacement distance is 0.13 mm.

7. The novel Koch difference measurement plane fractal eddy current sensor according to claim 6 is characterized by: The diameter of the circumscribed circle of each layer of pickup coil is 10 mm.

8. The novel Koch difference measurement plane fractal eddy current sensor according to claim 1 is characterized by: The excitation coil is located above the first layer of pickup coils.

9. Application of a novel Koch difference measurement planar fractal eddy current sensor, characterized in that: The sensor is applied to the detection system to detect defects on the test block.

10. The application of a novel Koch difference measurement plane fractal eddy current sensor according to claim 9, characterized in that: The detection system is used to detect surface and internal defects of components, and includes a function generator, a power amplifier, a digital multimeter, a three-dimensional scanning platform, a stepping motor, a phase-locked amplifier, an industrial computer and a probe, and the sensor is installed in the probe; The probe is fixed on a three-dimensional scanning table controlled by a stepper motor. The function generator outputs a sinusoidal excitation signal and a reference signal. The sinusoidal excitation signal is amplified by a power amplifier. The effective value of the excitation current is monitored in real time by a digital multimeter. The pickup coil of the probe obtains the crack signal and inputs it into the phase-locked amplifier for processing. Finally, the crack signal data is transmitted to the industrial computer through the host computer software. The scanning path of the probe is preset by the host computer to ensure that the entire detection area is covered. The probe moves along the set path through the three-dimensional scanning table and the stepper motor. The detected magnetic field change signal is converted into an electrical signal and transmitted to the host computer. The host computer processes these signals and generates a C-scan image to display the signal strength. 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; 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.

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