Eddy Current Probe With Rotating Magnetic Field for Deep Defect Detection
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Solution Overview
Problem
Conventional eddy current inspection methods face difficulties in detecting defects in deeper parts of test objects due to insufficient magnetic field information from deeper regions, even at lower frequencies, making defect inspection in these areas challenging.
Innovation Solution
An eddy current inspection device with multiple excitation coils arranged at even intervals in a circumferential direction, where the phase difference between adjacent excitation currents equals one cycle divided by the number of coils, generates a magnetic field that allows for deeper defect detection using a detection coil positioned inside the coil circumference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the frequency of excitation currents is decreased to enhance magnetic field penetration depth, then the penetration depth is improved, but the magnetic field information from deeper parts becomes far more deficient
Solution Approach 1:
The excitation coil is divided into multiple coil sections (first, second, third, and fourth coil sections) arranged circumferentially. Each section is independently controlled with specific phase differences to create a rotational magnetic field pattern that systematically probes deeper regions of the test object, thereby segmenting the inspection task to overcome information deficiency at depth.
Solution Approach 2:
The patent applies periodic excitation currents with specific phase differences (e.g., 90 degrees between adjacent sections) to generate a rotational magnetic field. This periodic action with controlled phase progression enables the magnetic field to systematically penetrate and sample deeper regions of the test object over time, recovering information that would be lost with single-frequency excitation.
2Reliability
If conventional single excitation coil configuration is used, then the device structure is simple, but the defect inspection capability in deeper parts is insufficient
Solution Approach 1:
The excitation coil is segmented into multiple coil sections (first, second, third, and fourth coil sections) arranged circumferentially around the detection coil. Each section is independently controlled with specific phase differences to create a rotational magnetic field pattern that systematically probes deeper regions of the test object, thereby segmenting the inspection task to overcome information deficiency at depth.
Solution Approach 2:
The patent applies periodic excitation currents with specific phase differences (e.g., 90 degrees between adjacent sections) to generate a rotational magnetic field. This periodic action with controlled phase progression enables the magnetic field to systematically penetrate and sample deeper regions of the test object over time, recovering information that would be lost with single-frequency excitation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables the detection of defects within deeper parts of test objects by enhancing the magnetic field penetration and signal strength, improving the reliability of defect inspection independent of defect direction.
Implementation Method 1
measuring a change in an eddy current caused in the test object by time-varying magnetic fluxes. The time-varying magnetic fluxes are generated by use of an excitation coil placed in the vicinity of the surface of the test object by applying time-varying electric current (excitation current) to the excitation coil.
Implementation Method 2
detecting a characteristic change such as a flaw or a change in material quality (hereinafter referred to as a 'defect') occurring on the surface or inside of the test object by measuring a change in an eddy current caused in the test object by time-varying magnetic fluxes
Data Source
Figure 1
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Figure 4
AI summary
Provided is an eddy current inspection device, an eddy current inspection probe (6) and an eddy current inspection method that make it possible to detect defects existing in deeper parts of test objects. Three or more odd number of excitation coils (61a-61e) are arranged at even intervals in a circumferential direction on a postulated circumference (64). Excitation currents applied to the excitation coils (61a-61e) are controlled so that the phase difference between excitation currents applied to adjacent ones of the excitation coils (61a-61e) arranged in the circumferential direction on the postulated circumference (64) equals one cycle divided by the number of excitation coils (61a-61e). A magnetic field generated according to an eddy current occurring in the test object due to a magnetic field caused by the application of the excitation currents to the excitation coils (61a-61e) is detected by use of a detector (62) arranged on a postulated plane (63) containing the postulated circumference (64) but inside the postulated circumference (64).