Vortex MTJ Magnetic Gradiometer for Weak-Material Defect Detection
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Solution Overview
Problem
Current nondestructive testing methods, such as magnetic flux leakage (MFL) testing, lack the spatial and depth resolution to detect small material defects or inhomogeneities in weakly magnetic materials, particularly when the defects are beneath the surface or obstructed, and are limited by magnetic signal decay over distance.
Innovation Solution
A magnetic gradiometer using magnetic tunnel junctions in magnetic vortex state (vortex MTJ) sensors, which includes a differential sensor configuration with a reference and signal vortex MTJ sensor arrays separated by a base length, capable of distinguishing ambient magnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic flux leakage (MFL) measurement is used to detect material defects, then the method can detect changes in magnetic fields, but the spatial and depth resolution is insufficient to detect small defects (5 cm or smaller) at required distances
Solution Approach 1:
The patent changes the magnetic sensor technology parameter from conventional MFL sensors to vortex MTJ sensors, which have fundamentally different magnetic field detection characteristics. The vortex MTJ sensors can detect weaker magnetic fields at greater distances while maintaining spatial resolution, directly addressing the contradiction between detection capability and signal decay.
Solution Approach 2:
The patent replaces the conventional MFL measurement system with a vortex MTJ-based magnetic gradiometer system. This substitution enables detection of small defects at required distances by using the vortex MTJ sensors' unique ability to detect magnetic field gradients with high sensitivity, overcoming the limitations of traditional MFL methods.
2Adaptability or versatility
If conventional MFL testing equipment is used, then the equipment can perform magnetic field detection, but it cannot detect defects in weakly magnetic materials such as magnetic cement with only 5% magnetic particle composition
Solution Approach 1:
The patent changes the detection parameter sensitivity by using vortex MTJ sensors that can detect much weaker magnetic fields compared to conventional MFL equipment. This parameter change enables the system to detect defects in weakly magnetic materials like magnetic cement with only 5% magnetic particle composition, significantly improving adaptability to various material types.
3Length of stationary object
If magnetic field detection is performed at distances required in real-world situations, then the detection range increases, but the magnetic signal decays and reduces detection capability for small defects
Solution Approach 1:
The patent changes the magnetic sensor's field detection parameter to enable operation at greater distances. The vortex MTJ sensors are designed to detect magnetic field gradients with high sensitivity, allowing the system to maintain defect detection capability at increased detection distances where conventional MFL signals would have decayed too much.
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
The magnetic gradiometer effectively detects defects or inhomogeneities in weakly magnetic materials, even at depths or beneath obstructions, with high sensitivity and immunity to ambient fields, providing real-time information for improved understanding of the drilling.
Implementation Method 1
an excitation coil encircling at least a portion of the PCB and configured to deliver an alternating current (AC) to generate an excitation magnetic field
Implementation Method 2
a differential sensor. The differential sensor can include a reference vortex MTJ sensor array proximal to the first end to generate a voltage based on the excitation magnetic field
Data Source
AI summary
A magnetic gradiometer can be used in systems or methods for nondestructive testing, even when the material being tested is weakly magnetic. The magnetic gradiometer can include a printed circuit board (PCB) comprising a first end and a second end separated by a base length; an excitation coil encircling at least a portion of the PCB and configured to deliver an alternating current (AC) to generate an excitation magnetic field; and a differential sensor. The differential sensor can include a reference magnetic tunneling junction in magnetic vortex state (vortex MTJ) sensor array at the first end to generate a voltage based on the excitation magnetic field; and a signal vortex MTJ sensor array at the second end to generate another voltage based on the excitation magnetic field due to a composition of the measurement target. The second end of the PCB can be oriented towards the measurement target.