Ferromagnetic Strip Sensor Offset Magnet Unidirectional Guided Waves
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Solution Overview
Problem
Conventional magnetostrictive sensors for generating unidirectional guided waves often require symmetric magnetic field configurations, which can limit their effectiveness in distinguishing anomalies on multi-dimensional structures, as they typically activate both sides of the ferromagnetic strip uniformly, making it difficult to attribute received signals to specific sides of the sensor.
Innovation Solution
A single magnetostrictive sensor with a ferromagnetic strip is used, where the permanent magnet is offset from the center axis, providing partial excitation and allowing for unidirectional guided wave generation by adjusting the width of the magnetized area and its offset, enabling constructive and destructive interference to control wave propagation direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If symmetric magnetic field configuration is used in magnetostrictive sensors, then the sensor can be manufactured with simple structure, but the ability to distinguish anomalies on specific sides of the sensor is reduced
Solution Approach 1:
The patent applies asymmetry by offsetting the permanent magnet from the center axis of the ferromagnetic strip, creating an asymmetric magnetic field configuration. This asymmetry causes non-uniform activation of the strip, with one side more strongly activated than the other, enabling directional guided wave generation and improved anomaly location discrimination while maintaining manufacturing simplicity
2Device complexity
If uniform activation of both sides of ferromagnetic strip is used, then the sensor structure is simple, but the directional control of guided waves is reduced
Solution Approach 1:
The permanent magnet is positioned asymmetrically relative to the ferromagnetic strip, creating a magnetic field that activates one side of the strip more than the other. This asymmetric activation enables unidirectional or preferential directional guided wave generation, improving directional control without significantly increasing device complexity
Solution Approach 2:
The magnetic field strength varies across different locations of the ferromagnetic strip, with one side experiencing stronger activation than the other. This local variation in activation quality enables directional wave propagation by creating different excitation conditions at different positions along the strip
3Adaptability or versatility
If symmetric sensor configuration is used, then the sensor can detect waves from both directions, but the ability to attribute signals to specific sides is reduced
Solution Approach 1:
The asymmetric magnet positioning creates different activation levels on opposite sides of the ferromagnetic strip. This asymmetry imprints directional characteristics on the generated guided waves, allowing the sensor to not only detect waves from both directions but also to identify which side the signal originated from based on the activation pattern
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 allows for effective unidirectional guided wave propagation across a wide frequency range, enhancing the ability to detect anomalies on structures by ensuring that signals from one side of the sensor can be distinguished from the other, even in non-ferromagnetic materials, with reduced spurious signals and improved directional control.
Implementation Method 1
A static magnetic field provided by a permanent magnet may be used to partially magnetize the ferromagnetic strip
Implementation Method 2
An AC coil may be used to generate a time varying magnetic field. The time varying magnetic field may generate elastic waves in the ferromagnetic strip through magnetostriction
Data Source
AI summary
A ferromagnetic strip sensor for use in magnetostrictive testing of various structures. In its simplest form, the sensor has a ferromagnetic strip with an electrical coil winding. A permanent magnet is positioned atop the strip, aligned with but offset from, a center axis of the strip. The sensor is operable such that a time varying current in the coil results in a unidirectional guided wave. This guided wave travels within the structure, and is reflected from anomalies in the structure.