雙激發線圈巨磁阻感測器於非破壞性檢測之開發與特性研究

Abstract

非破壞性檢測是現代工業技術中重要的領域，應用上包含交通運輸工具、石化工業管線、土木營建物等等。而渦電流檢測是其中一種非破壞性檢測，基於電磁感應的原理來運作，廣泛應用於多種工業領域中的金屬缺陷和裂紋檢測，本研究以金屬鋁板加工作為缺陷，運用針對導電材料的渦電流檢測法作非破壞性檢測。渦電流檢測法歷經數十年的研究，許多研究團隊開發出不同優勢的探頭，本研究的探頭是由巨磁阻感測器、偏壓線圈和兩組激發線圈組成。共設計了兩種探頭皆是使用巨磁阻感測器作為接收元件，搭配偏壓線圈來極化巨磁阻感測器。兩組激發線圈的設計上皆是採用反向纏繞的雙線圈並將線圈垂直交疊組合，以達到能夠同時量測不同方向的缺陷。實驗部分將加工鋁板模擬出不同缺陷並進行檢測，檢測表面缺陷時，提供越高的激發頻率越能夠清晰地量測出表面缺陷，並且信躁比和圖像的分辨率會隨著探頭拉遠鋁板而降低，檢測深埋缺陷時則是透過降低線圈的激發頻率去提升渦電流穿透深度達到能夠量測深埋在無損金屬下的缺陷。從量測結果來看第一種探頭只有最接近待測物的線圈提供訊號，因此製作了第二種改良探頭，將兩組激發線圈以交錯穿插的方式組合在一起，使兩組線圈和待測物的距離近乎相等。第二種探頭能夠量測出不同方向缺陷的存在和位置，能夠響應出寬度0.5 mm表面深度0.5 mm的表面淺裂紋，能夠量測出尺寸在寬1 mm長5 mm的表面短缺陷和埋藏在無損表面下深度1.5 mm的深埋缺陷。

Non-destructive testing (NDT) is an important field in modern industrial technology, and its applications include transportation vehicles, petrochemical industry pipelines, civil structures, etc. It is widely used in metal surface crack defect in various industrial fields. In this study, metal aluminum plate processing was used as a defect, and the eddy current detection method for conductive materials was used for NDT.The probe in this study is composed of a giant magnetoresistive sensor (GMR) , a bias coil and two sets of excitation coils. A total of two probes were designed, both of which use GMR sensors as receiving elements and are equipped with bias coils to polarize the GMR. The two sets of excitation coils are designed to use reversely wound double coils and vertically overlap the coils to measure defects in different directions at the same time.The first type of probe is to vertically overlap two sets of coils with different directions one above the other, but this will cause only the coil closest to the object to be measured to provide signals.Therefore, a second improved probe was produced, which combined two sets of excitation coils in a staggered manner so that the distance between the coils and the object to be mesure is nearly equal.In the experimental part, different defects will be simulated and detected by processing aluminum plates.When detecting surface defects, the higher the excitation frequency, the more clearly the surface defects can be measured.And the signal-to-noise ratio will decrease as the probe moves away from the aluminum plate.Especially for the penetration depth experiment of the improved probe, the surface of the aluminum plate is processed with defects of different depths and widths to measure surface cracks and deeply buried cracks of different depths. This can increase the eddy current of the probe when the excitation frequency is low. Indicating that the improved probe can detect deeply buried defects that cannot be seen with the naked eye.