Optimum eddy current excitation frequency for subsurface defect detection in SQUID based non-destructive evaluation

• Published in: NDT & E international : independent nondestructive testing and evaluation Vol. 43; no. 8; pp. 713 - 717
• Main Authors: Nagendran, R., Thirumurugan, N., Chinnasamy, N., Janawadkar, M.P., Baskaran, R., Vaidhyanathan, L.S., Sundar, C.S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.11.2010; Elsevier
• Subjects: Aluminum; Analysing. Testing. Standards; Applied sciences; Cross-disciplinary physics: materials science; rheology; Defects; Eddy current testing; Eddy currents; Exact sciences and technology; Excitation; Materials science; Materials testing; Metals. Metallurgy; Nondestructive testing; Optimization; Optimun excitation frequency; Physics; SQUID; SQUIDs; Superconducting quantum interference devices; Testing for defects; SQUID; Optimun excitation frequency; Eddy current testing; Superconducting devices; Internal defect; Nondestructive testing; Signal-to-noise ratio; Aluminium; Optimization; Electrical measurement; SQUID devices; High-Tc superconductors; Metrology; Height; Electromagnetic testing; Plates; Defect detection
• ISSN: 0963-8695; 1879-1174
• DOI: 10.1016/j.ndteint.2010.08.003

Detailed experimental studies have been carried out for the determination of optimum eddy current excitation frequencies for the defects located at different depths below the top surface of an aluminum plate. These subsurface defects were detected by using a highly sensitive superconducting quantum interference device (SQUID) based eddy current non-destructive evaluation (NDE) system. The signal to noise ratio was found to be significantly higher at the optimum excitation frequency, which depended on the depth of the defect. The optimum excitation frequencies have been evaluated for defects located at different depths from 2 to 14 mm below the top surface of the plate. The defect depth was varied in steps of 2 mm, while the overall total thickness of the stack of plates was kept constant at 15 mm. Each defect represented a localized loss of conductor volume, which was 60 mm in length, 0.75 mm in width and 1 mm in height. The experimental results show that the square root of the optimum excitation frequency is inversely proportional to the depth of defect.