Robert Hughes

Developments in near electrical resonance signal enhancement (NERSE) eddy-current methods

In industry, the detection of small defects above a background noise threshold is always a limiting factor. This is true for even the most sensitivity and reliable of NDT techniques. However, defect signals in eddy-current (EC) inspections have the potential to be boosted above noise thresholds by exploiting the near electrical resonance signal enhancement (NERSE) phenomena, resulting from resonant frequency-shifting of an EC system as the coil passes over a defect. Following on from the observation and characterisation of this phenomenon, NERSE based EC methods are being investigated and developed for the detection of sub-millimeter surface defects in Aerospace superalloys. This paper discusses current advances in the development of such techniques and explores the potential of NERSE exploitation as well as examining its limitations.

Eddy-current crack detection at frequencies approaching electrical resonance

The effect of operating an absolute eddy-current (EC) probe at frequencies around its electrical resonance was investigated. A defect signal enhancement phenomenon was observed and characterised. Experimental tests were performed on notch defects in typical aerospace superalloys. An absolute mode EC probe was operated by sweeping through a range of frequencies, in the MHz range, encompassing the electrical resonance of the system. Resonance decoupling above defects results in a signal-to-noise ratio (SNR) peak, within a band of frequencies approaching resonance, of up to 3.7 times that measured at 1MHz. This near electrical resonance signal enhancement (NERSE) phenomenon poses the possibility for a simple operational approach method for improving the sensitivity of conventional eddy-current testing.

Counting and accountability

1brings an important issue to greater attention and focus. Our organisation, Human Rights Watch, works to uphold the principle of government accountability, and an important part of this is to ensure that individuals—citizens and others within a state’s borders—are offi cially recognised and counted. The most widely adopted international human rights treaty in his tory, the 1989 Convention on the Rights of the Child, outlines governments’ obligations to pro vide birth registration. 2 Human Rights Watch’s documenta tion of govern ment denials of civil registra tion, especially concern ing refugees, migrants, and minor ity groups, 3,4

Chronic arsenical poisoning due to prolonged administration of a bromide and arsenic mixture.

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