In this paper, we propose a comprehensive framework for performance analysis of secure communications over non-small scale fading channels. Considering the three different cases where the main and eavesdropper channels experience independent/correlated log-normal fading, or independent composite fading, we study secrecy capacity and secrecy outage (including the probability of non-zero secrecy capacity and secure outage probability), respectively. The approximated closed-form expressions for secrecy capacity, the probability of non-zero secrecy capacity, and secure outage probability have been derived for these three different types of non-small fading channels, respectively. Finally, the accuracy of our performance analysis is verified by simulation results.

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In order to improve the sensitivity of online magnetic flux leakage (MFL) testing for steel pipe, a sensing method based on the magnetic guiding effect is proposed and investigated in this paper. Compared to the conventional contact sensing method using a non-ferromagnetic support, the proposed method creatively utilizes a ferromagnetic one to guide more magnetic flux to leak out. Based on Hopkinson’s law, the principle of the magnetic guiding effect of the ferromagnetic support is theoretically illustrated. Then, numerical simulations are conducted to investigate the MFL changes influenced by the ferromagnetic support. Finally, the probe based on the proposed method is designed and developed, and online MFL experiments are performed to validate the feasibility of the proposed method. Online tests show that the proposed sensing method can greatly improve the MFL sensitivity.