Smart sensing in the light of non-destructive testing and structural health monitoring

Non-destructive testing (NDT) is based on physical principles where acoustics and electromagnetics play a very significant role. NDT is specifically performed at damage critical locations and at defined intervals in time. Hand held but possibly also automated inspection processes are common. However often the locations to be inspected are quite hidden or generally difficult to access and may therefore lead to a time and hence cost consuming process. A means to alleviate those disadvantages has emerged with advanced sensor and materials technologies which allow sensors, or better sensor systems, to be adapted or generally integrated onto or into a structural component allowing NDT to become an integral part of the component. This is what is considered today to be structural health monitoring (SHM). Many of the SHM systems can therefore be seen as derivatives of NDT technology developed in a classical way. This paper will make reference to a variety of vibrations and elastic waves based principles used such as classical modal analysis, acoustic emission, phased array ultrasonics and guided waves as well as electromagnetic principles considering electromagnetic impedance, permeability, Barkhausen noise and higher harmonics analysis including advanced sensor signal processing.