Eddy current probes have been used for decades to detect flaws in metal objects. These probes are unusually sensitive to changes in the proximity distance to the test surface, and special techniques must be used to suppress this proximity signal when searching for flaws. More recently this proximity effect of a test coil has been recognized as useful for robotic sensing, and several sensors of this type are on the market. However, recent scientific advances in the design of eddy current flaw detection probes have not yet been applied to eddy current robotic sensors. A similar situation exists in connection with capacitive sensors, which were initially applied as intruder sensors, and more recently to a small degree, as robotic proximity sensors. A common criticism of these circuit-type sensors is that they do not provide sufficient spatial selectivity to be useful in robotic applications. However, recent studies of flaw detection probes have shown that desirable detection properties can be designed into the probe by using spatial frequency analysis to determine the optimum probe geometry for the task at hand. In this approach the probe is treated as a spatial filter, much like optical signal processing components, but in this case the electromagnetic field is nonradiating (or quasistatic). The purpose of this research is to develop a conceptual base and associated technology for electromagnetic sensor arrays applied to automated manufacturing, maintenance, and NDE. This paper discusses concepts and theory, while the experimental system and measurements are presented in a companion paper [1].</p
