The theory of electromagnetic flaw detection based on the Lorentz reciprocity theorem has been applied to quantitative modeling of the corrosion buildup problem in PWR steam generators. Formulation of the electromagnetic probe response in spatial Fourier transform domain clarifies the role of the probe as a spatial frequency filter. Examples are given of tailoring the spatial frequency response to achieve specific performance characteristics, such as liftoff noise discrimination and flaw shape characterization. The relationship of spatial frequency response to probe geometry is analyzed for two dimensional inductive and capacitive structures, and the use of signal compression for realizing good spatial resolution and improved signal‐to‐noise ratio in long probes is discussed.