Butterfly probes: estimating the derivative of the magnetic flux

The main way to increase the spatial selectivity of near field probes has been to make coils with smaller and smaller diameters. This is especially true for secure applications (side-channel attacks). In this paper, we investigate an alternative way with secure applications in mind. It consists in designing probes that measure the spatial derivative of the magnetic flux instead of the flux itself. The paper presents the motivation, the concept and preliminary results obtained with a first prototype.