The mathematical formulation of acoustic diffraction tomography is applied to the problem of low frequency, diffusive electromagnetic (EM) fields. EM tomographic inversion, in two‐dimensional (2-D) Cartesian geometry, is illustrated for a crosshole source‐receiver configuration. The object function of the conductivity distribution is related to the transformed and filtered data by an inverse Fourier transform in the vertical direction and an inverse Laplace transform in the lateral direction. The reconstructed conductivity image is found to be a band‐limited version of the actual conductivity distribution. To stabilize the inversion, a regularized least‐squares method is used for image reconstruction. As in the seismic case, the inversion quality can be understood by inspecting the wavenumber domain coverage of the object function. Numerical experiments show that the resolution is better in the vertical direction than in the horizontal and it is also a function of source operating frequency. The position and attitude of the target are recovered well.

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Circuit obfuscation techniques have been proposed to conceal circuit's functionality in order to thwart reverse engineering (RE) attacks to integrated circuits (IC). We believe that a good obfuscation method should have low design complexity and low performance overhead, yet, causing high RE attack complexity. However, existing obfuscation techniques do not meet all these requirements. In this paper, we propose a polynomial obfuscation scheme which leverages special designed multiplexers (MUXs) to replace judiciously selected logic gates. Candidate to-be-obfuscated logic gates are selected based on a novel gate classification method which utilizes IC topological structure information. We show that this scheme is resilient to all the known attacks, hence it is secure. Experiments are conducted on ISCAS 85/89 and MCNC benchmark suites to evaluate the performance overhead due to obfuscation.