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The ac field measurement technique (acfm) for sizing surface breaking cracks in metals exploits the fact that the high-frequency alternating current tends to flow in a thin skin on the metal and crack surfaces. The method seeks to interpret measured perturbations in the surface voltages produced by a crack so as to deduce its size and its shape and for this purpose a suitable mathematical model of the field is required. In the past, solutions of direct problems in which the crack shape is assumed to be known have been used for this purpose. This paper addresses the inverse problem in which the crack shape is not specified. The problem is formulated as a two-dimensional Laplace problem and a boundary element method is used for its iterative solution. The algorithm for predicting crack profile and size has been tested against synthetic input data obtained from known solutions of direct problems and also against surface voltage data obtained on real surface-breaking cracks. Good agreement has been found in all cases.

Light emitted from metal/oxide/metal tunnel junctions can originate from the slow-mode surface plasmon polariton supported in the oxide interface region. The effective radiative decay of this mode is constrained by competition with heavy intrinsic damping and by the need to scatter from very small scale surface roughness; the latter requirement arises from the mode’s low phase velocity and the usual momentum conservation condition in the scattering process. Computational analysis of conventional devices shows that the desirable goals of decreased intrinsic damping and increased phase velocity are influenced, in order of priority, by the thickness and dielectric function of the oxide layer, the type of metal chosen for each conducting electrode, and temperature. Realizable devices supporting an optimized slow-mode plasmon polariton are suggested. Essentially these consist of thin metal electrodes separated by a dielectric layer which acts as a very thin (a few nm) electron tunneling barrier but a relatively thick (several 10’s of nm) optically lossless region.