This article describes a passive, economical strategy towards enhancing the security feature of conventional plastic cards by embedding a set of electromagnetic (EM) material that emulates an invisible “watermarking”. This is an overlay strategy to prevailing security measures and consists of incorporating (invisibly embedding, say by ink-jet printing or otherwise) a set of foil/film-like grids of electromagnetic (EM) material (such as high-μ material or high-conductivity metal) within the cross-section of the card. The test-card when exposed to a suitable excitation of microwave (ISM band) excitation, the embedment of EM material in the card is rendered to yield distinct path-loss to the traversing EM energy. That is, by making each element of embedment a grid-frame made of vertical or set of horizontal strips, (relative to the plane of polarization of EM excitation), each grid-frame will offer high (logic 1) or low (logic 0) transmissions when the card is swiped across the EM field. By sensing appropriately, this differentiable EM attenuation across the card would depict an output signal annunciating the presence of a binary-logic encoding in the embedded “watermarking”. The proposed effort augments the existing security features of a plastic card design and robustly reduces the chances of malpractices, such as plastic card counterfeiting and misuse. The concept-design as proposed is positively verified through experimental test cards and also justified with theoretical considerations.
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