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- On κ-reducibility of pseudovarieties of the form V ∗DPublication . Costa, J. C.; Teixeira, M. L.; Nogueira, ConceiçãoThis paper deals with the reducibility property of semidirect products of the form V∗D relatively to graph equation systems, where D denotes the pseudovariety of definite semigroups. We show that, if the pseudovariety V is reducible with respect to the canonical signature κ consisting of the multiplication and the (ω − 1)-power, then V ∗ D is also reducible with respect to κ.
- Tunable square slot FSS EC modelling and optimisationPublication . Ferreira, David; Caldeirinha, Rafael Ferreira Silva; Cuiñas, Iñigo; Fernandes, Telmo RuiAn equivalent circuit model for tunable square slot frequency selective surfaces (FSS) is proposed. Tuning is achieved with the inclusion of a discrete capacitance element, at key points within the FSS unit cell. The equivalent circuit model takes into account the FSS physical attributes. The performance of the proposed equivalent circuit model was evaluated against results obtained from appropriate electromagnetic simulations. Results demonstrate the validity of the proposed equivalent circuit model, in which good estimations of the frequency response of FSS structures were obtained. A RMSE value of 190 MHz was extracted from the complete parametric simulation set. The model was further validated against measurements performed on a tunable active FSS prototype inside an anechoic chamber. Tuning of the FSS was achieved by means of bias voltage to modify the varicaps capacitance value. A relatively good agreement was verified between equivalent circuit model, electromagnetic simulations and measurements. Finally, this work is sought to be a useful contribution to the literature on this topic, by improving on the elementary models of such FSS structures and be useful as a good and fast first approach to determine approximate FSS unit cell dimensions.