Focusing Characteristic Analysis of Circular Fresnel Zone Plate Lens

Fresnel zone plate lens (FZPL) has widely been used in electromagnetic antenna applications. Most analysis method based on the potential (scalar) wave approximation has been applied to a few very limited and simplified cases. The present paper analyzes the FZPL in more general form including the diffraction and transmission using the method of moments (MoM). The focusing gain characteristics in the oblique incidence as well as in the normal incidence are considered. The MoM solution using the three-dimensional vectorial formulation requires a large memory space for the FZPL as it is operated at a short wavelength. This is simply overcome by using an iterative conjugate gradient method for the numerical evaluation. The MoM solutions are compared with the other solutions

Clustering of Nodes in Layered-Tree Topology for Wireless Sensor Networks

Wireless sensor network is composed of a large number of sensor nodes of limited energy resource. The node clustering approach can improve the scalability and lifetime of wireless sensor network. In this paper we propose a novel node clustering protocol based on layered-tree topology for self-organizing distributed wireless sensor networks. It decides optimal number of clusters by employing a new approach for setting threshold value, including the probability of optimum number of cluster-heads and residual energy of the nodes. We also introduce a new scheme for layered-tree construction in each cluster. As a result, the proposed scheme can significantly improve the energy efficiency of the network and increase its lifetime. Computer simulation shows that the proposed scheme effectively reduces and balances the energy consumption of the nodes, and thus significantly extends the network lifetime compared to the existing schemes