Single Layer Meta-material Lens with Graded Refractive Index

A new single layer meta-material lens design with frequency-dependent focal points is investigated. In the proposed design, the surface of the single layer dielectric material is divided into zones in the same plane with perforations of difierent speciflcations. The focal point for each frequency is achieved through varying the permittivity coe-cient of each zone. The variation of the permittivity of each zone is based on the changes of the perforations' speciflcations in the dielectric material. The paper presents a conceptual design of a lens with two zones; each zone is optimized for a speciflc frequency. The design can be optimized to provide several focal points, each for a speciflc frequency, meeting pre-deflned size constraints. 1. INTRODUCTION Meta-material lenses are of great importance in radiometry process, which allows the measurement of the temperature proflle in magnetic conflnement fusion devices (1). In practice, optical systems are optimized for a single frequency leading to losses in the transverse resolution at other frequencies. Thus, the increase and optimization of the transverse resolution require difierent focal points for difierent frequencies. In the literature, meta-material lenses with frequency-dependent focal points have been pro- posed (2) to replace conventional optical systems. In the former, the surface of the lens is divided into several zones; each provides a certain phase-shift for a certain frequency. As a result, each frequency would have a speciflc focal point (6{8). This was achieved using layered structure, con- sisting of periodic arrangements of capacitive patches and inductive wire grids, separated by a dielectric material.In each zone the capacitive patches and inductive wire grids act as band pass fllters allowing certain frequencies and providing a speciflc phase-shift (3). However, this appeared to be complex to design and manufacture due to the layered structure (2{5). In this paper, we propose a new design of the meta-material lens with frequency dependent focal points. Opposed to designs seen in the literature, we propose to use a single dielectric layer with difierent zones in the same plane. The phase-shift for each frequency is achieved through having a difierent refractive index in each zone. This reduces the complexity of both design and manufacture. This paper is divided into three main sections. Section 2 presents the unit cell characteristics and describes the efiect of the change in unit cell perforations diameter on the permittivity and on the optimal frequency of the unitcell. Section 3 describes the theory behind the lens design proposed in this paper. Finally, Section 4 discusses the conceptual design of the proposed two zones lens.