Radio frequency (RF) energy harvesting technologies have attracted different efforts from researchers to employ low energy in powering portable electronic devices. In this article, an Ultra-Wide Band (UWB) antenna based on a Vivaldi fractal antenna backed with a Metamaterial (MTM) array is exemplified for RF-energy harvesting in the modern 5G networks. The antenna is connected to a full wave rectifier circuit to obtain a rectified DC current. It is found that the exemplified antenna provides a maximum output voltage of 1.4 V and 1.3 V at 3.1 GHz and 4 GHz, respectively, when the incident RF power is around 17 Bm. The measured results and simulations show excellent agreement. The antenna is printed on a flexible Kodak photo paper of 0.5 mm thickness with ε r = 2 and loss tangent of 0.0015. The numerical simulations are conducted using CST MWS software package. The proposed antenna structure is fabricated using an ink jet printing technology based on conductive silver nanoparticle ink. Finally, from the obtained measurements after the comparison to their simulations, the proposed antenna covers the frequency band from 2.4 GHz up to 20 GHz with a gain of 1.8 dBi at 3.1 GHz and 4 dBi at 4 GHz. 1. INTRODUCTION Since the concept of metamaterial (MTM) structures was started from the optical domain in 1987 [1] as photonic band gap, they have received a lot of research attention. As of late, an intensive investigation has been applied to the effects on connecting the MTM structures to antenna performance for upgrading their performance [1]. MTM structures are periodic-like layers of exceptional surface wave concealment properties with unique constitutive electromagnetic parameters, permittivity, and permeability, which are not found in nature [2]. Based on their nontraditional electromagnetic properties, MTM structures were classified as: near zero refractive index [3], soft and hard surfaces [4], high-impedance surfaces [5], and artificial magnetic conductors [6]. It is worth to say that a few of these structures have relatively enhanced electromagnetic properties with low material losses [7]. Frequency Selective Surface (FSS) is another category of MTM structures that are periodically layered as dielectric and/or metallic unit cells in different manners [8] with high frequency selectivity. Recently, FSS classifications are defined according to their applications whether as filters [9], artificial magnetic conductors [10], photonic crystals [11], and photonic band gaps [12]. These structures can also be as artificial periodic and non-periodic layers to prevent and/or assist the incident wave propagation [13]. They possess high impedance in both TE and TM modes as found in mushroomlike structures [14], in which an in-phase reflection coefficient can be created [15]. Moreover, soft and hard surfaces operate as FSS structures [16], which include a wide range of applications in the antenna engineering researches and industries.
Summary The proposed work presents a design of a smart printed monopole antenna separated from a Hexagonal Matching Load (HML) with an air gap. The patch is fed by a coplanar waveguide, while the HML is connected to the ground plane through two pin diodes to realize antenna reconfiguration through controlling the surface current motion. The antenna structure is mounted on FR‐4 epoxy substrate with size of 23 mm × 30 mm to fit the portable devices. After running four different switching scenarios, an observable change in the antenna performance is demonstrated. The proposed antenna provides a gain of 3.1 dBi at 2.45 GHz when the two diodes are switched ON. However, the antenna gain is changed to 1.6 dBi when the two diodes are set OFF. It is demonstrated that the proposed technique shows an effective approach to control the antenna performance without the need for DC blocking capacitor for RF choke. Nevertheless, the Specific Absorption Rate (SAR) effects are evaluated with respect to the human head tissues for all considered scenarios. Finally, the antenna radiation leakages to the human body are also tested numerically and experimentally for validation.
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