This paper is a critical review of metasurfaces, which are planar metamaterials. Metamaterials offer bespoke electromagnetic applications and novel properties which are not found in naturally occurring materials. However, owing to their 3D-nature and resonant characteristics, they suffer from manufacturing complexity, losses and are highly dispersive. The 2-dimensional nature of metasurfaces allows ease of fabrication and integration into devices. The phase discontinuity across the metasurface offers anomalous refraction, thereby conserving the good metamaterial properties while still offering the low-loss characteristics. The paper discusses salient features and applications of metasurfaces; wavefront shaping; phase jumps; non-linear metasurfaces; and their use as frequency selective surfaces (FSS).

Abstract-This paper critically reviews the electromagnetic advantages of altering the dielectric substrate section of the antenna as opposed to the conducting elements. Changing the dielectric has been used to improve the bandwidth, efficiency and gain of antennas. Heterogeneous substrates have also been employed to lower the effective permittivity, suppress surface waves for high indexed substrate materials and reduce mutual coupling. In the second half of this paper, 3-D printing has been used to create substrates with reduced material consumption for a lightweight flexible wearable antenna.

Coupled complementary metasurfaces (CCMTS) exhibit a passband whose frequency is several times lower than that of the individual metasurface (MTS) passband frequency. In this paper we explain this phenomenon and propose a simple and accurate equivalent circuit for CCMTS comprised of slots and their Babinet complement, dipoles. An equivalent circuit is extracted from a coupled EFIE-MFIE equation using a synthetic basis function. The same procedure can be conveniently applied to any CCMTS. The model allows one to estimate the large downshift of resonant frequency and the bandwidth utilizing a simple formula. When used in a subresonant regime, the unit cell may have a dimension of a tenth of a free space wavelength with a moderate value of permittivity between the complementary layers.

This study presents empirical results from a measurement campaign to investigate futuristic body‐centric medical mesh networks for a hospitalised patient using flexible body‐contouring antennas. It studies path loss in a medical environment (in a hospital bed in an open hospital ward) for ultra‐wideband (UWB) and four narrowband schemes concurrently. It firstly investigates the antenna contouring effects due to mounting the flexible antennas on various body surfaces, then uses statistical analysis to explore optimal body locations for a master node to inform the allocation of processing power (assuming point‐to‐point link from other nodes). Results indicated how the most suitable body location varies depending on the posture and frequency scheme used. Also investigated are best route selections for multi‐hop mesh network topologies for opportunistic networking for each of the presented postures and frequencies; this reveals how fewer hops were required to navigate around the narrowband network compared to UWB which effectively reduces required processing power and data traffic. Understanding how disparate body‐centric medical devices communicate with one another in a body‐mesh network is instrumental to the strategic and informed development of next generation healthcare patient monitoring solutions.

At the network access layer, optical fibre deployment continues at pace but copper cables containing twisted pairs will remain for some time and face an increasing bandwidth and data rate demand. Surface waves have been proposed to address these requirements. This paper reports and investigates the existence of stop bands reaching over 50 dB insertion loss on 1 metre long, typical final drop cables under surface wave excitation at a few GHz. Coupled mode analysis shows that lack of helical symmetry enables the formation of a stop band in systems containing twisted pairs. A representative core model containing a single twisted pair alongside a straight wire is thoroughly studied. Numerical simulations and measurements confirm the crucial dependence of the stop band frequency on the twist rate of the twisted pair. Further investigation into the role of the dielectric coating and the distance of the straight wire are performed as well. Finally, in systems with multiple twisted pairs, we find that the twist rate associated with any pair can create a stop band effectively limiting surface wave propagation. Thus, careful design and deployment strategies are required for use of surface waves on legacy copper networks.