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In this article, we propose a novel glide-symmetric metallic holey unit cell loaded with a coaxial pin and investigate the propagation properties when embedded into parallel-plate waveguides. We demonstrate that the introduction of coaxial loading on the holey unit cell increases the effective refractive index and, together with glide-symmetry, greatly improves the isotropic properties compared to glide-symmetric holey structures. These two properties are desirable when designing graded-index lens antennas. To demonstrate the potential of the new coaxial unit cell, a fully metallic Mikaelian lens antenna is designed and manufactured using the CNC milling technique. The antenna works in the X-band and produces a directive fan beam that can be steered ±30° across the H-plane while keeping the scan loss and sidelobe levels acceptably low. The measured results of the antenna are in good agreement with the simulations.

Recently, there has been a growing interest in dielectric antennas and electromagnetic (EM) components based on periodic structures, since such components can be realized using new additive manufacturing technologies. The design of these components starts from the geometry of the unit cell, which determines not only the value of the effective refractive index but also the parameters of the entire considered component, like for example, the bandwidth of operation. For this reason, periodic structures with higher symmetry are of particular interest, since they can exhibit a wider bandwidth and other improved parameters. To analyze and design such components, we present a semianalytical method for calculating the guiding properties of parallel-plate waveguides (PPWs) loaded with periodic glide-symmetric dielectric structures. It is shown that the presence of glide symmetry can be simply included in the dispersion characteristic equation based on the transverse resonance condition. The derived expressions reveal that due to glide symmetry only the Bloch-Floquet modes of the same index parity interact and contribute to the dispersion properties. The accuracy of the discussed method is verified through the analysis of several 1-D and 2-D structures suitable for the design of planar lens antennas with a large frequency band of operation.

One challenge in designing RF wireless bioelectronic devices is the impact of the interaction between electromagnetic waves and host body tissues on far-field wireless performance. In this article, we investigate a peculiar phenomenon of implantable RF wireless devices within a small-scale host body related to the deformation of the directivity pattern. Radiation measurements of subcutaneously implanted antennas within rodent cadavers show that the direction of maximum radiation is not always identical with the direction to the closest body–air interface, as one would expect in larger-scale host bodies. For an implanted antenna in the back of a mouse, we observed the maximum directivity in the ventral direction with 4.6 dB greater gain compared to the nearest body-air interface direction. Analytic analysis within small-scale spherical body phantoms identifies two main factors for these results: the limited absorption losses due to the small body size relative to the operating wavelength and the high permittivity of the biological tissues of the host body. Due to these effects, the entire body acts as a dielectric resonator antenna, leading to deformations of the directivity pattern. These results are confirmed with the practical example of a wirelessly powered 2.4-GHz optogenetic implant, demonstrating the significance of the judicious placement of external antennas to take advantage of the deformation of the implanted antenna pattern. These findings emphasize the importance of carefully designing implantable RF wireless devices based on their placements and relative electrical dimensions in small-scale animal models.

This communication presents a method for the fast and accurate estimation of the gain pattern and maximum gain of an implanted antenna including the effect of the host body, under the assumption that the latter is electrically large. The estimation procedure is based on the radiation of an elementary dipole source placed in a planar body model. The derivation of closed-form expressions is based on spherical wave analysis and Green’s functions for layered media. The validity of this approximation for practical cases is shown on different implanted antennas, where the results are compared to full-wave simulations and measurements.

Design of curved metasurfaces is often a challenging task and requires the use of specialized analysis tools and methods. In this letter, we discuss a modification of the mode matching technique used for analyzing planar metasurfaces in order to efficiently apply it to the analysis of cylindrical structures. The first step in our procedure is to determine the optimal surface admittance of each curved metasurface unit cell for which the curvature effects are taken into account. Further, we introduce the resonance cancellation method to remove internal resonances that occur in closed canonical structures. This consequently allows us to extend the applicability of this approach to the analysis of inhomogeneous metasurface structures that occupy only a part of the curved surface. The developed analysis and design method is evaluated through comparison with reference designs based on circular–cylindrical metasurface examples demonstrating both completely cylindrical homogeneous and semicylindrical inhomogeneous cases.

The wireless power transfer (WPT) efficiency to implanted bioelectronic devices is constrained by several frequency-dependent physical mechanisms. Recent works have developed several mathematical formulations to understand these mechanisms and predict the optimal operating conditions. However, the existing approaches rely on simplified body models, which are unable to capture important aspects of WPT. Therefore, this article proposes the efficiency analysis approach in anatomical models that can provide insightful information on achieving the optimum operation conditions. First, this approach is validated with a theoretical spherical wave expansion (SWE) analysis, and the results for a simplified spherical model and a human pectoral model are compared. The results show that although a magnetic receiver outperforms an electric one for near-field operation and both the sources could be equally use in the far-field range, it is in the mid-field that the maximum efficiency is achieved with an optimum frequency between 1 and 5 GHz depending on the implantation depth. The receiver orientation is another factor that affects the efficiency, with a maximum difference between the best and worst case scenarios around five times for the electric source and over 13 times for the magnetic one. This approach is used to analyze the case of a deep-implanted pacemaker wirelessly powered by an on-body transmitter and subjected to stochastic misalignments. We evaluate the efficiency and exposure, and we demonstrate how a buffered transmitter can be tailored to achieve maximum powering efficiency. Finally, design guidelines that lead to optimal implantable WPT systems are established from the results obtained with the proposed approach.

This Letter discusses nonresonant modes excited on holey metasurfaces and their influence on the properties of spoof plasmonic states supported by the metasurface when a second surface is placed in its proximity. We consider here a metallic surface with periodic holes drilled in it. The field excited on each hole is projected onto a set of nonresonant modes in order to discuss their relative relevance. While previous simpler models assumed only the presence of the fundamental mode, we show that the simultaneous presence of several modes occurs when the surface is placed next to a metallic plate. Therefore, higher-order modes are responsible for the peculiar physical properties of wave propagation of spoof plasmons between two surfaces, which can lead to new gradient-index flat lenses for transceivers for space communications.

Modulation-averaging reflectors have recently been proposed as a means for improving the link margin in self-seeded wavelength-division multiplexing in passive optical networks. In this work, we describe simple methods for determining key parameters of such structures and use them to predict their averaging efficiency. We characterize several reflectors built by arraying fiber-Bragg gratings along a segment of an optical fiber and show very good agreement between experiments and theoretical models.

Temperature and strain sensors based on Fiber Bragg Gratings (FBG) are the most common optical sensors today. The properties of these sensors are well known, however interrogation techniques are still not standardized. The interrogator units typically have a high price, limiting the usage of such optical sensors. By carefully studying the properties of several interrogation techniques and developing an optimized version we will demonstrate that it is possible to significantly reduce the price of interrogation units. For this reason, presented are measurements of both temperature and strain sensitivity performed in various conditions that will be used in development of cost-optimized interrogator. [ABSTRACT FROM AUTHOR]