A miniaturized high selectivityfrequency selective rasorber (FSR) with a wide interabsorption high transparent bandpass based on multiple 2.5-dimensional (2.5-D) resonators is investigated. The main contribution is the achievement of a wide and high transparent passband by combining the large inductance of parallel resonators (PRs) and cascading two 2.5-D PRs, which also provide the function of miniaturization. The 2.5-D PR is implemented by connecting the interdigitated capacitor and the metal meandered strip-line on both surfaces of a lossy layer through metalized vias. The inductor and capacitor values of 2.5-D PR can be individually adjusted to shift the passband's central frequency. The lossy element is realized by inserting two 2.5-D strip-type PRs at the center of each side of a meandered cross-dipole loaded with two resistive sheets on both sides. An equivalent circuit model is proposed to analyze its operating principle. The dimensions of the miniaturized element are 0.12 λ _L × 0.12 λ _L × 0.118 λ _L . While maintaining a good wide passband (−1dB relative bandwidth is 21.2%), the miniaturized FSR satisfies the characteristic of polarization insensitivity (TE and TM), and angular insensitivity (up to 45°). A prototype of miniaturized FSR has been manufactured and measured, showing a reasonable agreement with simulations.

In recent years, the usage of radio frequency magnetic fields for biomedical applications has increased exponentially. Several diagnostic and therapeutic methodologies exploit this physical entity such as, for instance, magnetic resonance imaging, hyperthermia with magnetic nanoparticles and transcranial magnetic stimulation. Within this framework, the magnetic field focusing and shaping, at different depths inside the tissue, emerges as one of the most important challenges from a technological point of view, since it is highly desirable for improving the effectiveness of clinical methodologies. In this review paper, we will first report some of the biomedical practices employing radio frequency magnetic fields, that appear most promising in clinical settings, explaining the underneath physical principles and operative procedures. Specifically, we direct the interest toward hyperthermia with magnetic nanoparticles and transcranial magnetic stimulation, together with a brief mention of magnetic resonance imaging. Additionally, we deeply review the technological solutions that have appeared so far in the literature to shape and control the radio frequency magnetic field distribution within biological tissues, highlighting human applications. In particular, volume and surface coils, together with the recent raise of metamaterials and metasurfaces will be reported. The present review manuscript can be useful to fill the actual gap in the literature and to serve as a guide for the physicians and engineers working in these fields.

In this article, we demonstrate the near electric field reduction ability of spiral resonators arrays (SRAs) in resonant inductive wireless power transfer (WPT) applications. In particular, we show that a suitably designed planar SRA, placed in the proximity of the driver loop, can significantly decrease the electric field level at the operative frequency, thus reducing the potentially dangerous radiation (i.e., the specific absorption rate) in the case of human exposure. In addition, due to the thin structure of the SRAs, the system is able to enhance the performance with respect to a conventional simple driver–receiver system for a fixed working distance. A systematic study has been performed through electromagnetic simulations to evaluate the optimum number of array unit cells to eventually achieve a compromise between efficiency enhancement and electric field shielding on a two-coil system, selected as a test case. Finally, the numerical results have been confirmed through measurements conducted on fabricated prototypes of the proposed WPT configurations. The introduced solution can be remarkably useful in all the WPT applications requiring a close interaction with human operators where exposure is a concern, such as automotive applications, biomedical implants, and rechargeable devices.

In this paper, we introduce a novel antenna employing specifically-designed metasurfaces to improve the radiating performance in close proximity to the human body, as required in microwave biomedical applications. We firstly present design guidelines to realize a thin metasurface acting as an impedance matching layer between the radiating element and the biological tissue, based on the transmission line equivalent model. Additionally, for the first time to the best of our knowledge, we combine an artificial magnetic conductor as the backing element of the antenna, to improve the gain and reduce the undesired back radiation. To validate the proposed approach, we conceived a numerical test-case consisting of a bow-tie antenna operating close to a biological phantom at 2.56 GHz. Numerical simulations demonstrated the performance enhancement in terms of higher field penetration within tissues and better radiating behavior when the bow-tie antenna is working in presence of both the metasurfaces. Furthermore, measurements carried out over fabricated prototypes confirmed the numerical results, validating the overall design procedure. The herein presented methodology can be helpful in several applications when the radiating elements operate in close proximity to biological tissues, as in medical imaging, on-body communication, mobile phones and consumer devices.