A flexible dual-band antenna with a metamaterial structure (MS) is presented. Polyimide substance, which makes the antenna thin and bendable, is used as the substrate for the antenna. When the MS is placed between the antenna and the human's forearm, the antenna gain is increased by 9.3 and 5.37 dB, and the radiation efficiency is increased by 48.4% and 35.7%, at 2.45 and 5.8 GHz, respectively. In addition, the specific absorption rate is decreased by more than 70%, considering the limitations imposed by Federal Communications Commission and the regulation of International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the frequencies cited above. The fabricated prototype of the antenna with the integrated MS was investigated by placing it on different places of human body, as also on different human bodies. The obtained results show that the proposed antenna is safe and suitable for use, in terms of the ICNIRP standards of World Health Organization.

A compact implantable antenna is proposed for wireless health monitor microsystem, which is operated in frequency of the Industrial, Scientific, and Medical (ISM) band. A circular radiator is cut four L-shaped slots and loading a shortpin between the radiator and ground plane to implement the circular polarization. Two crossed rectangle slots are etched on the ground plane so that the impedance and axial ratio (AR) bandwidths have been expanded at the same time. In addition, to further verify the performance of the antenna for biomedical application, we simulate a microsystem that monitors human health; and establish the simulation environment of the human heart and head. Then, we evaluated the performance of the microsystem in the human tissue simulation environment. The maximum specific absorption rate value satisfies the IEEE standard safety guidelines. The experiment results indicate that the impedance and AR bandwidths of proposed antenna are 2.25–2.78 GHz and 2.32–2.63 GHz, respectively. The total dimensions of π × 4 ² × 1.27 mm ³ are obtained, which is equivalent to π × 0.032 λ ₀ ² × 0.0102 λ ₀ ( λ ₀ is the free-space wavelength at 2.4 GHz). This compact size is very suitable for the application in health monitoring microsystem.

To implement efficient isolation between units of a multi-input multi-output (MIMO) antenna, a defected ground structure (DGS) has been investigated. An antenna with two elements operating at 5.8 GHz and fed by coaxial is considered. To reduce mutual coupling between the elements, a zigzag groove is inserted into the center of two elements formed as a DGS. To verify this design, a scattering matrix was tested, such as reflection coefficient S₁₁ and transmission coefficient S₂₁ between two element ports. Meanwhile, radiation pattern, current distribution, envelope correlation coefficient (ECC), and diversity gain of the antenna were simulated and measured. The results showed that the mutual coupling was reduced by 28.8 dB when a DGS was used, and the ECC was less than 0.02. Owing to these good performances, each antenna element can operate almost independently, and this MIMO antenna can be efficiently applied to the narrow band Internet of Things system.

To meet an implantable device for human disease detection, a conformal multiple-input multiple-output (MIMO) antenna is investigated in this paper. The layout and decoupling of the antenna are designed according to the inherent electromagnetic properties of the implanted device based on the theory of characteristic modes (TCM). Compared with traditional methods, the TCM provides a method and theory to design a conformal implantable antenna with MIMO property. The designed antenna has the advantage of simple structure, low space occupation, and little multipath reflection. The new designed structure adopts two planar helical radiators to achieve size miniaturization. Some I-type patches located between two radiators and slotting structure on the ground plane to reduce coupling. The biocompatible flexible polyimide is used as a dielectric substrate, enabling the conformal property and compatibility with the human tissue. Measurements of the fabricated prototype have been finished in the minced pork and skin-mimicking gel. Results show in very good agreement with the simulations, which validate the suitability of the proposed antenna for the implantable devices. To our best knowledge, this is the first time that the TCM has been applied to guiding the design of implantable MIMO antennas.

This paper presents the analysis and design of a miniaturized polarization insensitive metamaterial absorber (MMA) for suppression of the electromagnetic interference (EMI) at microwave frequency range. The proposed MMA consists of a periodic array of double split ring structures printed on an FR4 substrate with a thickness of 0.07 λ ₀ . The simulated results derived from CST indicate that the absorption ratio of the MMA is over 90% with a wide frequency range from 8.3 GHz to 11.3 GHz for a normal incident electromagnetic (EM) wave. To understand the EM wave absorption mechanism, an equivalent circuit model of the MMA unit cell is constructed to investigate the absorbing characteristics, and the electric field and surface current distributions are analyzed at absorption peaks.. Both equivalent circuit model (ECM) and measured results show good agreement. What's more, the measurement data shows that the radiated electric field of the patch antenna at 1 meter is significantly reduced at 10 GHz while loading with the MMA. A maximum suppression of 18 dBμν/m is achieved at 10 GHz. As the proposed absorber possesses good ability on electromagnetic radiation absorption, it could be well applied on printed circuit board (PCB) level EMI suppression.