Given the increased interest in a fast, portable, and on-spot medical diagnostic tool that enables early diagnosis for patients with brain stroke, a new approach of wearable electromagnetic (EM) head imaging system based on polymer material is proposed. A flexible low profile, wideband, and unidirectional antenna array with electromagnetic band gap (EBG) and metamaterial unit cells reflector is utilized. The designed antenna consists of a 4×4 radiating patch loaded with symmetrical extended open-ended U-slots and fed by combination of series and corporate transmission lines. A mushroom-like 10-EBG unit cell arrays are arranged around the feeding network to reduce surface waves, whereas 4×4 metamaterial (MTM) unit cells are placed on the back-side of the antenna to enable unidirectional radiation. The antenna is designed and embedded on a multi-layer low cost, low loss, transparent and robust polymer poly-di-methyl-siloxane (PDMS) substrate and optimized to operate in contact with the human head. The simulated and measured results show that the antenna has a fractional bandwidth of 53.8% (1.16 GHz - 1.94 GHz), more than 80% of radiation efficiency, and satisfactory field penetration in the head tissues with a safe specific absorption rate (SAR). An eight-element array is then configured on 300 × 360 × 4.1 mm3 PDMS material covering an average human head size and used as a worn part of the imaging system. A realistic-shaped 3D SAM head phantom is used to verify the performance of the designed array. The imaging results indicate the possibility of using the designed conformal array to detect a bleeding inside the brain using a confocal image algorithm.

Next-generation communication systems and wearable technologies aim to achieve high data rates, low energy consumption, and massive connections because of the extensive increase in the number of Internet-of-Things (IoT) and wearable devices. These devices will be employed for many services such as cellular, environment monitoring, telemedicine, biomedical, and smart traffic, etc. Therefore, it is challenging for the current communication devices to accommodate such a high number of services. This article summarizes the motivation and potential of the 6G communication system and discusses its key features. Afterward, the current state-of-the-art of 5G antenna technology, which includes existing 5G antennas and arrays and 5G wearable antennas, are summarized. The article also described the useful methods and techniques of exiting antenna design works that could mitigate the challenges and concerns of the emerging 5G and 6G applications. The key features and requirements of the wearable antennas for next-generation technology are also presented at the end of the paper.

An approach towards designing and building of compact low-profile, wideband, unidirectional and conformal imaging antenna for electromagnetic (EM) head imaging systems is presented. The approach includes the realization of a custom-made flexible high-permittivity dielectric substrate to achieve a compact sensing antenna. The developed composite substrate is built using silicon-based poly-di-methyl-siloxane (PDMS) matrix and microscale of aluminium oxide (Al2O3) and graphite (G) powders. Al2O3 and G powders are used as fillers with different weight-ratio to manipulate and control the dielectric properties of the substrate for attaining better matched with the human head and reducing antenna’s physical size while keeping the PDMS flexibility feature. Using the custom-made substrate, a compact, wideband, and unidirectional on-body matched antenna for wearable EM head imaging system is realized. The antenna is configured as a multi-slot planar structure with four shorting pins, working as electric and magnetic dipoles at different frequency bands. The measured reflection coefficient (S11) shows an operating frequency band of 1 -4.3 GHz. The time-average power density and the amplitude of the received signal inside the MRI-based realistic head phantom demonstrate a unidirectional propagation and high-fidelity factor of more than 90%. An array of 13 antennas are fabricated and tested on a realistic 3D head phantom to verify the imaging capability of the proposed antenna. The reconstructed images of different targets inside the head phantom demonstrate the possibility of utilizing the conformal antenna arrays to detect and locate abnormality inside the brain using multistatic Delay-Multiply-And-Sum beamforming algorithm.

Portable light-weight electromagnetic head imaging systems for brain stroke detection are of great interest due to the need for fast and low-cost diagnosis tools. This paper presents a wideband and compact flexible meander-line antenna array for a wearable electromagnetic head imaging system. The antenna is designed and optimized on a 4-mm thick low-cost, flexible room-temperature-vulcanizing (RTV) silicone substrate in close vicinity to a multi-tissue head model. The antenna comprises two sections of meander-lines, a full ground plane, and a 50 Ω coaxial connector. The measured reflection coefficient |S11| on a human head shows that the proposed antenna operates effectively across the frequency band of 0.45-3.6 GHz, attaining fractional bandwidth (FBW) of 155%. The antenna achieves unidirectional radiations with greater than 9 dB of front-to-rear-ratio in the near field region, and safe-level maximum SAR below 0.2 W/kg using an input power of 10 dBm. A 16-element antenna array was assembled and experimentally utilized in an electromagnetic head imaging system. The reconstructed images of abnormality-emulating targets using a confocal imaging algorithm demonstrate the feasibility of utilizing such flexible and light-weight antennas for wearable electromagnetic head imaging systems.

This letter assesses the use of a flexible multilayered polydimethylsiloxane (PDMS) substrate in a multiple-input- multiple-output (MIMO) antenna array for WLAN applications at 5.8 GHz. The use of the innovative polymer-based PDMS technology features favorable mechanical properties such as flexibility, water/dust resistance, and optical transparency. Besides that, PDMS also has a relatively low loss tangent. All these properties are very relevant for future (wearable) WLAN MIMO antennas. The proposed 2 × 4 antenna array and its rear ground plane are embedded in a multilayered PDMS substrate and fed by two 50Ω coaxial ports. It is found that the multilayered PDMS substrate may yield a design with excellent MIMO parameters. The mutual coupling is better than -30 dB, the envelope correlation coefficient (ρ) is in the order of 0.001, and the efficiency is 72%. A high gain of 11.5 dB is achieved.

The timely treatment is the crucial element for the survival of patients with brain stroke. Thus, a fast, cost-effective, and portable device is needed for the early and on-the-spot diagnosis of stroke patients. A 3D electromagnetic head imaging system for rapid brain stroke diagnosis with a wearable and lightweight platform is presented. The platform comprises a custom-built flexible cap with a 24-element planar antenna array, and a flexible matching medium layer. The custom-built cap is made out of an engineered polymer-ceramic composite substrate of RTV silicone rubber and aluminum oxide (Al ₂ O ₃ ) for enhanced dielectric properties and mechanical flexibility and robustness. The array is arranged into two elliptical rings that are entirely incorporated into the flexible cap. The employed antenna elements within the system are compact with low SAR values over the utilized frequency range of 0.9-2.5 GHz. Moreover, a flexible matching medium layer is introduced on the front of the apertures of the antenna array to enhance the impedance matching with the skin. The detection capability of the system is experimentally verified on 3D realistic head phantoms at multiple imaging scenarios and different types of strokes. The reconstructed 3D and 2D multi-slice images using the beamforming and polar sensitivity encoding (PSE) image processing algorithms indicate the applicability and potential of the system for onsite brain imaging.