A Road towards 6G Communication—A Review of 5G Antennas, Arrays, and Wearable Devices

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.

The prediction of loss tangent of sewed multilayer fabric

The thickness and dielectric properties (dielectric constant and loss tangent) of fabric substrate play a key role in the design and properties of wearable antennas. Related research shows that a thicker substrate with a low dielectric constant and high loss tangent can enhance the bandwidth of antennas. Here, sewing multiple fabrics together was a good way to increase the thickness while maintaining flexibility, but it is hard to control the dielectric properties because of the lack of the relationship between the dielectric properties and that of the components. Although previous works have established the equivalent capacitance model of sewed multilayer fabric, they cannot obtain its dielectric properties completely. In this work, based on the circuit model proposed by Chin and Lee, the equivalent capacitance and resistance models of sewed multilayer fabric were established to predict its loss tangent. The sewed multilayer fabrics were fabricated and measured by split post dielectric resonator at 1.11 GHz to validate the model. From the comparison of the predicted and measured loss tangents of sewed multilayer fabrics, it was found that the predicted loss tangents agreed well with the experimental results. It is believed that the proposed model is beneficial to the rapid and rational configuration of the components for multilayer fabric according to thickness and dielectric properties of the components, and will provide a theoretical basis for the design of multilayer flexible electronic substrate.

3D-printed thermoplastic polyurethane for wearable breast hyperthermia

Microwave breast hyperthermia is a class of cancer treatment, where breast temperature is elevated by a focused electromagnetic (EM) radiation to impair cancer cells. While the current mainstream in microwave breast hyperthermia is centered on bulky and rigid systems, wearable antennas would offer considerable benefits such as superior conformity to individual patient anatomy and better comfort. In this proposition, this paper presents 3D-printed flexible antenna prototypes for wearable breast hyperthermia applications. Since the dielectric properties are expected to dominate the antenna gain but could be influenced by the solid volume percentage, this work first investigates the relationship between the dielectric properties and solid volume percentage of a 3D-printed flexible filament. From this, it is found that with decrease in the solid volume percentage, the dielectric constant decreases following the classic theory of dielectric mixture. Based on this observation, optimal antennas are designed for substrates in different infill levels by running a 3D full-wave EM simulator and fabricated by 3D printing a polyurethane filament. Temperature elevations in a synthetic breast tissue are measured by a thermometer and are ~ 5.5 °C and ~ 3.2 °C at the 5 mm- and 7 mm-deep locations, respectively. The infill percentage makes little difference in the heating efficacy. Based on these findings, this translational study sheds light on the possibility of wearable breast hyperthermia with the 3D-printed flexible and conformal antennas.

Design and Evaluation of a Flexible Dual-Band Meander Line Monopole Antenna for On- and Off-Body Healthcare Applications

The human body is an extremely challenging environment for wearable antennas due to the complex antenna-body coupling effects. In this article, a compact flexible dual-band planar meander line monopole antenna (MMA) with a truncated ground plane made of multiple layers of standard off-the-shelf materials is evaluated to validate its performance when worn by different subjects to help the designers who are shaping future complex on-/off-body wireless devices. The antenna was fabricated, and the measured results agreed well with those from the simulations. As a reference, in free-space, the antenna provided omnidirectional radiation patterns (ORP), with a wide impedance bandwidth of 1282.4 (450.5) MHz with a maximum gain of 3.03 dBi (4.85 dBi) in the lower (upper) bands. The impedance bandwidth could reach up to 688.9 MHz (500.9 MHz) and 1261.7 MHz (524.2 MHz) with the gain of 3.80 dBi (4.67 dBi) and 3.00 dBi (4.55 dBi), respectively, on the human chest and arm. The stability in results shows that this flexible antenna is sufficiently robust against the variations introduced by the human body. A maximum measured shift of 0.5 and 100 MHz in the wide impedance matching and resonance frequency was observed in both bands, respectively, while an optimal gap between the antenna and human body was maintained. This stability of the working frequency provides robustness against various conditions including bending, movement, and relatively large fabrication tolerances.

Full Ground Ultra-Wideband Wearable Textile Antenna for Breast Cancer and Wireless Body Area Network Applications

Wireless body area network (WBAN) applications have broad utility in monitoring patient health and transmitting the data wirelessly. WBAN can greatly benefit from wearable antennas. Wearable antennas provide comfort and continuity of the monitoring of the patient. Therefore, they must be comfortable, flexible, and operate without excessive degradation near the body. Most wearable antennas use a truncated ground, which increases specific absorption rate (SAR) undesirably. A full ground ultra-wideband (UWB) antenna is proposed and utilized here to attain a broad bandwidth while keeping SAR in the acceptable range based on both 1 g and 10 g standards. It is designed on a denim substrate with a dielectric constant of 1.4 and thickness of 0.7 mm alongside the ShieldIt conductive textile. The antenna is fed using a ground coplanar waveguide (GCPW) through a substrate-integrated waveguide (SIW) transition. This transition creates a perfect match while reducing SAR. In addition, the proposed antenna has a bandwidth (BW) of 7–28 GHz, maximum directive gain of 10.5 dBi and maximum radiation efficiency of 96%, with small dimensions of 60 × 50 × 0.7 mm3. The good antenna’s performance while it is placed on the breast shows that it is a good candidate for both breast cancer imaging and WBAN.