IEEE Access Special Section Editorial: Wearable and Implantable Devices and Systems

© 2013 IEEE. Circuit techniques, sensors, antennas and communications systems are envisioned to help build new technologies over the next several years. Advances in the development and implementation of such technologies have already shown us their unique potential in realizing next-generation sensing systems. Applications include wearable consumer electronics, healthcare monitoring systems, and soft robotics, as well as wireless implants. There have been some interesting developments in the areas of circuits and systems, involving studies related to low-power electronics, wireless sensor networks, wearable circuit behaviour, security, real-time monitoring, connectivity of sensors, and Internet of Things (IoT). The direction for the current technology is electronics systems on large area electronics, integrated implantable systems and wearable sensors. So far, the research in the field has focused on materials, new processing techniques and one-off devices, such as diodes and transistors. However, current technology is not sufficient for future electronics to be useful in new applications; a great demand exists to scale up the research towards circuits and systems. Recent developments indicate that, in addition to fabrication technology, special attention should also be given to design, simulation and modeling of electronics, while keeping sensing system integration, power management, and sensors network under consideration

Ultrawideband Technology for Medical In-Body Sensor Networks: An Overview of the Human Body as a Propagation Medium, Phantoms, and Approaches for Propagation Analysis

[EN] An in-body sensor network is that in which at least one of the sensors is located inside the human body. Such wireless in-body sensors are used mainly in medical applications, collecting and monitoring important parameters for health and disease treatment. IEEE Standard 802.15.6-2012 for wireless body area networks (WBANs) considers in-body communications in the Medical Implant Communications Service (MICS) band. Nevertheless, high-data-rate communications are not feasible at the MICS band because of its narrow occupied bandwidth. In this framework, ultrawideband (UWB) systems have emerged as a potential solution for in-body highdata-rate communications because of their miniaturization capabilities and low power consumption.This work was supported by the Programa de Ayudas de Investigación y Desarrollo (PAID-01-16) at the Universitat Politècnica de València, Spain; by the Ministerio de Economía y Competitividad, Spain (TEC2014-60258-C2-1-R); and by the European FEDER funds. It was also funded by the European Union’s H2020:MSCA:ITN program for the Wireless In-Body Environ-ment Communication–WiBEC project under grant 675353.Garcia-Pardo, C.; Andreu-Estellés, C.; Fornés Leal, A.; Castelló-Palacios, S.; Pérez-Simbor, S.; Barbi, M.; Vallés Lluch, A.... (2018). Ultrawideband Technology for Medical In-Body Sensor Networks: An Overview of the Human Body as a Propagation Medium, Phantoms, and Approaches for Propagation Analysis. IEEE Antennas and Propagation Magazine. 60(3):19-33. https://doi.org/10.1109/MAP.2018.2818458S193360

Biometric behavior authentication exploiting propagation characteristics of wireless channel

Massive expansion of wireless body area networks (WBANs) in the field of health monitoring applications has given rise to the generation of huge amount of biomedical data. Ensuring privacy and security of this very personal data serves as a major hurdle in the development of these systems. An effective and energy friendly authentication algorithm is, therefore, a necessary requirement for current WBANs. Conventional authentication algorithms are often implemented on higher levels of the Open System Interconnection model and require advanced software or major hardware upgradation. This paper investigates the implementation of a physical layer security algorithm as an alternative. The algorithm is based on the behavior fingerprint developed using the wireless channel characteristics. The usability of the algorithm is established through experimental results, which show that this authentication method is not only effective, but also very suitable for the energy-, resource-, and interface-limited WBAN medical applications

Implantable slot antenna with substrate integrated waveguide for biomedical applications

This work presents a new design of capsule slot antenna with substrate integrated waveguide (SIW) for wireless body area networks (WBANs) operating at the range of (2.5-4 GHz) which is located in the body area networks (BAN) standard in IEEE802.15.6. The proposed antenna was designed for WBANs. The substrate is assumed to be from Rogers 5880 with relative permittivity of 2.2, and thickness of 0.787 mm. The ground and the patch are created from annealed copper while the capsule is assumed to be a plastic material of medical grade polycarbonate. The antenna designed and summited using computer simulation technology (CST) software. A CST voxel model was used to study the performance of SIW capsule antenna and the ability of the band (2.5-4 GHz). Results indicated a wide bandwidth of 1.5 GHz between the range of (2.5-4) GHz at 3.3 GHz as center frequency, with return loss with more than -24.52 dB, a gain of -18.2 dB, voltage standing wave ratio (VSWR) of 1.17, and front-to-back ratio (FBR) of 10.07 dB. Through simulation, all considerable parameters associated with the proposed antenna including return loss, bandwidth, operating frequency, VSWR less than 2, radiation pattern were examined. Regarding size, gain, and frequency band, the proposed antenna is located with the standards of implantable medical devices (IMDs)

Microwave Devices for Wearable Sensors and IoT

The Internet of Things (IoT) paradigm is currently highly demanded in multiple scenarios and in particular plays an important role in solving medical-related challenges. RF and microwave technologies, coupled with wireless energy transfer, are interesting candidates because of their inherent contactless spectrometric capabilities and for the wireless transmission of sensing data. This article reviews some recent achievements in the field of wearable sensors, highlighting the benefits that these solutions introduce in operative contexts, such as indoor localization and microwave sensing. Wireless power transfer is an essential requirement to be fulfilled to allow these sensors to be not only wearable but also compact and lightweight while avoiding bulky batteries. Flexible materials and 3D printing polymers, as well as daily garments, are widely exploited within the presented solutions, allowing comfort and wearability without renouncing the robustness and reliability of the built-in wearable sensor

UWB Channel Characterization for Compact L-Shape Configurations for Body-Centric Positioning Applications

This paper presents an analysis on the body-centric channel parameters classification for various compact 3 base station L-Shape configurations utilizing only a 2D-plane for installation. Four different L-Shape configurations (x-z/y-z plane) are studied (facing-front/side/back) by varying the position of the base stations in an indoor environment. Results and analyses highlight the variation of the channel parameters with respect to the orientation of the base station configurations and presence of the human subject. Channel parameters values (peak power delay profile (PDP)/rms delay spread sigma/Kurtosis) are reported for (line of sight (LOS): -65 to -50 dB/0.5-5 nsec/40-60) and (non-line of sight (NLOS): -80 to -65 dB/ 10-25 nsec/ 5-25). The 3D localisation accuracy obtained is highest (1-3 cm) for the x-z plane L-Shape configuration facing-front which has maximum number of LOS links (70%).The accuracy decreases by 1-2 cm for the x-z plane L-Shape configuration facing-back due to increase in NLOS links (70%) between the wearable antennas and the base stations

Flexible skin-contact antenna with artifical magnetic conductor for health monitoring application

Flexible antenna plays a significant role to ensure efficient wireless communication in wearable devices. The choice of the dielectric substrate material of the antenna is one of the important factors to ensure good antenna performance while being tolerant to mechanical deformation. In addition, the size of the antenna becomes the main issue in designing the antenna for on-body applications. Furthermore, the radiation and transmissions performance of the on-body antenna suffers from performance degradation due to several factors such as dielectric properties of the human body as well as line of sight (LOS) and non line of sight (NLOS) transmission conditions. Therefore, this study presents a flexible Skin-Contact Antenna with Artificial Magnetic Conductor surface (SCA-AMC) made from medical-friendly material. Initially, three different types of medical materials which include transdermal cotton patch, semi-transparent film, and self-adhesive bandage were proposed for investigation as the antenna’s dielectric substrate. The dielectric properties of the proposed materials were measured prior to the antenna design. For preliminary design investigation, a conventional bowtie antenna was designed using the proposed medical materials and optimized to operate at frequency of 2.4 GHz. To achieve the objectives, the feasibility of medical material usage for the antenna’s substrate was explored based on wetness and repeatability test. The proposed SCA is intended for on-body wireless communication devices where there is a significant limitation on the overall size of the antenna. In order to develop a compact flexible antenna, a meandering technique is applied to the conventional bowtie antenna. By employing the meandering technique, the total length of the antenna can be reduced by 20 %. As the body protection against electromagnetic absorption is important, a dipole-like AMC structure was designed at frequency of 2.4 GHz and integrated with the meandered bowtie antenna. The proposed SCA-AMC is made of flexible material for the substrate and conducting parts, making it suitable for wearable applications. Furthermore, the factors that influence the antenna’s radiation and transmission performance have been determined. The experiments have been carried out considering various conditions such as body movements and the presence of either human body or obstacle in between the SCAAMC transmitter and the receiver. The results indicate that the human body introduces an additional 20 dBm power loss when present between the transmitter and receiver. Also, the presence o f the book causes 6 dBm reduction in received power while sweatshirts and cotton polo shirts contribute to a small variation of approximately from 0.5 to 1 dBm. Besides, wetness measurements were also carried out using tap water and sweat-like solution. The sweat-like solution had been developed using a mixture of sodium chloride, sodium bicarbonate, and water. The material characterization of the developed sweat-like solution was then performed. The developed sweat-like solution has a measured permittivity and loss tangent of 75.8 and 0.13, respectively at the frequency of 2.4 GHz. The proposed SCA-AMC was also tested in a real-life situation by merging it with an electrocardiogram (ECG) sensor node. The results obtained show that the wireless ECG pattern is comparable to the ECG pattern measured using a conventional ECG machine. The findings in this research have profound implications for future studies to develop an efficient wireless device, especially for on-body applications

ENG and NZRI Characteristics of Decagonal- Shaped Metamaterial for Wearable Applications

A decagonal-shaped split ring resonator metamaterial based on a wearable or textile-based material is presented in this work. Analysis and comparison of various structure sizes are compared considering a compact 6×6 mm2 metamaterial unit cell, in particular, where robust transmission-reflection (RTR) and Nicolson-Ross-Weir (NRW) methods have been performed to extract the effective metamaterial parameters. An investigation based on the RTR method indicated an average bandwidth of 1.39 GHz with a near-zero refractive index (NZRI) and a 2.35 GHz bandwidth when considering epsilon negative (ENG) characteristics. On the other hand, for the NRW method, approximately 0.95 GHz of NZRI bandwidth and 2.46 GHz of ENG bandwidth have been observed, respectively. These results are also within the ultra-wideband (UWB) frequency range, suggesting that the proposed unit cell structure is suitable for textile UWB antennas, biomedical sensors, related wearable systems, and other wireless body area network communication systems