Body-centric Wireless Systems Research Articles

Wearable Chipless Radio-Frequency Identification Tags for Biomedical Applications: A Review [Antenna Applications Corner

Wearable sensing technology and body-centric wireless systems have received widespread attention due to their tremendous prospective in e-health, the Internet of Things (IoT), and smart cities. Low-cost textile antennas for body-centric radio-frequency identification (RFID) sensing technology are the future for such wearable sensing systems. The antennas can sustain bending and stretching and offer a maintenance-free communication link with the human body, environment, and IoT infrastructure. Its sensing technology provides the seamless real-time wireless monitoring of important physiological signals. Understanding its significance in emerging applications, this article reviews wearable passive RFID tag sensors that monitor various physical parameters. The primary goal of these research works is to design RFID sensors and test their performances in various environmental conditions. Chip-based RFID sensors are too expensive for mass deployment, hence, chipless RFID tag sensors have become a low-cost and maintenance-free alternative, addressing market demands for the emerging IoT, where trillions of such sensors will be used. Observing the significance of the technology, a few important design parameters, such as tag radar cross section (RCS) and various form factors of tag antennas, are examined in this article. The article also presents some emerging applications of the developed sensors.

Mathematical Modeling of Ultra Wideband <italic>in Vivo</italic> Radio Channel

This paper proposes a novel mathematical model for an in vivo radio channel at ultra-wideband frequencies (3.1–10.6 GHz), which can be used as a reference model for in vivo channel response without performing intensive experiments or simulations. The statistics of error prediction between experimental and proposed model is RMSE = 5.29, which show the high accuracy of the proposed model. Also, the proposed model was applied to the blind data, and the statistics of error prediction is RMSE = 7.76, which also shows a reasonable accuracy of the model. This model will save the time and cost on simulations and experiments, and will help in designing an accurate link budget calculation for a future enhanced system for ultra-wideband body-centric wireless systems.

Subject-Specific Effect of Metallic Body Accessories on Path Loss of Dynamic on-Body Propagation Channels.

This paper presents the investigation of path loss variation for subject-specific on-body radio propagation channels, considering the effect of metallic spectacles and loop like metallic accessories. Adding metallic items may affect the operability of Body Centric Wireless Communications (BCWC). Measurements were carried out in an RF-shielded room lined with microwave absorbing sheets for strategically placed bodyworn antennas covering the upper front torso and the lower limbs. The path loss of the on-body radio channel was characterized explicitly taking into account the body size of the subjects. For metallic loop-like accessories, the results indicate that for underweight subjects, there was a slightly higher influence, up to 2%, compared to normal and overweight subjects. Our findings indicate that a noticeable effect exists on on-body channels for dynamic movements where the metallic watch acts as a local scatterer that affects the non-line-of-sight (NLOS) signal path between transmitter and receiver for underweight subjects in comparison to normal and overweight subjects. The path loss decreases when the receiving terminal was positioned very close to the metallic item. If a loop-like metallic accessory is not appropriately considered when designing the radio channel on a subject, the reliability of the body-centric wireless system may degrade.

Design of a textile ultra‐wideband antenna with stable performance for body‐centric wireless communications

The study proposes a flexible ultra-wideband (UWB) textile antenna for body-centric wireless system. The antenna consists of a circle-shaped radiator, a tapered microstrip-fed line and a ground plane with a rectangular slot. For body-centric applications, a cloth with 100% cotton is used as the substrate in the design of the antenna. To emulate the on-body condition, the antenna is studied when it is bent and crumpled, and when the feed line and ground plane are misaligned because of human body movement. The antenna is studied using computer simulation, and is also prototyped and measured for verification of simulation results. The feeding cable used in measurement affects the measured results, which is also studied. Simulated and measured results agree very well. Results show that the flexible UWB textile antenna has good performance in terms of bandwidth, realised gain, efficiency and radiation patterns, making it a good candidate for body-centric wireless communications.

A New Approach and Analysis of Modeling the Human Body in RFID-Enabled Body-Centric Wireless Systems

Body-centric wireless systems demand wearable sensor and tag antennas that have robust impedance matching and provide enough gain for a reliable wireless communication link. In this paper, we discuss a novel and practical technique for the modeling of the human body in UHF RFID body-centric wireless systems. What makes this technique different is that we base the human model on measured far-field response from a reference tag attached to the human body. Hereby, the human body model accounts for the encountered human body effects on the tag performance. The on-body measurements are fast, which allows establishing a catalog of human body models for different tag locations and human subjects. Such catalog would provide a ready simulation model for a wide range of wireless body-centric applications in order to initiate a functional design. Our results demonstrate that the suggested modeling technique can be used in the design and optimization of wearable antennas for different real-case body-centric scenarios.

Design and Implementation of Electro-Textile Ground Planes for Wearable UHF RFID Patch Tag Antennas

Localization, wireless monitoring, and emerging body-centric wireless systems demand low-cost and low-power devices that are efficient, maintenance-free, and comfortable to wear. Patch-type UHF radio frequency identification (RFID) tag antennas realized using electro-textiles are promising candidates for this purpose. In this letter, we design a patch-type tag antenna operating at 900 MHz and investigate how different types of ground planes using electro-textiles affect the antenna performance. Various conductive fabrics and embroidery structures are considered. We demonstrate that depending on the ground plane structure and density, it is possible to influence the tag impedance behavior and radiation characteristics. Furthermore, wireless reflectometry measurements are conducted to characterize the sheet resistance for the investigated electro-textiles. We then use the sheet resistance in modeling the conductive fabric ground planes in a full-wave electromagnetic solver. Our results contribute to deeper understanding of the complex electro-textiles structures and guidelines for future practical wearable antenna designs.