A personal, distributed exposimeter: procedure for design, calibration, validation, and application

This paper describes, for the first time, the procedure for the full design, calibration, uncertainty analysis, and practical application of a personal, distributed exposimeter (PDE) for the detection of personal exposure in the Global System for Mobile Communications (GSM) downlink (DL) band around 900 MHz (GSM 900 DL). The PDE is a sensor that consists of several body-worn antennas. The on-body location of these antennas is investigated using numerical simulations and calibration measurements in an anechoic chamber. The calibration measurements and the simulations result in a design (or on-body setup) of the PDE. This is used for validation measurements and indoor radio frequency (RF) exposure measurements in Ghent, Belgium. The main achievements of this paper are: first, the demonstration, using both measurements and simulations, that a PDE consisting of multiple on-body textile antennas will have a lower measurement uncertainty for personal RF exposure than existing on-body sensors; second, a validation of the PDE, which proves that the device correctly estimates the incident power densities; and third, a demonstration of the usability of the PDE for real exposure assessment measurements. To this aim, the validated PDE is used for indoor measurements in a residential building in Ghent, Belgium, which yield an average incident power density of 0.018 mW/m(2)

In situ characterization of two wireless transmission schemes for ingestible capsules

We report the experimental in situ characterization of 30-40 MHz and 868 MHz wireless transmission schemes for ingestible capsules, in porcine carcasses. This includes a detailed study of the performance of a magnetically coupled near-field very high-frequency (VHF) transmission scheme that requires only one eighth of the volume and one quarter of the power consumption of existing 868-MHz solutions. Our in situ measurements tested the performance of four different capsules specially constructed for this study (two variants of each transmission scheme), in two scenarios. One mimicked the performance of a body-worn receiving coil, while the other allowed the characterization of the direction-dependent signal attenuation due to losses in the surrounding tissue. We found that the magnetically coupled near-field VHF telemetry scheme presents an attractive option for future, miniturized ingestible capsules for medical applications

Wearable flexible lightweight modular RFID tag with integrated energy harvester

A novel wearable radio frequency identification (RFID) tag with sensing, processing, and decision-taking capability is presented for operation in the 2.45-GHz RFID superhigh frequency (SHF) band. The tag is powered by an integrated light harvester, with a flexible battery serving as an energy buffer. The proposed active tag features excellent wearability, very high read range, enhanced functionality, flexible interfacing with diverse low-power sensors, and extended system autonomy through an innovative holistic microwave system design paradigm that takes antenna design into consideration from the very early stages. Specifically, a dedicated textile shorted circular patch antenna with monopolar radiation pattern is designed and optimized for highly efficient and stable operation within the frequency band of operation. In this process, the textile antenna's functionality is augmented by reusing its surface as an integration platform for light-energy-harvesting, sensing, processing, and transceiver hardware, without sacrificing antenna performance or the wearer's comfort. The RFID tag is validated by measuring its stand-alone and on-body characteristics in free-space conditions. Moreover, measurements in a real-world scenario demonstrate an indoor read range up to 23 m in nonline-of-sight indoor propagation conditions, enabling interrogation by a reader situated in another room. In addition, the RFID platform only consumes 168.3 mu W, when sensing and processing are performed every 60 s

Wearable Antennas Backed by Artificial Magnetic Conductor for Enhanced Gain and Reduced Back Radiation

A Wireless Body Area Network (WBAN) is a system of wireless sensors and devices attached to a person’s body for continuous monitoring of physiological data. These measurements can be used for a variety of purposes such as fitness tracking, personal health management or as medical diagnostic tools. In many cases, WBANs need to communicate with an off-body device to send information to healthcare providers. Wireless Medical Telemetry provides numerous benefits but has a few challenges that need to be overcome. One of the key components in this system is the antenna, which is worn on the body and typically has a broadside pattern directed out. Additionally, flexibility and miniaturization of antennas is crucial for making a comfortable and wearable antenna. Finally, the back radiation must be minimal since the dielectric properties of the human body can significantly affect the return loss, which in turn reduces the gain and distorts the radiation pattern. The motivation of the present work is based on the need for improving the antenna, for its size, enhanced gain, with small to no back lobe and additionally on a flexible substrate to ensure patient comfort. In the present work, two antennas, a Slotted Dipole Antenna and Inverted-F Antenna have been designed at 2.5 GHz in the Unlicensed Industrial, Scientific and Medical band (ISM). The design and modeling have been done using ANSYS HFSS (High Frequency System Simulator). A Rectangular Patch Artificial Magnetic Conductor (AMC) which is a frequency selective surface has been designed and optimized. Both antennas are backed by this AMC layer to reduce backward radiation and enhance forward gain for off body radiation. The antennas were fabricated and validated by measurement. Both are on Rogers RT/duroid 5880 substrate (εr = 2.2, tan δ = 0.0009 and dielectric height h = 31mils). The Inverted-F Antenna is significantly smaller than the Slotted Dipole Antenna but has a much lower radiation gain on its own. When the antennas are integrated with the Rectangular Patch AMC their forward gains are very similar. However, the Inverted-F Antenna and AMC has a much larger front to back ratio than the Slotted Dipole Antenna and AMC. The Slotted Dipole Antenna is shown to be flexible, both concave and convex curvature are simulated. In HFSS, the effects of the human body are simulated using the Human Body Model. A SAR analysis is also performed to show the AMC layer not only directs the beam in the desired direction but reduces the amount of power absorbed by the human body significantly. The measured return loss and radiation patterns agree well with simulated results. Lastly, this work proposes an AMC unit cell that is significantly smaller than the Rectangular Patch unit cell, which has the potential to create a smaller AMC layer

Antenna and radio channel characterisation for low‐power personal and body area networks

PhDThe continuous miniaturisation of sensors, as well as the progression in wearable electronics, embedded software, digital signal processing and biomedical technologies, have led to new usercentric networks, where devices can be carried in the user’s pockets, attached to the user’s body. Body-centric wireless communications (BCWCs) is a central point in the development of fourth generation mobile communications. Body-centric wireless networks take their place within the personal area networks, body area networks and sensor networks which are all emerging technologies that have a wide range of applications (such as, healthcare, entertainment, surveillance, emergency, sports and military). The major difference between BCWC and conventional wireless systems is the radio channels over which the communication takes place. The human body is a hostile environment from a radio propagation perspective and it is therefore important to understand and characterise the effects of the human body on the antenna elements, the radio channel parameters and, hence, system performance. This thesis focuses on the study of body-worn antennas and on-body radio propagation channels. The performance parameters of five different narrowband (2.45 GHz) and four UWB (3.1- 10.6 GHz) body-worn antennas in the presence of human body are investigated and compared. This was performed through a combination of numerical simulations and measurement campaigns. Parametric studies and statistical analysis, addressing the human body effects on the performance parameters of different types of narrowband and UWB antennas have been presented. The aim of this study is to understand the human body effects on the antenna parameters and specify the suitable antenna in BCWCs at both 2.45 GHz and UWB frequencies. Extensive experimental investigations are carried out to study the effects of various antenna types on the on-body radio propagation channels as well. Results and analysis emphasize the best body-worn antenna for reliable and power-efficient on-body communications. Based on the results and analysis, a novel dual-band and dual-mode antenna is proposed for power-efficient and reliable on-body and off-body communications. The on-body performance of the DBDM antenna at 2.45 GHz is compared with other five narrowband antennas. Based on the results and analysis of six narrowband and four UWB antennas, antenna specifications and design guidelines are provided that will help in selecting the best body-worn antenna for both narrowband and UWB systems to be applied in body-centric wireless networks (BCWNs). A comparison between IV the narrowband and UWB antenna parameters are also provided. At the end of the thesis, the subject-specificity of the on-body radio propagation channel at 2.45 GHz and 3-10 GHz was experimentally investigated by considering eight real human test subjects of different shapes, heights and sizes. The subject-specificity of the on-body radio propagation channels was compared between the narrowband and UWB systems as well

A Low Profile Antenna for Millimeter-Wave Body-Centric Applications

Millimeter-Wave (mm-Wave) frequencies are a front runner contender for the next generation body-centric wireless communications. In this paper, the design of a very low-profile antenna is presented for body-centric applications operating in the mm-Wave frequency band centered at 60 GHz. The antenna has an overall size of 14 × 10.5 × 1.15 mm 3 and is printed on a flexible printed circuit board. The performance of the antenna is evaluated in off-body, on-body, and bodyto-body communication scenarios using a realistic numerical phantom and verified through measurements. The antenna has a bandwidth of 9.8 GHz and offers a gain of 10.6 dBi in off-body (free space) configuration, while 12.1 dBi in on-body configuration. It also achieves an efficiency of 74% in off-body and 63% in on-body scenario. The small and flexible structure of the antenna along with excellent impedance matching, broad bandwidth, high gain, and good efficiency makes it a suitable candidate to attain simultaneous data transmission/reception at mm-Wave frequencies for the 5G body-centric applications

A novel manufacturing process for compact, low-weight and flexible ultra-wideband cavity backed textile antennas

A novel manufacturing procedure for the fabrication of ultra-wideband cavity-backed substrate integrated waveguide antennas on textile substrates is proposed. The antenna cavity is constructed using a single laser-cut electrotextile patch, which is folded around the substrate. Electrotextile slabs protruding from the laser-cut patch are then vertically folded and glued to form the antenna cavity instead of rigid metal tubelets to implement the vertical cavity walls. This approach drastically improves mechanical flexibility, decreases the antenna weight to slightly more than 1 g and significantly reduces alignment errors. As a proof of concept, a cavity-backed substrate integrated waveguide antenna is designed and realized for ultra-wideband operation in the [5.15-5.85] GHz band. Antenna performance is validated in free space as well as in two on body measurement scenarios. Furthermore, the antenna's figures of merit are characterized when the prototype is bent at different curvature radii, as commonly encountered during deployment on the human body. Also the effect of humidity content on antenna performance is studied. In all scenarios, the realized antenna covers the entire operating frequency band, meanwhile retaining a stable radiation pattern with a broadside gain above 5 dBi, and a radiation efficiency of at least 70%