Statistics for Spatial Data.

Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

The introduction of intelligent textile systems to increase the wearer's level of protection has exposed the necessity of wearable communication tools and has led to research in textile antennas. However, most textile fabrics are quite thin (0.5 mm), making it challenging for antenna designers to provide an antenna which operates adequately and resiliently in the 2.4-2.4835-GHz industrial-scientific-medical bandwidth. Flexible pad foam is commonly available in protective clothing and overcomes these constraints by providing a uniform, stable, and sufficient thickness. Moreover, its cellular structure and properties, such as flame retardance and water repellence, make it an excellent substrate material for the integration of antennas into protective garments. In this paper, we describe the design, manufacture, and performance of the first textile planar antenna to be implemented on flexible protective foam, suitable for firefighter garments. We employed shock absorbing foam with a thickness of 3.94 mm and achieved a nearly circularly polarized antenna with a bandwidth of more than 180 MHz even when the antenna was compressed or bent. These outstanding substrate and antenna characteristics result in an antenna that is highly appropriate for garment integration.

A Textile Antenna for Off-Body Communication Integrated Into Protective Clothing for Firefighters

In the broad context of Wireless Body Sensor Networks for healthcare and pervasive applications, the design of wearable antennas offers the possibility of ubiquitous monitoring, communication and energy harvesting and storage. Specific requirements for wearable antennas are a planar structure and flexible construction materials. Several properties of the materials influence the behaviour of the antenna. For instance, the bandwidth and the efficiency of a planar microstrip antenna are mainly determined by the permittivity and the thickness of the substrate. The use of textiles in wearable antennas requires the characterization of their properties. Specific electrical conductive textiles are available on the market and have been successfully used. Ordinary textile fabrics have been used as substrates. However, little information can be found on the electromagnetic properties of regular textiles. Therefore this paper is mainly focused on the analysis of the dielectric properties of normal fabrics. In general, textiles present a very low dielectric constant that reduces the surface wave losses and increases the impedance bandwidth of the antenna. However, textile materials are constantly exchanging water molecules with the surroundings, which affects their electromagnetic properties. In addition, textile fabrics are porous, anisotropic and compressible materials whose thickness and density might change with low pressures. Therefore it is important to know how these characteristics influence the behaviour of the antenna in order to minimize unwanted effects. This paper presents a survey of the key points for the design and development of textile antennas, from the choice of the textile materials to the framing of the antenna. An analysis of the textile materials that have been used is also presented.

Textile materials for the design of wearable antennas: a survey.

Utilization of wearable textiles in the antenna segment has been seen on the rise due to the recent miniaturization of wireless devices. A wearable antenna is meant to be a part of the clothing used for communication purposes, which includes tracking and navigation, mobile computing and public safety. This literature review intend to disclose this unconventional antenna technology and provides readers with the background of the wearable antenna that would include about specification of the antenna, material for the antenna and analysis that must be done to design proper wearable antennas. All the designs presented are of the recent development in wearable technology.

A review of wearable antenna

A wearable multiband circularly polarized active antenna is presented for use in Global Positioning System and Iridium satellite phone applications. The square patch antenna is constructed using flexible foam and fabric substrates and conductors etched on thin copper-on-polyimide films. The feed substrate integrates a compact low-noise amplifier chip directly underneath the antenna patch. The antenna performance is studied under bending conditions and in the presence of a human body. The active antenna exhibits a gain higher than 25 dBi and a 3 dB axial ratio bandwidth exceeding 183 MHz in free-space conditions and is robust to bending and on-body placement.

/pdf/a-wearable-active-antenna-for-global-positioning-system-and-1yx26phdiq.pdf

A Wearable Active Antenna for Global Positioning System and Satellite Phone

For the first time, a personal distributed exposimeter (PDE) for radio frequency (RF) measurements is presented. This PDE is designed based on numerical simulations and is experimentally evaluated using textile antennas and wearable electronics. A prototype of the PDE is calibrated in an anechoic chamber. Compared to conventional exposimeters, which only measure in one position on the body, an excellent isotropy of 0.5 dB (a factor of 1.1) and a 95% confidence interval of 7 dB (a factor of 5) on power densities are measured. Bioelectromagnetics. 34:563–567. © 2013 Wiley Periodicals, Inc.

/pdf/personal-distributed-exposimeter-for-radio-frequency-bjidppug4m.pdf

Personal distributed exposimeter for radio frequency exposure assessment in real environments.

Wearable antennas are mostly constructed from fabric or foam, whereas e-textiles are often used as conductive parts A design obstacle is the lack of knowledge about the electromagnetic properties of these materials Moreover, most of these fabrics exhibit electromagnetic properties that depend on prevailing atmospheric conditions In this work, we present a dedicated characterization method to determine the complex permittivity of fabrics or foams, as well as the effective conductivity of e-textiles, and this as a function of relative humidity The method extracts the constitutive parameters by comparing measured and simulated antenna figures of merit such as input impedance and antenna efficiency This inverse problem is solved using a surrogate-based optimization technique as implemented in the Surrogate Modeling Toolbox, yielding a fast and accurate characterization The method is evaluated by characterizing six materials which are exposed to relative humidity levels ranging from 10% to 90% From the extracted complex permittivities of the six materials, two-phase dielectric mixing models based on the volumetric fractions of the absorbed moisture in the substrates are developed and evaluated in terms of accuracy For the materials exhibiting a high sensitivity to moisture, the model is observed to be less accurate However, the worst model accuracy is shown to be comparable with the estimated accuracy of the characterization procedure For materials with low sensitivity to moisture, the model fits the measured values very well

/pdf/environmental-high-frequency-characterization-of-fabrics-3np1d7o9pf.pdf

Environmental High Frequency Characterization of Fabrics Based on a Novel Surrogate Modelling Antenna Technique

The stability of wearable textile antennas after 20 reference washing cycles was evaluated by measuring the reflection coefficient of different antenna prototypes. The prototypes' conductive parts were screen-printed on several textile substrates using two different silver-based conductive inks. The necessity of coating the antennas with a thermoplastic polyurethane (TPU) coating was investigated by comparing coated with uncoated antennas. It is shown that covering the antennas with the TPU layer not only protects the screen-printed conductive area but also prevents delamination of the multilayered textile fabric substrates, making the antennas washable for up to 20 cycles. Furthermore, it is proven that coating is not necessary for maintaining antenna operation and this up to 20 washing cycles. However, connector detachment caused by friction during the washing process was the main problem of antenna performance degradation. Hence, other flexible, durable methods should be developed for establishing a stable electrical connection.

/pdf/performance-study-of-screen-printed-textile-antennas-after-4lw01u3e1c.pdf

Performance Study of Screen-Printed Textile Antennas after Repeated Washing

This paper presents the design and characterization of a compact wearable aperture-coupled shorted patch antenna combined with flexible solar cells covering the 902–928 MHz ISM band. The antenna is constructed solely out of flexible foam and textile materials. The parallel connected amorphous silicon (a:Si-H) solar cells are able to deliver a maximum DC power output of about 96 mW. Combining solar cells with a shorted patch antenna allows a simple realization of the DC output wire connections without disturbing the antenna's radiation characteristics. A measured on-body antenna gain and bandwidth of about 1.6 dBi and 63 MHz are realized, respectively.

https://biblio.ugent.be/publication/2015735/file/2015747.pdf

Frederick Declercq

Papers

A Wearable Active Antenna for Global Positioning System and Satellite Phone

Personal distributed exposimeter for radio frequency exposure assessment in real environments.

Environmental High Frequency Characterization of Fabrics Based on a Novel Surrogate Modelling Antenna Technique

Performance Study of Screen-Printed Textile Antennas after Repeated Washing

Wearable aperture-coupled shorted solar patch antenna for remote tracking and monitoring applications