Body-centric wireless communications: wearable antennas, channel modelling, and near-field antenna measurements

This thesis provides novel contribution to the field of body-centric wireless communications (BCWC) with the development of a measurement methodology for wearable antenna characterisation on the human body, the implementation of fully-textile wearable antennas and the on-body channel modelling considering different antenna types and user's dynamic effects. More specifically, a measurement methodology is developed for characterising wearable antennas on different locations of the human body. A cylindrical near-field (CNF) technique is employed, which facilitates wearable antenna measurements on a full-body solid anthropomorphic mannequin (SAM) phantom. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding radiation efficiency, which is an important parameter for optimising wearable system design. It appears as a cost- effective and easy to implement solution that does not require expensive positioning systems to rotate the phantom, in contrast to conventional roll-over-azimuth far-field systems. Furthermore, a flexible fully-textile wearable antenna is designed, fabricated and measured at 2.4 GHz that can be easily integrated in smart clothing. It supports surface wave propagation and exhibits an omni-directional radiation pattern that makes it suitable for on-body communications. It is based on a multilayer low-profile higher-mode patch antenna (HMMPA) design with embroidered shorting vias. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that play an important role in generating the optimal mode for on-body radiation. The radiation pattern shape of the proposed fully-textile antenna was found to be similar to a copper rigid antenna, exhibiting a high on-body radiation efficiency of 50 %. The potential of the embroidery technique for creating wearable antennas is also demonstrated with the fabrication of a circularly polarised spiral antenna that achieves a broadband performance from 0.9-3 GHz, which is suitable for off-body communications. By testing the textile spiral antenna on the SAM phantom, the antenna-body interaction is examined in a wide frequency range. Finally, a statistical characterisation of on-body communication channels is undertaken both with EM simulations and channel measurements including user's dynamic movement (walking and running). By using antenna types of different polarisation, the on-body channels are examined for different propagation conditions. Four on-body channels are examined with the one part fixed on the waist of the human body while the other part located on the chest, back, wrist and foot. Channel path gain is derived, while large-scale and small-scale fading are modelled by best-fit statistical distributions

NAFTA: Past, Present and Future

The North American Free Trade Agreement (NAFTA) – an extension of the Free Trade Agreement (FTA) between Canada and USA to include Mexico – went into effect on January 1, 1994, primarily as an agreement to eliminate restrictions on trade and investment over the course of twelve years. NAFTA is a trade agreement and after twelve years remains as such with limited prospects, if any, of widening or deepening the integration process. Despite its narrow scope, the agreement became, from the start, controversial – and continues to be so – not only for trade and investment matters but for a whole host of other related issues. The other related issues include: the dispute settlement mechanism and side agreements on labor and environmental issues

The future of the US Dollar and its competition with the Euro

Since the collapse of the Bretton Woods Global International System in 1971, the world economy has experienced significant currency volatility. The major economies of the world have addressed such volatility differently. The EU has chosen to follow a monetary union and introduced successfully a new currency. The U.S. has paid less attention to the fluctuations of the dollar and has pursued an independent monetary policy to promote national economic stability. Japan has seen its currency appreciate significantly. This paper argues that while trade and growth across the globe are doing well, financial developments are intensifying the competition between the U.S. dollar and the euro. Three possible future scenarios are developed and discussed.peer-reviewe

Asymmetrical economic and institutional changes in the Western Balkans : cooperation with the European Union

The Western Balkans have historically been a poor area of Europe. The total population of the Western Balkans is 24.7 million. Ethnic differences of long standing have led to conflicts and to political and economic instability. Poverty and instability have combined to produce a vicious circle of institutional backwardness. Recent conflicts in Croatia, Bosnia-Herzegovina and Kosovo have aggravated an already adverse economic situation. GDP in 1999 was substantially lower than that in 1989. The EU plans to enter into contractual relationships with all the Western Balkans in the form of Stabilization and Association Agreements (SAAs). The pacts are aimed at helping to establish economic and political stability, to implement institutional reforms, to practice regional free trade and cooperation and to privatize the economies of Western Balkans. These are also the presumed goals of the Western Balkans. This study focuses on a review of the progress made by the Western Balkans toward meeting the above stated challenges. A main conclusion is that the attainment of these goals has been asymmetrical for economic, political and institutional reasons.peer-reviewe

Broad-band embroidered spiral antenna for off-body communications

An embroidered wearable spiral antenna is presented in this study. The spiral antenna is compact and flexible, yet has broad-band performance. The novelty of this study includes considering the antenna–body interaction rather than just considering the antenna alone. The antenna has been simulated and measured on a specific anthropomorphic mannequin torso phantom and a real person. The far-field on-body performance of the embroidered antenna on the phantom has been measured using a novel cylindrical near-field to far-field transformation technique. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding far-field antenna characteristics on the human body without the need of rotating the phantom with expensive positioning systems. The on-body antenna performance including realised gain, directivity, radiation efficiency, radiation pattern and axial ratio have been presented

Notes on Profile Inversion and Closed Form Formulation of Compact GRIN Lenses

This note is an addendum to the paper Profile Inversion and Closed Form Formulation of Compact GRIN Lenses [1] and summarizes a few comments obtained after publication of [1]

Design, realisation and evaluation of a liquid hollow torso phantom appropriate for wearable antenna assessment

This paper examines the design, realization and evaluation of a lightweight and low cost hollow oval cross-section torso phantom appropriate for wearable antenna performance assessment. The phantom consists of an empty inner space (hollow) surrounded by a shell with double plastic walls between which there is a tissue simulating liquid. The phantom’s plastic shell is made of a low loss cast acrylic and the liquid is a commercially available one with properties calibrated for the frequency range of 2 - 6 GHz. The proposed phantom is compared, through simulations, with a full liquid torso phantom and a heterogeneous anthropomorphic voxel phantom. Additionally, the fabricated phantom is compared with human bodies and a homogeneous anthropomorphic solid phantom, through measurements. The phantom performance is tested in terms of electric field distribution of a wearable antenna on its surface and the path loss between two wearable antennas, on either side of the phantom. It is proved that the hollow phantom performance approximates the full liquid phantom when an RF absorbing material is placed in the central hollow region. The phantom performance in terms of S11 wearable antenna measurements is evaluated and found in good agreement with real human bodies in the examined frequency range (2 - 6 GHz). The far field wearable antenna performance of the proposed phantom shows deviation in gain less than 1.5 dB, compared with anthropomorphic phantom

On-body measurements of embroidered spiral antenna

This paper presents a compact and flexible embroidered spiral antenna that can be used for wearable applications. The antenna is embroidered by using a state of the art digital embroidery machine with multi-strand conducting thread Liberator™. The antenna has been measured on a Specific Anthropomorphic Mannequin (SAM) phantom and a real human. The measurement results show that the SAM phantom emulates the dielectric properties of the human body in a wide frequency band from 0.3 to 3 GHz. The far-field on-body performance of the antenna has been measured by placing the antenna on the SAM phantom in a tapered Anechoic Chamber. Near-field to far-field transformations have been used to produce the far-field performance including radiation pattern, directivity, realised gain and radiation efficiency

Higher‐mode textile patch antenna with embroidered vias for on‐body communication

This paper is a preprint of a paper accepted by IET Microwaves, Antennas and Propagation, and is subject to Institution of Engineering and Technology Copyright. When the final version is published, the copy of record will be available at IET Digital Library.This study presents a wearable textile higher-mode microstrip patch antenna (HMMPA) that has been designed to radiate omni-directionally at 2.4 GHz Industrial Scientific and Medical (ISM) band. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that plays an important role in generating the optimal mode for on-body radiation. The embroidery technique enabled a side-fed low-profile antenna which could be placed directly against the body. The proposed textile HMMPA antenna performance is compared with a probe-fed HMMPA antenna fabricated with rigid copper radiating parts, for both free space and on-body conditions. The on-body antenna performance has been tested by performing near-field measurements of the antenna on a full-body specific anthropomorphic mannequin phantom in an anechoic chamber. Results show that the proposed textile HMMPA antenna with vias made from conductive thread can radiate on-body with good efficiency while minimising the radiation in the broadside direction

Design, realisation and evaluation of a liquid hollow torso phantom appropriate for wearable antenna assessment

This paper is a postprint of a paper submitted to and accepted for publication in IET Microwaves, Antennas & Propagation and is subject to Institution of Engineering and Technology Copyright. The copy of record will be available at the IET Digital Library.This paper examines the design, realization and evaluation of a lightweight and low cost hollow oval cross-section torso phantom appropriate for wearable antenna performance assessment. The phantom consists of an empty inner space (hollow) surrounded by a shell with double plastic walls between which there is a tissue simulating liquid. The phantom’s plastic shell is made of a low loss cast acrylic and the liquid is a commercially available one with properties calibrated for the frequency range of 2 - 6 GHz. The proposed phantom is compared, through simulations, with a full liquid torso phantom and a heterogeneous anthropomorphic voxel phantom. Additionally, the fabricated phantom is compared with human bodies and a homogeneous anthropomorphic solid phantom, through measurements. The phantom performance is tested in terms of electric field distribution of a wearable antenna on its surface and the path loss between two wearable antennas, on either side of the phantom. It is proved that the hollow phantom performance approximates the full liquid phantom when an RF absorbing material is placed in the central hollow region. The phantom performance in terms of S11 wearable antenna measurements is evaluated and found in good agreement with real human bodies in the examined frequency range (2 - 6 GHz). The far field wearable antenna performance of the proposed phantom shows deviation in gain less than 1.5 dB, compared with anthropomorphic phantom