Antenna development for wearable wireless sensing systems

Embedded wireless sensor network (WSN) systems have been developed and used in a wide variety of applications such as local automatic environmental monitoring; medical applications analysing aspects of fitness and health energy metering and management in the built environment as well as traffic pattern analysis and control applications. While the purpose and functions of embedded wireless sensor networks have a myriad of applications and possibilities in the future, a particular implementation of these ambient sensors is in the area of wearable electronics incorporated into body area networks and everyday garments. Some of these systems will incorporate inertial sensing devices and other physical and physiological sensors with a particular focus on the application areas of athlete performance monitoring and e-health. Some of the important physical requirements for wearable antennas are that they are light-weight, small and robust and should also use materials that are compatible with a standard manufacturing process such as flexible polyimide or fr4 material where low cost consumer market oriented products are being produced. The substrate material is required to be low loss and flexible and often necessitates the use of thin dielectric and metallization layers. This paper describes the development of such a wearable, flexible antenna system for ISM band wearable wireless sensor networks. The material selected for the development of the wearable system in question is DE104i characterized by a dielectric constant of 3.8 and a loss tangent of 0.02. The antenna feed line is a 50 Ohm microstrip topology suitable for use with standard, high-performance and low-cost SMA-type RF connector technologies, widely used for these types of applications. The desired centre frequency is aimed at the 2.4GHz ISM band to be compatible with IEEE 802.15.4 Zigbee communication protocols and the Bluetooth standard which operate in this band.

The detuning effects of a wrist-worn antenna and design of a custom antenna measurement system

This paper investigates the effects of antenna detuning on wireless devices caused by the presence of the human body,particularly the wrist. To facilitate repeatable and consistent antenna impedance measurements, an accurate and low cost human phantom arm, that simulates human tissue at 433MHz frequencies, has been developed and characterized. An accurate and low cost hardware prototype system has been developed to measure antenna return loss at a frequency of 433MHz and the design, fabrication and measured results are presented. This system provides a flexible means of evaluating closed-loop reconfigurable antenna tuning circuits for use in wireless mote applications.

Antenna tuning for wearable wireless sensors

When miniaturized wireless sensors are placed on or close to the human body, they can experience a significant loss inperformance due to antenna detuning, resulting in degradationof wireless performance as well as decreased battery lifetime.Several antenna tuning technologies have been proposed formobile wireless devices but devices suitable for widespread integration have yet to emerge. This paper highlights the possible advantages of antenna tuning for wearable wireless sensors and presents the design and characterization of a prototype 433MHz tuner module.

A dual-band antenna enabling improved quality of service in multi-radio wireless sensor applications in indoor environments

Science Foundation Ireland (CSET - Centre for Science, Engineering and Technology, Grant No. 07/CE/11147)

Intrinsic measure of diversity gains in generalised distributed antenna systems with cooperative users

The diversity gains achievable in the generalised distributed antenna system with cooperative users (GDAS-CU) are considered. A GDAS-CU is comprised of M largely separated access points (APs) at one side of the link, and N geographically closed user terminals (UTs) at the other side. The UTs are collaborating together to enhance the system performance, where an idealised message sharing among the UTs is assumed. First, geometry-based network models are proposed to describe the topology of a GDAS-CU. The mean cross-correlation coefficients of signals received from non-collocated APs and UTs are calculated based on the network topology and the correlation models derived from the empirical data. The analysis is also extendable to more general scenarios where the APs are placed in a clustered form due to the constraints of street layout or building structure. Subsequently, a generalised signal attenuation model derived from several stochastic ray-tracing-based pathloss models is applied to describe the power-decaying pattern in urban built-up areas, where the GDAS-CU may be deployed. Armed with the cross-correlation and pathloss model preliminaries, an intrinsic measure of cooperative diversity obtainable from a GDAS-CU is then derived, which is the number of independent fading channels that can be averaged over to detect symbols. The proposed analytical framework would provide critical insight into the degree of possible performance improvement when combining multiple copies of the received signal in such systems.

Characterization of the chlorosome antenna of the filamentous anoxygenic phototrophic bacterium Chloronema sp strain UdG9001

The absorption and fluorescence properties of chlorosomes of the filamentous anoxygenic phototrophic bacterium Chloronema sp. strain UdG9001 were analyzed. The chlorosome antenna of Chloronema consists of bacteriochlorophyll (BChl) d and BChl c together with γ-carotene as the main carotenoid. HPLC analysis combined with APCI LC-MS/MS showed that the chlorosomal BChls comprise a highly diverse array of homologues that differ in both the degree of alkylation of the macrocycle at C-8 and/or C-12 and the alcohol moiety esterified to the propionic acid group at C-17. BChl c and BChl d from Chloronema were mainly esterified with geranylgeraniol (33% of the total), heptadecanol (24%), octadecenol (19%), octadecanol (14%), and hexadecenol (9%). Despite this pigment heterogeneity, fluorescence emission of the chlorosomes showed a single peak centered at 765 nm upon excitation at wavelengths ranging from 710 to 740 nm. This single emission, assigned to BChl c, indicates an energy transfer from BChl d to BChl c within the same chlorosome. Likewise, incubation of chlorosomes under reducing conditions caused a weak increase in fluorescence emission, which indicates a small redox-dependent fluorescence. Finally, protein analysis of Chloronema chlorosomes using SDS-PAGE and MALDI-TOF-MS revealed the presence of a chlorosomal polypeptide with a molecular mass of 5.7 kDa, resembling the CsmA protein found in Chloroflexus aurantiacus and Chlorobium tepidum chlorosomes. Several minor polypeptides were also detected but not identified. These results indicate that, compared with other members of filamentous anoxygenic phototrophic bacteria and green sulfur bacteria, Chloronema possesses an antenna system with novel features that may be of interest for further investigations.

Quadrifilar Loop Antenna

A new quadrifilar antenna has been developed for generating circularly polarized backfire radiation. The antenna consists of two orthogonal rectangular conducting loops, each incorporating capacitive coupling and fed using either a single or two coaxial cables. Though the geometry is much simpler than a conventional quadrifilar helix antenna, the radiation pattern performance is very similar. Measured and simulated patterns are compared for two antennas with different feed arrangements. It is shown that the resonant structure can produce a cardioid pattern with a directivity of 4.5 dB (120 3-dB beamwidth) and a front-to-back ratio of more than 20 dB at the center operating frequency. A 10% impedance bandwidth (VSWR

Quadratic Forms on Complex Random Matrices and Multiple-Antenna Systems

This research published in the foremost international journal in information theory and shows interplay between complex random matrix and multiantenna information theory. Dr T. Ratnarajah is leader in this area of research and his work has been contributed in the development of graduate curricula (course reader) in Massachusetts Institute of Technology (MIT), USA, By Professor Alan Edelman. The course name is "The Mathematics and Applications of Random Matrices", see http://web.mit.edu/18.338/www/projects.html

Liquid-crystal-based reflectarray antenna with electronically switchable monopulse patterns

A printed rcflectarray antenna, which generates a beam that can be electronically switched from a sum to a difference radiation pattern, is presented. This is achieved by applying a bias voltage of 20 V to one-half of the aperture, which is constructed above a 500 mu m cavity containing liquid crystals. Simulated results are shown to be in good agreement with measurements at X-band.

Dual-mode compact structure comprising of side-fed bifilar and quadrifilar helix antenna

A side-fed bifilar helix antenna can be integrated with a quadrifilar helix antenna in a piggy back configuration in order to achieve a dual-mode radiating structure. The overall length of the structure is 0.44 lambda at the resonant frequency (1.54 GHz) of the space mode antenna and 0.39 lambda at the resonant frequency (1.34 GHz) of the terrestrial mode antenna. The computed results are validated by experimental data.

Single feed low profile omnidirectional antenna with slant 45 degrees linear polarization

It is shown that a side-fed bifilar helix antenna with a single feed, can generate a slant 451 linearly polarized onmidirectional toroidal pattern. The antenna has a low profile and does not require a ground plane. The bifilar helix antenna provides slant 45 degrees polarization over a solid angle of almost 4 pi steradians as compared to a crossed dipole which generates a tilted 45 degrees linearly, polarized pattern only over a solid angle of 1.14 pi steradians. The computed results are validated by experimental data.

Effect of helix turn angle on the performance of a half wavelength quadrifilar antenna

The impedance and radiation pattern parameters of a lambda/2 quadrifilar helix antenna (QHA) with turn angles in the range 0 degrees to 235 degrees are analyzed. It is shown that by selecting the helix turn angle to satisfy the minimum bandwidth and beamwidth requirements, an improved electrical performance and a reduction in the physical size of the antenna is obtained. This is demonstrated by comparing the performance of a conventional half turn QHA with structures having a smaller pitch length. The computed results are validated by experimental data at L-band.

Side-fed bifilar helix antenna

A side-fed bifilar is shown to generate a similar radiation pattern as a dipole antenna, but the structure has a significantly reduced axial length. Simulated and measured results show that the helix turn angle can be used to control the ratio of the orthogonal linear field components and the input impedance.