Timothy F. Kennedy

Body-Worn E-Textile Antennas: The Good, the Low-Mass, and the Conformal

Support of ever increasing applications for wireless data and communications on a body-centric platform requires novel antenna systems that can be integrated with the body-worn environment, while maintaining free-range of movement and minimal mass impact. E-textile antennas show great promise due to their ease of integration with other textile materials, and they are inherently low-mass and flexible relative to conventional antenna materials. Much attention has been given recently to multiple-antenna communication systems due to the increased performance compared to conventional single-antenna systems. For body-centric applications, the low-mass, flexibility, and integration simplicity of e-textile antennas can enable multiple-antenna systems, which otherwise would be precluded by the rigidity and mass of conventional antenna materials. Several examples of this are considered here with e-textile antennas in an array environment. A conventional microstrip array constructed with e-textiles is shown to have robust performance with moderate amounts of bending, similar to that which might be seen with body-worn arrays. In addition to the conventional array, a wideband multiple-antenna system to support a variety of wireless communication protocols, while maintaining polarization diversity and excellent coverage over a majority of the radian sphere is demonstrated.

Detection, identification, location, and remote sensing using SAW RFID sensor tags

We consider the problem of simultaneous detection, identification, location estimation, and remote sensing for multiple objects in an environment. In particular, we describe the design and performance of a system capable of simultaneously detecting the presence of multiple objects, identifying each object, and acquiring both a low-resolution estimate of location and a high-resolution estimate of temperature for each object based on wireless interrogation of passive surface acoustic wave (SAW) radio-frequency identification (RFID) sensor tags affixed to each object. The system is being studied for application on the lunar surface as well as for terrestrial remote sensing applications such as pre-launch monitoring and testing of spacecraft on the launch pad and monitoring of test facilities. The system utilizes a digitally beam-formed planar receiving antenna array to extend range and provide direction-of-arrival information coupled with an approximate maximum-likelihood signal processing algorithm to provide near-optimal estimation of both range and temperature. We examine the theoretical performance characteristics of the system and compare the theoretical results with results obtained from controlled laboratory experiments.1,2

Modification and control of currents on monopole antennas using magnetic bead loading

Several methods to modify the currents on electrically long monopole antennas are investigated. The radiation pattern, input impedance, and resonant frequency are calculated for several configurations of monopoles loaded with magnetic materials, both as coatings and as small beads. Proper application of such loading is shown to cause the radiated fields and resonant frequency to mimic a shorter quarter-wave monopole.

Modification and control of currents on an electrically long monopole using magnetic bead loading

With the growing demand for wireless communication systems has come growing opposition to increasing the numbers of cellular towers. A possible alternative to simply trying to hide the antenna mounting structure is to use parts of the existing environment as the radiating element. The simplest parts of an existing structure with which to begin such a study are conducting wires that may be part of an existing structure; these wires are electrically long at the frequencies where wireless communications are employed. To turn these electrically long wires into radiating elements, methods for modifying and controlling the natural current distribution on the wires are needed. We have investigated the use of magnetic beads to load an electrically long monopole and alter its input impedance and radiation properties. The current distribution can be shaped to resemble that of a quarter wavelength monopole. To obtain the required result, however, a magnetic bead with a large relative permeability was used, which may not be available at current wireless communication frequencies. Using alternating sections of magnetic and dielectric beads, it was found that lower permeability materials could be used to make the electrically long antenna behave as though it were a smaller element.

Modification and Control of Currents on Electrically Large Wire Structures Using Composite Dielectric Bead Elements

Increasing the number of antennas for wireless communications, while concealing them within their environment, is an area of great importance as demand for wireless devices increases. One method to achieve this goal is to use the existing conducting objects in an environment as antennas. This requires altering the natural current distribution on conducting objects such that optimal radiation properties can be obtained. In this paper, a composite dielectric bead element is introduced for this purpose on electrically large wire structures. The operation of the bead element is described using transmission line theory, and a wire model of the element is given. Using the wire model, the loading for several electrically large wire structures is designed such that they resonate and radiate similarly to a half-wavelength dipole

Dielectric bead loading for control of currents on electrically long dipole antennas

Methods for the modification and control of currents on electrically long wires have been studied in order to determine the feasibility of using existing structures as efficient radiators. Such radiators would be formed from conducting surfaces present on buildings or other structures, thus providing an additional resource in concealing antennas used for wireless communication. An element composed of dielectric beads has been successfully used to modify the current distributions on electrically long wires, such that the wires radiate similarly to a much smaller element. A simple model of a composite element made up of dielectric beads is presented, and a genetic algorithm is used to design the loading of a 4/spl lambda//sub 0/ wire, such that the radiation pattern emulates that of a half-wave dipole. The simple model of the dielectric beads made it possible to run many simulations of the loaded wire using the GA. The ease with which dielectric bead loaded wires can be modeled suggests that the design of efficient radiators from existing, and more complicated, wire structures is possible.

Radiation pattern of an electrically long, sleeve choke-loaded monopole using magnetic and dielectric beads

The radiation pattern of a sleeve choke-loaded monopole can be modified to resemble a quarter-wavelength monopole with small radii chokes with the addition of magnetic and dielectric beads. An electrically long monopole loaded with a sleeve choke and magnetic and dielectric beads is given. Magnetic and dielectric beads are placed adjacent to the sleeve choke. The return loss and radiation pattern for this structure were computed using Ansofts finite element package, HFSS.

Characteristic modes for planar structure feed design

The frequency behavior of the first characteristic mode along a thin plate was presented. For this structure, the first mode retained the shape of its resonant current distribution below resonance but significant changes were seen above resonance. The rectangular planar monopole was analyzed, and tapering the monopole near the feed point was found to enhance the match with the feed. For each monopole width, a taper angle was identified to give the best match.

Modification and control of the radiation properties of electrically large conducting structures using dielectric loads

In this present work, control of currents on a more complicated planar structure, a model for a conducting window frame, will be introduced. The modification of the current distribution will be facilitated by the use of a type of dielectric loading, which can be adapted to other conducting structures. It will be shown that an electrically large window frame can be made to radiate similarly to a half-wavelength dipole by using dielectric loading