Christopher C. Davis

An underwater portable radio antenna operating in the 50 MHz band and efficient for launching surface electromagnetic waves at the seawater/air interface is presented. The antenna operation is based on the field enhancement at the antenna tip and on an impedance matching antenna enclosure, which is filled with de-ionized water. This enclosure allows us to reduce antenna dimensions and improve the coupling of electromagnetic energy to the surrounding salt water medium. Since surface wave propagation length far exceeds the skin depth of conventional radio waves at the same frequency, this technique is useful for broadband underwater wireless communication over several meters distances.

We present the design and performance of an extremely sensitive coherent remote vibration detection system using optical heterodyne vibration of phase shifts produced by laser light scattered off a remote target. The resulting phase-modulated intermediate RF of 200 MHz, which carries the vibrational motion of the target, is demodulated down to baseband using an RF in-phase and quadrature demodulator. Acquisition and calculation of the target phase angle is carried out on a custom-made control board which utilizes high-resolution A/D converters, variable gain amplifiers, and a Spartan-6 field programmable gate array.

Sensor networks that use line-of-sight (LOS) laser links can provide spatially efficient and physically secure connectivity. These features are advantageous for low-power communication networks over short distances in environments where LOS is available and where radio-frequency connectivity must be avoided because of interference, low data rates, or security problems. In order for optical wireless (OW) directional networks to provide viable short-range connectivity, the networks must provide signal coverage over an acceptable field of view and operate with efficient media access protocols to minimize random access times for the independent transmitting nodes within the network. In this paper, we present the performance of a directional media access control protocol applied to a uniquely designed OW sensor network. The protocol was implemented using vertical cavity surface-emitting lasers and microcontrollers. The results are discussed with respect to efficiency of operation and optimized performance.

Based on analogues from physical systems and science, we have investigated, developed, and evaluated prediction and control strategies for assured operation in high data rate, mobile wireless networks. The dynamic wireless networks, and their optimization, were analyzed by methods used in molecular dynamics. A significant outcome of this research is an application for a patent as follows: Systems, Methods, Devices, and Computer Program Products for Control and Performance Prediction in Wireless Networks. We considered wired as well as wireless networks, and we addressed the fundamental problems of how information should be fused over a network. In addition, we studied the performance and tradeoffs of integration of cooperative communication with network coding for assurance of information transfer.

Optical metamaterials are an exciting new field in optical science. A rapidly developing class of these metamaterials are those that allow the manipulation of volume and surface electromagnetic waves in desirable ways by suitably structuring the surfaces they interact with. They have applications in a variety of fields, such as materials science, photovoltaic technology, imaging and lensing, beam shaping and lasing. Describing techniques and applications, this book is ideal for researchers and professionals working in metamaterials and plasmonics, as well as those just entering this exciting new field. It surveys different types of structured surfaces, their design and fabrication, their unusual optical properties, recent experimental observations and their applications. Each chapter is written by an expert in that area, giving the reader an up-to-date overview of the subject. Both the experimental and theoretical aspects of each topic are presented.

This paper describes the results of an international intercomparison of specific absorption rate (SAR) measurements made with actual wireless telephones, following a similar program involving standard dipole antennas and flat phantoms. This study involved 17 laboratories in 11 different countries. All the participating laboratories supplied their data to the University of Maryland. The test of the reliability of dosimetric assessments involved an intercomparison of SAR measurements made in a head phantom filled with simulant fluid. These measurements are made using small electric field probes placed in the head phantoms. Two different wireless phones, a Motorola Model V290 and a Nokia Model 6310, were circulated to each participating laboratory, which provided its own electric field probes, head phantom, base station emulator to activate the phones, scanning system, and a simulant fluid prepared to a required prescription. The measurement technique to be followed was guided by the specifications given in the IEEE 1528 Compliance standard. At the conclusion of each laboratory's measurements, its results were communicated to the coordinators including 1 and 10 g maximum SARs for each phone at both 900 and 1800 MHz, and for the left and right cheeks, and left and right tilt positions relative to the phantom.

Metamaterials provide unprecedented freedom and flexibility in the creation of new structures, which control electromagnetic wave propagation in very unusual ways. Very recently various theoretical designs for an electromagnetic cloak were suggested and an experimental realization of a partial cloak operating in a two-dimensional cylindrical geometry were reported in the microwave frequency range. We report on an experimental two-dimensional reduced visibility structure that approximates the distribution of the radial component of the dielectric permittivity necessary to achive nonmagnetic cloaking in the visible frequency range.

The use of directional wireless communications to form flexible mesh backbone networks, which provide broadband connectivity to capacity-limited wireless networks or hosts, promises to circumvent the scalability limitations of traditional homogeneous wireless networks. The main challenge in the design of directional wireless backbone (DWB) networks is to assure backbone network requirements such as coverage and connectivity in a dynamic wireless environment. This paper considers the use of mobility control, as the dynamic reposition of backbone nodes, to provide assured coverage-connectivity in dynamic environments. This paper presents a novel approach to the joint coverage-connectivity optimization problem by formulating it as a quadratic minimization problem. Quadratic cost functions for network coverage and backbone connectivity are defined in terms of the square distance between neighbor nodes, which are related to the actual energy usage of the network system. Our formulation allows the design of self-organized network systems which autonomously achieve energy minimizing configurations driven by local forces exerted on network nodes. The net force on a backbone node is defined as the negative energy gradient at the location of the backbone node. A completely distributed algorithm is presented that allows backbone nodes to adjust their positions based on information about neighbors' position only. We present initial simulation results that show the effectiveness of our force-based mobility control algorithm to provide network configurations that optimize both network coverage and backbone connectivity in different scenarios. Our algorithm is shown to be adaptive, scalable and self-organized.