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Corrosion of reinforced concrete structures creates serviceability and safety issues, costing millions of dollars for inspection, repair, and rehabilitation. Recent efforts have focused on monitoring corrosion in situ, providing accurate real-time information for decision-making. The goal of this research is the creation of an embeddable ultrasonic sensing network for assessment of reinforcement deterioration. Toward this effort, guided ultrasonic waves were used to monitor reinforced mortar specimens undergoing accelerated uniform and localized corrosion. Longitudinal waves were invoked at higher frequencies (2-9 MHz), where the attenuation is a local minimum. Using a through-transmission configuration, waveforms were sensitive to both forms of corrosion damage. Scattering, mode conversions, and reflections from irregularities at the bar surface from uniform corrosion and the severely tapered cross section from localized corrosion are thought to cause the increase in attenuation. Because localized corrosion did not yield a discontinuity that was nearly perpendicular to the bar axis, incident waves were severely scattered, mode converted, and rapidly attenuated. As evidence, this was the inability of pulse-echo testing to detect reflected waveforms for localized corrosion. DOI: 10.1061/(ASCE)0733-9399(2009)135:1(9) CE Database subject headings: Ultrasonic methods; Wave propagation; Reinforced concrete; Corrosion; Damage; Nondestructive tests; Durability.

We explore the potential benefits of using pattern reconfigurable antennas in multiple-input multiple-output (MIMO) communication systems. First, theoretical capacity increases are calculated in a typical indoor multipath environment assuming ideal, fully reconfigurable antennas and compared to cases using theoretical isotropic antennas. Next, a real reconfigurable antenna built into a multiple element antenna system for MIMO use is described and analyzed to investigate the possible effects of beam tilts on capacity. Finally, this system is used to quantify the possible capacity improvements due to both antenna diversity and antenna gain that are enabled by antenna pattern reconfigurability in a scientifically reproducible environment that includes antenna coupling. Index Terms--Multiple-input multiple-output (MIMO) antenna, reconfigurable antennas.

We propose an extension to the concept of random antenna arrays. Three new array geometries are introduced which are intended to incorporate the wide bandwidth capability of a random array while having simplified geometry to increase their suitability for lower-cost applications. The behaviors of the periodic array of random subarrays, array of periodically rotated random subarrays, and array of randomly rotated random subarrays are each characterized probabilistically. Results indicate that subarray rotation can lower the sidelobe level of the array factor. An example of the design process is presented with calculated array factors. Index Terms--Antenna arrays, random arrays, subarrays, wideband arrays.

This work describes the integration of commercially available packaged radio frequency microelectromechanical system (RF MEMS) switches with radiation pattern reconfigurable microstrip antennas. Most applications of RF MEMS switches consider the switches as only circuit elements. In contrast, the implementation of packaged switches in this particular antenna must address not only the simple open/closed behavior of the switches but also their impact on the radiation characteristics of the reconfigurable antenna. Here, two Radant MEMS single-pole single throw (SPST) SPST-RMSW100 (packaged RF MEMS) switches are used to reconfigure the radiation patterns of a resonant square spiral microstrip antenna between endfire and broadside over a common impedance bandwidth. Switch insertion, matching network design, and other issues are addressed. Results for both simulated and measured antennas, as well as recommendations for future work in this area, are provided. Index Terms--Matching Networks, radio frequency microelectromechanical system (RF MEMS), Reconfigurable Antenna.

Corrosion of reinforced concrete is a chronic infrastructure problem, particularly in areas with deicing salt and marine exposure. To maintain structural integrity, a testing method is needed to identify areas of corroding reinforcement. For purposes of rehabilitation, the method must also be able to evaluate the degree, rate, and location of damage. Toward the development of a wireless embedded sensor system to monitor and assess corrosion damage in reinforced concrete, reinforced mortar specimens were manufactured with seeded defects to simulate corrosion damage. Taking advantage of waveguide effects of the reinforcing bars, these specimens were then tested using an ultrasonic approach. Using the same ultrasonic approach, specimens without seeded defects were also monitored during accelerated corrosion tests. Both the ultrasonic sending and the receiving transducers were mounted on the steel rebar. Advantage was taken of the lower frequency ( Keywords: Ultrasonics, Waveguides, Accelerated Corrosion Tests, Reinforced Concrete, Mortar

This study reports on the integration of a novel reconfigurable microstrip antenna capable of reconfiguring both its radiation pattern and frequency response onto a generic laptop computer structure. The purpose of such an exercise is to provide the relevant information necessary to integrate high performance antennas onto structures that can be used in ad hoc communication scenarios as well as other demanding applications. To pre-evaluate candidate antenna locations on the laptop chassis, an electromagnetic visibility study (EVS) is performed. Once integrated into candidate positions that have been analyzed by the EVS, the operation of the antenna on the host structure is measured and assessed with consideration to several realistic electromagnetic environments. The resulting performance and packaging issues are discussed. A formalized procedure for the integration of the antenna onto any host chassis using the EVS as a tool is also included. Index Terms--Antenna integration, antenna packaging, reconfigurable antenna.

A new active microstrip reflectarray element (unit cell) with an internal microwave integrated circuit amplifier is introduced. The amplifier resides in a small slot within the footprint of the square patch antenna and is connected between the feed points of the patch's orthogonal polarizations. This element results in reduced array element spacing, reduced transmission line losses through elimination of long feed lines, and a simplified fabrication process compared to other active reflectarray unit cells. Patch geometries with several slot shapes are studied with simulations to arrive at an antenna configuration with good return loss and isolation characteristics. The stability and gain of the system are analyzed over frequency. Measured radiation pattern and gain data for a single element and a small array agree well with predictions and demonstrate the element's capabilities. Limitations of the active element, approaches to mitigate these limitations, and directions for future work are discussed. Index Terms--Active antenna, active microstrip reflectarray, microstrip antenna.

A wide operating bandwidth for a single-layer coaxially fed rectangular microstrip patch antenna can be obtained by cutting a U-shaped slot on the patch. This antenna structure has recently been found experimentally to provide impedance bandwidths of 10%-40%, even with nonair substrates. However, design rules for this antenna have not yet been presented. This paper develops principle design procedures through examination of the structure's multiple resonant frequencies as well as the radiation and impedance properties of different antenna geometries. The approximate design rules are derived by analysis of former experiments, method of moments (MoM) simulations, and measurement results. Simulations and measurements of several antennas designed using these new rules are presented and directions for further study are discussed. Index Terms--Broad-band antenna, microstrip antenna, U-slot antenna.

This paper presents a predictive model for the resonant frequencies of rectangular microstrip antennas with flush and spaced superstrates. This closed-form model is suitable for CAD and is directly applicable for the integration of microstrip antennas beneath plastic covers or protective dielectric superstrates in portable wireless equipment. The model utilizes conformal mapping and the concept of equivalent capacitance to determine the effective permittivity of a covered microstrip structure. A comparison between calculated and measured resonant frequencies demonstrates that the model provides less than 1% errors for structures with low relative permittivities ([[Epsilon].sub.r] < 3) and slightly higher errors for structures that contain higher permittivity materials. Generally, the model predicts the resonant frequency of a spaced superstrate structure as accurately as possible within the tolerance range of the structure's electrical and physical parameters. Index Terms - Microstrip antennas, resonant frequency, superstrates.