The initiation and propagation of damage in composite laminates generate Acoustic Emission. The use of
real time AE monitoring has been quite extensive for in-service composite structures. In the present work,
experimental and numerical studies were performed to characterize the acoustic wave propagation in thin
glass/epoxy composite plates. Experimentally obtained and simulated emission signals were used to
identify and locate the source of the acoustic wave. Signal processing algorithms and a passive damage
diagnosis system based on AE techniques were proposed for continuously monitoring and assessing the
structural health of composite laminates. The local sensing and distributed processing features of the sensor
system result in a decreased demand for bandwidth and lower computational power needed at each node.
The demand for real-time or in situ structural health monitoring has stimulated efforts to integrate self and environmental
sensing capabilities into structural composite materials. Essential to the application of smart composites is the issue of
the mechanical coupling of the sensor to the host material. In this study various methods of embedding sensors within
the host composite material are examined. Quasi-static three-point bending (short beam) and fatigue three-point bending
(short beam) tests are conducted in order to characterize the effects of introducing the sensors or suitable simulated
sensors. The sensors that are examined include simulated sensors in the form of chip resistors with the original
packaging geometry and thin film sensors (PVDF). The sensors are integrated into the composite either by placement
between the layers of prepreg or by placement within precision punched cut-outs of the prepreg material. Thus, through
these tests we determine the technique that optimizes the mechanical properties of the host composite material.
Fiber reinforced polymer matrix (FRP) composites have a rich history of diagnosis and characterized using acoustic
emissions techniques. The highly dispersive, attenuating, and anisotropic nature of unidirectional composites places an
emphasis on high density local sensing as opposed to low density more-global sensing strategies.
A high density of sensors naturally implies large quantities of data requiring large bandwidth and substantial processing
power. By distributing processing with the sensors themselves results in a decreased demand for bandwidth and lower
computational power needed at each node in what is now a parallel processing computer. Desired information, time
constraints and mechanical considerations place both hard and soft constraints on our network helping to define its
architecture. I will present investigated computing architectures and their benefits and limitations as they relate to the
various constraints involved.
Metamaterial structures designed to have simultaneously negative permittivity and permeability are known as left-handed materials. Their complexity and our understanding of their properties have advanced rapidly to the point where direct applications are now viable. We present a radial gradient-index (GRIN) lens with an index-of-refraction ranging from -2.67(edge) to -0.97(center). Experimentally, we find the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.45 GHz and in excellent agreement with full-wave simulations. This lens is a demonstrate an newly pioneered advanced fabrication technique using conventional printed circuit board (PCB) technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.
The increasing demand for in-service structural health monitoring has stimulated efforts to integrate self and environmental sensing capabilities into materials and structures. To sense damage within composite materials, we are developing a compact network microsensor array to be integrated into the material. These structurally-integrated embedded microsensors render the composite information-based, so that it can monitor and report on the local structural environment, on request or in real-time as necessary. Here we present efforts to characterize the structural effects of embedding these sensors. Quasi-static three-point bending (short beam shear) and fatigue three-point bending (short beam shear) tests are conducted in order to characterize the effects of introducing sensors, or suitable dummy sensors in the form of chip resistors, and commonly used circuit board material, namely G-10/FR4 Garolite on the various mechanical properties of the host structural composite material. Furthermore, various methods and geometries of embedding the microsensors are examined in order to determine the technique that optimizes the mechanical properties of the host composite material. The work described here is part of an ongoing effort to understand the structural effects of integrating microsensor networks into a host composite material.