Patrick Rye

Partial focusing of radiation by a slab of indefinite media

Negative refraction can occur at the interface between vacuum and an indefinite medium—an anisotropic medium for which not all elements of the permittivity and permeability tensors have the same sign. We show experimentally and via simulations that a metamaterial composed of split ring resonators, designed to provide a permeability equal to −1 along the longitudinal axis, will redirect s-polarized electromagnetic waves from a nearby source to a partial focus. The dispersion characteristics of indefinite media prohibit the possibility of true aplanatic points for a planar slab; however, by contouring the surfaces aplanatic points may be realized, as well as other geometrical optical behavior.

Free-space microwave focusing by a negative-index gradient lens

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 lens with an index of refraction ranging from −2.67 (edge) to −0.97 (center). Experimentally, we find that the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.3GHz and in excellent agreement with full-wave simulations. We also demonstrate an advanced fabrication technique using conventional printed circuit board technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.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 lens with an index of refraction ranging from −2.67 (edge) to −0.97 (center). Experimentally, we find that the lens can produce field intensities at the focus that are greater than that of the incident plane wave. These results are obtained at 10.3GHz and in excellent agreement with full-wave simulations. We also demonstrate an advanced fabrication technique using conventional printed circuit board technology which offers significant design, mechanical, and cost advantages over other microwave lens constructions.

Free space microwave focusing by a negative-index gradient lens

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.

Integration of sensing networks into laminated composites

We summarize the methodology that we have used to address integrating sensing network into composite materials for structural self diagnosis. First, we have examined the effect of stress concentration that arises due to the embedment of sensors and external devices on the strength and endurance of laminated glass fiber composites. To analyze the mechanical response of the composite material under study subjected to in-plane or impact loads, we have fabricated a series of samples, with and without embedded (dummy) sensors/micro-processors, using S2 glass fiber/epoxy, and have characterized their response by acoustic emission. Guided by the corresponding results, we can select sensors and other necessary components in such way as to minimize the impact of the embedded electronics on the material integrity and, at the same time, to implement acoustic sensing monitoring functionalities within the material. A 4-tree hierarchical network of PVDF sensors capable of acquiring signals typically related to resin micro cracking phenomena has been developed and partially integrated into a cross ply laminate. The achieved results and ongoing research will be discussed.

Angle resolved microwave spectrometer for metamaterial studies

We describe an angle resolved microwave spectrometer (ARMS) based on a planar waveguide scattering chamber, capable of acquiring the angular distribution of TE polarized microwaves scattered from samples centered within the chamber. The spacing between the upper and lower conducting circular plates is 0.4 in. (∼1 cm), which, with the associated X-band waveguide adapters, fixes the frequency of operation of the ARMS to be optimally within the X-band frequency range (8–12 GHz). Microwave energy can be injected either as an apertured beam via an extended arm connected to the chamber, or via an antenna located in the center of the chamber. Power is detected at a waveguide adapter located on the periphery of the chamber, attached to a rotating arm that has an angular range of 180°. A computer controlled stepper motor attached to the rotating arm facilitates angular scanning with the data acquired at every angle in an automated fashion. The ARMS has excellent reproducibility and signal-to-noise characteristics,...

Optimization of the mechanical properties of composite materials with integrated embedded sensor networks

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.

Passive damage detection in composite laminates with integrated sensing networks

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.

Optimization studies of self-sensing composites

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.

Embedded microcontroller networks: acoustic materials health monitoring

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.