Isaac M. Ehrenberg

A three-dimensional self-supporting low loss microwave lens with a negative refractive index

Demonstrations of focusing with metamateriallenses have predominantly featured two dimensional structures or stacks of planar elements, both limited by losses which hinder realized gain near the focal region. In this study, we present a plano-concave lens built from a 3D self-supporting metamaterial structure featuring a negative refractive index between 10 and 12 GHz. Fabricated using macroscopic layered prototyping, the lens curvature, negative index and low loss contribute to a recognizable focus and free space gains above 13 dB.

Inventory Management with an RFID-equipped Mobile Robot

The use of RFID technology has increased in libraries where it is the centerpiece of emerging automated self-checkout, return, and theft detection systems. In this paper, we present LibBot, a robot equipped with an RFID reader, that automates the otherwise manual shelf-reading process and finds misplaced books autonomously. Our experiments with a single library shelf show that our robot-assisted approach to inventory management can not only detect misplaced books reliably, but also correctly determine the order of the books on the shelves and even localize each book with an accuracy of a few centimeters. Our work also shows to what extent RFID challenges such as metal shelves and thin books with RFID tags in close proximity affect the location accuracy.

Fully conformal FSS via rapid 3D prototyping

Prototype fabrication of microwave antennae and metamaterials has been dominated by planar manufacturing techniques, complicating experimental validation of designs that utilize more than two dimensions. This paper introduces a methodology that enables the rapid fabrication of electromagnetic prototypes with complex surfaces. As an example, a conformal frequency selective surface is presented in the form of a paraboloid patterned with an array of cross loop features. Experiments confirm the surface exhibits a stop band at 12.5 GHz, achieving a 30dB drop in power transmission.

Engine Misfire Detection with Pervasive Mobile Audio

We address the problem of detecting whether an engine is misfiring by using machine learning techniques on transformed audio data collected from a smartphone. We recorded audio samples in an uncontrolled environment and extracted Fourier, Wavelet and Mel-frequency Cepstrum features from normal and abnormal engines. We then implemented Fisher Score and Relief Score based variable ranking to obtain an informative reduced feature set for training and testing classification algorithms. Using this feature set, we were able to obtain a model accuracy of over 99 % using a linear SVM applied to outsample data. This application of machine learning to vehicle subsystem monitoring simplifies traditional engine diagnostics, aiding vehicle owners in the maintenance process and opening up new avenues for pervasive mobile sensing and automotive diagnostics.

Towards low-cost, wireless blood anomaly sensing: An RFID-based anemia detection sensor

Paper based diagnostic devices have great potential in the low-cost sensing of blood diseases. However, patient blood testing using these devices is limited by tedious manual intervention and qualitative colorimetric readouts. We present the novel design of an RFID-based anemia detection sensor that integrates a paper-based diagnostic device with a passive Ultra High Frequency (UHF) RFID tag. Differences in red blood cell (RBC) count in a patients blood manifests itself as a controlled time-dependent change in the tags signal response. We demonstrate that our sensor is capable of reliably differentiating between blood having 20, 30, 40 and 50% RBC concentration by volume - indicative of anemic vs. healthy blood. Furthermore the sensor can be read using off the shelf RFID equipment allowing for automated screening of blood specimens at large scale. Challenges in sensor design and future research directions are also discussed.

Fabrication of an X-Band conformal antenna array on an additively manufactured substrate

Conformal antenna arrays are useful for applications that require directive radiation patterns while constrained to non-planar geometries. Most prototype implementations achieve conformality by tiling planar elements or utilizing flexible substrates. In this paper, we demonstrate the fabrication of an array of X-Band patch radiators fabricated with their feed network directly atop a non-planar substrate which was produced using additive manufacturing. Measurements of the far field radiation patterns are consistent with simulations, which show the conformal array can achieve performance similar to a tiled or planar alternative.

Effects of cell geometry on thermal management in air-cooled battery packs

Batteries come in many different shapes and sizes. Determining which one is best for a particular application is straightforward in some cases and ambiguous in others. When hundreds or thousands of cells are combined into packs, the choice of shape is far from obvious. All too often, these decisions are made based on convenience or cost without fully considering the pack-level effects. This paper takes a closer look at the cost of thermal management of cylindrical, prismatic, and rounded prismatic cells in air-cooled packs. The results suggest that when it comes to air-cooling, not all form factors are created equal.

Incorporation of active RF circuit elements into additively manufactured substrates

Additive Manufacturing processes have matured in recent years and are now being applied to the rapid fabrication of functional electromagnetic structures and devices such as waveguides, antennae, and metamaterials. Key to a successful breakthrough into commercial viability for the industry is the incorporation of active RF elements. In this paper, we note some of the difficulties associated with including active elements within additively manufactured substrate designs, and report measurements from a microstrip transmission line with its transmission tuned by a voltage controlled analog phase shifter embedded within a 3D printed substrate. The results indicate that while active elements can be incorporated, performance could be improved by certain design and fabrication changes.

Advancement of 3D printed conformal FSS and active array

Summary form only given. The size and shape requirements imposed on many electronics applications today require innovative fabrication methods to surpass the limits of conventional printed circuit board manufacturing techniques. Flexible electronics based on thin films such as polyimide or elastic substrates like PDMS have contributed to the emergence of non-planar substrates, as has the use of omnidirectional printing, which enables the direct writing of conductive traces using metal-based inks on surfaces of arbitrary shape. Not without as host of issues, these methods are vulnerable to stretches and cracks, and often feature lower conductivity than PCBs due to the difficulty of fully sintering ink particles on polymer substrates.

Lightweight negative GRIN lens fabrication via rapid prototyping for radio applications

Summary form only given. In this paper, we report on the design, rapid fabrication, and evaluation of a flat lens with a negative gradient refractive index consisting of self-supporting 3D metamaterial elements. Recent work has shown that metamaterial structures with self-supporting architectures suffer from minimal losses compared to planar metamaterial elements that require extraneous dielectric material substrates. Low loss characteristics make multilayer devices with quality performance parameters possible. This was exemplified in a recent report on rapidly fabricated plano-concave lenses using negative refractive index 3D metamaterial. Both simulations and experiments showed that the lightweight lens benefitted from low loss and high gain in the focal region across the 10-12 GHz band. More importantly, it highlighted the fabrication flexibility afforded by rapid prototyping technology, which suggests that complex geometries and devices are readily accessible, which portends to the further actualization of metamaterial performance benefits. In order to transition from a curved lens profile of a homogenous medium to a planar lens with a graded index, the following steps were taken. First, a gradient refractive index profile was derived using geometric optics for a flat lens with a focal distance similar to other homogenous lenses. The refractive index profile was then discretized so it could be populated with metamaterial elements with matching refractive index parameters. To build a library of metamaterial geometries and their corresponding material parameters, a parametric sweep of different S-ring unit cell dimensions was performed. The refractive indices of the varied structured were retrieved using standard procedures. By arranging the S-ring structures accordingly, the gradient index profile was well approximated. Care was taken to ensure the overall structure was mechanically viable to avoid complications during fabrication. The performance of the lens was studied using geometric optics and physical optics. It was found that for an aperture of small electrical size, the focal points that result from geometric and physical optics appear at different locations. The discrepancy between these two methods was found to be different for lenses made from positive index materials and negative index materials.