Mechanical Engineering
Materials Science & Engineering

iMAPS New England 35th Annual Symposium & Expo



Tuesday, May 6, 2008

The conference held at the Holiday Inn Boxborough Woods in Boxborough, MA was attended by Graduate Students: Tracey Vincent, Huanan Duan, Shelley Dougherty, Nihar R. Pradhan, and Xiangping Chen.

Presentations for Session F: Microwave and RF

Co-Chairs: Tracey Vincent and Huanan Duan

Posters Presented

Template Assisted Fabrication of Protein and Polymer Nanostructures for Biomedical Applications

Authors:

Shelley Dougherty and J. Liang

Abstract

Bionanomaterials have recently begun to attract a great amount of interest and could potentially revolutionize biomedical research. In particular, nanotubular structures are a very attractive option in drug delivery and gene therapy research. For example, preliminary CNT studies have yielded very promising results. The use of carbon nanotubes for biomedical applications relies upon surface fictionalization to enhance the solubility, biocompatibility, and biochemical functionality. This adds to the complexity of the fabrication considerably. In addition CNT based biomedical technologies are still under great scrutiny due to inconclusive results concerning their cytotoxicity. Due to these drawbacks, the success of CNTs has led to an increased interest in fabricating nanotubes from biomaterials such as proteins, peptides and polymers.

Our research focuses on template assisted methods for the fabrication of bionanomaterials. Nanoporous anodized aluminum oxide (AAO) membranes are used as our templates. We employ two different protein nanotube fabrication methods which include the so called alternate immersion method which utilizes chemical crosslinks to covalently bind protein layers to the inner nanopore walls and the so called layer-by-layer method which utilizes electrostatic interactions between oppositely charged protein layers to bind to the inner nanopore walls. Finally, we employ a template wetting approach to form polymer nanotubes and nanorods within the AAO nanopore channels. The template wetting approach utilizes the interfacial driving forces between low energy polymer films and the high energy nanoporous AAO to pull thin film polymer melts into the nanopores. This presentation will discuss the processing and characterization of the nanostructures resulting from these template assisted methods.

Thermal Properties of Single and Multi-wall Carbon Nanotubes,"

Authors:

Nihar R. Pradhan, H. Duan, J. Liang, and G.S. Iannacchione

Abstract

Nanotubes are of great interest for their unique anisotropic electronic, mechanical, and thermal properties. Because of their small size, quantum effects can play a role and reveal 1D quantization of phonon transport, usually at very low temperatures. In this work, the specific heat (Cp) and thermal conductivity (?) of Single-Wall (SW), Multi-Wall (MW) Carbon nanotubes (CNT), and graphite powder are reported using ac-calorimetry from 300 to 400 K, in ordered composite sample+cell arrangements. These results indicate that the effective thermal conductivity of the MWCNT composite measured with the heat flow predominately parallel to the long-axis of the nanotubes is relatively higher than that measured in a perpendicular configuration. Inter-nanotube coupling is weak in the parallel configuration and may indicate quantum effects even at these high temperatures. For both SWCNT and MWCNT composite samples, the Cp exhibits similar linear temperature dependence in both configurations. However, ? for the MWCNT and SWCNT composites in the perpendicular heat flow configuration appears bulk-graphite-like until ~ 370 K, thereafter decreasing with increasing temperature, indicating the onset of phonon-phonon scattering.

Fabrication of Nanostructured Electrodes Based on Cu Nanorod Arrays for Li-ion Batteries

Authors:

Xiangping Chen, Huanan Duan, Zhentao Zhou, and Jianyu Liang

Abstract

Li-ion batteries are attractive candidates for power sources because of their high energy density and long cycle life. However, due to the slow solid-state diffusion of Li-ion within the electrode materials, the performance of conventional Li-ion batteries charged/discharged at high current rate (> 1C) is severely degraded. Therefore, there is a vigorous research effort in the use of nanomaterials to shorten Li-ion diffusion path length and thus to improve the rate capabilities of Li-ion batteries. Nanorod or nanowire current collectors are expected to bring many advantages: larger surface contact area between current collector and active materials; easier maintenance of short Li-ion diffusion length; and better accommodation of structure strains imposed by electrode reactions.

Here, we demonstrate a template-assisted means to fabricate Cu nanorod arrays on Cu foil to be used as current collector. Cu nanorods are potentiostatic deposited in the nanopores of anodized aluminum oxide (AAO) templates. The electrodeposition conditions are optimized. It is found that nanorods obtained in alkaline electrolye are the most uniform in length. In the future, we will load active materials on the Cu nanorod arrays to create nanostructured rapid rechargeable electrodes with high capacity for Li-ion batteries.

Material Topographic Influence on High Frequency Conductor Loss

Authors:

Tracey Vincent, Isa Bar-On and Christopher A. Brown

Abstract

The front-end, of a telecommunication system, contains transmission lines that carry analogue signals. The sole purpose of the printed conductor transmission line, on the surface of an insulated substrate, is as a guide to the electric signal – this signal at GHz frequencies comes in the form of an electromagnetic (EM) wave. The price that is paid for using this thin metal strip is attenuation of the signal in the form of conductor loss. Conductor loss is the major component of attenuated loss within the GHz frequency range. These printed conductive lines have several topographic factors that contribute to conductor loss, which include: slumping, edge definition, surface roughness and microstructure. Each of these features has been studied to ascertain their contribution over the radio-frequency range. These loss factors can only be mitigated once they have become well understood.

Theoretical Development for the Design of Thermal Via Size and Density within LTCC

Authors:

Mike Ehlert and Peter Barnwell, Barry Industries, Attleboro,MA; T. Vincent, Worcester Polytechnic Institute, Worcester, MA

Abstract

Increased power density applications especially for front end modules have created the need for adequate thermal management in microwave design. Although LTCC has a lower thermal resistance than PCB substrates it is still desirable to lower the resistance further by introducing thermal via arrays. A thermal imaging system using an infrared camera was used to measure the top surface temperature over a range of powers with samples that had varying via sizes and densities. The empirical data results from this study were compared to theoretical figures by using the simple rule-of-mixtures as a starting point. The rule-of-mixtures can indicate a trend when the fraction volume of the dissimilar materials is altered, but obviously does not show how via size and density influences the thermal conductivity when the % volume amount stays the same. The fact that the thermal conductivity of the filled via is so much greater than the LTCC material means that another method of theoretically calculating the resulting thermal conductivity can be used by studying the thermal path. This paper investigates the interface temperature of the filled via and LTCC and explores an alternative method of predicting thermal performance.

PCB Topographic Influence on GHz Frequency Loss

Authors

Tracey Vincent, C.A. Brown, and I. Bar-On, Worcester Polytechnic Institute, Worcester, MA

Abstract

The front-end, of a telecommunication system, contains transmission lines that carry analogue signals. The sole purpose of the printed conductor transmission line on an, insulated, substrate is as a guide to the electric signal - which comes in the form of an electromagnetic (EM) wave. The price that is paid for using this thin metal strip is attenuation of the signal in the form of conductor loss. Conductor loss is the major component of attenuated loss within the GHz frequency range. Thick film printed conductive lines have several topographic factors that contribute to conductor loss, these include: slumping, edge definition, surface roughness and microstructure. Each of these features has been studied to ascertain their loss contribution over the radio-frequency range. Slumping is a macroscopic feature where the printed conductor does not have uniform thickness across the width and slopes or slumps at the edges of the print. The other topographic effects are known to cause various forms of EM scattering. If an electromagnetic wave passes through a medium with non-uniform material properties, the wave is scattered. Essentially, scattering is where some of the signal is deviated from its original course. The surface of the substrate will not appear smooth to the EM wave at GHz frequencies. The printed edge of the thick film strip at a certain scale does not look defined but becomes ragged. There are also non-uniform microscopic features, for example, porosity and grain structure. Fractal analysis has been used to investigate different surface and edge parameters and their correlation to conductor loss.

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