Magneto-Mechanical Transmitters for Ultra-Low Frequency Near-field Communication

Electromagnetic signals in the ultra-low frequency (ULF) range below 3 kHz are well suited for underwater and underground wireless communication thanks to low signal attenuation and high penetration depth. However, it is challenging to design ULF transmitters that are simultaneously compact and energy efficient using traditional approaches, e.g., using coils or dipole antennas. Recent works have considered magneto-mechanical alternatives, in which ULF magnetic fields are generated using the motion of permanent magnets, since they enable extremely compact ULF transmitters that can operate with low energy consumption and are suitable for human-portable applications. Here we explore the design and operating principles of resonant magneto-mechanical transmitters (MMT) that operate over frequencies spanning a few 10's of Hz up to 1 kHz. We experimentally demonstrate two types of MMT designs using both single-rotor and multi-rotor architectures. We study the nonlinear electro-mechanical dynamics of MMTs using point dipole approximation and magneto-static simulations. We further experimentally explore techniques to control the operation frequency and demonstrate amplitude modulation up to 10 bits-per-second.Comment: 10 pages, 9 figure

Fabrication and electrical integration of robust carbon nanotube micropillars by self-directed elastocapillary densification

Vertically-aligned carbon nanotube (CNT) "forest" microstructures fabricated by chemical vapor deposition (CVD) using patterned catalyst films typically have a low CNT density per unit area. As a result, CNT forests have poor bulk properties and are too fragile for integration with microfabrication processing. We introduce a new self-directed capillary densification method where a liquid is controllably condensed onto and evaporated from CNT forests. Compared to prior approaches, where the substrate with CNTs is immersed in a liquid, our condensation approach gives significantly more uniform structures and enables precise control of the CNT packing density and pillar cross-sectional shape. We present a set of design rules and parametric studies of CNT micropillar densification by this method, and show that self-directed capillary densification enhances the Young's modulus and electrical conductivity of CNT micropillars by more than three orders of magnitude. Owing to the outstanding properties of CNTs, this scalable process will be useful for the integration of CNTs as functional material in microfabricated devices for mechanical, electrical, thermal, and biomedical applications

Electro-Optical Materials: Electrically Addressable Hybrid Architectures of Zinc Oxide Nanowires Grown on Aligned Carbon Nanotubes (Adv. Funct. Mater. 15/2010)

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77962/1/2469_ftp.pd

Rapid Anisotropic Photoconductive Response of ZnO-Coated Aligned Carbon Nanotube Sheets

We investigate the rapid and anisotropic UV-induced photoconductive response of hybrid thin films comprising zinc oxide (ZnO) nanowires (NWs) directly grown on horizontally aligned (HA-) carbon nanotube (CNT) sheets. The films exhibit anisotropic photoconductivity; along the CNTs, conductivity is dominated by the CNTs and the photoconductive gain is lower, whereas perpendicular to the CNTs the photoconductive gain is higher because transport is influenced by ZnO nanoclusters bridging CNT-CNT contacts. Because of the distributed electrical contact provided by the large number of ZnO NWs on top of the HACNT film, this hybrid nanoarchitecture has a significantly greater photocurrent than reported for single ZnO NW-based devices at comparable UV illumination intensity. Moreover, the hybrid architecture where a thin basal film of ZnO ohmically contacts metallic CNTs enables rapid transport of photogenerated electrons from ZnO to CNTs, resulting in sub-second photoresponse upon pulsed illumination. The built-in potential generated across ZnO–CNT heterojunctions competes with the externally applied bias to control the photocurrent amplitude and direction. By tuning the anisotropic conductivity of the CNT network and the morphology of the ZnO or potentially other nanostructured coatings, this material architecture may be engineered in the future to realize high-performance optical and chemical sensors