Nanostructured materials exhibit useful properties that are not found in the same materials in bulk form. (1) Dramatically increase surface and area and roughness of nanostructured materials is advantageous for evaporative cooling, which is one of the main subjects in this dissertating, due to the strong capillary effect and high density of gas-liquid-solid triple junctions. (2) In magnetic materials, when the size of the magnetic material is decreased to submicron or nano size, magnetic coercivity increases since magnetic domains are confined by the size of the material. (3) Also, unique optical properties of materials in nano size can be utilized for thermal managing and energy saving application.

In Chapter 2 of this dissertation, I described the demonstration of using nanoporous membranes in evaporative cooling. Nanoporous membranes have been proposed and theoretically shown as a promising candidate for high heat flux evaporative heat transfer. However, the experimentally demonstrated heat flux has so far been significantly lower than the theoretical prediction, which has cast doubt on the feasibility of achieving a high heat flux from nanoporous membranes. Here we carried out evaporative heat transfer experiments using isopropyl alcohol (IPA) through anodized aluminum oxide (AAO) membranes. For membranes with a 200nm average pore size on a 0.5cm2 size area, we demonstrated a high evaporative heat flux of 210W/cm2 based on the overall AAO surface area, or ~400W/cm2 if only the pore area is considered. This heat flux is close to the theoretical value of 572 W/cm^2 (based on the pore area) for IPA evaporation through nanoporous membranes. Using time synchronized high-speed images, it was verified that evaporation was the main heat transfer mode in the high heat flux regime. The demonstration of high heat flux evaporation through nanoporous membranes, close to the theoretical limit and on a relatively large area (0.5cm2), is significant for the future development of high heat flux thermal management technology for electronic devices.

In chapter 3, I presented a noble technique to achieve exchange coupling of hard phase magnetic materials and soft phase magnetic materials. Exchange coupled spring magnets have been suggested as a possible replacement of rare earth contained strong magnets. We have chosen LPT-MnBi as hard phase and FeCo as soft phase magnetic material, as many early conducted theoretical modeling suggests. The optimal size of hard phase magnet for the exchange coupling (approximately twice of single magnetic domain size, ~2µm for MnBi) was achieved by conventional ball milling process, and the shell layer of FeCo was deposited by a noble process called sonic agitation assisted physical vapor deposition (SAA-PVD). TEM image and EDX mapping shows uniform coating of FeCo outer shell layer on the MnBi core. The thickness of the shell layer was in the range of 10~35nm which is slightly less than twice of single domain size of FeCo. Magnetic remanence of ball milled MnBi particles was increased from Ms = 36 emu/g to 51 emu/g after SAPVD process while the coercivity was slghtly decreased from 1.1T to 1.0T. (BH)max of the particles after the SAA-PVD process was about 2.5MGOe. Smooth demagnetization curve that resembles that of single magnetic materials and high increase of magnetic remanence suggest that exchange coupling was achieved.

In chapter 4, a new route to synthesize thermochromic VO2 particles and properties of the film using the particles was presented. A temperature responding fully reversible metal to insulator phase transition (MIT) accompanied by a change of optical properties only found in Vanadium dioxide monoclinic phase (VO2 (M)) has potential for huge energy saving application by controlling the amount of infrared (IR) light enter into buildings. More synthetic routes are still worthy to be explored because of difficulty in mass production of VO2 (M). In this work, we demonstrated a combination of thermal decomposition method subsequent ball milling process to produce pure VO2 (M) particles. The size of the synthesized particles was between 20 and 200nm. IR modulating smart film was fabricated by blade casting mixture of synthesized VO2 (M) particles and PVP on PET film. The thickness of the film was about 300nm and particles were uniformly dispersed in the film. Despite the irregular shape of the particles and the fact that few portion of the synthesized particles exceeding suggested optimal size range, the transmittance of little less than 40% and the IR modulation of about 20% which values are practically useful was achieved.

In many sensor networks, data or events are named by attributes. Many of these attributes have scalar values, so one natural way to query events of interest is to use a multi-dimensional range query. An example is: "List all events whose temperature lies between 50° and 60°, and whose light levels lie between 10 and 15." Such queries are useful for correlating events occurring within the network.

In this paper, we describe the design of a distributed index that scalably supports multi-dimensional range queries. Our distributed index for multi-dimensional data (or DIM) uses a novel geographic embedding of a classical index data structure, and is built upon the GPSR geographic routing algorithm. Our analysis reveals that, under reasonable assumptions about query distributions, DIMs scale quite well with network size (both insertion and query costs scale as O(√N)). In detailed simulations, we show that in practice, the insertion and query costs of other alternatives are sometimes an order of magnitude more than the costs of DIMs, even for moderately sized network. Finally, experiments on a small scale testbed validate the feasibility of DIMs.

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We present an energy-efficient high resolution image acquisition approach based on a two-tiered system comprising low-cost, low-power, non-actuated, extremely resource-constrained stereo image sensor platforms and more capable but more power-consumptive high resolution imaging platforms with actuation capability. The resource constrained platforms are used to compute 3D object location and subsequently to compute appropriate pan/tilt/zoom settings for the high resolution imaging platforms. The high resolution imaging platforms with actuation capability acquire high resolution images which can be utilized for various recognition purposes. We present our design methodology and system architecture and evaluate coverage, latency and energy tradeoffs in our system. Experimental results show that use of the two-tiered network significantly reduces energy consumption and latency of high resolution image acquisition versus a single-tiered network while preserving the coverage of the system.

One of the most important goals of current and future sensor networks is energy-efficient communication of images. This work presents a quantitative comparison between the energy costs associated with 1) direct transmission of uncompressed images and 2) sensor platform-based JPEG compression followed by transmission of the compressed image data. JPEG compression computations are mapped onto various resource-constrained sensor platforms using a design environment that allows computation using the minimum integer and fractional bit-widths needed in view of other approximations inherent in the compression process and choice of image quality parameters. Advanced applications of JPEG such as region of interest coding and successive/progressive transmission are also examined.

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