Hardware Development of an Ultra-Wideband System for High Precision Localization Applications

A precise localization system in an indoor environment has been developed. The developed system is based on transmitting and receiving picosecond pulses and carrying out a complete narrow-pulse, signal detection and processing scheme in the time domain. The challenges in developing such a system include: generating ultra wideband (UWB) pulses, pulse dispersion due to antennas, modeling of complex propagation channels with severe multipath effects, need for extremely high sampling rates for digital processing, synchronization between the tag and receivers’ clocks, clock jitter, local oscillator (LO) phase noise, frequency offset between tag and receivers’ LOs, and antenna phase center variation. For such a high precision system with mm or even sub-mm accuracy, all these effects should be accounted for and minimized. In this work, we have successfully addressed many of the above challenges and developed a stand-alone system for positioning both static and dynamic targets with approximately 2 mm and 6 mm of 3-D accuracy, respectively. The results have exceeded the state of the art for any commercially available UWB positioning system and are considered a great milestone in developing such technology. My contributions include the development of a picosecond pulse generator, an extremely wideband omni-directional antenna, a highly directive UWB receiving antenna with low phase center variation, an extremely high data rate sampler, and establishment of a non-synchronized UWB system architecture. The developed low cost sampler, for example, can be easily utilized to sample narrow pulses with up to 1000 GS/s while the developed antennas can cover over 6 GHz bandwidth with minimal pulse distortion. The stand-alone prototype system is based on tracking a target using 4-6 base stations and utilizing a triangulation scheme to find its location in space. Advanced signal processing algorithms based on first peak and leading edge detection have been developed and extensively evaluated to achieve high accuracy 3-D localization. 1D, 2D and 3D experiments have been carried out and validated using an optical reference system which provides better than 0.3 mm 3-D accuracy. Such a high accuracy wireless localization system should have a great impact on the operating room of the future

Investigation of pulse dispersion in a carrier-based UWB system with LO leakage cancellation

Local oscillator (LO) leakage in a carrier-based ultrawideband (UWB) system is a major design concern. In many cases, mixer LO-RF isolation is not sufficient and the LO leakage is well above the useful UWB signal. However, this leakage can be substantially reduced by using a notch filter located before the UWB transmitting antenna as long as it will not lead to unacceptable signal distortion. Therefore, various filter parameters, such as the filter order and 3 dB rejection bandwidth, have been studied to see their effects on providing sufficient band rejection level to reduce the unwanted LO leakage while minimizing the transmitted pulse dispersion. Time domain simulations and measurements have been utilized to evaluate the pulse dispersion using both the relative signal's first pulse amplitude and the pulse time delay spread. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64339/1/20390_ftp.pd

Mechanical durability of superhydrophobic surfaces: the role of surface modification technologies

Various surface modification technologies have been used to develop superhydrophobic surface, however their durability has been recognized as the major obstacle for the real applications. Here a quantitative investigation was conducted to evaluate the effects of different surface modification methods on the surfaces’ mechanical durability. The superhydrophobic surfaces were prepared by the combination of two surface roughing methods (etching and sandblasting) with chemical modifications with four low surface energy materials: silica sol (SS), octadecanoic acid (OA), heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane (HDFS) and hexadecyltriethoxysilane (HTS). XPS was used to analyze the elements composition and AFM was used to measure the roughness of the surfaces. The durability of these surfaces was tested by a sandpaper abrasion experiment. The collective results showed that the low surface energy materials had significant effects on the surface roughness, which would then play an important role in the durability of these rough surfaces. The SS modified rough surfaces possessed higher roughness and better durability than the surfaces modified by other three low surface energy materials. SS modified rough surfaces could bear 60 cycles of abrasion with 10 g weights on 1500 CW sandpaper