Randomized Algorithms for Approximating a Connected Dominating Set in Wireless Sensor Networks

A Connected Dominating Set (CDS) of a graph representing a Wireless Sensor Network can be used as a virtual backbone for routing through the network. Since the sensors in the network are constrained by limited battery life, we desire a minimal CDS for the network, a known NP-hard problem. In this paper we present three randomized algorithms for constructing a CDS. We evaluate our algorithms using simulations and compare them to the two-hop K2 algorithm and two other greedy algorithms from the literature. After pruning, the randomized algorithms construct a CDS that are generally equivalent in size to those constructed by K2 while being asymptotically better in time and message complexity. This shows the potential of significant energy savings in using a randomized approach as a result of the reduced complexity

A Fully-Implantable Low-Noise Emi-Resistant Piezoelectric-Polymer Microphone and Amplifier for the Middle Ear

We present a fully implantable piezoelectric microphone designed to operate with a cochlear implant. This thesis details the design, fabrication, and potential surgical implantation scheme for a fully differential and shielded cantilever made from polyvinylidene difluoride (PVDF)—a common piezoelectric polymer, as well as a low noise differential charge amplifier designed for small capacitance sensors. The amplifier and sensor combination has a noise floor of 385 e− (0.062 fC) over its bandwidth of 100 Hz to 20 kHz, equivalent to 0.015 nm of displacement. When implanted, we achieve a pressure sensitivity of 80–100 fC/Pa referenced to ear canal pressure below 2 kHz and 8–10 fC/Pa above 4 kHz. We expect this sensitivity at high frequency to substantially improve when measured relative to free-field sound pressure, as the horn-like outer ear and ear canal provide up to 20 dB pressure gain above 1 kHz. Our design also provides significant EMI protection—we measured a sensitivity to external electric potentials of only 0.6 fF compared to over 200 fF for an unshielded 4 mm-diameter sphere. We believe this microphone design is competitive with commercial electret microphones used for cochlear implants, especially since our design is fully implantable and interfaces with the existing middle ear structures.M.Eng