Application of microfabrication in electrochemical sensing.

In this work, micro fabrication techniques are explored not only to simplify the production of complex lab on-a-chip devices (LOC), but also micro fabrication will be utilized to create intelligent design features that will enhance an electrochemical sensor\u27s capabilities. First, a low temperature adhesive bonding procedure for LOC glass devices was evaluated for capillary electrophoresis (CE) applications. This low temperature method utilizes UV adhesive to bond the glass microchips under the assistance of a mask aligner. The bonding process was carried out at room temperature in \u3c 30 minutes, and provided a near 100% success rate. Microchips exhibited similar electroosmotic flow, separation characteristics, stable long-term performance, excellent chip-to-chip reproducibility, as their thermally bonded counter parts. This bonding approach required new but easily implemented structural features. In addition to cost effective and reliable fabrication techniques, microchips designed for long-term unattended electrochemical sensing have been evaluated. Specific advantages of the micro fabrication approach include the capability to create an intelligent design containing features such as redundant sensing electrodes, on-chip reference and auxiliary electrodes, and in situ electrode regeneration/calibration. One system targeted involves continuous pH monitoring in drinking water at solid-state iridium oxide electrodes. Microchips utilized consist of a flow-through silicon platform containing patterned gold electrodes onto which iridium oxide was deposited electrochemically. To simulate drinking water detection scenarios, sensors were integrated into a flow system. Elven equivalent pH electrodes where evaluated for electrode-to-electrode reproducibility, long-term drift, and response to expected interfering agents. With on-chip voltage treatment, absolute potentials measured for an electrode array are within ± 4 mY, with identical (±1 mY/pH unit) calibration slopes. This performance level is sustainable over weeks. Sensors for exhaustive coulometry were designed, fabricated and evaluated. Microchips contained thin-film gold working and Ag/AgCI pseudo-reference electrodes. A custom flow cell containing a counter electrode chamber was constructed to integrate the sensor and to create an electrolysis chamber with a fixed volume. Different chip designs were evaluated for reproducibility and longevity using Fe(CN)63-/4- as model analytes. The relative standard deviation (RSD) for a chip (over 42 days) was 5.5% whereas the sensor-to-sensor reproducibility was within 6.3%. A more practical application for utilizing exhaustive coulometry by the determination of free chlorine in drinking water is briefly evaluated. Initially studies will outline the challenges involved by analyzing hypochlorite

Precise Orbit Determination of CubeSats

CubeSats are faced with some limitations, mainly due to the limited onboard power and the quality of the onboard sensors. These limitations significantly reduce CubeSats' applicability in space missions requiring high orbital accuracy. This thesis first investigates the limitations in the precise orbit determination of CubeSats and next develops algorithms and remedies to reach high orbital and clock accuracies. The outputs would help in increasing CubeSats' applicability in future space missions

Design of an integrated airframe/propulsion control system architecture

The design of an integrated airframe/propulsion control system architecture is described. The design is based on a prevalidation methodology that used both reliability and performance tools. An account is given of the motivation for the final design and problems associated with both reliability and performance modeling. The appendices contain a listing of the code for both the reliability and performance model used in the design

Doctor of Philosophy

dissertationLow-cost wireless embedded systems can make radio channel measurements for the purposes of radio localization, synchronization, and breathing monitoring. Most of those systems measure the radio channel via the received signal strength indicator (RSSI), which is widely available on inexpensive radio transceivers. However, the use of standard RSSI imposes multiple limitations on the accuracy and reliability of such systems; moreover, higher accuracy is only accessible with very high-cost systems, both in bandwidth and device costs. On the other hand, wireless devices also rely on synchronized notion of time to coordinate tasks (transmit, receive, sleep, etc.), especially in time-based localization systems. Existing solutions use multiple message exchanges to estimate time offset and clock skew, which further increases channel utilization. In this dissertation, the design of the systems that use RSSI for device-free localization, device-based localization, and breathing monitoring applications are evaluated. Next, the design and evaluation of novel wireless embedded systems are introduced to enable more fine-grained radio signal measurements to the application. I design and study the effect of increasing the resolution of RSSI beyond the typical 1 dB step size, which is the current standard, with a couple of example applications: breathing monitoring and gesture recognition. Lastly, the Stitch architecture is then proposed to allow the frequency and time synchronization of multiple nodes' clocks. The prototype platform, Chronos, implements radio frequency synchronization (RFS), which accesses complex baseband samples from a low-power low-cost narrowband radio, estimates the carrier frequency offset, and iteratively drives the difference between two nodes' main local oscillators (LO) to less than 3 parts per billion (ppb). An optimized time synchronization and ranging protocols (EffToF) is designed and implemented to achieve the same timing accuracy as the state-of-the-art but with 59% less utilization of the UWB channel. Based on this dissertation, I could foresee Stitch and RFS further improving the robustness of communications infrastructure to GPS jamming, allow exploration of applications such as distributed beamforming and MIMO, and enable new highly-synchronous wireless sensing and actuation systems