ECE Utah

Topic: Advances and Challenges in Bioelectromagnetics for Implantable Devices: Current and Future Applications.

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UNIVERSITY OF UTAH

ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT

THESIS DEFENSE FOR THE DEGREE OF

MASTER OF SCIENCE

by

Lucas Thomson

Advisor:  Cynthia Furse

Crosstalk and Coupling in Reflectometry Testing of Electrical Wire Faults

  The focus of this thesis is the impact and use of crosstalk and coupling in reflectometry testing of electrical wire faults.  This thesis describes a method for detecting and locating faults on cable shields using an adapted reflectometry system.  A signal transmitted on the inner conductor is coupled to the outside through the fault, which creates a small aperture in the cable shielding. This very small signal is then detected and correlated with the original signal transmitted on the inner conductor. The signals that leak out of the aperture, the damaged shield, and propagate down the outside of the cable are quantified as a function of the aperture size and frequency. A ferrite loaded toroidal sensor design is also proposed for receiving this external signal in order to both detect and localize the shield damage. Both simulations and measurements validate the effectiveness of this method.

  Unshielded discrete wires are another common type of transmission line. While unshielded wires are primarily used for DC power, they are still subject to degradation over time and require maintenance. Unlike shielded cables, there is a significant amount of coupling that occurs between adjacent wires during a reflectometry test. This coupling is quantified and evaluated for two applications.  The first is simultaneous testing of multiple adjacent wires in a bundle.  In this case, minimizing the coupling is desirable in order to reduce noise in the reflectometry signature.  The second is the exploration of the potential for a single reflectometry test to locate faults on adjacent wires without directly testing them.  When a single test is performed in a multi-wire bundle, the reflectometry signature will be a superposition of reflections from all nearby conductors. This thesis addresses the testing a multiconductor wiring structure with a common signal reference and with an isolated signal reference. In order to accurately detect faults on multiconductor wiring structures, both testing methods must be considered. A fault between a conductor and its reference conductor is easily detectable. A cross fault between two non-reference conductors is not. For cross fault consideration, the only method for detection is using a common signal reference and analyzing the data on adjacent lines.

  Thursday, May 2, 2013

2:00 p.m.

CS Conference Room

3105 MEB

UNIVERSITY OF UTAH

ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT

THESIS DEFENSE FOR THE DEGREE OF

MASTER OF SCIENCE

by

Je-Min Yoo

Advisor:  Florian Solzbacher

Laser Deinsulation of Parylene-C Coated Utah Electrode Array

Implantable microelectrode arrays are biomedical devices used in-vivo serving as neural interfaces between the nervous system and external systems such as neuroprosthetics. They are designed to be chronically implanted in the central or peripheral nervous system and record or stimulate neural signals. The Utah electrode array (UEA) is a representative example of silicon-based neural interfaces. They are typically encapsulated with the USP Class VI biocompatible material, Parylene-C, on the inactive areas to insulate and encapsulate the electrodes and minimize damage to the neural tissue. In order to record or stimulate neural signals, the active electrode sites must be deinsulated. Tip deinsulation of Parylene-coated UEAs is typically performed by a reactive ion etching (RIE) process using an O2 plasma, and an aluminum foil mask. This technique has limitations due to nonuniform tip exposure lengths contributing to large impedance variations (σ > 0.5 MΩ), and difficulty in controlling the magnitude of tip exposure, especially, for tip exposures less than 40 μm, which are needed to increase its selectivity in recording or stimulating single or multiple neurons. Moreover, foil masks cannot be used for more complex electrode geometries, such as variable height electrodes.

In this work, excimer laser ablation of Parylene from an UEA using a tip metallization of iridium oxide (IrOx) was investigated as an alternative deinsulation technique. A hybrid method of etching Parylene-C using a combination of laser ablation and the O2 RIE was investigated in the efforts to minimize electrode damage and remove carbonaceous residues. The median impedance for fine tip (< 20 µm) electrodes was ~ 4.6 MΩ immediately after laser ablation. However, significant amounts of carbon residue on the exposed surface were removed, generating improved impedances to ~ 0.7 MΩ by including a maskless RIE process using 1 min O2 RIE. 

We also observed that reduction of IrOx could occur at relatively mild (> 180 °C) temperatures in reducing ambients, resulting in dramatic changes to the structural and electrical properties of the tip metallization. The reduced IrOx material was found to tolerate significantly more laser irradiation than the fully oxidized material. The median impedance, cathodal charge storage capacity (CSCc), and charge injection capacity (CIC) for the reduced electrodes with 40 µm exposure were ~ 25 kΩ, ~ 40 mC/cm2, and ~ 0.8 mC/cm2, respectively. These results suggest that a hybrid laser ablation using an excimer laser and RIE is promising for deinsulation of UEAs. 

  Thursday, April 25, 2013

1:00 p.m.

SMBB Conference Room

4100 SMBB

UNIVERSITY OF UTAH

ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT

THESIS DEFENSE FOR THE DEGREE OF

MASTER OF SCIENCE

by

Most. Sultana Nasrin

Advisor:  Faisal Khan

Quantifying Component Degradation and Level of Aging in Power Converter Circuits Using Spread Spectrum Time Domain Reflectometry

Power converters are frequently exposed to electrical stresses such as over voltage, over current and switching impulses during their regular operations. These stresses may not result in immediate failure of a power converter. However over longer periods they cause gradual degradation of critical components inside the converter, which ultimately leads to a complete failure of the converter. Failure of a power converter might disrupt the operation of the entire system, occasionally causing catastrophic outcomes. Estimating a converter’s state of health and predicting the remaining life involves extensive research in semiconductor device physics and circuit theory, and is both important and challenging.

There is always a dire need to determine the level of aging in power converters so that an approximate time to failure could be predicted. A reflectometry technique was applied to power converters to identify failure and aging associated to critical components inside a power converter. In addition, mechanisms for gradual shift in measurable electrical parameters of power converter components over long durations have been studied under the scope of the project. While there exist several other techniques for predicting reliability and aging of power converters, they are limited to characterizing isolated components only. Whereas using the proposed technique, estimating the component degradation in energized circuits is possible. Spread spectrum time domain reflectometry (SSTDR) has been commercially used for detecting aircraft wiring faults during the last decade, however, it was never applied to components in a power converter. During the preliminary stage of this project SSTDR was applied to a DC-DC converter circuit, and several key parameters such as MOSFETs ON resistance was extracted to characterize MOSFET aging. Later on, this technique was applied to different other components in an H-bridge AC-AC converter for failure rate estimation and reliability analysis. The MTTF (mean time to failure) was calculated based on the SSTDR generated data.

The conducted research has initiated other SSTDR based prognostics and state of health measurement methods applicable to PV panels, electric machines and batteries.

  Wednesday, April 24, 2013

9:00 a.m.

ECE Conference Room

3235 MEB