Daniel J. Dickrell

Electrical Contact Resistance Degradation of a Hot-Switched Simulated Metal MEMS Contact

Electrical contact resistance testing was performed by hot-switching a simulated gold-platinum metal microelectromechanical systems contact. The experimental objective was to determine the sensitivity of the contact resistance degradation to current level and environment. The contact resistance increased sharply after 100hot-switched cycles in air. Hot-switching at a reduced current and in nitrogen atmosphere curtailed contact resistance degradation by several orders of magnitude. The mechanism responsible for the resistance degradation was found to be arc-induced decomposition of adsorbed surface contaminants

Direct Contact-Area Computation for MEMS Using Real Topographic Surface Data

Direct computation of interfacial contact area for microelectromechanical-system applications was performed numerically using the measured device surface topography and the material hardness to define the flow stress of an individual element. The simulation results compared well with the established contact-area determination methods and also introduced new capabilities that enabled the visualization of the spatial distribution of contact spots to be computationally mapped and rendered directly onto device surfaces.

Evolution of Wear in a Two-Dimensional Bushing

A model for the evolution of wear for the shaft and bushing for a simple two-dimensional bushing system was developed under the assumptions of uniform contact pressure and constant applied load. A simple laboratory apparatus was constructed to test the model. Two experiments were run; one showed wear on the shaft only and the other showed wear on the bushing only. The results showed the predicted linear progression of wear.

Silicone Oil Contamination and Electrical Contact Resistance Degradation of Low-Force Gold Contacts

Hot-switched low-force gold electrical contact testing was performed using a nanomechanical test apparatus to ascertain the sensitivity of simulated microelectromechanical systems (MEMS) contact to silicone oil contamination. The observed cyclic contact resistance degradation was dependent on both closure rate and noncontact applied voltage. The decomposition of silicone oil from electrical arcing was hypothesized as the degradation mechanism

The Electrical Contact Resistance of Two Rough Surfaces with Varying Phase Conductivity

Electrical contact materials deposited via thin-film processes enable the structuring of interfaces that optimize electrical contact performance. The performance gains are accomplished by structuring the contact material such that a conductive pathway is always present in the composite, a phenomenon related to the percolation threshold. The relationship between film composition and percolation threshold was explored by combined three-dimensional contact area and resistance modeling as well as experimental efforts. An optimal composite structure was found based on deposition parameters and compositional phase selections.

An image-based software tool for screening retinal fundus images using vascular morphology and network transport analysis

As the number of digital retinal fundus images taken each year grows at an increasing rate, there exists a similarly increasing need for automatic eye disease detection through image-based analysis. A new method has been developed for classifying standard color fundus photographs into both healthy and diseased categories. This classification was based on the calculated network fluid conductance, a function of the geometry and connectivity of the vascular segments. To evaluate the network resistance, the retinal vasculature was first manually separated from the background to ensure an accurate representation of the geometry and connectivity. The arterial and venous networks were then semi-automatically separated into two separate binary images. The connectivity of the arterial network was then determined through a series of morphological image operations. The network comprised of segments of vasculature and points of bifurcation, with each segment having a characteristic geometric and fluid properties. Based on the connectivity and fluid resistance of each vascular segment, an arterial network flow conductance was calculated, which described the ease with which blood can pass through a vascular system. In this work, 27 eyes (13 healthy and 14 diabetic) from patients roughly 65 years in age were evaluated using this methodology. Healthy arterial networks exhibited an average fluid conductance of 419 ± 89 μm3/mPa-s while the average network fluid conductance of the diabetic set was 165 ± 87 μm3/mPa-s (p < 0.001). The results of this new image-based software demonstrated an ability to automatically, quantitatively and efficiently screen diseased eyes from color fundus imagery.