Publications

Proposed for publication in Journal of Manufacturing Processes.

Prasad, Somuri V.; Prasad, Somuri V.; Christenson, Todd R.; Dugger, Michael T.

Abstract not provided.

Stein, David J.; Okandan, Murat O.; Wessendorf, Kurt O.; Christenson, Todd R.; Lemp, Thomas K.; Shul, Randy J.; James, Conrad D.; Myers, Ramona L.

Retinal prosthesis projects around the world have been pursuing a functional replacement system for patients with retinal degeneration. In this paper, the concept for a micromachined conformal electrode array is outlined. Individual electrodes are designed to float on micromachined springs on a substrate that will enable the adjustment of spring constants-and therefore contact force-by adjusting the dimensions of the springs at each electrode. This also allows the accommodation of the varying curvature/topography of the retina. We believe that this approach provides several advantages by improving the electrode/tissue interface as well as generating some new options for in-situ measurements and overall system design.

TRANSDUCERS 2003 - 12th International Conference on Solid-State Sensors, Actuators and Microsystems, Digest of Technical Papers

Okandan, Murat O.; Wessendorf, Kurt O.; Christenson, Todd R.; Lemp, T.; Shul, Randy J.; Baker, M.; James, Conrad D.; Myers, Ramona L.; Stein, David J.

Retinal prosthesis projects around the world have been pursuing a functional replacement system for patients with retinal degeneration. In this paper, the concept for a micromachined conformal electrode array is outlined. Individual electrodes are designed to float on micromachined springs on a substrate that will enable the adjustment of spring constants-and therefore contact force-by adjusting the dimensions of the springs at each electrode. This also allows the accommodation of the varying curvature/topography of the retina. We believe that this approach provides several advantages by improving the electrode/tissue interface as well as generating some new options for in-situ measurements and overall system design.

Prasad, Somuri V.; Prasad, Somuri V.; Christenson, Todd R.; Dugger, Michael T.; Michael, Joseph R.; Vanecek, Charles W.

Abstract not provided.

Proceedings of SPIE - The International Society for Optical Engineering

Kemme, S.A.; Spahn, Olga B.; Christenson, Todd R.; Sweatt, W.C.; Wendt, J.R.; Peters, D.W.; Carter, T.R.; Samora, S.

The design and on-going fabrication of an opto-electro-mechanical microsystem that acts as a four-function optical fiber switch will be presented. The four functions of the 2×2 optical switch include 1) Normal mode, where channel A and channel B pass light straight through, 2) Loopback mode, where light originating in channel A is detected in the B leg, 3) Monitor A mode, where a probe pulse is inserted into channel B and any reflections are detected in the A leg, and 4) Monitor B mode, the compliment of 3) above. The Monitor A and Monitor B modes allow the microsystem to operate as an Optical Time Domain Reflectometer (OTDR). High spatial frequency gratings etched in fused silica configure the light beams through free-space substrate-mode propagation. The design for an OTDR-mode transmission grating that normally passes light from an incidence angle of 45 degrees within the silica substrate as well as passes light from a normal incidence straight through the silica will be discussed. A miniature commercial drive motor, positioned with LIGA alignment plates, rotates the optical grating disk into one of the four implemented function positions. The impact of required tolerances and packaging limitations on the optics, LIGA alignment plates, and the complete microsystem will be presented.

Shul, Randy J.; Kravitz, Stanley H.; Christenson, Todd R.; Schubert, William K.; Casalnuovo, Stephen A.; Wessendorf, Kurt O.; Zipperian, Thomas E.

Abstract not provided.

Fang, H.E.; Miller, Samuel L.; Dugger, Michael T.; Prasad, Somuri V.; Reedy, Earl D.; Thompson, Aidan P.; Wong, Chungnin C.; Yang, Pin Y.; Battaile, Corbett C.; Battaile, Corbett C.; Benavides, Gilbert L.; Ensz, M.T.; Buchheit, Thomas E.; Chen, Er-Ping C.; Christenson, Todd R.; De Boer, Maarten P.

This report summarizes materials issues associated with advanced micromachines development at Sandia. The intent of this report is to provide a perspective on the scope of the issues and suggest future technical directions, with a focus on computational materials science. Materials issues in surface micromachining (SMM), Lithographic-Galvanoformung-Abformung (LIGA: lithography, electrodeposition, and molding), and meso-machining technologies were identified. Each individual issue was assessed in four categories: degree of basic understanding; amount of existing experimental data capability of existing models; and, based on the perspective of component developers, the importance of the issue to be resolved. Three broad requirements for micromachines emerged from this process. They are: (1) tribological behavior, including stiction, friction, wear, and the use of surface treatments to control these, (2) mechanical behavior at microscale, including elasticity, plasticity, and the effect of microstructural features on mechanical strength, and (3) degradation of tribological and mechanical properties in normal (including aging), abnormal and hostile environments. Resolving all the identified critical issues requires a significant cooperative and complementary effort between computational and experimental programs. The breadth of this work is greater than any single program is likely to support. This report should serve as a guide to plan micromachines development at Sandia.

Christenson, Todd R.; Garino, Terry J.; Venturini, Eugene L.

A microfabrication process is described that provides for the batch realization of miniature rare earth based permanent magnets. Prismatic geometry with features as small as 5 microns, thicknesses up through several hundred microns and with submicron tolerances may be accommodated. The processing is based on a molding technique using deep x-ray lithography as a means to generate high aspect-ratio precision molds from PMMA (poly methyl methacrylate) used as an x-ray photoresist. Subsequent molding of rare-earth permanent magnet (REPM) powder combined with a thermosetting plastic binder may take place directly in the PMMA mold. Further approaches generate an alumina form replicated from the PMMA mold that becomes an intermediate mold for pressing higher density REPM material and allows for higher process temperatures. Maximum energy products of 3--8 MGOe (Mega Gauss Oersted, 1 MGOe = 100/4{pi} kJ/m{sup 3}) are obtained for bonded isotropic forms of REPM with dimensions on the scale of 100 microns and up to 23 MGOe for more dense anisotropic REPM material using higher temperature processing. The utility of miniature precision REPMs is revealed by the demonstration of a miniature multipole brushless DC motor that possesses a pole-anisotropic rotor with dimensions that would otherwise prohibit multipole magnetization using a multipole magnetizing fixture at this scale. Subsequent multipole assembly also leads to miniaturized Halbach arrays, efficient magnetic microactuators, and mechanical spring-like elements which can offset miniaturized mechanical scaling behavior.