Abstract : Continuous-filament Cu-Nb and Cu-Ag composites were fabricated as candidate high strength electrical conductors. Microfilamentary Cu-Nb composites achieved remarkable strength levels while maintaining good electrical conductivity. By examining the superconducting properties of the Cu-Nb composites, it was determined that some recovery processes were active in the Nb fibers at relatively low annealing temperatures. However, the fine-filament Cu- Nb wires exhibited excellent pulsed current capabilities. A novel testing regime called pulsed current fatigue demonstrated the impact of composite design and pulse conditions on pulsed current lifetime. Cu-Ag composites were fabricated to provide a higher conductivity alternative to Cu-Nb. Although the CU-AG results were promising, a second-generation composite is needed to extend the benefits to the highest strength levels.
Abstract Chronic implantation of intracortical microelectrode arrays (MEAs) capable of recording from individual neurons can be used for the development of brain-machine interfaces. However, these devices show reduced recording capabilities under chronic conditions due, at least in part, to the brain’s foreign body response. This creates a need for MEAs that can minimize the foreign body response to enable long-term recording. A potential approach to reduce the foreign body response is the use of ultrathin MEAs. Here, we fabricated ultrathin (cross-sectional area: 160 µm 2 ) amorphous silicon carbide (a-SiC) MEAs with sixteen electrode channels and implanted them into the motor cortex of seven female Sprague-Dawley rats. A-SiC was chosen as the fabrication base for its high chemical stability, good electrical insulation properties, and amenability to thin film fabrication techniques. Electrochemical analysis and neural recordings were performed weekly for 4 months. MEAs were characterized in vitro pre-implantation and in vivo using electrochemical impedance spectroscopy and cyclic voltammetry at 50 mV/s and 50,000 mV/s. Neural recordings were analyzed for single unit activity. At the end of the study, animals were sacrificed for immunohistochemistry analysis. We observed statistically significant, but small, increases in 1 and 30 kHz impedance values and 50,000 mV/s charge storage capacity over the 16-week implantation period. Slow sweep 50 mV/s CV and 1 Hz impedance did not significantly change over time. Impedance values increased from 11.6 MΩ to 13.5 MΩ at 1 Hz, 1.2 MΩ to 2.9 MΩ at 1 kHz, and 0.11 MΩ to 0.13 MΩ at 30 kHz over 16 weeks. The median charge storage capacity of the implanted electrodes at 50 mV/s were 58.1 mC/cm 2 on week 1 and 55.9 mC/cm 2 on week 16, and at 50,000 mV/s were 4.27 mC/cm 2 on week 1 and 5.93 mC/cm 2 on week 16. Devices were able to record neural activity from 92% of all active channels at the beginning of the study, At the study endpoint, a-SiC devices were still recording single-unit activity on 51% of electrochemically active electrode channels. In addition, we observed that the signal-to-noise ratio experienced a small decline of only −0.19 per week. We also classified the units as fast and slow spiking based on the trough-to-peak time. Although the overall presence of single units declined, fast and slow spiking units declined at a similar rate. Furthermore, immunohistochemistry showed minimal foreign body response to the a-SiC devices, as highlighted by statistically insignificant differences in activated glial cells between implanted brains slices and contralateral sham slices, as evidenced by GFAP staining. NeuN staining revealed the presence of neural cell bodies close to the implantation site, again statistically not different from a contralateral sham slice. These results support the use of ultrathin a-SiC MEAs for long-term implantation and use in brain-machine interfaces.
Thin metal plates (flyers) were launched from an aluminum-coated glass support using nanosecond and picosecond Nd: yttrium aluminum garnet laser pulses at 1.06 μm. The velocity of the flyers was measured as a function of incident fluence and of the delay between two consecutive laser pulses using a time-of-flight method. Profilometric scans of the craters formed on the substrate provided an accurate mapping of the crater’s morphology and enabled a realistic estimation of the flyer’s mass. The combination of these measurements allowed the determination of the flyer’s kinetic energy and hence the efficiency of the launching process as a function of the initiating laser’s energy. Threshold fluences of 1.3–2.0J∕cm2 and acceleration efficiencies up to 0.45 were measured under our experimental conditions. The results show that acceleration efficiency rises with the energy of initiating laser and drops when the delay time between two pulses of 10-ns full width at half maximum becomes larger. The acceleration efficiency is also reduced (relative to a 10-ns laser pulse) when the process is initiated by a single 20-ps pulse. On the basis of these data we assume that the launching efficiency may be optimized by using 2-ps laser pulses with a subnanosecond delay time between them.
This article reviews the electrochemistry and optical switching performance of variable transmittance electrochromic devices based on the a-WO{sub 3}/a-IrO{sub 2} (a = amorphous) combination of electrochromic materials. The review concentrates on past research at EIC Laboratories on a-WO{sub 3}/a-IrO{sub 2} devices containing polymeric proton (H{sup +}) conductors with an ancillary discussion of devices using c-K{sub x}WO{sub 3+(x/2)} and the mixed oxide a-Mo{sub x}W{sub 1{minus}x}O{sub 3} as the primary electrochromic material. Approximately one half of the data presented has not been published previously, with the remaining data taken from articles in earlier SPIE volumes and the journal Solar Energy Materials. In recent years, there has been considerable interest in the development of electrochromic devices for control of solar throughput in building windows and for automotive applications. This review is concerned with complementary electrochromic windows based on cathodically coloring WO{sub 3} in combination with anodically coloring IrO{sub 2}. In the complementary configuration, both electrochromic materials participate in the coloration process, enhancing the efficiency of optical modulation while providing intrinsic charge-balance.
This paper describes recent results from the Extremely High Temperature Photonic Crystal System Technology (XTEMPS) technology program. The XTEMPS program has developed a Photonic Crystal (PhC) based high efficiency IR emitter array for use in the emerging generation of wide field of view high performance scene projectors. Cyan's approach provides high dynamic range, multispectral emission from SWIR to LWIR and is uniquely capable of accurately simulating very realistic system spectral signatures. The PhC array is fabricated from refractory materials to provide high radiance and long service lifetime. Cyan is teamed with Sandia National Laboratories for design and fabrication of the emitter and with Nova sensors to utilize their advanced Read In Integrated Circuit (RIIC). PhC based emitters show improved inband output power efficiency when compared to broad band "graybody" emitters due to the absence of out-of-band emission. Less electrical power is required to achieve high operating temperature, and non-Lambertian emission pattern puts a large fraction of the emitted energy into a straight ahead beam. Both effects significantly boost effective radiance output. Cyan has demonstrated pixel designs compatible with Nova's medium format RIIC, which ensures high apparent output temperatures with modest drive currents and low operating voltages of less than five volts. Unit cell pixel structures for high radiative efficiency have been demonstrated and arrays using PhC optimized for up to four spectral bands have been successfully patterned and fabricated into high yield wafers.
Objective. With ever increasing applications of neural recording and stimulation, the necessity for developing neural interfaces with higher selectivity and lower invasiveness is inevitable. Reducing the electrode size is one approach to achieving such goals. In this study, we investigated the effect of electrode geometric surface area (GSA), from 20 μm2 to 1960 μm2, on the electrochemical impedance and charge-injection properties of sputtered iridium oxide (SIROF) coated electrodes in response to current-pulsing typical of neural stimulation. These data were used to assess the electrochemical properties of ultra-small SIROF electrodes (GSA < 200 μm2) for stimulation and recording applications. Approach. SIROF charge storage capacities (CSC), impedance, and charge-injection characteristics during current-pulsing of planar, circular electrodes were evaluated in an inorganic model of interstitial fluid (model-ISF). Main results. SIROF electrodes as small as 20 μm2 could provide 1.3 nC/phase (200 μs pulse width, 0.6 V versus Ag|AgCl interpulse bias) of charge during current pulsing. The 1 kHz impedance of all electrodes used in this study were below 1 MΩ, which is suitable for neural recording. Significance. Ultra-small SIROF electrodes are capable of charge injection in buffered saline at levels above some reported thresholds for neural stimulation with microelectrodes.
Commercial production quantities of Sn-core-processed MF Nb 3 Sn have recently been manufactured and delivered. The 1.73 mm (0.068") diameter strand contains 721 02, 2 micron filaments and 49% stabilizing copper protected by a diffusion barrier. Critical current density in the filament bronze region can be optimized to exceed 2×10 5 amps/cm 2 at 10 Tesla 4.2 K and 3.7 × 10 4 amps/ cm 2 at 14 Tesla 4.2 K. Critical current as a function of applied tensile strain has been measured at 14 Tesla 4.2 K on samples of this material drawn to 0.36 mm (0.014") diameter. The peak in the Jc-ε curve occurs at ε = 0.28% and Jc = 1.25 Jc o .
Penetrating multielectrode arrays with electrode coatings of sputtered iridium oxide (SIROF) have been implanted chronically in cat cortex for periods over 300 days. The ability of these electrodes to inject charge at levels above expected thresholds for neural excitation has been examined in vivo by measurements of voltage transients in response to current-controlled, cathodal stimulation pulsing. The effect of current pulse width from 150 (is to 500 (is and voltage biasing of the electrodes in the interpulse period at two levels, 0.0 V and 0.6 V vs. Ag|AgCl, were also investigated. The results of in vivo characterization of the electrodes by open-circuit potential measurements, cyclic voltammetry and impedance spectroscopy are also reported.
