Over 2.5 billion people do not have access to safe and effective sanitation. Without a sanitary sewer infrastructure, self-contained modular systems can provide solutions for these people in the developing world and remote areas. Our team is building a better toilet that processes human waste into burnable fuel and disinfects the liquid waste. The toilet employs energy harvesting to produce electricity and does not require external electrical power or consumable materials. RTI has partnered with Colorado State University, Duke University, and Roca Sanitario under a Bill and Melinda Gates Foundation Reinvent the Toilet Challenge (RTTC) grant to develop an advanced stand-alone, self-sufficient toilet to effectively process solid and liquid waste. The system operates through the following steps: 1) Solid-liquid separation, 2) Solid waste drying and sizing, 3) Solid waste combustion, and 4) Liquid waste disinfection. Thermoelectric energy harvesting is a key component to the system and provides the electric power for autonomous operation. A portion of the exhaust heat is captured through finned heat-sinks and converted to electricity by thermoelectric (TE) devices to provide power for the electrochemical treatment of the liquid waste, pumps, blowers, combustion ignition, and controls.
The TWIST platform is an optical evanescent wave sensor which enables a label-free immunoassay-based portable
instrument. The approach is based on input grating coupler sensors serving as functionalized sensing devices. Binding of
the target analyte to the receptor-coated grating is detected by wavelength interrogation in the telecom spectral range.
We have demonstrated that high performance volumetric sensing can be achieved using a compact, low-cost telecom
laser as light source. The system footprint including light source, detectors and digitizers is compact. The platform is
amenable to multiplexed operation. We demonstrated a two-output system which enables detection of an analyte with an
on-chip reference signal.
A planar optical waveguide with an input grating coupler was used as an affinity-based
biodetection device. Nanoimprint lithography was used to integrate the grating patterns with
low loss silicon oxynitride thin-film waveguides. A widely tunable laser source at 1550nm was
used to characterize the device sensitivity to bulk medium changes, to thin film adsorption, and
to streptavidin protein. For each test, a comparison was performed between the sensitivity of
wavelength interrogation and the more standard angular interrogation approach. The effects of
surface reflections on the measured coupling curves were observed and interpreted, with
mitigation options being considered.
The use of coded apertures in a large area MWIR system introduces a number of difficulties including the effects of
diffraction and other distortions not observed in shorter wavelength systems. A new approach is being developed that
addresses the effects of diffraction while gaining the benefits of coded apertures, thus providing the flexibility to vary
resolution, possess sufficient light gathering power, and achieve a wide field of view (WFOV). The photonic MEMS
artificial eyelid array technology is currently being applied as the coded aperture in this program for surveillance
enabling technology development. Speed, lifetime, packaging and scalability are all critical factors for the MEMS eyelid
technology to determine system efficacy as well as military and commercial usefulness. The electronic eyelid is the
fundamental addressable unit for adaptive code generation and will allow the system to multiplex in time for increased
resolution. The proposed system consists of four subsystems in parallel with each subsystem consisting of four subapertures.
Each sub-aperture contains an artificial eyelid array capable of 36 different, independent patterns of open
500µm eyelids corresponding to 36 different look directions. Dynamic aperture arrays were fabricated on both quartz
and sapphire substrates for operation in the visible to MWIR. Both 8x8 and 40x40 element arrays were designed,
fabricated, and tested with the capability of 4, 8, and 16 unique pattern combinations. Process and device improvements
have been implemented to improve the yield of the MEMS arrays. In addition to mechanical evaluations, the eyelid
arrays were tested optically to demonstrate the capability of multiple look directions.
Extension of coded apertures to the MWIR introduces the effects of diffraction and other distortions not observed in
shorter wavelength systems. A new approach is being developed under the DARPA/SPO funded LACOSTE (Large
Area Coverage Optical search-while Track and Engage) program, that addresses the effects of diffraction while gaining
the benefits of coded apertures, thus providing flexibility to vary resolution, possess sufficient light gathering power, and
achieve a wide field of view (WFOV). The photonic MEMS "eyelid" array technology is currently being instantiated in
this DARPA Surveillance program study as the "heart", mediating the flow of the incoming signal. However, speed,
lifetime, packaging and scalability are critical factors for the MEMS "eyelid" technology which will determine system
efficacy as well as military and commercial usefulness. The electronic eyelid array is the fundamental addressable unit
for adaptive code generation and will allow the system to multiplex in time for increased resolution. The binary code
which determines whether a 500μm eyelid is open or closed is referred to as the "eyelid code." Groups of eyelids can
work together as a "super aperture" by virtue of a "macro-code." A macro code becomes relevant to describe how
dispersed eyelids across the 0.19m x 0.19m aperture will function together. Dynamic aperture arrays were fabricated on
both quartz and sapphire substrates for operation in the visible to MWIR. Both 8x8 and 40x40 element arrays were
designed, fabricated, and tested with macro-codes consisting of 4, 8, and 16 unique combinations. The die were
packaged and tested in ambient for robust eyelid operations. The point spread function was also measured in an optical
setup with the eyelid arrays located in the aperture plane.
This work focuses on the effects of custom-designed, two-dimensional grating structures on the sensitivity of optical
waveguides biosensors in the input grating coupler configuration. Calculations suggest that suitably designed diffractive
structures with optimum pitch in two orthogonal directions can increase the sensitivity of devices when compared to a
conventional one-dimensional grating under the same conditions. A set of six diffractive structures designed for 1550 nm
wavelength were fabricated by thermal nano-imprint lithography on silicon oxynitride waveguides; the silicon master
stamp was patterned by deep UV stepper lithography. Preliminary experimental results indicate a sensitivity
enhancement of a factor two due to the 2D diffractive couplers.
Grating-based optical waveguide devices offer label-free biodetection capabilities relying on optical
response to adsorption of analytes and corresponding changes of refractive index. Various
configurations of this measurement approach were explored with the goal of obtaining a
miniaturized system. In particular, we evaluated the use of a two-dimensional grating coupler both
experimentally and theoretically. Design criteria for optimized sensing structures are presented.
Silicon oxynitride optical waveguides with a grating coupler were used for a label-free detection approach that measures the change of refractive index at the grating surface. Two approaches were used for the grating fabrication: (i) commercially available linear gratings were used as stamps for imprint lithography and the pattern was transferred by dry-etching; (ii) polystyrene microspheres self-assembly in an ordered close-packed array was exploited to obtain a two-dimensional grating with hexagonal symmetry. Optical coupling into slab waveguides of both visible (633nm) and tunable infrared (1550 nm) lasers was characterized as a function of incident angle in a custom-made automated apparatus. Sensitivity to different aqueous solutions was demonstrated with low loss waveguides fabricated using low-frequency plasma-enhanced chemical vapor deposition. The exploitation of the tunability of telecom infrared lasers and of the two-dimensional hexagonal grating coupler has the ultimate goal of providing a high performance, compact sensor that does not require mechanical moving parts.
KEYWORDS: Composites, Actuators, Particles, Glasses, Polymers, Photonic crystals, Crystals, Simulation of CCA and DLA aggregates, Spectroscopy, Reflectivity
Physically robust photonic bandgap (PBG) composites based on electrostatically stabilized polymeric colloidal particles are presented. The glass transition (Tg)of the composites can be varied over a large temperature range through the selection of the monomer(s) used to fabricate the composite. Composites with a subambient Tg exhibited a mechanochromic response and were integrated with a peizoelectric actuator to produce a prototype device which exhibited a fully reversible tunable rejection wavelength, capable of a ca. +/- 86 nm (172 nm full range)stop band shift.
Highly oriented, (100) textured diamond films have been grown on single-crystal Si substrates via microwave plasma enhanced chemical vapor deposition. A multistep deposition process including bias-enhanced nucleation and textured growth was used to obtain smooth films consisting of epitaxial grains with only low-angle grain boundaries. Boron-doped layers were selectively deposited onto the surface of these oriented films and temperature-dependent Hall effect measurements indicated a 3 to 5 times improvement in hole mobility over polycrystalline films grown under similar conditions. Room temperature hole mobilities between 135 and 278 cm2/V-s were measured for the highly oriented samples as compared to 2 to 50 cm2/V-s for typical polycrystalline films. Grain size effects and a comparison between the transport properties of polycrystalline, highly oriented and homoepitaxial films will be discussed. Metal-oxide- semiconductor field-effect transistors were then fabricated on the highly oriented films and exhibited saturation and pinch-off of the channel current.
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