In the functional 3D-printing field, poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) has been shown to be a more promising choice of material over polyvinylidene fluoride (PVDF), due to its ability to be poled to a high level of piezoelectric performance without a large mechanical strain ratio. In this work, a novel presentation of in situ 3D printing and poling of PVDF-TrFE is shown with a d${}_{33}$ performance of up to 18 pC N${}^{-1}$, more than an order of magnitude larger than previously reported in situ poled polymer piezoelectrics. This finding paves the way forward for pressure sensors with much higher sensitivity and accuracy. In addition, the ability of in situ pole sensors to demonstrate different performance levels is shown in a fully 3D-printed five-element sensor array, accelerating and increasing the design space for complex sensing arrays. The in situ poled sample performance was compared to the performance of samples prepared through an ex situ corona poling process.

We report the latest progress on fabrication of rare earth doped single crystal yttrium aluminum garnet (YAG) core/undoped YAG cladded fibers. Rare-earth doped single crystal core fibers were grown with laser heated pedestal growth methods. In a second step, epitaxial methods were used to grow a single crystalline undoped YAG cladding onto the core fiber. Hydrothermal and liquid phase epitaxy methods utilize the core doped fiber as the seed. X-ray diffraction of cladding reveals an equilibrium (110) morphology. Energy-dispersive X-ray spectroscopy analysis shows there is minimal diffusion of rare-earth dopants into the cladding structure. The use of scandium doping is shown to substitute at the Al³⁺ site, thereby allowing an additional tunability of refractive index of core structure material besides conventional Y³⁺ site dopants. The use of these epitaxial growth methods enables material compatibility, tuning of refractive index, and conformal growth of cladding structures onto core fibers for optical devices.

Recent work at the U.S. Naval Research Laboratory studied atmospheric turbulence on dynamic links with the goal of developing an optical anemometer and turbulence characterization system for unmanned aerial vehicle (UAV) applications. Providing information on the degree of atmospheric turbulence, as well as wind information and scintillation, in a low size, weight and power (SWaP) system is key for the design of a system that is also capable of adapting quickly to changes in atmospheric conditions. The envisioned system consists of a bi-static dynamic link between a transmitter (Tx) and a receiver (Rx), relying on a small UAV. In a dynamic link, the propagation distance between the Tx/Rx changes rapidly. Due to SWaP constraints, a monostatic system is challenging for such configurations, so we explored a system in which the Tx/Rx is co-located on a mobile platform (UAV), which has a mounted retroreflector. Beam divergence control is key in such a system, both for finding the UAV (increased beam divergence at the Tx) and for signal optimization at the Rx. This led us to the concept of using adaptive/active elements to control the divergence at the Tx but also to the implementation of an adaptive/active retroreflector in which the return beam divergence can be controlled in order to optimize the signal at the Rx. This paper presents the design, fabrication and characterization of a low SWaP adaptive retroreflector.

Solid oxide fuel cells (SOFCs) can generate electricity efficiently and with broad fuel flexibility, but practical applications require them to be more durable and resistant to degradation when subjected to impurities. In order to better understand poisoning mechanisms and guide strategies for developing more durable materials and devices, we have used operando optical methods combined with electrochemical measurements and exhaust gas analysis to investigate the effects of chlorine and sulfur on Ni/YSZ anodes in high temperature (700 °C) SOFCs. The effects of chlorine contamination were found to be more severe for methane than hydrogen operation based on studies of anode-supported Ni/YSZ SOFCs with 100-300 ppm CH₃Cl. Reduced anode activity was indicated by suppressed carbon formation from Raman measurements and fewer oxidation products from infrared emission results. Evidence regarding the degradation mechanism is provided by the differences in recovery for hydrogen and methane. The anode activity is also reduced for operation on methane in the presence of 170 ppm H₂S during both electrochemical and stream removal of carbon. Changes in endothermic methane cracking reactions at the anode are monitored with near infrared thermal imaging while gas and surface species are observed with infrared emission spectroscopy, thereby providing some of the first operando studies of sulfur effects on SOFC anodes.

While solid oxide fuel cells (SOFCs) promise efficient electricity production and high fuel flexibility, trace sulfur and chlorine constituents commonly found in desirable fuel sources such as syngas and biogas pose challenges. Sulfur poisoning is a well-established phenomenon that can lead to rapid loss of electrochemical performance in SOFCs that operate at high temperatures (650 – 800 °C). State-of-the-art Ni/YSZ (yttrium stabilized zirconia) anodes lose significant catalytic activity upon exposure to even ppm-levels of H₂S, but details regarding how the catalyst degrades and the specific effects on electro-catalytic processes remain unclear. One approach to solving this shortcoming is to understand the degradation mechanisms through real time correlation of electrochemical performance with in situ, molecular specific observations. This current study uses infrared emission from the Ni/YSZ anode surface of an operating SOFC to simultaneously characterize 1) gas species using Fourier transform infrared emission spectroscopy (FTIRES) and 2) temperature changes using near infrared (NIR) thermal imaging. These data are collected with electrochemical potential when the SOFC is operated at 75% maximum current at 700 °C using CH₄, with and without 170 ppm H₂S added. In situ FTIRES measurements show that the CO₂ oxidation product and the CO electrochemical intermediate are suppressed when cell potential deteriorates with H₂S present. Simultaneous NIR thermal imaging measurements of surface temperatures show that cooling also reflects evolving processes at the anode. After each trial, electrochemical oxidation of deposited carbon showed that H₂S also hindered carbon accumulation. These results together have begun to provide direct insight into how sulfur poisoning affects electrochemical processes in SOFCs through correlations of electrochemical potential, surface temperature changes, and gas species at the anode.

Vibrational Raman spectroscopy, IR emission spectroscopy and near IR thermal imaging coupled with voltammetry and impedance measurements was used to explore the effects of chlorine on electrolyte supported solid oxide fuel cell (SOFC) performance and durability. Ni-YSZ SOFC anodes were exposed to 110 ppm dry CH₃Cl at 650°C and 700˚C for up to four hours while intermittently exposing the cell to either methane (CH₄) or a biogas surrogate (methane/carbon dioxide; 50:50 by mole fraction) for ten minute intervals. In these experiments Raman spectroscopy was used to monitor carbon accumulation kinetics. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements performed with cells at 650˚C operating with CH₄ (and exposed to CH­₃Cl) showed marked degradation. Degradation with biogas was even more aggressive. In both instances, degradation was irreversible as removal of the chlorine source did not result in complete recovery of performance. These findings stand in contrast to previously reported results of SOFCs operating with H₂ in the presence of a chlorine contaminant. Curiously, at 700˚C degradation slows significantly with cell performance diminishing slightly before reaching an asymptotic limit. These results suggest that the presence of carbon facilitates formation of volatile nickel chloride species resulting in substantive damage to anode microstructure.