Tunable narrowband spectral filtering across arbitrary optical wavebands is highly desirable in a plethora of applications, from chemical sensing and hyperspectral imaging to infrared astronomy. Yet, the ability to reconfigure the optical properties, with full reversibility, of a solid-state large-area narrowband filter remains elusive. Existing solutions require either moving parts, have slow response times, or provide limited spectral coverage. Here, we demonstrate a 1-inch diameter continuously tunable, fully reversible, all-solid-state, narrowband phase-change metasurface filter based on a GeSbTe-225 (GST)-embedded plasmonic nanohole array. The passband of the presented device is ∼ 74 n m with ∼ 70 % transmittance and operates across the 3–5 µm thermal imaging waveband. Continuous, reconfigurable tuning is achieved by exploiting intermediate GST phases via optical switching with a single nanosecond laser pulse, and material stability is verified through multiple switching cycles. We further demonstrate multispectral thermal imaging in the mid-wave infrared using our active phase-change metasurfaces. Our results pave the way for highly functional, reduced power, compact hyperspectral imaging systems and customizable optical filters for real-world system integration.
Laminar fuel-air counterflow diffusion flames (CFDFs) were studied using axisymmetric convergent-nozzle and straight-tube opposed jet burners (OJBs). The subject diagnostics were used to probe a systematic set of H m a -a i r CFDFs over wide ranges of fuel input (22 to 100% Ha), and input axial strain rate (130 to 1700 Us) just upstream of the airside edge, for both plug-flow and parabolic input velocity profiles. Laser Doppler Velocimetry (LDV) was applied along the centerline of seeded air flows from a convergent nozzle OJB (7.2 mm i.d.), and Particle Imaging Velocimetry (PIV) was applied on the entire airside of both nozzle and tube OJBs (7 and 5 mm i.d.1 to characterize global velocity structure. Data are compared to numerical results from a one-dimensional (1-D) CFDF code based on a stream function solution for a potential flow input boundary condition. Axial strain rate inputs at the airside edge of nozzle-OJB flows, using LDV and PIV, were consistent with 1-D impingement theory, and supported earlier diagnostic studies. The LDV results also characterized a heat-release hump. Radial strain rates in the flame substantially exceeded 1-D numerical predictions. Whereas the 1-D model closely predicted the max I min axial velocity ratio in the hot layer, it overpredicted its thickness. The results also support previously measured effects of plug-flow and parabolic input strain rates on CFDF extinction limits. Finally, the submillimeter-scale LDV and PIV diagnostics were tested under severe conditions, which reinforced their use with subcentimeter OJB tools to assess effects of aerodynamic strain, and fueVair composition, on laminar CFDF properties, including extinction. x = axial coordinate, cm. X(i) = mole fraction of species i, input jet.
A hybrid wing body transport aircraft model was tested in NASA Langley's 14 by 22Foot Subsonic Tunnel to evaluate proposed "low noise" technology. The experiment was set up to evaluate the community noise impact of the hybrid wing body design, as well as study the noise components of propulsion-airframe noise and shielding. A high fidelity 5.8-percent scale model, including landing gear, cruise and drooped wing leading edges, trailing edge elevons, vertical tail options, and engine noise simulators, was built to test both aerodynamic and acoustic configurations. The aerodynamic test data were used to establish appropriate flight conditions for the acoustic test.To accomplish the acoustic portion of this test, two major upgrades were required of NASA Langley's 14 by 22 Foot Subsonic Tunnel; first, a fuel delivery system to provide realistic gas temperatures to the jet engine simulators; and second, a traversing microphone array and side towers to measure full spectral and directivity noise characteristics.The results of this test provide benchmark hybrid wing body aircraft and noise shielding data to assist in achieving NASA's 2020 noise emission goals. I.
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