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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records

FAIR Data and Interpretable AI Framework for Architectured Metamaterials

Our interdisciplinary effort successfully generated FAIR (Findable, Accessible, Interoperable, and Reusable) benchmark datasets for mechanical metamaterials while introducing a novel Artificial Intelligence (AI) framework known as Learning Refined Compositional Rules (LRCR). This framework was specifically designed to bridge the gap across varying computational length scales and extract the underlying physical mechanisms that connect a material's structural geometry to its bulk acoustic properties. Historically, the discovery of such structured materials relied heavily on human intuition or opaque, black-box optimization algorithms that were difficult to generalize. By combining interpretable machine learning techniques with rigorous experimental validation, this project established clear, generalizable design guidelines for tuning wave dispersion and controlling vibrations. Ultimately, the public availability of these structured datasets and algorithms will significantly reduce computational costs and accelerate the design of advanced multi-functional acoustic devices, offering broad societal impacts across fields like aerospace engineering, telecommunications, and biomedical implant design.

36 MATERIALS SCIENCE↗

High-bandwidth density silicon photonic resonators for energy-efficient optical interconnects

The growth of artificial intelligence applications demands ever larger and more complex deep learning models, dominating today's—and tomorrow's—data center and high-performance computing systems. While traditional electronics are failing to keep pace with application demands, silicon photonic (SiPh) interconnects have emerged as a necessary technology to support these systems. SiPh-driven wavelength-division multiplexing (WDM) offers a particularly promising path toward supporting incredibly high-aggregate link bandwidth in a compact and efficient form factor. One of the basic building blocks of these integrated WDM interconnects is the SiPh resonator. Their inherent wavelength selectivity and compact footprint allow for efficient data transmission multiplexed across dozens of carrier wavelengths. Used as add-drop (AD) filters, SiPh resonators are critical to constructing integrated tunable wavelength-selective optical circuit switches as well as for demultiplexing the different carrier wavelengths toward independent wavelength-insensitive photodiodes in a dense wavelength-division multiplexing receiver. Resonators in the all-pass (AP) configuration are widespread as well, allowing for wavelength-selective modulation to drive aggregate link bandwidths far beyond the individual channel data rate. Unlike SiPh Mach–Zehnder modulators (MZM), resonant modulators can be driven using low, complementary metal-oxide-semiconductor drive voltages, allowing for tight co-integration between photonic integrated circuits, fabricated with larger process node technologies, and electronic integrated circuits, designed to exploit the advantages of the latest node. To push toward practical peta-scale interconnects, a comprehensive review of SiPh resonators is required, addressing bottlenecks and design constraints at both the architecture and device levels. We first describe the predominant integrated link architectures and identify their limits. We then discuss the device-level design considerations that can be made for both AD and AP configuration resonators to overcome the system level limits with novel resonator device designs. Analytical models and numerical simulation of resonators are validated by experimental measurement of devices fabricated in a commercial 300-mm foundry, showing a clear path toward volume manufacturing. The demonstrated resonant modulators and filters support the feasibility of increasing the aggregate bandwidth of resonator-driven SiPh interconnects into the peta-scale regime.

42 ENGINEERING↗

Non-degenerate parametric mixing and Q-enhancement in ALN Lamb wave resonator

In this Letter, we explore a non-degenerate phase independent parametric quality factor (Q)-enhancement technique for aluminum nitride (AlN) Lamb wave resonators. Unlike other active Q-enhancement techniques which require precise phase control of the electronic feedback loop, this technique is implemented by parametrically pumping AlN material stiffness to realize a negative resistance seen at the signal path. The negative resistance is dependent on the nonlinear material modulation and multi-resonance coupling in the device. A nonlinear circuit model is developed to simulate the parametric coupling of each resonance and extract the nonlinearity of AlN from experimental data. With proper pump frequency and pump power, the device quality factor is boosted in both simulation and experiment. The demonstrated Q-enhancement method is simple to implement and can be applied to other types of resonators that have nonlinear behavior and support multi-resonance operation.

42 ENGINEERING↗

Two-frequency RF fields induced multipactor in coaxial transmission lines

This study presents a comprehensive investigation of two-surface multipactor discharge in coaxial transmission lines under two-frequency radio frequency (RF) excitation using one-dimensional Monte Carlo simulations validated against three-dimensional particle-in-cell simulations and experimental data. The results show that introducing a second carrier mode can suppress multipactor by reshaping and shrinking the susceptibility region, with the extent and location of suppression strongly dependent on the device's aspect ratio and the relative phase of the second carrier mode. Distinct suppression patterns are observed across different fd regimes, while in some cases, susceptibility expansion also occurs under two-frequency operation. A key outcome is the identification and delineation of pure and mixed multipactor modes in coaxial geometry, where analytical mode boundaries are not readily available. Unlike planar geometries, pure-mode regions in coaxial systems overlap with mixed-mode domains, complicating mode identification. Additionally, image charge forces are found to have negligible influence on susceptibility thresholds but strongly affect electron growth rates. These findings offer valuable insights into the use of waveform engineering for controlling multipactor in high-power RF systems.

43 PARTICLE ACCELERATORS↗

Quasi-deterministic localization of Er emitters in thin film TiO 2 through submicron-scale crystalline phase control

With their shielded 4f orbitals, rare-earth ions (REIs) offer optical and electron spin transitions with good coherence properties even when embedded in a host crystal matrix, highlighting their utility as promising quantum emitters and memories for quantum information processing. Among REIs, trivalent erbium (Er 3+ ) uniquely has an optical transition in the telecom C-band, ideal for transmission over optical fibers, making it well suited for applications in quantum communication. The deployment of Er 3+ emitters into a thin film TiO 2 platform has been a promising step toward scalable integration; however, like many solid-state systems, the deterministic spatial placement of quantum emitters remains an open challenge. Here, we investigate laser annealing as a means to locally tune the optical resonance of Er 3+ emitters in TiO 2 thin films on Si. Using both nanoscale x-ray diffraction measurements and cryogenic photoluminescence spectroscopy, we show that tightly focused below-gap laser annealing can induce anatase to rutile phase transitions in a nearly diffraction-limited area of the films and improve local crystallinity through grain growth. As a percentage of Er:TiO 2 is converted to rutile, the Er 3+ optical transition blueshifts by 13 nm. We explore the effects of changing laser annealing time and show that the amount of optically active Er:rutile increases linearly with laser power. We additionally demonstrate local phase conversion on microfabricated Si structures, which holds significance for quantum photonics.

36 MATERIALS SCIENCE↗

Color center in β -Ga 2 O 3 emitting at the telecom range

Transition metal (TM) ions incorporated into a host from a wide bandgap semiconductor are recognized as a promising system for quantum technologies with enormous potential. In this work, we report on a TM color center in β-Ga 2 O 3 with physical properties attractive for quantum information applications. The center is found to emit at 1.316 μm and exhibits weak coupling to phonons, with optically addressable higher-lying excited states, beneficial for single-photon emission within the telecom range (O-band). Using magneto-photoluminescence (PL) complemented by time-resolved PL measurements, we identify the monitored emission to be internal 1 E→ 3 A 2 spin-forbidden transitions of a 3d 8 TM ion with a spin-triplet ground state—a possible candidate for a spin qubit. We tentatively attribute this color center to a complex involving a sixfold coordinated Cu 3+ ion.

36 MATERIALS SCIENCE↗