News and Events
Acoustic metamaterials have been used to enable exotic wave manipulation including demonstrations of negative refractive index, non-reciprocity, and wave focusing along with many other examples. These exotic functionalities are achieved by designing structures such that sub-wavelength features interact with incident waves to achieve effective material properties. The rise of additive manufacturing (AM) or 3D printing has been crucial to demonstration of metamaterial concepts due AM’s accessibility and its utility in fabrication of complex geometries not producible by other methods. Despite widespread AM use in the acoustics community, specifically in the area of acoustic metamaterials, many of the consolidated materials resulting from AM processes are under-characterized for relevant material properties at length scales of interest. This material characterization problem is complicated by the wide range of printer settings that the user can select when fabricating a printed part. While these user selections are qualitatively understood to result in deviations in printed geometry or variability in material properties, studies which quantify these properties are extremely limited. This talk will provide background on the wave manipulation via acoustic metamaterials and highlight the fabrication challenges encountered due to required complex and multi-scale geometry. Recent efforts will be described which utilized an interlaboratory study to characterize vibration performance of multi-scale geometry built via fused deposition modeling at six institutions.
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Selected Publications
The search for new useful molecular ferroelectrics is a non-trivial problem. We present the application of an automated symmetry-searching method (FERROSCOPE) to the Cambridge Structural Database (CSD) in order to identify polar structures with a closely-related non-polar phase. Such structures have the possibility of undergoing a polarization-switching phase transition thus forming a ferroelectric-paraelectric pair. FERROSCOPE successfully identifies this relationship in 84% of a curated list of 156 known molecular ferroelectrics from the literature and identifies an additional 17 000 potentially ferroelectric compounds in the CSD. Our analysis shows that the method identifies CSD structures which have potentially been described in incorrect space groups, extending previous analyses. We describe experimental case studies which reveal phase transitions in two polar systems predicted to have related non-polar phases.
Adaptive mesh refinement efficiently facilitates the computation of gravitational waveforms in numerical relativity. However, determining precisely when, where, and to what extent to refine when solving the Einstein equations poses challenges; several ad hoc refinement criteria have been explored in the literature. This work introduces an optimized resolution baseline derived in situ from the inspiral trajectory (ORBIT). This method uses the binary’s orbital frequency as a proxy for anticipated gravitational waves to dynamically refine the grid, satisfying the Nyquist frequency requirements on grid resolution up to a specified spin-weighted spherical harmonic order. ORBIT sustains propagation of gravitational waves while avoiding the more costly alternative of maintaining high resolution across an entire simulation—both spatially and temporally. We find that enabling ORBIT decreases waveform noise by an order of magnitude and better resolves high-order wave amplitudes through merger. Combined with WAMR and other improvements, updates to Dendro-GR decrease waveform noise, decrease constraint violations, and boost refinement efficiency each by factors of 𝒪(100), while reducing computational cost by a factor of 4. ORBIT and other recent improvements to Dendro-GR begin to prepare us for gravitational wave science with next-generation detectors.
Understanding and harnessing X-ray quantum effects could open new, to our knowledge, frontiers in imaging and quantum optics. In this study, we measured the process of X-ray parametric down-conversion, where a single high-energy X-ray photon splits into two lower-energy photons. Using the SACLA X-ray free electron laser in Japan at 9.83 keV, we found clear evidence that pairs of photons were produced along the energy-angle relationship that conserved both energy and momentum, as predicted for down-conversion, and consistent with quantum entanglement of X-ray photons. By matching specific photon pairs for energy and momentum conservation, we observe a signal rate of 1250 pairs per hour, confirming that correlated photon pairs can be generated and observed in the absence of explicit time correlations. Our results show that with further refinement, the number of entangled photons produced per laser pulse could increase by an order of magnitude. This paves the way for demonstrating quantum-enhanced X-ray imaging, and confirmation of X-ray photon entanglement.
A unique circuit technique utilizing the active quasi-circulator (AQC) for impedance measurement is presented. Overcoming limitations of size, frequency, and sensitivity, the technique enables sensitive MHz impedance measurements for wearable applications. The AQC measures the impedance of the device-under-test (DUT) at MHz excitation frequencies through nulling the output at the DUT match point while offering enhanced sensitivity. A circuit analysis presents the theory of operation and models the AQC to extract the DUT impedance. Fabricated in a 180-nm CMOS process, the circuit occupies an active area of 0.012 mm2 and demonstrates impedance measurement at excitation frequencies up to 25 MHz. The proposed circuit is attractive for measuring living tissues that exhibit strong bioimpedance response at MHz frequencies.
Galaxies with polar structures (of which polar-ring galaxies (PRGs) are a prominent subclass) contain components that are kinematically decoupled and highly inclined relative to the major axis of the host galaxy. Modern deep optical surveys provide a powerful means of detecting low surface brightness (LSB) features around galaxies, which offers critical insights into the formation and evolution of galaxies with polar structures. UGC 10043 is an edge-on galaxy that is notable for its prominent bulge, which extends orthogonally to the disk plane. In addition, the galaxy displays a well-defined integral-shaped disk warp and multiple dust features crossing the bulge along the minor galaxy axis. We present new deep optical photometry of UGC 10043 down to μg = 29.5 mag arcsec−2 and perform a detailed analysis of its LSB and polar structures. The observations reveal a stellar stream aligned along the polar axis, alongside other signatures of tidal interaction, including a flat, tilted LSB envelope that extends toward the neighboring galaxy MCG +04-37-035, with which UGC 10043 is connected by an HI bridge. Our results suggest that the polar component of UGC 10043 comprises an older, triaxial polar bulge and a younger, forming polar structure that likely originates from the ongoing disruption of a dwarf satellite galaxy. It also simultaneously participates in active interaction with MCG +04-37-035.
Though some LHC searches for new physics exceed the TeV scale, there may be discoveries waiting to be made at much lower masses. We outline a simple quirk model, motivated by models that address the hierarchy problem through neutral naturalness, in which new electroweakly charged states with masses as low as 100 GeV have not yet been probed by the LHC. We also describe a novel search strategy which is complementary to current search methods. In particular, we show its potential to discover natural quirks over regions of parameter space that present methods will leave unexplored, even after the LHC’s high-luminosity run.