An official website of the United States government
Abstract The acoustic response of defect‐based acoustic interferometer‐like designs, known as Coupled Resonator Acoustic Waveguides (CRAWs), in 2D phononic crystals (PnCs) is reported. The PnC is composed of steel cylinders arranged in a square lattice within a water matrix with defects induced by selectively removing cylinders to create Mach‐Zehnder‐like (MZ) defect‐based interferometers. Two defect‐based acoustic interferometers of MZ‐type are fabricated, one with arms oriented horizontally and another one with arms oriented diagonally, and their transmission features are experimentally characterized using ultrasonic spectroscopy. The experimental data are compared with finite element method (FEM) simulations and with tight‐binding (TB) calculations in which each defect is treated as a resonator coupled to its neighboring ones. Significantly, the results exhibit excellent agreement indicating the reliability of the proposed approach. This comprehensive match is of paramount importance for accurately predicting and optimizing resonant modes supported by defect arrays, thus enabling the tailoring of phononic structures and defect‐based waveguides to meet specific requirements. This successful implementation of FEM and TB calculations in investigating CRAWs systems within PnCs paves the way for designing advanced acoustic devices with desired functionalities for various practical applications, demonstrating the application of solid‐state electronics principles to underwater acoustic devices description.
more »
« less
This content will become publicly available on June 1, 2026
Thermally-switchable Bragg gaps in additively manufactured phononic crystals
Abstract Recently, additive manufacturing (AM) fabrications are commonly applied to produce acoustic metamaterials or phononic crystals (PnCs) as tools for complex geometrical designs. However, the material properties of those additive manufactured materials are less involved in the core portion of those PnC designs. Here we report a purely materials-driven, temperature switchable PnC in which Bragg gaps appear or vanish as the lattice medium toggles between liquid water and solid ice. Six widely used AM polymers were acoustically characterized, where stereolithography (SLA) resins showed an impedance mismatch of ≈50% with water but <1% with ice, whereas inkjet agar gel exhibited the opposite trend. A 10 × 10 SLA resin PnC therefore displayed >20 dB on/off contrast at 145 kHz and around 300 kHz when cycled across 0 °C, confirmed experimentally and with plane wave and simulation models. Unlike previous thermally tuned PnCs that depend on volumetric swelling or liquid metal infiltration, the present approach preserves geometry, requires no external actuators and operates with sub 1 °C stability. This simple, robust strategy lays the foundation for band pass filters, steerable lenses and non-reciprocal acoustic circuits that can be frozen or thawed on demand.
more »
« less
- Award ID(s):
- 1741677
- PAR ID:
- 10629131
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Smart Materials and Structures
- Volume:
- 34
- Issue:
- 6
- ISSN:
- 0964-1726
- Page Range / eLocation ID:
- 065020
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The functionality of thermally active phononic crystals (PnC) and metamaterials can be greatly enhanced by utilizing the temperature-dependent physical characteristics of heat-sensitive materials within the periodic structure. The phase transformation between water and ice occurs within a narrow range of temperatures that can lead to significant changes in its acoustic transmission due to the modification of the elastic properties of periodic phononic structures in an aqueous medium. A phononic crystal with acrylic scatterers in water is designed to function as an acoustic filter, beam splitter, or lensing based on the device’s temperature due to changes in the phase of the ambient medium. The transition from room temperature to freezing point reduces the contrast in acoustic properties between the ice-lattice and the scatterer materials (acrylic) and switches off the metamaterial of the water-based PnC. The numerically simulated equi-frequency contours and wave propagation characteristics demonstrate the switchable meta-material to the periodic phononic structure’s normal behavior due to the phase transition of water. Effects such as Van Hove’s singularity and filamentation-like effects in an acoustic meta-material system can be thermally tuned.more » « less
-
Abstract As a class of semiconductor nanocrystals that exhibit high photoluminescence quantum yield (PLQY) at tunable wavelengths, perovskite nanocrystals (PNCs) are attractive candidates for optoelectronic and light‐emitting devices. However, attempts to optimize PNC integration into such applications suffer from PNC instability and loss of PL over time. Here, we describe the impact of organic and polymeric N‐oxides when used in conjunction with PNCs, whereby a significant increase in PNC quantum yield is observed in solution, and stable PL emission is obtained in polymeric nanocomposites. Specifically, when using aliphatic N‐oxides in ligand exchange with CsPbBr3PNCs in solution, a substantial boost in PNC brightness is observed (~40% or more PLQY increase), followed by an alteration of the perovskite chemistry. When N‐oxide substituents are positioned pendent to a poly(n‐butyl methacrylate) backbone, the optically clear flexible nanocomposite films obtained have bright PL emission and maintain optical clarity for months. X‐ray diffraction is useful for characterizing the PNC crystalline structure following exposure to aliphatic N‐oxides, while electron microscopy (EM) and small‐angle X‐ray scattering (SAXS) measurements of the PNC‐polymer nanocomposites show this polymeric N‐oxide platform to cleanly disperse PNCs in flexible polymer films.more » « less
-
Abstract Metal halide perovskite nanocrystals (PNCs) have recently garnered tremendous research interest due to their unique optoelectronic properties and promising applications in photovoltaics and optoelectronics. Metal halide PNCs can be combined with polymers to create nanocomposites that carry an array of advantageous characteristics. The polymer matrix can bestow stability, stretchability, and solution‐processability while the PNCs maintain their size‐, shape‐ and composition‐dependent optoelectronic properties. As such, these nanocomposites possess great promise for next‐generation displays, lighting, sensing, biomedical technologies, and energy conversion. The recent advances in metal halide PNC/polymer nanocomposites are summarized here. First, a variety of synthetic strategies for crafting PNC/polymer nanocomposites are discussed. Second, their array of intriguing properties is examined. Third, the broad range of applications of PNC/polymer nanocomposites is highlighted, including light‐emitting diodes (LEDs), lasers, and scintillators. Finally, an outlook on future research directions and challenges in this rapidly evolving field are presented.more » « less
-
Abstract Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a versatile surface-sensitive technique for characterizing both hard and soft matter. Its chemical and molecular specificity, high spatial resolution, and superior sensitivity make it an ideal method for depth profiling polymeric systems, including those comprised of both inorganic and organic constituents (i.e., polymer nanocomposites, PNCs). To best utilize ToF-SIMS for characterizing PNCs, experimental conditions must be optimized to minimize challenges such as the matrix effect and charge accumulation. Toward that end, we have successfully used ToF-SIMS with a Xe+ focused ion beam to depth profile silica nanoparticles grafted with poly(methyl methacrylate) (PMMA-NP) in a poly(styrene-ran-acrylonitrile) matrix film by selecting conditions that address charge compensation and the primary incident beam angles. By tracking the sputtered Si+ species and fitting the resultant concentration profile, the diffusion coefficient of PMMA-NP was determined to be D = 2.4 × 10−14 cm2/s. This value of D lies between that measured using Rutherford backscattering spectrometry (6.4 × 10−14 cm2/s) and the value predicted by the Stokes–Einstein model (2.5 × 10−15 cm2/s). With carefully tuned experimental parameters, ToF-SIMS holds great potential for quantitatively characterizing the nanoparticles at the surfaces and interfaces within PNC materials as well as soft matter in general.more » « less
