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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. 

The principle of the conventional ultrasound test states that the detectable voids cannot be smaller than the acoustic wavelength. However, by using effective medium approximation, the fraction of small voids can be estimated by the variation of the effective density. In this study, a non-contacting ultrasound-based porosity fraction mapping methodology is developed for estimated small voids in coal with long operating wavelength in air. This novel ultrasonic technique based on the mechanical properties of coal offers a rapid scan of the effective density mapping and distribution of void fraction over a large sample area, which overcame the limitation of small voids detection in the conventional ultrasound testing. 

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. 

Abstract Rapid thermokinetics associated with laser-based additive manufacturing produces strong bulk crystallographic texture in the printed component. The present study identifies such a bulk texture effect on elastic anisotropy in laser powder bed fused Ti6Al4V by employing an effective bulk modulus elastography technique coupled with ultrasound shear wave velocity measurement at a frequency of 20 MHz inside the material. The combined technique identified significant attenuation of shear velocity from 3322 ± 20.12 to 3240 ± 21.01 m/s at 45 $$^\circ$$ ∘ and 90 $$^\circ$$ ∘ orientations of shear wave plane with respect to the build plane of printed block of Ti6Al4V. Correspondingly, the reduction in shear modulus from 48.46 ± 0.82 to 46.40 ± 0.88 GPa was obtained at these orientations. Such attenuation is rationalized based on the orientations of $$\alpha ^\prime$$ α ′ crystallographic variants within prior columnar $$\beta$$ β grains in additively manufactured Ti6Al4V. 

An acoustic metamaterial superlattice is used for the spatial and spectral deconvolution of a broadband acoustic pulse into narrowband signals with different central frequencies. The operating frequency range is located on the second transmission band of the superlattice. The decomposition of the broadband pulse was achieved by the frequency-dependent refraction angle in the superlattice. The refracted angle within the acoustic superlattice was larger at higher operating frequency and verified by numerical calculated and experimental mapped sound fields between the layers. The spatial dispersion and the spectral decomposition of a broadband pulse were studied using lateral position-dependent frequency spectra experimentally with and without the superlattice structure along the direction of the propagating acoustic wave. In the absence of the superlattice, the acoustic propagation was influenced by the usual divergence of the beam, and the frequency spectrum was unaffected. The decomposition of the broadband wave in the superlattice’s presence was measured by two-dimensional spatial mapping of the acoustic spectra along the superlattice’s in-plane direction to characterize the propagation of the beam through the crystal. About 80% of the frequency range of the second transmission band showed exceptional performance on decomposition.