Phononic crystals are a kind of artificial acoustic metamaterial whose mass density and elastic modulus are periodically arranged. The precise and efficient design of phononic crystals with specific bandgap characteristics has attracted increasing attention in past decades. In this paper, an improved adaptive genetic algorithm is proposed for the reverse customization of two-dimensional phononic crystals designed to maximize the relative bandwidth at low frequencies. The energy band dispersion relation and transmission loss of the optimal structure are calculated by the finite-element method, and the effective wave-attenuation effect in the bandgap range is verified. This provides a solution for the custom-made design of acoustic metamaterials with excellent low-frequency bandgap sound insulation or other engineering applications.

Chiral elastic metamaterials, owing to their exceptional properties distinct from conventional materials and their superior mechanical performance, exhibit significant potential for applications in vibration reduction, noise suppression, energy absorption, and cushioning. To address the challenge of low-frequency vibration control, this paper proposes a dual-component chiral elastic metamaterial structure with four ligament elements. The study explores the bandgap characteristics and elastic wave propagation behavior of this structure within the 1000 Hz frequency range. By analyzing the vibration modes of the unit cell and calculating the group and phase velocities of elastic waves, the physical mechanism underlying bandgap formation is elucidated. The results demonstrate that the proposed four-ligament chiral elastic metamaterial exhibits excellent bandgap properties, with the bandgap covering more than 80.4% of the frequency range below 1000 Hz. This highlights its capability for low-frequency elastic wave control and offers a theoretical reference for the design of novel vibration reduction and noise suppression structures, as well as for low-frequency elastic wave regulation.

Evolution of current harmonics excited by the third harmonic series resonance between the external circuit and plasma under varying discharge conditions was experimentally investigated in atmospheric pressure pulsed radio frequency (RF) discharges. Fast Fourier Transform analysis of voltage and current waveforms revealed the following: (1) At a fixed pulse repetition frequency, reducing the duty cycle caused the quasi-steady-state third harmonic resonance point at the tail of the pulse plateau to shift toward the high-power region; (2) under fixed pulse parameters, when the RF power at the trailing edge of the pulse plateau exceeds the resonance threshold, the transient harmonic resonance point during the plateau phase exhibits a progressive shift from the trailing edge toward the leading edge with increasing power; (3) during the pulse rising edge phase, the amplitude and position of the harmonics exhibited complex changes based on the pulse-off time. These results indicate that these changes in resonance points are attributed to the ability of the discharge capacitor to achieve the values required for harmonic series resonance under various operating parameters.

AgSbTe ₂ possesses an intrinsically low lattice thermal conductivity and a large Seebeck coefficient, rendering it a promising p-type thermoelectric material for the mid-temperature regime. Here, we combine first-principles calculations with Boltzmann transport theory to systematically investigate the lattice thermal conductivity, Seebeck coefficient, and electrical conductivity of intrinsic and Vanadium (V)- and/or Chromium (Cr)-doped AgSbTe ₂ . Resonant levels are identified in the electronic structure via the k-projection band-folding method. Single or co-doping introduces distinct resonant states that modify the band curvature—and hence the effective mass—near the Fermi level, producing either band flattening or sharpening and, consequently, disparate electrical-transport behaviors. Among the configurations examined, Ag ₁₆ Sb ₁₅ Cr ₁ Te ₃₂ exhibits an exceptional power factor (19.08 μW cm ⁻¹ K ⁻² ), an ultra-low lattice thermal conductivity (0.24 W m ⁻¹ K ⁻¹ ), and a correspondingly high figure of merit zT = 1.78 at the operating temperature. These findings underscore the synergistic optimization of electronic and thermal transport achievable through selective doping and provide microscopic insight into the resonant-level mechanism governing the thermoelectric performance of AgSbTe ₂ .

Attaining broadband, low-frequency sound absorption within a sub-wavelength footprint remains an outstanding challenge. We introduce a triangular fractal acoustic metamaterial that couples perforated facesheets with coiled, cavity-backed channels. By means of thermo-viscous acoustic theory and finite-element simulations, we quantify how the fractal order, number of layers, channel width, channel thickness, and inlet area govern the absorption spectrum. Spatial maps of the sound pressure field and the resulting thermo-viscous loss reveal that the dominant loss mechanism is the synergistic interference of multiple slow-wave modes confined to the fractal network. Optimizing the fractal order alone shifts the fundamental absorption peak continuously from 63 to 80 Hz without any increase in overall thickness. Ultimately, the metamaterial prototype was manufactured by means of additive manufacturing (3D printing). Subsequent experimental characterization of its acoustic performance revealed that the as-fabricated architecture yields multiple distinct absorption peaks at frequencies below 500 Hz, while maintaining an overall thickness of merely λ/125.

The optomechanical crystal nanobeam resonator has attracted the attention of researchers due to its high optomechanical coupling rate and small modal volume. In this study, we propose a high-optomechanical-coupling-rate heterostructure with a gradient cavity, and the optomechanical rates of the single mirror and hetero-optomechanical crystal nanobeam resonators are calculated. The results demonstrate that the heterostructure based on the utilization of two mirror regions realizes better confinement of the optical and mechanical modes. In addition, the mechanical breathing mode at 9.75 GHz and optical mode with a working wavelength of 1.17 μm are demonstrated with an optomechanical coupling rate g₀ = 3.81 MHz between them, and the mechanical quality factor is increased to 3.18 × 10⁶.