Li Li

Negative Poisson’s ratios commonly arise from internal rotational mechanisms. However, conventional honeycombs generally remain non-auxetic because their ligaments behave as classical beams with largely decoupled axial, shear, and rotational responses. Here, antichiral and chiral metabeams containing periodically embedded rotating bodies are introduced to encode element-level tension–rotation coupling (TRC) and tension–shear–rotation coupling (TSRC), respectively. Using these metabeams as structural building blocks, two complementary classes of mechanical metastructures are developed. First, metabeams are embedded into conventional antichiral and chiral honeycombs, tailoring the magnitude and sign of their effective Poisson’s ratios. Second, metabeams are incorporated into conventional hexagonal honeycombs, where inclined ligaments are represented by complete stiffness matrices. Closed-form relationships between Poisson’s ratio and stiffness coefficients are derived, identifying the axial–shear stiffness term as the key governing parameter and demonstrating sign reversal to negative Poisson’s ratios even under positive skew angles. A deformation-competition perspective further elucidates how rotation of main rings, TRC/TSRC-induced metabeam deformations and direct bending of metabeams jointly govern auxeticity in these metastructures. Overall, this work establishes an element-level coupling strategy for programmable auxeticity and presents metabeams as mechanically interpretable building blocks for lightweight, functionally tunable mechanical metamaterials.

Underwater acoustic backscatter offers a low-power approach to communication with submerged sensor nodes. This study examines a piezoelectric reflector with a steel backing and a lead zirconate titanate (PZT, grade 5H) element and evaluates an exponentially weighted moving average (EWMA) threshold detector for binary amplitude-shift keying (2ASK). An electromechanical model and a two-dimensional axisymmetric finite-element model were used to compare candidate reflector structures near 200 kHz. In tank tests, the received peak-to-peak voltages in the two load states were approximately 900 and 770 mV for a commercial Leqi transducer, 870 and 650 mV for a DYW-63-G transducer, and 870 and 640 mV for the fabricated transducer. These observations correspond to normalized received-voltage contrasts of approximately 14.4%, 25.3%, and 26.4%, respectively; they do not constitute calibrated acoustic reflection coefficients. A 16-bit 2ASK sequence was recovered in laboratory tests with the commercial reference transducers at 100 bit/s. Link-level simulation was used separately to compare fixed and adaptive threshold detection under time-varying channel assumptions.

In this paper, a theoretical framework is developed and validated for the damped vibration analysis of visco-Pasternak-supported porous beams under localized heat exposure. The formulation incorporates porosity-dependent material gradation, thermal fields with different longitudinal distributions, and foundation damping effects, thereby capturing the multi-physics interactions that govern dynamic behavior. Benchmark comparisons against established solutions confirm the accuracy and reliability of the present approach. Extensive parametric investigations are then performed to reveal the influence of key variables, including temperature rise and heated length ratio, porosity coefficient, slenderness, and foundation stiffness and damping parameters, on the damped frequencies, real parts of the eigenvalues, and relative damping ratios. Results highlight the competing roles of stiffness degradation, mass reduction, and porosity-modified thermal stresses, leading to non-monotonic or stabilizing trends not observed in simpler models. The proposed framework provides new insights into the coupled thermomechanical behavior of porous nanostructured beams and offers a versatile tool for the design and assessment of advanced lightweight structural elements in thermally varying environments.