Narrow Results

In the past two decades, auxetic metamaterials have shown their potential in many fields such as energy absorption and vibration mitigation. Many mechanisms have been proposed to guide the design of their microstructures. More recently, structural optimization methods, especially topology optimization, have been employed for the design and optimization of metamaterials. In this paper, topology optimization was employed with the SIMP method and MMA optimizer for the design of auxetic metamaterials. The negative Poisson’s ratio was verified by numerical simulation. Bandgap study was also conducted on the optimized layout and it showed that the optimization also achieved auxetic metamaterials with two narrow locally resonant bandgaps in addition to broadening and lowering the bandgap of the initial configuration.

Elastic metamaterials, renowned for their ability to control elastic waves, have garnered widespread scholarly attention in recent years. In the field of bandgap engineering, designing the unit cell structure of an elastic metamaterial focuses on achieving a lower opening frequency and a higher relative bandwidth for the first local resonance bandgap (LRBG), while maintaining practical structural considerations. This study explores the effect of the spiral rod on the relative bandwidth of the first LRBG and proposes a spiral rod–mass 3D unit cell structure (SMS). Numerical band structure calculations reveal that the corresponding metamaterial possesses an LRBG with an exceptionally low frequency and a relative bandwidth of 150%. Furthermore, the analysis demonstrates that the opening and closing frequencies of the first LRBG in the proposed SMS can be adjusted independently, enriching the bandgap characteristics of the structure. To achieve this, we develop a scheme to independently adjust the opening and closing frequencies of the first LRBG by modifying the two parameters individually without affecting the static effective stiffness of the structure. The SMS unit cell and corresponding meta-structure are fabricated using 3D printing. The transmission spectrum is analyzed through numerical calculations and vibration experiments. These results confirm the isolation of elastic waves within the bandgap. Finally, quasi-static compression tests are performed on the 3D-printed samples. The results demonstrate that the SMS has an acceptable static effective stiffness, further validating its practical potential.

This work presents a comprehensive investigation of the quantum capacitance and the associated effects on the carrier transit delay in armchair-edge graphene nanoribbons (A-GNRs) based on semi-analytical method. We emphasize on the realistic analysis of bandgap with taking edge effects into account by means of modified tight binding (TB) model. The results show that the edge effects have significant influence in defining the bandgap which is a necessary input in the accurate analyses of capacitance. The quantum capacitance is discussed in both nondegenerate (low gate voltage) and degenerate (high gate voltage) regimes. We observe that the classical capacitance limits the total gate (external) capacitance in the degenerate regime, whereas, quantum capacitance limits the external gate capacitance in the nondegenerate regime. The influence of gate capacitances on the gate delay is studied extensively to demonstrate the optimization of switching time. Moreover, the high-field behavior of a GNR is studied in the degenerate and nondegenerate regimes. We find that a smaller intrinsic capacitance appears in the channel due to high velocity carrier, which limits the quantum capacitance and thus limit the gate delay. Such detail analysis of GNRs considering a realistic model would be useful for the optimized design of GNR-based nanoelectronic devices.

The vibration induced by low-frequency elastic wave reduces the working accuracy of precision instruments. The locally resonant phononic crystal provides a feasible measure for low-frequency vibration isolation because of its bandgap characteristics. In this paper, a locally resonant phononic crystal structure with a broad bandgap is proposed, which consists of a periodic phononic crystal plate with double-sided steel stubs coated by rubber layers. Through finite element analysis, it can be found that the proposed structure can produce a bandgap with 355 Hz bandwidth within the range of 0–500 Hz and isolate vibration in the range of bandgap. By analyzing the local resonance modes of the proposed structure, we further propose the equivalent mass–spring model to predict its bandgap range. The predicted bandgap results from equivalent models of the proposed structure agree well with the results from the finite element analysis. These equivalent models provide an effective and simple method for bandgap optimization of the proposed phononic crystal structure.