ABSTRACT With the development and applications of nano-electro-mechanical systems, academic interest in the mechanical behavior of piezoelectric structures at nanoscale is increasing. Interesting unconventional phenomena have been observed either experimentally or through molecular dynamics simulation. The most common and also important one is the size-dependent characteristics. Classical continuum mechanics with necessary modifications has been proven to be very powerful in explaining these particular characteristics in a relatively simple theoretical framework. This article reviews the recent advances in understanding the size-dependent dynamic responses of piezoelectric nanostructures from the viewpoint of modified continuum mechanics. Particular attentions are paid to three advanced theories of piezoelectricity (e.g. gradient piezoelectricity, surface piezoelectricity, and nonlocal piezoelectricity) and their abilities to predict unconventional vibration and wave characteristics in piezoelectric structures and devices at the nanoscale. The article could serve as a useful reference for the future research on or design of nanostructures with multifield couplings. Graphical Abstract

https://www.tandfonline.com/doi/pdf/10.1080/19475411.2022.2091058?needAccess=true

Size-dependent vibrations and waves in piezoelectric nanostructures: a literature review

The endohedral functionalization of carbon nanotubes (CNTs) with nanowires (NWs), i.e., NWs@CNTs, has been the center of attention in a lot of research due to the applications of NWs@CNTs in nanoelectronic devices, heterogeneous catalysis, and electromagnetic wave absorption. To this end, based on the classical molecular dynamics (MD) simulations, the effect of four pentagonal structures of encapsulated metallic nanowires (mNWs), namely the eclipsed pentagon (E), the deformed staggered pentagon (Ds), staggered pentagon (S), and staggered pentagonal structure without the monatomic chain passing through the centers of the parallel pentagons (R) configurations on the vibrational behavior of CNTs, is investigated. Also, the effects of geometrical parameters such as length and radius of CNTs on the natural frequencies of simulated models are explored. The results illustrate that by increasing the length, the natural frequency of pure CNTs and mNWs@CNTs decreases. In a similar length, mNWs@CNTs possess lower natural frequencies compared to the pure CNTs. According to the results, the highest and lowest natural frequencies are calculated by inserting the S structure of sodium NW and Ds structure of aluminum NW inside their proper armchair CNT, i.e., Na-S NW@ (9,9) CNT and Al-Ds NW@ (7,7) CNT, respectively.

Fundamental frequency analysis of endohedrally functionalized carbon nanotubes with metallic nanowires: a molecular dynamics study

Modeling and analysis of the static bending of piezoelectric nanowires with the consideration of surface effects

In this review, we review the recent research progress and results of piezoelectric energy harvesters applying mechanical tuning techniques in terms of literature background, methods of mechanical tuning, and practical applications. In the past few decades, piezoelectric energy harvesting techniques and mechanical tuning techniques have received increasing attention and made significant progress. Mechanical-tuning techniques are those that allow the resonant vibration energy harvesters the mechanical resonant frequency values to be adjusted to coincide with the excitation frequency. According to the different tuning methods, this review classifies mechanical-tuning techniques based on magnetic action, different piezoelectric materials, axial load, the variable center of gravity, various stresses, and self-tuning and summarizes the corresponding research results, comparing the differences between the same methods. In addition, the current application of the mechanical-tuning techniques is introduced, and the future development of mechanical tuning techniques is analyzed, facilitating the reader to better understand how mechanical-tuning techniques can improve the output performance of energy harvesters.

Piezoelectric energy harvesting systems using mechanical tuning techniques.

PurposeConsidering the size-dependent influence ignored by classical continuum mechanics, a new non-classical Euler–Bernoulli beam model is proposed in this paper. The new fractional viscoelastic nanobeam model is set up using the fractional Kelvin–Voigt viscoelastic model and Hamilton’s principle. And the new model studies the total effects of nonlocal elasticity, modified couple stress, and surface energy.MethodsThe model represented the fractional integral-partial differential governing equation is solved by Galerkin’s and predictor–corrector methods. First, the effects of nonlocal elasticity, modified couple stress, surface energy, and their coupling impact on the nonlinear time response of free vibration of fractional viscoelastic nanobeam are analyzed. Then, in the frame of nonlocal couple-stress elasticity and surface energy theory, the effects of different parameters on the nonlinear time responses of free and forced vibration of fractional viscoelastic nanobeam are discussed.Results and ConclusionThe numerical results show that the fractional order must be considered in the modeling of viscoelastic nanobeam, and the system’s damping enhances by the increase of fractional order. Moreover, owing to the correlation between fractional order and excitation frequency, the nonlinear time responses of fractional order to free and forced vibration are different. 

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Hongjun Han

Papers

Vibration and Buckling Analysis of Piezoelectric Nanowires Based on Surface Energy Density

Diffraction of SV waves by a surface effective elliptic cavity