Kaifa Wang

The electromechanical coupling behavior of piezoelectric nanowires: Surface and small-scale effects

The influence of the surface and small-scale effects on electromechanical coupling behavior of a piezoelectric nanowire is studied by using the beam bending model. An explicit formula for the electromechanical coupling (EMC) coefficient of the piezoelectric nanowire is obtained based on the nonlocal electroelasticity theory. It is found that the inclusion of the nonlocal effect in the model produces a significant difference from the past model which ignores the nonlocal effect in the prediction of the EMC coefficient and the electric field in the nanowire, confirming the significance of including the surface and small-scale effects in the analysis of piezoelectric nanowires. In particular, the influence of surface effects on the electric field is dominant for smaller nonlocal parameters. If the nanowire is subjected to an applied concentrated load and without surface effect, the nonlocal effect has no effect on its bending and electric field. This study might be helpful for understanding the size-dependent electromechanical properties of piezoelectric nanowires and design of piezoelectric-beam–based nanogenerators.

Effects of residual surface stress and surface elasticity on the nonlinear free vibration of nanoscale plates

This paper studies the influence of surface effects (including the residual surface stress and surface elasticity) on the nonlinear free vibrations of nanoscale plates. The motion equations are derived by using the Hamilton’s principle and solved numerically. It is found that the influence of surface effects on the normalized period of nanoscale plates becomes increasingly significant when the thickness of the plate decreases. More importantly, the influence of the surface effects on the normalized vibration period reduces if the initial amplitude of the vibration increases. This tendency is more pronounced for the Mindlin plate theory, which includes the transverse shear effect of the plates. In addition, it is found that both the positive residual surface stress and surface elasticity increase the magnitude of the vibration velocity.

Timoshenko beam model for the vibration analysis of a cracked nanobeam with surface energy

Free vibration of a cracked nanobeam with consideration of surface energy and transverse shear deformation is studied. The cracked nanobeam is simplified to a system of two segments joined by a rotational spring located at the cracked section. Numerical examples demonstrate that the surface energy increases the natural frequency of the beam. However, the influence of surface energy on the natural frequency becomes smaller for the higher modes. In addition, the effect of transverse shear deformation on the frequency becomes more significant for the higher modes.

Vibration modeling of carbon-nanotube-based biosensors incorporating thermal and nonlocal effects

The vibration behavior of a bridged single walled carbon nanotube with a bio-mass adsorbed at various positions subjected to temperature change is investigated. The frequency equation of the sensor is derived analytically based on nonlocal Euler–Bernoulli beam theory. The relationship between the vibration frequency, the temperature change, the nonlocal parameter, the attached bio-mass and its location was obtained. Results without temperature change are compared with available results of analytical and molecular mechanics. It is found that the influence of thermal effect on the frequency and sensitivity of the biosensor is significant if its length-to-diameter ratio is large. On the other hand, the effect of nonlocal parameter on the frequency and sensitivity of the biosensor increases if its length-to-diameter ratio decreases.

Surface effects on the energy-generating performance of piezoelectric circular nanomembrane energy harvesters under pressure loading

The influence of surface effects on the energy-generating performance of piezoelectric circular nanomembrane energy harvesters under blood pressure is studied. The effects of surface elasticity, surface piezoelectricity, residual surface stress and geometry nonlinear strain are incorporated in the present model. An approximated closed-form solution for the electrical energy of the nanomembrane is derived by using the energy method. Results show that positive surface elasticity and residual surface stress reduce the electrical energy and the surface piezoelectricity effect increases the electrical energy. The influence of surface effect on the energy-generating performance of piezoelectric circular membranes is more significant for a membrane with a small thickness and a large radius-to-thickness ratio.

Effect of surface energy on the sensing performance of bridged nanotube-based micro-mass sensors

The governing equation of a nanotube-based mass sensor is derived with consideration of surface energy, transverse shear deformation, and rotary inertia. Dependencies of the frequency shift and the sensitivity of the sensor on the attached mass are obtained in closed form. The results show that the traditional model, which neglects the surface energy, predicts a higher attached mass and lower sensitivity of the sensor. On the other hand, neglecting the transverse shear deformation and rotary inertia of the sensor will result in a lower prediction of attached mass and a higher prediction of sensitivity of the sensor. It is also found that the surface energy has no effect on the mode shape of the sensor. However, the effect of the location of the attached mass on the mode shape is significant. In particular, if the attached mass is close to the midpoint of the sensor, the frequency shift and sensitivity become very significant.