Nonlinear dynamics and applications of MEMS and NEMS resonators.

Rich nonlinear behaviours have been observed in microelectromechanical and nanoelectromechanical systems (MEMS and NEMS) resonators. This dissertation has performed a systematic study of nonlinear dynamics in various MEMS and NEMS resonators that appear to be single, two coupled, arrayed, parametric driven and coupled with multiple-fields, with the aim of exploring novel applications. New study on dynamic performance of a single carbon nanotube resonator taking account of the surface induced initial stress has been performed. It is found that the initial stress causes the jumping points, the whirling and chaotic motions to appear at higher driving forces. Chaotic synchronization of two identical MEMS resonators has been theoretically achieved using Open-Plus-Closed-Loop (OPCL) method, and the coupled resonating system is designed as a mass detector that is believed to possess high resistance to noise. The idea of chaotic synchronization is then popularized into wireless sensor networks for the purpose of achieving secure communication. The arising of intrinsic localised mode has been studied in microelectromechanical resonators array that is designed intentionally for an energy harvester, which could potentially be used to achieve high/concentrated energy output. Duffing resonators with negative and positive spring constants can exhibit chaotic behaviour. Systematic calculations have been performed for these two systems driven by parametric pumps to unveil the controllability of chaos. Based on the principle of nanomechanical transistor and quantum shuttle mechanism, a high sensitive mass sensor that consists of two mechanically coupled NEMS resonators has been postulated, and the mass sensor which can be realized in large-scale has also been investigated and verified. Furthermore, an novel transistor that couples three physical fields at the same time, i.e. mechanical, optical and electrical, has been designed, and the coupled opto-electro-mechanical simulation has been performed. It is shown from the dynamic analysis that the stable working range of the transistor is much wider than that of the optical wave inside the cavity

Dynamic model for piezotronic and piezo-phototronic devices under low and high frequency external compressive stresses (Featured)

In this work, we aim to establish a theoretical method for modelling the dynamic characteristics of piezotronics and piezo-phototronic devices. By taking the simplest piezotronic device, PN junction as an example, we combine the small signal model and the unified approach to investigate its diffusion capacitance and conductance when it is under both low and high frequency external compressive stresses. This approach is different from the traditional considerations that treat the piezopotential as a static value. Furthermore, we expand the theory into piezo-phototronic devices, e.g., a light emitting diode. The dynamic recombination rate and light emitting intensity are quantitatively calculated under different frequencies of external compressive stresses

Optical sensing interface based on nano-opto-electro-mechanical systems

A novel optical sensing interface based on nano-opto-electro-mechanical systems (NOEMS) is proposed, in which the light can be coupled with quantum tunneled electrons via weak mechanical coupling. By taking optical pump power and mechanical coupling strength as varying parameters, respectively, bifurcation diagrams of three involved dynamical states of the NOEMS, i.e., optical, electrical and mechanical mode, are calculated, from which an effective coupling region for tunneled electrons and light is revealed. Self-oscillation, transient dynamics and the threshold of the NOEMS are further characterized, and it is found that the effective coupling region has a special transient time. The work sheds light in developing ultra-sensitive photon detectors using physical mechanisms rather than the conventional PN junction based

Nonlinear Dynamics of Silicon Nanowire Resonator Considering Nonlocal Effect

In this work, nonlinear dynamics of silicon nanowire resonator considering nonlocal effect has been investigated. For the first time, dynamical parameters (e.g., resonant frequency, Duffing coefficient, and the damping ratio) that directly influence the nonlinear dynamics of the nanostructure have been derived. Subsequently, by calculating their response with the varied nonlocal coefficient, it is unveiled that the nonlocal effect makes more obvious impacts at the starting range (from zero to a small value), while the impact of nonlocal effect becomes weaker when the nonlocal term reaches to a certain threshold value. Furthermore, to characterize the role played by nonlocal effect in exerting influence on nonlinear behaviors such as bifurcation and chaos (typical phenomena in nonlinear dynamics of nanoscale devices), we have calculated the Lyapunov exponents and bifurcation diagram with and without nonlocal effect, and results shows the nonlocal effect causes the most significant effect as the device is at resonance. This work advances the development of nanowire resonators that are working beyond linear regime

The realization of optomechanical complete synchronization and its application in sensors

In this work, we study the realization of stable complete synchronization in two coupled optomechanical systems with a master-slave configuration. By taking the open-plus-close-loop method as coupling scheme, it is revealed that the corresponding mechanical and optical mode from the two considered systems with parameters mismatched can be simultaneously synchronized both in linear and nonlinear regime, and even in chaotic state. Based on the achieved synchronization, the coupled systems are then explored in sensing applications. First, we investigate how the perturbations of laser driving from one of the coupled systems make impact on the established synchronization, during which three forms of perturbations, i.e., constant, linear and periodic are considered, and the results show these types of perturbations can be sensed via detecting the change of synchronizing status. Second, by taking one of the coupled as sensing part we develop the coupled system setting in complete synchronization as a mass sensor. It is found that tiny mass added on the sensing part will lead to desynchronization, and the quantities of added mass can be determined by calculating a designed similarity measure

Orthogonal experimental research on sensitivity of acoustic wave velocity of similar material of coal-rock

In view of problem that current researches mostly focused on mechanical properties of similar material of coal-rock, but not change law of acoustic wave velocity, similar material of coal-rock was made by use of raw materials of coal slime, sand, cement and water, and influence of different ratio of the similar materials on acoustic wave velocity was investigated by adopting range analysis method and orthogonal experiment. The experimental results show that acoustic wave velocity of the similar material is similar to coal-rock and can be adjusted in a large range, which meets requirements of acoustic wave velocity of coal-rock to similar material; acoustic wave velocity of the similar material is obviously influenced by cement content, next by coal slime content and little by sand content, and acoustic wave velocity is postively related to cement content and coal slime content; there is a good linear positive correlation between primary wave velocity and shear wave velocity of the similar material. Empirical equations for calculating ratio of the similar material were obtained by multiple linear regression of the experiment data, which were for making similar material of coal-rock meeting requirement of acoustic wave velocity

Analysis of intrinsic localised mode for a new energy harvesting cantilever array

Electromechanical model of an energy harvester that is comprised of 64 identical pairs of cantilever beams has been built in this work. Each pair consists of a short and a long cantilever with the same width and thickness. All the beams are bi-layer structures that include a piezoelectric layer and a substrate layer, which are coupled by the overhang part. The model is focused on analyzing the nonlinear dynamic behavior of the device, specifically when it is operated at intrinsic localized mode (ILM). The electrical charge generated on the surface of the piezoelectric layer has been derived using the beam theory and the piezoelectric equations. It has been found from numerical simulations that spatiotemporal chaos, in particular ILMs can arise during abrupt frequency changes of the external driving source, which could potentially be used to achieve high/concentrated energy output