Design and development of a parametrically excited nonlinear energy harvester

An energy harvester has been designed, fabricated and tested based on the nonlinear dynamical response of a parametrically excited clamped-clamped beam with a central point-mass; magnets have been used as the central point-mass which pass through a coil when parametrically excited. Experiments have been conducted for the energy harvester when the system is excited (i) harmonically near the primary resonance; (ii) harmonically near the principal parametric resonance; (iii) by means of a non-smooth periodic excitation. An electrodynamic shaker was used to parametrically excite the system and the corresponding displacement of the magnet and output voltages of the coil were measured. It has been shown that the system displays linear behaviour at the primary resonance; however, at the principal parametric resonance, the motion characteristic of the magnet substantially changed displaying a strong softening-type nonlinearity. Theoretical simulations have also been conducted in order to verify the experimental results; the comparison between theory and experiment were within very good agreement of each other. The energy harvester developed in this paper is capable of harvesting energy close to the primary resonance as well as the principal parametric resonance; the frequency-band has been broadened significantly mainly due to the nonlinear effects as well as the parametric excitation

Extraordinary second harmonic generation modulated by divergent strain field in pressurized monolayer domes

The most prominent form of nonlinear optical (NLO) frequency conversion is second harmonic generation (SHG), where incident light interacts with a nonlinear medium producing photons at double the input frequency, which has vast applications in material and biomedical science. Emerging two-dimensional nonlinear optical materials led by transition metal dichalcogenides (TMDs) have fascinating optical and mechanical properties and are highly anticipated to overcome the technical limitations imposed by traditional bulky NLO materials. However, the atomic scale interaction length and low conversion efficiency in TMD materials prevent their further implementation in NLO applications. While some uniaxial strain-engineering studies intensively investigated the anisotropic SHG response in TMDs, they did not realize giant SHG enhancement by exploiting the opto-mechanical characteristics. Herein, we employ proton (H+) irradiation to successfully fabricate large pressurized monolayer TMD domes (d ≥ 10 μm) and conduct a comprehensive investigation and characterization of their SHG performance enhancement. We show that the intensity of SHG is effectively enhanced by around two orders of magnitude at room temperature. Such giant enhancement arises from the distinct separation distance induced by capped pressurized gas and the hemi-spherical morphology, enabling constructive optical interference. Moreover, the unique divergent strain field in TMD domes promotes the first experimental study on the anisotropic nonlinear optical behavior based on biaxial strain conditions in terms of varying strain orientation and relative weights. Our work demonstrates a promising system with enhanced NLO performance and well-preserved biocompatibility, paving a way toward the future nano-scaled quantum optics design and biomedical applications

Enhanced broadband vibration based energy harvesting coupling geometric nonlinearity and parametric excitation

In this work, theoretical, numerical, and experimental investigations for vibration based energy harvesters (VBEH) have been conducted. To improve the current limitations of VBEHs, a combination of parametric excitation, geometric nonlinearity arising from centreline extensibility (mid-plane stretching), geometric imperfection, mechanical stoppers and an array configuration have all been explored as suitable mechanisms for increasing the broadband behaviour of a VBEH. This work mainly focused on the increased broadband behaviour of a doubly-clamped beam resonator with a magnetic tip mass and electromagnetic induction as the transduction mechanism; however, cantilever beam setups were also used in some cases when combining this work with existing methods in the literature. A comparison of a transversely and parametrically system was conducted first to assess the benefits of parametric excitation; a model identification procedure was proposed and it was found, sustained oscillations could be achieved and this led to a greater nonlinear broadband behaviour. Using parametric excitation, the effects of electrical damping, load resistance, initial axial displacement, geometric imperfection have been investigated; it was found that by slightly adjusting geometry, the fundamental and parametric resonance were combined and using imperfections an initial softening followed by strong hardening behaviour was observed. Furthermore, the end of this thesis explores using parametric excitation and geometric nonlinearity with conventional methods in the literature, such as, mechanical stoppers and an array configuration; it was found that parametric resonance offered an increased bandwidth and power harvested for the VBEH devices fabricated. Parametric excitation, geometric nonlinearity and other nonlinear mechanisms have a significant effect on the qualitative and quantitative change in the frequency bandwidth of a VBEH device. This behaviour can be used to further enhance the bandwidth, power, efficiency, and performance of VBEH technology

A review on performance enhancement techniques for ambient vibration energy harvesters

Due to increased demands for energy and the current limitations of batteries, a future prospective technology are vibration energy harvesters that convert kinetic vibration energy into electrical energy. These energy harvesters have the potential to be used in powering small electronic devices such as measurement equipment in remote or hostile environments where batteries are not a viable option. Current limitations of vibration based energy harvesters is the total available power generated and the frequency at which they effectively collect ambient vibration sources for producing power; this paper aims to review the current techniques that are being employed to enhance the performance of these devices. These techniques have been categorised into amplification techniques, resonance tuning methods and introducing nonlinear oscillations. Before this technology can be used effectively in applications enhancing the performance of ambient vibration energy harvesters needs to be addressed

Experimental nonlinear vibrations of an MRE sandwich plate

The nonlinear vibration analysis of a magneto-rheological elastomer (MRE) sandwich plate is conducted experimentally. Experiments have been performed in order to construct the frequency-response curves in the vicinity of the fundamental natural frequency of an MRE sandwich plate (plate A) in either the absence or presence of a localised external magnetic field at 3 different geometrical locations, for both small and medium magnetic fields. Furthermore, experiments have also been conducted on a pure aluminium plate (plate B) with an equal thickness to the MRE sandwich plate (plate A) in order to examine the influence of the MRE layer on the nonlinear dynamics of the system. An electrodynamic shaker was used to directly force each system and the displacement at the centre of the plate was measured. Meanwhile, permanent magnets were used to apply a localised magnetic field for the experiments where the MRE sandwich plate was subject to an external magnetic field. It was observed all the MRE systems displayed strong hardening-type nonlinear behaviour, however, with increasing magnetic field this behaviour transitioned to a weak hardening-type nonlinearity

Design, Fabrication, and Test of a Coupled Parametric-Transverse Nonlinearly Broadband Energy Harvester

A coupled parametric-transverse nonlinearly broadband energy harvester utilizing mechanical stoppers has been designed, fabricated, experimentally tested, and in some cases theoretically verified. An energy harvester with coupled parametric and transverse cantilever beams with additional tip-masses was excited using an electrodynamic shaker. A piezoelectric bimorph has been attached to each cantilever beam; when the excitation frequency was in the vicinity of the parametric or transverse resonances, the mechanical strain developed in the piezo-bimorphs was converted into electrical energy across a purely resistive ac load. For the cases involving no stoppers, a weak softening-type nonlinear frequency-voltage behavior was observed for the parametrically excited cantilever beam; however, with the addition of mechanical stoppers, both the transverse and parametrically excited cantilever beams displayed a strong hardening-type nonlinear frequency-voltage behavior. The stoppers substantially increased the operating bandwidth for both the parametric and transversely excited cantilever beams compared to the case without stoppers. For the theoretical investigations, a good agreement for both the fundamental frequencies and frequency-response curves was obtained. It is shown that by coupling transverse and parametric cantilevers with mechanical stoppers, the nonlinear energy harvested by the system takes place over a much broader frequency-bandwidth when compared to the singular transverse cantilever mechanism (by about 163.5%)

Probing the chaotic boundary of a membrane resonator with nanowire arrays

Mechanically induced nonlinearities in nano-electromechanical systems (NEMSs) are typically avoided in design due to their unpredictable nature; however, by incorporating these normally unwanted nonlinear and chaotic phenomena, the performance of NEMS devices displays substantially different characteristics opening a broad new range of potential applications for their use. In this work, experiments have been conducted for probing the chaotic boundary of a circular membrane mechanical resonator with and without a silicone nanowire array (Si NWA). The NWA resonator can transition from linear to nonlinear quasi-periodic behaviour, and further transition into a chaotic state at resonance. Moreover, the NWA resonator demonstrated a high level of complex nonlinear behaviours, as the device expands the power spectral response from a single frequency at a linear regime to a wideband continuous frequency spectrum when chaotic behaviour was initiated; the threshold power of this transition decreased with a smaller NWA diameter. It was also observed that the NWA resonator had higher damping compared to the resonator without a NWA; however, as the vibration velocity of the NWA resonator increased, complex air damping and thin squeeze film damping lowered the threshold for probing the chaotic boundary condition of the NWA resonator