The usually high eigenfrequencies of miniaturized oscillators can be significantly lowered by reducing the stiffness through stiffness compensation. In this work, a mechanical design for a compliant ortho-planar mechanism is proposed in which the stiffness is compensated to such a degree that it can be identified as statically balanced. The mechanism was fabricated using laser micro-machining and subsequently preloaded through packaging. The statically balanced property of the mechanism was experimentally validated by a measurement of the force-deflection relation. A piezoelectric version of the design was fabricated for the purpose of energy harvesting from low-frequency motion. For a sub 1 Hz excitation, the device demonstrated an average power output of 21.7 μW and an efficiency that compares favorably to piezoelectric energy harvesters reported in the literature. Therefore, it was found that stiffness compensation is a promising method for the design of piezoelectric energy harvesters for low-frequency motions.

There is a high demand for novel flexible micro-devices for energy harvesting from low-frequency and random mechanical sources. The research of new functional designs is required to strategically enhance the performances and to increase the control on mechanical flexibility. In this work we report the fabrication and characterization of bi-stable and statically balanced thin-film piezoelectric transducers based on Aluminum Nitride (AlN). The device consists of a piezoelectric layer sandwiched between two thin Molybdenum electrodes that were deposited on a Kapton substrate by reactive sputtering and patterned by UV lithography. In order to improve the out-of-plane flexibility, the mechanical design is distinguished by a post-buckled flexure that introduces a negative stiffness to compensate the otherwise positive stiffness of the system. The buckling was introduced by a new method, called Package-Induced Preloading (PIP) where the mechanisms are laminated over a package with a geometry extending out-of-plane. The induced buckling resulted in bi-stable and statically balanced mechanisms which demonstrated an enhanced voltage output during a triggered snapping step. A preliminary study shows potential for the statically balanced designs and the PIP method for wind energy harvesting, revealing prospective applications and future improvements for the development of energy harvesters.

In this paper a method is demonstrated for tuning the stiffness of building blocks for statically balanced compliant ortho-planar mechanisms. Three post-buckled mechanisms are proposed where the flexural rigidity can be manipulated over a part of their length in order to tune the ratio between the first two critical loads. A sensitivity analysis using finite element simulation showed that the best balancing performance is obtained in these mechanisms when this ratio was maximized. The results were validated experimentally by capturing the force-deflection relations.

In this paper, a novel design concept and manufacturing method for the compliant bistable structure is proposed. The pulsed laser technique is utilized as the manufacturing method for both the fabrication and the introduction of desired pre-stresses, simultaneously. Based on this concept, a novel bistable structure consisted of one pre-compressed main beam, and a pair of supporting beams is designed and fabricated. The deformation difference between the main beam and the supporting beams induced by laser heating residual stress make the main beam to buckle under the constraints of two supporting beams and possess a bistable feature. The bistable structures can be implemented into other devices in the form of cantilevers thanks to the internal integration of the buckled beam and the boundary conditions. The characteristics of this new bistable structure, including its stable shape and snap-through response, are investigated both experimentally and numerically. During the snap forth and back process with the snapping load of 19 mN and the required energy of 77 mN·mm, an impressive energy dissipation with a loss factor value of 0.3 exists. Finally, a parametric study was carried out to find the critical performance parameters.

Residual stress from thermal oxidation can cause plastic deformation in silicon microelectromechanical systems (MEMS). This paper presents a novel method to distinguish elastic and plastic strain in silicon beams, by removing the oxide layer to show the plastic strain. A lever mechanism is used as a mechanical amplifier. The plasticity model by Alexander and Haassen (AH) is used in a numerical model to predict the elastic and plastic strain. Experiments in epitaxially grown silicon show significantly less plastic strain than predicted by the model. We conclude that the AH model is not valid for epitaxially grown silicon with very little initial dislocations. Since epitaxially grown silicon generally has less dislocations compared to floating zone silicon we recommend using the former when plastic deformation is to be avoided.

This work presents a novel design, model and prototype of a motion energy harvester based on bi-stability and frequency up-conversion. The Parametric Frequency up-converter Generator (PFupCG). The PFupCG was designed to harvest energy under conditions where the amplitude of the driving motion is larger than the internal displacement limit. Instead of an impact member, the PFupCG uses a compliant suspension mechanism that combines a bi-stable characteristic with a strong stiffening behavior as a result of geometric effects. This resulted in a prototype of the PFupCG with an internal-to-applied motion amplitude ratio of 0.2. A case study was carried out where the PFupCG was analyzed by simulation and experiment for vibration conditions representative of human walking motion (2Hz, 25 mm).

Vibration energy harvesters based on piezoceramics can provide a sustainable source of energy for low-power electronics. The greatest issue preventing these systems from being widely used is their poor reliability. With the aim to maximise their power output, the devices are often operated close the point of yielding, which results in microcracks and fatigue in the piezoceramic layer. This paper offers a comparative review of design principles that aim to improve the reliability of piezoelectric vibration energy harvesters. Three different design principles are investigated with the focus on strain limitation. The results show that strain homogenisation, strain limitation and compressive strains can be effective design principles to increase reliability without sacrificing efficiency.

Microtransmission mechanisms made of elastic materials present an opportunity for exploring scalable mechanical systems integrated with sophisticated functionalities. This paper shows how the fundamentally limited range of motion in elastic mechanisms can be circumvented to create a frequency doubling functionality analog to angular velocity doubling in classical gears. The proposed mechanism utilizes the elastic deformation of its internal architecture and buckling of microflexures to perform frequency doubling kinematics. We demonstrate this by the fabrication of a microtransmission device for application in mechanical wrist watches. A key benefit of the proposed method is that such a transmission system can be integrated and fabricated as an embedded part of microarchitected materials to boost the frequency characteristics of energy storage, actuators, and inertial sensors to perform adequately for different applications.

Although motion energy harvesting at the small scales has been a research topic for over 20 years, the implementation of such generators remains limited in practice. One of the most important contributing factors here is the poor performance of these devices under low-frequency excitation. In this research, a new metric is proposed to evaluate the performance and bandwidth of generators at low frequencies. For that, a classification based on the dynamics was made. It was found that the highest efficiencies were found in single-degree-of-freedom resonators where a large motion amplification was achieved. Smaller generators can be designed by limiting the motion through end-stops at the cost of a reduced efficiency. Moreover, it was argued that upon miniaturization, resonators could be outperformed by generators using a frequency up-conversion principle.

Static balancing is used to reduce the actuation stiffness in a translational stage compliant mechanism. The planar and monolithic compliant mechanism is preloaded using a buckling beam of which the top part is guided by a double folded flexure. Hooks, that lock the top part of the beam in place, ensure a permanent static balancing of the entire device. The preloading action is caused by an external shaking or shock to the device. A theoretical micro electromechanical system (MEMS) model with a radius of 18.6 mm is developed and a scale 6:1 prototype is fabricated and tested for static balancing, first eigenfrequency (EF) and eigenmode (EM). Finite element modelling is used to predict static balancing and EM behaviour. Experiments on two equally fabricated prototypes show a reduction of -123 % and -126% actuation stiffness where -104.5% was predicted. The expected reduction for the designed MEMS device is 98.4^%. The experimental first EF of the prototype is 3.10±0.25 Hz against a theoretical value of 3.09 Hz. The theoretical first EF of the MEMS model is 21.8 HZ. The prototypes are successfully preloaded by applying shaking or shock by hand. The predicted minimal energy requirement for this is found to be 4.9e-3 J, while 6.4e-3 J and 5.9e-3 J were calculated based on experimental results. The expected minimal energy required for preloading the designed MEMS device is 1.0e-5 J.

Vibration energy harvesting can be used as a sustainable power source for various applications. Usually, the generators are designed as devices with a single degree of freedom (SDoF) along the direction of the driving motion. In this research, harvesting from multi-directional (translational) motion sources will be investigated. Three strategies are assessed: a reference SDoF generator, a SDoF generator using an orientation strategy, and a Multi Degree of Freedom (MDoF) system. This led to the development of a design metric by which any 2D design problem can be described by two dimensionless parameters: the relative strength of vibrations, p_v, and the relative dimension of the design space, p_l. It was shown that the relative power density (RPD) of a 2DoF system compared to a reference SDoF system only depends on the product p^∗=p_vp_l, and has a maximum of 1.185 for p^∗=1. The application of powering a hearing aid is investigated as a case study. It was found that the vibrations in the area of the human head while walking can be represented by a two-directional vibration source with p_v=0.55. Three different design spaces are assessed for a miniaturized generator and three different optimal embodiments are found. For one of the considered situations where p^∗=1.1, a 2DoF system was found to have a 16% higher power output compared to a SDoF reference. The aim of future work will be the validation of the developed metric.