Compliant mechanisms gain at least part of their mobility from the deflection of flexible member. They are characterised by high precision, as well as no backlash and wear. Several analytical and numerical methods are used in this work to characterise the behaviour of compliant rotational mechanisms, known as cross-spring pivots, aimed at micropositioning applications. When ultra-high precision is required, the limits of applicability of approximated calculation algorithms have to be determined. The results obtained by employing these methods are thus compared with results obtained by using nonlinear finite element calculations tuned with experimental data reported in literature. The finite element model allows also considering the influence of lateral loads and of non-symmetrical pivot configurations where the angle or point of intersection of the leaf springs, or even the initial curvature of the springs, can be varied. The aim of this part of the work is to determine the influence of the cited design parameters on the minimisation of the parasitic shifts of the geometric centre of the pivot as well as on the minimisation of the variability of the rotational stiffness of the pivot so as to ensure its stability. The obtained results allow therefore determining design solutions applicable in ultra-high precision micropositioning applications, e.g. in the field of production or of handling and assembly of MEMS.
Scavenging of low-level ambient vibrations i.e. the conversion of kinetic into electric energy, is proven as effective means of powering low consumption electronic devices such as wireless sensor nodes. Cantilever based scavengers are characterised by several advantages and thus thoroughly investigated; analytical models based on a distributed parameter approach, Euler-Bernoulli beam theory and eigenvalue analysis have thus been developed and experimentally verified. Finite element models (FEM) have also been proposed employing different modelling approaches and commercial software packages with coupled analysis capabilities. An approach of using a FEM analysis of a piezoelectric cantilever bimorph under harmonic excitation is used in this work. Modal, harmonic and linear and nonlinear transient analyses are performed. Different complex dynamic effects are observed and compared to the results obtained by using a distributed parameter model. The influence of two types of finite elements and three mesh densities is also investigated. A complex bimorph cantilever, based on commercially available Midé Technology® Volture energy scavengers, is then considered. These scavengers are characterised by an intricate multilayer structure not investigated so far in literature. An experimental set-up is developed to evaluate the behaviour of the considered class of devices. The results of the modal and the harmonic FEM analyses of the behaviour of the multilayer scavengers are verified experimentally for three different tip masses and 12 different electrical load values. A satisfying agreement between numerical and experimental results is achieved.
There is an evident need for monitoring pollutants and/or other conditions in river flows via wireless sensor networks. In a typical wireless sensor network topography, a series of sensor nodes is to be deployed in the environment, all wirelessly connected to each other and/or their gateways. Each sensor node is composed of active electronic devices that have to be constantly powered. In general, batteries can be used for this purpose, but problems may occur when they have to be replaced. In the case of large networks, when sensor nodes can be placed in hardly accessible locations, energy harvesting can thus be a viable powering solution. The possibility to use three different small-scale river flow energy harvesting principles is hence thoroughly studied in this work: a miniaturized underwater turbine, a so-called ‘piezoelectric eel’ and a hybrid turbine solution coupled with a rigid piezoelectric beam. The first two concepts are then validated experimentally in laboratory as well as in real river conditions. The concept of the miniaturised hydro-generator is finally embedded into the actual wireless sensor node system and its functionality is confirmed.
The design of a piezoelectric device aimed at harvesting the kinetic energy of random vibrations on a vehicle’s wheel is
presented. The harvester is optimised for powering a Tire Pressure Monitoring System (TPMS). On-road experiments are
performed in order to measure the frequencies and amplitudes of wheels’ vibrations. It is hence determined that the
highest amplitudes occur in an unperiodic manner. Initial tests of the battery-less TPMS are performed in laboratory
conditions where tuning and system set-up optimization is achieved. The energy obtained from the piezoelectric bimorph
is managed by employing the control electronics which converts AC voltage to DC and conditions the output voltage to
make it compatible with the load (i.e. sensor electronics and transmitter). The control electronics also manages the
sleep/measure/transmit cycles so that the harvested energy is efficiently used. The system is finally tested in real on-road
conditions successfully powering the pressure sensor and transmitting the data to a receiver in the car cockpit.
Vibration energy harvesting devices based on piezoelectric bimorphs have attracted widespread attention. In this work experimental set-ups are developed to assess the performances of commercially available piezoelectric energy harvesters. Bending tests allow determining the equivalent bending stiffness of the scavengers. On the other hand, dynamic tests allow obtaining frequency response functions in terms of produced voltage and power outputs vs. base acceleration around the fundamental resonance frequency. The results allow determining the influence of the voltage feedback on the dynamic response of the devices, the dependence of output voltages and powers on the applied resistive loads, the values of the loads and frequencies for which the output power is maximized, as well as the comparison of the experimental data with those obtained by using the recently developed coupled electromechanical modal model. All of this creates the preconditions for the development of optimized vibration energy harvesting devices.
One of the main requirements in wireless sensor operation is the availability of autonomous power sources sufficiently
compact to be embedded in the same housing and, when the application involves living people, wearable. A possible
technological solution satisfying these needs is energy harvesting from the environment. Vibration energy scavenging is
one of the most studied approaches in this frame. In this work the conversion of kinetic into electric energy via
piezoelectric coupling in resonant beams is studied. Various design approaches are analyzed and relevant parameters are
identified. Numerical methods are applied to stress and strain analyses as well as to evaluate the voltage and charge
generated by electromechanical coupling. The aim of the work is increasing the specific power generated per unit of
scavenger volume by optimizing its shape. Besides the conventional rectangular geometry proposed in literature, two
trapezoidal shapes, namely the direct and the reversed trapezoidal configuration, are analyzed. They are modeled to
predict their dynamic behavior and energy conversion performance. Analytical and FEM models are compared and
resulting figures of merit are drawn. Results of a preliminary experimental validation are also given. A systematic
validation of characteristic specimens via an experimental campaign is ongoing.