Development of piezoelectric harvesters with integrated trimming devices

Piezoelectric cantilever harvesters have a large power output at their natural frequency, but in some applications the frequency of ambient vibrations is different fromthe harvester\u2019s frequency and/or ambient vibrations are periodicwith some harmonic components. To copewith these operating conditions harvesters with integrated trimming devices (ITDs) are proposed. Some prototypes are developed with the aid of an analytical model and tested with an impulsive method. Results show that a small trimming device can lower the main resonance frequency of a piezoelectric harvester of the same extent as a larger tip mass and, moreover, it generates at high frequency a second resonance peak. A multi-physics numerical finite element (FE) model is developed for predicting the generated power and for performing a stress-strain analysis of harvesters with ITDs. The numerical model is validated on the basis of the experimental results. Several configurations of ITDs are conceived and studied. Numerical results show that the harvesters with ITDs are able to generate relevant power at two frequencies, owing to the particular shape of the modes of vibration. The stress in the harvesters with ITDs is smaller than the stress in the harvester with a tip mass trimmed to the same frequency

A face-smoothed cell method for static and dynamic piezoelectric coupled problems on polyhedral meshes

Low-order discretization schemes are suitable for modeling 3-D multiphysics problems since a huge number of degrees of freedom (DoFs) is typically required by standard high-order Finite Element Method (FEM). On the other hand, polyhedral meshes ensure a great flexibility in the domain discretization and are thus suitable for complex model geometries. These features are useful for the multiphysics simulation of micro piezoelectric devices with a thin multi-layered and multi-material structure. The Cell Method (CM) is a low-order discretization scheme which has been mainly adopted up to now for electromagnetic problems but has not yet been used for mechanical problems with polyhedral discretization. This work extends the CM to piezo-elasticity by reformulating local constitutive relationships in terms of displacement gradient. In such a way, piecewise uniform edge basis functions defined on arbitrary polyhedral meshes can be used for discretizing local constitutive relationships. With the CM matrix assembly is completely Jacobian-free and do not require Gaussian integration, reducing code complexity. The smoothing technique, firstly introduced for FEM, is here extended to CM in order to avoid shear locking arising when low-order discretization is used for thin cantilevered beams under bending. The smoothed CM is validated for static and dynamic problems on a real test case by comparison with both second-order FEM and experimental data. Numerical results show that accuracy is retained even if a much lower number of DoFs is required compared to FEM

Roadmap on thermoelectricity

The increasing energy demand and the ever more pressing need for clean technologies of energy conversion pose one of the most urgent and complicated issues of our age. Thermoelectricity, namely the direct conversion of waste heat into electricity, is a promising technique based on a long-standing physical phenomenon, which still has not fully developed its potential, mainly due to the low efficiency of the process. In order to improve the thermoelectric performance, a huge effort is being made by physicists, materials scientists and engineers, with the primary aims of better understanding the fundamental issues ruling the improvement of the thermoelectric figure of merit, and finally building the most efficient thermoelectric devices. In this Roadmap an overview is given about the most recent experimental and computational results obtained within the Italian research community on the optimization of composition and morphology of some thermoelectric materials, as well as on the design of thermoelectric and hybrid thermoelectric/photovoltaic devices

The engineering development program of RFX

A review of the engineering developments of RFX, relevant to its plasma performances, is presented. In particular the actions already taken or under way to achieve a better control of the plasma parameters, to limit and control the effects of the plasma-wall interaction and to improve the quality of the confinement fields are discusse

The structure of the power supplies for ITER-FEAT additional heating and current drive systems

Different systems are foreseen for the plasma additional heating and current drive of ITER-FEAT, to provide preionization, assisted current startup, bulk central heating and on- and off-axis current drive. Three different systems of radio frequency (RF) heating (ion cyclotron (IC), electron cyclotron (EC) and lower hybrid (LH)) and a couple of neutral beam injectors (NBI) were designed. The RF generators employ a number of different types of high power vacuum tubes (tetrode (IC), gyrotron (EC) and klystron (LH)) while the neutral injectors consist of coordinated ion production, acceleration and neutralization systems. All these equipments require dedicated dc power supplies PSs; their description and the discussion of their characteristics is done in the paper

Closed-loop control of plasma current and toroidal field in RFX

In the paper the design of a control loop for both plasma current and toroidal field for RFX machine is presented. The requirements of the loads are described and both the static and dynamic performances of the control schemes in terms of precision, response time and stability are discussed. Simulations with different plasma models are then performed to test the behaviour of the control loops under different operating conditions

Preliminary tests on a low cost two-port TEM cell

A modified version of a low cost two-port TEM cell, with a 230 MHz highest operating frequency, has been realized. Two main aspects characterize this new version: the septum is now laterally sustained, and an easier soldering of the septum itself to the output terminals is obtained, by modifications of the septum ends and of the TEM cell terminations. A preliminary series of tests have been performed and the Voltage Standing Wave Ratio (VSWR) has been measured at different frequencies. Presently, a set-up with a VSWR lower than 1.35 in the whole operating frequency range has been realized