H. Vocca

A real vibration database for kinetic energy harvesting application

In this article, we discuss the project of a vibration signal database for energy harvesting purpose. After a brief description where we present the technologies used to create the database and the procedures to acquire the signals, we show some results obtained using selected environmental noises from the database to characterize nonlinear energy harvesters.

Bistable electromagnetic generator based on buckled beams for vibration energy harvesting

Bistable piezoelectric generators have been demonstrated to outperform linear spring–mass–damper systems in terms of frequency bandwidth and harvested power from wideband vibrations. In this work, a nonlinear vibration energy harvester consisting of clamped–clamped buckled beams combined with a four-pole magnet across coil generator is investigated. By buckling the support beams, an elastic Duffing potential is provided so that the seismic mass can pass from being dynamically monostable to bistable. A theoretical model of the system is presented, and experimental tests are performed on a prototype. In the unbuckled state, the device exhibits higher maximum power at resonance than in the buckled, but, in general, no significant difference is noted in terms of average harvested power between monostable and bistable regimes under harmonic and band-limited stochastic vibrations. However, for an optimal acceleration level, the bistable configuration shows a factor of 2.5 times wider bandwidth and higher power outside from the natural resonance as compared with the monostable regime. It is also observed that the benefits of bistable dynamics mostly depend on the ratio between the characteristic cutoff frequency of the electrical circuit and the mechanical resonance.

Low-frequency internal friction in silica glass

Precise low-frequency internal friction measurements on vitreous silica, taken over a wide temperature (4 K 160 K the loss angle develops a distinct step-like structure followed by a plateau, both independent of ν, thus signalling the onset of a competing relaxation mechanism with much higher an activation energy. Copyright c EPLA, 2007

Nonlinear noise harvesters for nanosensors

Abstract The nanosensor network is an interesting technology that promises a wide range of applications in human life. Nowadays a sensor node is typically battery powered and should operate without attendance for a relatively long period of time. Usually it is very difficult, or even impossible to change or recharge batteries. Moreover batteries are not a feasible solution at the nanoscale. In this paper we present a green alternative to power nanosensors, which consists of harvesting energy from the environment. We focus our attention on piezoelectric harvester capable to convert random environmental vibrations into electrical power. In particular we present an alternative method to gather energy from a wide frequency range based on the exploitation of nonlinear dynamics to enhance power production with respect to traditional linear kinetic harvesters.

A parallel Beowulf-based system for the detection of gravitational waves in interferometric detectors

The detection, in a modern interferometric detector like Virgo, of a gravitational wave signal from a coalescing binary stellar system is an intensive computational task both for the on-line and off-line computer systems. A parallel computing scheme using the Message Passing Interface (MPI) is described. Performance results on a small scale cluster are reported.

Fused silica suspension for the VIRGO optics: status and perspectives

Thermal noise in mirror suspension wires is the main limitation of low-frequency sensitivity of interferometric gravitational wave detectors. In order to minimize the pendulum thermal noise, a monolithic design, using a low dissipation material, is proposed for VIRGO. High mechanical Qs and high breaking strengths have been obtained for monolithic fused silica fibres. A low-dissipation and high-strength bonding technique using potassium silicate bonding is proposed.

Kinetic Energy Harvesting

The recovery of wasted energy present in the ambient that is a reject of artificial or natural processes to power wireless electronics is paving the way for enabling a huge number of applications. One of the main targeted technologies that meets the levels of harvestable power, typically few hundreds of microwatts, is represented by wireless sensor networks (WSNs) [1]. This technology consists of a grid of spatially-distributed wireless nodes that sense and communicate information like acceleration, temperature, pressure, toxicity of the air, biolog‐ ical parameters, magnetic field, light intensity and so on, among each other and up to the end user through a fixed server. In the next years, WSNs will be massively employed in a wide range of applications such as structural monitoring, industrial sensing, remote healthcare, military equipment, surveillance, logistic tracking and automotive monitoring. In fact, harvesting energy directly from the ambient not only represents a realistic mean to integrate or substitute batteries, but is the sole way for enabling many contemporary and future wireless applications that will be all integrated in the so called “internet of things” [2].

Electromagnetic Buckled Beam Oscillator for Enhanced Vibration Energy Harvesting

In this work, a nonlinear vibration energy harvester consisting of a buckled beam and an electromagnetic transducer is proposed. An advantage of this device is that there is no need of permanent magnets to create the bistable potential. Theoretical modeling and experimental investigations on a prototype are presented. The prototype demonstrates a peak power of 2.96 mW at resonance of 52 Hz under 0.32 g of acceleration in the unbuckled configuration, while under bistable regime, it shows a gain up to 115% of power. Besides, both systems show a large bandwidth response compared to resonant cantilever devices.

Monocrystalline fibres for low thermal noise suspension in advanced gravitational wave detectors

Thermal noise in mirror suspension will be the most severe fundamental limit to the low-frequency sensitivity of future interferometric gravitational wave detectors. We propose a new type of materials to realize low thermal noise suspension in such detectors. Monocrystalline suspension fibres are good candidates both for cryogenic and for ambient temperature interferometers. Material characteristics and a production facility are described in this paper.

Mechanical quality factor of mirror substrates for VIRGO

Thermal noise in the mirror substrates is expected to be the main limit to the VIRGO sensitivity in the 50–500 Hz frequency range. The mechanical quality of the mirror substrates and the geometry of their suspension are expected to affect the noise level of the detector output. High mechanical Q have been obtained for different large fused silica substrates under VIRGO suspension conditions. Moreover, calcium fluoride substrates are shown to provide a more promising option for the design of future cryogenic, low thermal noise interferometers.