F. Maiorca

Performance characterization of different nonlinear-transduction mechanisms for piezoelectric energy harvesting

This paper deals with the analysis of different configurations for piezoelectric energy harvesters. The theory is based on the nonlinear approach applied in PZT-based oscillators. The oscillators that will be exploited and characterized are composed of single and multiple magnetically-coupled bi-stable cantilevers excited through ambient vibrations as external energy sources. Three systems have been validated and compared in terms of calibration diagram, power budget, efficiency, spectral content. The proposed transducers are suitable to be used as converters or sustainers in order to supply smart nodes, wireless sensor networks or to perform autonomous measurement systems.

Multiple nonlinear oscillators for autonomous Wireless Sensor Nodes

In this paper, we present an array of coupled nonlinear oscillators suitable to be applied in Wireless Sensor Nodes and autonomous devices. The energy to be harvested comes from ambient vibrations as external energy sources. In particular, we consider two sources increasingly available in the ambient or in the human body and often both are mixed together: periodic induced waveforms and stochastic sources. The oscillator is composed of multiple magnetically-coupled bi-stable cantilevers with different natural frequencies inside each single well. The structure of the oscillator, modeling, simulations and measurement data will be here described. The principle has been validated and compared with other nonlinear techniques already proposed in literature. In particular the results show the possibility to efficiently recovery energy from mixed-sources having rich spectrum dictated by random vibrations and low frequency peaks consequence of periodic sources. The proposed device, based on piezoelectric output, is suitable to be used as converter in order to supply wireless sensor networks, autonomous nodes or it can be applied as power sustainer for communication of integrated devices and contactless measurement systems.

Energy Harvesting from weak random vibrations: Bistable strategies and architectures for MEMS devices

This paper deals with the problem of gathering electrical energy from sources readily available in the environment. In particular we focus on vibrations that are almost ubiquitous and that very often appear as random, weak and low frequency signals. The above listed features may significantly reduce the efficiency of traditional linear resonant and therefore alternative innovative strategies need to be explored. In this paper we present some devices that have been analytically modeled and experimentally verified for tackling this issue. The basic idea is centered on the use of bistable oscillators to realize vibration harvesters that can scavenge energy from broadband, weak, random vibrations: this idea will be expanded here toward some solutions where bistability is obtained by using magnets but also where it descends from purely mechanical devices. A brief review on solutions developed that exploit magnetic and non magnetic strategies for obtaining bistability is presented, finally the issue of MEMS fabrication for the devices conceived will be discussed.

“Vibration driven” mechanical switches: A novel transduction methodology with applications to DC-DC “diode-less” voltage multipliers

Voltage multiplication is often needed to perform accurate measurement of both DC and AC voltages or in the energy accumulation section of transducers used for energy harvesting. Traditional voltage multipliers, are usually composed of capacitors, inductors, diodes and switches. This approach implies the adoption of active elements (i.e. transistors, MOS, etc.) and a supply voltage is required in order to guarantee the desired effects. However disadvantages in terms of power consumption are expected that can affect the total power budget in low power systems and energy harvesting devices. We consider here transduction systems embedded into an environment where vibrations are present that can be used as energy source. A novel transduction strategy is proposed here to realize vibration driven DC-DC voltage multipliers transducers; our strategy uses mechanical switches, driven by environmental vibrations, and capacitors but not diodes. Implementation of the working principle into a real device will be discussed with analytical models and numerical simulations. Furthermore, an experimental prototype is presented together with some preliminary experimental results that validate the ideas discussed in this papers.

Anti-phase coupled bistable transducers: A review of recent progress

This paper provides an overview of the state of the art and the progress of novel nonlinear behaviors in MEMS devices useful as wide-band vibration energy harvesters, power converters, integrated signal conditioning circuits and filters. Remarkable progress has been made in the field of nonlinear systems and integrated coupled structures, in particular a novel family of device named anti-phase bistable architecture has been developed and patented by authors, here a brief overview will be provided and several aspects, such methodologies and microscale fabrication based on PZT layers, will be exploited.

Autonomous bistable microsensors for noninvasive AC electrical current measurements

An autonomous bistable MEMS sensor for noninvasive monitoring of AC electrical currents is proposed in this work. The main idea is presented together with simulations and feasibility study. The sensor is composed of a piezoelectric cantilever beam equipped with two permanent magnets having opposed magnetization (one on its free end and one external and fixed) in order to achieve bistable behaviour. The beam snaps between its two stable equilibrium states by means of the magnetic force due to the interaction of the magnetic fields generated by the permanent magnets and the electrical current to be measured. The measurement of AC electrical currents is performed by counting the number of commutations of the bistable structure that are related to the magnitude of the current to be measured. An adjustable threshold allows for tuning of the device sensitivity, of its operative range and of its robustness to external noise. The piezoelectric bistable device is also able to harvest the energy needed to make the system autonomous. The proposed current sensor provides intrinsic digital output, the bistable behaviour allows for obtaining good performances at the industrial frequency even if the mechanical resonance frequency of the beam is larger due to the small dimension of the sensor and to the material properties. The sensor has been modeled and several simulation results are provided in order to assess the device working principle.