Nonlinear Multi-frequency Converter Array for Energy Harvesting from Broadband Low-Frequency Vibrations
This work proposes and experimentally validates a vibration energy harvester which combines the multi-frequency and nonlinear approaches into a converter array. The converter array consists of four piezoelectric cantilevers composed of ferromagnetic subst
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Introduction
Piezoelectric energy harvesters from vibrations and motion can be based on linear resonant converter systems which achieve the best harvesting effectiveness when operated at mechanical resonance, but they are suboptimal with frequency-varying and broadband low-frequency vibrations. The exploitation of multi-element harvesters combining the outputs from multiple converters with different frequency responses into a multi-frequency converter array (MFCA) was investigated [1]. However, for a given excitation frequency, mostly one single converter at a time contributes to the output power, with a corresponding limitation in the whole power density. To widen the bandwidth of the converter, the exploitation of nonlinear effects [2] and in particular of bistable systems was introduced, creating external nonlinear forces by means of magnets [3]. The presence of bistability makes the system capable to rapidly switch between the stable states, thereby increasing the converted power and widening the bandwidth of the harvester, but the conversion effectiveness is dependent on the vibration amplitude [4, 5]. To overcome these limitations, the combination of the multi-frequency and nonlinear approaches into an innovative converter array is proposed.
D. Alghisi (*) • M. Baù • M. Ferrari • V. Ferrari Department of Information Engineering, University of Brescia, Via Branze 38, Brescia 25123, Italy e-mail: [email protected] 393 C. Di Natale et al. (eds.), Sensors and Microsystems: Proceedings of the 17th National Conference, Brescia, Italy, 5-7 February 2013, Lecture Notes in Electrical Engineering 268, DOI 10.1007/978-3-319-00684-0_75, © Springer International Publishing Switzerland 2014
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a
b Piezoelectric film
V1
Top electrode Ferromagnetic substrate N S
V2 Spring
LeCroy DSO LT374M
Agilent Waveform Gen. 33220A
V4
V3 Moving magnet
Input mechanical vibrations
Brüel & Kjær Power amplifier type 2719
Brüel & Kjær Vibration exciter type 4808
Fig. 1 Nonlinear multi-frequency converter array. Schematic diagram (a) and the prototype (b) realized with four piezoelectric cantilevers on ferromagnetic substrates and a central permanent moving magnet
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Nonlinear Multi-frequency Converter Array
The converter array is composed of four piezoelectric cantilevers made by ferromagnetic stainless steel substrates with screen-printed PZT layers, coupled with a permanent moving magnet spring suspended at the center of the array base, as shown in Fig. 1a. The piezoelectric cantilevers were fabricated by screen-printing PZT films starting from a paste. The PZT paste is composed of commercial powders (Piezokeramica APC 856) and a low-curing-temperature polymeric binder. The printed films were cured at 150 °C for 10 min and then poled at 300 V at the same temperature for 10 min. The steel substrates have planar dimensions of 40 mm × 5 mm and thickness between 100 and 200 μm, while the PZT layer thickness is about 65 μm. Differences in steel thickness and tip masses among cantilevers determine
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