International Journal of Energy and Power, Volume 5 2016 www.ijep.org doi: 10.14355/ijep.2016.05.001
A Multiple Direction Broad Frequency Band Piezoelectric Energy Harvester Hongbing WANG, Chunhua Sun, Zhirong LI, Yiping Zhang Department of Mechanical & Electrical Engineering, Suzhou Vocational University, Suzhou, China Abstract A multiple direction broad frequency band piezoelectric energy harvester is proposed for harvesting ambient vibration energy with a variable frequency in different directions. The harvester is composed of eight cantilevers which point to different direction. The single cantilever consists of a base, two ceramic pieces and a proof mass which would be glued together. The finite element model of the harvester is constructed and the effects of structure parameters of the harvester on effective work frequency, electricity generating capability and maximal stress value are analyzed. The results indicate the effective work frequency scope of the harvester is about 13‐20Hz. The harvester can harvest relatively more energy in different excitation. The electric potential of a harvester is about 720.136V at the ambient load of 400Pa and the harvester is well suited for some wireless communication systems. Keywords Multiple Direction; Broad Frequency Band; Piezoelectric; Energy Harvester
Introduction At present lots of portable electrical devices and devices embedded into surroundings have increased greatly and the energy requirements of such devices have significantly decreased. However, the main maintenance problem still remains because batteries need to be replaced or recharged. In order to overcome this problem various energy harvesting techniques have been developed to transform different environmental energy sources into electrical energy suitable for devices[1‐4]. Piezoelectric energy harvesting is found to be a feasible alternative especially when mechanical vibration energy is the dominant energy source compared to solar radiation or temperature gradients[5‐6]. Various types of piezoelectric energy harvesters have been studied which scavenge the wasted energy from human bodies and vibrating machines[7‐9]. In these piezoelectric energy harvesters the cantilever piezoelectric harvester has been adapted widely because of its low stiffness and high sensitivity[10‐11]. The past researches had focused on studying the power performance of a single cantilever. Because of the ambient unstable vibration, a single cantilever can hardly match to the frequency of the ambient vibration source and harvest vibration energy fully. So the ambient unstable vibration influences the power performance of a single cantilever. At the same time, the single cantilever only harvests energy from one direction. But the ambient vibration sources vibrate from all direction. The paper designed a piezoelectric harvester which had many different cantilevers. The cantilevers had different work frequency and point to different direction. The harvester can harvest effectively energy from the ambient unstable vibration. Structure of the Harvester The structure of the harvester is shown in Fig.1. The harvester has a clamp base and eight different cantilevers which point to different direction. The eight cantilevers are clamped by the clamp base which has two parts. The structure of the single cantilever is shown in Fig.2. The single cantilever is composed of a base, two ceramic sheets and a mass proof. The two ceramics sheets are glued on the upper and under surface of the base. The mass proof is attached on the end of the upper ceramic sheet. The natural frequency of the cantilever is easily controlled by the mass proof. One end of the single cantilever is fixed between the clamp base and another end is free. When the harvester is placed among the environment, the cantilever may bent and induce free charge because of ambient vibration.
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