2013 IEEE XXXIII International Scientific Conference Electronics and Nanotechnology (ELNANO) 349 A Friendly Approach to Increasing the Frequency Response of Piezoelectric Generators Sam Ben-Yaakov, Gil Hadar, Amit Shainkopf and Natan Krihely Power Electronics Laboratory, Department of Electrical and Computer Engineering Ben-Gurion University of the Negev, P.0.Box 653, Beer-Sheva 84105, ISRAEL Abstract — A wide bandwidth piezoelectric generator (PZG) was constructed and tested experimentally. The PZG was characterized using chirp and wideband random excitations. The experimental results showed that by proper shaping of an attached cantilever beam it is possible to increase the number of vibration modes of the PZG and, hence, to improve the effectiveness of the energy harvesting as compared with a conventional cantilever PZG configuration. The proposed structure was designed to produce 3 vibration modes, which extend the operation around the frequencies 35Hz, 57Hz and 76Hz. As a result, the bandwidth was widened by a factor of 2.81 as compared with a conventional harvester. Keywords—Harvesting, piezoelectric devices, resonant power conversion. I. INTRODUCTION Ambient mechanical vibration energy is characterized by different frequency spectra. A piezoelectric harvester is a high Q resonant device that can effectively pick up ambient vibration energy only at or near a particular resonant frequency. This is also evident from the expression of the output average power Pavg as function of vibration frequency [1], 2 3 res avg 22 2 res res m (f f ) P [1 (f f )] (2 f f ) ζδ = - + ζ (1) where f res is the resonant frequency and m, ζ and δ are parameters of the PZG. In applications where the frequency of ambient vibration varies periodically, such as in vehicles and with human motion, the PZG might not always be tuned to the resonance condition. As a result, the efficiency of a PZG with one fixed resonant mode at frequency f res drops significantly (1). Increasingly, efforts are being made to develop broadband energy harvesters that can harvest energy over a large frequency interval. Typically, this is achieved by electrically and/or mechanically connecting energy harvesters whose operating frequencies are slightly different from, but very close to each other [2]. However, these assembled generators must be carefully designed so that each individual generator does not effect the others. This makes such a configuration more complex to design and fabricate and the final volume of the device depends on the number of PZGs utilized. It has also been shown that bandwidth widening can be achieved using mechanical stoppers, nonlinear springs or bi-stable structures [3]-[5]. These strategies can be broadly classified as: 1) bandwidth widening along with increased output power, 2) bandwidth widening without power enhancement. A conventional PZG harvester usually consists of piezoelectric cantilever beam (Fig. 1a) with or without a proof mass attached to the free end. The other end of the harvester is bonded to a vibrating base. All commercial PZGs exhibit this elementary configuration [6]. However, a limitation of this approach lies in the fact that the generator is, by definition, designed to work at a single frequency (1). This study demonstrates a simple and friendly solution to extend the frequency response of the generator, based on the work presented in [7]. The behavior of energy harvesting systems subject to a random broadband excitation is less obvious than the classic sinusoidal case [8]. Therefore, the efficacy of the proposed configuration has been demonstrated under the effect of abnormal vibrations. II. PROPOSED STRUCTURE In many piezoelectric harvesting applications, a conventional PZG includes one or more piezoelectric transducer (PZT) patches that are attached to a flexible beam [9]. Such a concept underpins the conventional cantilever- based generator shown in Fig. 1a. As can be seen in the figure, an additional beam has been clamped to the PZG using a clamping support and screws. In our work, this rectangular beam-based harvester serves as a reference structure, denoted henceforth as “conventional PZG”. A commercial piezoelectric bimorph V20W (Mide Technology) [6] has been selected as the basic platform to be improved. The proposed PZG depicted in Fig. 1b is targeted to the following key objectives [7]: 1) simplified configuration construction approach, 2) cost- and volume- effectiveness, 3) matching practical ambient vibration frequencies around 30Hz-200Hz [1]. 978-1-4673-4672-6/13/$31.00 ©2013 IEEE