Impact based Frequency Increased Piezoelectric Vibration Energy Harvester for Human Motion Related Environments Miah A. Halim, Sungwon Khym, Jae Y. Park* Micro/Nano Devices and Packaging Lab, Department of Electronic Engineering, Kwangwoon University, Seoul, 139-701, Korea *Corresponding Author: Jae Y. Park, jaepark@kw.ac.kr Abstract— This paper presents a frequency increased piezoelectric vibration energy harvesting device where the low frequency periodic impact of a driving beam with a horizontally extended rectangular tip makes two piezoelectric generating beams to vibrate at the same time, with their higher resonant frequencies, producing higher power output. The dimension of the flexible driving beam was 58×4.8×1 mm 3 and that of each piezoelectric generating beam with styrene support was 15×3.5×0.8 mm 3 . Each generating beam of the proposed energy harvester produced a maximum peak output power of 46.51 μW across an optimum resistive load of 200 K under 4 ms -2 acceleration and was increased up to 129.15 μW while the acceleration was increased up to 6 ms -2 at an operating frequency of 12.5 Hz. The output of both generating beams with series connection doubled the overall output of the device. Keywords-Frequency increased generator; Styrene support; Vibration energy harvesting; Flexible driving beam I. INTRODUCTION With the recent advances on wireless and micro- electromechanical system (MEMS) technology, energy harvesting becomes one of the most promising technologies as the alternatives of the conventional battery. The life of the battery is limited and short compared to the working life of the portable electronics and wireless devices. Sometimes it is inefficient to replace or recharge battery. Therefore, a good number of researchers have been investigating since past few years for the energy harvesting technology as a self-power source of these portable electronics and wireless devices. Energy harvesting from ambient vibration is a clean and regenerative means of powering small-scale systems [1,2]. Vibration energy is typically converted into electrical energy using electromagnetic, piezoelectric, electrostatic, or magnetoelectric transduction mechanisms. In our environment around, most of the ambient vibrations take place in low frequency range. Human based applications desirable for powering portable and implantable systems are also characterized by low frequency and large amplitude displacements [3]. However, it has been observed that harvesters with low resonant frequencies typically suffer from reduced electrical power generation. Maximum power occurs at resonance and power flow decreases with the decrease in frequency. Thus, it is quite difficult to produce significant amount of power in low resonant frequency by electromechanical coupling. This leads to think of new techniques for energy scavenging from low frequency ambient vibration. Impact based frequency increased generator is one of the efficient solutions to improve the output power in the low frequency applications environment. Several authors have demonstrated such generators that utilize mechanical frequency up conversion technique [4-9]. In this paper, the impact based frequency increased piezoelectric vibration energy harvester is newly proposed and demonstrated. It is comprised of one low frequency flexible driving beam having horizontally extended rectangular tip and two high frequency piezoelectric generating beams with flexible support to generate increased output power. When two generating beams are both impacted by the extended tip of the driving beam at the same time, the output power is obtained. The proposed device offers high energy transfer as well as increased power generation. II. DESIGN AND FABRICATION A. Device Structure The geometric structure of the proposed energy harvester is shown in Fig. 1. The low frequency driving beam is made of flexible (polymer) material having lower stiffness with proof mass attached to the horizontally extended rectangular tip that hits the free ends of the generating beams at the same time. The unimorph type piezoelectric generating beams having higher resonant frequencies are composed of a piezoelectric layer mounted over a non-piezoelectric layer which acts as a support. When an external vibration is applied to the harvester, Fig. 1. Bird's-eye view (a), side view (b), and piezoelectric generating beam with plastic support layer (c) of the proposed frequency increased piezoelectric vibration energy harvester. 978-1-4673-6352-5/13/$31.00 ©2013 IEEE NEMS2013,Suzhou,China,April 7-10,2013 949