354 IEEE JOURNAL ON EMERGING AND SELECTED TOPICS IN CIRCUITS AND SYSTEMS, VOL. 4, NO. 3, SEPTEMBER 2014 Characterization of Human Body-Based Thermal and Vibration Energy Harvesting for Wearable Devices Maisam Wahbah, Student Member, IEEE, Mohammad Alhawari, Student Member, IEEE, Baker Mohammad, Senior Member, IEEE, Hani Saleh, Member, IEEE, and Mohammed Ismail, Fellow, IEEE Abstract—Energy harvesting is an important enabling tech- nology necessary to unleash the next shift in mm-scale and W power computing devices, especially for wireless sensor nodes. Energy harvesting could play an important role in biomedical devices where it extends the lifetime of the system. Furthermore, it eliminates the need for periodic maintenance such as exchanging or recharging the battery. This paper presents experimental results of thermal and vibration energy harvested from human body using the thermoelectric generator and the piezo electric harvester, respectively. Contemporary research revealed that most of the published data, including harvesters datasheets, are adjusted for industrial or laboratory-setting environment. This paper focuses on obtaining experimental data from the human body using off-the-shelf harvesters, and discrete electrical com- ponents. Our experimental results showed that for 9 cm area of thermoelectric generator, up to 20 W of power can be generated at 22 C room temperature. In addition, 0.5 cm piezo electric harvester can generate up to 3.7 W when running at 7 mi/h. These data correspond to a power density of 2.2 W/cm and 7.4 W/cm for thermoelectric generator and piezo electric har- vester, respectively. As such, the harvested energy from thermal and vibration of human body could potentially power autonomous wearable and implantable devices. Index Terms—Energy harvesting, piezo electric harvester, ther- moelectric generator, ultra-low power systems, wearable devices, wireless sensor nodes. I. INTRODUCTION B ATTERY lifetime has become one of the most important design criteria in advanced mm-scale and W power com- puting devices for achieving long time operation. In the last two decades, there has been an exponential growth in many mo- bile computing parameters such as CPU speed, memory size, and wireless transfer rates [1]. However, the battery capacity did not scale at the same rate; rather, it increased at a rate of 8%–10% per year [2]. This slow increase does not support any- more the long lifetime, small size and cost requirements of wire- less sensor nodes (WSNs). An easy solution to extend the life- time of the devices is to replace their batteries. However, re- Manuscript received March 02, 2014; revised May 26, 2014; accepted June 26, 2014. Date of publication September 09, 2014; date of current version September 09, 2014. This work is supported by the ATIC-SRC Contract 2013-HJ-2440. This paper was recommended by Guest Editor G. Wang. The authors are with the Department of Electrical and Computer Engineering, Khalifa University, Abu Dhabi, UAE. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JETCAS.2014.2337195 Fig. 1. Power budget versus lifetime for different batteries [11]. placing the batteries might not be desirable or even feasible in many applications such as implantable devices, and hard to reach areas such as structural sensors and pipelines. As such, the need for autonomous device operation that can run for long period of time without any maintenance or intervention has thus far been elusive. Fig. 1 shows a comparison between three types of standard batteries, namely Alkaline AA, 20 mm Lithium Coin, and a 1 mm Lithium Thin-film [3]–[5]. Further, the power density of a 1 mm harvester is shown in Fig. 1. For ultra-low power sensing applications, energy harvesting could potentially play an important role in reducing the form factor of the device since smaller batteries are needed which can be recharged by small energy harvesters [6], [7]. In addition, supercapacitor or solid state batteries can be used so that device size could be further re- duced [8]. Note that for implantable applications, small size and high energy density batteries are still used as standard energy sources, for example in pacemakers. However, recent research showed that energy can be harvested from the inner ear which can potentially operates implantable devices autonomously [9], [10]. Circuit design techniques played a major role in reducing the power consumption of devices and extending their lifetime. In addition, power management units with their power reduction techniques, such as power and clock gating [12], provided the basic techniques for sleep mode operations in WSNs. These low power techniques helped in integrating energy harvesting sources so that batteries can be recharged continuously to achieve autonomous operation. 2156-3357 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.