Maximizing Output Power of a CFPG Micro Energy- Harvester for Wearable Medical Sensors Mehdi Dadfarnia 1 , Kamran Sayrafian 2 , Paul Mitcheson 3 , John S. Baras 1 1 Institute for Systems Research and Electrical & Computer Engin. Dept. University of Maryland, College Park, USA 2 Information Technology Laboratory National Institute of Standards & Technology, Gaithersburg, USA 3 Department of Electrical & Electronic Engineering Imperial College London, London, UK ∗ Abstract—Energy Harvesting refers to the process of capturing and storing energy from the ambient environment. Kinetic energy harvested from the human body motion seems to be one of the most convenient and attractive solutions for wearable wireless sensors in healthcare applications. Due to their small size, such sensors are often powered by small batteries which might necessitate frequent recharge or even sensor replacement. Energy harvesting can prolong the battery lifetime of these sensors. This could directly impact their everyday use and significantly help their commercial applications such as remote monitoring. In this paper, our aim is to develop a Simulink model of the CFPG device that can be used to study temporal behavior of the generated power. Having such a dynamic model, not only helps to have a more accurate estimation of the amount of power generated from various human movements, but also allows us to further optimize the design parameters of the micro-harvester (e.g. size/dimension, electrostatic holding force, etc.) with the characteristics of the input acceleration (i.e. human activity). Index Terms—Micro energy-harvester, body sensors, mathematical modelling I. INTRODUCTION Wearable medical sensors have become a promising interdisciplinary research area in pervasive health information technology. However, various challenging issues including miniaturized sensing/actuator technology, security, reliability and power efficiency still remain. Wireless wearable sensors offer an attractive set of e-health applications among which we can point to various medical & physiological monitoring such as temperature, respiration, heart rate, and blood pressure [2]. As these sensors mainly rely on very small batteries to carry their functions, prolonging their operational lifetime could significantly help their successful commercial application. Energy Harvesting (EH) refers to the process of capturing and storing energy from the ambient environment. There are ∗ The work of M. Dadfarnia was supported by the National Institute of Standards and Technology (NIST) through grant 70NANB11H148 and through an internship. The work of J.S. Baras was partially supported by (NIST) grant 70NANB11H148 and by NSF grant CNS- 1035655. 1 Simulink is a product of MathWorks, Inc. Simulink has been used in few sources from which we can harvest energy for wearable medical sensors; amongst them are light, body heat and typical movements of the human body. Kinetic energy harvested from human body motion seems to be one of the most convenient and attractive solutions for wearable wireless sensors in healthcare applications. Miniaturized energy harvesting devices, also known as micro-generators, which harvest energy from kinetic motion consists of a mass-spring-damper (MSD), a transducer, and an interfacing power-processing circuit as depicted in Figure 1 [10]. Fig. 1. Generic Electromechanical Block Diagram of an Inertial Microgenerator [10] Kinetic microgenerators either utilize direct application of force on the device or they make use of inertial, ambient forces acting on a proof mass. These forces are captured with the MSD component. Unlike microgenerators that utilize a direct application of force, their inertial counterparts require only one point of attachment to the moving structure. This allows for greater mounting flexibility and also a greater degree of miniaturization that is ideal for wearable sensors. A generic model of such a MSD system is depicted in Figure 2 [1]. In this model, the displacement of the mass from its rest position relative to the frame is denoted by (). The absolute motion of the frame is () and that of the proof mass is () = () + (). The proof mass is able to move between the upper and lower bounds i.e. +/-  ! , and is attached to a spring-like structure with spring constant k. Energy is converted when MOBIHEALTH 2014, November 03-05, Athens, Greece Copyright © 2014 ICST DOI 10.4108/icst.mobihealth.2014.257413