Microelectronics Journal 37 (2006) 1584–1590 Energy scavenging and power management in networks of autonomous microsensors E. Cantatore à , M. Ouwerkerk Philips Research, High Tech Campus 5, 5656AE Eindhoven, The Netherlands Received 24 August 2005; received in revised form 22 February 2006; accepted 19 April 2006 Available online 28 August 2006 Abstract Networks of autonomous microsensors promise to revolutionize the way people interact with electronics, enabling ambient intelligence. In this paper we investigate different energy scavenging options in real applications to find out which devices are more suitable to power a microsensor having a volume of only 100 mm 3 . Photovoltaic cells are the most promising power generators when a power level of 100 mW is required. If the power consumption can be reduced to about 10 mW, MEMS-based vibration-driven scavengers and thermoelectric generators can also be used. The paper presents as well a power management architecture that enables the use of a scavenger as power source, and discusses some consequences of the limited available volume on power electronics. r 2006 Elsevier Ltd. All rights reserved. Keywords: Autonomous microsystems; Energy scavenging; Power management; MEMS 1. Introduction Ambient intelligence, a vision where electronics is seamlessly integrated with the environment, adaptive and responsive to the needs of people, requires a large number of sensors embedded everywhere. These sensors provide the information that electronic systems need to respond to changes in the environment and enable new ways to interface the electronics with the user [1]. It is natural to think to such a set of sensors as a self- configuring network, where each sensor is an energetically autonomous microsystem, able to elaborate the measure- ments it performs and to exchange information with its peers via radio links [2]. Crucial for this vision is the fact that autonomous sensors should be unobtrusively spread in the human environment, a requirement that limits severely the sensor size. In this paper, a target volume of 100 mm 3 for the sensor, its electronics, the power source and the local energy storage will be assumed. Ideally, microsensors should be completely autonomous from an energetic point of view; able to get the energy they need from the environment. This would eliminate the expensive and cumbersome maintenance associated with battery-powered systems. The paper will focus on the devices that can produce electric power for autonomous microsensors ‘‘scavenging’’ energy from the environment and on a power management approach suitable to these autonomous microsystems. In Section 2, a survey of state of the art devices able to collect energy from the environment will be presented. The energy levels that can be produced with each kind of energy scavenger when the generator is miniaturized and used in practical applications will be analyzed. In Section 3 we present a power management approach able to maximize the power output of an energy scavenger, and we point out the constraints that scavenger device characteristics and integration needs impose to this power management system. Section 4 concludes our work with a summary of our findings. 2. Energy scavenging for autonomous microsensors 2.1. Vibration energy scavengers Vibrations are widely present in our environment, in vehicles, pieces of machinery, buildings (doors, windows, ARTICLE IN PRESS www.elsevier.com/locate/mejo 0026-2692/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2006.04.014 à Corresponding author. Tel.: +31 40 2744392; fax: +31 40 2744113. E-mail address: eugenio.cantatore@philips.com (E. Cantatore).