Prototyping Energy Harvesting Active Networked Tags: Phase II MICA Mote-based Devices Maria Gorlatova †* , Zainab Noorbhaiwala † , Abraham Skolnik § , John Sarik † , Michael Zapas † , Marcin Szczodrak § , Jiasi Chen † , Luca Carloni § , Peter Kinget † , Ioannis Kymissis † , Dan Rubenstein § , Gil Zussman † † Department of Electrical Engineering, § Department of Computer Science Columbia University, New York, NY, 10027 [mag2206, zzn2101, as2635, jcs2160]@columbia.edu [mcz2104, mks2158, jc2883]@columbia.edu, luca@cs.columbia.edu [kinget, johnkym]@ee.columbia.edu, danr@cs.columbia.edu, gil@ee.columbia.edu ABSTRACT With the convergence of ultra-low-power communications and energy-harvesting technologies, networking self-sustainable ubiquitous devices is becoming practical. Hence, we have been recently developing new devices referred to as Energy Harvesting Active Networked Tags (EnHANTs). These small, flexible, and energetically self-reliant tags can be seen as a new class of devices in the domain between RFIDs and sensor networks. EnHANTs are made possible by the ad- vances in ultra-low-power ultra-wideband (UWB) commu- nications and in organic semiconductor-based energy har- vesting materials. They will enable novel tracking applica- tions, such as continuous monitoring of objects and locat- ing misplaced items. In this demo we present Phase II En- HANT prototypes. Phase II prototypes are based on MICA2 motes integrated with an energy sensing module and an en- ergy harvesting module. The prototypes base their commu- nication decisions on the parameters of their energy mod- ules, thus demonstrating energy harvesting-adaptive com- munications. A custom monitoring system is used to interac- tively demonstrate prototypes’ adjustments to environmental energy availability conditions. Keywords Energy harvesting, energy adaptive networking, ultra-low- power communications, active tags, indoor light. 1. INTRODUCTION Energy Harvesting Active Networked Tags (EnHANTs) belong to the domain between RFIDs and sensor networks [12]. Small, flexible, and energetically self-reliant, EnHANTs will be attached to objects that are traditionally not networked, such as books, furniture, walls, doors, toys, keys, produce, and clothing. In their capacity as active tags, EnHANTs will enable ubiquitous networking of commonplace objects, and thus will provide the infrastructure for novel tracking applications, such as locating misplaced items, continuous * Corresponding author. Custom Sensor Board Thin film/ organic semiconductor solar cell Digital potentiometer Photometric light sensor Crystalline Si solar cell Energy Harvesting Module Energy Characterization Module MICA2 Mote Small battery Arduino board Figure 1: Components of Phase II EnHANT prototype. monitoring of objects, and determining locations of disaster survivors. Recent advances in ultra-low-power circuit de- sign, ultra-wideband (UWB) wireless communications [7], and organic energy harvesting techniques will enable the re- alization of EnHANTs in the near future. Additional infor- mation about the EnHANTs project is available at [2]. One of the key enabling technologies for EnHANTs is en- ergy harvesting, which allows perpetual operation of devices and has recently attracted attention from industry [3–5] and academia [8, 9, 14–20]. In traditional battery-based commu- nications, the devices minimize energy spending to extend network lifetime. With energy harvesting, rather than min- imizing energy consumption, the devices optimize the en- ergy spending according to environmental conditions. The adjustments of energy spending in energy-harvesting sys- tems can be done, for example, by varying devices’ duty cycles [15, 19], activation patterns [16], or data collection rates [8, 17]. Current sensor networking research on radiant energy harvesting mostly focuses on outdoor Solar energy. Since we expect many EnHANT applications to function in- doors, the EnHANT research focuses on harvesting indoor radiant (light) energy. As part of our research activities, we 1