WISPCam: A battery-free RFID camera

Abstract

Energy-scavenging devices with general-purpose microcontrollers can support arbitrarily complex sensing tasks in theory, but in practice, energy limitations impose severe constraints on the application space. Richer sensing such as image capture would enable many new applications to take advantage of energy scavenging. Richer sensing faces two key challenges: efficiently retaining the necessary amount of harvested energy, and storing and communicating large units of sensor data. This paper presents the WISPCam, a passive UHF RFID camera tag based on the Wireless Identification and Sensing Platform that overcomes these two challenges to support reliable image capture and transmission while powered by an RFID reader. The WISPCam uses a novel charge-storage scheme designed specifically to match the image sensor's needs. This scheme optimally balances capacitance and leakage to improve the sensitivity and efficiency of the power harvester. The WISPCam also uses a novel data storage and communication scheme to reliably support the transfer of complete images to an RFID reader application. The WISPCam makes battery-free image capture practical for applications such as mechanical gauge reading and surveillance, both demonstrated in this paper, and opens the door to richer sensing applications on battery-free devices.

Hibernus++: A Self-Calibrating and Adaptive System for Transiently-Powered Embedded Devices

“…For IoT devices that have constrained dimensions, such as implantable wearable bio-sensors [9], personalized healthcare [10], home and building automation [11] and RFID devices [12], it is desirable to power systems directly from the energy harvester without using any energy storage other than decoupling and parasitic capacitance. However, this makes systems susceptible to frequent power interruptions and resets caused by the transient supply.…”

Graceful Performance Modulation for Power-Neutral Transient Computing Systems

“…As an illustration, two AA-sized batteries on a Crossbow Telos mote occupy over half of its overall volume [13]. In systems with constrained dimensions, such as implantable bio-sensors for medical applications and wearable consumer devices [14], assisted living and health-care [15], home and building automation [16], and RFID applications [17], the inherent lack of storage may limit their effectiveness. It is desirable to reduce the size of the energy harvester and the storage as far as possible, to limit the cost and dimensions of sensor systems.…”

μMonitor: In-situ energy monitoring with microwatt power consumption

“…Pulses can be counted by a logic system in order to estimate energy availability. The µMonitor turns the WISPCam [4] (or any other energy scavenging system) into an energy-aware device that can make appropriate decisions based on its remaining energy as well as on the measured value of incoming harvested power.…”