Sensor networks with battery-powered nodes can seldom simultaneously meet the design goals of lifetime, cost, sensing reliability and sensing and transmission coverage. Energy-harvesting, converting ambient energy to electrical energy, has emerged as an alternative to power sensor nodes. By exploiting recharge opportunities and tuning performance parameters based on current and expected energy levels, energy harvesting sensor nodes have the potential to address the conflicting design goals of lifetime and performance. This paper surveys various aspects of energy harvesting sensor systems- architecture, energy sources and storage technologies and examples of harvesting-based nodes and applications. The study also discusses the implications of recharge opportunities on sensor node operation and design of sensor network solutions.

Energy Harvesting Sensor Nodes: Survey and Implications

Wireless power technology offers the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as data are transmitted through the air. Initial work on the use of magnetically coupled resonators for this purpose has shown promising results. We present new analysis that yields critical insight into the design of practical systems, including the introduction of key figures of merit that can be used to compare systems with vastly different geometries and operating conditions. A circuit model is presented along with a derivation of key system concepts, such as frequency splitting, the maximum operating distance (critical coupling), and the behavior of the system as it becomes undercoupled. This theoretical model is validated against measured data and shows an excellent average coefficient of determination of 0.9875. An adaptive frequency tuning technique is demonstrated, which compensates for efficiency variations encountered when the transmitter-to-receiver distance and/or orientation are varied. The method demonstrated in this paper allows a fixed-load receiver to be moved to nearly any position and/or orientation within the range of the transmitter and still achieve a near-constant efficiency of over 70% for a range of 0-70 cm.

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Analysis, Experimental Results, and Range Adaptation of Magnetically Coupled Resonators for Wireless Power Transfer

We present the design of a communication system that enables two devices to communicate using ambient RF as the only source of power. Our approach leverages existing TV and cellular transmissions to eliminate the need for wires and batteries, thus enabling ubiquitous communication where devices can communicate among themselves at unprecedented scales and in locations that were previously inaccessible.To achieve this, we introduce ambient backscatter, a new communication primitive where devices communicate by backscattering ambient RF signals. Our design avoids the expensive process of generating radio waves; backscatter communication is orders of magnitude more power-efficient than traditional radio communication. Further, since it leverages the ambient RF signals that are already around us, it does not require a dedicated power infrastructure as in traditional backscatter communication. To show the feasibility of our design, we prototype ambient backscatter devices in hardware and achieve information rates of 1 kbps over distances of 2.5 feet and 1.5 feet, while operating outdoors and indoors respectively. We use our hardware prototype to implement proof-of-concepts for two previously infeasible ubiquitous communication applications.

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Ambient backscatter: wireless communication out of thin air

This paper presents the wireless identification and sensing platform (WISP), which is a programmable battery-free sensing and computational platform designed to explore sensor-enhanced radio frequency identification (RFID) applications. WISP uses a 16-bit ultralow-power microcontroller to perform sensing and computation while exclusively operating from harvested RF energy. Sensors that have successfully been integrated into the WISP platform to date include temperature, ambient light, rectified voltage, and orientation. The microcontroller encodes measurements into an electronic product code (EPC) Class 1 Generation 1 compliant ID and dynamically computes the required 16-bit cyclical redundancy checking (CRC). Finally, WISP emulates the EPC protocol to communicate the ID to the RFID reader. To the authors' knowledge, WISP is the first fully programmable computing platform that can operate using power transmitted from a long-range (UHF) RFID reader and communicate arbitrary multibit data in a single response packet.

http://www.alansonsample.com/publications/docs/2008%20-%20TIM%20-%20Design%20RFID%20Based%20Battery%20Free%20Programmable%20Sensing%20Platform.pdf

Design of an RFID-Based Battery-Free Programmable Sensing Platform

Recently, Wireless Sensor Networks (WSNs) have attracted lot of attention due to their pervasive nature and their wide deployment in Internet of Things, Cyber Physical Systems, and other emerging areas. The limited energy associated with WSNs is a major bottleneck of WSN technologies. To overcome this major limitation, the design and development of efficient and high performance energy harvesting systems for WSN environments are being explored. We present a comprehensive taxonomy of the various energy harvesting sources that can be used by WSNs. We also discuss various recently proposed energy prediction models that have the potential to maximize the energy harvested in WSNs. Finally, we identify some of the challenges that still need to be addressed to develop cost-effective, efficient, and reliable energy harvesting systems for the WSN environment.

Energy harvesting in wireless sensor networks: A comprehensive review

Techniques and mechanisms for providing access to an accommodation-capable eye-mountable device via a user interface of an auxiliary device. In an embodiment, the user interface provides prompts for a user of the eye-mountable device to perform various viewing actions, where the eye-mountable device receives from the auxiliary device communications indicating respective times of the viewing actions. Based on the communications, the eye-mountable device generates configuration information indicating a correspondence of respective states of the eye-mountable device to respective characteristics of the viewing actions. In another embodiment, operational modes of the eye-mountable device are defined based on the configuration information.

Method, device and system for accessing an eye-mountable device with a user interface

Advances in energy harvesting, low-power radios, and biometric sensing have enabled new applications in medical and scientific monitoring. In medicine, unobtrusive biosensors promise to wirelessly relay critical patient information including temperature, heart rate, or blood pressure. This paper describes key technologies needed to integrate complex, wirelessly-powered health monitors.

Low power IC design for energy harvesting wireless biosensors

Methods and systems described herein relate to broadcasting an advertisement event on a wireless channel. An example method includes generating, based on data, a data signal including one or more data packets, where each of the one or more data packets is a non-connectable and non-scannable data packet; generating an RF signal using an oscillator circuit; directly modulating the RF signal, based on the data signal, to generate a modulated RF signal; amplifying the modulated RF signal; broadcasting the amplified modulated RF signal on the wireless channel, where the amplified modulated RF signal is associated with the advertisement event.

Transmitter IC for Single-channel Bluetooth Beacon

An eye-mountable device includes an enclosure material, a sensor system, and a controller. The enclosure material has a first surface and a second surface. The first surface is configured to be removeably mounted over a cornea and the second surface is configured to be compatible with eyelid motion when the concave surface is so mounted. The sensor system is disposed within the enclosure material. The sensor system has at least one value that varies with changes in a gazing direction of the cornea. The controller is disposed within the enclosure material and electrically connected to the sensor system. The controller is configured to measure the value of the sensor system to detect the changes in the gazing direction.

Contact lens with gaze tracking

The present disclosure relates to a method that includes calculating a first frequency drift associated with an oscillator at a current temperature; based on the calculation, generating a first signal indicative of temperature compensation data; generating a second signal indicative of packet data and a modulation scheme; using the first signal, the second signal, and a first predetermined signal to generate a first tuning signal; and using the first tuning signal to tune a first capacitor array coupled to the oscillator and a second tuning signal to tune a second capacitor array coupled to the oscillator such that (i) the oscillator generates a modulated RF signal indicative of the packet data and (ii) the modulated RF signal has a second frequency drift that is less than a threshold.

Daniel J. Yeager

Papers

Method, device and system for accessing an eye-mountable device with a user interface

Low power IC design for energy harvesting wireless biosensors

Transmitter IC for Single-channel Bluetooth Beacon

Contact lens with gaze tracking

Temperature-stable FBAR transmitter