Category Energy Harvesting for Autonomous Systems

About the Editors

Stephen Beeby obtained his Ph. D. in micromechanical resonators from the Univer­sity of Southampton, U. K., in 1998. He was awarded a prestigious EPSRC advanced research fellowship in 2001 and is currently a reader in the School of Electronics and Computer Science at the University of Southampton. His research interests in­clude energy harvesting, MEMS, active printed materials development, and biomet­rics. He is the coordinator of an EU Framework Integrated Project “MICROFLEX” and is the principal or coinvestigator on a further 6 projects. Beeby is a cofounder of Perpetuum Ltd. He has coauthored one other book, MEMS Mechanical Sensors, and published over 150 publications in the field and 7 patents.

Neil White holds a personal chair in intelligent sensor systems in the School of Ele...

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Concluding Remarks

Neil White and Stephen Beeby

School of Electronics and Computer Science, University of Southampton, Southampton, United Kingdom

This book has presented an overview of the design and implementation of autono­mous systems that are powered using ambient forms of energy within the operating environment. The availability, over recent years, of low-cost and low-power radio frequency devices has led to the development of many commercial wireless sensor nodes. Examples have been given of how such systems can be used in specific appli­cation areas. A variety of energy harvesting mechanisms has been described within this text; these include techniques based on kinetic, solar, and thermal energy...

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Demonstration Sequence

For the demonstration the two remote nodes (RN1 and RN2) are set up with differ­ing message priority levels, with RN1 having a message priority of MP2 and RN2

Demonstration Sequence

Figure 8.10 Energy-aware, energy-harvesting node components. (1: core node, 2: energy mul­tiplexer subsystem, 3: supercapacitor energy store, 4: thermal energy harvester, 5: wind energy harvester, 6: solar energy harvester, 7: vibration energy harvester.)

having a level of MP4. The sink node is attached to a PC, with the PC configured to display the messages received by the sink node on a terminal window.

In its initial state the energy-aware, energy-harvesting node and the energy multiplexer subsystem are connected to the supercapacitor energy storage module, which is uncharged, and to the vibration and solar harvesting mod...

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Energy Sources for Demonstration

As it was required to be able to control the quantity of energy available to the energy harvesters during the demonstration, controllable energy sources were pro­vided for each of the four energy harvester types being utilized. The energy sources used are as follows:

• Solar energy harvester: For this module the ambient illumination was used, along with some paper clouds that could be used to partly or fully occlude the active face of the solar module and thus simulate variations in incident brightness.

• Vibration energy harvester: As the device used with this module is designed to operate from vibrations from machines powered by the mains electricity supply, a small mains-operated vacuum pump was used as the test source...

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Energy-Aware, Energy-Harvesting Node Demonstration

To demonstrate the energy-aware, energy-harvesting node that has been described here, it has been used with supporting hardware to facilitate data flow and also to provide energy sources for the energy harvesters to utilize.

8.6.1 Supporting Nodes for Demonstration

In the demonstration previously outlined, the energy-harvesting node communi­cates with two remote nodes and a sink node. The remote nodes consist of CC2430 nodes powered by batteries. The nodes have a control allowing the user to set the message priority (MP) of the readings that it makes from the attached sensor module when a measurement is requested. This control was implemented so that by varying the MP the intelligent routing aspects of the energy-aware node can be demonstrated...

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Information Reported by the Energy-Harvesting Node

The energy-harvesting node relays information to the sink node in the form of set message types. Messages are sent using the RF link to the sink node containing the following information:

• Sensor readings from the sensor modules attached to the energy-harvesting node and to the remote nodes: The sensor messages contain the source of the measurement, the measured value, and the message priority level for the message.

• Energy multiplexer module changes: These messages contain details of mod­ules added or removed from the energy multiplexer subsystem presented as

module type and physical location on the energy multiplexer subsystem and whether it has been added or removed.

• Energy module readings: These messages contain the current energy produc­tion rate in the case of harvesting mod...

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Intelligent Energy Management

Within the intelligent energy management process there are several techniques to be used in conjunction to optimize the life of the node and its availability with the final goal being an energy-neutral operation. The first process used is to monitor the availability of energy from the different energy sources and the quantity of en­ergy available from the attached energy store(s). This enables decisions to be made regarding how long the node should spend in the low-power sleep mode if the en­ergy used while in its active state is to be replaced and thus yield an energy-neutral operation...

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Energy-Harvesting Sensor Node Software Design

8.5.1 Node Software

Energy-Harvesting Sensor Node Software Design Energy-Harvesting Sensor Node Software Design

The software used within the node also needs to be written with energy conserva­tion in mind, both in the overall operations being performed and also in the code

Figure 8.8 Demonstration network topology.

implementation. A key strategy used to operate the node in an energy-neutral man­ner is to track the level of available energy and to vary the duty cycle of the node accordingly. In this system this is achieved by interrogating the level of charge of the storage module(s) and assigning the node’s energy level to one of a set number of levels ranging from zero energy to full. At lower levels the sleep duration of the node will be increased, reducing as the energy store reaches higher levels...

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