Size and power requirements of wireless sensor nodes are gradually decreasing and this has allowed data collection
across a range of spatial and temporal ranges. These nodes have power requirements that often necessitate batteries as an
energy source. As the power requirements decrease for these sensors, alternative energy sources become more attractive.
One such technology is thermal energy harvesting. Thermal energy harvesting requires a differential temperature
between a heat source and a cool sink. As heat energy flows from source to the sink, energy can be harvested and utilized
to power sensor nodes. By exploiting the temperature difference between a sun-warmed plate and a heat sink immersed
in water, electrical energy can be harvested. The proposed concept utilizes a thermoelectric device to convert solar
energy into electrical power. Initial experiments were carried out at the CSIRO Energy Centre for a variety of winter
time intervals in 2009, with peak power outputs in the order of 50mW. Results indicate such a system could power a
wireless sensor node continuously at ocean, lake and river water interfaces. We are presently in the process of evaluating
the concept by powering a CSIRO Fleck<sup>TM</sup> wireless node to transmit water temperature and battery voltage data.
Seventy percent of the Earth's surface is covered by water and all living things are dependent upon this resource. As
such there are many applications for monitoring environmental data in and around aquatic environments. Wireless sensor
networks are poised to revolutionise this process as the reduction in size and power consumption of electronics are
opening up many new possibilities for these networks. Aquatic sensor nodes are usually battery powered, so as sensor
networks increase in number and size, replacement of depleted batteries becomes time consuming, wasteful and in some
cases unfeasible. Additionally, a battery that is large enough to last the life of a sensor node would dominate the overall
size of the node, and thus would not be very attractive or practical. As a result, there is a clear need to explore novel
alternatives to power sensor nodes/networks, as existing battery technology hinders the widespread deployment of these
networks. By harvesting energy from their local environment, sensor networks can achieve much greater run-times, years
not months, with potentially lower cost and weight. A potential renewable energy source in aquatic environments exists
via the temperature gradient present between the water layer and ambient air. A body of water will be either a few
degrees warmer or colder than the air directly above it dependant on its latitude, time of year and time of day. By
incorporating a thermal energy harvesting device into the sensor node deployment which promotes the flow of heat
energy across the thermal gradient, a portion of the energy flow can be converted into useable power for the sensor node.
To further increase this temperature difference during the day the top section can be heated to temperatures above the
ambient air temperature by absorbing the incoming sunlight. As an initial exploration into the potential of this novel
power source we have developed a model of the process. By inputting environmental data, the model calculates the
power which can be extracted by a thermal energy harvesting device. Initial outputs show a possibility of up to 10W/m2
of power available from measured sites assuming a thermal energy harvester operating with Carnot efficiency.
By scavenging energy from their local environment, portable electronic devices such as mobile phones, radios
and wireless sensors can achieve greater run-times with potentially lower weight. Vibration energy harvesting is
one such approach where energy from parasitic vibrations can be converted into electrical energy, through the
use of piezoelectric and electromagnetic transducers. Parasitic vibrations come from a range of sources such as
wind, seismic forces and traffic.
Existing approaches to vibration energy harvesting typically utilise a rectifier circuit, which is tuned to the
resonant frequency of the harvesting structure and the dominant frequency of vibration. We have developed a
novel approach to vibration energy harvesting, including adaption to non-periodic vibrations so as to extract
the maximum amount of vibration energy available. Experimental results of an experimental apparatus using
off-the-shelf transducer (i.e. speaker coil) show mechanical vibration to electrical energy conversion efficiencies
of 27 - 34%. However, simulations of a more electro-mechanical efficient and lightly damped transducer show
conversion efficiencies in excess of 80%.