Many devices and processes produce low grade waste heat. Some of these include combustion engines, electrical
circuits, biological processes and industrial processes. To harvest this heat energy thermoelectric devices, using the
Seebeck effect, are commonly used. However, these devices have limitations in efficiency, and usable voltage. This
paper investigates the viability of a Stirling engine coupled to an artificial muscle energy harvester to efficiently convert
heat energy into electrical energy. The results present the testing of the prototype generator which produced 200 μW
when operating at 75°C. Pathways for improved performance are discussed which include optimising the electronic
control of the artificial muscle, adjusting the mechanical properties of the artificial muscle to work optimally with the
remainder of the system, good sealing, and tuning the resonance of the displacer to minimise the power required to drive
it.
A novel energy harvester based around capturing the motion of trees has been built and tested. The device consists of an
electromagnetic generator located close to ground level, attached via an inelastic cord to a point on the trunk of a 5-6
meter tall eucalypt tree. The device uses the movement of the tree to drive the generator in one direction, rotationally,
and a mass to keep the cord taught when the tree returns to its resting position. The electrical output is sent to electrical
circuitry that rectifies, stores and switches the electrical power to supply a wireless sensor node. The initial configuration
stored energy in a super-capacitor, the voltage of which indicates storage charge level. Once there was sufficient power
to operate the sensor node it transmits local information such as temperature, and energy state, in terms of capacitor
voltage, to a base node located approximately 80m away. Results show that there is sufficient energy in this method to
power a wireless sensor node continuously in wind as low as 3-4m/s. In order to allow continuous operation in lower
wind speeds a number of alterations have been investigated. These are reported here and include: operation with a
secondary battery in place of the storage capacitor, increasing the electrical storage capacity and varying the connection
point on the tree and the electronic duty cycle.
KEYWORDS: Antennas, Sensors, Sensor networks, Solar energy, Transmitters, Energy harvesting, Power supplies, Telecommunications, Capacitors, Chemical elements
A system has been designed that will allow a network of sensor nodes to request power from a base node and receive it
wirelessly. The system consists of a central transmitting node which can be powered from an indefinite power source or
from a reliable source of energy harvesting such as solar. This energy is converted into UHF radio waves and transmitted
to individual stationary or mobile nodes making up the remainder of the network. When a sensor node detects that its
onboard power supply is at a critical level it will request a top up from the base station. The base station will scan
through 360° for the sensor node and once located begins charging. The charging station will remain in this position until
the sensor batteries are fully charged. At this point the base station will seek out another sensor node if required, or go
into a standby mode. If a mobile node is moved out of the charging position or interference of the beam occurs this is
indicated to the charging station and the transmitting node will scan again until another node is relocated. Results
indicate that charging can be obtained within a radius of up to 1.5 meters or greater for a higher transmission power. The
sensor positioning and power monitoring aspects of the system could be retained for a laser based system, which would
increase the transmission range. The system has the advantage that if sufficient solar energy can be captured during the
day, charging of the sensor nodes can be maintained over night allowing the battery size of each sensor node to be
reduced significantly.
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 FleckTM wireless node to transmit water temperature and battery voltage data.
KEYWORDS: Domes, Thermoelectric materials, Temperature metrology, Sensors, Resistance, Transmission electron microscopy, Solar energy, Water, Aluminum, Wind energy
Over the last decade, wireless computing and mobile devices have decreased in size and power requirements. These
devices traditionally have power requirements that necessitate the need for batteries as a power source. As the power
requirements reduce, alternative means of power become available. One of these is the use of thermal energy. The use of
thermal energy requires a high temperature source and a lower temperature sink. Energy is extracted as heat flows from
the hot side to the cold side. The magnitude of the heat source is not as critical as the magnitude of the temperature
difference between the source and sink. One source of temperature difference is that between a body of water and a solar
heated object. A device has been designed and tested to capture thermoelectric energy where one side of the device is
immersed in water. The other side is exposed to solar radiation. Typically, during the day this is warmer than the water.
However, at night this situation is reversed. This paper discusses the design and manufacture of an innovative thermal
energy capturing device. This device was used to capture energy across an air water boundary. Theoretical estimations of
power available from measured temperature differences are compared with the results of the designed device.
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