20 June 2013
Launching satellites is expensive and time-consuming and today they form an essential part of our world’s infrastructure. So keeping satellites operational for as long as possible and knowing how ‘healthy’ they are is extremely important. To help in this satellites incorporate health monitoring devices including temperature, vibration and radiation sensors. These need to be powered and interrogated, adding more wiring to the spacecraft, increasing mechanical and routing problems, and launch weight. Earth orbit also provides a harsh environment for wiring. This all leads to still greater costs.
Making the sensors wireless could significantly reduce these issues, but the sensors would then require individual power sources. However, the microwave antennas of broadcasting satellites have inherent spill-over losses, where a lot of electromagnetic power is actually wasted - diffused on the body of the satellite itself. This high frequency EM energy, available as long as the data links are functional, is a potential power source for on-board systems.
Tapping this wasted energy is the aim of the work reported in a Letter by a collaboration of researchers from the French National Centre for Scientific Research’s (CNRS) Laboratory of Analysis and Architecture of Systems (LAAS) at the University of Toulouse, the French Space Agency (CNES) and Thales Alenia Space (TAS).
Their work demonstrates for the first time the feasibility of microwave energy harvesting for powering autonomous wireless sensors on-board broadcasting geostationary satellites. Using a very simple single Schottky diode topology, exposed to K-band radiation levels in the ranges present on such satellites they show that sufficient power can be provided for the requirements of recent short range wireless communications transceivers.
The team put the success of the work down to the close collaboration of the three partner organisations. CNRS LAAS provided the design, circuit and EM simulations as well as fabrication and measurement facilities. CNES provided funding, established the general technical requirements and performed thermal cycling during the measurement steps. TAS established a mapping of the available electromagnetic energy in the microwave bands (C, X, Ku, K) currently used by broadcasting satellites.
“The major challenge,” said team member Dr Alexandru Takacs “was to prove that the energy harvesting and scavenging techniques at high frequencies (proposed mainly for terrestrial applications at lower frequency bands) are mature enough and compatible with the energy needs of wireless sensors.”
Their proposed energy harvesting technique is based on a very simple topology that is ready to be qualified for space applications. The thermal cycling tests performed at CNES have already partially proved the robustness of the solution, but to fully qualify the technique mechanical and radiation safety tests need to be performed and the overall reliability evaluated.
The next steps toward application of the energy harvester will include integrating it with a wireless transceiver, the other major element of a complete system. There is also adaptation work to be done to ensure the harvester will work with the range of sensor types used in satellite health monitoring, the current demonstrator being designed for a temperature sensor.
Having successfully shown that their design can produce a useful level of power the team are now working on increasing the efficiency of the RF-to-DC conversion to increase the level of the harvested DC-power. This includes working on more complex topologies and designs and they say that the preliminary experimental results are very promising.
This work has a very specific application, but the research group’s wider interest is the field of micro and nanosystems for wireless communications with a focus on wireless sensors networks. This includes wireless, passive and chipless sensors; microwave passive circuits using substrate integrated waveguide (SIW) technology; compact multi-band antennas and millimetre-wave rectennas; and EM modelling of multi-scale structures.
“We see RF energy harvesting technology as a key technique to provide autonomous and environmental friendly wireless sensors for various applications and so it is harmoniously integrated with our long term research activities,” explains Takacs “High or medium levels of microwave/EM energy for frequencies beyond 10 GHz are unusual for terrestrial applications. Consequently the proposed harvesting technique cannot be used as it is for terrestrial applications. Nevertheless wireless power transfer techniques (basically using quasi-identical topologies and technical solutions) for powering sensors at distance can be envisaged for terrestrial application especially in environments where deploying wires is not possible or prohibitive.”
This article is based on the Letter: Microwave energy harvesting for satellite applications (new window).
A PDF version (new window) of this feature article is also available.
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