The EPFL researchers managed to merge antennas and solar cells in a mixed device that promises unprecedented efficiency, this is the first step towards the development of more compact and lighter satellites, but also to the improvement of mobile communication systems used in case of disaster.
Traditionally, telecommunication antennas and solar cells do not mix. They must function independently not to interfere. This constraint has such an impact on the weight and size of satellites: they must have an area large enough to accommodate both an antenna system – for transmitting and receiving data – and solar panels for the electricity supply.
As part of his master project carried out within the Perruisseau-Carrier Group, Philippe Dreyer proposes to merge antennas and solar cells. In collaboration with Transparent Conductive Oxides (TCOs) Laboratory (PV-LAB) group has developed a joint surface, which helps maintain excellent performance as the antenna for the photovoltaic cell.
That substantially reduces the volume, weight and cost of satellites. But not only. Communication stations portable and autonomous, which are often used to establish contacts in natural disasters, could be of advantage. With this new technology, they could become lighter and therefore move more easily. “Our approach is compatible with flexible implementations. Conceivably bend our device, so that it unfolds once arrived in the disaster areas,” illustrates Professor Perruisseau-Carrier, who oversaw the project.
A simple “layers” structure
For their study, researchers favored the use of so-called reflectarray antennas (RA), which have the advantage of being flat, inexpensive and highly efficient. They combined these antennas with solar cell in thin amorphous silicon layers, developed by the Laboratory of Photovoltaics and Thin Film Electronics (PV-Lab).
The device is composed of solar cells on which a set of conductors (resonators) was tabled. This “in layer” structure preserves up to 90% of the photovoltaic performance. “This is not the first attempt to merge antennas and solar cells. But our method is special as it provides good performance for both the antenna and the photovoltaic device, all without affecting the structure of the original solar cell. From a technological point of view, just take a solar cell and adding a conductive layer.”
Two variants of antennas have been developed: one with a copper resonator, which does not pass of optical beams where the metal is deposited, but which ensures high performance of the antenna, and another with a transparent conductor says, which emphasizes the performance of the solar cell.
Thus, for future applications, one will use either method, depending on whether one wants to enhance the operation of the antenna, or the solar panels. “We are especially pleased that these results are the fruit of a single master thesis, which has been extended to a few months,” says Julien Perruisseau-Carrier.
Antennas and solar cells of tomorrow
Still uncommon, the devices selected for this study were not randomly chosen: they are promising for space. Developed over 20 years in the (PV-Lab), solar cells thin amorphous silicon layers have the advantage of being lightweight and resistant to radiation. “With a yield of 10 to 11%, they are not as effective as cells III-V multijunction traditional” concede Christophe Ballif and Monica Morales Masis, PV-Lab. “However, they allow better power to weight ratio (in terms of W/kg).”
RA antennas are considered part of tomorrow’s technologies. “NASA will send a satellite equipped with this type of antennas and solar panels in a technology demonstration mission in 2014,” says Julien Perruisseau-Carrier, for example. For this mission, NASA uses a platform with side panels and antennas on the other. The possibility of merging the two devices in this case would already saved the surface.