Novel triboelectric generator can power satellite communication system in harsh conditions
The Arctic is more impacted by climate change than any other region on Earth. Its average temperature is rising at three times the global average, causing a rapid loss of sea ice and a decline in snow cover. In a very real way, what happens in the Arctic shifts the climate balance of the whole planet, so it is critical that conditions there are continuously monitored. Battery-powered sensor platforms (e.g., free-floating buoys) with on-board satellite communication systems are the default option for researchers looking to collect valuable data from across isolated parts of the Arctic Ocean. But low temperatures and limited battery capacity mean these systems rarely operate for more than a few months.
A team from the Pacific Northwest National Laboratory say that they have a potential solution – a robust triboelectric nanogenerator that harvests low-frequency wave energy, and uses it to power environmental sensors and a satellite transmitter. They report on their research in Nano Energy [DOI: 10.1016/j.nanoen.2023.108633].
A key first step in designing any energy harvesting system is to establish how much energy is available. In their location of interest (LOI) – the Arctic Ocean off the coast of Alaska – wave conditions vary drastically throughout the year. For 195 days, the ocean surface is frozen solid. For the remaining 170 days, the average wave frequency is just 0.2 Hz. Air temperatures are low too, reaching − 40 °C.
In order to successfully operate in these conditions, the researchers designed a cylindrical triboelectric nanogenerator (TENG) consisting of two main components: an internal rotor and an external stator, both of which were 3-D printed using polylactic acid (PLA). The stator contains aluminium pads, strips of rabbit fur, and a magnet. The rotor contains multiple fluorinated ethylene propylene (FEP) strips, a magnet, and a weight. The magnets on the stator and rotor repel each other, and the rabbit fur acts as a soft contact between the FEP and PLA. The TENG is then encased in a buoy, where it operates as follows. When the buoy is at the trough of a wave, the mass and magnet in the TENG’s stator are slightly off-centre because of the repelling magnets. As the buoy moves higher on the wave, it causes the stator to pitch, changing the relative positions of the FEP and PLA pads, and increasing the angle of the rotor relative to gravity. As the buoy crests the wave, the angle continues to increase until the force from the weight in the stator overcomes the magnetic repulsion force. The rotor then rapidly oscillates, creating triboelectric energy.
The team first reported their novel TENG design in August 2022. In that initial paper [DOI: 10.1016/j.nanoen.2022.107365], they focused on low-power applications, so the TENG under question was relatively small. In order to power a satellite communication system, researchers had to adjust the design significantly; making the device longer and wider, increasing the surface area of the aluminium and FEP pads, and increasing the number of the soft contacts between them. The resulting device, dubbed Arctic-TENG, was first tested in a wave simulator at room temperature. It achieved its maximum output power when it had 30 FEP-Al pairs. The electrical characteristics of Arctic-TENG were then tested at − 40 °C and 0.2 Hz by placing the wave simulator in a chest freezer. The peak open-circuit voltage of the device was 1000 V, 250 V higher than the output at room temperature, and the short-circuit current of the TENG was also found to be higher in low-temperature conditions. The peak power density of Arctic-TENG reached 21.4 W/m3.
To evaluate the durability of the Arctic-TENG, its electrical performance was tested by emulating one year of operation, or 3 million wave cycles. The authors reported “a rapid increase in open-circuit voltage” initially, followed by a stable voltage output of “about 120% higher than the initial value.”
They then tested a benchtop satellite communication system at − 40 °C, measuring how much energy was consumed during 30 transmissions of varying duration. The team found an average of 15.6 J per transmission. And finally, they implemented a power management circuit and a supercapacitor to investigate the overall performance of the Arctic-TENG. They write, “The total energy generated per year from Arctic-TENG is 8.59 kJ. One Arctic-TENG can transmit 540 bytes of data per day over a year, which demonstrates the power supply capability of ArcticTENG for long-term operation of a satellite communication system.”
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Hyunjun Jung, Brianna Friedman, Wonseop Hwang, Andrea Copping, Ruth Branch, Zhiqun Daniel Deng. “Self-powered arctic satellite communication system by harvesting wave energy using a triboelectric nanogenerator,” Nano Energy 114 (2023) 108633. DOI: 10.1016/j.nanoen.2023.108633