They connect to the internet and share data with other items, creating the network called the Internet of Things (IoT). Therefore, the idea of making these objects autonomous by giving them the ability to power themselves, has been very anticipated, especially for portable and wearable devices.
Hence, a miniaturized thermoelectric generator can possibly allow this in the near future. Silicon nanowires have emerged as a highly promising material that can be used to build an effective generator. They have a relatively low thermal conductance and a high electric conductance.
Conventional silicon-based thermoelectric generators have used long, silicon nanowires of about 10-100 nanometers, suspended on a cavity to cutoff the bypass of the heat current and secure the temperature difference across the silicon nanowires. However, these generators have a pretty weak mechanical strength and they cost a lot to be fabricated massively.
A team of Japanese researches from Waseda University, Osaka University, and Shizuoka University found a solution to this problem. They developed a silicon-nanowire thermoelectric generator that showed outstanding results. It demonstrated a power density of 12 microwatts per square centimeter at a thermal difference of 5ºC. This will be enough to power sensors or to realize intermittent wireless communication.
Additionally, according to Professor Takanobu Watanabe of Waseda University, the generator uses the same manufacturing technology with semiconductor integrated circuits. Therefore, the mass production’s cost will be reduced significantly. He expects the generator to allow us to develop and produce autonomously-driven IoT devices that will charge from environmental or body heats. Maybe, we will have a smartwatch that will be able to charge itself to 100% during our morning jog.
Let’s break down how the researchers achieved this success. The newly developed generator lost the cavity structure and shortened the silicon nanowires to 0.25 nanometers. Simulations showed that by minimizing the device, the thermoelectric performance improves. Despite the change in the structure, power density was not reduced. Additionally, you can multiply it by ten and suppress the resistance by thinning the generator’s silicon substrate from the conventional 750 nanometers to 50 nanometers.
Currently, a lot of improvements can be done. The quality of the generator for stationary power generation in various conditions is not the best at the moment. But the results obtained by the Japanese researchers can serve to support power technology in the IoT-based society a lot.