Pulsating micro-bubbles produce harvestable energy

Wireless sensing systems are utilized in a wide range of engineering fields, but despite the research improving functionality power management in these sensors remains suboptimal. Instead of using chemical and short-lived batteries, a new paper by Jang et al. proposes an alternative energy harvesting strategy using micro-bubbles submerged in water.

From small mechanical oscillations, vibrations of microbubbles are harvested into electrical energy used for wireless sensing systems. These microbubbles are light-activated with a laser and deposited on a microchip. Once the microchip absorbs the light and generates heat, the bubble thermally expands. The expanded bubble returns to its original state when the light is turned off.

Accordingly, the illumination of the light from the optothermal pulses produce periodic vibrations in piezocantilevers in contact with the bubble. The piezocantilevers convert bubble-induced mechanical vibrations to an electrical output, which is measured with a digital oscilloscope. The pulsating motions of these light-activated micro-bubbles exert a sizable vibration that results in electric power generation.

The researchers tested and compared the amount of energy produced by piezocantilevers made of both hydrophilic and hydrophobic materials submerged in water. They found piezocantilevers made with hydrophobic surfaces produce more electrical power than hydrophilic surfaces. The generated voltage tends to be proportional to the light intensity regardless of the hydrophilicity of the material. Using more piezocantilevers is predicted to increase electrical output harvested.

These results show that pulsating bubbles activated with light create vibrations that can be harvested with optimized piezocantilevers, converting mechanical energy to electric power. According to the authors, these devices will be useful in sensing sensitive electric and heat signals wirelessly.

Source: “Optothermally pulsating microbubble-mediated micro-energy harvesting in underwater medium,” by Deasung Jang, Jeongmin Lee, Hyeonseok Song, Heebum Park, Jiwoo Hong, and Sang Kug Chung, Review of Scientific Instruments (2019). The article can be accessed at https://doi.org/10.1063/1.5097298 .