Scientists from the Technical University of the North, Ibarra have developed a baryon acoustic generator, a device that can extract microwatts of energy from ordinary urban noise. The generator can be powered by low-frequency acoustic vibrations: the hum of ventilation systems, vehicle traffic or industrial equipment. In the future, this technology could be used to power sensors and smart city components with the noise produced by modern infrastructure.
Modern technologies for harvesting energy from the environment face a few limitations. For instance, piezoelectric and electromagnetic generators are only effective with strong vibrations or at high frequencies, whereas triboelectric devices are sensitive to moisture and pollution. The Ecuadorian researchers have proposed bypassing these problems by eliminating moving solid parts in favor of a more subtle physical mechanism: the movement of ions in a liquid under the influence of sound pressure.
Their idea is based on the use of a Helmholtz resonator, an acoustic cavity with a narrow channel that resembles a bottle into which air is blown. This resonator can amplify pressure fluctuations at a specific frequency. The amplified sound vibrations are then directed at a membrane made of porous aluminum oxide through which an electrolyte fluid passes. Under pressure, the fluid starts flowing through the membrane’s nanoscopic pores, carrying ions with it. This creates a so-called streaming potential, an electrical voltage difference that can be measured across the electrodes.
Calculations have shown that the device can generate a voltage of up to 100 millivolts per square centimeter of membrane and a power of approximately one microwatt per square centimeter under optimal conditions. Although this is not much, this amount of energy is sufficient for low-power electronics, such as temperature, vibration or air quality sensors that only transmit data intermittently.
In order to test their calculations, the researchers created a 3D model of the generator, which is about 4 cm tall. It consists of three main parts: a housing with an acoustic cavity, a holding ring with an anodized aluminum oxide membrane and a lid with a narrow neck through which sound enters. The design is tuned to a frequency of some 120 hertz, which is typical of ventilation systems and vehicle traffic. Simulations showed that a device of this size does have the ability to amplify acoustic pressure and create a sufficient pressure differential across the membrane to generate the calculated voltage.
One of the greatest advantages of the new generator is its simplicity. The device is completely sealed and has no moving parts, which means that it can operate for a long time even in dusty or humid environments. The researchers believe that microgenerators like this one could be installed inside ventilation ducts, in window frames of buildings near busy roads, or at industrial facilities where low-frequency noise is constantly present.
The next step is to create an experimental prototype and test it in real-world conditions: in air ducts, on building facades or near industrial installations. If the technology proves effective, urban infrastructure could power some of its sensors and monitoring systems with its own everyday noise.
