Combining microbial fuel cell and ultra-low power event-driven audio detector for zero-power sensing in underwater monitoring

Achieving zero-power always-on sensing is an attractive challenge for academic and industrial researchers. Long-term and perpetual monitoring are particularly important for battery-operated systems, such as wearable and IoT devices and necessary in a wide range of applications. Zero-power sensing is crucial for devices that are supposed to collect data and important events in inaccessible places, such as under the water, where the replacement of batteries is almost impossible or inconvenient. In this paper, we present a novel ultra-low power always-on event-driven acoustic sensor able to feature pattern recognition with up to eight simultaneous time-frequency features exploiting mixed-signal low power design. Moreover, this paper achieves a zero-power acoustic smart sensor combining the event-driven acoustic detector with a microbial fuel cell, aiming long-term monitoring in underwater applications. Experimental results show that our solution is able to recognize a specific audio pattern in less than 1 seconds with 50μW to 55μW power consumption for single and multi-frequency detection respectively. Finally, we achieve a zero-power smart sensor able to work perpetually when powered with microbial fuel cells providing only 0.4mW of continuous power.