System-On-Mud: Ultra-Low Power Oceanic Sensing Platform Powered by Small-Scale Benthic Microbial Fuel Cells

A self-sustainable sensing platform powered entirely by small-scale benthic microbial fuel cells (MFCs) for oceanic sensing applications is presented. An ultra-low power chip featuring an ARM Cortex-M0 processor, 3 kB of SRAM, and power management unit (PMU) is designed to consume 11 nW in sleep mode for perpetual sensing operation. The PMU includes a switched-capacitor DC/DC converter designed for efficient energy harvesting and step-down conversion for a wide range of input and output power. A small-scale MFC with 21.3
${\rm cm}^{2}$
anode surface area was connected to the PMU to charge a thin-film battery of 1 mAh capacity. A 49.3-hour long-term experiment with 8-min sleep interval and 1-s wake-up time demonstrated the sustainability of system-on-mud concept. During sleep mode operation, the system charges the 4 V battery at 380 nA from the micro-MFC generating 5.4
$\mu{\rm W}$
of power, which allows up to 20 mA of active mode current with net energy neutrality.