A microbial fuel cell powering an all-digital piezoresistive wireless sensor system

Microbial fuel cells (MFCs) are energy sources, which generate electrical charge thanks to bacteria metabolism. We report on a full custom pressure wireless sensor node especially designed to operate with MFCs, comprising an ultra-low-power Impulse-Radio Ultra-Wide-Band Transmitter operating in the low 0-960 MHz band, a nanostructured piezoresistive pressure sensor connected to a discrete component digital read-out circuit, and an MFC energy supply system. The sensor device comprises an insulating matrix of polydimethylsiloxane and nanostructured multi-branched copper microparticles as conductive filler. Our prototype system comprises two MFCs connected in series to power both the UWB transmitter, which consumes 40 mu W, and the read-out circuit. The two MFCs generate an open circuit voltage of 1.2 +/- A 0.1 V. Each MFC prototype has a total volume of 0.34 L and comprises two circular poly(methyl methacrylate) chambers (anode and cathode) separated by a cation exchange membrane. The paper reports measurements on a fully working prototype that enables the separate transmission of pressure information and MFC voltage level at the same time. The complete sensor node powered by the MFC, thanks to its nature can be located either in harsh environments where there is no connection to energy grids, or in environments where the MFC, hence the complete node, can self-sustain.