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Microbial Fuel Cells (MFCs) are energy sources which generate electrical charge thanks to
bacteria metabolism. Although functionally similar to chemical fuel cells (both including reactants
and two electrodes, and anode and cathode), they have substantial advantages, e.g. 1) operation at
ambient temperature and pressure; 2) use of neutral electrolytes and avoidance of expensive catalysts
(e.g. platinum); 3) operation using organic wastes. An MFC can be effectively used in environments
where ubiquitous networking requires the wireless monitoring of energy sources. We then report on
a simple monitoring system for MFC comprising an ultra-low-power Impulse-Radio Ultra-Wide-Band Transmitter (TX) operating in the low 0-960MHz band and a nanostructured piezoresistive
pressure sensor connected to a discrete component digital read-out circuit. The sensor comprises an
insulating matrix of polydimethylsiloxane and nanostructured multi-branched copper microparticles
as conductive filler. Applied mechanical stress induces a sample deformation that modulates the
mean distance between particles, i.e. the current flow. The read-out circuit encodes pressure as a
pulse rate variation, with an absolute sensitivity to the generated MFC voltage. Pulses with variable
repetition frequency can encode battery health: the pressure sensor can be directly connected to the
cells membrane to read excessive pressure. A prototype system comprises two MFCs connected in
series to power both the UWB transmitter which consumes 40μW and the read-out circuit. The two
MFC generate an open circuit voltage of 1.0±0.1V. Each MFC prototype has a total volume of 0.34L
and is formed by two circular Poly(methyl methacrylate) (PMMA) chambers (anode and cathode)
separated by a cation exchange membrane. The paper reports on the prototype and measurements
towards a final solution which embeds all functionalities within a MFC cell. Our solution is
conceived to provide energy sources integrating energy management and health monitoring
capabilities to sensor nodes which are not connected to the energy grid.
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