Zero Power Ballast Control (ZPBC) is a technology that relies on microbial energy harvesting developments to enable unsupervised underwater sensing with subsequent surfacing and reporting capabilities. Zero Power Ballast Control (ZPBC) is developed by the Naval Research Laboratory Bioenergy and Biofabrication Section in the Chemistry Division and the Physical Acoustics Branch of the Acoustic Division.

Underwater Sensor Powered by Microbial Fuel CellWith an ultimate goal of producing simple, small, power-efficient data harvesting nodes with variable buoyancy the device will be able to monitor ocean temperatures with a stay time ranging from weeks to months and eventually years, providing a longer term than other mechanisms such as the Expendable Bathythermograph (XBT).

During testing of two ZPBC systems, the rise and fall of the devices were supported by on-board pressure and temperature sensor data and direct observation. The bacterial fuel source (inoculated gas production vessel) was then attached and the two ZPBC devices were deployed in situ off a military pier in Sattahip, Thailand, and held in place by mooring lines for seven days.

Using a low-power (1 to 10 milliwatt [mW]) timer, or only the rate of microbial gas generation that requires zero power input, the device can be alternatively configured to surface “on-demand.” Sensors (e.g., acoustic, magnetic) attached to the ZPBC could be used to detect and classify, monitor the rise to the surface, report using RF or other communication, then re-submerge and continue monitoring operations.

In the future, the ZPBC will provide input for robust modeling of ocean temperatures and other parameters. The ZPBC could also be used to provide in-water optical data to enhance models for underwater visibilities, laser penetration depths, diver and target vulnerability assessments, electro-optical system performance predictions, and refining numerical models.