Batteries and Portable Power

Fraunhofer debuts TEG-powered Energy Harvesting Sensor Wristband

The Fraunhofer Institute for Integrated Circuits IIS presents two innovations in the area of integrated energy supplies: flexible battery management for complex battery systems and the energy-independent sensor armband BlueTEG. Battery systems for high voltages are comprised of a number of individual battery cells in order to attain system voltages of between 50 and 400 Volts. The individual cells must be monitored separately by the battery management system to make use of the maximum available capacity of each cell and to guarantee safe operation. Furthermore, different battery technologies provide different cell voltages and peak currents and so the number of required battery cells depends on the battery technology in use. Thus, the battery management system must always be tailored to the specific number of individual battery cells and cell configurations.

The flexible battery management system of Fraunhofer IIS is able to work with different cell numbers and combinations. It can monitor any series or parallel connection of battery cells. A small electronics module at each cell detects cell parameters such as voltage and temperature. This cell module controls active balancing to ensure an equal state-of-charge of the different cells. Optimized bus communication between these electronic modules minimizes the need for wiring between the cells. Superordinate module controllers allow any combination of different modules, either in parallel or in series connection. Power switches in the module controllers execute the safety functions.

The flexible battery management system is also capable of precisely predicting the remaining capacity and the state-of-health by means of shunt- or resistance-based current measurements. This allows run time or range forecasts to be made, which eliminates the need for a safety buffer. The advantage of this is that the maximum capacity of the battery cells can be used to its fullest.

The BlueTEG sensor wristband measures sensor readings such as the ambient temperature or acceleration rates and transmits this data via Bluetooth to a smartphone or tablet PC. Integrated in a wristband, BlueTEG uses the temperature difference between the skin and the surrounding air to produce electrical energy to supply the electronic systems. It is the first Bluetooth module powered by thermal gradients between body and ambient temperature.

To this end, a conventional thermogenerator and a special voltage converter from Fraunhofer IIS are used. BlueTEG does not require a battery that needs to be recharged or exchanged, unlike conventional devices. It can be used with all types of body-worn or wireless sensor systems and can also be integrated in multifunctional or GPS watches, for example.

Fraunhofer Institute for Integrated Circuits IIS
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