Heating up IoT – thermal energy harvesting for batteryless microelectronic systems
The hype of Internet of Things is peaking these days with ever larger forecasts of how many billion devices will be implemented everywhere around us and several big insight reports trying to keep up with the growing business estimates. When deploying sensor devices, the energy source is a continuous barrier issuing unwanted challenges regarding cost, installation, service/maintenance and user experience. A barrier creating a heavy environmental burden, with not only the disposal of dead batteries, but often disposal of the whole electronic device due to the cost of the actual battery replacement. It is cheaper to just install a new device.
Removing these barriers, self-powered microelectronic IoT devices can be achieved by implementation of energy harvesting technologies. Photovoltaic solutions have matured years ago and many products use solar cells as primary energy source or as a secondary source topping up a battery and extending the battery lifetime. However for indoor applications, limited light is available. Typical energy levels available from solar cell placed in office is 1uW/cm2 @40 lux, leaving most monitoring applications too power hungry for a solar powered solution.
Alternatives such as harvesting energy from vibrations, magnetic fields and RF exists but especially promising is energy harvesting from temperature gradients through thermoelectric generators showing great potential with technologies currently maturing and being implemented in many applications for monitoring applications in the oil and gas industry, power regeneration in the automotive industry, cooking products for the consumer industry, metering applications in the home automation industry and many more.
Thermal energy harvesting is the process of converting thermal gradients into electrical energy through thermoelectric generators (TEGs). These consist of an array of thermocouples sandwiched between ceramic plates and when exposed to a temperature gradient, one side of the TEG warm and the other side cold, it generates electrical energy (converting the heat flux into electrical energy).
Energy can be generated from temperature gradients of a few degrees, e.g. between a human body and the surrounding air or gradients with hundreds of degree’s difference on hot exhaust pipes etc. These sources of energy ranges from microwatts to kilowatts and the dynamic behavior of temperature changes due to evident changes in the surrounding environment between day and night, changing weather and seasonal changes, results in varying energy generation. To ensure a stable power source to the application power management circuits are used. Standard components (ICs) are available for generic purposes, but often with limited specifications and low efficiency. Optimized application specific integrated circuits (ASICs) for energy harvesting power management can enable both high efficiency with minimum leakage currents as well as optimizing the energy generation through impedance matching and maximum power point tracking (MPPT). Further in the case of exposing a thermal generator to low temperature gradients, the generated voltage typically is in the 10 mV range needing sophisticated boost converter designs, as common power conversion ICs seldom cover below 1V.
DELTA helps companies assessing the benefit of energy harvesting and implementing new self-powered technologies in their products. DELTA has the low power competencies to ensure optimized power management solutions incl. ASIC design and test facilities to validate the performance of new energy harvesting systems.