This website presents the the progress on the development of an energy-autonomous tracker for mammals at the University of Freiburg – IMTEK.
With our tracker, new fields of possibilities in long-term monitoring are opened for biologists, farmers and researchers, leading to a better understanding in behavior, and needs of our wildlife or livestock.
Our tracker uses the temperature-gradient between mammal and environment for harvesting with a thermoelectric energy generator (TEG) small amounts of electric energy. This is enough for fulfilling the basic needs:
- Tracking the position of the animal
- Monitoring activity
- Monitoring temperature
Our test system consists of a mobile tracker and our base-station. The mobile tracker has three thermoelectric generators (TEGs) which are placed between a heatsink and a massive aluminum part which acts as a thermal connector to the fur of our sheep. The TEGS convert electric energy out of the temperature-gradient that exists between heatsink and the animal. This energy is used to power our system which measures for evaluation purposes the temperature of both sides and transmits them to our base-station.
In this article we are going to show the general idea and components of the system that makes the tracker energy-autonomous.
The energy for the tracker is converted from the temperature difference between the mammal and the outer environment. A thermoelectric generator (TEG) can use this temperature difference to supply electric parts
Unfortunatley the temperater difference is in the range of 1 – 2 K, resulting in very low output voltages in the range of 20 – 40 mV at the TEG. This way to small to supply any electronics and has to be upconverted by a factor around 100 to 2 V. A great challenge is the efficiency for a device that is capable to do this. Our Step up Converter can reach here outstanding 60 %, thus 40 % of the available input power is already lost in upconversion the voltage.
The now usable energy is stored in a capacitor – and commulated to a point where there is enough available that the rest of the circuitry can be turned on to do their tasks:
- Measure the temperature of inner and outer side of the TEG
- Measure the acceleration/activity of the mammal
- Encode this data
- Transmit the encoded data wireless
With that our tracker already works without any batteries, transmitting roughly every 2s.
Our paper „Development of a batteryless VHF-Beacon and tracker for mammals“ got the outstanding paper award at the international conference PowerMEMS 2017. At this conference we presented our first version of the tracker in a talk and also demonstrated the system in a live demo. As we had no sheep, we used a small peltier-element to provide some heat. Attached is the graph of the measured temperaturegradient at the PowerMEMS.
From monday, 24th of august, the first energy-autonomous tracker (without batteries), our tame sheep was waring our modified collar in Freiburg.
Our system was attached to a sheep as a collar, collecting for several days the temperature gradient at the TEGs, activity and energy-state of the system. All data was directly sent through a gateway on the farm to the webserver, displaying the data live here. The displayed the incoming data is not filtert, nor postprocessed. Transmission errors also occour, leading to false temperatures.