3D Printed Thermoelectric generators
Thermoelectric generators are very handy things. They convert ambient heat into electrical power, providing a means to run sensor systems without relying on batteries, anywhere where there is a heat differential present. They work thanks to a property of physics known as a thermocouple, in which two conducting materials made of different substances, are coupled together.
It has long been known that all conducting materials generate a voltage along their length when they're placed in what is known as a thermal gradient when one end of the material is next to a candle and the other is not, for example. Current flows along the conductor away from the heat, or towards the cold. With no candle present, but a block of ice on one end, the same thing will occur, with current flowing towards the ice.
All electrical systems require a circuit to be of use, but a circuit made of the same material will nullify the current, as both sides will be exposed to the same temperature gradient going opposite ways, and cancel out each other's currents. This is why two different conductors have to be used to complete the circuit. One is then more efficient than the other, and a charge is left over once they are done cancelling each other out. This charge can then be used to run devices along the circuit such as a remote sensor.
Thermoelectric generators are thus very cheap and easy to produce. You simply have ot be aware of the conductive properties of the materials you wish to use. However, until now they've had to be traditionally assembled, as they consist of wires laid out in a specific pattern. If we could build a thermocoupled circuit by material deposition, we would be able to include thermoelectric generators inside 3D printed sensor systems, greatly reducing the cost, and allowing for much more intricate designs in what are essentially atmospheric-powered sensor systems.
Well, researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials in Bremen, Germany, have succeeded in doing just that. Presented at the Electronica trade fair in Munich earlier this month, they have devised a methd to 3D print thermoelectric generators in custom designs to the requirements of a given sensor system. As such they can be manufactured entirely inside the sensor, providing permanent power supplies in ways traditional manufacturing finds impossible, as well as manufacturing them at the same time as the rest of the sensor.
Wireless sensor networks facilitate the monitoring of safety-related components, explains Dr. Volker Zöllmer, Head of Functional Structures, whose work focuses on the topic of Energy Harvesting at the Fraunhofer IFAM. For sensors to work at optimum capacity, they must be attached directly to the components interface or even integrated into the component. The power supply is usually obtained via cable or battery. However, the limited storage capacity and battery life, as well as the issue of recycling, are critical subjects for the user, appreciates Zöllmer. In our experience, a replaceable battery contributes significantly to the design of an application and as such restricts the flexible layout.
These 3D printed generators make use of metallic conductors, for maximum energy potential. Even so, the total energy produced is measured in milliwatts. However, if the sensor is part of an intelligent network, then it is only really active when sending and receiving data, so milliwatts are all that are required. Even so, this power source will not be an option for every sensor system, but it does add another very powerful tool in the toolbox towards building a comprehensive sensor web.