Thermomagnetic generators

In the transition to a low-carbon economy, the recovery of waste heat is becoming increasingly important. One promising solution is miniaturized thermal energy converters that convert waste heat into electricity. With increasing demand for portable and autonomous systems, such as wearables and devices for the Internet of Things (IoT), miniaturized thermal energy recovery could enable their power autonomy.

State of the art

To enable efficient energy conversion on a small scale, research has already made considerable progress in terms of materials, design and scaling. Thermoelectric generators (TEGs) and pyroelectric generators are currently being used. TEGs are based on the Seebeck effect, which generates electricity from a temperature gradient in a material. Pyroelectric generators, on the other hand, use the pyroelectric effect to generate electricity from temperature changes in materials with spontaneous polarization. However, both technologies have limitations in terms of efficiency and performance.

Technology

In contrast, the thermomagnetic generators (TMGs) developed at the Institute of Microstructure Technology (IMT) at KIT use the temperature-dependent magnetic properties of a ferromagnetic foil to generate electricity even from small temperature differences. This foil is applied to the tip of a flexible cantilever, which is also equipped with a permanent magnet and a miniature pick-up coil. When the temperature changes, the magnetization of the film changes significantly and the cantilever starts to move up and down rapidly, leading to the vibration of the miniature pick-up coil inducing an electrical voltage. A resonant self-actuation of the system can be achieved through the targeted design of the system, such as cantilever length or magnetic field strength. As a result, the cantilever vibrates continuously and generates steady electrical pulses in the coil.

Advantages

TMGs are particularly suitable for applications at small temperature differences. The mechanism of resonant self-actuation enables efficient conversion into electrical energy. In addition, the compact design enables integration in the tightest of spaces. With no moving wearing parts, maintenance-free long-term operation is guaranteed.

Options for companies

The compact size and high power density (up to 50 µW per cm²) are attractive for further upscaling of the footprint and number of oscillators to enable a reliable, self-sufficient power supply for wireless sensors, control systems and microelectronics. KIT is looking for partners for further development and application.