At present, there are no sensors currently available that can endure very high pressures and temperatures. As part of the “eHarsh” lighthouse project, eight Fraunhofer Institutes have currently designed a technology platform for constructing this type of sensor system.
Ceramic circuit board with integrated circuits resistant to high temperatures. (Image Credit: © Fraunhofer IZM).
The new sensor system can even monitor the inner workings of turbines and deep boreholes for geothermal systems. They can sense disruptive vibrations, raise alerts when a machine is getting too hot and identify damaged parts on a production line.
Sensors have a crucial role to play in current production processes. Entire production lines are handled using dependable sensing devices and artificial eyes.
Yet, it has still not been possible to set up these alert assistants in all areas of industry: Conventional sensors are unable to last long in surroundings that are categorized as very harsh. These include the inner workings of aircraft turbines or power plants and boreholes in the ground, where pressures and temperatures are high. Sensors are also impaired by harsh liquids and gases, or dust.
To resolve this issue, eight Fraunhofer Institutes have come together in the “eHarsh” project to create the first extremely robust sensors for extremely challenging environments.
We have a lot of in-depth knowledge within the individual institutes. We know a lot about heat-resistant ceramics and we have the ability to test material properties and produce robust microelectronic circuits. On our own, though, none of us were capable of creating this type of sensor. It was only through cooperation and the combination of many individual technologies that we were able to succeed.
Holger Kappert, eHarsh Coordinator, Institute for Microelectronic Circuits and Systems IMS, Fraunhofer
Signal Processing Right on Site
The researchers first concentrated on applications with high pressures and temperatures – the above-mentioned boreholes and turbines. The aim was not only to integrate powerful pressure and thermal elements into the boreholes and turbines but also to integrate the electronic components to assess the measurements.
The advantage of having the electronic components on site and of having signal processing take place in the sensor itself is that it improves the quality of the sensor signals. It also means we can network the sensors better in the future, saving on cabling effort.
Holger Kappert, eHarsh Coordinator, Institute for Microelectronic Circuits and Systems IMS, Fraunhofer
This would be especially beneficial in aircraft engines as it would decrease their weight. These engines are intricate. Air flows, electrical power and voltages have to be carefully regulated depending on the flight movement.
Using tiny, powerful sensors well within the engine, the status of the engine could be computed and the combustion process regulated with much greater meticulousness in the future, for example, to make sure fuel is used more efficiently.
The sensor casing is composed of metal and the sensor elements from ceramic that can handle temperatures up to 500°C. The internal electronics can endure about 300°C. One challenge was to integrate the different parts so they would not collapse even when repeatedly cooled and heated, regardless of being designed from materials that expand and contract at varying rates.
Among the materials employed were heat-resistant ceramic circuit boards and conductors with a tungsten admixture that is also used in light bulb filament.
Sensors for Geothermal Systems
The sensors are heat resistant as well as pressure-resistant to about 200 bar – nearly a hundred times the pressure in a car tire. One likely future application for these sensors is in pumps for geothermal systems.
In geothermal systems, hot water from the earth is used to heat buildings. The pumps are located deep down in the borehole and need to endure both the heat and the pressures at that depth. These new sensors render it possible to screen the pumps effortlessly and permanently. These improved possibilities can also assist machine manufacturers to verify the service life of their sensors.
These tests expose components to high temperatures or pressures so that they age more rapidly, which makes it possible to establish the product’s service life within a manageable time frame.
If the sensors are able to work in more extreme situations, it will be possible to attempt the tests with a higher load. This will considerably decrease testing time.
Overall, the interdisciplinary nature of ‘eHarsh’ has allowed us to successfully develop a technology platform for robust sensor systems for many different uses.
Holger Kappert, eHarsh Coordinator, Institute for Microelectronic Circuits and Systems IMS, Fraunhofer