From impedance to Raman spectroscopy

Electrical and thermal impedance spectroscopy for the analysis of liquids

From impedance to Raman spectroscopy

Analysis of liquids and films using ATR-measurement

Liquid analysis

Impedance spectroscopy

Fraunhofer IPM is currently developing innovative sensor concepts based on combined electrical and thermal impedance spectroscopy. Impedance measurement can be used to detect changes in the thermal characteristics of a liquid. Such characteristics are directly linked with other characteristics, such as viscosity. Combining several thermal measurement structures also makes it possible to measure flow rate and direction. Impedance spectroscopy can be used to measure the aging of oils as well as sooting and other processes in chemical reactors.


3Omega method

Fraunhofer IPM develops robust sensor technology in microsystems technology for measurements at temperatures up to 250 °C which are suitable for industrial applications. A novel online measurement system aims at detecting unwanted contaminations and films on surfaces, known as »fouling« in chemical plants and reactors. These measurements are based on the 3Omega method, which has not been applied in this context before. The 3Omega method is based on the interpretation of a thermal signal and enables the additional determination of other temperature dependent process parameters. Among them are heat flow, density, thermal conductivity and capacity. The 3Omega method turns out to be a highly powerful tool for process monitoring. Currently, the method is tested in chemical, pharmaceutical and biotechnological applications.


ATR - attenuated total reflection

For more than 15 years, Fraunhofer IPM has been developing measurement and monitoring systems for liquid analysis based on attenuated total reflection (ATR) in the middle infrared. The systems are suitable for integration into industrial processes. Data of the chemical composition of liquids is provided online, thus enabling direct process control.


Raman spectroscopy

Raman spectrometers provide characteristic »fingerprints« of liquids which allows to distinguish between very similar molecule structures. Raman spectroscopy offers some significant advantages if compared to conventional infrared reflection spectroscopy. This is why Fraunhofer IPM increasingly counts on Raman spectroscopy for liquid analysis.

Using robust Raman spectrometers suitable for industrial application, IPM currently aims at developing a fully automated process control for chemical and food industry.

»Electronic tastes«?

© Photo Fraunhofer IPM

Thermal and electrical impedance spectroscopy are proven tools for determining the characteristics of liquids and solids. As »electronic tongues« or by way of »electronic haptics« microstructured probes are capable of measuring various parameters simultaneously.

  • Physical parameters such as temperature, conductivity, capacity, charge carrier mobility, thermal boundary resistance
  • Chemical parameters such as ph-value, boundary potential, corrositivity
  • Mechanical parameters such as elasticity, hardness, surface roughness, pressure or flow

Multisensor signals yield more detailed information than single sensors, raising the scope of qualification, enhancing measurement accuracy and reliability, and reducing interference. In addition, measurements can be carried out in a wide temperature range.

There are manifold applications for thermal and electrical impedance spectroscopy in production control, robotics, environmental monitoring or quality control.