Volume 78, Issue 1 -

Robust sensors for non-destructive contactless measurements in the laboratory and under industrial conditions are of increasing technical and economical interest. This article deals with the development and application of modular broadband impedance spectroscopic hardware and software concepts suitable for process measurement in the field and the laboratory. Special attention is paid to technical and biophysical aspects of bioimpedance spectroscopy.

Planar chemical sensors often consist of interdigital electrodes (IDE) patterned onto a substrate and embedded in several functional layers such as metal oxides or ionic conductors. The impedances of such sensors exhibit quite similar characteristic spectra which indicates a common functional principle. The calculation of the sensor impedance requires a physics-based model which describes the causal relation between the sensor impedance on the one hand and material parameters of the layers employed, the device geometry, and the operational temperature on the other hand. Starting from classical semiconductor theory we calculate the current through the sensor. The effect of mobile ions is taken into account by an electrostatic approximation. Next the sensor impedance spectrum is derived from the first harmonics of the time-varying driving voltage and the resulting device current. This is in accordance with the approach usually implemented in commercial impedance spectrometers. By the variation of individual model parameters one is now able to investigate the temperature dependence or to deduce design rules for device optimization.

Dielectric spectroscopy in the range of radio waves, also named radiospectroscopy, is an analytical approach to determine the composition of materials, the particle size distribution, and even the molecular behaviour in solid, liquid and gaseous matter. This method of measurement has been studied and used in laboratories for decades. However, only a few devices for inline measurement are available and very often are customized to support a small range of applications. In this contribution a universal, compact, and inline-capable radiospectroscopy system is presented that acquires dielectric spectra for the characterization of fluid substances.

Various measuring methods are applied for the characterization of fuel cells and fuel cell components. Beside ex-situ surface analytical methods like scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) in-situ electrochemical investigation methods are used also. The electrochemical method most commonly used is recording a polarization curve (U-I characteristic) which is determined by electrochemical, ionic, and electronic conductivities; at higher current densities also a diffusion term can be found. The quantitative and qualitative determination of the different contributions is not of basic interest only but offers also the possibility to improve the membrane-electrode-assembly (MEA) and cell design. The electrochemical impedance spectroscopy (EIS) is a highly suitable method for the simultaneous determination of different contributions over a wide potential or current density range.

Eddy current measurements are successfully applied for contactless distance measurement and crack detection on electrically conductive semifinished products. The measurement of shape based on this industrially suitable principle has not been realized so far. Often, optical measurements are used in this task. Especially for red-hot products and exposure to drilling or cutting fluids increases the effort for such applications significantly. Measurement systems based on high frequency eddy currents are more robust and thus better suited for such applications because of their simple construction. Preliminary investigations indicate that this method is capable to detect deviations in geometry as small as a few micrometers. Two measurement methods of the influence of the eddy current in the product on the spectral impedance of a resonant circuit will be discussed.

Specular surfaces can be measured with deflectometric methods. The solutions form a one-parameter family whose properties are discussed in this paper. We show in theory and experiment that the shape sensitivity of solutions decreases with growing distance from the optical center of the imaging component of the sensor system and propose a novel regularization strategy. Recommendations for the construction of a measurement setup aim for benefiting this strategy as well as the contrarian standard approach of regularization by specular stereo.

This paper corrects an error in the C function.