The use of ultra-wideband signals for moisture sensing by electromagnetic wave interaction provides more information on the material under test compared to single tone or narrowband approaches, regarding spatial and frequency dependent phenomena. Current activities to regulate the emission of electromagnetic waves in the spectral band up to 10 GHz for sensor applications open new perspectives for microwave moisture sensing. Therefore, improved and cost effective ultra-wideband measurement principles will become more and more interesting. The use of short pulses or swept sine waves are classic approaches to cover a large spectral band. However, this paper deals with some variants of an alternative method, which applies pseudo-random codes, namely M-sequences, to stimulate the test objects. The method permits monolithic integration of the RF-electronics in SiGe technology. The signal generation and data capturing are referred to a common stable single tone clock and they are controlled by steep trigger signals. This provides for very stable operation, which allows for measurements in both time and frequency domain. Two versions of an M-sequence approach will be considered and their functioning will be demonstrated by means of simple measurement examples.

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Precise inline process analysis, as an instrument for securing product qualities and enhanced process efficiency, nowadays often requires not only a temporal but also a spatial investigation of relevant physical process parameters. From the variety of available methods that allow for a tempo-spatial medium analysis, the ultrasonic-based tomographic approach and its direct application for inline monitoring of liquid systems is discussed in the present contribution. As an application example, the localization and characterization of an a priori unknown multiphase layer system has been performed by means of a simple ultrasonic transmitter–receiver arrangement. The data acquisition is based on the ultrasonic waves that are transmitted through the medium under test. Those signals represent the input of the tomographic process imaging. Using a linear model describing the homogeneous wave propagation and a fast estimation algorithm running on a normal PC, the extraction of information regarding layer thicknesses, materials and boundary properties has been performed in real time. The corresponding results are verified by simulations and semi-numeric studies and are additionally confirmed by first experimental tests.

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