The electrical impedance measurement of a suspension is a valid method to monitor crystallization processes. Since it allows measurement of conductivity and permittivity it enables the characterization of non-conductive suspensions. The results obtained show that the concentration of an organic compound of interest can be determined by evaluating its electrical and thermal properties. As the analytical analysis of independent process parameters is a challenging task, a machine learning approach is investigated to extract essential parameter dependency for automated process control purposes.

In the process industry, measurement systems are required for process development and optimization, as well as for monitoring and control. The processes often involve multiphase mixtures or flows that can be analyzed using tomography systems, which visualize the spatial material distribution within a certain measurement domain, e.g., a process pipe. In recent years, we studied the applicability of soft-field electromagnetic tomography methods for multiphase flow imaging, focusing on concepts for high-speed data acquisition and image reconstruction. Different non-intrusive electrical impedance and microwave tomography systems were developed at our institute, which are sensitive to the local contrasts of the electrical properties of the materials. These systems offer a very high measurement and image reconstruction rate of up to 1000 frames per second in conjunction with a dynamic range of up to 120 dB. This paper provides an overview of the underlying concepts and recent improvements in terms of sensor design, data acquisition and signal processing. We introduce a generalized description for modeling the electromagnetic behavior of the different sensors based on the finite element method (FEM) and for the reconstruction of the electrical property distribution using the Gauss–Newton method and Newton’s one-step error reconstructor (NOSER) algorithm. Finally, we exemplify the applicability of the systems for different measurement scenarios. They are suitable for the analysis of rapidly-changing inhomogeneous scenarios, where a relatively low spatial resolution is sufficient.

In this contribution, we present broadband microwave measurements on developed biomedical phantom materials. Therefore, we illustrate the reproducible mixing process of the realized phantom materials that are generated in different shapes with a potting compound and barium titanate. Moreover, three microwave measurement systems, including a coaxial probe, a microwave tomography system, and a radar ellipsometry system, characterize the dielectric behavior of the samples in different frequency bands.

Microwave tomography (MWT) is an imaging method that has been investigated as alternative technique for industrial process monitoring and multiphase flow imaging. These applications require data acquisition units with a high measurement rate in conjunction with a high dynamic range and a wide frequency range at reasonable costs, which is one major challenge designing MWT systems. In this work, we present a MWT system concept including a parallel hardware architecture which potentially allows for a measurement rate greater than 100 measurement cycles per second. We realized a 2-channel prototype electronics which allows for fast and precise single-frequency transmission parameter measurements in frequency range from 0.7 GHz to 5.5 GHz achieving a dynamic range of approximately 75 dB at a data acquisition time of 1 ms. In order to investigate the applicability of the prototype electronics for multiphase flow imaging, we conducted measurements using an 8-port MWT sensor and a 2 × 8 switching matrix. Qualitative approximations of the permittivity distributions in case of different static dielectric phantoms modeling oil-gas-water flow distributions were successfully reconstructed.

Microwave imaging (MWI) is a noninvasive diagnosis method, which has been investigated for a wide range of applications. MWI techniques include radar-based approaches as well as microwave tomography (MWT). One major challenge designing broadband MWI systems is the development of a data acquisition unit that allows for fast broadband scattering parameter measurements with a high measurement precision and a high dynamic range (DR), at reasonable cost. The cost-performance criteria cannot readily be achieved using commercial, continuous wave (CW) vector network analyzers (VNA) or pulse-based systems. Therefore, in this paper we propose a data acquisition unit, based on the well-known method of frequency modulated continuous wave (FMCW) network analysis. It offers fast scattering parameter measurements without compromising the measurement precision and the DR, and is particularly advantageous for MWI systems requiring a high number of frequency samples. A 2-port metadyne prototype electronics with low hardware complexity was developed, which allows very fast, precise, and accurate reflection and transmission measurements in the frequency range from 0.5 GHz to 5.5 GHz. To the best of the authors' knowledge, a system with combined performance in terms of bandwidth, sweep time (1 ms), DR (80 dB) and maximum signal-to-noise-and-spurious ratio (65 dB) has not previously been reported. The design, the calibration, and the characterization of the prototype electronics are described in detail, and the measurement results are compared to those obtained with commercial high-end CW VNA. The advantages and limitations of the metadyne FMCW technique compared to the heterodyne CW technique are discussed. The applicability of the prototype electronics and the described calibration technique for microwave imaging has been demonstrated based on measurements using an 8-port MWT sensor and a switching matrix.

Plasma diagnostics is a crucial tool for numerous of industrial processes using technical plasmas. For an effective process control, the determination of the process parameters at multiple positions inside the plasma reactor is required. Utilizing the concept of the multipole resonance probe (MRP), different parameters of low-pressure plasmas required for process control can be derived based on a single broadband measurement of the complex reflection coefficient. In this paper, we present a prototype electronics for fast and accurate reflection measurements of multiple probes based on linear frequency ramps. Its performance has been analyzed by measurements in the frequency range from 0.1 GHz to 5.5 GHz in case of different microwave filters. The results are in very good agreement with those obtained with a commercial vector network analyzer (VNA), whereas the sweep time of 1 ms is significantly shorter. The applicability of the prototype electronics for plasma diagnostics at multiple positions over a wide range of plasma process parameters has been demonstrated by measurements using a double inductively coupled plasma reactor.

A broadband coaxial line to rectangular waveguide transition for a microwave tomography sensor is presented. It consists of two parts: a coaxial line to double ridged waveguide transition and a double ridged to rectangular waveguide transformer. The transition is well matched (reflection coefficient below -10 dB) and has a low insertion loss (below 3 dB) in a wide frequency range from approximately 0.85 GHz to 4.4 GHz. Due to the symmetric design of the double ridged waveguide, a large single mode propagation bandwidth (0.6 GHz to 3.2 GHz) and a good higher order mode suppression (greater than 10 dB above 3.2 GHz) is achieved. The transition design is described in detail, analyzed by 3D electromagnetic field simulations, and validated by measurements.

The accurate measurement of multiphase flows is a major challenge in the process industry. In this paper, we present an experimental 8-port microwave tomography system for imaging of multiphase flows in metal pipes, primarily intended for oil–gas–water flows. A special sensor design is proposed which accounts for the requirements of the process industry and allows for broadband measurements in the frequency range from 0.7GHz to 5.5GHz. The electromagnetic behaviour of the sensor can be accurately modelled by a 2D model based on the finite element method (FEM) resulting in a moderate computational effort for image reconstruction. The hardware for data acquisition and the algorithm for image reconstruction are reported, focussing on the sensor design and the modelling of sensor's electromagnetic behaviour. The permittivity distributions in case of different static dielectric phantoms modelling oil/water-in-gas and gas/water-in-oil flow distributions were successfully reconstructed at frequencies between 1.25GHz and 2.5GHz using the one-step Gauss–Newton method.

In this paper, we propose a frequency ramp generator for very fast network analysis in the frequency range from 0.4 GHz to 6 GHz. Highly linear analog frequency ramps are synthesized at high frequencies (8.4 GHz to 14 GHz), using a wideband voltage-controlled oscillator (VCO) stabilized by a fractional-N phase locked loop (PLL), and are mixed down to the desired frequency band using a second PLL-stabilized VCO at a constant frequency of 14.4 GHz. In order to achieve a wideband PLL-stabilization, the loop gain variation is reduced by inserting a voltage dependent damping network between the loop filter and the wideband VCO. This leads to an almost constant transient and phase noise performance in the complete frequency range. The overall phase noise at the output of the ramp generator is below -99dBc/Hz at offset frequencies above 10 kHz. The proposed ramp generator allows for fast and accurate network analysis which is demonstrated by means of measurements with a homodyne prototype system. The sweep time of the system (0.5 ms) is significantly shorter compared to previously published ramp based systems and commercial network analyzers, and allows monitoring of rapidly changing measurement scenarios.

A new method for the calibration of a multiport microwave tomography (MWT) system measured with a 2-port vector network analyzer (VNA) is presented. The two VNA ports are mapped to the eight input ports of the MWT system by means of a switching network. This contribution deals with the calibration of the switching matrix. In consideration of the application, the proposed approach reduces the mechanical complexity of the calibration procedure significantly, by eliminating transmission connections between nonadjacent ports. This enables a simplified automation of the measurement setup. In addition, every step of the calibration procedure utilizes self-calibration techniques. Thereby, increasing the diversity of the procedure. Furthermore, the proposed method reduces the number of measurements required for the calibration in relation to comparable methods.

A method for the calibration of an ultra-wideband microwave tomography system is presented. The objective for this measurement system is to calculate the spatial distribution of the dielectric parameters and thereby different materials. Scattering parameters are used to describe the setup and are given to the reconstruction algorithm for evaluation. The measured wave parameters of this system are influenced by the measurement instrument as well as by the setup itself. In addition, it is also necessary for the reconstruction to obtain the scattering parameters at a well defined reference plane. Both requirements can be achieved by the help of a multiport error correction algorithm used for the calibration of a Vector Network Analyzer (VNA). In a first step, an error model for the tomographic system is presented. Secondly, this paper provides a concept for calibration standards which can be used for this application. Since a tomographic system do not offer the possibility for the use of classic reflection standards or a change in the mechanical length of the transmission other calibration standards have to be found. The idea of a homogeneous filling of the tomograph is presented. With the help of a simulation model the requirements for the system as well as the accuracy of the results are analyzed. In addition, measurement results are shown to validate the proposed approach.

In the petroleum industry, precise information about the individual flow rates of oil-gas-water flows are needed for safe and economical production. The determination of the individual flow rates requires an accurate measurement of the individual volume fractions which is a complicated task because of varying properties of the media. The measurement uncertainty of common three-phase flowmeters is strongly dependent on the flow regime. In this contribution, we propose an ultra-wideband (UWB) tomography concept to determine the individual volume fractions of multiphase flows in metal measurement pipes accounting for different flow regimes. A microwave coupling structure has been developed, which consists of a dielectric window and a waveguide with an UWB coaxial-to-rectangular-waveguide transition. A 2-channel test system has been realized and the complex transmittances and reflectances have been measured in the frequency range from 1.1 GHz to 6.0 GHz for different homogeneous media (air, rapeseed oil, and water with different salinities). The measurement results confirm the assumption of the proposed concept that it is possible to distinguish between the oil, gas, and water because of their different complex permittivities. The impact of the waveguides on the measurement results can be compensated in the frequency range from 1.1 GHz to 3.0 GHz by means of a TRL-calibration. Above 3 GHz, the excitation of higher-order waveguide modes lead to narrowband resonances in the measured frequency responses.

In this paper the development of a 0.5 W DC/DC converter is presented. The special feature of the converter is that the flyback converter is laid out without a core on a PCB. The paper shows a way of the implementation of the coreless planar transformer. An analysis shows some results by different geometry and frequency of the planar transformer. This DC/DC converter is adjusted for special current sensors, which are developed in the research group. it will be shown different variants of a layout structure. The issue of the development is the realise a DC/Dc converter with a high isolation voltage.

In this paper is shown the implementation of different layouts of a coreless planar transformer for a flyback converter. In addition, a 0.5W DC/DC converter was developed. The converter is based on a flyback converter for simple applications. The transformer is designed in a form as a spiral coil on a PCB. The special feature of the converter is that the flyback converter is laid out without a core. The area (diameter) of a spiral coil should be bigger as a coil with a core because the air is not a good energy store. The advantage of a coreless transformer is the PCB-Design. An analysis shows some results by different geometry and frequency of the planar transformer.