Publications (78)48.41 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: The measurement of volume fractions of different components in multiphase flows is of great interest in many industrial applications. Ultrasound process tomography is well-suited for the differentiation of gaseous and liquid phases. Simulations and measurements were conducted for a measurement concept using a ring of 32 ultrasound transducers on a measurement pipe. A reflection-mode reconstruction technique was used to obtain the system’s point spread function and examine the performance on inhomogeneous configurations of water containing multiple gaseous objects. Furthermore, the possibility of reducing the number of transducers used as transmitters and its effect on the quality of the reconstructed images were investigated.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, a system design for ultrasound process tomography of multiphase flows is presented. First, different basic aspects of the system’s design and of the utilized reconstruction techniques are discussed. Two reconstruction algorithms based on transmission and reflection measurements are described. Afterwards, the realized system including 32 broadband fan-shaped beam ultrasound transducers is presented. Finally, measurement and reconstruction results of static scenarios, which have been used to evaluate the performance of the system, are presented.
- [Show abstract] [Hide abstract] ABSTRACT: The measurement of volume fractions and their spatial distribution in multiphase flows is of great interest in many industrial applications. Ultrasound methods are well-suited for the differentiation between liquid and gaseous phases. In a system for ultrasound process tomography, the signal transmission characteristics strongly vary with the composition and the spatial distribution of the phases in the multiphase flow. In this contribution, a simulation technique for ultrasound process tomography of gas / liquid flows is presented, which uses ray-tracing for the simulation of ultrasound wave propagation. The received signals obtained after transmission through the liquid phase and scattering at the interfaces between the liquid and the gaseous inhomogenities are efficiently calculated in the frequency domain. The simulation concept and some results of simulated exemplary scenarios are discussed.
- [Show abstract] [Hide abstract] ABSTRACT: Electrical impedance tomography (EIT) is used to determine the spatial conductivity distribution of a measurement environment, what involves several applications in the area of process engineering or medical science. In common systems a measurement environment is usually stimulated by defined current patterns in a serial time-multiplexing manner. Higher measurement rates can be achieved with code-multiplexed (CDM) excitations for parallel measurements. In order to optimize channel separation and dynamic range, orthogonal Walsh-Hadamard codes have been implemented on a fast EIT system. The crosstalk between different channels has been analyzed for 9 parallel coded excitation signals. Furthermore reconstructed conductivity distributions have been compared to reconstruction results obtained from frequency-multiplexed (FDM) measurements (root mean square difference of 0.02%).
- [Show abstract] [Hide abstract] ABSTRACT: Ultrasound cross-correlation flowmeters are utilized to measure the flow velocity of liquids or gases in pipes. The basic concept is to measure the time interval needed by the flow for travelling a given distance between two measurement channels, each consisting of a pair of ultrasound transducers. At each channel, ultrasound waves are emitted in a direction perpendicularly to the flow, and phase and amplitude modulations, which are caused by turbulences and naturally occurring speed of sound variations inside the flowing medium, are assessed. In this paper, different configurations of circular and linear ultrasound transducers have been evaluated for flow velocity measurement in small pipes. The specific problem is that the apertures of the utilized ultrasound transducers are relatively large compared to the diameter of the pipe. The crosstalk between the two channels is another problem, especially for ultrasound beams with large opening angles. Experiments have been performed using different setups consisting of an acrylic glass pipe with 8 mm inner diameter and two measurement channels at a distance of 12 mm from each other. Measurements have been performed using circular (8 mm diameter, 2 MHz frequency) and, alternatively, linear transducers (8 mm length, 1 mm width, 1.4 MHz frequency), and a turbine flowmeter has been used as a reference. It will be shown that the normalized covariance function can be used as a measure to assess the performance of the cross-correlation flowmeter and the reliability of flow velocity estimates. Results of measurements obtained with degassed water have shown that in the case of highly homogeneous liquids the best performance of the flowmeter is achieved by using the phase modulation signals for the cross-correlation.
Chapter: Sonography of the Skin[Show abstract] [Hide abstract] ABSTRACT: Sonography is the oldest noninvasive cross-sectional method to study the skin. Due to technical improvements and advances in signal and image processing in the past 30 years, high-resolution sonography has become a routine diagnostic tool in dermatology. To study the uppermost skin layers, the axial and lateral resolution was increased significantly. In normal palmar skin, the horny layer is represented as echopoor band below the skin entry echo, traversed by echorich coils, which correspond to eccrine sweat gland ducts. The thickness of this band markedly increases after occlusive application of petrolatum. Its lower border is defined by a thin, echorich line, representing the stratum corneum/stratum Malpighii interface. Underneath, a second echopoor band is visible, which corresponds to the viable epidermis plus the papillary dermis, bordered by the scattered echo reflexes of the reticular dermis. Sonograms of normal glabrous skin show only one echopoor band between the entry echo and the dermal reflexes, corresponding to the viable epidermis plus the papillary dermis. The horny layer cannot be distinguished as a separate structure. Using image analysis and statistical methods on sonograms of skin tumors (malignant melanoma, naecocellurlar nevus, scborhocic keratosis, basal cell carcinoma) and inflammatory diseases (psoriasis, lichen planus) we were able to evaluate the usefullness and the limits of high resolution sonography. Our results show that sonography is a valuable tool for in vivo examination of different normal and pathological skin conditions, ranging from the upper epidermis the to .muscle fascia.
- [Show abstract] [Hide abstract] ABSTRACT: The measurement of volume fractions of different components in multiphase flows is of great interest in many industrial applications such as oil production. Ultrasound based methods, especially ultrasound tomography, have a great potential for the differentiation between liquid and gaseous phases in a measurement pipe. Some well-established methods are using transducers with fan-shaped beams to allow for a small measurement time. In this contribution a design of a piezoceramic ultrasound transducer in the shape of a tube segment is discussed. The transducer does not protrude into the measurement pipe and the fan-shaped beam pattern is obtained by focusing onto the inner wall of the pipe. After a brief discussion of the transducer's geometry and the choice of materials, the performed simulations and derived results are presented. Finally, results of measurements, which have been performed with an implemented transducer, are discussed and compared to the results of the simulations.
- [Show abstract] [Hide abstract] ABSTRACT: The focus of this chapter is on engineering concepts, technical solutions, and new modalities for high-resolution ranging and cross-sectional imaging by utilizing high-frequency ultrasound (HFUS) in the frequency range of 20 MHz and above. It gives an overview over of the state of the art of HFUS imaging systems, available ultrasound transducer technology, and basic system design considerations. The chapter discusses system implementations and signal processing techniques for 1D ranging and imaging. It introduces techniques for 2D cross-sectional imaging. Focusing of ultrasound waves is an important issue in this context, and reconstructive imaging modalities, including spatial compounding and multidirectional tissue characterization. The chapter gives examples of applications of HFUS for skin imaging and small-animal imaging.Controlled Vocabulary Termsadaptive signal processing
- [Show abstract] [Hide abstract] ABSTRACT: Electrical Impedance Tomography (EIT) is a well suited measurement method to determine the spatial conductivity distribution of multi-phase flows. In common systems a measurement environment is stimulated by a defined current pattern in a serial time-multiplexing manner. In order to increase the measurement rate, an EIT system with parallel multi-carrier excitation has been designed and implemented, which allows for data acquisition with up to 976 complete measurement cycles per second with 1024 samples per receive channel. In this work the implemented frequency-multiplexing concept will be compared to the more common time-multiplexing measurement approach. Furthermore a correction procedure for fluids with strongly frequency-dependent electrical properties will be presented. © 2014 International Society for Industrial Process Tomography.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper a concept for multi-spectral analysis of radar echo signals is presented, which is aimed at level measurement of bulk goods in silos. Severe problems given in these applications result from the conditions that bulk goods build up a heap and that the microwaves are backscattered at both, its complicated surface and also from inside the heap. The proposed frequency-diversity technique has been evaluated by means of echo measurements in silos filled with plastic pellets and chalk powder. A Frequency Modulated Continuous Wave (FMCW) radar system with 25 GHz center frequency and 2 GHz bandwidth has been used for the measurements. Results show that echo signal fluctuations, which are very strong with the conventional single-band approach, are now largely minimized, what allows for robust and reliable level measurement. Furthermore, we suggest a variance analysis of echo signals from the multiple frequency sub-bands as a method for classification. It will also be shown with experimental results that this strategy can successfully be applied to distinguish between echoes caused by backscattering from randomly arranged inhomogeneities in the bulk solids and spatially separated disturbing radar-targets. The latter are for example given by weld seams at the silo wall, whose echoes may cause severe disturbances of the level measurement.
- [Show abstract] [Hide abstract] ABSTRACT: Existing SAR systems are often limited in resolution by their small bandwidth of below 10 GHz. In this contribution an ultra-wideband 80 GHz FMCW radar sensor for SAR imaging with 25.6 GHz bandwidth is presented. It is based on a custom low-power SiGe-MMIC including all high frequency components, using a nested PLL concept in combination with off-the-shelf PLL synthesizer ICs. In single direction radar measurments, a resolution of 8.09mm is shown. Additionally, results of SAR measurements with a point target show that a good spatial resolution of 12.0 mm × 8.1 mm (Tukey window, α = 0.25, -6 dB width) is achieved. Furthermore, high resolution SAR images of a bike acquired with the sensor are presented.
- [Show abstract] [Hide abstract] ABSTRACT: Quantitative analysis of liquids is of interest for industrial process technology in order to assess concentrations (volume or mass fraction) of different components in mixtures (solutions, suspensions, and emulsions). The measurement of acoustic parameters of a given liquid using ultrasound is a suitable and straightforward technique for this task in many cases. In contrast, the inverse problem of quantitatively estimating the liquid's composition from the measured acoustic parameters is challenging. In this paper a methodology for multivariate analysis of parameters, selection of suitable parameters, and also for solving the inverse problem based on a parameterized analytical model is presented. The proposed concept has been evaluated by measurements with a high-frequency ultrasound (HFUS) bypass measurement cell working in the 15 to 35 MHz frequency range.
- [Show abstract] [Hide abstract] ABSTRACT: A phase-locked loop (PLL) based frequency synthesizer capable of generating highly linear broadband frequency sweeps as signal source of a high resolution 80 GHz FMCW radar system is presented. The system achieves a wide output range of 24.5 GHz starting from 68 GHz up to 92.5 GHz. High frequencies allow the use of small antennas for small antenna beam angles. The wide bandwidth results in a radar system with a very high range resolution of below 1.5 cm. Furthermore, the presented synthesizer provides a very low phase noise performance of -80 dBc/Hz at 80 GHz carrier frequency and 10 kHz offset, which enables high precision distance measurements with low range errors. This is achieved by using two nested phase-looked loops with high order loop filters. The use of a fractional PLL divider and a high phase frequency discriminator (PFD) frequency assures an excellent ramp linearity.
- [Show abstract] [Hide abstract] ABSTRACT: In this contribution, a measurement concept for the volume fraction determination of pneumatic conveyed rice, named pseudo transmission measurement, is presented. The theoretical background of the pseudo transmission measurement as well as an adequate permittivity mixing equation is discussed in detail. Due to the essential knowledge of the rice's permittivity for the mixing equation, a waveguide cut-off frequency measurement for bulked materials is introduced. Because the pseudo transmission measurement is based on a cross polarization effect, a transpolarizing reflector is introduced and simulation results are presented. Additionally the pseudo transmission measurement is performed and evaluated on various amounts of dispersed rice inside a borosilicate glass tube.
- [Show abstract] [Hide abstract] ABSTRACT: Due to advances in technology, resulting in coverage of even higher, and rarely used, frequency regions with low-cost semiconductors, ultra wideband radar systems are getting more feasible for several kinds of applications. In this contribution, the effects of using radar systems with an ultra high spatial resolution, in combination with high precision distance measurements, especially for solid bulk material, and short range synthetic aperture radar (SAR) imaging are discussed. Furthermore, measurements with a wideband (24.5GHz bandwidth) radar sensor in these applications have been done to demonstrate the advantages, of the high resolution. Especially distance measurement applications with many targets or disturbing scatterers benefit from the wide bandwidth. Here, for the measured scenario an accuracy enhancement of a factor 4 to 8 has been obtained by increasing the bandwidth from 4GHz to 24.5 GHz. Furthermore, short range SAR images with a nearly isotropic resolution of 1.3 cm in range, and 1.5 cm in azimuth direction (−6 dB width, Hanning window) are presented. The use of 24.5 GHz bandwidth, and the accordingly better range resolution, which is now in the same dimension as the azimuth resolution, drastically increases the image quality compared to images taken with 4 GHz bandwidth.
- [Show abstract] [Hide abstract] ABSTRACT: An imaging system, using mechanically moved high frequency ultrasound (HFUS) transducers (20 MHz and 40MHz), has been realized, which utilizes the synthetic aperture concept for focused HFUS transducers and combines it with limited angle spatial compounding. This combination leads to a high and range independent spatial resolution as well as to speckle reduction and artifact suppression. The system can be applied to investigations which do not require real time operation, for example imaging of soft tissue areas like tumors. Post mortem imaging experiments on small animals (abdomen of young rats, subcutaneous tumors of nude mice) have been carried out.
- [Show abstract] [Hide abstract] ABSTRACT: Ultra high resolution SAR imaging is useful for many applications, where existing systems are often limited in resolution by their small bandwidth of below 10 GHz. In this contribution an ultra-wideband 80 GHz FMCW radar sensor for SAR imaging with 25.6 GHz bandwidth is presented. It is based on a custom low-power SiGe-MMIC including all high frequency components, using a nested PLL concept in combination with off-the-shelf PLL synthesizer ICs. Results of SAR measurements with a point target show that a good spatial resolution of 12.0 mm × 8.1 mm (Tukey window, α = 0.25, −6 dB width) is achieved. Furthermore, high resolution SAR images acquired with the sensor are presented.
- [Show abstract] [Hide abstract] ABSTRACT: In this contribution a measurement concept, named pseudo transmission method, is presented. It aimes at volume fraction determination in multi phase flows which is a relevant physical quantity for the mass flow determination in latter systems. Fundamentals concerning the material composition as well as necessary mixing equations for effective permittivities are investigated, discussed and adopted to the pseudo transmission measurement concept. In addition a transpolarizing reflector, which is essential for the pseudo transmission measurement method is discussed and evaluated in electromagnetic simulations. The proposed monitoring concept is validated in various electromagnetic field simulations. Finally, measurements that were performed with a calibrated vector network analyzer on plastic phantoms inserted into a glass tube are presented and discussed in detail.
KROHNE Messtechnik GmbHDuisburg-Hamborn, North Rhine-Westphalia, Germany
Bochum, North Rhine-Westphalia, Germany
- • Research Group for High Frequency Engineering
- • Faculty of Electrical Engineering and Information Technology
- • Department of Plastic Surgery