[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: 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.
Synthetic Aperture Radar, 2012. EUSAR. 9th European Conference on; 01/2012
[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: 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.
Electromagnetics in Advanced Applications (ICEAA), 2012 International Conference on; 01/2012
[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.
[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.
Synthetic Aperture Radar, 2012. EUSAR. 9th European Conference on; 01/2012
[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: High-frequency ultrasound (HFUS) imaging systems are routinely used for medical diagnostics (skin, eyes) and for medical research (small animal imaging). Although systems with array transducers are already commercially available, imaging systems with single-element transducers are still of interest and available as well, because this type of transducer is less complex, less expensive, and technically mature. Nevertheless, drawbacks exist, for example, the need for mechanical scanning units and the limited depth of field. In this paper, we present a high-frequency (20 MHz) ultrasound imaging system equipped with a spherically focused transducer. Limited-angle spatial compounding is utilized to improve the image contrast, to suppress speckle and noise, and to reduce imaging artifacts. To overcome the limitation in depth of field, the system uses a novel synthetic aperture focusing technique based on the correlation of the recorded echo signals with the simulated point spread function of the imaging system. This method results in lower side lobe levels and greater noise reduction compared with delay-and-sum focusing, which is demonstrated by wire phantom measurements. When used in combination with limited-angle spatial compounding, as presented in this paper, the resulting image quality is superior to conventional single-element HFUS imaging systems and to array systems. Examples of measurements on tissue phantoms and small animals (ex vivo) are presented and discussed in detail.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 07/2011; 58(7):1355-65. · 1.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents a novel density measuring concept for gas/coal particle compositions in pneumatic conveying systems. The proposed monitoring system uses horn antennas to perform complex electromagnetic transmittance measurements through the cross section of the conveying tube. The phase of the complex transmittance gives information about the effective permittivity, which is related to the mean volume fraction of the coal. Electromagnetic field simulations have been performed for the evaluation of the concept and the performance of the designed setup. A test stand for measurements on coal dust under reproducible conditions and with well-defined particle concentrations has been developed and implemented. The test tube has a diameter of 200 mm and a length of 400 mm. Coal particles with a diameter between 20 mum and 100 mum have been dispersed by injecting nitrogen gas inside the test tube. Complex transmission measurements are performed in the implemented setup with a calibrated vector network analyzer within a frequency range of 8-12 GHz. Results of the conceptual evaluation by measurements with different concentrations of coal particles are presented and discussed.
[Show abstract][Hide abstract] ABSTRACT: In this contribution, a novel density measuring concept for gas/coal particle compositions in pneumatic conveying systems is discussed. The proposed monitoring system uses horn antennas to perform complex transmittance measurements through the cross section of the conveying tube. The phase of the complex transmittance contains information about the effective permittivity, which is connected to the volume fraction of the coal. Electromagnetic field simulations have been performed for the evaluation of the concept and the performance of the designed setup. A test stand for measurements on coal dust under repro- ducible conditions and with well-defined particle concentrations has been developed and implemented. Coal particles with a diameter between 20 μm and 100 μm have been dispersed inside the test tube with a diameter of 200 mm and a length of 400 mm by injecting nitrogen. In the implemented setup the transmission measurements are performed with a calibrated vector network analyzer. Results of the evaluation of the concept by measurements with different concentrations of coal particles are presented and discussed in detail. I. INTRODUCTION Pneumatic conveying systems are utilized in handling and transportation of particulate bulk materials like grain, pellets, and pulverized fuels like coal dust in power plants. With a precise knowledge of the mass flow rate of the pulverized fuel, the combustion processes can be controlled and optimized. Flow velocity, mass density and volume concentration of the solid particles inside the conveying tube are parameters to be taken into consideration (1). Common approaches for the measurement of the particles velocity are correlation based methods and Doppler techniques. Available techniques for the monitoring of the volume concentration are based on cut- off frequency measurements (2), determination of backscatter coefficients (3), different resonator properties (4) and vari- ous optical, acoustical and electro-statical concepts. In this contribution, concepts for the measurement of the volume concentration by means of microwaves are discussed and evaluated. The proposed concept is based on transmission measurements through the cross-section of a conveying tube. The complex transmittance between the antennas is measured in order to determine electrical material properties of the gas/dust composition, which are representative for the volume fraction of the pulverized coal. The applied wide frequency range (8-12 GHz) permits a robust and precise analysis.
[Show abstract][Hide abstract] ABSTRACT: The analysis of homogeneous liquids and immiscible mixtures of different liquids (emulsions) is of interest in many industrial processes. Ultrasound based methods allow to measure various acoustic parameters (speed of sound, acoustic impedance, frequency-dependent attenuation), which are suitable to quantitatively characterize liquids and emulsions. In this work, a high-frequency ultrasound (HFUS) measurement cell working in the range from 15 to 35 MHz is presented. The design of the cell and approaches for quantitative ultrasound analysis are discussed based on an analytical one-dimensional model for the propagation of ultrasound waves. Appropriate echo signal processing strategies for parameter extraction and calibration techniques have been developed. Results of the evaluation of the implemented system are presented.
[Show abstract][Hide abstract] ABSTRACT: In this contribution, two measurement concepts for the determination of volume fractions in multi phase flows are presented. Essential requirements for the proper functionality of double transmission measurement concepts, such as the feed side reflection suppression, are presented. The first measuring method uses a two state modulator which allows a high accurate feed side reflection suppression. The second measuring method makes use of a transpolarizing reflector which improves measuring speed and decreases setup complexity. In order to verify the introduced measuring methods, various electromagnetic field simulations and measurements on a borosilicate glass tube are presented and discussed in detail.
[Show abstract][Hide abstract] ABSTRACT: At last year's conference, we presented a synthetic aperture image reconstruction technique (PSF-SAFT) for fixed-focus single-element ultrasound transducers. It is based on the correlation of the recorded echo signals with the simulated depth-dependent point spread function (PSF) of the ultrasound imaging system. Compared to conventional delay-and-sum (DAS) methods, it results in a higher signal-to-noise-ratio (SNR) but lower axial and lateral resolution. In this contribution the synthetic aperture focusing technique is further developed by inverse filtering of the simulated PSFs and coherence factor (CF) weighting for increased resolution and suppression of side lobes, respectively. The proposed method was evaluated using a 20 MHz ultrasound system with a spherically-focused transducer. With measurements on a wire phantom the transducer's resolution in focus was determined and compared to DAS-SAFT and PSF-SAFT processed datasets, with and without CF-weighting. While the spatial resolution does not differ significantly, PSF-SAFT with CF-weighting results in the highest reduction of noise and side lobes.
[Show abstract][Hide abstract] ABSTRACT: In this contribution a mono-static synthetic aperture focusing image reconstruction technique for high-frequency ultrasound imaging systems with fixed-focus single element transducers is suggested. It is based on the correlation of recorded echo signals with the simulated point spread function of the system. The simulation is based on the real transducer properties and takes the echo signal's phase and direction-dependent magnitude into account for reconstruction. The proposed concept has been evaluated by measurements with a 20 MHz ultrasound system on a wire phantom and with small animal imaging experiments. By synthetic aperture focusing the lateral resolution is improved and nearly constant over the whole depth range.
Synthetic Aperture Radar (EUSAR), 2010 8th European Conference on; 07/2010
[Show abstract][Hide abstract] ABSTRACT: A detailed review is given of the application of high-frequency ultrasound (HFUS) at frequencies of 20 MHz and above for high-resolution, cross-sectional imaging of biological soft tissue. The state of the art of HFUS imaging systems is discussed with respect to the underlying engineering concepts, system designs, and available transducer technology. Furthermore, the dependency of the spatial resolution on the system's parameters is analysed. Skin imaging, eye imaging, small animal imaging for preclinical research, and intravascular ultrasound in coronary arteries for arteriosclerotic disease diagnostics are presented as examples for the application of HFUS imaging in medical diagnostics. It is shown that, in the frame of the indicated applications, ultrasound in the frequency range 20-100MHz gives a good compromise between the contrary demands for a good spatial resolution and a sufficiently large penetration depth of ultrasound waves into the tissue. Scanning schemes for the imaging of tissue morphology are considered, including spatial compounding as a multidirectional imaging technique.
Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine 01/2010; 224(2):225-40. · 1.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In industrial process measurement instrumentation, radar systems are well established for the measurement of filling levels of liquids in tanks. Level measurements of bulk goods in silos, on the other hand, are more challenging because the material is heaped up and its surface has typically a relatively complex shape. In this paper, the application of synthetic aperture radar (SAR) reconstruction with a frequency modulated continuous wave (FMCW) radar system for level measurements of bulk goods is evaluated. In the proposed monostatic setup, echo signals are acquired at discrete antenna positions on top of the silo. Spatially resolved information about the surface contour of a bulk good heap is reconstructed by coherent 'delay and sum' processing. The concept has been experimentally evaluated with a 24 to 26 GHz FMCW radar system mounted on a linear stepping motor positioning unit. Measurements on a thin metal wire at different range and on a curved test-object with a diffusely scattering surface have been performed to analyze the system's point spread function (PSF) and performance. Constant range and azimuth resolutions (-6 dB) of 15 cm and 8 cm, respectively, have been obtained up to a range of 6 m, and results of further evaluations show that the proposed concept allows more accurate and reliable level reconstructions of surface profiles compared to the conventional approach with measurements at a single antenna position.
[Show abstract][Hide abstract] ABSTRACT: A synthetic aperture focusing approach is presented, which is based on the cross-correlation of the measured data with the simulated depth-dependent response to a point scatterer of the imaging system. The method has been evaluated by measurements using a 20 MHz ultrasound system with a fixed-focus single-element transducer. The simulation of the system's response is carried out with Field II. Measurements of a wire phantom show a depth-independent lateral and axial resolution below the focal point, even for large imaging depths and an increase of signal-to-noise ratio (SNR). These results are confirmed with small animal imaging experiments. The method is applicable to the near- and the far-field of the transducer, given that it is possible to simulate the system response.
[Show abstract][Hide abstract] ABSTRACT: In this paper, an approach for the imaging of planar surface structures with high-frequency ultrasound in the 20 MHz frequency range is presented and evaluated. Planar material samples are placed in the far field of a single element transducer, and echo signals are acquired in a monostatic, side looking configuration during one or more scans along the azimuth direction. Synthetic aperture focusing is utilized for the reconstruction of B-mode images, which represent the echogenicity along the two-dimensional planar surface. The concept has been evaluated with a spherically focused transducer under the assumption of a virtual point source and under the approximation that spherical waves emanate from the transducer focus. Results from both, simulated echo data and measurement data from test objects, are presented and discussed.