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Fine powders are generated in large volumes by industrial activities such as mining, metallurgical processing, energy generation and processing of waste. To meet specifications for further use, powder processing such as comminution and size classification are commonly applied. To optimise the design and operation of air-flow based classification processes, continuous on- line, monitoring of variations in dust particle concentration are an asset. This paper reports on the development of a novel ultrasonic measurement system suitable for robust monitoring of air-borne dust concentration variations during the operation of powder classification installations. The system was tested on a pilot-scale classifier designed for air-borne separation and recovery of ultrafine powders from coal combustion fly ashes. The monitoring method is based on a measurement of ultrasonic wave attenuation by particles suspended in the air-flow of the classifier.

The purpose of this work was to develop a multichannel ultrasonic measurement method for monitoring a spatially non-uniform blood clotting process. This novel method is based on simultaneous multi-channel measurements of ultrasound propagation velocities in different horizontal cross-sections of clotting blood. The most common method used for determining blood-clotting time is the capillary tube method. For this purpose ultrasonic methods based on measurements of the velocities of ultrasound waves in clotting blood are also used. Measurement results essentially depend on the propagation path of the ultrasonic wave in a blood sample. The ultrasound velocity changes as fresh blood transforms into clot plus serum. The objective of this work was to develop a measurement method that allows one to measure ultrasound velocity and its evolution in time and space in an evolving clot while avoiding the influence of serum. To achieve this objective, a novel method has been proposed that is based on ultrasound propagation velocity measurements in different horizontal cross-sections of clotting blood using a pulse-echo mode. Such a technique enables researchers to monitor the clotting process and a clot's spatial structure, which are different in different layers due to the influence of gravity. The four-channel measurement chamber utilizing this method has been designed and manufactured. For the generation and reception of ultrasonic waves of high frequency, wide band (3-20MHz at -6dB) ultrasonic transducers were developed. To verify that the multi-channel measurement system was operational, a special procedure based on monitoring of a polymerisation process in the acrylamide solution was proposed. Performance of the developed method was investigated by measuring clotting blood (sample volumes of less than 0.6ml) at the frequency of 12MHz. The results revealed that a clot structure indeed varies within a blood sample due to the influence of gravity; clotting times are different in different horizontal layers of the clot and range from 9 to 15min, defined by the standard capillary method. Clotting times are determined precisely from abrupt increases in ultrasound velocity. Uncertainty of the ultrasound velocity measurements was less than ±0.05m/s. The experiments were performed at 36.90±0.01°C. The proposed method may be exploited for monitoring polymerisation reactions in the chemistry field, as well.

The ultrasonic testing technique using Lamb waves is widely used for the non-destructive testing and evaluation of various structures. For air-coupled excitation and the reception of A0 mode Lamb waves, leaky guided waves are usually exploited. However, at low frequencies (&lt, 100 kHz), the velocity of this mode in plastic and composite materials can become slower than the ultrasound velocity in air, and its propagation in films is accompanied only by an evanescent wave in air. To date, the information about the attenuation of the slow A0 mode is very contradictory. Therefore, the objective of this investigation was the measurement of the attenuation of the slow A0 mode in thin plastic films. The measurement of the attenuation of normal displacements of the film caused by a propagating slow A0 mode is discussed. The normal displacements of the film at different distances from the source were measured by a laser interferometer. In order to reduce diffraction errors, the measurement method based on the excitation of cylindrical but not plane waves was proposed. The slow A0 mode was excited in the polyvinylchloride film by a dry contact type ultrasonic transducer made of high-efficiency PMN-32%PT strip-like piezoelectric crystal. It was found that that the attenuation of the slow A0 mode in PVC film at the frequency of 44 kHz is 2 dB/cm. The obtained results can be useful for the development of quality control methods for plastic films.

Lead magnesium niobate-lead titanate (PMN-PT) single crystal has first been successfully grown in 1990 by the Bridgman method using PbO as a flux. These single crystals have excellent piezoelectric properties. The PMN-PT crystals with different vibration modes may be used for development of novel high efficiency ultrasonic transducers due to high piezoelectric properties.

Longitudinal and shear ultrasonic wave velocities were measured versus temperature in the viscosity standards of Paragon S8000S, N30000S and Cannon N2700000. The measurements were performed by the through-transmission method at the frequency of 2 MHz. Ultrasonic pulses were sent via polymethyl methacrylate (PMMA) waveguides between the tips of which a small amount of the particular standard liquid was placed. The velocities of longitudinal and shear waves were determined to depend on the viscosity of the liquid and increase with the viscosity.

An ultrasonic technique, invariant to temperature changes, for a density measurement of different liquids under in situ extreme conditions is presented. The influence of geometry and material parameters of the measurement system (transducer, waveguide, matching layer) on measurement accuracy and reliability is analyzed theoretically along with experimental results. The proposed method is based on measurement of the amplitude of the ultrasonic wave, reflected from the interface of the solid/liquid medium under investigation. In order to enhance sensitivity, the use of a quarter wavelength acoustic matching layer is proposed. Therefore, the sensitivity of the measurement system increases significantly. Density measurements quite often must be performed in extreme conditions at high temperature (up to 220 °C) and high pressure. In this case, metal waveguides between piezoelectric transducer and the measured liquid are used in order to protect the conventional transducer from the influence of high temperature and to avoid depolarization. The presented ultrasonic density measurement technique is suitable for density measurement in different materials, including liquids and polymer melts in extreme conditions. A new calibration algorithm was proposed. The metrological evaluation of the measurement method was performed. The expanded measurement uncertainty Uρ = 7.4 × 10(-3) g/cm(3) (1%).

The discovery of high piezoelectric properties for lead magnesium niobate–lead titanate (PMN–32%PT) enables to develop ultrasonic transducers with significantly improved performance. The domain engineering technologies could be improved by employing techniques enabling continuous monitoring of the piezoelectric properties during poling process of the single crystals at different times.

Application of air-coupled ultrasonic measurements is problematic due big acoustic transduction losses of conventional ultrasonic air-coupled transducers. One of the ways to solve this problem is application of more efficient ultrasonic transducers made of PMN-32 %PT crystals. The objective of this work was development of novel effective air-coupled ultrasonic transducer with PMN-32% PT crystal plates. The high electromechanical factor of the transverse extension mode enables to achieve a good performance of air-coupled transducers. The developed and investigated ultrasonic transducer possesses in a transmission mode 10 times better efficiency than a PZT composite ultrasonic transducer.

Due to very high piezoelectric properties of PMN-PT crystals they may significantly improve performance of air-coupled ultrasonic transducers. For these purpose vibrations of PMN-PT rectangular plates and strips were investigated. An air-coupled ultrasonic transducer and array consisting of 8 single piezoelectric strips were designed. Operation of the transducer was simulated by the finite element method using ANSYS Mechanical APDL Product Launcher software. Spatial distributions of displacements inside piezoelectric elements and matching strip were obtained. Experimental investigations were carried out by the laser Doppler vibrometer Polytec OFV-5000 and the Bruel&Kjaer microphone 4138 with the measurement amplifier NEXUS WH 3219. It was found that performance of the ultrasonic transducer with PMN–32PT crystals was a few times better than of a PZT based ultrasonic transducer.

The wide group of large engineering constructions made from welded metal components and modern composite materials during daily exploitation under non-stationary loads, continuous influence of vibrations and complicated environmental conditions have demand of periodical tests in order to avoid appearance and evolution of the defects. All of them have one common feature – large areas to be tested and the complex geometry. The objective is to improve air-coupled and contact type testing techniques for excitation and reception of appropriate modes of ultrasonic guided waves in large and complex structures. Also, to develop inspection techniques which enable to detect required types of internal defects. The air-coupled and contact ultrasonic techniques for investigation of large and complex geometry objects, such as composites for aerospace applications and petroleum tanks, have been developed. The investigation of propagation effects of ultrasonic guided (Lamb) waves in the plates of the tank floor has indicated relation between reconstructed properties of guided waves and expected presence of corrosion deposits.

For improvement of the efficiency of air-coupled ultrasonic transducers PMN-32%PT piezoelectric crystals which possess very high piezoelectric properties may be used. The electromechanical coupling factor of such crystals for all main vibration modes such as the thickness extension and transverse extension modes is more than 0.9. Operation of ultrasonic transducers with such piezoelectric elements in transmitting and receiving modes is rather different. Therefore, for transmission and reception of ultrasonic signals, separate piezoelectric elements with different dimensions must be used. The objective of this research was development of novel air-coupled ultrasonic receivers with PMN-32%PT strip-like piezoelectric elements vibrating in a transverse-extension mode with electromechanically controlled operation and suitable for applications in ultrasonic arrays. Performance of piezoelectric receivers made of the PMN-32%PT strip-like elements vibrating in this mode may be efficiently controlled by selecting geometry of the electrodes covering side surfaces of the piezoelectric element. It is equivalent to introduction of electromechanical damping which does not require any additional backing element. For this purpose; we have proposed the continuous electrodes to divide into two pairs of electrodes. The one pair is used to pick up the electric signal; another one is exploited for electromechanical damping. Two types of electrodes may be used—rectangular or non-rectangular—with a gap between them directed at some angle, usually 45°. The frequency bandwidth is wider (up to 9 kHz) in the case of non-rectangular electrodes. The strip-like acoustic matching element bonded to the tip of the PMN-32%PT crystal may significantly enhance the performance of the ultrasonic receiver. It was proposed to use for this purpose AIREX T10.110 rigid polymer foam, the acoustic impedance of which is close to the optimal value necessary for matching with air. It was found that in order to get a wide bandwidth the length of the matching strip should be selected not a quarter wavelength λ/4 at the antiresonance frequency but at lower frequency. It allowed achieving the frequency bandwidth (14–18)% with respect to the central frequency at −3 dB level.

For long time, blood clot retraction was measured only by thromboelastographic or platelet contractile force measurement techniques. The purpose of the present study was development of a novel ultrasonic method based on simultaneous monitoring of variations in the ultrasound velocity and the frequency spectrum of the signal propagating in clotting blood and its application for automatic evaluation of blood clotting parameters. Simultaneous measurement of ultrasound velocity and variations in the frequency spectrum of wideband ultrasonic signals in clotting blood samples was performed. All measurements were performed in pulse-echo mode. Standard clinical data were obtained using routine clinical laboratory methods. The amplitudes of ultrasonic signals during native blood coagulation varied up to ten times for different frequencies. The measurement results of the start and duration of blood clot retraction differed between patient samples: different components of the blood coagulation system had significant impact on the blood clot retraction process. Our results showed that during blood clotting, the ultrasound velocity and variations in frequency spectrum should be used simultaneously to determine the beginning and duration of blood clot retraction. Our results also showed that blood clot retraction is controlled by the activity of factor XIII.

Air-coupled ultrasonic techniques are being increasingly used for material characterization, non-destructive evaluation of composite materials using guided waves as well as for distance measurements. Application of those techniques is mainly limited by the big losses of ultrasonic signals due to attenuation and mismatch of the acoustic impedances of ultrasonic transducers and air. One of the ways to solve this problem is by application of novel more efficient piezoelectric materials like lead magnesium niobate-lead titanate (PMN-PT) type crystals. The objective of this research was the development and investigation of low frequency (

Anisotropic microstructure of uniaxially pressed powders has been reported in the literature, and is often reflected in direction-dependent physical properties such as thermal conductivity and firing shrinkage. Quantification of direction-dependency could be an important tool to predict such physical variations. For the first time, an ultrasound technique in combination with a microstructural investigation were applied to access anisotropy in green uniaxially pressed stoneware tiles. The longitudinal ultrasound wave velocity was measured parallel and perpendicular to the pressing direction. The sample microstructure was investigated by scanning electron microscopy, porosimetry and X-ray powder diffraction analyses in combination with crystallographic texture analyses using the Rietveld method. It was found that the anisotropic character, quantified as the ratio between the velocities measured perpendicular and parallel to the pressing direction, increased with increasing compact density. Based on the microstructure analyses, these results were attributed to texture of the porous structure as well as the constituting minerals.

The objective of this study was to adapt ultrasonic and radiographic techniques for the inspection of wind turbine blades and to compare the obtainedresults. The measurements performed show that radiographic techniques are capable of reliably detecting a number of structural defects within the blade. The adapted air-coupled ultrasonic technique, using Lamb waves, proved to be the most promising in terms of implementation as it only requires access to one side. However, the novel combination of contact pulse-echo and immersion techniques using a moving container of water identified the shape and size of defects better. Through comparisons of images obtained using both radiographic and ultrasonic techniques, different defect properties can be identified. Hence, the best results are achieved when both techniques are combined together.

Ultrasonic measurements are used in product sizing in various industrial technologies. The advantage of such techniques is that measurements can be performed contactless on a conveyer using an air-coupled ultrasonic method. Nevertheless, implementation of such systems is complicated due to temperature variations, a nonconstant movement velocity, and geometry of the object necessary to measure. In this paper, an ultrasonic technique for the measurement of geometric parameters of objects transported by a conveyer is presented. Operation of the system is based on precise measurements of the distance between the transducer and the surface of an object. The measurement technique includes such stages as detection of the object, recognition of a typical profile, using a feature extraction algorithm, and measurement of object dimensions at selected positions. As an example of implementation of such a measurement technique, the ultrasonic air-coupled system for the measurement of the thickness of chocolate during the production process is presented.

In some nuclear reactors the core is intended to be cooled by means of liquid metal, for example, lead-bismuth eutectic alloy. For safety and licensing reasons, an imaging method of the interior of reactor has thus to be developed. The paper is devoted to development of ultrasonic imaging and measurement technique suitable for performance in the liquid Pb/Bi alloy.

Two different single-side air-coupled ultrasonic techniques for detection and visualisation of defects in aerospace composite materials are presented in this paper. The first technique is based on the pitch-catch arrangement of the transducers and application of the Lamb wave which is shielded by defects. The second method, which gives more accurate results of defect geometry estimation, is based on the same orientation of the transmitter and the receiver for reception of the Lamb wave scattered-reflected by the defect. The damage visualisation results of both techniques are investigated. The results of in situ damage detection are presented. The possibilities of the air-coupled ultrasonic technique for the rapid detection of defects in composite materials are investigated.

Nowadays air-coupled ultrasonic techniques are increasingly used for non-destructive evaluation. The biggest problem is big losses of ultrasonic signals mainly due mismatch of acoustic impedances of ultrasonic transducers and air. One of the ways to solve this problem is application of novel more efficient piezoelectric materials like PMN-PT type crystals. The objective of this research was development of wide band air-coupled ultrasonic transducers and arrays with an improved performance using PMN-32%PT crystals.

A novel ultrasonic measurement technique for density measurements of different liquids in extreme conditions has been developed. The proposed density measurement method is based on transformation of the acoustic impedance of the measured liquid. The higher accuracy of measurements is achieved by means of the λ/4 acoustic matching layer between the load and the ultrasonic waveguide transducer. Introduction of the matching layer enhances sensitivity of the measurement system. Sometimes, the density measurements must be performed in very complex conditions: high temperature (up to 200 °C), pressure (up to 10 MPa), and high chemical activity of the medium under measurement. In this case, the special geometry metal waveguides are proposed to use in order to protect the piezoelectric transducer surface from influence of a high temperature. The experimental set-up of technique was calibrated using the reference liquids with different densities: ethyl ether, ethyl alcohol, distilled water, and different concentration (20%, 40%, and 60%) sugar-water solutions. The uncertainty of measurements is less than 1%. The proposed measurement method was verified in real conditions by monitoring the density of a melted polypropylene during manufacturing process.

This paper is devoted to the development of high temperature, gamma, and neutron radiation resistant ultrasonic sensors that must operate continuously in a liquid Pb/Bi alloy up to a temperature of 450 degC. The main problems are acoustic coupling of a piezoelectric element to a protector and wetting of the sensor by a heavy liquid metal. The piezoelement was attached to the sensor body by a gold to gold diffusion bonding process, monitored ultrasonically. Long-lasting wetting of the active surface of the sensors was achieved by coating the front face with a protective diamond-like carbon (DLC) layer. Due to the high radiation, only a limited number of materials could be used in the sensor design. The best performance was obtained using bismuth titanate piezoelectric elements, which showed no noticeable changes of pulse responses and transfer coefficients during irradiation and high-temperature tests. The housing of the sensors is made of stainless steel AISI 316 and is laser welded, and a high-temperature otimes 1-mm 15-m-long mineral cable is used. The ultrasonic velocity in the liquid Pb/Bi in the temperature range 160 degC-460 degC was measured using developed sensors, and the signal losses at various distances up to 0.8 m were evaluated

In some nuclear reactors or accelerator-driven systems (ADS) the core is intended to be cooled by means of a heavy liquid metal, for example, lead-bismuth (Pb/Bi) eutectic alloy. For safety and licensing reasons, an imaging method of the interior of ADS, based on application of ultrasonic waves, has thus to be developed. This paper is devoted to the description of developed various ultrasonic transducers suitable for long term imaging and measurements in the liquid Pb/Bi alloy. The results of comparative experimental investigations of the developed transducers of different designs in a liquid Pb/Bi alloy up to 450/spl deg/C are presented. Prototypes with different high temperature piezoelectric materials were investigated: PZT, bismuth titanate (Bi/sub 4/Ti/sub 3/O/sub 12/), lithium niobate (LiNbO/sub 3/), gallium orthophosphate (GaPO/sub 4/) and aluminum nitride (AlN). For acoustic coupling with the metal alloy, it was proposed to coat the active surface of the transducers by diamond-like carbon (DLC). The radiation robustness was assessed by exposing the transducers to high gamma dose rates in one of the irradiation facilities at SCK/spl middot/CEN. The experimental results proved that the developed transducers are suitable for long-term operation in harsh conditions.

In-line real time monitoring and measurement of density of manufactured products is very important in various industrial applications, especially during extrusion of polymer melts. In this case measurements must be performed in very complex conditions, for example at high temperature (up to 400°C), high pressure (up to 10 MPa) and high chemical activity of the medium, mechanical impacts. Such extreme conditions limit the number of measurement techniques which can be used. The objective of this work was to develop and investigate an in line ultrasonic density measurement technique of polymer melts.

In order to perform monitoring of the polymerisation process, it is necessary to measure viscosity. However, in the case of non-Newtonian highly viscous fluids, viscosity starts to be dependent on the vibration or rotation frequency of the sensing element. Also, the sensing element must possess a sufficient mechanical strength. Some of these problems may be solved applying ultrasonic measurement methods, however until now most of the known investigations were devoted to measurements of relatively low viscosities (up to a few Pas) of Newtonian liquids. The objective of the presented work is to develop ultrasonic method for measurement of viscosity of high viscous substances during manufacturing process in extreme conditions. For this purpose the method based on application of guided Lamb waves possessing the predominant component of in-plane displacements (the S0 and the SH0 modes) and propagating in an aluminium planar waveguide immersed in a viscous liquid has been investigated. The simulations indicated that in the selected modes mainly in-plane displacements are dominating, therefore the attenuation of those modes propagating in a planar waveguide immersed in a viscous liquid is mainly caused by viscosity of the liquid. The simulation results were confirmed by experiments. All measurements were performed in the viscosity standard Cannon N2700000. Measurements with the S0 wave mode were performed at the frequency of 500kHz. The SH0 wave mode was exited and used for measurements at the frequency of 580kHz. It was demonstrated that by selecting the particular mode of guided waves (S0 or SH0), the operation frequency and dimensions of the aluminium waveguide it is possible to get the necessary viscosity measurement range and sensitivity. The experiments also revealed that the measured dynamic viscosity is strongly frequency dependent and as a characteristic feature of non-Newtonian liquids is much lower than indicated by the standards. Therefore, in order to get the absolute values of viscosity in this case an additional calibration procedure is required. Feasibility to measure variations of high dynamic viscosities in the range of (20-25,000) Pas was theoretically and experimentally proved. The proposed solution differently from the known methods in principle is more mechanically robust and better fitted for measurements in extreme conditions.

Known ultrasonic transducers for simultaneous generation of longitudinal and shear waves are reviewed: ąuartz and lithium niobate crystals tilted CdS and ZnO films. A special attention is devoted to the rotated cuts of PZT piezoceramics, literature data theoretical background conclusions are analysed. Manufacturing technology of dual mode PZT transducers with different cut angles and thickness was developed. Reliable electrodes suitable for soldering are made chemically in electroless nickel (EN) plating bath. Nickel electrodes are additionally dectroplated with silver. Various types of PZT ceramics were successfully used. From impedance measurements longitudinal and shear resonances were determined for typical thicknesses 45-100 µm. The cut angle 36° for equal efficiency of both waves was experimentally determined. Operation of transducers soldered to the steel rods and measurement bodies of the certain geometry was investigated. Measurements were provided in a temperature range 20-160 °C. Axial load experiments up to 234 MPa were provided and corresponding linear dependencies were determined. Experiments showed good performance of developed dual mode PZT ultrasonic transducers.http://dx.doi.org/10.5755/j01.u.66.1.263

Background The ability to quantify non-invasively the effect of posture on intracranial physiology by using cine phase-contrast MRI may lead to the development of new diagnostic tests to evaluate such functions as regulation of CBF and ICP, and the effect of pathologies on these functions. Methods Results similar to MRI technology can be obtained using non-invasive ultrasonic method (Vittamed) for intracranial blood volume pulse wave (IBVPW) measurement and intracraniospinal compliance (ICC) monitoring. Findings IBVPW have been investigated in supine and upright positions of healthy volunteers using Vittamed technology. A group of 13 healthy volunteers (nine females, four males, mean age 25.1±3.4) was studied. More than 3,000 IBVPW were analysed in order to show the difference of shape and amplitude in supine and upright positions. Averaged shape of ten IBVPW waves was presented in the normalized window with dimensions 1.0×1.0. Conclusions The results show significant difference between averaged IBVPW shapes in upright (highest intracraniospinal compliance) and supine (lower intracraniospinal compliance) body positions. Body posture caused IBVPW subwave P2 and P3 changes ΔP2=18% and ΔP3=11%. Amplitude of IBVPW in upright body position was significantly higher than in the supine one. The value of IBVPW amplitude’s ratio in supine and upright positions was 1.55±0.61.

In this paper the techniques developed for investigation of liquid Pb/Bi alloy acoustic properties and experimental results are presented. Measurements of ultrasound velocity were performed using pulse echo technique and a correlation processing in a temperature range 160/spl divide/460/spl deg/C. For transmission and reception of ultrasonic signals bismuth titanate Pz46 5 MHz ultrasonic transducers with a stainless steel waveguide were developed. Various acoustic coupling methods between the waveguide and liquid metal alloy were investigated. The ultrasound velocity dependency upon temperature is presented. The investigation carried out confirms the feasibility of the ultrasonic technique for imaging of the interior of the MYRRHA [1] type nuclear system.

The developed ultrasonic method is based on the experimentally established fact that the ultrasound velocity in a blood sample is changing in a specific way during the blood clotting process. For ultrasound velocity measurements pulse echo method was selected. Implementation of this approach has a few problems caused by small dimensions of the measurement cell. All elements of the cell contacting with the blood are made of biologically compatible materials. The length of Pd coated chamber is 5 mm, volume 0.2 ml. Data of measurements are stored and processed by PC. The ultrasound velocity in a sample is displayed as it changes in time during the experiment; the temperature is monitored as well. Application of the digital filtering allows to smooth the coagulation curve and reach the sensitivity up to +/-3 cm/s. The coagulation curves were obtained at frequency 5 MHz and they represent peculiar stages of blood clotting characterised by their duration and ultrasound velocity differences. Fine structure of ultrasonic velocity changes is registered from the very beginning of the clotting to lysis. Such experiments were carried out using blood samples taken from a few hundred volunteers. For dynamic calibration and periodic checking of the measuring system the liquid medium in which acrylamide polymerisation reaction takes place is proposed as a reference liquid. Such a liquid mimics clotting blood from the point of view of ultrasonic velocity changes.

Ultrasonic waveguide sensor for measurement of viscosity of highly viscous fluids has been developed. The measurement principle is based on application of guided shear-horizontal SH0 mode of the Lamb waves propagating in an aluminium planar waveguide immersed in a viscous liquid. Attenuation of the guided wave depends on viscosity of the surrounding liquid and is used for viscosity estimation. The developed sensor is mechanically robust and may be used for in-line process control of viscous liquids.

A novel ultrasonic non-destructive technique (NDT) based on application of a transmission tomography of guided ultrasonic waves is proposed for floor inspection of large storage tanks and detection of non-uniformities, such as corrosion. The technique needs access only to the outer edge of the tank floor and does not require emptying the tank. Theoretical estimations have been verified by laboratory experiments using a scaled physical model of the tank. Estimation of the attenuation of different wave modes propagating in steel plates and determination of the losses in the lap welds showed that most suitable is S0 Lamb wave mode which possesses smallest losses and consequently enables investigation of tank floors up to average diameter 20–30 m. The in situ experiments carried out in a real 8 m diameter tank demonstrated that the developed technique could be used for reconstruction of the spatial distribution of the non-uniformities in a tank floor.

Biological fluids are specific objects for acoustical investigation due to the wide spectra of relaxation processes, especially nonstationary fluids such as blood during its coagulation process. The proposed method combines measurement of ultrasound attenuation over a frequency range and, ultrasound velocity dispersion being negligible, precise measurement of velocity variations at fixed frequency. In the dynamic spectroscopy method the wideband ultrasonic signal transmitted through the media is digitized with a sample rate of 200 MHz, averaged, and processed by a PC. Ultrasound absorption frequency dependency with intervals of 1 min is determined from amplitude spectra. Using small volume (1 ml) cell with multiple reflections, in the range of 2–17‐MHz, diffraction corrections and ultrasonic attenuation were determined in low‐absorptive standard liquid, conservative, and native coagulating blood. The clot formation process in the native blood is also monitored at frequencies 5 or 10 MHz using the time‐of‐flight method with the acquisition of the results. In the cell of 0.2 ml volume sensitivity of 0.2 ns is achieved. Cell parameters and influence of the pulse bandwidth are analyzed. According to the ultrasound velocity variations, four typical blood coagulation phases were observed during 30 min, less expressed being the first phase (0–2 min).

The paper describes the development of high temperature, /spl gamma/ and neutron radiation resistant ultrasonic transducers which must operate continuously in liquid Pb/Bi up to 450/spl deg/C. Known ultrasonic transducers are not intended for such harsh conditions. The main problems are acoustic coupling of the piezoelement to the protector and wetting of the transducer by a heavy liquid metal. For the first time, the piezo-element was attached to the transducer body by a gold-to-gold diffusion bonding process; acoustic coupling between the transducer and the liquid metal alloy was achieved by coating the front face by a protective diamond-like carbon (DLC) layer. Due to the high radiation, only a limited number of materials may be used in the transducer design. Transducers with bismuth titanate piezoelectric elements showed no noticeable changes of pulse responses and transfer coefficients. The housing of the transducer is made of AISI 316 stainless steel, it is laser welded and high temperature 1 mm diameter, 15 m long, mineral cable is used.