Algirdas Voleisis

High temperature ultrasonic transducers for imaging and measurements in a liquid Pb/Bi eutectic alloy

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.

Ultrasonic method for the whole blood coagulation analysis

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.

Development of Ultrasonic Sensors for Operation in a Heavy Liquid Metal

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

Investigation of ultrasonic properties of a liquid metal used as a coolant in accelerator driven reactors

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.

Ultrasonic technique for the investigation of structural properties of biological fluids

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‐...

Online Profiling of Nonplanar Objects by High-Resolution Air-Coupled Ultrasonic Distance Measurements

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.

Ultrasonic measurement of zirconium tubes used in channel-type nuclear reactors

Abstract An ultrasonic technique for the determination of the inner and outer diameters and wall thickness of zirconium tubes used in channel-type nuclear reactors has been developed. The method is based on the time-of-flight technique of ultrasonic waves reflected by the front and back walls of the tube. The measurements are performed around the circumference and along the axis of the tubes. The influence of eccentricity of the measuring probe is studied both theoretically and experimentally. It is shown that the absolute measurement error is less than 100 μtm for the diameters and 50 μm for the wall thickness. In situ tests carried out at the Ignalina state nuclear power plan:, Lithuania, proved the good performance of the system in a harsh environment.

Ultrasonic method for monitoring the clotting process during whole blood coagulation

HIGHLIGHTSUltrasonic multi‐channel method for monitoring blood clotting process.Dynamic verification method based on monitoring polymerization process in the acrylamide solution.Ultrasound velocity measurements in clotting blood.Ultrasonic monitoring of polymerization reactions in space and time domains. ABSTRACT 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 clots 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 (3–20 MHz at −6 dB) 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 0.6 ml) at the frequency of 12 MHz. 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 15 min, 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 ±0.05 m/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.

A novel ultrasonic method for evaluation of blood clotting parameters

PurposeFor 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.MethodsSimultaneous 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.ResultsThe 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.ConclusionsOur 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.

Development of PZT piezoelements for simultaneous generation and reception of longitudinal and shear ultrasonic waves

Ultrasonic methods are often used for measurement of various non-electric quantities, for example, pressure or displacements. In this case in order to increase accuracy of measurements longitudinal L and shear SH ultrasonic waves simultaneously propagating in solids along the same path must be used. For simultaneous generation/reception of L and SH waves dual mode PZT transducers may be used, but up to now only theoretical studies are known with a little experimental confirmation. A dual mode piezoelement can be manufactured as a rotated Z-cut element from a large thick PZT block. Objective of our study was investigation of transient processes in dual mode PZT piezoelements, optimization of their geometry and development of manufacturing technology. Vibrations of rotated Z-cut disc and rectangular shape piezoelectric elements in a pulse mode were investigated by a numerical modeling using ANSYS finite elements code. The volume of the disc was meshed using the SOLID5 elements. Modeling results were verified by experiments using steel measurement bodies and a good correspondence has been obtained. At the angle θ=36° L and SH waves of similar amplitudes are excited.