Reimondas Sliteris

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.

Waveguide sensor for measurement of viscosity of highly viscous fluids

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.

Ultrasonic guided wave tomography for the inspection of the fuel tanks floor

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.

Measurement of viscosity of highly viscous non-Newtonian fluids by means of ultrasonic guided waves

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.

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‐...

Air-Coupled Low Frequency Ultrasonic Transducers and Arrays with PMN-32%PT Piezoelectric Crystals

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.

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.