Rymantas Kazys

Principles of high-frequency ultrasonography for investigation of skin pathology

Ultrasonography is a valuable diagnostic tool widely used in medicine. During the last three decades, this non‐invasive skin imaging method has been extended to dermatology. High‐frequency ultrasonography with higher than 20 MHz scanners is well‐established for measuring tumour thickness and skin thickness when treating inflammatory skin diseases such as scleroderma or psoriasis. High‐frequency ultrasonography has become extremely helpful for the preoperative assessment of skin melanoma. The correlation between ultrasonic and histological measurements of melanomas thickness is significantly similarly good using transducers of 20, 75 or 100 MHz frequency (r range from 0.895 to 0.99) and better compared with transducers of 7.5 MHz frequency (r = 0.76). The preoperative sonographically estimated thickness of skin melanoma is sometimes overestimated, because of an underlying inflammatory infiltrate and other reasons. Assessment of skin melanoma thickness using transducers of 100 MHz frequency has better agreement with histology, compared with ultrasonography with 20 MHz transducers. However, the ultrasonic penetration depth is limited to 1.5 mm in case of 100 MHz. The newer ultrasonic techniques such as high‐frequency ultrasonography and colour Doppler sonography could be used for assessment of the tumour vascularization and its metastatic potential. The wide variety of diagnostic information provided by high‐frequency ultrasonography undoubtedly improves the management of oncological and inflammatory skin conditions and underlines its essential position in dermatological practice.

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.

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

Ultrasonic Thickness Measurement of Multilayered Aluminum Foam Precursor Material

Metallic foams are prospective materials for use in the aerospace and automotive industry for crash energy absorption safety parts or lightweight constructions. During manufacturing, artifacts in the foamable precursor material or material quality variations can influence the foam structure after the foaming process; thus, such a process requires quality control. The advantage of ultrasonic techniques is the possibility to perform noncontact and one-sided access measurements online. A three-layer system consisting of a layer of aluminum foam precursor sandwiched between two aluminum sheets has been investigated. The problems of ultrasonic nondestructive characterization of such materials are due to the very similar density and ultrasound velocity of the adjacent layers, which produce very weak reflections of ultrasonic waves, and the thin layers also give overlapped reflections in the time domain. The objective of this paper was to develop an ultrasonic technique that is suitable for measurement of the total thickness and the thickness of individual layers. The proposed technique is based on the identification of object parameters. The numerical iterative deconvolution technique was investigated, analyzed, and adapted to measure the thickness of individual layers with similar density and ultrasound velocity of the multilayered aluminum foam precursor material. Theoretical analysis and experimental investigations have shown that application of the proposed numerical iterative deconvolution enables the thickness measurement of individual layers with the expanded uncertainty of less than plusmn10 mum.

Application of orthogonal ultrasonic signals and binaural processing for imaging of the environment

Data acquisition rates in ultrasonic imaging systems are limited by the finite value of the speed of ultrasonic waves. In order to improve the imaging speed, it is proposed to perform simultaneous scanning of the environment in different directions. In order to avoid cross-talk between adjacent channels in different directions, different orthogonal signals are transmitted. Application of cross-correlation processing and non-linear iterative deconvolution enables the reliable separation of signals transmitted by different sources and reflected by multiple targets. The spatial positions of the targets are found using the data obtained after the non-linear deconvolution as the initial data for binaural or tri-aural processing. This approach has been exploited in ultrasonic sonar used for navigation of mobile robots.

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.

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.

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.

Propagation of Ultrasonic Guided Waves in Composite Multi-Wire Ropes

Multi-wire ropes are widely used as load-carrying constructional elements in bridges, cranes, elevators, etc. Structural integrity of such ropes can be inspected by using non-destructive ultrasonic techniques. The objective of this work was to investigate propagation of ultrasonic guided waves (UGW) along composite multi-wire ropes in the cases of various types of acoustic contacts between neighboring wires and the plastic core. The modes of UGW propagating along the multi-wire ropes were identified using modelling, the dispersion curves were calculated using analytical and semi-analytical finite element (SAFE) techniques. In order to investigate the effects of UGW propagation, the two types of the acoustic contact between neighboring wires were simulated using the 3D finite element method (FE) as well. The key question of investigation was estimation of the actual boundary conditions between neighboring wires (solid or slip) and the real depth of penetration of UGW into the overall cross-section of the rope. Therefore, in order to verify the results of FE modelling, the guided wave penetration into strands of multi-wire rope was investigated experimentally. The performed modelling and experimental investigation enabled us to select optimal parameters of UGW to be used for non-destructive testing.