Ultrasonic Phased Array Transducer Research Articles

Monitoring of an ascending air bubble in a viscous fluid/fiber matrix medium using a phased array transducer

Detecting porosities of different scales, both micro and macro, is a current problem in the development of composite materials. This is especially true for composite materials manufactured using Resin Transfer Molding (RTM). When injecting resin in the fibrous preform porosities appear, originating essentially because of air trapped in the fiber matrix. Consequently, the interaction between air bubbles and fibers has been the subject of several numerical investigations. In this study, we propose an original experimental method to monitor the interaction of air bubbles with a fibrous matrix. A 10 MHz center frequency ultrasonic phased array transducer is used to monitor air bubbles in the millimeter range. The ultrasonic imaging method is first tested only with bubbles ascending in a channel containing silicone oil. Then it is tested again in a sample of fiber matrix immersed in the same channel. The results prove the effectiveness of the measurement process. These results then can be used to find a correlation between the appearance of porosities and the processes that generate them in order to consider how to improve RTM. They can also be used to understand the interaction phenomena between bubbles and folds in order to improve RTM process.

Design and optimization of an OPFC ultrasonic linear phased array transducer

In contrast to piezoceramics, orthotropic piezoelectric fibre composites (OPFC) which can be used as actuator/sensor elements in damage detection show clear advantages because of their high sensitivity along the fibre direction and directivity. The focusing acoustic field distribution of the OPFC phased array transducer is analyzed by the finite element method together with directivity analysis in metallic materials. The optimal array parameters such as spacing, width and number of elements are obtained by studying the total displacement changes as various parameters change at the focus point. The feasibility of an OPFC ultrasonic phased array transducer for damage detection is validated.

Thermal Dispersion Method for a Medical Ultrasonic Phased Array Transducer

초음파 영상 품질의 향상을 위해 트랜스듀서의 구동전압을 높이게 되면 트랜스듀서에서 열이 발생하여 환자의 피부 화상 및 트랜스듀서의 성능 저하를 초래할 수 있다. 따라서, 이렇게 온도가 상승하지 않도록 트랜스듀서 내의 열을 효율적으로 분산할 수 있는 방안에 대해 연구하였다. 이때 열 분산 해석 대상으로 중심주파수가 3 MHz이고 32채널을 가진 위상배열 트랜스듀서를 선정하였다. 먼저 트랜스듀서의 동작에 따른 발열 구조를 이론적으로 분석하였고, 그 결과로서 재료의 감쇠와 음압의 크기가 발열에 영향을 미치는 것을 확인하였다. 나아가 유한요소 해석을 통해 트랜스듀서 구성소자의 물성이 열 분산에 미치는 영향을 분석하였다. 분석된 결과를 바탕으로 트랜스듀서 내 열이 잘 분산되기 위한 구성소자의 열물성을 정하였다. 도출된 열 물성을 유한요소 해석 모델에 적용한 결과 환자와 접촉되는 부분인 음향렌즈의 최고온도가 원래 값의 51 %로 저하되었다. When the driving voltage of an ultrasound transducer is increased to improve the quality of ultrasound images, heat is generated inside the transducer that can cause patient's skin burn and degradation of transducer performance. Hence, in this paper, a method to disperse the heat of the transducer has been studied. The phased array transducer having 3 MHz center frequency and 32 channels was selected for analyses of the thermal dispersion. First, mechanism of the heat generation was investigated in relation to the transducer operation through theoretical analysis, and material damping and sound pressure amplitude were confirmed to be influential on the heat generation. Further, we investigated the effects of the properties of the materials constituting the transducer on the thermal dispersion through finite element analysis. Based on the analysis results, we determined the thermal properties of the constituent materials that could facilitate the thermal dispersion inside the transducer. The determined thermal properties were applied to the finite element model, and the results showed that the maximum temperature at an acoustic lens contacting with a patient was decreased to 51 % of its initial value.

3P3-5 Thermal Dispersion Method for an Ultrasonic Phased Array Transducer

3P3-5 Thermal Dispersion Method for an Ultrasonic Phased Array Transducer

A time-domain synthetic aperture ultrasound imaging method for material flaw quantification with validations on small-scale artificial and natural flaws

A direct time-domain reconstruction and sizing method of synthetic aperture focusing technique (SAFT) is developed to improve the spatial resolution and sizing accuracy for phased-array ultrasonic inspections. The basic idea of the reconstruction algorithm is to coherently superimpose multiple A-scan measurements, incorporating the phase information of the sampling points. The algorithm involves data mapping and in-phase summation according to time-of-flight (TOF). Data mapping refers to the process of placing each of the sampling points to a two-/three-dimensional grid that represents the geometry model of the object being inspected. The value for each of the cells of the grid is a summation of all sampling points mapped into the cell. A sizing method based on the concept of 6dB-drop is proposed to characterize the flaw boundary. The extents, orientation and the shape of the flaw can then be inferred to provide more information for life assessment calculations. Lab experiments are performed using a 10MHz phased-array ultrasonic transducer to collect data from a cylinder material block with closely spaced artificial flaws and from a material block with a natural flaw. The developed method is used to process the experimental data to characterize the flaws. Using the developed method, the improvement of spatial resolution is observed. Results indicate that four closely spaced 0.794mm-diameter flat-bottomed holes are clearly identified, and the quantification of size and orientation of the natural flaw is very close to the actual measurement made from digital microscopy after cutting the testing piece apart.

Optimization of Element Parameters for a New OPFC Ultrasonic Phased Array Transducer

An orthotropic piezoelectric fiber composite (OPFC) element and related OPFC ultrasonic phased array transducer which applied in damage detection of metal structures are investigated by theoretical analysis, numerical simulation and experimental verification methods. Based on electromechanical coupling, the influence of the material characteristics and geometry parameters on actuation performance is studied for the thickness expansion type OPFC elements. In view of lack in the mechanic-electronic parameter design of the existing single PZT element for modern ultrasonic phased array transducer, the related OPFC ultrasonic phased array transducer which used in metal structural damage detection is designed, which have the merits such as low voltage and limit the effects on grating lobe. The focusing acoustic field distribution is analyzed by finite element method together with directivity analysis in metals. The optimal array parameters such as phased array element interval, array element width and number of element are obtained by studying the total displacement changes as various parameters changes at focus point. The preparation of OPFC actuator used in metal structural damage detection is studied. The performance of interdigital OPFC element is also obtained by testing and comparing with the traditional PZT element. The experimental results displayed good agreement with the theoretical predictions.

Annular Phased Array Dynamic Focusing Method for Large Target Ultrasonic Testing

A novel method called dynamic focusing immersed ultrasonic testing (DFIUT) is proposed which utilizes an annular phased array ultrasonic transducer (APAUT) and one of the distinguished advantages is dynamic focusing. The proposed DFIUT is aimed at solving the focus deviation problem in the detection of large targets. The design methodology of APAUT and implementation of DFIUT method are presented in this paper. Furthermore, an annular phased array immersed ultrasonic testing (APAIUT) system is also set up. An experiment over the large molybdenum target using the DFIUT is conducted to verify the effectiveness of the proposed method.

Modeling Study of a Linear Ultrasonic Phased Array Transducer

A numerical simulation model based on the finite element method (FEM) and wave analysis is proposed to study the acoustic field of a linear instructions and ultrasonic phased array (LUPA) transducer. The ultrasonic wave propagation in the isotropic solid is studied. The delay law controlling for electronic scanning of a LUPA transducer is analyzed. The ultrasonic wave propagation in the inspection material can be visualized in the form of displacement cloud images by FEM modeling. Experiments show that the model can efficiently and accurately predict the radiation field of beam focusing, steering and electronic scanning of a linear phased array transducer. By employing the proposed method, parameters can be conveniently changed to study the acoustic field of the ultrasonic beam in the medium. It is very helpful for designing and applying the linear phased array transducer and flaw inspection in NDT field.

Crack Orientation and Depth Estimation in a Low-Pressure Turbine Disc Using a Phased Array Ultrasonic Transducer and an Artificial Neural Network

Stress corrosion cracks (SCC) in low-pressure steam turbine discs are serious hidden dangers to production safety in the power plants, and knowing the orientation and depth of the initial cracks is essential for the evaluation of the crack growth rate, propagation direction and working life of the turbine disc. In this paper, a method based on phased array ultrasonic transducer and artificial neural network (ANN), is proposed to estimate both the depth and orientation of initial cracks in the turbine discs. Echo signals from cracks with different depths and orientations were collected by a phased array ultrasonic transducer, and the feature vectors were extracted by wavelet packet, fractal technology and peak amplitude methods. The radial basis function (RBF) neural network was investigated and used in this application. The final results demonstrated that the method presented was efficient in crack estimation tasks.

원전 소구경 배관 소켓용접부 위상배열 초음파검사 기술 개발

소구경 배관 용접부 손상은 원자력발전소에서 빈번하게 발생되고 있는 문제이며, 이러한 손상은 보수를 위한 불시정지를 야기하고 결과적으로 발전소에 경제적인 손실을 초래한다. 따라서 소켓용접부의 제작결함 검출과 초기 성장 결함의 검출은 매우 중요하다고 할 수 있다. 지금까지 해당부위에 대한 검사는 ASME Code Section XI 요건에 의하여 표면검사를 적용하여 왔으나 강화검사로 체적검사기법인 초음파검사를 병행하여 수행하고 있다. 그러나 가동중에 발생되는 피로균열을 검출하기 위하여 적용되고 있는 일반 수동 초음파검사는 소켓용접부의 접근성과 초음파 탐촉자의 접촉 문제 등으로 인하여 검사 결과의 신뢰성에 문제가 있어 왔다. 본 연구에서는 위상배열 초음파검사 기술을 적용하여 소구경 배관 소켓용접부의 검사 신뢰성과 속도를 향상하고자 하였다. 이를 위하여 소구경 배관 소켓용접부 검사를 위한 3.5 MHz 위상배열 초음파 탐촉자를 제작하고 탐촉자의 접촉 조건과 일정한 신호 품질을 유지하기 위하여 수동 엔코더 스캐너를 개발하였다. 또한 검사 시스템을 구성하고 현장 검사를 위한 절차서도 개발하였다. Failure of small bore piping welds is a recurring problem at nuclear power plants. And the socket weld cracking in small bore piping has caused unplanned plant shutdowns for repair and high economic impact on the plants. Consequently, early crack detection, including the detection of manufacturing defects, is of the utmost importance. Until now, the surface inspection methods has been applied according to ASME Section XI requirements. But the ultrasonic inspection as a volumetric method is also applying to enforce the inspection requirement. However, the conventional manual ultrasonic inspection techniques are used to detect service induced fatigue cracks. And there was uncertainty on manual ultrasonic inspection because of limited access to the welds and difficulties with contact between the ultrasonic probe and the OD(outer diameter) surface of small bore piping. In this study, phased array ultrasonic inspection technique is applied to increase inspection speed and reliability. To achieve this object, the 3.5 MHz phased array ultrasonic transducer are designed and fabricated. The manually encoded scanner was also developed to enhance contact conditions and maintain constant signal quality. Additionally inspection system is configured and inspection procedure is developed.

Laser-scanning photoacoustic microscopy with ultrasonic phased array transducer

In this paper, we report our latest progress on proving the concept that ultrasonic phased array can improve the detection sensitivity and field of view (FOV) in laser-scanning photoacoustic microscopy (LS-PAM). A LS-PAM system with a one-dimensional (1D) ultrasonic phased array was built for the experiments. The 1D phased array transducer consists of 64 active elements with an overall active dimension of 3.2 mm × 2 mm. The system was tested on imaging phantom and mouse ear in vivo. Experiments showed a 15 dB increase of the signal-to-noise ratio (SNR) when beamforming was employed compared to the images acquired with each single element. The experimental results demonstrated that ultrasonic phased array can be a better candidate for LS-PAM in high sensitivity applications like ophthalmic imaging.

Development of Conformable Wedge for Ultrasonic Phased Array

A conformable wedge for ultrasonic phased array transducer has been developed for the inspection of power generation components with various surface geometries. This low-cost wedge uses a standard linear phased array coupled to the pipe-work surface via a low-loss rubber-based tissue mimicking material impregnated with oil. This material has a longer usable life than hydrogel tissue mimicking material. After comparison testing between the conformable wedge and conventional rigid wedge technology was performed in terms of velocity and attenuation of longitudinal waves at temperatures from 0 to 60°C, the influence was investigated of deformation of conformable wedge on the velocity. The test reveals the conformable wedge is expected to be useful from practical point of view.

Ultrasound monitoring of bubble size and velocity in a fluid model using phased array transducer

Experimental studies on composite materials highlighted the existence of gas bubbles (voids) at different scales (micro and macro). These voids, resulting from the fabrication process, are sources of weakness for the end-user material. Therefore, several studies focus on the evaluation and the minimization of void rate. During injection of resin into the fibrous matrix, bubbles appear. Some are dispersed while others persist and diminish the overall quality of the finished product. This study consists in detecting bubbles during the resin transfer molding (RTM) process using an original method based on ultrasound. However, in practice we have to face with several problems due to the heterogeneity of the environment, such as the differentiation of a bubble from a strand or fiber. Due to the complexity of the problem, an experimental setup was built in order to detect bubbles using an ultrasonic phased array transducer in a flow of viscous fluid only, without the presence of fiber matrix. The study deals with the flow of a model fluid, which simulates the injected resin, with presence of air bubbles trapped in a channel production. Since the ultrasonic characteristics of the experimental setup are well known and characterized, the number, velocity and size of air bubbles could be evaluated.

Model-based simulation of focused beam fields produced by a phased array ultrasonic transducer in dissimilar metal welds

Phased array ultrasound testing (PAUT) can produce steerable and tightly focused ultrasonic beams, so it is widely used for detecting flaws. However, inspection of dissimilar metal welds (DMWs) using phased array ultrasound is not easy at all, since ultrasonic beams are skewed and distorted severely in the welds that are anisotropic and inhomogeneous elastic media. So, to increase focusing efficiency and have optimized conditions for inspecting the welds, quantitative prediction of phased array ultrasonic beams is needed. This paper proposes a modeling approach that includes modeling the grain orientation of the welds with buttering, calculating the ray path for the determination of focal laws, and applying the linear phasing multi-Gaussian beam model in order to focus the ultrasonic beams produced by a phased array transducer mounted on a wedge contacted to the interrogated DMW. This paper also presents an example of the model-based simulation of the focused beam fields produced in the DMW. The proposed model allows us to increase the focusing efficiency by accurately simulating the ultrasonic testing of welded components and to propose a new tool to associate welding design with the ultrasonic assessment of structural integrity.

Non-destructive evaluation of fatiguebythermal, acoustic and electromagnetic techniques

This paper considers nondestructive evaluation techniques for integrity ofaustenite stainless steelwith mechanical fatigue. In order to ensure long time operation of facilities, exact remaining life of each structural componentshould be predicted by estimating the degreeof material degradation including earlier stage before crack initiation.To do it, specimens with several fatigue degrees are preparedwhichissuitable for nondestructive evaluation. Austenite stainless steel has weak magnetism due tomartensite phase induced duringprocessing, whose volume fraction increases according to mechanical fatigue and stress concentration. Magnetic flux leakage testing with high sensitivity can estimatethe extent and the distribution of the fatigued region. Whenwe apply a cyclic magnetic field to the specimen, the fatigued region is selectively heated from its magnetic hysteresis, which can be visualized asaninfrared image byathermography. The mechanical fatigue also influences the acoustic properties of the material through the change of the microscopic structure.Itisalso shown that the acoustic impedancedecreases with fatigue.A phased array ultrasonic transducer is developed to obtain the distribution of the acoustic impedance. Feasibility of the proposed techniques is discussed from the view pointsof qualitative and local estimations.

Imaging for Borehole Wall by a Cylindrical Linear Phased Array

A new ultrasonic cylindrical linear phased array (CLPA) transducer is designed and fabricated for the borehole wall imaging in petroleum logging based on the previous theoretical researches. First, the CLPA transducer, which is made up of numbers of the piezoelectric elements distributed on the surface of a cylinder uniformly, is designed and fabricated. By transmitting and receiving acoustic waves with 16 active elements and using different groups of the elements under the control of the electric system, the CLPA can scan all areas of the borehole wall dynamically and rapidly without a traditional mechanism around the borehole axis. Then, the theoretical and experimental investigations are conducted in detail for the borehole wall scanning and imaging by the steel pipe and casing borehole with defects distributed in different shapes and directions. It is shown by experiments that the CLPA transducer has good focusing characteristic and good resolution for the borehole wall imaging in acoustic logging.

Observation and correction of transient cavitation-induced PRFS thermometry artifacts during radiofrequency ablation, using simultaneous Ultrasound/MR imaging

MR thermometry based on the proton resonance frequency shift (PRFS) is the most commonly used method for the monitoring of thermal therapies. As the chemical shift of water protons is temperature dependent, the local temperature variation (relative to an initial baseline) may be calculated from time-dependent phase changes in gradient-echo (GRE) MR images. Dynamic phase shift in GRE images is also produced by time-dependent changes in the magnetic bulk susceptibility of tissue. Gas bubbles (known as "white cavitation") are frequently visualized near the RF electrode in ultrasonography-guided radio frequency ablation (RFA). This study aimed to investigate RFA-induced cavitation's effects by using simultaneous ultrasonography and MRI, to both visualize the cavitation and quantify the subsequent magnetic susceptibility-mediated errors in concurrent PRFS MR-thermometry (MRT) as well as to propose a first-order correction for the latter errors. RF heating in saline gels and in ex vivo tissues was performed with MR-compatible bipolar and monopolar electrodes inside a 1.5 T MR clinical scanner. Ultrasonography simultaneous to PRFS MRT was achieved using a MR-compatible phased-array ultrasonic transducer. PRFS MRT was performed interleaved in three orthogonal planes and compared to measurements from fluoroptic sensors, under low and, respectively, high RFA power levels. Control experiments were performed to isolate the main source of errors in standard PRFS thermometry. Ultrasonography, MRI and digital camera pictures clearly demonstrated generation of bubbles every time when operating the radio frequency equipment at therapeutic powers (> or = 30 W). Simultaneous bimodal (ultrasonography and MRI) monitoring of high power RF heating demonstrated a correlation between the onset of the PRFS-thermometry errors and the appearance of bubbles around the applicator. In an ex vivo study using a bipolar RF electrode under low power level (5 W), the MR measured temperature curves accurately matched the reference fluoroptic data. In similar ex vivo studies when applying higher RFA power levels (30 W), the correlation plots of MR thermometry versus fluoroptic data showed large errors in PRFS-derived temperature (up to 45 degrees C absolute deviation, positive or negative) depending not only on fluoroptic tip position but also on the RF electrode orientation relative to the B0 axis. Regions with apparent decrease in the PRFS-derived temperature maps as much as 30 degrees C below the initial baseline were visualized during RFA high power application. Ex vivo data were corrected assuming a Gaussian dynamic source of susceptibility, centered in the anode/cathode gap of the RF bipolar electrode. After correction, the temperature maps recovered the revolution symmetry pattern predicted by theory and matched the fluoroptic data within 4.5 degrees C mean offset. RFA induces dynamic changes in magnetic bulk susceptibility in biological tissue, resulting in large and spatially dependent errors of phase-subtraction-only PRFS MRT and unexploitable thermal dose maps. These thermometry artifacts were strongly correlated with the appearance of transient cavitation. A first-order dynamic model of susceptibility provided a useful method for minimizing these artifacts in phantom and ex vivo experiments.

Multiple matching scheme for broadband 0.72Pb(Mg(13)Nb(23))O(3)-0.28PbTiO(3) single crystal phased-array transducer.

Lead magnesium niobate-lead titanate single crystal 0.72Pb(Mg(13)Nb(23))O(3)-0.28PbTiO(3) (abbreviated as PMN-PT) was used to fabricate high performance ultrasonic phased-array transducer as it exhibited excellent piezoelectric properties. In this paper, we focus on the design and fabrication of a low-loss and wide-band transducer for medical imaging applications. A KLM model based simulation software PiezoCAD was used for acoustic design of the transducer including the front-face matching and backing. The calculated results show that the -6 dB transducer bandwidth can be improved significantly by using double lambda8 matching layers and hard backing. A 4.0 MHz PMN-PT transducer array (with 16 elements) was fabricated and tested in a pulse-echo arrangement. A -6 dB bandwidth of 110% and two-way insertion loss of -46.5 dB were achieved.

Analysis of phased array transmitters and beamformers.

As phased array ultrasonic transducers become more wide spread in underwater acoustic measurement applications, a better understanding of their basic performance characteristic is of benefit. The beam patterns of a phased array can be approximated by a steady state analysis. This approach indicates the directional response of an array in response to a sinusoidal excitation. However, a steady state examination does not properly describe transient behavior of the transmit waveform and also the received signal that is subsequently beamformed. We further investigate the transient performance of the beamformer using a closed-form solution to the acoustic wave equation for a multielement ultrasonic phased array transducer. The model produces transducer beam patterns and transient beamformer output for a series of reflective targets in the far-field of the transducer. The results show a close agreement with laboratory measurements and provide a tool for further investigation of phased array transducer design and performance.

Modeling the radiation of ultrasonic phased-array transducers with Gaussian beams

A new transducer beam model, called a multi-Gaussian array beam model, is developed to simulate the wave fields radiated by ultrasonic phased-array transducers. This new model overcomes the restrictions on using ordinary multi-Gaussian beam models developed for large single-element transducers in phased-array applications. It is demonstrated that this new beam model can effectively model the steered and focused beams of a linear phased-array transducer.