Ultrasonic Linear Phased Array Research Articles

Ultrasonic array imaging of highly attenuative materials with spatio-temporal singular value decomposition

With the increasing use of high density polyethylene (HDPE) pipes in nuclear industry which puts safety at the forefront, ultrasonic array imaging methods play a vital role in the structural integrity of HDPE pipe materials. However, the viscoelastic attenuation of HDPE pipe materials significantly decreases the level of signals, leading to a low signal-to-noise ratio caused by electronic noise. In this work, a domain-adapted spatio-temporal singular value decomposition (STSVD) processing algorithm combined with the total focusing method is proposed to improve the ultrasonic array image quality. First, the real-valued radio frequency (RF) data or A-scan signals are demodulated into the complex analytic signals containing in-phase and quadrature (I/Q) components. Then, the STSVD processing algorithm is used to filter the I/Q data, and the filtered I/Q data is converted into RF signals. Finally, the total focusing method is applied to the processed RF signals to produce the image of the region under detection as a stage of post-processing. Experiments are carried out with an ultrasonic linear phased array in contact with the HDPE pipe materials containing multiple side-drilled holes and through-wall notches. Results show that the proposed method can produce images with high quality to provide good inspection and characterization of defects in highly attenuative materials, especially the deeper defects.

Point cloud-based elastic reverse time migration for ultrasonic imaging of components with vertical surfaces

This work presents a new ultrasonic imaging framework for non-destructive evaluation of components with vertical or steeply dipping surfaces and demonstrates its ability of accurately characterizing multiple defects hidden in the interior of the component based on a limited coverage of ultrasonic linear phased array. Central to the framework is a point cloud-based elastic reverse time migration (PC-based ERTM) method. First, a surface reconstruction is derived from the point cloud provided through photos of an object from multiple views by bundle adjustment. Second, by taking the surface reconstruction as a geometric background estimate for elastic reverse time migration, the algorithm considers information of multiple scattering and mode conversions as well as multiple wave reflections from the component’s bottom and aims at detecting internal defects. The effectiveness and accuracy of the PC-based ERTM approach is examined by experiments with multiple defects in extruded aluminum specimens with vertical surfaces. Experimental results show that notches and side-drilled holes in components can be reconstructed accurately.

Fatigue crack inspection and characterisation using non-collinear shear wave mixing

In recent years, nonlinear ultrasonic techniques have been developed rapidly for defect detection and characterization at its early development stage. In this paper, non-collinear shear wave mixing is used for fatigue crack detection and characterization, exploring how orientation and size may be determined. This is achieved through measuring the amplitude of the generated longitudinal wave from a crack of interest. This amplitude is a function of the interaction angle and frequency ratio of two incident shear waves and the resulting amplitude parameter space is termed the nonlinear fingerprint of the crack. Numerical analysis of the nonlinear interaction between two incident shear waves and cracks was performed using two-dimensional finite element models to explore a broader parameter space than possible experimentally. It is shown that the interaction angle which leads to the maximum generated longitudinal wave amplitude is related to the orientation angle of the crack. To confirm these conclusions the model was validated using experimental measurements of vertical fatigue cracks grown using 3-point bending tests from initiation notches. The polarity flipping method was used to improve signal to noise ratio in such measurements. It is shown that there is a good agreement between the experimentally measured fingerprints and those simulated using finite element methods. Finally, an approximate method for sizing fatigue cracks was introduced that uses multiple non-collinear measurements along the crack length to determine its extent. As expected, the measured sizes from the proposed method indicate greater crack lengths than seen with linear ultrasonic phased array images due to the closed fatigue cracks being undetectable with linear arrays.

Application of Dual Focused Ultrasonic Phased Array Transducer in Two Orthogonal Cross-Sections for Inspection of Multi-Layered Composite Components of the Aircraft Fuselage.

Our previous studies have shown that the application of the proposed technique of a dual focused ultrasonic beam in two orthogonal cross-sections in passive (elevation) and active (azimuth) apertures of linear ultrasonic phased array transducer (ULPAT) enhances the 3D spatial resolution in the case of the inspection of conventional defects (flat bottom holes) or measurement of thickness of multi-layered metal composites. The objective of this work is to apply the proposed technique to enhance the spatial resolution of the ULPAT in the cases of detection and sizing demonstration of internal defects possessing spatially complex geometry, and during the inspection of defective multi-layered thin composite components (e.g., GLARE) of the aircraft fuselage. The specially prepared aluminium specimen possessing an internal defect of complicated geometry (crescent-shaped) was investigated. The simulation results and experiments demonstrate the resolution enhancement, higher amplitude of the reflections (e.g., 2.5 times or +8 dB) and spatial improvement in the defect detection even in the case of the non-perpendicular incidence of ultrasonic waves to the complex geometry surface of the internal defect. During the experiments, the multi-layered GFRP-metal based composite sample GLARE 3-3/2 was investigated in the case of the single-side access to the surface of the sample. The internal artificial delamination type defect of 25 mm was detected with a higher accuracy. Compared to the limitations of conventional ULPAT, the relative error (32%) (at the −6 dB level) of lateral defect dimensions estimation was completely reduced.

Research on the Actuation Performance of 2D-Orthotropic Piezoelectric Composite Materials Linear Phased Array Transducer.

Ultrasonic linear phased array actuator for electric-acoustic conversion is the key component of the ultrasonic phased array test system. Focusing on the existing deficiency of using phased array ultrasonic testing technology into complex engineering structure, using the 2D orthotropic piezoelectric composite materials (2D-OPCM) into the research of linear phased array actuator can achieve orientable exciting. The single OPCM element and its array actuator was designed and their mechanical properties of focusing were tested by experiment. The experimental results show that 2D-OPCM ultrasound phased array actuator can achieve precise phased array focusing and deflection, which might be of great promising in the nondestructive evaluation engineering application.

Development of the technique for independent dual focusing of contact type ultrasonic phased array transducer in two orthogonal planes

Due to a low lateral resolution in elevation plane, the application of linear ultrasonic phased array transducers (ULPAT) is limited. The objective is to enhance the spatial resolution by means of spatial dual focusing technique of ULPAT in two orthogonal planes – azimuth and elevation.A design of a special delay line possessing a convex cylindrical lens has been proposed. The lens enables fixed geometrical focusing of the excited beam in the elevation plane, while in the other, azimuth, plane the beam is electronically focused at an arbitrary point by the active aperture of the ULPAT. The simulation results demonstrate the extended possibilities of resolution enhancement. Experiments show that the undetectable defect is detected using the designed acoustic lens. In addition, the interfaces of the intermediate layer of metal composite were detected.

A Fast Method to Calculate the Spatial Impulse Response for 1-D Linear Ultrasonic Phased Array Transducers.

A method is developed to accurately determine the spatial impulse response at the specifically discretized observation points in the radiated field of 1-D linear ultrasonic phased array transducers with great efficiency. In contrast, the previously adopted solutions only optimize the calculation procedure for a single rectangular transducer and required approximation considerations or nonlinear calculation. In this research, an algorithm that follows an alternative approach to expedite the calculation of the spatial impulse response of a rectangular linear array is presented. The key assumption for this algorithm is that the transducer apertures are identical and linearly distributed on an infinite rigid plane baffled with the same pitch. Two points in the observation field, which have the same position relative to two transducer apertures, share the same spatial impulse response that contributed from corresponding transducer, respectively. The observation field is discretized specifically to meet the relationship of equality. The analytical expressions of the proposed algorithm, based on the specific selection of the observation points, are derived to remove redundant calculations. In order to measure the proposed methodology, the simulation results obtained from the proposed method and the classical summation method are compared. The outcomes demonstrate that the proposed strategy can speed up the calculation procedure since it accelerates the speed-up ratio which relies upon the number of discrete points and the number of the array transducers. This development will be valuable in the development of advanced and faster linear ultrasonic phased array systems.

METHODS AND TOOLS FOR MEASUREMENT OF ULTRASOUND LINEAR PHASED ARRAY SPATIAL-TEMPORAL CHARACTERISTICS

Ultrasound nondestructive testing system with linear phased array is widely used during aircraft maintenance. Resolution of such systems depends on spatial-temporal characteristics of linear phased array. The article describes the methods for ultrasonic linear phased array spatial-temporal characteristics measurements. Mathematical models and block diagrams of designed measurement systems are presented. Output parameters for designed systems are measured and their values are used for simulation. The comparative analysis results of theoretical and experimental linear phased array temporal-spatial characteristics research are presented. The results of simulation are in good agreement with experimental data. Simulated data allowed to estimate measurement systems output parameters influence their own ultrasound linear phased array parameters.

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.

Obstacle detection and location using acoustic technology in time domain for visually impaired

An obstacle detector using ultrasonic phased array with the principle of beam steering by time of flight method is proposed. To detect and locate linear ultrasonic phased array it is designed using ultrasonic piezo-sensors. The motivation was to design/evolve an economical system/gadget, which is capable of detecting, ranging and determining bearing/relative angular position of an obstacle. With this aim, an ultrasonic phased array system was designed and developed. The designed linear array detects and locates objects with range resolution of 2.5 cm and bearing resolution of 4.23 degree. The problem of grating lobes in the transmitter array are minimised by adjusting the interelement spacing of the receiver array. This helps in proper reception of the echo signal and hence accurate distal and angular information about the object. The designed system is economically reliable, measurements are performed in time domain reducing complex computation and giving enough and accurate information to a visually impaired person to travel. This paper presents the design details, results of the experiments that were conducted to confirm the capability to transmit and receive in the desired direction and estimate the distance of the target.

Research on Acoustic Field of Ultrasonic Linear Phased Array Based on Spatial Impulse Response of Rectangular Planar Transducer

An analytical method for calculating spatial impulse response of rectangular transducer without far-field or paraxial approximations is presented.According to symmetry of rectangular,the coordinate of observe point is transformed in the fourth quadrant.The solution using only inverse trigonometric functions and simple coordinate transformation,and impulse response of rectangular transducer with different length-width ratios can be calculated.Ultrasonic phased array can freely control the focus point position by exciting each element with independent phase delay,the focus laws of the ultrasonic l-D phased array are derived and the delay time of each element is obtained,then delay time is applied in every transducer element,and the impulse response of phased array transducer is obtained by superposition spatial impulse response of each element.Simulations are carried out for a l-D array transducer in different focusing angles,and the resolution of different distance between the transmitting elements is discussed.Results show that this method can efficiently and accurately predict the radiation field of linear phased array transducer over a wide range of steering angles.

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.

Acoustic field characteristics of ultrasonic linear phased array for an interface condition

Acoustic field characteristics of an ultrasonic linear phased array are studied under the condition of an interface. The issue about a phased array transducer with a wedge is reasonably simplified into a liquid-solid interface problem. According to ray acoustics theory, the acoustic field produced by a single element on the liquid-solid interface is computed. Then focus laws are derived and the expressions of the sound field and the displacement of the ultrasonic linear array with a liquid-solid interface are obtained. Simulations are carried out for a phased array transducer mounted on a wedge. The focusing-generated effects on axial and horizontal acoustic field of transducer are discussed. It is shown that the focusing can enhance sensitivity and resolution, but degrades the performance of beams beyond the focal region. So focusing should be reasonably used in actual testing.

Characterization of the system functions of ultrasonic linear phased array inspection systems

This work characterizes the electrical and electromechanical aspects of an ultrasonic linear phased array inspection system, using a matrix of system functions that are obtained from the measured response of individual array elements in a simple reference experiment. It is shown that for the arrays tested all these system functions are essentially identical, allowing one to use a single system function to characterize the entire array, as done for an ordinary single element transducer. The variation of this single system function with the number of elements firing in the array or with changes of the delay law used is examined. It is also demonstrated that once such a single system function is obtained for an array, it can be used in a complete ultrasonic measurement model to accurately predict the array response measured from a reference reflector in an immersion setup.

Nonparaxial multi-Gaussian beam models and measurement models for phased array transducers

A nonparaxial multi-Gaussian beam model is proposed in order to overcome the limitation that paraxial Gaussian beam models lose accuracy in simulating the beam steering behavior of phased array transducers. Using this nonparaxial multi-Gaussian beam model, the focusing and steering sound fields generated by an ultrasonic linear phased array transducer are calculated and compared with the corresponding results obtained by paraxial multi-Gaussian beam model and more exact Rayleigh–Sommerfeld integral model. In addition, with help of this novel nonparaxial method, an ultrasonic measurement model is provided to investigate the sensitivity of linear phased array transducers versus steering angles. Also the comparisons of model predictions with experimental results are presented to certify the accuracy of this provided measurement model.

Radiation Acoustic Field of a Linear Phased Array on aCylindrical Surface

A new linear ultrasonic phased array fixed on a cylindrical surface isdesigned. This kind of the cylindrical phased array can meet thespecific requirements of the application in testing pipe quality insidepipes. Using the transducer, we can not only avoid mechanical rotatingbut also test the quality of any point in a pipe by ultrasonic phasearray technology. The focused acoustic field distributions in the axial,radial and tangential directions of the transducer are investigatedtheoretically by numerical simulation. The energy flux density, thewidth of the main lobe, the imaging resolution, the grating lobeelimination and other characteristics are analysed. The effect of thefocal distance, effective aperture, transducer radius, number of totalelement, and steering angle on the acoustic field distribution is alsostudied thoroughly. Many important results are obtained.

Adaptive dynamic focusing system for ultrasonic nondestructive testing of pipeline girth welds

An adaptive dynamic focusing system used for the ultrasonic nondestructive testing of pipeline girth welds is developed. This system relies on ultrasonic linear phased array transducers connected to a multichannel acquisition system, which provides delay and amplitude laws, allowing one to control the ultrasonic beams dynamically. We introduce a testing method for welds and the system’s structure. Optimization of array transducers has also been pursued based on a mathematical model of the acoustic field for a linear phased array. The experimental results have proved that the phased array transducers system has the same capability to detect as a conventional ultrasonic transducers system, but the components of the system can be simplified greatly, and the testing flexibility and the testing speed can be improved greatly. It provides an excellent basis for further research and development of defect inspection of pipeline girth welds.

A Parametric Study of Beam Steering for Ultrasonic Linear Phased Array Transducer

All the parameters of a linear phased array may affect the performance and cost of the ultrasonic inspection system. The characteristic of the acoustic field for an array transducer is the most important factor whether the echo information of the inspected area in a specimen can be obtained and utilized effectively, and it is the main basis of designing a phased array. A mathematical model was presented to simulate the characteristic of an acoustic field radiated from an ultrasonic linear phased array on the basis of Huygens' principle. Based on the model, the beam directivity function can be obtained, and the effects of inter-element spacing, number of elements, element width, and transducer center frequency on beam directivity and steerability in a linear phased array transducer are systematically discussed.

Three-dimensional beam directivity of phase-steered ultrasound

A model is developed to compute the three-dimensional far-field acoustic pressure distribution of the waves radiated from an ultrasonic linear phased array with finite elemental dimensions. Based on the model, the three-dimensional beam directivity function is introduced and analyzed to investigate the effects of geometric parameters on the steering performance. It is confirmed that the elevation dimension does not influence the beam directivity in the azimuthal plane. This is not true, however, in nonazimuthal planes. In general, increasing the elevation dimension reduces the energy leaking into nonazimuthal directions. The influences of other transducer parameters, including the number of elements, interelement spacing, and aperture length, are also investigated. It is found that they have only trivial effects on the sideleaking, although they are the important factors that influence the directivity in the azimuthal plane.

Optimum beam steering of linear phased arrays

A model was developed to compute acoustic pressure distribution of the waves radiated from an ultrasonic linear phased array. Based on the model, beam directivity and steerability were studied for various transducer parameters such as number of elements, inter-element spacing, element width, and transducer frequency. Optimal transducer parameters were determined to obtain the best beam directivity by minimizing the main lobe width, eliminating grating lobes, and suppressing side lobes. It was shown that the solutions for the phased arrays can be reasonably approximated by the simple solutions of discrete line sources, if the element width is reasonably smaller than the wavelength or the steering angle is relatively small. The inter-element spacing as well as the number of elements plays an important role in determining transducer performances.