Phased Array Focusing Research Articles

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images.

In this paper, we utilize micro-computed tomography (micro-CT) to obtain micro-CT images with a resolution of 60 μm and establish a micro-CT model based on the k-wave toolbox, which can visualize the microstructures in trabecular bone, including pores and bone layers. The transcranial ultrasound phased array focusing field characteristics in the micro-CT model are investigated. The ultrasonic waves are multiply scattered in skull and time delays calculations from the transducer to the focusing point are difficult. For this reason, we adopt the pulse compression method and the linear frequency modulation Barker code to compute the time delay and implement phased array focusing in the micro-CT model. It is shown by the simulation results that ultrasonic loss is mainly caused by scattering from the microstructures of the trabecular bone. The ratio of main and side lobes of the cross-correlation calculation is improved by 5.53 dB using the pulse compression method. The focusing quality and the calculation accuracy of time delay are improved. Meanwhile, the beamwidth at the focal point and the sound pressure amplitude decrease with the increase in the signal frequency. Focusing at different depths indicates that the beamwidth broadens with the increase in the focusing depth, and beam deflection focusing maintains good consistency in the focusing effect at a distance of 9 mm from the focal point. This indicates that the phased-array method has good focusing results and focus tunability in deep cranial brain. In addition, the sound pressure at the focal point can be increased by 8.2% through amplitude regulation, thereby enhancing focusing efficiency. The preliminary experiment verification is conducted with an ex vivo skull. It is shown by the experimental results that the phased array focusing method using pulse compression to calculate the time delay can significantly improve the sound field focusing effect and is a very effective transcranial ultrasound focusing method.

Phased array guided wave propagation in curved plates

For the monitoring of plate structures, phased array guided wave has great application prospects to effectively determine damage location and size. Locating damage via phased array focusing is a challenging task, especially in curved plates. Hence, a systematic understanding of the behavior of the phased array guided wave propagation in curved plates is needed. In this study, a phased array focusing method was proposed for the damage localization of curved plates. Different damage scenarios and phased array focusing schemes are investigated in the finite element plate models with different radii. A high-speed signal generation and acquisition system including PZT actuators and sensors is set up. Experimental tests are carried out on a curved aluminum plate with embedded piezoelectric elements to verify the finite element models. Parametric studies are then performed to evaluate the effect of different radii and damage scenarios on the behavior of phased array guided wave propagation in curved plates. Numerical simulations and experimental results show that the proposed PA method has the capabilities of wave focusing and damage identification in curved plates. The damage localization method using phased array guided wave has the potential to be applied to the real-time monitoring of structures with curved plates.

Research on 3D Defect Reconstruction in Plate with Phased Array Ultrasonic Test (PAUT)

In order to clarify the distribution and shape information of the defects inside the workpiece, it has become a new industrial testing requirement to display the defects more intuitively in three dimensions(3D). In this paper, by introducing 3D volume rendering method, the expansion of PAUT from 2D to 3D is realized. The method is used to reconstruct specific “gu-shaped [[CHECK_DOUBLEQUOT_ENT]] (“Gu” is the Pinyin in Chinese characters, and at the same time, “Gu” is the shape of the defect in the plate discussed in the paper.) defects, and the results of reconstruction are compared with actual defects. By using ultrasonic phased array focusing to detect defect C-scan images of different depths, the collected C-scan images were preprocessed and reconstructed according to the defect contour by volume rendering. The results show that the defect morphology with different depths can be well obtained by focused detection, and the reconstruction effect is good, which is consistent with the actual defect.

Multi-channel drive system of phased array based on DDS chips

Ultrasonic phased array focusing transducer has the advantages of adjustable focusing and achieving transcranial focusing. A multi-channel high-precision phase control drive system is one of the key technologies that determine whether it can be used in clinical practice. This paper proposes a design scheme of a phased array drive system based on direct digital synthesizer (DDS) chips. The scheme not only realizes the high-precision phase-controlled output of sine wave and square wave but also in the technical implementation, one electronic channel can be increased with only one main controller general-purpose input/output (GPIO) consumed. This means that the expansion of the number of channels much easier, solving the problem of complicated control circuit caused by the array with dense elements and large aperture. Based on the proposed scheme, a 49-channel array drive system with a phase resolution of 12-bit was fabricated using a microcontroller unit (MCU) as the main control chip. The circuit board test and ultrasonic focusing experiment results show that the phase control error of the multi-channel signal generation board is less than 0.2 degree. And the results of acoustic field distribution obtained by experimental measurement are very similar to those obtained by theoretical simulation, which indicates that the frequency and phase of the output waveform of the array drive system are stable. The design method can provide a reference value for the design of the drive system of phased array transducer with different numbers of elements.

Ultrasonic Guided Wave Phased Array Focusing Technology and Its Application to Defrosting Performance Improvement of Air-Source Heat Pumps

Previous studies have indicated that a basic frost layer negatively affects the heat-transfer efficiency and is difficult to remove using a single ultrasonic transducer. Herein, an ultrasonic phased array technology is proposed for evaporator coil defrosting. First, the dispersion curve of the guided wave in the vibration transfer plate and frosting fin is calculated, and the advance time of each ultrasonic vibrator and the ultrasonic near-field pressures under different velocities are determined through numerical calculations using the MATLAB software. Next, according to the advance time, ultrasonic array focusing is performed to remove the basic frost layer. Finally, the power consumption, heat-supply enthalpy difference, and coefficient of performance (COP) of the air-source heat pump (ASHP) unit are analysed. The theoretical analysis, numerical calculations, and experimental results consistently revealed that ultrasonic array focusing compensates for the energy dissipation and expends the effective defrosting area. Additionally, the perpendicular stress elicited by the Lamb wave and the differential transverse shear stress generated by the SH wave exceed the tensile strength and adhesion stress of the basic frost layer. The basic frost layer cracks and falls away, owing to the combination of the ultrasonic stress effect and the cavitation effect. The defrosting power consumption of the ASHP unit under ultrasonic array excitation decreases from −3.27% to 0.12%, whereas the heat-supply enthalpy difference increases from 4.47% to 10.86%. Therefore, the percentage increment of the COP is between 7.16% and 11.12%, and the power consumption of the reverse-cycle defrosting is 3–12 times that of ultrasonic array defrosting.

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.

Implementation of High Time Delay Accuracy of Ultrasonic Phased Array Based on Interpolation CIC Filter.

In order to improve the accuracy of ultrasonic phased array focusing time delay, analyzing the original interpolation Cascade-Integrator-Comb (CIC) filter, an 8× interpolation CIC filter parallel algorithm was proposed, so that interpolation and multichannel decomposition can simultaneously process. Moreover, we summarized the general formula of arbitrary multiple interpolation CIC filter parallel algorithm and established an ultrasonic phased array focusing time delay system based on 8× interpolation CIC filter parallel algorithm. Improving the algorithmic structure, 12.5% of addition and 29.2% of multiplication was reduced, meanwhile the speed of computation is still very fast. Considering the existing problems of the CIC filter, we compensated the CIC filter; the compensated CIC filter’s pass band is flatter, the transition band becomes steep, and the stop band attenuation increases. Finally, we verified the feasibility of this algorithm on Field Programming Gate Array (FPGA). In the case of system clock is 125 MHz, after 8× interpolation filtering and decomposition, time delay accuracy of the defect echo becomes 1 ns. Simulation and experimental results both show that the algorithm we proposed has strong feasibility. Because of the fast calculation, small computational amount and high resolution, this algorithm is especially suitable for applications with high time delay accuracy and fast detection.

Ultrasonic Inspection and Data Analysis of Glass- and Carbon-Fibre-Reinforced Plastics

Non-destructive testing (NDT) helps to find material defects without having an influence on the material itself. It is applied as a method of quality control, for online structural health monitoring, and for inspection of safety related components. Due to the ability of automation and a simple test setup ultrasonic testing is one major NDT technique next to several existing options. Whereas contact technique allows the use of higher frequencies of some MHz and phased array focusing, air-coupled ultrasonic testing (ACUT) shows different advantages. Most significant for ACUT is the absence of any coupling fluid and an economical test procedure respective time and costs. Both contact technique and ACUT have been improved and enhanced during the past years. One important enhancement is the development of airborne transducers based on ferroelectrets, like charged cellular polypropylene (cpp), which makes the application of any matching layers being mandatory in conventional piezoelectric transducers unnecessary. In this contribution we show ultrasonic inspection results of specimens made of carbon- and glass-fibre-reinforced plastic. These specimens include defects represented by drill holes and artificial delaminations of various size and depth. We compare inspection results achieved by using contact technique to those achieved by ACUT. For ACUT, conventional piezoelectric transducers and transducers based on cpp were used, both focused as well as non-focused types. Contact inspections were performed with a multi-channel matrix array probe. Once the inspection data is recorded it can be analysed in order to detect and evaluate defects in the specimen. We present different analysing strategies and compare these regarding detection rate and sizing of defects.

SAFT-assisted sound beam focusing using phased arrays (PA-SAFT) for non-destructive evaluation

Focusing of sound has always been a subject of interest in ultrasonic non-destructive evaluation. An integrated approach to sound beam focusing using phased array and synthetic aperture focusing technique (PA-SAFT) has been developed in the authors' laboratory. The approach involves SAFT processing on ultrasonic B-scan image collected by a linear array transducer using a divergent sound beam. The objective is to achieve sound beam focusing using fewer elements than the ones required using conventional phased array. The effectiveness of the approach is demonstrated on aluminium blocks with artificial flaws and steel plate samples with embedded volumetric weld flaws, such as slag and clustered porosities. The results obtained by the PA-SAFT approach are found to be comparable to those obtained by conventional phased array and full matrix capture – total focusing method approaches.

Beam Control System for Ultrasound Scanning Device

The problems of FPGA based beam control system for ultrasound scanning system is considered. As a result of enhancement of algorithm of linear phased array focusing method for increasing efficiency of phased array elements is proposed. The application of the method for the real ultrasound scanning system is also considered.

Intensity Control of Ultrasonic Phased Array Focusing and Steering

When we detect an object by ultrasonic phased array focusing and steering in Non-Destructive Testing (NDT), the ultrasonic attenuation due to material damping will merge noise in the main signal and make data processing difficult. This paper presents an intensity control method developed to ensure that the intensities of eight subwaves are same when they are focusing or steering to the damage location. The mathematics model was established between eight elements and their corresponding magnification factors. We realized the intensity control function by adding an intensity controller model, which is designed on the basis of FPGA technology, into ultrasonic actuator/sensor. Some validation tests were made by using the development platform of Altera CycloneⅡseries. It was shown that both the precision and speed of the model can meet the requirement.

Advances in defect characterisation using long-range ultrasonic testing of pipes

Ultrasonic guided waves have been used for the rapid screening of pipes and pipelines for corrosion over the past 10 years. The hardware used in guided wave testing has improved since the early equipment, and now has up to 24 transmit-receive channels. This added capability has facilitated step changes in the way these tests are conducted, and has led to the introduction of better phased array focusing of guided waves and greatly enhanced post-processing techniques.The focusing technique provides increased sensitivity to defects and information about their circumferential position and extent. However, it relies on defects being detected in the initial screening test to identify the locations at which to apply the focused excitation.This paper presents an enhanced signal display technique that presents the operator with more information from the initial screening test, helping to prevent false negatives and to choose effective focal positions. A defect characterisation method is then presented that convolves information from this focused inspection with the information from the initial screening test to give defects a severity rating. Defect severity and position can be assessed with a higher degree of confidence than was previously achievable. The process has been tested under field conditions and has been shown to give good results.

Application of the time reversal technique to the focusing of long-range ultrasound in pipelines

The novel time reversal method of focusing has been applied to long-range ultrasonic propagation in pipelines. Some preliminary results on a 170 mm-diameter pipe of 7.1 mm wall thickness with a 9% CSA simulated crack defect are presented which show that significant increases in the signal-to-noise ratio of defect echoes can be obtained with this approach. The results equated to a signal-to-noise ratio of 2 (6 dB), which gives a 95% POD (probability of detection) according to the normal probability integral, for a 1% CSA crack. Using the same instrumentation without focusing, the crack size must be increased to 2% CSA to achieve the same POD. The results were also slightly better than those obtained using phased array focusing with a four-element array encircling the pipe. These preliminary results display promise of further improvement. The time reversal principle is described in simple terms both by a particle mechanics analogy and using geometrical optics, ie ray theory.

Phased array focusing with guided waves in a viscoelastic coated hollow cylinder

Guided wave phased array focusing has shown many advantages in long-range pipeline inspection, such as, longer inspection distance, greater wave penetration power and higher detection resolution. Viscoelastic coatings applied to a large percentage of pipes for protection purposes created some challenges in terms of focusing feasibility and inspection ability. Previous studies were all based on bare pipe models. In this work, guided wave phased array focusing in viscoelastic coated pipes is studied for the first time. Work was carried out with both numerical and experimental methods. A three-dimensional finite element model was developed for quantitatively and systematically modeling guided waves in pipes with different viscoelastic materials. A method of transforming measured coating properties to finite element method inputs was created in order to create a physically based model of guided waves in coated pipes. Guided wave focusing possibilities in viscoelastic coated pipes and the effects from coatings were comprehensively studied afterwards. A comparison of focusing and nonfocusing inspections was also studied quantitatively in coated pipe showing that focusing increased the wave energy and consequently the inspection ability tremendously. This study provides an important base line and guidance for guided wave propagation and focusing in a real field pipeline under various coating and environmental conditions.

Numerical analysis of ultrasonic transmission and absorption of oblique plane waves through the human skull.

Ultrasonic transmission and absorption of oblique plane waves through the human skull are analyzed numerically for frequencies ranging from 1/2 to 1 MHz. These frequencies are optimum for noninvasive ultrasound therapy of brain disorders where numerical predictions of skull transmission are used to set the phase and amplitude of source elements in the phased array focusing system. The idealized model of the skull is a three-layer solid with ivory outer and inner layers and a middle marrow layer. Each layer is modeled as a flat, homogeneous, isotropic, linear solid with effective complex wave speeds to account for focused energy losses due to material damping and scattering. The model is used to predict the amplitude and phase of the transmitted wave and volumetric absorption. Results are reported for three different skull thicknesses: 3 mm, 6 mm, and 9 mm. Thickness resonances are observed in the transmitted wave for 3 mm skulls at all frequencies and for the 6 mm skulls below 0.75 MHz. Otherwise, the transmission is dominated by the direct wave. Skull phase errors due to shear waves are shown to minimally degrade the power at the focus for angles of incidence up to 20 degrees from normal even for low material damping. The location of the peak volumetric absorption occurs either in the outer ivory or middle marrow layer and shown to vary due to wave interference.