Linear Phased Array Research Articles

Research and experimental testing of a new kind electrokinetic logging tool

We designed a new downhole electrokinetic logging tool based on numerical simulations and petrophysical experiments. Acoustic and electric receivers cannot be arranged at the same depth, and the proposed composite electrokinetic logging tool offers a solution to this problem. The sound field characteristics of the detectors were tested in a water tank in the laboratory. Then, we calculated the sound pressure of the radiated acoustic field and the transmitting voltage response of the transmitting transducers; in addition, we analyzed the directivity and application of the acoustic transmitting probe based on linear phased array. The results suggest that the sound pressure generated at 1500 mm spacing reaches up to 47.2 kPa and decreases with increasing acoustic source frequency. When the excitation signals delay time of adjacent acoustic transmitting subarrays increases, the radiation beam of the main lobe is deflected and its energy gradually increases, which presumably enhances the acoustoelectric conversion efficiency.

Acoustic Field Calculation of Ultrasonic Phased Array Concave Cylindrical Transducer

The focus law and acoustic field computation method about circular arc linear phased array have been discussed in the paper. Acoustic field of transducers is given by the use of the coordinate transformation and an approximation with rectangle element instead of circular arc element, and was calculated using Rayleigh-Sommerfeld Integral.

An Ultrasonic-Adaptive Beamforming Method and Its Application for Trans-skull Imaging of Certain Types of Head Injuries; Part I: Transmission Mode

A new adaptive beamforming algorithm for imaging via small-aperture 1-D ultrasonic-phased arrays through composite layered structures is reported. Such structures cause acoustic phase aberration and wave refraction at undulating interfaces and can lead to significant distortion of an ultrasonic field pattern produced by conventional beamforming techniques. This distortion takes the form of defocusing the ultrasonic field transmitted through the barrier and causes loss of resolution and overall degradation of image quality. To compensate for the phase aberration and the refractional effects, we developed and examined an adaptive beamforming algorithm for small-aperture linear-phased arrays. After accurately assessing the barrier's local geometry and sound speed, the method calculates a new timing scheme to refocus the distorted beam at its original location. As a tentative application, implementation of this method for trans-skull imaging of certain types of head injuries through human skull is discussed. Simulation and laboratory results of applying the method on skull-mimicking phantoms are presented. Correction of up to 2.5 cm focal point displacement at up to 10 cm depth under our skull phantom is demonstrated. Quantitative assessment of the method in a variety of temporal focusing scenarios is also reported. Overall temporal deviation on the order of a few nanoseconds was observed between the simulated and experimental results. The single-point adaptive focusing results demonstrate strong potential of our approach for diagnostic imaging through intact human skull. The algorithms were implemented on an ultrasound advanced open-platform controlling 64 active elements on a 128-element phased array.

Alterations in cardiac structure and function in a modified rat model of myocardial hypertrophy.

This study was aimed to establish a stable animal model of left ventricular hypertrophy (LVH) to provide theoretical and experimental basis for understanding the development of LVH. The abdominal aorta of male Wistar rats (80-100 g) was constricted to a diameter of 0.55 mm between the branches of the celiac and anterior mesenteric arteries. Echocardiography using a linear phased array probe was performed as well as pathological examination and plasma B-type natriuretic peptide (BNP) measurement at 3, 4 and 6 weeks after abdominal aortic constriction (AAC). The results showed that the acute mortality rate (within 24 h) of this modified rat model was 8%. Animals who underwent AAC demonstrated significantly increased interventricular septal (IVS), LV posterior wall (LVPWd), LV mass index (LVMI), cross-sectional area (CSA) of myocytes, and perivascular fibrosis; the ejection fraction (EF), fractional shortening (FS), and cardiac output (CO) were consistently lower at each time point after AAC. Notably, differences in these parameters between AAC group and sham group were significant by 3 weeks and reached peaks at 4th week. Following AAC, the plasma BNP was gradually elevated compared with the sham group at 3rd and 6th week. It was concluded that this modified AAC model can develop LVH, both stably and safely, by week four post-surgery; echocardiography is able to assess changes in chamber dimensions and systolic properties accurately in rats with LVH.

Evaluation of crack closure stress by analyses of ultrasonic phased array images during global preheating and local cooling

Crack closure stress (CCS) is an important parameter that affects crack propagation rate. However, the method for measuring CCS in practical fields has yet to be developed. In this study, we propose a practical method of estimating CCS. In our experiment, a closed fatigue crack was imaged by a linear phased array (PA) method during crack opening by global preheating and local cooling (GPLC). Here, we assumed that the crack appears in PA images after the thermal stress induced by GPLC exceeds CCS. Therefore, we calculated the thermal stress induced by GPLC using an analytical solution and thereby estimated CCS. Then, to validate the CCS estimation method, we simulated the PA images by a finite difference time domain (FDTD) method with a damped double node (DDN) model, where CCS was relieved by the calculated thermal stress. Consequently, the temporal variation in crack depth observed in the PA image was successfully reproduced in the simulation. Thus, the CCS estimation method was verified by comparing experimental results with analysis results.

Theory of ESPAR Design With Their Implementation in Large Arrays

A generalized formulation as well as a simple design approach is presented for electronically steerable parasitic array radiators (ESPAR). Based on the presented design procedure, a low-cost rectangular dielectric resonator parasitic phased array antenna is designed. An E-plane linear dielectric resonator phased array coupled to symmetric narrow slot apertures is investigated. The driven element is mutually coupled to the parasitic elements and reactive loads are utilized to control the phase to achieve a particular beam scanning direction. The use of low-cost reactive loads instead of expensive conventional phase shifters allows for more economic fabrication. Based on this design, a five elements planar array is designed and measured. In addition, a large array using ESPAR subarrays is presented.

PATTERN SYNTHEISS OF LINEAR PHASE ARRAY USING ARTIFICIAL NEAURAL NETWORK BASED ON PARTICLE SWARM OPTIMIZATION

This paper focuses on the antenna synthesis of uniformly spaced linear phase array using artificial neural network (ANN) based on Particle Swarm Optimization (PSO). The weights of the Artificial Neural Networks (ANN) are trained by Particle Swarm Optimization (PSO). Subsequently the Particle Swarm Optimization (PSO) algorithm is applied in order to select the "global best" ANNs for the future investment decisions and to adapt the weights of other networks towards the weights of the best network. Chebyshev method is used to compare with this approach. Although, Chebyshev method is able to generate perfectly leveled side lobes, PSONN does not have the phenomena of up-swing in edges amplitude of the excitation and grating lobes does not appear in PSONN when the distances between elements are increased. The basic rule is to alter the weights (current distributions of elements) such that the error between the output values and the target values (desired values) is minimized. In this paper, single layer feed forward neural network with PSO training is used.

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.

Optimization of acoustic emitted field of transducer array for ultrasound imaging

A method is proposed to calculate the weight vector of a transducer array for ultrasound imaging to obtain a low-sidelobe transmitting beam pattern based on the near-field response vector. An optimization problem is established, and the second-order cone (SOC) algorithm is used to solve the problem to obtain the weight vector. The optimized acoustic emitted field of the transducer array is then calculated using the Field II program by applying the obtained weight vector to the array. The simulation results with a 64-element 26 MHz linear phased array show that the proposed method can be used to control the sidelobe of the near-field transmitting beam pattern of the transducer array and achieve a low-sidelobe level. The near-field sound pressure distribution of the transducer array using the proposed method focuses much better than that using the standard delay and sum (DAS) beamforming method. The sound energy is more concentrated using the proposed method.

Focusing Modeling of OPFC Linear Array Transducer by Using Distributed Point Source Method

The improvement of ultrasonic phased array detection technology is a major concern of engineering community. Orthotropic piezoelectric fiber composite (OPFC) can be constructed to multielement linear array which may be applied conveniently to actuators and sensors. The phased array transducers can generate special directional strong actuator power and high sensitivity for its orthotropic performance. Focusing beam of the linear phased array transducer is obtained simply only by adjusting a parabolic time delay. In this work, the distributed point source method (DPSM) is used to model the ultrasonic field. DPSM is a newly developed mesh-free numerical technique that has been developed for solving a variety of engineering problems. This work gives the basic theory of this method and solves the problems from the application of new OPFC phased array transducer. Compared with traditional transducer, the interaction effect of two OPFC linear phased array transducers is also modeled in the same medium, which shows that the pressure beam produced by the new transducer is narrower or more collimated than that produced by the conventional transducer at different angles. DPSM can be used to analyze and optimally design the OPFC linear phased array transducer.

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.

Simulation of diagnostic ultrasound imaging with the fast nearfield method

Software for simulating diagnostic ultrasound imaging with the fast nearfield method is now available in FOCUS (http://www.egr.msu.edu/~fultras-web). The implementation of ultrasound imaging simulations in FOCUS first decomposes the excitation pulse into two shorter pulses that, when convolved together, are equivalent to the original excitation pulse. These two shorter pulses are applied to the transmit and receive apertures, reciprocity is applied to the receive aperture, and then the results of the intermediate pressure calculations are convolved to obtain the simulated pulse-echo signal. Simulation results using point scatterers are compared to Field II (http://field-ii.dk/) for simulations with a linear phased array. Results show that FOCUS achieves equal or smaller errors in less time than Field II, and the FOCUS results require much smaller sampling frequencies. The FOCUS results are achieved with an analytically equivalent algorithm that avoids aliasing problems by calculating pressures with the fast nearfield method combined with time-space decomposition. To further improve the efficiency of the imaging simulation in FOCUS, intermediate signals are computed, stored, and re-used. Ongoing efforts to incorporate new features into ultrasound imaging simulations with FOCUS will also be discussed. [This work was supported in part by NIH Grant R01 EB012079.]

Accelerating and Abruptly-Autofocusing Beam Waves in the Fresnel Zone of Antenna Arrays

We introduce the concept of spatially accelerating (curved) beam waves in the Fresnel region of properly designed antenna arrays. These are transversely localized EM waves that propagate in free space in a diffraction-resisting manner, while at the same time laterally shifting their amplitude pattern along a curved trajectory. The proposed beams are the radiowave analogue of Airy and related accelerating optical waves, which, in contrast to their optical counterparts, are produced by the interference of discrete radiating elements rather than by the evolution of a continuous wavefront. Two dyadic array configurations are proposed comprising 2D line antennas: linear phased arrays with a power-law phase variation and curved power-law arrays with in-phase radiating elements. Through analysis and numerical simulations, the formation of broadside accelerating beams with power-law trajectories is studied versus the array parameters. Furthermore, the abrupt autofocusing effect, that occurs when beams of this kind interfere with opposite acceleration, is investigated. The concept and the related antenna setups can be of use in radar and wireless communications applications.

Widening Frequency Band of Uniform SPL Distribution Using Adaptive Genetic Algorithm

Uniform sound pressure level (SPL) distribution of linear phased loudspeaker array is limited by frequency. This paper widens the applicable frequency band of uniform SPL distribution in a linear listening area. By using an improved adaptive genetic algorithm (which contains a novel objective function, modified genetic operators and parameter setups) to control the directivity pattern details accurately, uniform distribution of SPL on a linear listening line in a wider frequency is achieved. The simulation and experimental results show that the SPLs on the test listening line are basically uniform from 200Hz to 500Hz, which demonstrates that the improvement of adaptive genetic algorithm is effective.

A Comparison of three commercially available Contrast-Detail phantoms and evaluation of the effect of Instrument Settings on the performance

Contrast detail is an important characteristic of an ultrasound imaging system. Contrast detail is the measure of a systems ability to distinguish between different intensities or gray levels within an image. A range of Contrast-Detail phantoms are currently commercially available from a variety of manufacturers although no comparison of the usefulness of these phantoms for contrast-detail performance has been carried out. The aim of this study was to compare three such commercial available phantoms two produced by Dansk Phantoms Inc. and one by Gammex-RMI. In this study a range of instrument settings were investigated to determine which had the greatest impact on contrast-detail performance. The effect of damaged crystals was also investigated by simulating dropped elements on one of the transducers. The ultrasound machines used in this project were the Philips HDI 3000 and the Siemens Sonoline Antares. The two machines each had a linear array, curvilinear array and phased array transducer. The default settings on each machine were only used initially to acquire the baseline images of the phantoms. The data collection method involved optimising the conventional image of the appropriate targets and storing the image for off-line analysis on a PC using a contrast-details image analysis program which evaluated the Contrast_to_Noise Ratio, the Lesion Signal_to_Noise Ratio and the Contrast Ratio. The results obtained from each of the phantoms will be presented with a recommendation to the contrast detail measurement which is most sensitive to changes in contrast detail performance.

Characterisation of ultrasonic structural noise in multiple scattering media using phased arrays

The ultrasonic inspection of multiple scattering media gives rise to structural noise which makes it difficult to detect potential damage or crack inside the component. In order to predict the performances of ultrasonic inspection over such complex media, scattering models can be used. Such models rely on specific key parameters describing the multiple scattering process, which can be determined by specific measurements and post-processing techniques. Such experiments were carried out on stainless steel plates using linear phased-arrays. They consist in recording the response matrix constituted by impulse responses between all the elements of the array. By conducting post-processing on this matrix, we measure the elastic mean free path le and the correlation distance dc of the recorded noise. Additionally, the dynamic behaviour of the coherent backscattering effect was studied in order to measure the diffusion constant D. Plane-wave beamforming has been applied to the response matrix to improve the angular resolution and the signal-to-noise ratio of the backscattered intensity. Details of postprocessing techniques will be shown.

Towards semi-automated non-destructive evaluation

A demonstrator has been developed showing feasibility of semi-automatic characterisation of large planar flaws in steel using ultrasonic transducer arrays. The unit is based on a real-time ultrasonic imager deploying National Instruments hardware and software, is connected to an IMASONIC linear phased array containing 128 elements and incorporates a novel flaw characterisation algorithm, which is a model-based variant of Total Focusing Method, taking into account undulations in inspection surface. It has been shown to process RF data collected in immersion reasonably fast and be capable of detecting and characterising with reasonable accuracy large planar defects.

High-selectivity imaging of closed cracks using elastic waves with thermal stress induced by global preheating and local cooling

The authors developed a practical method based on the thermal stress dependence of cracks for the accurate imaging of closed cracks with high selectivity. A tightly closed fatigue crack was visualized in linear phased array (PA) images by opening the crack with the tensile thermal stress induced by global preheating and local cooling (GPLC), although the conventional method of using only local cooling could not fully open the crack. Furthermore, by the subtraction of the PA images before and after GPLC, only the closed crack was extracted with high selectivity while canceling the other linear scatterers.

Simulation and Analysis on Grating Lobe Effect and its Avoidance for Planar Phased Array Antenna

Grating lobe effect often exists in the measurement and simulating of phased array antenna's directional pattern. The emergency of grating lobe effect often leads to angle multi valuedness, which will result in the receiver error tracking the grating lobe. The traditional papers mainly focus on the grating lobe effect of linear phased array antenna, whereas pay little attention to the planar phased array antenna. Thus, in this paper, the cause, location and avoidance of grating lobe effect of planar phased array antenna are investigated in theory and the correctness of conclusion was verified by using simulation experiment. The result shows that the method proposed in this article will play a guiding role in engineering practice of restraining the grating lobe effect.

Reducing crosstalk in array structures by controlling the excitation voltage of individual elements: A feasibility study

This paper describes a procedure to minimize crosstalk between the individual elements of a piezoelectric transducer array. A two-dimensional finite elements model was developed and the excitation voltages predicted by the model were applied to the array prototypes made of PZT 27 ceramic. Symmetric and asymmetric linear phased arrays operating at approximately 450kHz were tested in the feasibility study. The studies were carried out at low frequency to facilitate the fabrication of the transducer arrays and to check the feasibility in this case. The novelty of our approach is to offer active cancellation of crosstalk in transducer arrays generating continuous waves, even in the presence of fabrication defects.The experimental results showed the validity of the approach and demonstrated that crosstalk can be reduced by about 6–10dB. In ultrasonic imaging systems, this method could be introduced by using a multichannel generator providing electrical signals containing both phased signals required to focalize and deflect the acoustic beam associated with the correction signals.