Damage localization in aluminum plate with compact rectangular phased piezoelectric transducer array

In this work, a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 \times 5$</tex> stacked patch rectangular phased array, along with its feeding network, is designed and fabricated in a multilayered low-temperature co-fired ceramic (LTCC) substrate. The single element of the phased array is a dual linear polarized stacked patch microstrip antenna which has improved impedance as well as 3-dB gain bandwidth due to the stacked patch approach. Based on the field distributions, the single element's orientation is optimized to reduce the mutual couplings between the adjacent elements for a wide beam scanning range over a wide frequency band. The features of multilayered implementation, low dielectric loss, and excellent packaging properties ensure a compact and high-efficiency phased array design and qualify this design as an antenna-in-packaging (AiP) design.

Phased array approach to generate guided waves and extract phase velocities using the V(z) method.

Phased array ultrasonic total focusing method (TFM) imaging has attracted much attention due to its high detection image resolution and large dynamic range. However, due to the small emission energy of its single element, the echo signal is weak and susceptible to noise interference, resulting in a relatively low signal-to-noise ratio (SNR). Especially when detecting high sound attenuation carbon fiber reinforced polymer (CFRP) composites, the signal amplitude can decrease with depth to a level lower than the electronic noise introduced by the signal acquisition system. To solve this problem, a new imaging algorithm was proposed that combines the Golay code excitation using linear frequency modulation (LFM) signal as the carrier with the TFM algorithm (LFM-Golay TFM). Meanwhile, in order to further overcome the disadvantage of the LFM-Golay code encoding excitation method requiring two excitations, an AB code encoding excitation conversion factor was introduced, two sets of echo data were obtained through processing single excitation, TFM imaging based on LFM-Golay code single excitation (IMP-LFM-Golay TFM) is realized. Simulation and experimental studies were conducted to compare the TFM imaging performance of single-pulse excitation (Pulse TFM), Barker coding excitation (Barker TFM), LFM excitation (LFM TFM), and improved LFM-Golay coding excitation. The results show that IMP-LFM-Golay TFM has the best SNR, axial resolution, and depth resolution.

We propose a compact wideband phased array with 2-D wide-angle scanning and low radar-cross Section (RCS) performance. The antenna elements comprise two pairs of split-ring (SR) particles and U/E-slot microstrip antennas. Specifically, the SR particles are equivalent to an antiphase metal-plate monopole array in the band to broaden the half-power beamwidth (HPBW) of the microstrip antenna. Meanwhile, the microstrip antenna functions as part of the absorbing structure out of the band to improve the absorption performance. The proposed design provides a simple and universal method to simultaneously manipulate the radiation and scattering characteristics of the microstrip antenna. In particular, an expanded checkerboard <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times4$ </tex-math></inline-formula> array is presented and investigated using the proposed elements. Precisely, the array examination is conducted to demonstrate the good performance of a wide operating band from 6.9 to 9.3 GHz (29.6%) and wide-angle scanning up to ±60° in the E-/H-plane, and up to ±65° in the D-plane with a gain fluctuation of less than 3.5 dB. The array also achieves ultra-wideband monostatic RCS reductions in the band from 6.5 to 15 GHz (79%) for the co-polarization, and in the band from 6 to 15 GHz (85.7%) for the cross-polarization of incident waves.

In order to fully explore the great potential of terahertz (THz) waves in networked wireless sensing both as sensing probes and carrier waves, beam steering techniques are required. However, conventional beam steering approaches with delay-line based phased arrays would face technical difficulties due to the too high frequency of THz waves. In this paper, we propose to electrically control the THz beam propagation based on surface-wave scattering from structured MEMS surfaces, which would lead to very compact and low-cost THz phased arrays.

Ultrasonic arrays have been widely employed in industrial applications because of their ability to perform quick inspections for detection and characterization of flaws. The total focusing method (TFM) is an advanced ultrasonic imaging technique that utilizes the full matrix capture (FMC) data of the phased array elements to generate a high-resolution image by focusing on every image pixel in both transmission and reception. In this work, the time of flight framework involved for the TFM post-processing is illustrated for an angular wedge configuration. Further, the TFM algorithm is extended for imaging using multiple direct and half-skip wave modes by taking into account the wave mode conversions in the specimen. The implications of the mode conversions on the TFM images are analyzed, and the challenges posed on the TFM, specific to weld inspection, are explained in detail. In this work, experimental studies are performed on weld specimens with five common weld defects using the TFM algorithm. FMC data is acquired from the ultrasonic instrument and is post-processed to get the TFM images. The TFM results of weld defects show high resolution, better defect detectability, and easy visualization of defects compared to phased array sector scan images.KeywordsUltrasonic arraysFull matrix captureTotal focusing methodAngular wedgeWeld inspection

A novel automatic ultrasonic system used for the inspection of welds in T nodes is developed, in which a linear phased array transducer using electronic scan is adopted. This paper introduces the testing method of welds in T nodes, and the structure of the whole testing system. Optimization of array transducer has been also pursued based on a mathematical model of acoustic field for linear phased array. The experimental results have proved that the phased array transducer system had the same detectability as that of conventional ultrasonic transducer system, but the component part of the system can be simplified greatly, and the testing flexibility and the testing speed can be improved greatly. It provides an excellent base for the further research and development of the defect inspection of welds in TKY nodes.

The acoustic hologram has made it possible to shape ultrasound waves and project complex pressure patterns in 2D and in 3D, as we have also recently shown. The hologram contains tens of thousands of elements which can be used to form sophisticated pressure patterns by setting the phase and/or amplitude across the wavefront of a sound wave. It thereby offers more degrees of freedom than conventional phased array transducers (PATs). However, the hologram is generally static, whereas PATs are dynamic. PATs do not only have fewer elements, but they are also more difficult to fabricate and require complex electronics. In this talk, I will describe our efforts to combine the best of both worlds. For this, we are exploring the use of light waves as a means to control ultrasound waves. I will describe direct and indirect approaches that can be used to control and modulate holographic ultrasound fields.

Phased Array (PA) uses a single focus in emission and Dynamic Depth Focusing (DDF) in reception, while Total Focusing Method (TFM) focuses every image pixel in emission and in reception. By contrast, TFM lacks the A-scan information, which is standard in PA and can be very useful for evaluation. Another issue common to both techniques is the difficulty associated with two media propagation and unknown interface geometry. A further TFM drawback is the limited image extent due to memory and time consumption. This work addresses these problems by proposing the new Total Focus Phased Array (TFPA) technique that combines the advantages of PA and TFM. TFPA builds A-scan lines as in PA, but focused in emission and in reception at all depths. This process is achieved in real-time by N+1 focusing hardware blocks that do not limit the length of every A-scan. Furthermore, TFPA can operate with the Virtual Array concept that avoids the problems of refraction in two propagation media applications. TFPA has many advantages: A-scan information is preserved, image is focused in emission and in reception, moderate complexity with real-time capability, no refraction issues and no limit on the depth or the number of pixels/samples in the image.

Real-time imaging, using ultrasound techniques, is a complex task in non-destructive evaluation. In this context, fast and precise control systems require design of specialized parallel architectures. Total focusing method (TFM) for ultrasound imaging has many advantages in terms of flexibility and accuracy in comparison to traditional imaging techniques. However, one major drawback is the high number of data acquisitions and computing requirements for this imaging technique. Due to those constraints, the TFM algorithm was earlier classified in the field of post-processing tasks. This paper describes a multi-FPGA architecture for real-time TFM imaging using the full matrix capture (FMC). In the acquisition process, data are acquired using a phased array and processed with synthetic focusing techniques such as the TFM algorithm. The FMC-TFM architecture consists of a set of interconnected FPGAs integrated on an embedded system. Initially, this imaging system was dedicated to data acquisition using a phased array. The algorithm was reviewed and partitioned to parallelize processing tasks on FPGAs. The architecture was entirely described using VHDL language, synthesized and implemented on a V5FX70T Xilinx FPGA for the control and high-level processing tasks and four V5SX95T Xilinx FPGAs for the acquisition and low-level processing tasks. The designed architecture performs real-time FMC-TFM imaging with a good characterization of defects.

Performance of Two Dimensional Displacement and Strain Estimation Techniques Using a Phased Array Transducer

A series of ultrasonic elements arranged in a phased array transducer can provide the capability to activate each element separately but in a programmed sequence. This will help the acoustic signal to be generated at desired focusing distances and anticipated angles for specific materials and structures. In case of composite material inspection, this characteristic of the phased array method can improve the undesirable effects of the high attenuation and anisotropic structure of composite materials on response signals. In this study different phased array probes and wedges which are commercially available were evaluated for their response signals’ characteristics. First, the capability and resolution of bulk wave generation were studied for each set of probe and wedge, and the response signals were compared to that of the conventional single element ultrasonic transducers for different thicknesses composite plates. Then the resolution of the response signals and their sensitivity to defect size were evaluated and compared to the single element transducers as well. Next, each phased array probe and wedge set was used to generate plate waves in aluminum plates based on plate wave propagation theory, probe and wedge physical properties and the definition of delay law. Results show a general improvement in response signals’ strength and resolution for phased array method in comparison to the single element transducers. Also some plate wave modes could be generated with optimized signal generation parameters in phased array system.

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.

Present state of the art sizing measurements of defects by ultrasonic techniques has been inadequate, especially in support of a quantitative fracture mechanical analysis of the strength of a material. Present capabilities of defect sizing in some cases do not allow an accept/reject decision to be made. Currently, ultrasonic imaging systems including phased array, synthetic aperture, and wavefront reconstruction systems are being developed to quantitatively measure defect sizes. Also, in the medical field phased array systems have been developed for imaging purposes. Ibis work describes an annular phased array system which is being developed for general NDE applications on metal and ceramic materials. The main usefulness of phased array techniques is the ability of electronically changing the focus of the acoustic beam radiating from a phased array transducer or reflecting from a defect in a solid material.

Previous work has led to the design, simulation, and development of a linear phased array transducer. The intention of the array is to be used as a non-destructive ultrasonic device to monitor and evaluate the health of a given specimen. The phased array has been manufactured and tested for the detection and characterization of defects on a target. The array was fabricated with a four-row stepped design with four wires to transfer data and one wire for grounding. The stepped design allows for the interrogation of a larger region using time delays and beam sweeping without the use of additional electrical channels. The array was designed to be utilized in a water immersion environment with about one inch between the array and the target specimen. An OmniScan MX system was used to operate the phased array and perform real-time linear and sectorial scans on a set of rectangular plates. S-scans allow for beam sweeping over an angle range as well as adjustments for time delays and a true-depth display. The array was operated with sixteen active elements and an angle range of 0 to 30 degrees. The phased array was tested with a variety of targets and was used to investigate and characterize different types of defects such as cracking, warping, and corrosion. The ability of the phased array to distinguish between defect types as well as resolve defect size was evaluated.