Phased Array Detector Research Articles

Study on Denoising Method of Weld Defect Signal Based on SSA-VMD-WPD

Defects in welds can affect the structural safety and reliability of workpieces. Currently, the method of using phased array ultrasonic inspection technology for non-destructive testing of weld structures with high detection efficiency, good sensitivity, and good visualization of the results is widely used. However, the defective A-scan data collected by the ultrasonic phased array detector inevitably contain noise data, including the test piece material structure noise, equipment noise, and environmental noise, which undoubtedly affects the analysis of the A-scan signal. In addition, when defects are interpreted, the presence of noise also interferes with the process, which affects the accuracy of the interpretation. Therefore, to enhance the accuracy of defect identification based on phased array ultrasonic inspection technology, we must prevent the series of consequences caused by misjudgments. In this study, ultrasonic phased array inspection experiments were carried out, and the specific process flow of ultrasonic phased array inspection of flat plate butt welds was summarized. Utilizing pre-fabricated flat plate butt specimen blocks containing five types of typical defects, defect A-sweep signals based on ultrasonic phased array inspection were obtained. Combining the sparrow optimization algorithm (SSA), variational mode decomposition (VMD), and wavelet packet decomposition (WPD), a defect signal noise reduction method based on parameter optimization was studied. A noise reduction study was carried out using the noise-added simulated signal, and the results indicated that the noise reduction method proposed in this paper had a better noise reduction effect and the proposed method could effectively retain the detailed features of the ultrasonic phased array defective A-scan signal and realize the noise reduction processing of the defective A-scan signal.

Staring high-resolution imaging algorithm based on random coded-wavefront

In order to solve the staring imaging problem of phased array detector, a high-resolution imaging algorithm based on random phase coding is proposed in this paper. Random phase coding is used to realize more complex wavefront of detection beam for phased array detector, and it can intercept more effective information from strong scattering points in the target area carried, the scattering factor matrix of detection target area can be restructured accurately through proposed modified sparsity adaptive matching pursuit algorithm, and adaptive monopulse response curve is used for high-resolution azimuth angle measurement during the signal processing. The proposed algorithm can lead the measured angle profile focusing, the resolution of measured angle from proposed algorithm is about 10 times beyond the actual beam scanning imaging algorithm, and the RMSE of imaging is reduced to 2 m.

Broadband RF Phased Array Design with MEEP: Comparisons to Array Theory in Two and Three Dimensions

Phased array radar systems have a wide variety of applications in engineering and physics research. Phased array design usually requires numerical modeling with expensive commercial computational packages. Using the open-source MIT Electrogmagnetic Equation Propagation (MEEP) package, a set of phased array designs is presented. Specifically, one and two-dimensional arrays of Yagi-Uda and horn antennas were modeled in the bandwidth [0.1–5] GHz, and compared to theoretical expectations in the far-field. Precise matches between MEEP simulation and radiation pattern predictions at different frequencies and beam angles are demonstrated. Given that the computations match the theory, the effect of embedding a phased array within a medium of varying index of refraction is then computed. Understanding the effect of varying index on phased arrays is critical for proposed ultra-high energy neutrino observatories which rely on phased array detectors embedded in natural ice. Future work will develop the phased array concepts with parallel MEEP, in order to increase the detail, complexity, and speed of the computations.

Beamforming for large-area scan and improved SNR in array-based photoacoustic microscopy

Beamforming enhances the performance of array-based photoacoustic microscopy (PAM) systems for large-area scan. In this study, we quantify the imaging performance of a large field-of-view optical-resolution photoacoustic-microscopy system using an phased-array detector. The system combines a low-cost pulsed-laser diode with a 128-element linear ultrasound probe. Signal-to-noise ratio (SNR) and generalized contrast-to-noise ratio (gCNR) are quantified using the phased-array detector and applying three beamforming strategies: a no-beamforming method equivalent to a single-element flat transducer, a fixed focus beamforming method that mimics a single-element focused transducer, and a dynamic focus beamforming using a delay-and-sum (DAS) algorithm. The imaging capabilities of the system are demonstrated generating high-resolution images of tissue-mimicking phantoms containing sub-millimetre ink tubes and an ex vivo rabbit’s ear. The results show that dynamic focus DAS beamforming increases and homogenizes SNR along 1-cm2 images, reaching values up to 15 dB compared to an unfocused detector and up to 30 dB compared to out-of-focus regions of the fixed focus configuration. Moreover, the obtained values of gCNR using the DAS beamformer indicate an excellent target visibility, both on phantoms and ex vivo. This strategy makes it possible to scan larger surfaces compared to standard configurations using single-element detectors, paving the way for advanced array-based PAM systems.

Three-dimensional reconstruction of ceramic membrane with internal defects based on ultrasound imaging technique applying triangular matrix-synthetic aperture focusing

To realize a three-dimensional (3D) visual display and evaluate the internal defects of a ceramic hollow plate membrane, a method for creating a 3D reconstruction of the internal defects based on an ultrasound imaging technique applying triangular matrix–synthetic aperture focusing is proposed. First, a phased array detector is used to scan the surface of the ceramic membrane, and ultrasound imaging is achieved based on the triangular matrix–synthetic aperture focusing technology. The acquired B-scan images are pre-processed and a 3D reconstruction is achieved based on the contours of the internal defects. Finally, a 3D visualization of the internal defects of a hollow plate ceramic membrane is realized. The use of a triangular matrix focusing method can improve the detection efficiency because the amount of data acquired and the number of calculations are reduced by nearly half. In addition, the synthetic aperture focusing method can ensure a high imaging resolution, which leads to an improved recognition accuracy of the defect size. As a result, the error of the diameter measurements of the inner hole defects ranges between 2% and 3%, and the error of the diameter and length measurements of the crack line defects ranges between 2% and 4%. Experimental results with real datasets are presented to demonstrate the efficiency and accuracy of our method as compared with traditional methods.

A high-impedance detector-array glove for magnetic resonance imaging of the hand.

Densely packed resonant structures used for magnetic resonance imaging (MRI), such as nuclear magnetic resonance phased-array detectors, suffer from resonant inductive coupling, which restricts coil design to fixed geometries, imposes performance limitations, and narrows the scope of MRI experiments to motionless subjects. Here, we report the design of high-impedance detectors, and the fabrication and performance of a wearable detector array for MRI of the hand, that cloak themselves from electrodynamic interactions with neighboring elements. We experimentally verified that the detectors do not suffer from signal-to-noise degradation mechanisms typically observed with the use of traditional low-impedance elements. The detectors are adaptive and can accommodate movement, providing access to the imaging of soft-tissue biomechanics with unprecedented flexibility. The design of the wearable detector glove exemplifies the potential of high-impedance detectors in enabling a wide range of applications that are not well suited to traditional coil designs.

Error quantification in pharmacokinetic parameters derived from DCE-MRI data using a novel anthropomorphic dynamic prostate phantom

Pharmacokinetic (PK) modelling of dynamic contrast enhanced (DCE) MRI data has shown considerable promise in the detection of many cancers, including prostate. However, the clinical implementation of DCE-MRI acquisition protocols suitable for PK modelling has been greatly hindered by the lack of consistency with published PK parameter values, such as the volume-transfer constant ( K trans ), with widely varying acquisition protocols and PK modelling approaches adding to the confusion. A novel anthropomorphic dynamic prostate phantom has been developed to address this shortcoming. The device is capable of simultaneously producing two distinct contrast time-intensity curves (CTCs), representative of those observed in DCE-MRI data from healthy and tumorous prostate tissue, in an environment which closely mimics the male pelvic region. CTCs were measured using a custom-built optical scanner, and ‘ground truth’ PK parameter values derived from the data. DCE-MRI data were acquired using a 3T scanner (Achieva, Philips, Netherlands) and a 16-channel phased array detector coil (3D-SPGR, TR/TE = 3.6/1.75 ms, flip = 10°, voxel size = 1.1 × 1.1 × 4 mm 3 , FOV = 224 × 224 × 72 mm 3 , slices = 18). The parallel imaging factor and number of signal averages were varied to give temporal resolutions from 2.3 s to 20.3 s. K trans values derived from MR data from the phantom were compared with the ground truth values and were found to differ by −8.1% to −44.6%, with the lowest variance from ground truth values achieved at a temporal resolution of 6.8 s. The phantom provides a model system on which the quantitative validation of new prostate DCE-MRI protocols can be performed, and could contribute to the standardisation of clinical prostate DCE-MRI acquisition protocols.

Noise figure limits for circular loop MR coils

Circular loops are the most common MR detectors. Loop arrays offer improved signal-to-noise ratios (SNRs) and spatial resolution, and enable parallel imaging. As loop size decreases, loop noise increases relative to sample noise, ultimately dominating the SNR. Here, relative noise contributions from the sample and the coil are quantified by a coil noise figure (NF), NF(coil), which adds to the conventional system NF. NF(coil) is determined from the ratio of unloaded-to-loaded coil quality factors Q. Losses from conductors, capacitors, solder joints, eddy currents in overlapped array coils, and the sample are measured and/or computed from 40 to 400 MHz using analytical and full-wave numerical electromagnetic analysis. The Qs are measured for round wire and tape loops tuned from 50 to 400 MHz. NF(coil) is determined as a function of the radius, frequency, and number of tuning capacitors. The computed and experimental Qs and NF(coil)s agree within approximately 10%. The NF(coil) values for 3 cm-diameter wire coils are 3 dB, 1.9 dB, 0.8 dB, 0.2 dB, and 0.1 dB, at 1T, 1.5T, 3T, 7T, and 9.4T, respectively. Wire and tape perform similarly, but tape coils in arrays have substantial eddy current losses. The ability to characterize and reliably predict component- and geometry-associated coil losses is key to designing SNR-optimized loop and phased-array detectors.

Preliminary Experience with Visualization of Intracortical Fibers by Focused High-Resolution Diffusion Tensor Imaging

The inherent low anisotropy of gray matter and the lack of adequate imaging sensitivity and resolution has, so far, impeded depiction of axonal fibers to their intracortical origin or termination. We tested the hypothesis that an experimental approach with high-resolution diffusion tensor imaging (DTI) provides anisotropic data for fiber tractography with sufficient sensitivity to visualize in vivo the fine distribution of white matter bundles at the intracortical level. We conducted phantom measurements of signal-to-noise ratio (SNR) and obtained diffusion tensor maps of the occipital lobe in 6 healthy volunteers using a dedicated miniature phased array detector at 3T. We reconstructed virtual fibers using a standard tracking algorithm. The coil array provided a SNR of 8.0 times higher at the head surface compared with a standard quadrature whole head coil. Diffusion tensor maps could be obtained with an in-plane resolution of 0.58 x 0.58 mm(2). The axonal trajectories reconstructed from the diffusion data penetrate into the cortical ribbon perpendicular to the pial surface. This is the expected pattern for the terminations of thalamocortical afferent fibers to the middle layers of the occipital cortex and is consistent with the known microstructural organization of the mammalian cerebral cortex. High-resolution DTI reveals intracortical anisotropy with a distinct parallel geometrical order, perpendicular to the pial surface, consistent with structures that may be identified as the terminal afferents in cortical gray matter.

Phased array detectors and an automated intensity-correction algorithm for high-resolution MR imaging of the human brain.

Two- and four-coil phased array detectors were developed to increase the sensitivity and resolution of MR imaging of the human brain cortex, especially for detecting cortical dysplasias in pediatric epilepsy patients. An automated intensity correction algorithm based on an edge-completed, low-pass filtered image was used to correct the image intensity for the inhomogenous reception profile of the coils. Seven phased array coils were constructed and tested. The sensitivity of these coils was up to 600% higher at the surface of the cortex than that achieved with a conventional head coil and up to 30% greater at the center of the head. The sensitivity obtained was comparable with that of a conventional small surface coil, but extended over the larger dimensions of the array and previously inaccessible areas such as the top of the head. The advantages of the improved sensitivity are demonstrated with high resolution images of the brain.

Proton spectroscopic imaging of the human brain using phased array detectors.

Two and four-coil phased array detectors have been developed to increase the sensitivity of proton spectroscopic imaging of the human brain. These include a quadrature figure-8 coil for the study of the vertex, several arrays of 2-4 small overlapping (6-8 cm diameter) circular coils and a combination figure-8 coil plus circular coil. These were constructed in our laboratory and tested to assess their utility for brain spectroscopy. Methods for optimally combining the data from the independent receivers based on the analytical coil maps or measured signal to noise ratios (SNRs) of the data were investigated. High spatial resolution (0.2-0.4 cm3 voxel size) two- or three-dimensional chemical shift images of normal brain were obtained in 17-minute acquisitions. These spatial resolutions are comparable to those previously obtained with conventional small surface coils, but the specialized detectors allow this sensitivity to be achieved for a larger region or for previously inaccessible areas such as the top of the head. The coverage and SNR increases demonstrated are similar to those obtained in magnetic resonance phased array imaging.