Synthetic Phased Array Research Articles

Real-time 3D plane-wave imaging using annular capacitive micromachined ultrasonic transducer array

Imaging methods and 2D sparse arrays have been extensively researched to realize real-time 3D volumetric imaging with higher frame rates. In this study, we developed a 3D plane-wave imaging method using an annular capacitive micromachined ultrasonic transducer (CMUT) array as a breakthrough technique for realizing 3D imaging with a limited number of elements. We adopted the double oxidation and wafer bonding processes for creating the cavity of a CMUT with a 2 µm silicon membrane. To ensure surface uniformity before the bonding process, we implemented an additional reactive ion etching process after the second oxidation. The characterization results showed that the resonant frequency of the proposed device was 6.2 MHz with 65 V collapse voltage. The demonstration of real-time 3D volumetric imaging was conducted in oil using a Vantage 64 ultrasound research system. A plane-wave imaging scheme was used to detect wire phantoms immersed in the oil, with 289 plane waves transmitted over a range of 20° from the center of the annular array. The reconstructed data were used to create three orthogonal cross sections of the target region. The − 6 dB lateral and axial resolutions were 0.56 mm and 0.35 mm for the wires positioned at 18 mm from the proposed device, which were narrow enough to detect a wire phantom of 380 µm diameter. The normalized frame rate was calculated and compared with that in a previous study. We verified that plane-wave imaging has advantages in real-time imaging when compared with the classic phased array and synthetic phased array. Thus, the annular CMUT array is a promising mechanism for real-time 3D imaging with higher frame rate than that possible with previous methods.

Rectilinear Planar Near-Field Measurements From the Perspective of the Synthetic Phased Array

A new far-field valid angle equation for rectilinear planar near-field measurements is derived. The new valid angle equation is derived by viewing the near-field to far-field transformation process as the generation of a pseudo plane wave by a synthetic phased array and subjecting the antenna-under-test (AUT) to the radiation from this synthetic array. The synthetic phased array does not physically exist; rather, the array is formed during the postprocessing of the planar near-field measurements. The resultant valid far-field angle computed with the new equation is compared against previously established and popularly accepted valid angle equations. A brief discussion is offered on the measurement of low-directivity antennas with a planar near-field measurement system and on amplitude tapering of the near-field measurements to improve the quality of the pseudo plane wave inside the test zone.

Computer program for modeling space synthetic aperture radar active phased array antenna characteristics

Computer program for modeling space synthetic aperture radar active phased array antenna characteristics

Deriving Spatio-Temporal Development of Ground Subsidence Due to Subway Construction and Operation in Delta Regions with PS-InSAR Data: A Case Study in Guangzhou, China

Subways have been an important method for relieving traffic pressures in urban areas, but ground subsidence, during construction and operation, can be a serious problem as it may affect the safety of its operation and that of the surrounding buildings. Thus, conducting long-term ground deformation monitoring and modeling for subway networks are essential. Compared with traditional geodetic methods, the Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) technique offers wider coverage and denser measurements along subway lines. In this study, we mapped the surface deformation of the Guangzhou subway network with Advanced Synthetic Aperture Radar (ASAR) and Phased Array Type L-band Synthetic Aperture Radar (PALSAR) data using the Interferometric Point Target Analysis (IPTA) technique. The results indicate that newly excavated tunnels have regional subsidence with an average rate of more than 8 mm/year, as found on Lines Two, Three, Six, and GuangFo (GF). Furthermore, we determined the spatio-temporal subsidence behavior of subways with PALSAR in delta areas using Peck’s formula and the logistic time model. We estimated the tunneling-related parameters in soft soil areas, which had not been previously explored. We examined a section of line GF, as an example, to estimate the ground settlement trough development. The results showed the maximum settlement increased from −5.2 mm to −23.6 mm and its ground loss ratio ranged from 1.5–8.7% between 13 July 2008 and 19 January 2011. In addition, we found that the tunnels in line GF will become stable after a period of about 2300 days in peak subsidence areas. The results show that the proposed approach can help explain the dynamic ground subsidence along a metro line. This study can provide references for urban subway projects in delta areas, and for the risk assessment of nearby buildings and underground pipelines along metro lines.

A comprehensive interferometric process for monitoring land deformation using ASAR and PALSAR satellite interferometric data

This study was conducted to apply the enhanced differential interferometric process to interferometric data obtained from C-band Advanced Synthetic Aperture Radar (ASAR) and Phased Array type L-Band Synthetic Aperture Radar (PALSAR) systems, in the Marand plain, Iran. In advance, the capability of each sensor was examined with regard to the signal coherency for sensor–target interactions, which emphasized on the terrific excellency of PALSAR (L-band) to ASAR (C-band) measurements in study area. In the interferometric process, in addition to resolving the topography and baseline related errors (which is conventional in the standard D-InSAR process), subtle quantitative methods were outlined to minimize the secondary, but momentous errors (i.e., orbital and atmospheric) from differential phases. Subsequently, based on the outlined process, the mean deformation as well as three-dimensional displacement maps (using ascending and descending modes) were generated. The deformation maps significantly indicated the downward motion of the surface with the maximum rate of −0.5 millimetre per day for the period, i.e., from 2004 to 2010, with relative dominance in eastern and central to northern parts of the Marand plain. Finally, the results were validated and the source of deformation was inspected using field data such as seismic history; changes in piezometric levels and cross-checking the results from radar measurements itself.

GPU-Based Real-Time Volumetric Ultrasound Image Reconstruction for a Ring Array

Synthetic phased array (SPA) beamforming with Hadamard coding and aperture weighting is an optimal option for real-time volumetric imaging with a ring array, a particularly attractive geometry in intracardiac and intravascular applications. However, the imaging frame rate of this method is limited by the immense computational load required in synthetic beamforming. For fast imaging with a ring array, we developed graphics processing unit (GPU)-based, real-time image reconstruction software that exploits massive data-level parallelism in beamforming operations. The GPU-based software reconstructs and displays three cross-sectional images at 45 frames per second (fps). This frame rate is 4.5 times higher than that for our previously-developed multi-core CPU-based software. In an alternative imaging mode, it shows one B-mode image rotating about the axis and its maximum intensity projection, processed at a rate of 104 fps . This paper describes the image reconstruction procedure on the GPU platform and presents the experimental images obtained using this software.

A Synthetic Phased Array Surface Acoustic Wave Sensor for Quantifying Bolt Tension

In this paper, we report our findings on implementing a synthetic phased array surface acoustic wave sensor to quantify bolt tension. Maintaining proper bolt tension is important in many fields such as for ensuring safe operation of civil infrastructures. Significant advantages of this relatively simple methodology is its capability to assess bolt tension without any contact with the bolt, thus enabling measurement at inaccessible locations, multiple bolt measurement capability at a time, not requiring data collection during the installation and no calibration requirements. We performed detailed experiments on a custom-built flexible bench-top experimental setup consisting of 1018 steel plate of 12.7 mm (½ in) thickness, a 6.4 mm (¼ in) grade 8 bolt and a stainless steel washer with 19 mm (¾ in) of external diameter. Our results indicate that this method is not only capable of clearly distinguishing properly bolted joints from loosened joints but also capable of quantifying how loose the bolt actually is. We also conducted detailed signal-to-noise (SNR) analysis and showed that the SNR value for the entire bolt tension range was sufficient for image reconstruction.

Volumetric real-time imaging using a CMUT ring array

A ring array provides a very suitable geometry for forward-looking volumetric intracardiac and intravascular ultrasound imaging. We fabricated an annular 64-element capacitive micromachined ultrasonic transducer (CMUT) array featuring a 10-MHz operating frequency and a 1.27-mm outer radius. A custom software suite was developed to run on a PC-based imaging system for real-time imaging using this device. This paper presents simulated and experimental imaging results for the described CMUT ring array. Three different imaging methods--flash, classic phased array (CPA), and synthetic phased array (SPA)--were used in the study. For SPA imaging, two techniques to improve the image quality--Hadamard coding and aperture weighting--were also applied. The results show that SPA with Hadamard coding and aperture weighting is a good option for ring-array imaging. Compared with CPA, it achieves better image resolution and comparable signal-to-noise ratio at a much faster image acquisition rate. Using this method, a fast frame rate of up to 463 volumes per second is achievable if limited only by the ultrasound time of flight; with the described system we reconstructed three cross-sectional images in real-time at 10 frames per second, which was limited by the computation time in synthetic beamforming.

Beam Steering in Global Positioning System Receivers using Synthetic Phased Arrays

This correspondence introduces a concept of synthetically generated phased arrays to the area of Global Positioning System (GPS). GPS antennas generated at different spatial locations are combined into a synthetic phased array to improve the beam sharpening performance without increasing the antenna's physical size. A fast Fourier transforms (FFT)-based method is applied for simultaneous steering of the synthetic array's beams in multiple directions. The synthetic beam-steering approach discussed can be applied for improving GPS robustness to RF interference and for simultaneous tracking of multiple signal sources (i.e., direct signal and multipath reflections). Simulation results and experimental test results are presented to demonstrate the efficacy of synthetic beam steering techniques for GPS antennas.

Frontiers in NDE research nearing maturity for exploitation to ensure structural integrity of pressure retaining components

In this paper, research and developmental efforts that demonstrate high sensitivity detection and characterization of defects and assessment of microstructural degradation, residual stresses and fatigue damage in materials using different non-destructive evaluation (NDE) techniques, have been discussed. Applications of eddy current techniques for quantitative defect characterization and for generalized applications, and remote field eddy current technique for inspection of steam generator and heat exchanger tubes have been discussed. Advanced ultrasonic methods such as time of flight diffraction, synthetic aperture focusing technique, phased array and signal processing for detection, characterization and imaging of defects have been discussed. Applications of ultrasonics and magnetic Barkhausen emission techniques for characterization of microstructures and residual stresses have been discussed. Applications of acoustic emission and infrared thermography techniques for weld quality evaluation of critical nuclear components as part of intelligent processing of materials (IPM) work have been discussed. Application of acoustic emission technique for integrity assessment of pressurized components has been discussed. Development of a software called assets and infrastructure management system (AIMS), for storing and retrieving information for various materials, components and systems, has also been highlighted. The techniques and applications discussed are result of systematic and innovative R&D efforts in the multidisciplinary areas of physics, materials, instrumentation, sensors and softwares for providing solutions to various challenging problems.

Dual-polarized slot-coupled microstrip antenna with very high isolation

A wideband dual-polarized slot-coupled stacked microstrip antenna with very high isolation and low cross-polarization is presented. To improve isolation between two polarization ports, the stacked patches are excited by an open-ended and a T-shaped micros-trip lines both via two H-shaped slots placed in a “T” configuration. The measured isolation is better than 40.5 dB over the bandwidth from 8.8 to 9.8 GHz with cross-polarization level less than −28.5 dB. The measured VSWR⩽2 bandwidths reach 20.7% and 19.1% at the vertical and horizontal polarization ports, respectively. This antenna is suitable to be used as array elements in spaceborne synthetic aperture radars (SAR) and active phased array radars.

Synthetic phased-array terahertz imaging

We demonstrate terahertz (THz) imaging with enhanced spatial resolution by a synthetic phased array. A single mirror is used to separately form two different coherent, diffraction-limited THz images of the same point source. The two images are combined to yield a 4x resolution-enhanced image of the source in one dimension.

Correlation processing for correction of phase distortions in subaperture imaging

Ultrasonic subaperture imaging combines synthetic aperture and phased array approaches and permits low-cost systems with improved image quality. In subaperture processing, a large array is synthesized using echo signals collected from a number of receive subapertures by multiple firings of a phased transmit subaperture. Tissue inhomogeneities and displacements in subaperture imaging may cause significant phase distortions on received echo signals. Correlation processing on reference echo signals can be used for correction of the phase distortions, for which the accuracy and robustness are critically limited by the signal correlation. In this study, we explore correlation processing techniques for adaptive subaperture imaging with phase correction for motion and tissue inhomogeneities. The proposed techniques use new subaperture data acquisition schemes to produce reference signal sets with improved signal correlation. The experimental test results were obtained using raw radio frequency (RF) data acquired from two different phantoms with 3.5 MHz, 128-element transducer array. The results show that phase distortions can effectively be compensated by the proposed techniques in real-time adaptive subaperture imaging.

Synthetic phased array for non-destructive testing

Synthetic phased array for non-destructive testing