Signal detectability in diffusive media using phased arrays in conjunction with detector arrays

Two dimensional echographic imaging of the left ventricle: Comparison of mechanical and phased array systems in vitro

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.

Phased array radar systems are used for a wide variety of applications including the precise tracking of airborne craft for air traffic control and providing accurate atmospheric condition information important in weather forecasting. Reducing the cost and size of these radar systems will open new fields to the use of this technology. Using phase control implemented through liquid crystal materials we have created a compact, phased array radar system operating in the microwave range. We report on the construction and testing of a linear, eight element phased array antenna system operating at 32 GHz with element phase controlled by a dual frequency nematic liquid crystal media used as a tunable dielectric. The system was designed using CST Design Studios and Ansys HFSS software. Dual frequency liquid crystals are used to improve beam steering response times. We demonstrate 42 millisecond beam switching times, defined as the time to change the beam focus from one point to another point, controllable beam formation, and beam steering profiles consistent with analytical results and simulation models. The device footprint is a square with sides 9.5 cm long and a thickness less than 2.5 mm. Such a module is easily stackable to create an 8 × 8 phased array system. Our design incorporates a modular construction using PCB for the antennas and input circuitry and a liquid crystal phase control cell with microwave glass substrates. This design simplifies design, construction, and testing as compared to on-glass designs. The device shows an improvement in point-to-point scanning speeds by a factor of 3 as compared to similar liquid crystal based devices and provides continuously variable tuning. Such a device can be used in a system for reduced visibility, directional range finding suitable for automobile collision avoidance systems and rotary wing aircraft landing aids.

This paper is a follow-on of [1] and [2], presented at 1996 and 2003 IEEE Intl. Symposium on Phased Array Systems and Technology, respectively. After a brief recall of 3D Long Range phased array concepts, already presented in [2], the focus is on the G-band multifunction radar systems and on the technological capabilities that SELEX-Sistemi Integrati is developing by taking advantage of its Research and Development facilities. At the end, future trends about new challenging applications and technological issues are presented and discussed.

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.

In this paper, an optimization procedure for synthesizing shaped beams with an arbitrary geometry phased array system with real-time capability is presented. The algorithm involves a combination of an arbitrary extension of the Woodward-Lawson synthesis procedure with the magnitude least-squares optimization method. This simple combination significantly reduces the optimization time, enabling real-time beam shaping in response to changing requirements on beam shape or evolving geometry in distributed arrays. The technique places no restrictions on element positioning in all three spatial dimensions and is demonstrated to accurately reproduce the desired beam shape in both angular dimensions. The algorithm is demonstrated for multiple beam cases with a large, randomly generated array in computational simulation. The applicability of the algorithm to practical phased array hardware is also demonstrated using full-wave electromagnetic simulations and measurements of a realized arbitrary phased array system using a near-field scanner in an anechoic chamber.

For over more than a decade, ultrasound phased arrays have been playing a leading role in domains such as noninvasive diagnostic examination, nondestructive testing and sonar, and will continue to be indispensable in a wide range of new applications. Unlike the aforementioned traditional scanning systems, many new applications require a transmit-only configuration and work in the low ultrasound frequency range, consequently posing new challenges in low-cost phased array design. However, two sought-after features are still missing in current low-cost ultrasound phased array systems, namely broadband transmission and wide angular beam steering. In this work, a low-cost ultrasound phased array system is presented that enables the transmission of both narrowband and broadband signals. Accurate beam steering is achieved through the concept of Direct Digital Synthesis (DDS). The design features small, wide bandwidth MEMS transducers enabling grating lobe free beam patterns at high frequency and a broad angular beam steering range. The presented prototype supports 64 speaker elements and allows very fine amplitude and phase control over each transducer stage with respectively 10-bit and 12-bit resolution. The beam steering performance is validated for a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1}\times {10}$ </tex-math></inline-formula> calibrated uniform linear array design. In these measurements, an accuracy in the order of just a few degrees was observed, even at a steering angle of 70° off-axis.

MR imaging of the prostate can be greatly improved by using a phased array that combines the signals from individual receiver coils to form a composite image. Endourethral coils and a dual-coil endorectal probe were constructed and combined with a surface coil in a phased array system. Various phased array configurations were tested with in vivo canine experiments, which resulted in high-resolution images that clearly showed the anatomy of the prostate and surrounding structures such as the neurovascular bundles. The endourethral coils were useful in imaging the anterior portion of the prostate, while the endorectal coils provided high SNR in the posterior region of the prostate.

Single‐element scanning techniques are widely used in the NDT industry and have seen a number of successful applications. They require moving the sensor in time‐consuming raster scan to create two‐dimensional scan patterns and several transducers are required to focus at different levels in the inspected material. However, phased array technology is an emerging NDI technology which offers means to focus the ultrasonic beam at different locations and steer it to reach defects at hidden parts in complex structures, hence, substantially reducing the scanning time and simplifying the scanning pattern by scanning electronically in milliseconds instead of scanning mechanically in a few seconds. The motivation of this work is to investigate and compare electronic and SAFT (synthetic focusing) of the ultrasonic waves using linear phased array transducers. Experimental tests were done on an aluminum block with side‐drilled holes to simulate defects. Reduction of calculation time for the SAFT algorithm was achieved using beam width limitation. Experimental SAFT results and results from phased array system were compared. Practical SAFT advantages and limitations are then highlighted and requirements for better performance are discussed.

Purpose: Accurate monitoring of RF (radio frequency) power and phase is a key part of quality assurance (QA) for phased-array hyperthermia systems. In order to assess the steering capability of the BSD 2000 3D facility, an independent measurement system has been implemented, using a vector voltmeter (VVM) as the measuring device.Methods: This paper describes the calibration of the RF signal paths from each of the 12 BSD Dodek amplifier outputs to the VVM instrument readout. Periodical network analyser measurements show that the uncertainty of the measured power using the VVM system is <4% for all channels, while the uncertainty of the phase measurements is <0.3°. The values are comparable to those reported for similar monitoring systems and are considered adequate for monitoring of the BSD Dodek steering parameters.Results: Using the VVM system to investigate the accuracy of the BSD Dodek amplifier power and phase control, systematic differences were observed between the requested and the measured power for all channels: At a requested power level of 25 W per channel, the measured power level was on average 15% lower than nominal, whereas at 100 W it was nearly 20% higher. It was also observed that the absolute phase values are nearly 30° higher at 25 W per channel than at power levels ≥50 W per channel. Under certain circumstances, these issues may reduce target steering accuracy for the BSD 2000 3D system; on the other hand, the Dodek power and phase control stability is found to be acceptable.Conclusions: The results emphasize the need for accurate, independent online power and phase QA during regional hyperthermia treatments using phased array systems.

This paper introduces the requirements of naval radar systems from past to present. It describes phased array technologies (digital and analog) that are presently available in the market. Power sources architectures, A/D evolutions, transceiver architecture and system on chip configurations are described as the main technologies at phased array system. The correlation between the various technologies and phased array architectures trends is also discussed.

This paper presents the application of CORPS (coherently radiating periodic structures) for feeding CRA (concentric rings array) with a reduced number of phase shifters. The proposed design technique for the structure of concentric rings provides a better scanning capability with respect to other existing configurations. This design technique utilizes 2 × 3 or 4 × 7 CORPS networks depending on the configuration or the number of antenna elements in the phased array system. These CORPS networks are set strategically in the feeding network to provide several advantages with respect to others in the scanning capability and the reduction of the number of phase shifters of the array system. The contribution of this paper is the full antenna system design of phased CRA for analyzing scanning and the reduction of phase shifters. The proposed phased array reduces the number of phase shifter devices in CRA for a scanning range of ±25° in the elevation plane. Differential evolution (DE) was applied to optimize the amplitudes of the proposed system. Several design cases were analyzed using full-wave simulation results to verify the phased array model and to take mutual coupling into account. Full-wave simulation results provide radiation patterns with low SLL in all scanning directions. The proposed phased array was validated by experimental measurements of the full antenna system prototype.

The modulation frequency characteristics of an erbium-doped fiber amplifier are analyzed theoretically and experimentally for various values of modulation frequency. The theoretical predictions by the approximate equations in the low and high frequency modulation and that by the Runge-Kutta method for all modulation frequencies are in good agreement with the experimental results. In the low frequency modulation, the population inversion is depleted because of the saturation effect due to the instantaneous power of the incident light, and a distorted output is obtained without phase delay. In the high frequency modulation, the linear amplification is obtained with the gain depletion determined by the time averaged power of the incident signal. In the intermediate frequency modulation, the highly distorted output is obtained with phase delay.

Sparse synthetic transmit aperture (STA) imaging systems are a good alternative to the conventional phased array systems. Unfortunately, the sparse STA imaging systems suffer from some limitations, which can be overcome with a proper design. In order to do so, a simulated annealing algorithm, combined with an effective approach can used for optimization of a sparse STA ultrasound imaging system. In this paper, three two-stage algorithms for optimization of both the positions of the transmit sub-apertures and the weights of the receive elements are considered and studied. The first stage of the optimization employs a simulated annealing algorithm that optimizes the locations of the transmit sub-aperture centers for a set of weighting functions. Three optimization criteria used at this stage of optimization are studied and compared. The first two criteria are conventional. The third criterion, proposed in this paper, combines the first two criteria. At the second stage of optimization, an appropriate weighting function for the receive elements is selected. The sparse STA system under study employs a 64-element array, where all elements are used in receive and six sub-apertures are used in transmit. Compared to a conventional phased array imaging system, this system acquires images of better quality 21 times faster than an equivalent phased array system.

In this paper, we show a scalable architecture for ultrasound phased array system. The biggest issue here to modularize phased array system is phase synchronization across arrays. Its timing constraint is quite severe because the phase error between arrays directly hits focusing performance. We employ EtherCAT network protocol to achieve scalable precise phase synchronization and effective communication. A new designed phased array unit connects each other in a daisy chain topology with precise timing synchronization, high frame rate, and large capacity communication.