Dynamic phased arrays and ultrasound modulators

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

Acoustic holography underpins the number of modern acoustics applications. The usage of multi-focal acoustic holograms with phased array transducers (PATs) in ultrasonic tactile displays and acoustic levitation are increasing, and achieving a high-quality hologram are of significant interest. Inspired by the latest optical hologram optimizer, we developed a novel acoustic hologram optimizer for PATs called Diff-PAT [T. Fushimi, K. Yamamoto, and Y. Ochiai, “Acoustic hologram optimisation using automatic differentiation”]. Diff-PAT is based on a gradient-descent algorithm and automatic differentiation. The performance of Diff-PAT was numerically evaluated using three array configurations and it achieved superior accuracy over the conventional optimizers. For example, when two focal points are generated with 196 ultrasonic (40 kHz) transducers; the state of art optimizer (with phase and amplitude modulation) based on Eigensolver has an average error of 4.07 % where Diff-PAT (with only phase modulation) achieve average error of 0.0174%. These results show that amplitude and phase modulation may not be necessary for PATs to be successful. Furthermore, we demonstrate the versatility of Diff-PAT by applying it to binary acoustic holograms, simultaneous modulation of acoustic amplitude and phase at the target plane, and phase plates. [Work supported by Pixie Dust Technologies, Inc., Diff-PAT is patent pending (JP2020-167367A).]

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

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.

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.

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.

The problem of producing real-time, 3-D (volumetric) ultrasonic images can be divided into two main tasks: (1) acquiring 3-D echo data from a target volume in a sufficiently short time, and (2) reducing this 3-D data set into a suitable 2-D image. Both of these tasks can be accomplished simultaneously by a method, dubbed `Slit-O-Vision,' wherein a diverging lens is used to expand the (normally collimated) elevation beam pattern of a conventional linear or phased array transducer into a `fan beam.' The 2-D images produced in this manner make an object in the target volume appear three-dimensional, because the fan beam integrates the echoes at a given range across the entire `slice thickness' of the tomogram, thus projecting (collapsing) the volumetric echo data into a single 2-D projection image. This also allows the volumetric image to be updated 30 times per second. Slit-O-Vision may be useful in medical or sonar imaging applications.

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.

As phased array ultrasonic transducers become more wide spread in underwater acoustic measurement applications, a better understanding of their basic performance characteristic is of benefit. The beam patterns of a phased array can be approximated by a steady state analysis. This approach indicates the directional response of an array in response to a sinusoidal excitation. However, a steady state examination does not properly describe transient behavior of the transmit waveform and also the received signal that is subsequently beamformed. We further investigate the transient performance of the beamformer using a closed-form solution to the acoustic wave equation for a multielement ultrasonic phased array transducer. The model produces transducer beam patterns and transient beamformer output for a series of reflective targets in the far-field of the transducer. The results show a close agreement with laboratory measurements and provide a tool for further investigation of phased array transducer design and performance.

As a new functional composite material, Orthotropic Piezoelectric Fiber Composite (OPFC) may be developed conveniently actuators and sensors. By constructing multi-element linear array, the phased array transducers can generate special directional strong actuator power and high sensitivity. The advantage of the transducers is that no mechanical movement is needed to scan an object. Focusing beam is obtained simply only by adjusting a parabolic time delay. The DPSM (distributed point source method) is used to model the ultrasonic field by OPFC linear array transducer. Using this approach, beam directivity and pressure distributions are studied to predict the behavior of focusing as compared to current formulation of traditional transducer. The interaction effect of two OPFC phased array transducers is also modeled in the same medium. Which shows the pressure beam produced by the OPFC array transducer is narrower or more collimated than that produced by the conventional transducer at different angles.

On the use of sky images for intra-hour solar forecasting benchmarking: Comparison of indirect and direct approaches

Peculiarities of anisotropic light diffraction in a periodic acoustic field excited by a phased array transducer with the phase shift by π are studied theoretically. Possibilities of this system application for control of unpolarized optical radiation are discussed.

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

The high frequency, wideband acousto-optic light deflector is an excellent candidate in many EW systems such as radar warning receivers and communications signal processing. In order to provide such needs, broad bandwidth acousto-optic Bragg cells for the gigahertz frequency range are developed. To track Bragg angle for broadband operation, a phased array design is employed and therefore its performance needs to be well understood, especially at microwave frequencies. In this paper we propose a new acoustic phased array transducer model. A microwave model for conversion of an RF signal to an acoustic beam is presented. The model is based on calculating the phased array transducer interdigital capacitance from coupled transmission lines theory. We also discuss the impact of other transmission line effects at electromagnetic wavelengths. The microwave phased array transducer model is then used to predict the behavior of the electrode voltages and currents and of the overall capacitance.