2D Ultrasonic Array Research Articles

A 2D Ultrasonic Phased Array Optimization Framework Enabled by Reconfigurable Laser Induced Phased Arrays

Abstract Three-dimensional (3D) ultrasonic imaging enables the viewing of internal features in a more accurate way than cross-sectional imaging. 3D imaging requires two-dimensional (2D) ultrasonic phased arrays to resolve all three spatial dimensions through beamforming along azimuthal and elevation angles. 2D phased arrays pose a manufacturing and control challenge due to the requirement of large number of elements to satisfy the Nyquist sampling limit. This problem can be alleviated through the use of sparse ultrasonic array designs. The optimization process is critical, as this dictates the efficiency of suppression of grating lobes. The aim of this work is to establish a framework for design of optimized sparse 2D phased arrays. This is enabled by exploiting the reconfigurability of Laser Induced Phased Arrays (LIPAs). LIPAs are synthetic arrays produced by scanning one laser for ultrasound generation and another for ultrasound detection, independently of each other. The reconfigurability and decoupled ultrasonic generation and detection of this systems enables easy and fast implementation of any arbitrary array layout. The framework consists of an analytical model for parametric evaluation of designs. The model performs a parametric sweep on the generation and detection element positions for each array design in order to identify the optimal parameters, based on mean and maximum side-lobe level. In the presented framework, four array designs are utilized for the optimization process: matrix, random, Vernier and a novel array design the Rotated Array (RA).

A Wearable Ultrasonic Neurostimulator-Part II: A 2D CMUT Phased Array System With a Flip-Chip Bonded ASIC.

A 2D ultrasonic array is the ultimate form of a focused ultrasonic system, which enables electronically focusing beams in a 3D space. A 2D array is also a versatile tool for various applications such as 3D imaging, high-intensity focused ultrasound, particle manipulation, and pattern generation. However, building a 2D system involves complicated technologies: fabricating a 2D transducer array, developing a pitch-matched ASIC, and interconnecting the transducer and the ASIC. Previously, we successfully demonstrated 2D capacitive micromachined ultrasonic transducer (CMUT) arrays using various fabrication technologies. In this paper, we present a 2D ultrasonic transmit phased array based on a 32 × 32 CMUT array flip-chip bonded to a pitch-matched pulser ASIC for ultrasonic neuromodulation. The ASIC consists of 32 × 32 unipolar high-voltage (HV) pulsers, each of which occupies an area of 250 μm × 250 μm. The phase of each pulser output is individually programmable with a resolution of 1/fC/16, where fC is less than 10 MHz. This enables the fine granular control of a focus. The ASIC was fabricated in the TSMC 0.18- μm HV BCD process within an area of 9.8 mm × 9.8 mm, followed by a wafer-level solder bumping process. After flip-chip bonding an ASIC and a CMUT array, we identified shorted elements in the CMUT array using the built-in test function in the ASIC, which took approximately 9 minutes to scan the entire 32 × 32 array. A compact-form-factor wireless neural stimulator system-only requiring a connected 15-V DC power supply-was also developed, integrating a power management unit, a clock generator, and a Bluetooth Low-Energy enabled microcontroller. The focusing and steering capability of the system in a 3D space is demonstrated, while achieving a spatial-peak pulse-average intensity ( ISPPA) of 12.4 and 33.1 W/ cm2; and a 3-dB focal volume of 0.2 and 0.05 mm3-at a depth of 5 mm-at 2 and 3.4 MHz, respectively. We also characterized transmission of ultrasound through a mouse skull and compensated the phase distortion due to the skull by using the programmable phase-delay function in the ASIC, achieving 10% improvement in pressure and a tighter focus. Finally, we demonstrated a ultrasonic arbitrary pattern generation on a 5 mm × 5 mm plane at a depth of 5 mm.

Design of 2D Sparse Array Transducers for Anomaly Detection in Medical Phantoms.

Aperiodic sparse 2D ultrasonic array configurations, including random array, log spiral array, and sunflower array, have been considered for their potential as conformable transducers able to image within a focal range of 30–80 mm, at an operating frequency of 2 MHz. Optimisation of the imaging performance of potential array patterns has been undertaken based on their simulated far field directivity functions. Two evaluation criteria, peak sidelobe level (PSL) and integrated sidelobe ratio (ISLR), are used to access the performance of each array configuration. Subsequently, a log spiral array pattern with −19.33 dB PSL and 2.71 dB ISLR has been selected as the overall optimal design. Two prototype transducers with the selected log spiral array pattern have been fabricated and characterised, one using a fibre composite element composite array transducer (CECAT) structure, the other using a conventional 1–3 composite (C1–3) structure. The CECAT device demonstrates improved coupling coefficient (0.64 to 0.59), reduced mechanical cross-talk between neighbouring array elements (by 10 dB) and improved operational bandwidth (by 16.5%), while the C1–3 device performs better in terms of sensitivity (~50%). Image processing algorithms, such as Hough transform and morphological opening, have been implemented to automatically detect and dimension particles located within a fluid-filled tube structure, in a variety of experimental scenarios, including bespoke phantoms using tissue mimicking material. Experiments using the fabricated CECAT log spiral 2D array transducer demonstrated that this algorithmic approach was able to detect the walls of the tube structure and stationary anomalies within the tube with a precision of ~0.1 mm.

Triad system for object's 3D localization using low-resolution 2D ultrasonic sensor array

AbstractIn the recently published researches in the object localization field, 3D object localization takes the largest part of this research due to its importance in our daily life. 3D object localization has many applications such as collision avoidance, robotic guiding and vision and object surfaces topography modeling. This research study represents a novel localization algorithm and system design using a low-resolution 2D ultrasonic sensor array for 3D real-time object localization. A novel localization algorithm is developed and applied to the acquired data using the three sensors having the minimum calculated distances at each acquired sample, the algorithm was tested on objects at different locations in 3D space and validated with acceptable level of precision and accuracy. Polytope Faces Pursuit (PFP) algorithm was used for finding an approximate sparse solution to the object location from the measured three minimum distances. The proposed system successfully localizes the object at different positions with an error average of ±1.4 mm, ±1.8 mm, and ±3.7 mm in x-direction, y-direction, and z-direction, respectively, which are considered as low error rates.

3D ultrasonic inspection of anisotropic aerospace components

Two-dimensional (2D) ultrasonic arrays for non-destructive evaluation will enable the detection and characterisation of sub-surface defects in three-dimensions (3D). This type of volumetric inspection is desirable when testing engineering components that have an inherent 3D internal structure or may contain defects orientated at a range of angles. One potential industrial application for this technology is the in-situ inspection of jet-engine turbine blades for root cracking. However, modern turbine blades are manufactured from single crystals of nickel-based superalloys for the excellent mechanical properties these materials exhibit at elevated temperatures. Single-crystal materials are elastically anisotropic, which causes ultrasonic waves to propagate with different velocities depending on the direction of the wave. If unaddressed, this significantly reduces the quality of the inspection and the 3D images that can be produced with an ultrasonic array. In this paper, a model of wave propagation in anisotropic media is used to correct an ultrasonic imaging algorithm to enable the reliable volumetric inspection of single-crystal aerospace components.

2D ultrasonic arrays with low-voltage operation for high density electronics

The use of ultrasonic array transducers for NDT is growing rapidly, as commercial array controllers become more widely available. However, conventional 1D array designs limit the flexibility of such systems, for example, making it impossible to skew the beam on curved surfaces. As 2D arrays allow 3D beam steering, they are thus of major interest. However, the use of conventional excitation voltages, typically 200 V, with the many elements in 2D arrays may be inconvenient, making investigation of low-voltage operation worthwhile. The work reported here relates to array design for low-voltage operation for NDT. A 1D array was first produced, operating at approximately 1.5 MHz. This was based on a piezocomposite plate made with PZT 5A ceramic and epoxy resin. The plate was bonded to a PCB whose copper tracks defined the array elements, 10 mm long, 0.28 mm wide, and with edge-to-edge separation of 0.4 mm. The device was excited with a standard logic voltage of 3.3 V on a 75 mm-thick aluminium block. The pulse-echo insertion loss, using a signal reflected from the back wall of the aluminium, was found to be 59 dB. A 2D ultrasonic array has also been produced, with 16 elements in a 4 x 4 matrix, using the same piezocomposite material. In this case, the element size is 1.2 mm x 1.2 mm, and the edge-to-edge separation is 0.4 mm. In tests with 3.3 V peak-to-peak excitation voltage, the insertion loss was found to be 73 dB. The results suggest that arrays made with monolithic piezocomposite material have better performance for NDT than previous arrays made with monolithic ceramic and that low-voltage excitation will be viable in practice, with low noise amplification and appropriate signal processing.

Fabrication of multilayer 2D ultrasonic transducer microarrays by green machining

This paper presents a fabrication technique for multilayer 2D ultrasonic transducer arrays based on wet building and mechanical machining of piezoelectric PZT ceramics. The arrays are intended for microparticle trapping and manipulation using ultrasonic standing waves in microfluidic devices. The developed fabrication technique is relevant also for the miniaturization of other multilayer piezoceramic components. Array elements were fabricated monolithically on a common carrier with voids integrated behind each element, to work as acoustic reflectors. Their function was later proved by identification of thickness resonances of the supported multilayer transducers. The voids were integrated by using sacrificial material that was removed during firing of the component. Electrodes, vias, sacrificial material and finally the array itself were structured in the green state using a high precision dicing saw. The fabrication technique with integrated multilayer electrodes and electrical vias was shown to allow for miniaturized array elements working above 10 MHz with lateral dimensions down to 350 × 350 µm2. The resolution of electrode patterning was below 10 µm with insulating spaces down to 30 µm. The smallest dimension of via interconnects was 20 µm and integrated voids were fabricated with lateral dimensions reaching from 10 µm to 600 µm.

Spot Weld Analysis With 2D Ultrasonic Arrays.

This paper describes a threefold method of testing the performance of an array-based ultrasonic tool for nondestructive testing of spot welds. The tool is described in its capabilities, use, and advantages over existing counterparts. Performance testing for and the results from carrying out the testing are described. The three performance testing methods include 1) the use of calibrated samples, 2) comparisons with actual spot-welds, and 3) a performance evaluation of the embedded fitting software. The test of the fitting software was carried out by a comparison of results with reference fits supplied by the National Institute of Standards and Technology.

Stack based multidimensional ultrasonic transducer array

Multilayer piezoelectric fabrication methods are used to produce nD (e.g., 1.5D and 2D) ultrasonic transducer arrays. One embodiment concerns a 1.5 linear transducer in which impedance compensation is provided between the elemental transducers forming the array by varying the number of layers in each row of transducers. In another embodiment, a 2D transducer array is provided wherein elemental transducers are produced by dicing a conventional multilayer actuator to form equal sized elements which are embedded in a polymer matrix.

Improving the probability of detection for a 2D ultrasonic array using digital signal processing techniques

An experiment was conducted to investigate the potential of using a linear array of probes consisting of a single transmitter (Tx) and multi-passive receivers (Rx) to improve defect detection. The array consisted of three 5 MHz straight-beam probes were located at distances of 22.5 mm and 45 mm from the transmitter. A V1 calibration block was used to ensure repeatability, and the 2 mm notch was utilised as substitute defect. The probes were used in a single transmission with dual-receiver formation in alternate positions. This experimental set-up was used to reveal the clearest interpretation of the received signal. The readings were taken from the area before the first echo to eliminate confusion due to the sidewall reflections. Ultrasonic theory suggests that the reflected beam intensity would have insufficient signal-to-noise ratio (SNR) to be of practicable use with this probe array geometry. Work presented in this paper shows that the pre-processed SNR (in the order of 1.5 dB for a distance of 22.5 mm and less than zero at 45 mm), can be improved to around 20 dB by DSP techniques.

A 2D static ultrasonic array of passive probes for improved probability of detection

An experiment was conducted to investigate the potential of using the passive (awaiting active pulsing) transducers in a 2D ultrasonic array as signal receivers. This paper will demonstrate that this new technique normal probe diffraction (NPD) which can increase the probability of detection (POD), without increasing the amount of false positives. Three 10 mm diameter, 5 MHz straight beam probes were used at linear distances of 22.5 and 45 mm, from the transmitter. A V1 calibration block was used as an aid to experimental repeatability, and the 2 mm notch was utilized as a pseudo defect. The probes were used in a single transmission (Tx) with dual receiver (Rx) formation in alternate positions, to collect information from areas of the sound field that would be lost using a standard pulse echo technique. The readings were taken from the area prior to the first backwall echo because this eliminates confusion due to the sidewall reflections. The experiments will show that the diffracted echo signal can be detected using the passive probes using NPD techniques.

2D ultrasonic transducer array for two dimensional and three dimensional imaging

An ultrasonic 2D array has elements extending in two dimensions which can be individually controlled and operated to form a 2D array for scanning a volumetric region in three dimensions. Individual ones of the elements can also be selected and operated together to form a 1D array for scanning a planar region in two dimensions. The array transmits scanlines to scan the volumetric region and the planar region in a time interleaved manner with the frame rate of the planar region be higher than that of the volumetric region. A spectral display may also be produced of a sample volume located in the planar region.

A small 2D ultrasonic array for NDT applications

A prototype of two-dimensional transducer array with reduced number of elements, based on segmented annular distribution is presented. The capability of this array to produce volumetric imaging is compared to the equivalent conventional 2D squared matrix array. The comparison between both apertures is made for the cases of the full-array emission/reception mode and SAFT mode. From the analysis it is deduced that the segmented annular arrays produce lower grating lobes than squared arrays, improving the image contrast. The fabrication process of a segmented annular array of 64 elements and the experimental work made with this array transducer is also presented in this paper.

64 Elements two-dimensional piezoelectric array for 3D imaging

Ultrasound has a large potential on non-invasive inspection with main applications in medical imaging and non-destructive testing (NDT). The increasing interest in 3D imaging applications leads to investigate new solutions for two-dimensional (2D) ultrasonic arrays with an affordable number of electronic channels without resolution degradation. 2D segmented annular arrays (SAAs) are a good compromise between resolution—image quality—and number of electronically active channels. A 1–3 piezoelectric composites are used as basis material to manufacture the array transducers due to their low planar coupling and high electromechanical coupling coefficients. A 1.5 MHz SAA of 64 elements and 20 mm of diameter was designed, manufactured and tested. The design key point is the use of a flexible circuit with electrodes and tracks that define the array geometry. The piezocomposite was used as a monolithic support. Soft backing and one matching layer were used. The array elements have been tested electrically and acoustically showing good agreement with a KLM-based simulation model. Acoustical field measurements in water at different steering angles were made and compared with simulations performed with a model that uses an exact solution of the impulse response approach. Side lobes are important because the array geometry used was designed to work in metals for NDT purposes. Smaller array elements should be made for medical applications.