Fabrication and Characterization of a 20-MHz Microlinear Phased-Array Transducer for Intervention Guidance

AZ31B magnesium alloy matching layer for Lens-focused piezoelectric transducer application

Compared with planar transducers, focused transducers have higher ultrasound intensity and better lateral resolution in the focal zone. At present, the matching layer materials for focused transducers are mainly 0-3 composite materials, which have problems such as non-uniformity, difficulty to fabricate at high frequencies, and large sound attenuation. In this paper, finite element analysis is carried out to simulate lens-focused transducers with different matching layer structures and materials. It is found that the focused transducer with magnesium alloy matching layer has the best comprehensive performance. A lens-focused PZT-5H ultrasonic transducer was then fabricated with AZ31B magnesium alloy as the first matching layer. The measured results show that the center frequency of the transducer is 4.38 MHz, the -6-dB bandwidth is 68.35 % and the insertion loss is -13.88 dB. Benefiting from the high uniformity, high acoustic impedance and extremely low acoustic attenuation of magnesium alloy, the transducers in this research exhibit superior performances than other reported transducers with conventional matching layer. The current work suggests that AZ31B magnesium alloy is a promising matching layer material for ultrasonic transducers.

Fine Pitch Flexible Printed Circuit Board Patterning for Miniaturized Endoscopic MicroUltrasound Arrays

Microultrasound (micro-US) has become an invaluable tool for preclinical research and in emerging applications in clinical diagnosis and treatment guidance. Several such applications can benefit from arrays with a small footprint and endoscopic form factor. However, critical challenges arise in making electrical connections to array elements in such spatial constraints. In this work, we describe a method to pattern a high-density flexible circuit cabling on a copper-on polyimide film, using laser ablation of a polymer resist and wet etching, and then demonstrate a connection to a micro-US array. We investigate laser ablation process parameters and evaluate the ability to consistently pattern continuous copper traces. A minimum 30- [Formula: see text] pitch was achieved with 5- [Formula: see text]-wide electrode lines, and continuity of a 5-m-long trace is demonstrated. A flexible circuit with 30-mm-long traces with 30- [Formula: see text] line and 30- [Formula: see text] space before fan-out was fabricated to connect in an interleaved manner to a 32-element array with 30- [Formula: see text] element pitch. Metal deposition and laser ablation were used to connect and pattern the element electrodes to the copper traces of the flexible circuit. Electrical and acoustic measurements show good yield and consistent impedance across channels. Element pulse-echo tests demonstrated device functionality; the two-way pulse had 43-MHz center frequency and 40% fractional bandwidth (-6 dB). The proposed manufacturing methods facilitate the prototyping and fabrication of flexible endoscopic or small-footprint micro-US devices.

Development of a 16-Channel Broadband Piezoelectric Micro Ultrasonic Transducer Array Probe for Pipeline Butt-Welded Defect Detection

Butt welding is extensively applied in long-distance oil and gas pipelines, and it is of great significance to conduct non-destructive ultrasonic testing of girth welds in order to avoid leakage and safety accidents during pipeline production and operation. In view of the limitations of large transducer size, single fixed beam angle, low detection resolution and high cost of conventional ultrasonic inspection technologies, a 16-channel piezoelectric micro ultrasonic transducer (PMUT) array probe was developed through theoretical analysis and structural optimization design. After the probe impedance characterization, the experimental results show that the theoretical model can effectively guide the design of the ultrasonic transducer array, offering the maximum operating frequency deviation of less than 5%. The ultrasonic echo performance tests indicate that the average -6 dB bandwidth of the PMUT array probe can be up to 77.9%. In addition, the fabricated PMUT array probe has been used to successfully detect five common internal defects in pipeline girth welds. Due to the multiple micro array elements, flexible handling of each element, large bandwidth and high resolution of defect detection, the designed PMUT array probe can provide a good application potential in structural health monitoring and medical ultrasound imaging fields.

Design and Fabrication of a High-Frequency Microconvex Array Transducer for Small Animals Imaging

High-frequency convex array transducer, featuring both high spatial resolution and wide field of view, has been successfully developed for ophthalmic imaging. To further expand its application range to small animals' imaging, this work develops a high-frequency microconvex array transducer possessing smaller aperture size and wider scanning angle. This transducer featured 128 array elements arranged in a curvilinear 2-2 piezoelectric composite configuration, yielding a maximum view angle of 97.8°. The array was composed of two front matching layers, a nonconductive backing layer, and a customized flexible circuit that electrically connected array elements to coaxial cables. The center frequency and the -6-dB fractional bandwidth were about 18.14 MHz and 69.15%, respectively. The image of a tungsten wire phantom resulted in approximately 62.9- [Formula: see text] axial resolution and 121.3- [Formula: see text] lateral resolution. The image of the whole kidney of a rat as well as its internal arteries was acquired in vivo, demonstrating the imaging capability of the proposed high-frequency microconvex array transducers for small animals' imaging applications.

Recent Advancements in Ultrasound Transducer: From Material Strategies to Biomedical Applications

Ultrasound is extensively studied for biomedical engineering applications. As the core part of the ultrasonic system, the ultrasound transducer plays a significant role. For the purpose of meeting the requirement of precision medicine, the main challenge for the development of ultrasound transducer is to further enhance its performance. In this article, an overview of recent developments in ultrasound transducer technologies that use a variety of material strategies and device designs based on both the piezoelectric and photoacoustic mechanisms is provided. Practical applications are also presented, including ultrasound imaging, ultrasound therapy, particle/cell manipulation, drug delivery, and nerve stimulation. Finally, perspectives and opportunities are also highlighted.

Laser Scanning Guided Localization Imaging with a Laser-Machined Two-Dimensional Flexible Ultrasonic Array

Advances in flexible integrated circuit technology and piezoelectric materials allow high-quality stretchable piezoelectric transducers to be built in a form that is easy to integrate with the body’s soft, curved, and time-dynamic surfaces. The resulting capabilities create new opportunities for studying disease states, monitoring health/wellness, building human–machine interfaces, and performing other operations. However, more widespread application scenarios are placing new demands on the high flexibility and small size of the array. This paper provides a 8 × 8 two-dimensional flexible ultrasonic array (2D-FUA) based on laser micromachining; a novel single-layer “island bridge” structure was used to design flexible array and piezoelectric array elements to improve the imaging capability on complex surfaces. The mechanical and acoustoelectric properties of the array are characterized, and a novel laser scanning and positioning method is introduced to solve the problem of array element displacement after deformation of the 2D-FUA. Finally, a multi-modal localization imaging experiment was carried out on the multi-target steel pin on the plane and curved surface based on the Verasonics system. The results show that the laser scanning method has the ability to assist the rapid imaging of flexible arrays on surfaces with complex shapes, and that 2D-FUA has wide application potential in medical-assisted localization imaging.

PIN-PMN-PT Single Crystal 1-3 Composite-based 20 MHz Ultrasound Phased Array

Based on a modified dice-and-fill technique, a PIN-PMN-PT single crystal 1-3 composite with the kerf of 12 μm and pitch of 50 μm was prepared. The as-made piezoelectric composite material behaved with high piezoelectric constant (d₃₃ = 1500 pC/N), high electromechanical coefficient (k_t = 0.81), and low acoustic impedance (16.2 Mrayls). Using lithography and flexible circuit method, a 48-element phased array was successfully fabricated from such a piezoelectric composite. The array element was measured to have a central frequency of 20 MHz and a fractional bandwidth of approximately 77% at -6 dB. Of particular significance was that this PIN-PMN-PT single crystal 1-3 composite-based phased array exhibits a superior insertion loss compared with PMN-PT single crystal and PZT-5H-based 20 MHz phased arrays. The focusing and steering capabilities of the obtained phased array were demonstrated theoretically and experimentally. These promising results indicate that the PIN-PMN-PT single crystal 1-3 composite-based high frequency phased array is a good candidate for ultrasound imaging applications.

Co-Integrated PIN-PMN-PT 2-D Array and Transceiver Electronics by Direct Assembly Using a 3-D Printed Interposer Grid Frame

Tiled modular 2-D ultrasound arrays have the potential for realizing large apertures for novel diagnostic applications. This work presents an architecture for fabrication of tileable 2-D array modules implemented using 1-3 composites of high-bandwidth (BW) PIN-PMN-PT single-crystal piezoelectric material closely coupled with high-voltage CMOS application-specific integrated circuit (ASIC) electronics for buffering and multiplexing functions. The module, which is designed to be operated as a λ -pitch 1.75-D array, benefits from an improved electromechanical coupling coefficient and increased Curie temperature and is assembled directly on top of the ASIC silicon substrate using an interposer backing. The interposer consists of a novel 3-D printed acrylic frame that is filled with conducting and acoustically absorbing silver epoxy material. The ASIC comprises a high-voltage switching matrix with locally integrated buffering and is interfaced to a Verasonics Vantage 128, using a local field programmable gate array (FPGA) controller. Multiple prototype 5 ×6 element array modules have been fabricated by this process. The combined acoustic array and ASIC module was configured electronically by programming the switches to operate as a 1-D array with elements grouped in elevation for imaging and pulse-echo testing. The resulting array configuration had an average center frequency of 4.55 MHz, azimuthal element pitch of [Formula: see text], and exhibited average -20-dB pulsewidth of 592 ns and average -6-dB fractional BW of 77%.

Fabrication and Characterization of a Miniaturized 15-MHz Side-Looking Phased-Array Transducer Catheter

This paper describes the development of a miniaturized 15-MHz side-looking phased-array transducer catheter. The array features a 2-2 linear composite with 64 piezoelectric elements mechanically diced into a piece of PMN-30%PT single crystal and separated by non-conductive epoxy kerfs at a 50-μm pitch, yielding a total active aperture of 3.2 mm in the azimuth direction and 1.8 mm in the elevation direction, with an elevation natural focal depth of 8.1 mm. The array includes non-conductive epoxy backing and two front matching layers. A custom flexible circuit connects the array piezoelectric elements to a bundle of 64 individual 48-AWG micro-coaxial cables enclosed within a 1.5-m long 10F catheter. Performance characterization was evaluated via finite element analysis simulations and afterwards compared against obtained measurement results, which showed an average center frequency of 17.7 MHz, an average bandwidth of 52.2% at -6 dB, and crosstalk less than -30 dB. Imaging of a tungsten fine-wire phantom resulted in axial and lateral spatial resolutions of approximately 90 μm and 420 ìm, respectively. The imaging capability was further evaluated with colorectal tissue-mimicking phantoms, demonstrating the potential suitability of the proposed phased-array transducer for the intraoperative assessment of surgical margins during minimally invasive colorectal surgery procedures.

Noninvasive sub-organ ultrasound stimulation for targeted neuromodulation

Tools for noninvasively modulating neural signaling in peripheral organs will advance the study of nerves and their effect on homeostasis and disease. Herein, we demonstrate a noninvasive method to modulate specific signaling pathways within organs using ultrasound (U/S). U/S is first applied to spleen to modulate the cholinergic anti-inflammatory pathway (CAP), and US stimulation is shown to reduce cytokine response to endotoxin to the same levels as implant-based vagus nerve stimulation (VNS). Next, hepatic U/S stimulation is shown to modulate pathways that regulate blood glucose and is as effective as VNS in suppressing the hyperglycemic effect of endotoxin exposure. This response to hepatic U/S is only found when targeting specific sub-organ locations known to contain glucose sensory neurons, and both molecular (i.e. neurotransmitter concentration and cFOS expression) and neuroimaging results indicate US induced signaling to metabolism-related hypothalamic sub-nuclei. These data demonstrate that U/S stimulation within organs provides a new method for site-selective neuromodulation to regulate specific physiological functions.

Stimulation of peripheral nerve activity may be used to treat metabolic and inflammatory disorders, but current approaches need implanted devices. Here, the authors present a non-invasive approach, and show that ultrasound-mediated stimulation can be targeted to specific sub-organ locations in preclinical models and alter the response of metabolic and inflammatory neural pathways.

Design, Fabrication, and Evaluation of Multifocal Point Transducer for High-Frequency Ultrasound Applications

The present study illustrates the design, fabrication, and evaluation of a novel multifocal point (MFP) transducer based on polyvinylidene fluoride (PVDF) film for high-frequency ultrasound application. The fabricated MFP surface was press-focused using a computer numerical control (CNC) machining tool-customized multi-spherical pattern object. The multi-spherical pattern has five spherical surfaces with equal area and connected continuously to have the same energy level at focal points. Center points of these spheres are distributed in a linear pattern with 1 mm distance between each two points. The radius of these spheres increases steadily from 10 mm to 13.86 mm. The designed MFP transducer had a center frequency of 50 MHz and a −6 dB bandwidth of 68%. The wire phantom test was conducted to study and demonstrate the advantages of this novel design. The obtained results for MFP transducer revealed a significant increase (4.3 mm) of total focal zone in the near-field and far-field area compared with 0.48 mm obtained using the conventional single focal point transducer. Hence, the proposed method is promising to fabricate MFP transducers for deeper imaging depth applications.

Fabrication and Characterization of a 20-MHz Microlinear Phased-Array Transducer for Intervention Guidance

This paper describes the design and fabrication of a miniature ultrasonic phased-array transducer used for intervention guidance. Currently, ultrasound probes are often placed at the body surface of the patients, leading to several drawbacks including the limitation of penetration and image quality. In order to improve the reliability of the guiding process, we propose a miniature phased-array transducer that can be placed adjacent to the intervention device during the interventional procedure. In this paper, we report the work that has been carried out on the development of this miniature phased-array transducer. It comprised 48 elements housed in a 3-mm-diameter needle. A specially designed flexible circuit was used for accommodating the transducer array in the long, thin needle housing. The center frequency and the fractional bandwidth were approximately 20 MHz and 42%, respectively, with an average crosstalk lower than -30 dB. The axial and azimuth resolutions were approximately 80 and [Formula: see text], respectively. The imaging capability of the transducer was further evaluated by acquiring the B-mode images of a needle in a cow liver. The performance of the proposed phased-array transducer demonstrates the feasibility of such an approach for interventional guidance.