Single-element Ultrasonic Transducer Research Articles

Ultrasonic phased array testing to quantify material texture for metal additive manufacturing

Metal additive manufacturing (AM) processes result in complex microstructures, porosity, material texture, and residual stresses. These properties may vary throughout AM parts. Ultrasonic nondestructive evaluation (NDE) is essential for understanding the processes leading to these variations. However, the use of single-element transducers to scan AM parts with complex geometries can be challenging. Such measurements may require multiple scans to level a surface or excite various wave types within a part. On the contrary, phased array ultrasonic transducers (PAUTs) can be much more efficient for these studies. In this presentation, custom AM sample designs are discussed which allow multiple ultrasonic wave speeds to be measured using a PAUT. The manufactured samples were assessed with the sectorial scan feature of the PAUT to scan multiple positions and directions quickly without moving the probe. Data from these scans were then used to estimate material wave speeds, material texture, and residual stress along multiple directions within the samples. The results from these scans were also compared with experiments that used single-element ultrasonic transducers. This presentation will describe the sample designs, the experiments, and the analysis in order to highlight the usefulness of PAUTs for scanning AM parts.

Estimation of joint torque in dynamic activities using wearable A-mode ultrasound

The human body constantly experiences mechanical loading. However, quantifying internal loads within the musculoskeletal system remains challenging, especially during unconstrained dynamic activities. Conventional measures are constrained to laboratory settings, and existing wearable approaches lack muscle specificity or validation during dynamic movement. Here, we present a strategy for estimating corresponding joint torque from muscles with different architectures during various dynamic activities using wearable A-mode ultrasound. We first introduce a method to track changes in muscle thickness using single-element ultrasonic transducers. We then estimate elbow and knee torque with errors less than 7.6% and coefficients of determination (R2) greater than 0.92 during controlled isokinetic contractions. Finally, we demonstrate wearable joint torque estimation during dynamic real-world tasks, including weightlifting, cycling, and both treadmill and outdoor locomotion. The capability to assess joint torque during unconstrained real-world activities can provide new insights into muscle function and movement biomechanics, with potential applications in injury prevention and rehabilitation.

A phased array ultrasonic transducer linear sinusoidal driving system for ultrasound neuromodulation

Ultrasound application has been proven to be a promising noninvasive neuromodulation technique due to the high penetration depth, and high focusing properties. Compared to single-element ultrasonic transducers, phased array transducers have the advantages of adjustable focusing targets and higher focusing accuracy, making them more suitable for transcranial neuromodulation technology. However, there is currently limited research on phased array ultrasonic transducer linear sinusoidal driving systems for precise transcranial neuromodulation. This paper develops a new type of phased array linear driving system, using sine wave as input wave, and designs a new OCL-AB power amplifier circuit based on the Output CapitorLess circuit (OCL) and Class-AB circuit. Furthermore, the dedicated input signal generator and focusing control module are designed and combined with the excitation circuit to form a balanced transformerless (BTL) structure to further boost the output voltage. The experimental results show that the 16-channel prototype of the system can meet various parameter requirements for neural regulation under standard mode ±60 V and BTL mode ±120 V output voltage at 100KHz-1 MHz, and has smaller focusing spot and higher frequency accuracy.

Noninvasive Bolus Transit Detection in Cervical Esophagus Utilizing Ultrasound Characteristics.

This pilot study aims to identify characteristic A-mode ultrasound features relevant to noninvasive detection of esophageal bolus transit in the proximal esophagus. Ultrasound signals at a lateral neck site were obtained via a single-element ultrasonic transducer with synchronous videofluoroscopic swallowing studies images of swallows of differing viscosities in 21 adult dysphagia outpatients. Characteristic ultrasound features were extracted to differentiate a bolus-filled from a collapsed esophagus. From 21 subjects, 412 swallows exhibited 4 reproducible waveform patterns associated with bolus transit as displayed in a heatmap: (1)Strong Reflectors; (2)Echo Shifts; (3)Distal Acoustic Enhancement; and (4)Speckling: One or more of these features were observed in the swallow series for all 21 subjects. Distinct acoustic waveform features acquired by single-element ultrasonic transducers can identify bolus transit through the cervical esophagus.

High-temperature piezoelectric ultrasonic transducer based on BiScO3-PbTiO3 ceramics

High-temperature ultrasonic detection technology has attracted unprecedented attention in recent years. However, the detection capability of piezoelectric ultrasonic transducers at high temperatures is limited by the properties of piezoelectric ceramics. To tackle this, 0.125 mol% Nb5+ doped 0.36BiScO3-0.64PbTiO3 (BSPT-0.125 Nb) ceramics were prepared by the conventional solid-state reaction method. The dielectric, ferroelectric, and piezoelectric properties of BSPT-0.125 Nb as a function of temperature were characterized systematically, and compared to those of commercial Pb(Zr,Ti)O3 (PZT) ceramics (PZT-4, PZT-5A, and PZT-8). The results indicate that the BSPT-0.125 Nb exhibits better temperature stability than PZT ceramics, showing greater potential for high temperature piezoelectric device application. To exemplify, two high-temperature single-element ultrasonic transducers based on BSPT-0.125 Nb and PZT-5A were fabricated. The impedance and echo response of the transducers were tested on a heating platform at different temperatures. The results show that the transducer based on BSPT-0.125 Nb ceramics had stronger pulse-echo response signal at high temperature, and could maintain a stable electrical resonance and received echo responses until 400 °C, which is attributed to high Curie temperature and large piezoelectric voltage coefficient. The results verify the greater potential of BSPT-0.125 Nb ceramics over PZT system ceramics in high-temperature ultrasonic transducers for ultrasonic detection applications.

A human ear-inspired ultrasonic transducer (HEUT) for 3D localization of sub-wavelength scatterers

The proposed technology aims to enable 3D localization of scatterers using single element ultrasonic transducers, which are traditionally limited to 1D measurements. This is achieved by designing a bespoke acoustic lens with a spiral-shaped pattern similar to the human outer ear, a shape that has evolved for sound source localization. This lens breaks the surface symmetry of the transducer, allowing ultrasonic waves arriving from different directions to be encoded in a certain way that can later be decoded to extract directional information. By employing the mechanism of spatial-encoding of the received signals and decoding via signal processing, the location of sub-wavelength scatterers can be detected in 3D with a single measurement for sparsely distributed scatterers. The proposed technology is first verified through a simulation study, and then 3D printed acoustic lenses are used to demonstrate the 3D encoding functionality of the Human Ear-inspired Ultrasonic Transducer (HEUT) experimentally. A framework is created to localize scatterers in 3D by processing received signals acquired by a HEUT prototype. With this technology, a single transducer can obtain multi-dimensional information with a single pulse-echo measurement, reducing the number of elements required for performing 3D ultrasound localization. The proposed spatial-encoding and -decoding technology can be applied to other wave-based imaging methods to develop affordable, practical, and compact sensing devices.

High piezoelectricity performance in PSBZT ceramic for ultrasonic transducer

Lead zirconate titanate (PZT) ceramics possess great potential for practical applications and thus improving their piezoelectric properties is crucial. [Formula: see text][Formula: see text][Formula: see text][Formula: see text][Formula: see text][Formula: see text]O3 (PSBZT) ceramics with high Curie temperature and excellent piezoelectric properties were fabricated via a conventional solid-state method, and the effect of Ba[Formula: see text] doping on the structural, dielectric, piezoelectric and ferroelectric properties was studied in detail. It is shown that doping of Ba[Formula: see text] significantly enhanced the piezoelectric properties of PSZT, the maximum [Formula: see text]533 pC/N and [Formula: see text]361[Formula: see text]C at [Formula: see text]= 0.02 were acquired. Furthermore, PSZT and PSBZT ceramics were used to prepare single element ultrasonic transducers, and their performance were compared and evaluated. The results demonstrate that the PSBZT ceramic-based transducer possesses better sensitivity and bandwidth than the PSZT ceramic-based transducer.

Enhancement of 10 MHz single element ultrasonic transducers based on alternating current polarized PIN-PMN-PT single crystals

Enhancement of 10 MHz single element ultrasonic transducers based on alternating current polarized PIN-PMN-PT single crystals

Acoustic Localization of an Intruder in a Strongly Scattering Medium

Localizing an intruder submerged in a strongly scattering medium, such as a dense granular suspension, is a practical challenge. Here we extract the coherent ultrasonic echo from a steel ball submerged in a dense glass-bead packing saturated by water, by using a standard single-element ultrasonic transducer thanks to a configuration averaging process. Different configurations of the granular packing are created by the nonaffine motion of the beads with a mixing blade, akin to the Brownian motion, in the vicinity of the intruder. We investigate the efficiency of this process to reduce the so-called material noise from multiply scattered ultrasound, as a function of the configuration number, the shear rate and the blade-intruder distance. Nonaffine motions of the beads in the shear zone induced by the blade are then analyzed on the basis of a split-bottom rotating shear cell. This method helps to develop not only ultrasonic imaging tools of buried objects in turbid marine sediments, but also the local rheology based on a ball falling monitored by ultrasonic tracking.

Preclinical robotic device for magnetic resonance imaging guided focussed ultrasound.

A robotic device featuring three motion axes was manufactured for preclinical research on focussed ultrasound (FUS). The device comprises a 2.75MHz single element ultrasonic transducer and is guided by Magnetic Resonance Imaging (MRI). The compatibility of the device with the MRI was evaluated by estimating the influence on the signal-to-noise ratio (SNR). The efficacy of the transducer in generating ablative temperatures was evaluated in phantoms and excised porcine tissue. System's activation in the MRI scanner reduced the SNR to an acceptable level without compromising the image quality. The transducer demonstrated efficient heating ability as proved by MR thermometry. Discrete and overlapping thermal lesions were inflicted in excised tissue. The FUS system was proven effective for FUS thermal applications in the MRI setting. It can thus be used for multiple preclinical applications of the emerging MRI-guided FUS technology. The device can be scaled-up for human use with minor modifications.

3D-printed gradient-index phononic crystal lens for transcranial focused ultrasound

Transcranial focused ultrasound (tFUS) shows great promise as a noninvasive tool to treat neurological conditions such as essential tremor. The existing clinical phased array systems are mostly intended for ultrasound delivery to the center of the brain (as in thalamotomy for essential tremor), in addition to being complex and expensive. To seek an alternative focusing approach especially for the brain periphery, we explore a 3D-printed gradient-index (GRIN) lens as a simple and an orders of magnitude more cost-effective approach. The lens is constructed using a phononic crystal (PC) architecture with varying lattice geometry and hence refractive index distribution. Specifically, the lens uses an axisymmetric hyperbolic secant refractive index profile to focus ultrasonic waves generated by a 1 MHz single-element ultrasonic transducer. Finite element simulations are performed to design and analyze the GRIN-PC lens, and to explore the effects of various parameters such as the distance from the skull and the incidence angle. The numerical results are validated experimentally for a 3D-printed lens by scanning the 3D pressure field generated through a temporal bone. This cost-effective approach to tFUS can open new possibilities to 3D print lenses based on patient computed tomography scans for various applications from tissue ablation to neurostimulation.

Nb and Mn Co-Modified Na0.5Bi4.5Ti4O15 Bismuth-Layered Ceramics for High-Frequency Transducer Applications.

Lead-free environmentally friendly piezoelectrical materials with enhanced piezoelectric properties are of great significance for high-resolution ultrasound imaging applications. In this paper, Na0.5Bi4.5Ti3.86Mn0.06Nb0.08O15+y (NBT-Nb-Mn) bismuth-layer-structured ceramics were prepared by solid-phase synthesis. The crystallographic structure, micromorphology, and piezoelectrical and electromechanical properties of NBT-Nb-Mn ceramics were examined, showing their enhanced piezoelectricity (d33 = 33 pC/N) and relatively high electromechanical coupling coefficient (kt = 0.4). The purpose of this article is to describe the development of single element ultrasonic transducers based on these piezoelectric ceramics. The as-prepared high-frequency tightly focused transducer (ƒ-number = 1.13) had an electromechanical coupling coefficient of 0.48. The center frequency was determined to be 37.4 MHz and the −6 dB bandwidth to be 47.2%. According to the B-mode imaging experiment of 25 μm tungsten wires, lateral resolution of the transducer was calculated as 56 μm. Additionally, the experimental results were highly correlated to the results simulated by COMSOL software. By scanning a coin, the imaging effect of the transducer was further evaluated, demonstrating the application advantages of the prepared transducer in the field of high-sensitivity ultrasound imaging.

Performance enhancement of ultrasonic transducer made of textured PNN-PZT ceramic

In this paper, 0.36Pb(Ni[Formula: see text]Nb[Formula: see text])O3–0.24PbZrO3–0.40PbTiO3(PNN-PZT) ceramic was prepared, and texture engineering was performed on this PNN-PZT ceramic to improve its electromechanical properties and temperature stability. Single element ultrasonic transducers were prepared using PNN-PZT, PNN-PZT textured ceramics, and their performance were evaluated and compared using a PZT-5H ceramic based transducer as the benchmark. It is shown that the sensitivity and bandwidth of the PNN-PZT textured ceramic-based transducer are much superior to regular PNN-PZT ceramic and PZT-5H ceramic based transducers.

Effects of Composition Segregation in PMN-PT Crystals on Ultrasound Transducer Performance.

This study investigates the relationship between the composition segregation in lead magnesium niobate-lead titanate (PMN-PT; PMN-29%PT, PMN-29.5%PT, PMN-30%PT, PMN-30.5%PT, and PMN-31%PT) single crystals within morphotropic phase boundary (MPB) and the corresponding ultrasonic transducer performance through PiezoCAD modeling and real transducer testing. For five crystals with compositions distributed across the main body of a crystal ingot, the piezoelectric coefficient and free relative permittivity values were measured to vary by over 30%, whereas the transducer bandwidth and center frequency values were modeled to change by less than 10%. For the single-element ultrasonic transducers fabricated using those crystals without matching layers, the variations of -6-dB bandwidth, insertion loss, receiver-free field voltage response, and center frequency were measured to be 9.61%, -15.23%, 9.76%, and 1.41%, respectively, confirming the modeling results. Using the Mason and Krimholtz, Leedom, and Matthaei (KLM) models, it is found that the relatively stable transducer performance can be attributed to the relatively consistent electromechanical coupling coefficient, acoustic impedance, and clamped relative permittivity originated from the stable elastic compliance properties among the crystals of various compositions. It is expected that the relatively stable performance could be extended to multielement transducers with matching layers for the same contributing mechanisms. Our results suggest that it is possible to use crystal plates of different compositions within the MPB region, obtained from one and the same ingot, to fabricate a batch of ultrasonic transducers that will exhibit a similar performance, significantly reducing the cost of materials.

Experimental evaluation of high intensity focused ultrasound for fat reduction of ex vivo porcine adipose tissue.

The present study was stimulated by the continuous growth of commercially available high intensity focused ultrasound (HIFU) systems for fat reduction. Herein, HIFU was utilised for fat ablation using a single-element ultrasonic transducer operating in thermal mode. The custom-made concave transducer that operates at 1.1MHz was assessed on excised porcine adipose tissue for its ability to reduce fat. Ultrasonic sonications were executed on the adipose tissue utilising acoustical power between 14 and 75W and sonication time in the range of 1-10min. The mass of the adipose tissue sample was weighed afore and after ultrasonic sonications and the effect of the sonication on the mass change was recorded. Mass change was linearly dependent with either increasing acoustical power or sonication time and was in the range of 0.46-1.9g. High acoustical power of 62.5W for a sonication time of 1min and a power of 75W for a sonication time of 5min, respectively resulted in the formation of a lesion or possible cavitation on the piece of excised adipose tissue. The study demonstrated the efficacy of the proposed transducer in achieving a reduction of excised fat tissue. The present findings indicate the potential use of the transducer in a HIFU system indicated for the reduction of subcutaneous adipose tissue where increased values of acoustical power can result in increased amounts of fat reduction.

Image-Free Ultrasound Blood-Flow Monitoring Circuit System with Automatic Range-Gate Positioning Scheme: A Pilot Study

This work proposes a proof-of-concept ultrasound blood-flow-monitoring circuit system using a single-element transducer. The circuit system consists of a single-element ultrasonic transducer, an analog interface circuit, and a field-programmable gate array (FPGA). Since the system uses a single-element transducer, an ultrasound image cannot be reconstructed unless scanning with mechanical movement is used. An ultrasound blood-flow monitor basically needs to acquire a Doppler sample volume by positioning a range gate at a vessel region on a scanline. Most recent single-transducer-based ultrasound pulsed-wave Doppler devices rely on a manual adjustment of the range gate to acquire Doppler sample volumes. However, the manual adjustment of the range gate depends on the user’s experience, and it can be time consuming if a transducer is not properly positioned. Thus, automatic range-gate-positioning is more desirable for image-free pulsed-wave Doppler devices. This work proposes a circuit system which includes a new automatic range-gate-positioning scheme. It blindly tracks the position of a blood vessel on a scanline by using the accumulation of Doppler amplitude deviations and a hysteresis slicing function. The proposed range-gate-positioning scheme has been implemented in an FPGA for real-time operation and is based on addition-only computations, except for filter parts to reduce the complexity of computation in the hardware. The proposed blood-flow-monitoring circuit system has been implemented with discrete commercial chips for proof-of-concept purposes. It uses a center frequency of 2 MHz and a system-clock frequency of 20 MHz. The FPGA only utilizes 5.6% of slice look-up-tables (LUTs) for implementation of the range-gate-positioning scheme. For measurements, the circuit system was utilized to interrogate a customized flow phantom model, which included two vessel-mimicking channels. The circuit system successfully acquired Doppler sample volumes by positioning a range gate on a fluid channel. In addition, the estimated Doppler shift frequency shows a good agreement with the theoretical value.

A Cost-Efficient Multiwavelength LED-Based System for Quantitative Photoacoustic Measurements.

The unique ability of photoacoustic (PA) sensing to provide optical absorption information of biomolecules deep inside turbid tissues with high sensitivity has recently enabled the development of various novel diagnostic systems for biomedical applications. In many cases, PA setups can be bulky, complex, and costly, as they typically require the integration of expensive Q-switched nanosecond lasers, and also presents limited wavelength availability. This article presents a compact, cost-efficient, multiwavelength PA sensing system for quantitative measurements, by utilizing two high-power LED sources emitting at central wavelengths of 444 and 628 nm, respectively, and a single-element ultrasonic transducer at 3.5 MHz for signal detection. We investigate the performance of LEDs in pulsed mode and explore the dependence of PA responses on absorber’s concentration and applied energy fluence using tissue-mimicking phantoms demonstrating both optical absorption and scattering properties. Finally, we apply the developed system on the spectral unmixing of two absorbers contained at various relative concentrations in the phantoms, to provide accurate estimations with absolute deviations ranging between 0.4 and 12.3%. An upgraded version of the PA system may provide valuable in-vivo multiparametric measurements of important biomarkers, such as hemoglobin oxygenation, melanin concentration, local lipid content, and glucose levels.

Piezoelectric P(VDF-TrFE) film inkjet printed on silicon for high-frequency ultrasound applications

We investigated the innovative processing of poly(vinylidene fluoride-trifluoroethylene) P(VDFx-TrFE1-x) (x = 83 mol. %) by inkjet printing to deliver uniform and thickness-controlled layers on silicon substrates. Here, we provide detailed processing steps and optimize film deposition conditions. The thickness coupling factor for a P(VDF-TrFE) film around 11 μm thick was 22%, demonstrating good electromechanical performance after poling. These multilayer structures were specifically for high-frequency, single-element ultrasonic transducer applications. The measurements of electro-acoustic responses were in water. The maximal frequency was centered at 33.2 MHz and had a fine axial resolution at 22 μm, corresponding to a fractional bandwidth at −6 dB of 100%. In the context of technological evolutions aimed at miniaturized devices and integrated electronics, these results allow for the consideration of complex structures such as multi-element transducers for high-frequency imaging applications.

Modeling and Experimental Characterization of Bonding Delaminations in Single-Element Ultrasonic Transducer.

Ultrasonic transducers performance can be seriously deteriorated by loss of adhesion between some constitutive elements such as the active element, the backing, or the matching layer. In the present work, the influence of bonding delaminations on the performance of a single-element ultrasonic transducer, which is composed of a piezoelectric disk, a backing, and a matching layer, is studied numerically and experimentally. Based on the positions between layers, two cases, i.e., delaminations between ceramic and backing or between ceramic and matching layer, are considered. Each case involves three different types of delaminations, which are marked as delamination type (DT)-I, II, and III. DT-I, a circular shape delamination, starts from the center and expands towards the peripheric zone; DT-II, an annular shape delamination, starts from the peripheric zone and expands towards the center; DT-III is a sector shape delamination with a given angle. The numerical simulations are performed by the finite element method and the influence of delaminations on the electromechanical admittance (EMA) of the transducer is investigated. 3D printed backings and matching layers are mounted on a PZT sample to assemble delaminated single-element transducers. An impedance analyzer is used for experimental measurements. Comparison between numerical and experimental results shows a reasonable agreement making changes in EMA an interesting indicator to inform about the occurrence and severity of delaminations in a single-element ultrasonic transducer.

2-D Ultrasonic Array-Based Optical Coherence Elastography.

Acoustic radiation force optical coherence elastography (ARF-OCE) has been successfully implemented to characterize the biomechanical properties of soft tissues, such as the cornea and the retina, with high resolution using single-element ultrasonic transducers for ARF excitation. Most currently proposed OCE techniques, such as air puff and ARF, have less capability to control the spatiotemporal information of the induced region of deformation, resulting in limited accuracy and low temporal resolution of the shear wave elasticity imaging. In this study, we propose a new method called 2-D ultrasonic array-based OCE imaging, which combines the advantages of 3-D dynamic electronic steering of the 2-D ultrasonic array and high-resolution optical coherence tomography (OCT). The 3-D steering capability of the 2-D array was first validated using a hydrophone. Then, the combined 2-D ultrasonic array OCE system was calibrated using a homogenous phantom, followed by an experiment on ex vivo rabbit corneal tissue. The results demonstrate that our newly developed 2-D ultrasonic array-based OCE system has the capability to map tissue biomechanical properties accurately, and therefore, has the potential to be a vital diagnostic tool in ophthalmology.