Array Transducer Research Articles

Study of the acoustic scattering characteristics of a rigid sphere in a vortex acoustic field

This paper investigates the scattering sound field of a rigid sphere positioned in a vortex beam generated by a phase-modulated circular transducer array. The effects of the dimensionless parameter ka, the number of array elements, the topological charge, the radius of the transducer array, the distance between the array and the sphere, and its offset position on the scattering sound field distribution of a sphere are studied. Simulation results show that as the ka increases, the incident wave intensity and the scattering sound field of a rigid sphere increase, and the angle between the two main lobes decreases. Once ka is determined, the number of the array elements has no effect on the scattering pattern. However, the topological charge of the vortex beam has greater effect on the scattering sound field. As the topological charge increases, the incident wave intensity decreases, but the angle between two main lobes of the scattering field increases. The radius of the array has an effect on the intensity of the scattering field and the larger the radius, the larger the area of low intensity radiation between the two main lobes. In addition, the distance between the sphere and the array has a weak effect on the scattering pattern when it exceeds a certain value. For an off-axis sphere, the scattering pattern becomes more complex as the topological charge changes. These results can be used to adjust the constituent factors of the transducer array and to investigate the advantages of the vortex beam for underwater target detection.

A Novel Nondestructive Testing Probe Using AlN-Based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs).

Ultrasonic nondestructive testing (NDT) usually utilizes conventional bulk piezoelectric transducers as transceivers. However, the complicated preparation and assembly process of bulk piezoelectric ceramics limits the development of NDT probes toward miniaturization and high frequency. In this paper, a 4.4 mm × 4.4 mm aluminum nitride (AlN) piezoelectric micromachined ultrasonic transducer (PMUT) array is designed, fabricated, characterized, and packaged for ultrasonic pulse-echo NDT of solids for the first time. The PMUT array is prepared based on the cavity silicon-on-insulator (CSOI) process and packaged using polyurethane (PU) material with acoustic properties similar to water. The fabricated PMUT array resonates at 2.183 MHz in air and at around 1.25 MHz after PU encapsulation. The bandwidth of the packaged PMUT receiver (244 kHz) is wider than that of a bulk piezoelectric transducer (179 kHz), which is good for axis resolution improvement. In this work, a hybrid ultrasonic NDT probe is designed using two packaged PMUT receivers and one 1.25 MHz bulk transmitter. The bulk transmitter radiates an ultrasonic wave into the sample, and the defect echo is received by two PMUT receivers. The 2D position of the defect could be figured out by time-of-flight (TOF) difference, and a 30 mm × 65 mm detection area is acquired. This work demonstrates the feasibility of applying AlN PMUTs to ultrasonic NDT of solids and paves the way toward a miniaturized NDT probe using AlN PMUT technology.

High-frequency surface-micromachined optical ultrasound transducer array for 3D micro photoacoustic computed tomography.

This Letter reports a new, to the best of our knowledge, high-frequency surface-micromachined optical ultrasound transducer (HF-SMOUT) array for micro photoacoustic computed tomography (µPACT). An 11 × 11 mm2 2D array of 220 × 220 elements (35 µm in diameter) is designed, fabricated, and characterized. The optical resonance wavelength (ORW) of ≥90% of the elements falls within a 6-nm range. The acoustic center frequency and bandwidth of the elements are ∼14 MHz and ∼18 MHz (129%), respectively. The noise equivalent pressure (NEP) is 161 Pa (or 18 m P a/H z) within a measurement bandwidth of 5-75 MHz. The standard deviation of the ORW drift is 0.45 nm and 0.93 nm within 25°C-55°C, respectively, and during a seven-day continuous water immersion. PACT experiments are conducted to evaluate the imaging performances of the HF-SMOUT array. The spatial resolution is estimated as 90 µm (axial) and 250-750 µm (lateral) within a 10 × 10 mm2 field of view (FoV) and the imaging depth of 16 mm. A 3D PA image of a knotted black hair target is also successfully acquired. These results demonstrate the feasibility of using the HF-SMOUT array for µPACT applications.

First assessment of flow phenomena of acute and chronic thrombosis in the jugular veins using new ultrasound vector-flow imaging.

First assessment of flow changes in the jugular veins using high resolution ultrasound vector flow. 15 patients (8 males, 7 females) with an age range of 35 to 82 years (mean age 58.53±12.26 years) were examined by an experienced examiner using high power ultrasound equipment (Resona R9, Mindray) with probe technology (Mindray L9-3U Linear Array transducer, 2.5 to 9.0 MHz). This group was compared with five healthy subjects (mean age 35.4±13.79 years) as a reference. To assess flow changes, the color-coded duplex sonography and the novel vector flow technique were used. The evaluation was performed of vector morphology changes, turbulence, and wall resistance measurements. There were changes after acute and chronic thrombosis in 9 cases, and venous compression in 7 cases. Turbulence was measurable from 0.01 % to 64.44 %, the average turbulence was 19.73±22.06 %. Wall resistance measurement showed values from 0.01 Pa to 3.14 Pa, depending on the age of the thrombosis or compression. The reference veins showed turbulence of 0.94±1.5 % and a mean wall resistance of 0.05±0.05 Pa. There are statistically significant differences between normal and thrombotic or compressed veins in terms of maximum wall stress (p = 0.006) and mean degree of turbulence (p = 0.012), while the difference in mean wall stress is not statistically significant (p = 0.058). Despite still existing technical limitations, the combination of V-flow and wall stress measurements in jugular vein changes suggests a high diagnostic potential.

Demonstration of MHz piezoelectric micromachined ultrasonic transducers array and its potential application for biomedical treatment

In this paper, we successfully developed the 24 × 31 piezoelectric micromachined ultrasound transducers (PMUTs) array with 8 inch complementary metal oxide semiconductor (CMOS) compatible processes. Scandium aluminum nitride (ScxAl1−xN) thin film (x = 20%) was used as the piezoelectric material. The PMUTs array was fabricated on 8 inch cavity silicon-on-insulator wafers with the device silicon layer thickness of only 3 μm and a cavity pitch of 59 μm. The wafer-level electrical test was conducted using inline auto-prober and the yield rate >90% was achieved across the 8 inch wafer. The following acoustic test on our PMUTs array (1.5 mm × 2.0 mm) indicated the transmit sensitivity of 18.4 kPa V−1 @ 10 mm @ 11.6 MHz in oil with −3 dB bandwidth of 2.3 MHz. In order to validate the potential of using PMUTs array for biomedical treatments, subsequent ultrasonic heating experiments were carried out on a silicone block. A temperature rise of 4 °C was achievable in about 50 s. These results demonstrate that the potential of using PMUTs array as a disposable biomedical device in many therapeutic applications, for example, a treatment for dry eye disease.

Low-Cost Scalable PCB-Based 2-D Transducer Arrays for Volumetric Photoacoustic Imaging.

Photoacoustic (PA) imaging provides deep tissue molecular imaging of chromophores with optical absorption contrast and ultrasonic resolution. Present PA imaging techniques are predominantly limited to one 2D plane per acquisition. 2D ultrasound transducers, required for real-time 3D PA imaging, are high-cost, complex to fabricate and have limited scalability in design. We present novel PCB-based 2D matrix ultrasound transducer arrays that are capable of being bulk manufactured at low-cost without using laborious ultrasound fabrication tools. The 2D ultrasound array specifications are easily scalable with respect to widely available PCB design and fabrication tools at low cost. To demonstrate scalability, we fabricated low (11 MHz) frequency 8x8 matrix array and high (40 MHz) frequency 4x4 matrix array by directly bonding an undiced polyvinylidene fluoride (PVDF) piezoelectric material of desired thickness to the custom designed PCB substrate. Characterization results demonstrate wideband PA receive sensitivity for both low (87%) and high (188%) frequency arrays. Volumetric PA imaging results of light absorbing targets inside optical scattering medium demonstrate improved spatial resolution and field of view with increase in aperture size.

Element Position Calibration for Matrix Array Transducers with Multiple Disjoint Piezoelectric Panels.

Two-dimensional ultrasound transducers enable the acquisition of fully volumetric data that have been demonstrated to provide greater diagnostic information in the clinical setting and are a critical tool for emerging ultrasound methods, such as super-resolution and functional imaging. This technology, however, is not without its limitations. Due to increased fabrication complexity, some matrix probes with disjoint piezoelectric panels may require initial calibration. In this manuscript, two methods for calibrating the element positions of the Vermon 1024-channel 8 MHz matrix transducer are detailed. This calibration is a necessary step for acquiring high resolution B-mode images while minimizing transducer-based image degradation. This calibration is also necessary for eliminating vessel-doubling artifacts in super-resolution images and increasing the overall signal-to-noise ratio (SNR) of the image. Here, we show that the shape of the point spread function (PSF) can be significantly improved and PSF-doubling artifacts can be reduced by up to 10 dB via this simple calibration procedure.

Numerical analysis of the phased array imaging with a stacked plate buffer

Abstract This paper discusses the imaging with a phased array transducer attached with a stacked thin plate buffer using the calculations of wave propagation. The buffer is designed to guarantee the performance of phased array transducer based on the properties of dispersion nature of the S0 mode of Lamb wave. First, numerical analyses showed the limitations of the imaging with a stacked plate buffer due to the multiple reflections at the buffer ends. Then the effective detecting region (EDR) of the phased array transducer with a stacked plate buffer was investigated theoretically and numerically. The imaging results of the numerical calculations agreed with the theoretical predictions on the EDR. Final numerical analyses also presented the longer buffer provides the wider EDR as predicted by the theoretical investigations.

3-D Passive Cavitation Imaging Using Adaptive Beamforming and Matrix Array Transducer With Random Apodization.

With the development of promising cavitation-based treatments, the interest in cavitation monitoring with passive acoustic mapping (PAM) is significantly increasing. While most of studies regarding PAM are performed in 2-D, 3-D imaging modalities are getting more attention relying on either custom-made or commercial matrix probes. Unless specific phased-arrays are used for a specific application, limitations due to probe apertures often results in poor performances of the 3-D mapping, due to the use of a delay-and-sum (DAS) classic beamformer, which results in strong artifacts and large main lobe sizes. In this article, 3D-PAM is achieved by performing adaptive beamforming in the frequency domain (FD) in 3-D, and using a random sparse apodization of a commercial matrix array driving only 256 elements among the 1024 available. It reduces the computation time and makes use of only one 256-channel research platform. Three beamformers have been implemented in 3-D and in the FD: the DAS beamformer, which corresponds to the beamformer used in previous 3D-PAM studies, the robust capon beamformer (RCB), an adaptive algorithm widely used in 2D-PAM for its high performances, and the MidWay (MW) beamformer, an adaptive algorithm with a computation complexity equivalent to the one of DAS. These algorithms are evaluated both in simulations and experiments with a harmonic source at different positions, and are also applied to real cavitation signals. The results show that, in the case of matrix arrays of small aperture such as generic commercial matrix probes, the DAS beamformer leads to large main lobe sizes, while adaptive beamformers largely improve the performances of the mapping. The low computation time and its parameter-free character make MW beamformer a good compromise for 3D-PAM applications. It thus appears that a random sparse apodization combined with adaptive beamforming is a good solution to achieve high-performance 3D-PAM with manageable devices.

Electronic Focus Steering Capabilities of a Diagnostic-Type Linear Ultrasound Array Designed for High Power Therapy and Its Visualization

The focus steering capabilities of a 1 MHz linear phased array transducer (64 rectangular elements, 14.8 × 51.2 mm aperture) intended for drug delivery applications in abdominal organs were assessed and compared with its design-stage computer model. Acoustic fields generated by the transducer and predicted by the models of an ideal array with uniformly vibrating elements and either a plane or a cylindrically focused surface were simulated using the Rayleigh integral and angular spectrum methods. The boundary conditions for the transducer were reconstructed from acoustic holography measurements performed for selected focusing configurations of the array and also synthesized from holography data measured for each of its individual elements. It was shown that the transducer field with electronic focus steering can be accurately synthesized based on the holography data of its elements, which significantly simplified acoustic field characterization. Variability of the power and directivity patterns of the array elements were analyzed. A twofold smaller range of electronic steering in the transverse direction for the transducer compared to its computer model is discussed.

Phase Correction of the Channels of a Fully Populated Randomized Multielement Therapeutic Array Using the Acoustic Holography Method

The acoustic holography method was used to characterize a therapeutic focused fully populated 256-element ultrasonic transducer array. Elements of the array with the shape of equal area polygons are densely arranged in an irregular pattern on a spherically concave surface with a radius of curvature of 150 mm and a diameter of 200 mm. The array has a central frequency of 1.2 MHz and is designed to operate in water. The performance of individual array elements was studied based on the holographically reconstructed normal velocity distribution over the array surface. It was shown that with the same electrical signals applied to the elements, their acoustic responses had a phase deviation relative to the nominal values, which can be caused either by the asphericity of the array surface, or by the introduction of additional phase delays by the electrical matching network. To compensate for the detected parasitic phase shifts of the elements and restore the effective sphericity of the radiating surface, the Verasonics V-1 control system was used. The hologram measured after making the correction, as well as the shape of the focal region and acoustic pressure magnitude at the focus, separately measured by a hydrophone, showed that the proposed method reconstructed the nominal operating parameters of the array with high accuracy.

Biaxial Excitation and Reception Method Applied to Ultrasound Imaging.

The biaxial method consists of the utilization of orthogonal electric fields in single-element piezoceramics both in transmission and reception. This study demonstrates the application of the biaxial method to broadband transducers. We developed a three-element biaxial transducer array to demonstrate the feasibility of biaxial method in imaging applications. Finite element analysis was used to model the response of a single transducer element. An electric characterization was performed at each transducer element to determine their driving frequency. Each transducer was driven at 6.25 MHz and tested in different phases to determine the phase that produced the maximum pressure amplitude and shortest pulsewidth. Both simulations and experimental results showed that the acoustic pressure and half-pulsewidth followed a sinusoidal response as a function of the difference in phase applied to the lateral electrodes, as it has been described in our previous work. An imaging test was performed by placing a 0.36-mm diameter nylon wire 20 mm away from the transducer while driving and receiving each element with different combinations of conventional and biaxial driving. By applying a biaxial rephasing at the receiving electrodes during the data analysis, we obtained a maximum reduction in the axial resolution from 4.6 to 1.3 mm and signal-to-noise ratio (SNR) improvements from 15.2 to 24.4 dB, when compared to conventional driving.

Development of a wideband medical ultrasonic linear array transducer with a double-sided FPCB

Medical ultrasound transducers are being used to acquire medical image information from a patient. In order to acquire high-quality images, studies have been conducted to improve the performance of the transducer. Among them, the high acoustic impedance de-matching layer is effective in improving the sensitivity and bandwidth of the transducer using the backward reflected wave. First, the performance trend of the transducer according to the thickness of the acoustic de-matching layer was analyzed through theoretical calculation and finite element method. It was confirmed that the sensitivity and bandwidth of the transducer increased by adjusting the time delay of the backward reflected wave according to the thickness of the acoustic de-matching layer. Based on the analyzed results, a new structure of a transducer applied with a double-sided FPCB was devised. The time delay of the backward reflected wave was simply controlled by changing the thickness of the polyimide in the FPCB. The bandwidth of the transducer can be increased by changing the thickness of the polyimide in the FPCB. Also, a prototype of a transducer having a designed structure was manufactured and its performance was measured, and it was confirmed that the designed structure was effective in increasing the bandwidth of the transducer.

Non-Invasive Plant Root Tomography Through Optimized Sonar Array Transducer Antenna Design Using Genetic Swarm Metaheuristic

Plant root imaging is crucial for progress in various domains such as plant breeding and crop optimization. Traditionally, root tomography involves invasive methods that disrupt plant systems and yield non-reproducible results. As a result, non-invasive techniques, particularly electrical tomography, have gained significant attention. Despite the advantages, these techniques have limitations in terms of radiation efficiency and directivity due to suboptimal antenna design. This paper presents a comprehensive simulation on antenna design optimization focusing on dimensions, spacing, and integration of advanced algorithms. A micropatch transducer antenna was engineered for an existing in-silico plant root setup operating within a 3–5 MHz frequency range. The optimized dimensions of the antenna are 109.32 mm × 140.67 mm × 2.55 mm, and it resonates effectively within a frequency range of 3.1–5.68 MHz. Using scalar minimization techniques, patch transducers were interconnected into an antenna array with an optimized 3 mm spacing. Utilizing multi-objective optimization algorithm based on sperm fertilization procedure and shuffled frog leaping algorithm, optimal frequencies were obtained at 3,989,796.88 Hz and 3,989,951.83 Hz, respectively. Validated using CADFEKO software, the proposed antenna design demonstrated distinctive voltage distribution, superior directivity of 9.24 dBi, gain of 9.15 dBi, and 98.6% radiation efficiency when compared to the existing silicon-based root tomography antenna setups.

Experimental study on the nonlinear mixing of ultrasonic waves in concrete using an array technique

This research develops a procedure that combines ultrasonic array technology with non-collinear ultrasonic wave mixing to detect and scan internal microscale damage in concrete. Exploiting the underlying mechanics of nonlinear wave mixing, two incident shear wave beams generated by two ultrasonic transducer arrays (and with frequencies low enough to propagate without being overly scattered by the aggregate) are used to create a longitudinal mixed wave, the amplitude of which is a direct measure for the amount of localized, internal damage. The arrays enable beam steering, making it possible to scan for damage along an arc. The effectiveness of the proposed technique is demonstrated by characterizing different types of microscale damage embedded at known locations in a concrete prism specimen. These results establish the feasibility of using a nonlinear wave mixing array technique for the efficient inspection of internal microscale damage in a large concrete structure.

Real-time acoustic holography with physics-reinforced contrastive learning for acoustic field reconstruction

Acoustic holography (AH) provides a promising technique for arbitrary acoustic field reconstruction, supporting many applications like robotic micro-nano manipulation, neuromodulation, volumetric imaging, and virtual reality. In AH, three-dimensional (3D) acoustic fields quantified with complex-valued acoustic pressures are reconstructed by virtue of two-dimensional (2D) acoustic holograms. Phase-only hologram (POH) is recently regarded as an energy-efficient way for AH, which is typically implemented by a dynamically programmable phased array of transducers (PATs). As a result, spatiotemporal precise acoustic field reconstruction is enabled by precise, dynamic, and individual actuation of PAT. Thus, 2D POH is required per arbitrary acoustic fields, which can be viewed as a physical inverse problem. However, solving the aforementioned physical inverse problem in numerical manners poses challenges due to its non-linear, high-dimensional, and complex coupling natures. The existing iterative algorithms like the iterative angular spectrum approach (IASA) and iterative backpropagation (IB) still suffer from speed-accuracy trade-offs. Hence, this paper explores a novel physics-iterative-reinforced deep learning method, in which frequency-argument contrastive learning is proposed facilitated by the inherent physical nature of AH, and the energy conservation law is under consideration. The experimental results demonstrate the effectiveness of the proposed method for acoustic field reconstruction, highlighting its significant potential in the domain of acoustics, and pushing forward the combination of physics into deep learning.

Comparison of transrectal and transabdominal transducers for use in fast localized abdominal sonography of horses presenting with colic.

Abdominal ultrasonography is valuable in the diagnosis of equine colic. Fast localized abdominal sonography of horses (FLASH) enables practitioners with limited experience to perform ultrasonography in emergency settings. However, many practitioners only possess rectal format linear array transducers (RFLT). The hypotheses are: (a) A low frequency curvilinear transducer (LFCT) and RFLT will detect free abdominal fluid and abnormal small intestinal loops with similar frequency during FLASH, and (b) there will be a difference between the transducers for detection of gastric abnormalities and nephrosplenic entrapment. The objective is to compare transcutaneous abdominal ultrasonographic detection of abnormalities in horses presenting with colic using a LFCT and RFLT. Twenty-four horses requiring FLASH for investigation of colic were enrolled. Horses that were too painful to undergo transcutaneous abdominal ultrasonographic examination were excluded. A single investigator performed FLASH on all horses using a RFLT, while one of three other clinicians simultaneously performed FLASH using a LFCT. Comparison of abnormal findings between the two transducers was performed using Chi square, Fisher's exact or Wilcoxon tests. The incidence of identification of abnormal findings was similar between the two transducers for all comparisons except the visibility of the left kidney and stomach (kidney LFCT 81.25% vs. RFLT 22.92%, stomach LFCT 87.5% vs. RFLT 62.5%). While there are limitations to using a RFLT to identify nephrosplenic entrapment of the colon and detection of the stomach, it reliably detects other common abnormalities, including peritoneal effusion, lesions of the small intestine, and changes to the wall of the large colon and cecum.

3-D Contrast-Enhanced Fusion Ultrasound for Accurate Volume Assessment of Vessel Lumen and Plaque in Carotid Artery Disease as Compared With Computed Tomography Angiography

ObjectiveThree-dimensional contrast-enhanced fusion ultrasound (3D-CEFUS) of atherosclerotic carotid arteries provides spatial visualisation of the vessel lumen, creating a lumenography. As in 3D computed tomography angiography (3D-CTA), 3D-CEFUS outlines the contrast-filled lumen. Plaque and vessel contours are distinguished in 3D-CEFUS, allowing plaque volume quantification as a valid estimate of carotid plaque burden. 3D-CEFUS is unproven in inter-modality studies, vindicating the assessment of 3D-CEFUS applicability and comparing 3D-CEFUS and 3D-CTA lumenography as a proof-of-concept study. MethodsUsing an ultrasound system with magnetic tracking, a linear array transducer, and SonoVue contrast agent generated 3D-CEFUS acquisitions by spatial stitching of serial 2D images. From 3D-CEFUS and 3D-CTA imaging, the atherosclerotic carotid arteries were reconstructed with lumenography in an offline software programme for lumen and plaque volume quantification. Bland-Altman analysis was used for inter-image-modality agreement. ResultsThe study included 39 carotid arteries. Mean lumen and plaque volume in 3D-CEFUS were 0.63 cm3 (SD 0.26) and 0.62 cm3 (SD 0.26), respectively. Lumen volume differences between 3D-CEFUS and 3D-CTA were non-significant, with mean difference of 0.01 cm3 (SD 0.02, p = .26) and limits of agreement range (LoA-range) of ±0.11 cm3. Mean plaque volume difference was -0.12 cm3 (SD 0.19, p = .006) with LoA-range of ±0.39 cm3. ConclusionStrong agreement in lumenography between 3D-CEFUS and 3D-CTA was found. The inter-image-modality difference in plaque volumes was substantial due to challenging vessel wall definition in 3D-CTA. 3D-CEFUS is viable in quantifying carotid plaque volume burden and can potentially monitor plaque development over time.

Performance investigation and element optimization of 2D array transducer using Bat Algorithm

Performance investigation and element optimization of 2D array transducer using Bat Algorithm

Ultrasound-Guided Mechanical High-Intensity Focused Ultrasound (Histotripsy) Through an Acoustically Permeable Polyolefin-Based Cranioplasty Device.

Recently, a biocompatible, polyolefin-based cranioplasty device was developed to allow ultrasound (US) transmission into the intracranial space with minimal distortion. In this study, we investigated the in vitro feasibility of applying US-guided histotripsy procedures across the prosthesis. Pressure waveforms and beam profiles were collected for single- and multi-element histotripsy transducers. Then, high-speed optical images of the bubble cloud with and without the prosthesis were collected in water and tissue-mimicking agarose gel phantoms. Finally, red blood cell (RBC) tissue phantom and excised brain tissue experiments were completed to test the ablative efficacy across the prosthesis. Single element tests revealed increased pressure loss with increasing transducer frequency and increasing transducer-to-prosthesis angle. Array transducer measurements at 1 MHz showed average pressure losses of >50% across the prosthesis. Aberration correction recovered up to 18% of the pressure lost, and high-speed optical imaging in water, agarose gels, and RBC phantoms demonstrated that histotripsy bubble clouds could be generated across the prosthesis at pulse repetition frequencies of 50-500 Hz. Histologic analysis revealed a complete breakdown of brain tissue treated across the prosthesis. Conclusion & Significance: Overall, the results of this study demonstrate that the cranial prosthesis may be used as an acoustic window through which intracranial histotripsy can be applied under US guidance without the need for large transcranial array transducers.