Ultrasonics最新文献

Sapphire ultrasonic vibration-assisted flexible polishing (UVAFP) is a promising technique for comprehensively improving the surface integrity of machined parts. The technique was performed on an ultra-precision machine tool with the in-situ monitoring systems in this paper, which aims to provide a new perspective for understanding the material removal mechanisms in the sapphire UVAFP process. A Taguchi L₉ (4³) orthogonal experiment was conducted to investigate the effects of feed distance, spindle speed, ultrasonic vibration (UV), and polishing time on the surface finish and material removal in the process. In addition, the effect of a polyurethane ball tool is not trivial. A single-factor experiment was conducted for exploring it. Based on a laser displacement measurement system and an acoustic emission sensor system, the characteristics of time-dependent ultrasonic amplitude and ultrasonic frequency for the sapphire UVAFP system were analyzed, with the effectiveness of UV demonstrated. Based on a three-component force measurement system, the characteristics of normal force and its relationship with process parameters and tool deformation were analyzed, with macro- and micro-level examined. In conclusion, this paper presents the characterization of UV and polishing force in the sapphire UVAFP process, providing novel insights into understanding the material removal mechanisms of sapphire and even more manufacturing problems.

The use of particle localisation and tracking algorithms on Contrast Enhanced Ultrasound (CEUS) or other ultrasound mode image data containing sparse microbubble (MB) populations, can produce super-resolved vascularization maps. Typically such data stem from conventional delay and sum (DAS) beamforming that is used widely in ultrasound imaging modes. Recently, adaptive beamforming has shown significant improvement in spatial resolution, but its value to super-resolution image analysis approaches is not fully understood. The in silico study here evaluates the performance of combining minimum variance beamformers (MV BF), established to provide improved lateral resolution, compared to DAS BFs with single particle detection. The isolated effect of a range of simplified image-affecting factors such as flow profile, pulse length, noise, vessel separations and data availability is considered. The study aims to assess the vessel recovery performance using the different beamformers and investigate the link with MB detection and localisation. The MV BF was shown to provide improved microvessel position accuracy compared to conventional DAS BFs. In particular, vessel separations between 0.3–4 λ provided superior localisation uncertainty with the MV. In addition, for a separation of 0.36λ, vessel recovery was achieved with both methods but the use of MV eliminated artifacts that appear as additional vessels. These results were found to be linked to improved MB detection and localisation for the MV BF, which is proposed as suitable for testing in Ultrasound Localisation Microscopy (ULM) imaging using patient data.

This paper offers a comprehensive critical appraisal and experimental comparison of leading linear baseline-free techniques applied in guided wave-based structural health monitoring (GWSHM). The paper extensively examines the most popular linear baseline-free techniques, namely Time Reversal (TR), Virtual Time Reversal (VTR), Instantaneous Baseline (IB), and reciprocity-based methods. Detailed discussions on the principles, strengths, and limitations of each technique provide a thorough understanding of their capabilities and challenges. Critical factors affecting performance that influence the performance of baseline-free techniques in damage detection and localization is the main focus of the paper. These factors encompass varying environmental conditions such as temperature fluctuations, geometric and structural complexities, and diverse damage scenarios.

The research reported conducts experimental comparisons among VTR, IB, and reciprocity-based techniques as related to the challenging case of composite materials, considering single and dual Barely Visible Damage (BVID) scenarios, temperature variations, boundary reflections, and structural complexities like stiffeners. The results demonstrate that the investigated baseline-free techniques are capable of identifying and localizing damages, albeit with differing capabilities.

Medical Speed-of-sound (SoS) imaging, which can characterize medical tissue properties better by quantifying their different SoS, is an effective imaging method compared with conventional B-mode ultrasound imaging. As a commonly used diagnostic instrument, a hand-held array probe features convenient and quick inspection. However, artifacts will occur in the single-angle SoS imaging, resulting in indistinguishable tissue boundaries. In order to build a high-quality SoS image, a number of raw data are needed, which will bring difficulties to data storage and processing. Compressed sensing (CS) theory offers theoretical support to the feasibility that a sparse signal can be rebuilt with random but less sampling data. In this study, we proposed an SoS reconstruction method based on CS theory to process signals obtained from a hand-held linear array probe with a passive reflector positioned on the opposite side. The SoS reconstruction method consists of three parts. Firstly, a sparse transform basis is selected appropriately for a sparse representation of the original signal. Then, considering the mathematical principles of SoS imaging, the ray-length matrix is used as a sparse measurement matrix to observe the original signal, which represents the length of the acoustic propagation path. Finally, the orthogonal matching pursuit algorithm is introduced for image reconstruction. The experimental result of the phantom proves that SoS imaging can clearly distinguish tissues that show similar echogenicity in B-mode ultrasound imaging. The simulation and experimental results show that our proposed method holds promising potential for reconstructing precision SoS images with fewer signal samplings, transmission, and storage.

Background

Amyotrophic lateral sclerosis (ALS) is marked by the deterioration of both cortical and spinal cord motor neurons. Despite the underlying causes of the disease remain elusive, there has been a growing attention on the well-being of cortical motor neurons in recent times. Focused ultrasound combined with microbubbles (FUS/MB) for opening the blood–brain barrier (BBB) provides a means for drug delivery to specific brain regions, holding significant promise for the treatment of neurological disorders.

Objectives

We aim to explore the outcomes of FUS/MB-mediated delivery of arctiin (Arc), a natural compound with anti-inflammatory activities, to the cerebral motor cortex area by using a transgenic ALS mouse model.

Methods

The ALS mouse model with the SOD1^G93A mutation was used and subjected to daily Arc administration with FUS/MB treatment twice a week. After six-week treatments, the motor performance was assessed by grip strength, wire hanging, and climbing-pole tests. Mouse brains, spinal cords and gastrocnemius muscle were harvested for histological staining.

Results

Compared with the mice given Arc administration only, the combined treatments of FUS/MB with Arc induced further mitigation of the motor function decline, accompanied by improved health of the gastrocnemius muscle. Furthermore, notable neuroprotective effect was evidenced by the amelioration of motor neuron failure in the cortex and lumbar spinal cord.

Conclusion

These preliminary results indicated that the combined treatment of FUS/MB and arctiin exerted a potentially beneficial effect on neuromuscular function in the ALS disease.

Aluminum honeycomb sandwich structure has been widely used in the aeronautic and astronautic fields. As the core part, aluminum honeycomb needs to be machined but defects are easily generated. Ultrasonic cutting is an advanced machining technology for honeycomb materials due to improved machining quality. However, ultrasonic cutting aluminum honeycomb by straight-blade knife is usually accompanied by cell wall deformation, which results in poor machining quality. To facilitate the industrial use of ultrasonic cutting aluminum honeycomb with a straight-blade knife, a finite element (FE) model was developed, and experimental studies had been performed. The effects of the blade-inclined angle and lead angle of the straight-blade knife were studied by analyzing the cutting force, the stress and deformation in the cutting zone. Results showed that the cell wall deformation was significantly suppressed when cutting with a corresponding blade-inclined angle and a lead angle. Meanwhile, effects of ultrasonic cutting parameters on the cell wall deformation were also studied, indicating that a well-machined cell wall could be obtained when cutting with large ultrasonic amplitude.

Non-contact ultrasonic testing of debonding in honeycomb sandwich structure has been a major challenge in industry. In this study, the air-coupled local defect resonance (LDR) technique with coda wave analysis is proposed for nondestructive testing (NDT) of debonding in honeycomb sandwich structure. Numerical simulations have been conducted to visualize the LDR behavior of debonding in honeycomb sandwich structure by air-coupled excitations, and a decorrelation analysis method is proposed for determining the interval of coda wave from received signals. Results indicate that the start moment of coda wave should be determined as the time corresponding to decorrelation coefficient exceed to 0.2 and the duration is 2.5 ms. Air-coupled LDR scanning experiments were conducted on the honeycomb sandwich specimens with different deboning. Experimental results indicate that the proposed technique is effective for NDT of the debonding in honeycomb sandwich structures. The research provides an efficiency non-contact ultrasonic NDT method for honeycomb sandwich structure.

Ultrasound Localization Microscopy (ULM) facilitates structural and hemodynamic imaging of microvessels with a resolution of tens of micrometers. In ULM, the extraction of effective microbubble signals is crucial for image quality. Singular Value Decomposition (SVD) is currently the most prevalent method for microbubble signal extraction in ULM. Most existing ULM studies employ a fixed SVD filter threshold using empirical values which will lead to imaging quality degradation due to the insufficient separation of blood signals. In this study, we propose an adaptive and non-threshold SVD filter based on canopy-density clustering, termed DCC-SVD. This filter automatically classifies the components of the SVD based on the density of their spatiotemporal features, eliminating the need for parameter selection. In in vitro tube phantom, DCC-SVD demonstrated its ability to adaptive separation of blood and bubble signal at varying microbubble concentrations and flow rates. We compared the proposed DCC-SVD method with the Block-match 3D (BM3D) filter and a classical adaptive method called spatial similarity matrix (SSM), using concentration-variable in vivo rat brain data, as well as open-source rat kidney and mouse tumor datasets. The proposed DCC-SVD improved the global spatial resolution by approximately 4 μm from 30.39 μm to 26.02 μm. It also captured vessel structure absent in images obtained by other methods and yielded a smoother vessel intensity profile, making it a promising spatiotemporal filter for ULM imaging.

It is essential to characterize the high-field properties of piezoelectric composites for their applications in ultrasonic transducers. This study involved the development of an experimental characterization system of piezoelectric impedance spectra and mechanical quality factors under high-field conditions to analyze the properties of PMN-PT piezoelectric single-crystal composites. The impedance spectra and mechanical quality factors of a [0 0 1]_c-poled 0.69PMN-0.31PT single crystal/epoxy 1–3 composite disk with filling ratio φ = 0.4 under thickness resonance mode were tested at different driving voltages ranging from 1 to 120 V_pp to explore the influence of AC electric field on the material properties. By utilizing a theoretical approach, an evaluation was conducted on the variations in the material properties such as stiffness, permittivity, piezoelectric coefficient, and electromechanical coupling factor, along with respective loss factors. Our results suggest that as the AC electric field increases, the elastic modulus $c_{33}^D$ and the mechanical quality factor Q_m decrease, while the piezoelectric strain coefficient d₃₃ and the electromechanical coupling factor k_t increase. However, the dielectric coefficient ${\epsilon }_{33}^X$ does not show an obvious change in this field range. Furthermore, the elastic loss factor $\tan \varphi$, the dielectric loss factor $\tan {\delta }_{33}^{\prime }$, the piezoelectric loss factor $\tan {\theta }_{33}^{\prime }$, and the electromechanical coupling loss factor $\tan {\chi }_t$ all increase, indicating that the loss of the piezoelectric composite becomes more evident as the AC electric field grows.