Ultrasonics最新文献

In order to investigate the influence of ultrasonic vibration (UV) on microstructural evaluation of amorphous coating, the Fe-based amorphous (Fe_41.5Co_12.2Cr_7.4Mo_37.3C_0.3B_0.5Y_0.4Al_0.4) coatings with and without UV were fabricated by laser cladding technology. The microstructure and corrosion resistance of the coatings were studied in detail to understand the mechanism of the UV on amorphous coatings. It can be found that the cavitation effect generated by UV refines and breaks the columnar crystals at the interface. Compared to the coatings without UV, the average length of columnar crystals of coatings with UV decreases by 57.52 %, reducing from 25.26 ± 5.89 μm to 10.73 ± 3.91 μm. In addition, the sound pressure gradient drives the accelerated flow of the molten pool, resulting in a flow velocity of up to 0.134 m/s. The acoustic streaming effect of UV promotes the uniform distribution of elements and inhibits the segregation of the intermetallic compounds, which increases the amorphous content from 68.5 % to 75.3 %. The acoustic streaming and cavitation effects refine the microstructure and increase the amorphous content by using of UV, which contributes to improve the corrosion resistance.

Recently airborne standing-wave acoustic levitation has seen great advances, and its applicability has been broadened due to the development of cavities constructed with arrays of compact ultrasonic sources. Yet, the numerical methods employed to study and predict the pressure distributions inside these cavities do not consider the effect of multiple reflections on the boundaries, hiding their resonant effects. This work presents an analytical, numerical, and experimental study of the effect of multiple reflections inside ultrasonic cavities based on arrays of transducers exhibiting their influence on the pressure amplitudes of focused standing waves. Our numerical results come from a modified version of the Matrix Method to numerically compute the multiple wave reflections of cavities constructed by two opposite arrays of multiple compact sources as boundaries. The correlation between numerical and experimental results reveals that intra-cavity reflections are relevant in focused axisymmetric cavities based on two arrays of multiple ultrasonic sources having a considerable impact on the amplitude of the standing waves and consequently, on the acoustic levitation performance. Thus, intra-cavity reflections must be considered for optimal cavity designs.

Standard ultrasonic thickness measurements require the sound velocity of the sample to be known and vice versa. We present a method, which we have termed combined mode local acoustic spectroscopy (CoMLAS) for simultaneously determining a plate’s thickness and sound velocities without requiring such a priori knowledge. It is based on a combination of three guided wave modes sustained by a plate at discrete frequencies, which we generate and detect using laser ultrasound. We use a pulsed laser that is shaped into a periodic line pattern on the sample’s surface to generate elastic waves and measure the response at the pattern’s center with a vibrometer. The surface acoustic wave mode produces an interference peak in the response spectrum at the frequency corresponding to the wavelength matching the pattern line spacing. By limiting the total size of the excitation pattern, we can simultaneously generate two zero-group-velocity plate resonances, providing two additional peaks in the spectrum. The plate’s local thickness and longitudinal and transverse sound velocities are calculated from the peak frequencies. We demonstrate the feasibility of CoMLAS on steel and aluminum sheets with a thickness of around 2 mm by resolving thickness steps and temperature-induced changes in the sound velocities. Using numerical simulations and control experiments, we provide insights into the method’s accuracy and limitations. The choice of excitation pattern, the method’s sensitivity, and the influence of sample inhomogeneity and anisotropy are discussed. CoMLAS does not require scanning mechanics and provides local plate properties. The results shown are achieved with low-energy lasers and signal averaging. Considerations on signal-to-noise ratio indicate that a realization with available lasers of higher energy will enable single-shot measurements. This qualifies the method for use on moving samples in an industrial environment.

Acoustic droplet ejection (ADE) has become the preferred method for liquid transfer in a variety of applications including synthetic biology, genotyping and drug discovery.

Comparing with traditional pipetting techniques, the accuracy and data reproducibility of ADE based liquid transfer are improved, waste and cost are reduced, and cross-contamination is eliminated. The key component in the ADE system is the ultrasound transducer, which is responsible for generating focused ultrasound beam for droplet ejection. However, current ADE systems commonly utilize a single-element focused transducer with a fixed focal length that require mechanical movement to focus on the liquid surface, resulting in reduced liquid transfer efficiency. In this study, we first present a high-frequency annular array transducer for the ADE technology, which enables rapid and dynamic axial focusing to the liquid surface without mechanically moving the transducer, thereby accelerating liquid transfer. Experimental results show that the proposed 10 MHz, 5-element annular array transducer has good dynamic axial focusing ability, and can achieve accurate and stable droplet ejection of nanoliter volume at the designed focal length of 26–32 mm. Our results highlight the potential of the annular array transducer in advancing ADE system for rapid liquid transfer. This technology is expected to be useful in a variety of applications where precise and high-throughput liquid transfer is crucial.

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.