Ultrasonics最新文献

To address the problem of the high hardware requirements and insufficient data storage capacity in current ultrasonic imaging testing, a novel approach is developed using a programmable device, which combines spatial-frequency parallel subsampling with the distributed compressive sensing simultaneous orthogonal matching pursuit (DCS-SOMP) algorithm to achieve fast and high-quality ultrasonic imaging inspection with a small amount of subsampled data. The spatial sparse measurement method was employed to achieve spatial subsampling and minimize the count of signals. Additionally, frequency subsampling was utilized to significantly reduce the data volume of time-domain signals while ensuring signal quality by truncating the primary testing frequency components. The subsampled data was then reconstructed using distributed compressive sensing (DCS) for multi-channel data reconstruction. The experiment of ultrasonic scanning imaging was conducted on a carbon steel specimen containing six transverse through-holes with a diameter of Ф1.5 mm at different depths. The ultrasonic signals were acquired using the spatial-frequency parallel subsampling method, and subsequently reconstructed using the DCS-SOMP algorithm. The results show that the proposed method achieves comparable image quality to that obtained with complete data, using only 1/8 of the complete data, while accurately locating and quantifying defects.

Air-coupled transducer with a flat plate structure have many applications in the fields of ground weather observation, ultrasonic defoaming, and directional strong acoustic radiation. In this paper, an analytical equation of the far-field radiation directivity of a fixed boundary ring-excited thin circular plate (RTCP) is deduced using Rayleigh integration method. A finite element model of the RTCP is established, and the relationship between the far-field radiation directivity and the excitation position, excitation area and working frequency is studied by considering the third-order axisymmetric flexural vibration of the RTCP. Computation results show that, for a RTCP, the excitation position has more effect on its radiation directivity. When the plate is excited at the positions between first two nodes, the directivity can be enhanced. When the excitation position is in the trough of the normal displacement curve along radius direction, the side lobes of the radiation directivity of the RTCP are minimized. The area of excitation region has smaller influence on the frequency and radiation directivity of the RTCP. However, working frequency has a great influence on the radiation directivity of the RTCP. When the working frequency is close to the vibration frequency of the circular plate, the sound radiation directivity is the best. A prototype fixed boundary circular plate excited by a longitudinal sandwich transducer was designed and manufactured. For comparison, its finite element model was also setup to simulate its acoustic radiation directivity. Experimental results were found to be in agreement with the theoretical calculations and finite element simulation results.

In observatory seismology, the effective automatic processing of seismograms is a time-consuming task. A contemporary approach for seismogram processing is based on the Deep Neural Network formalism, which has been successfully applied in many fields. Here, we present a 4D network, based on U-net architecture, that simultaneously processes seismograms from an entire network. We also interpret Acoustic Emission data based on a laboratory loading experiment. The obtained data was a very good testing set, similar to real seismograms. Our Neural network is designed to detect multiple events. Input data are created by augmentation from previously interpreted single events. The advantage of the approach is that the positions of (multiple) events are exactly known, thus, the efficiency of detection can be evaluated. Even if the method reaches an average efficiency of only around 30% for the onset of individual tracks, average efficiency for the detection of double events was approximately 97% for a maximum target, with a prediction difference of 20 samples. Such is the main benefit of simultaneous network signal processing.

This study investigates the feasibility of nonlinear coda wave interferometry (NCWI) for evaluating compressive damage in concrete, with a particular focus on the interference caused by the compressive stress-induced slow dynamics. Slow dynamics refers to a phenomenon in which the stiffness of concrete immediately decreases after moderate mechanical conditioning and then logarithmically evolves back to its initial value over time. A series of experiments were conducted to validate this concept. The experimental findings indicate that slow dynamics following the unloading of concrete specimen significantly interfere with NCWI testing. The changes in $\mathrm{dv}/v$ caused by the slow dynamics are opposite to those induced by the pump wave in NCWI. After the slow dynamics have been eliminated, an evaluation indicator, defined as the efficient nonlinear level ${\alpha }_{\mathrm{dv}/v}$, demonstrates an excellent correlation with compressive damage. The value of the indicator decreases with increasing compressive stress. Furthermore, the coda wave interferometry (CWI) and direct wave interferometry (DWI) are performed as comparisons. In summary, the feasibility and superiority of NCWI are demonstrated in concrete compressive damage evaluation.

Ultrafast ultrasound Doppler imaging facilitates the assessment of cerebral hemodynamics with high spatio-temporal resolution. However, the significant acoustic impedance mismatch between the skull and soft tissue results in phase aberrations, which can compromise the quality of transcranial imaging and introduce biases in velocity and direction quantification of blood flow. This paper proposed an aberration correction method that combines deep learning-based skull sound speed modelling with ray theory to realize transcranial plane-wave imaging and ultrafast Doppler imaging. The method was validated through phantom experiments using a linear array with a center frequency of 6.25 MHz, 128 elements, and a pitch of 0.3 mm. The results demonstrated an improvement in the imaging quality of intracranial targets when using the proposed method. After aberration correction, the average locating deviation decreased from 1.40 mm to 0.27 mm in the axial direction, from 0.50 mm to 0.20 mm in the lateral direction, and the average full-width-at-half-maximum (FWHM) decreased from 1.37 mm to 0.97 mm for point scatterers. For circular inclusions, the average contrast-to-noise ratio (CNR) improved from 8.1 dB to 11.0 dB, and the average eccentricity decreased from 0.36 to 0.26. Furthermore, the proposed method was applied to transcranial ultrafast Doppler flow imaging. The results showed a significant improvement in accuracy and quality for blood Doppler flow imaging. The results in the absence of the skull were considered as the reference, and the average normalized root-mean-square errors of the axial velocity component on the five selected axial profiles were reduced from 17.67% to 8.02% after the correction.

Piezoelectric composite ceramics, as the key components of ultrasonic transducers, have their vibration modes, electromechanical coupling performance, and acoustic impedance closely related to the volume fraction of ceramics. This study employed a novel digital light processing 3D printing technique (DLP) to fabricate 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT)-based 1–3 piezoelectric composite ceramics with different ceramic volume fractions (15.6 %, 23.5 %, 36.2 %, 48.4 %, 59.5 %). It demonstrates the suitability of the DLP process for the fabrication of 1–3 piezoelectric composite ceramics and investigates the influence of ceramic volume fraction on the performance of these ceramics. When the piezoelectric ceramic volume fraction was 59.5 %, the piezoelectric coefficient effective d₃₃ of the 1–3 piezoelectric composite device reached 315 pC/N, demonstrating excellent piezoelectric performance. The acoustic impedance Z was 16.3 MRayl, and the thickness electromechanical coupling coefficient k_t was 0.55, indicating high energy conversion efficiency. The air-coupled ultrasonic transducer prepared from the 1–3 piezoelectric composite ceramics with a ceramic volume fraction of 59.5 % exhibited a round-trip insertion loss (IL) of −70.32 dB and a −6 dB bandwidth (BW_-6dB) of 7.42 %. This work provides a more convenient and new method for the preparation of lead-free piezoelectric ceramic ultrasonic transducers.

Numerical analyses are performed to investigate ultrasonic wave propagation in fluid–solid half-spaces subject to a directional source. This research is particularly concerned with the behavior of refracted waves within fluid mediums and their utility in determining the acoustic velocities of solid materials. The simulations encompass solids with various mechanical parameters and highlight the influence of incident angles on wave propagation. The analysis reveals that as the disparity between incident and critical angles increases, both the dominant frequencies and amplitudes of the corresponding refracted waves decrease substantially, which is detrimental to the accurate extraction of solid velocities. For the low-velocity solid characterized by its shear wave velocity being less than the fluid’s acoustic velocity, refracted longitudinal waves are susceptible to interference from direct and reflected waves. This interference often results in underestimated velocity measurements. The challenge can be addressed by either extending the source-receiver offset or by adjusting the incident angle closer to the critical angle. Regarding solids with shear wave velocities exceeding the fluid’s acoustic velocity, although the velocity–time correlation (VTC) method can accurately determine longitudinal wave velocities, shear wave velocity extraction may be compromised by the presence of the leaky Rayleigh wave. We further compare velocities calculated by dividing the spacing distance of two receivers by the time difference of their respective wave packet arrivals. Results indicate that the initial trough and peak of the S wave packet are predominantly influenced by refracted shear waves and the leaky Rayleigh wave, respectively. This occurs because refracted shear waves propagate slightly faster than the leaky Rayleigh wave. Consequently, using the first trough of the shear wave packet as the wave onset can mitigate the impact of the leaky Rayleigh wave, yielding precise shear wave velocity measurements. These studies are of considerable importance for applications in geophysical downhole measurements and nondestructive testing.

High-temperature ultrasonic transducer (HTUT) is essential for non-destructive testing (NDT) in harsh environments. In this paper, a HTUT based on BiScO₃-PbTiO₃ (BS-PT) piezoelectric ceramics was developed, and the effect of different backing layers on its bandwidth were analyzed. The HTUT demonstrates a broad bandwidth and excellent thermal stability with operation temperature up to 400 °C. By using a 10 mm thick porous alumina backing layer, the HTUT achieves a broad −6 dB bandwidth of 100 %, which is about 4 times superior to the transducer with an air backing layer. The center frequency (f_c) of the HTUT remains stable with fluctuations of less than 10 % across the temperature range from room temperature to 400 °C. The HTUT successfully detected simulated defects in pulse-echo mode for NDT over 200 °C. This research not only advances high-temperature ultrasonic transducer technology but also expands the NDT applications in harsh environmental conditions.

Underwater inspection is important to ensure the safety, integrity and functionality of underwater structures. Although numerous conventional methods have been adopted for underwater inspection, successful application of most methods relies on the surface condition of the object, which, however, is typically covered by marine growth. Consequently, routine inspection requires thorough cleaning of marine growth, which is time-consuming and costly. Hence a method which can inspect objects without the need for extensive surface cleaning is necessary. Two methods have the potential to achieve this: pulse eddy current (PEC) and electromagnetic acoustic transducer (EMAT). PEC attains a significant lift-off distance, enabling inspection through marine growth. However, it suffers from high sensitivity to environmental conditions and low inspection accuracy due to ‘relative’ property which means its results are interpreted by comparing received signals to reference values. In contrast to PEC, EMAT provides ‘absolute’ measurements, ensuring precise results in the inspection. But it is limited by a small lift-off distance ($<2\sim$3 mm), rendering it unsuitable for underwater applications with marine growth. Therefore, if the lift-off distance can be enhanced to a specific value, this method may offer a superior solution for underwater inspections. In this paper, a quantitative measurement method is proposed through employing a shear wave EMAT with high lift-off performance. A repelling configuration of magnets is introduced to achieve a significantly improved maximum effective lift-off distance of up to 5 mm in both air and seawater conditions with only 400 Vpp applied. This EMAT is then demonstrated to measure thickness through marine growth, showing excellent underwater performance in quantitative thickness mapping for corrosion inspection.