Carbon Fiber Reinforced Polymers (CFRP) are extensively utilized in high-performance engineering, yet localized structural discontinuities can severely compromise their integrity. This paper aims to achieve high-sensitivity characterization of such anomalies using a proposed acoustic shearography technique based on continuous acoustic excitation. A comprehensive finite element model (FEM) was developed to clarify the mechanical-energy coupling between the acoustic fields and localized surface strain field modulations. By exploiting ultrasonic energy coupling, the localized features of discontinuities were identified through full-field, non-contact optical measurement of localized phase distortions. Key parameters, including shearing amount, excitation frequency, driving voltage, and geometric characteristics of blind flat-bottom holes (BFBH), were systematically investigated. The results demonstrate a high correlation between FEM simulations and experimental observations quantitatively elucidating how defect diameter and hole depth modulate surface strain distributions. The proposed hybrid acoustic optical approach achieves near-instantaneous full field imaging within a millisecond timeframe typically under 200 ms. Additionally, the methodology leverages localized acoustic resonance to significantly boost the signal-to-noise ratio (SNR) resulting in highly quantified phase map contrast.

We conduct a chronological, sedimentological and palynological study of the YMZ11 borehole from East Lake (Wuhan) covering the last 15,000 cal yr BP, to clarify linkages among local hydroclimate, lake evolution, and human activity. Main stages are identified: Delta deposition occurred during the warm B & oslash;lling-Aller & oslash;d interval, with mixed coniferous-broad-leaved forests and few evergreens. The cold-wet Younger Dryas after 12,800 cal yr BP favored coniferous forests, reduced ferns and expanded herbs, triggering lake formation. A rapid rise in broadleaved trees in the early Holocene revealed warm-wet conditions, maintaining relatively stable and deep lake levels, and favoring human settlements on highlands. Warm-dry conditions between 6000 and 3300 cal yr BP supported sparse ferns and shallow lake levels. This interval was characterized by land exposure, lowland settlements, facilitated rice domestication, and increased wildfires. After 3300 cal yr BP, a shift to cool-wet condition promoted an increase in coniferous trees relative to broad-leaved trees, stable and deep lake conditions, and expansion of the Paleo-Yunmengze Lakes. The increasing dominance of anthropogenic activities over natural processes is evidenced by intensified metal use and growing population, although high humidity limited lowland settlements. Holocene water-level at East Lake followed a relatively deep-shallow-deep pattern, consistent with records from Dongting Lake, Dajiuhu Peatland and flood/lake-level sequences in the middle Yangtze River. These limnological changes corresponded to a wet-dry-wet hydroclimate trend. The relationship between Holocene hydroclimate and human activities in the Middle Yangtze Valley was characterized by a shift from water-driven human migration to human-water coexistence. Our results yield vital references for monsoonal hydroclimateJianghan Lakes interactions, as well as for human adaptation to future climate change.

Mollisols (black soils) are the most fertile and productive soils worldwide, yet intensive cultivation has caused severe degradation, including decline in soil organic matter (SOM) content. However, the fundamental processes in the transformation and turnover dynamics of carbon fractions under cultivation remain unclear. Here we used natural stable carbon isotope (δ13C) and C/N ratios of bulk SOM and mineral-associated organic matter (MAOM), and accelerator mass spectrometry radiocarbon (AMS 14C) dating analysis of five profiles and 30 pairs of cropland/natural topsoil samples from Phaeozems along a latitude transect to elucidate cultivation-induced SOM dynamics. Cropland topsoils showed higher δ13C values (mean −22.9‰, ranging from −18.8‰ to −25.5‰) than natural topsoils (mean −25.2‰, from −21.9‰ to −27.7‰), suggesting influence of cultivated corn (C4 plant). Below the plough horizon (0–20 cm), grassland-dominated profiles exhibited upward increases in δ13CSOC due to late-Holocene C4 grass expansion, while forest-region profiles showed downward increases in δ13CSOC, mostly due to increasing contributions of microbial-derived organic matter as evidenced by the downward decreasing C/N ratios of both SOM and MAOM. An average enrichment of 1.5‰ ± 1.3‰ in 13C of SOC from 20 cm to 0 cm within the plough horizon indicated that corn residues contributed 28% ± 13% to SOC. δ13CMAOC was lower than δ13CSOC by 0.63‰ at 0–5 cm and by 0.23‰ at 15–20 cm, suggesting progressive transfer of corn-derived C from particulate organic matter (POM) to MAOM from surface downward. Variations in δ13C profiles within the plough horizon suggest the various impacts of corn cultivation on C transfer and transformation from POM to MAOM, both temporally along the soil profiles and geographically across Mollisols in Northeast China.

Ultrasonics structural health monitoring (SHM) is widely recognized as an effective technique that enables early damage detection in large-scale structures and helps prevent potential catastrophic failures. Ultrasonic phased array technology has gained prominence in SHM due to its ability to inspect a large area with high spatial resolution. However, conventional systems often rely on physical wired sensor networks, limiting their deployment for hard-to-access regions. In this study, we present a wireless ultrasonic phased array system capable of dual-mode operation for both wall thickness measurement and structural damage detection. The system integrates wireless power transfer (WPT) modules and customized matching circuits, enabling efficient and flexible deployment. Proof-of-concept experiments demonstrate successful wall thickness evaluation and accurate defect localization in metallic structures using both delay-and-sum (DAS) and minimum variance (MV) imaging methods, with the MV algorithm offering improved imaging resolution. Future work will focus on advancing real-time monitoring through machine learning, enabling 3D imaging, and extending system applicability to anisotropic composite materials.

In order to explore the interactions among human activities, hydroclimate, and sea-river-lake level fluctuations in the mid-lower Yangtze Valley since the Neolithic, this study, based on AMS 14C and OSL dating of the Core JH002 along with geophysics, geochemistry, and microfossils, reconstructs the hydroclimate changes, sedimentary evolution, and human adaptations in the Jianghan Plain since 13,000 cal a BP. The results show that solar radiation controlled the intensity of the East Asian monsoon. Meanwhile, 5 wet-dry climate alternation phases and 30 flood-prone periods were identified. Hydroclimates and sea level changes affected the regional environment evolution and human activities. During 13,000-11,700 cal a BP (transition of Paleolithic and Neolithic), high-energy riverbed environments and extreme floods constrained human activities, with the riverbed linked to the deeply incised valleys from the Last Glacial Maximum and low sea levels during the Younger Dryas period. During 11,700-7800 cal a BP (early Neolithic), the elevated river and lake water levels caused by warm-wet conditions and rising sea levels created wetlands, facilitating human activities. The earliest evidence of human activities in the interior of Jianghan Plain dates back to about 11,300 cal a BP. From 7800 to 4000 cal a BP (mid-late Neolithic), frequent typical floods and a turbulent delta environment collectively hindered human activities. During 4000-3000 cal a BP (Xia-Shang Dynasties), high water level and expansion of Paleo-Yunmeng Lake Group limited human activities such as rice cultivation. Since 3000 cal a BP, improved water management allowed Chu people to coexist with floods, leading to the prosperity of Chu Culture. This study offers critical insights into the interactions between regional environment changes, ancient culture evolution, and human adaptations in the Yangtze region.

Nondestructive characterization of elastic constants for laminated composites is critical for certifying manufactured composites before their use in various engineering applications. This paper presents an ultrasonic guided wave-based inversion approach, which leverages (i) noncontact laser Doppler vibrometry, (ii) frequency-wavenumber analysis, as well as (iii) an inversion algorithm with a unique objective function based on Legendre orthogonal polynomial expansion (LOPE) and genetic algorithm (GA) optimization, for determining the elastic constants of laminated composites. To implement this approach, laser vibrometry is used to acquire time-space wavefields of guided waves. The wavefields are then transformed into frequency-wavenumber spectra via multi-dimensional Fourier transform, unveiling the frequency-wavenumber relations in different directions, which are subsequently processed by our LOPE-based inversion algorithm. Particularly, this algorithm allows for robustly determining multiple elastic constants without requiring guided wave mode identification. Additionally, it is a generalized approach applicable to laminated composites with various anisotropic lamina properties and layups.

Underground or underwater pipe-like structures are usually subjected to corrosion or plastic deformation, during which the micro-cracks probably appear and gradually evolve into macro-cracks, resulting in the leakage of pipes. Therefore, to avoid catastrophic accidents, it is necessary to locate micro-cracks accurately and repair or replace pipes in time. Wave mixing has the advantages of micro-crack localization compared with second harmonics, and it can avoid the interference of nonlinearities in measurement systems. However, few reports are available on nonlinear mixing of counter-propagating guided waves caused by contact acoustic nonlinearity (CAN) in pipes. In this paper, the interaction of the guided wave mixing and micro-cracks in pipe-like structures is theoretically and numerically investigated via CAN and vector analyses, as well as pulse-inversion techniques and two-dimensional fast Fourier transforms (2D-FFT), respectively. It is theoretically demonstrated that the amplitudes of second-order harmonics increase monotonically with e0/e0, while the amplitudes of third-order harmonics first increase and then drop with e0/e0. In simulations, nonlinear mixing of counter-propagating guided waves occurs in the regions that contain micro-cracks, and the generated difference-frequency components or sum-frequency components propagate to both ends of pipes at the same time. The difference-frequency components mainly contain F(m,1) modes, and the sum-frequency components mainly contain F(m,2) modes and F(m,3) modes, which are predicted in advance by theoretical investigations. In addition, the normalized amplitudes of difference-frequency components and sum-frequency components exhibit "mountain-shape" trends between 0 degrees and 90 degrees as well as during 90 degrees and 180 degrees, with the peaks corresponding to micro-crack angles of 45 degrees and 135 degrees Note that they reach the minimums when angles of micro-cracks equal to 0 degrees, 90 degrees or 180 degrees, which is in a good agreement with the theoretical investigations. Finally, the z-coordinates of micro-cracks can be determined by the relationship between the normalized amplitudes of difference-frequency components or sum-frequency components and positions of mixing zones. The rp-coordinates of micro-cracks can be obtained based on normalized amplitudes of difference-frequency components in Uz with respect to rp-coordinates.

The development of smart materials capable of dynamic shape morphing and rapid responsiveness has garnered significant interest for applications in soft robotics, tissue engineering, programmable materials, and adaptive structures. Hydrogels, owing to their intrinsic biocompatibility and flexibility, are promising candidates for such systems. Embedding micro- scale materials within hydrogel networks can further enhance their mechanical and functional properties. In this study, we present a hybrid fabrication platform that integrates surface acoustic wave (SAW)-based acoustofluidics with digital light processing (DLP) photopolymerization to fabricate smart hydrogel composites with programmable shape-memorable behavior. Using the SAW-induced acoustic potential field, silicon carbide (SiC) micro-whiskers are aligned within a custom UV-curable hydrogel ink and subsequently fixed via high-resolution DLP photopolymerization. This dual-control approach enables independent manipulation of micro-whisker orientation and structural geometry. Numerical simulations and Laser Doppler vibrometry-based validation were employed to characterize the acoustic field. To evaluate shape-memory behavior, the fabricated hydrogels were subjected to dehydration and rehydration cycles. The resulting shape transformations, driven by internal stress gradients within the aligned microparticle framework, enabled humidity-responsive actuation. This work establishes a novel strategy for constructing 4D-printed smart hydrogels, offering a versatile platform for the development of next-generation programmable materials and adaptive structures.

Guided wave phased arrays, which use multiple sensors in compact patterns to perform damage imaging through phase delays, have garnered significant interest for the rapid inspection of large composite panels. Previous phased arrays typically used large, wired ultrasonic transducers attached to composites, limiting array reconfigurability and preventing contactless inspection from a distance. This study presents a fully noncontact guided wave phased array imaging approach, which utilizes a dual laser-based guided wave generation and sensing system, namely a pulsed laser-scanning laser Doppler vibrometer (PL-SLDV) system, along with synthetic phased array beamforming and wavefield analysis. The PL-SLDV system employs a Q-switched PL module to generate nanosecond laser pulses that excite ultrasonic guided waves through the thermoelastic effect. To ensure consistent laser-to-ultrasound energy conversion across different composites and prevent potential thermal damage to composites, the laser pulses are directed onto a thin aluminum patch bonded on the composite. The SLDV acquires guided wave signals based on the Doppler effect, and its integrated galvo mirrors can quickly steer laser beam directions to scan a composite plate, thereby acquiring guided wave signals at various array points. Time/phase delays are then applied to the acquired signals through post-processing for synthetic phased array beamforming. To generate inspection images using the acquired wave signals, an improved delay-and-sum (DAS) imaging algorithm is introduced. It uses adaptive weighting factors and incorporates phase delay and back-propagation phase shift, accounting for the frequency- and direction-dependent dispersion relation, to overcome the dispersion effect and directional dependency of waves in anisotropic materials. Moreover, the fusion of phased array imaging and a wavefield analysis approach, which can extract frequency-wavenumber dispersion relations from experimental wavefields, enables our phased array method to perform damage imaging without requiring prior knowledge of composite properties, such as mechanical properties or theoretical dispersion curves. Additionally, the noncontact wave generation/acquisition feature of our PL-SLDV system allows for inspecting composites from a distance and easily constructing phased arrays with different patterns. Proof-of-concept experiments demonstrate that multiple defects in different directions can be successfully detected. Additionally, this study reveals that PL-generated guided waves can contain multiple modes, such as A0, S0, SH0, A1, S1, and SH1 modes, offering valuable insights for researchers interested in using PL-generated guided waves.

With the growing application of composite materials in sectors such as aerospace, automotive, and wind energy, accurately assessing their mechanical properties is critical for effective non-destructive testing (NDT) and structural health monitoring (SHM). In this paper, a three-dimensional finite element model was developed to generate the fundamental A0 Lamb wave mode within an 8-layer orthotropic laminate, addressing the complexities associated with the anisotropic behavior of composites. Utilizing the Legendre Orthogonal Polynomial Expansion (LOPE) method, we characterized the wave number profile, revealing significant directional dependence in wave propagation across multilayer laminates. The results demonstrated strong agreement between the analytical predictions from the LOPE method and the finite element simulations, confirming the robustness of our modeling approach. Additionally, we introduced an innovative omnidirectional wavefield representation method, effectively mitigating the influence of phase and group velocity steering angles. These findings enhance our understanding of guided wave dynamics in composite materials, offering valuable insights for the development of more effective detection strategies and assessments of structural integrity in complex composite systems.

Ultrasonic guided wave detection technology can feasibly measure and monitor the state of charge. The experimental studies in a customized cell were also performed to acquire the relationship between guided waves generated in a pitch-catch mode and battery states of charge (SOC). An analytical acoustic model was developed to model the guided wave propagation characteristics of lithium-ion battery with different SOC. The multi-layered and porous structure of lithium-ion battery was considered by combining the state-vector formalism and the Legendre polynomial method with the Biot theory. Concurrently, the chemo-mechanical coupling problem in the electrochemical reaction process was considered by using the Mechanics of Incremental Deformations theory. Based on this, the relationships between structural characteristics, dynamic coupling characteristics, state of charge and guided wave behavior in commercial lithium-ion batteries were numerically analyzed. The feasibility and accuracy of the numerical model were proved by the comparison of previous experimental time of flight results (Ladpli et al., 2018) [1] and its corresponding theoretical solutions. Furthermore, the extracted experimental time of flights was in good agreement with the theoretical results. The mapping relationship between the state of charge and the propagation characteristics lays a foundation for the nondestructive evaluation and quantitative estimation of the state characteristics of lithium-ion batteries.

AbstractSurface acoustic waves (SAWs) have shown great potential for developing sensors for structural health monitoring (SHM) and lab‐on‐a‐chip (LOC) applications. Existing SAW sensors mainly rely on measuring the frequency shifts of high‐frequency (e.g., >0.1 GHz) resonance peaks. This study presents frequency‐locked wireless multifunctional SAW sensors that enable multiple wireless sensing functions, including strain sensing, temperature measurement, water presence detection, and vibration sensing. These sensors leverage SAW resonators on piezoelectric chips, inductive coupling‐based wireless power transmission, and, particularly, a frequency‐locked wireless sensing mechanism that works at low frequencies (e.g., <0.1 GHz). This mechanism locks the input frequency on the slope of a sensor's reflection spectrum and monitors the reflection signal's amplitude change induced by the changes of sensing parameters. The proof‐of‐concept experiments show that these wireless sensors can operate in a low‐power active mode for on‐demand wireless strain measurement, temperature sensing, and water presence detection. Moreover, these sensors can operate in a power‐free passive mode for vibration sensing, with results that agree well with laser vibrometer measurements. It is anticipated that the designs and mechanisms of the frequency‐locked wireless SAW sensors will inspire researchers to develop future wireless multifunctional sensors for SHM and LOC applications.

The Quaternary transgression had a significant impact on environmental changes and ancient human activities in eastern China. However, due to the lack of reliable core records, the history of the transgression and its impact on human activities along the eastern coast of Zhejiang Province remains unclear. Here, multi-proxy indicators including lithology, AMS14C dating, grain size, total organic carbon (TOC), total nitrogen (TN), elemental geochemistry, and microfossils in a new core (QTZ1) from the Wenzhou Coastal Plain (WCP) are employed to reconstruct sedimentary evolution, which experienced four phases as follows: (1) The terrestrial environment dominated by delta facies (before 11,700 cal a BP); (2) The marine-terrestrial transitional environment dominated by littoral facies (11,700-9,400 cal a BP); (3) The marine environment dominated by shallow marine facies (9,400-6,200 cal a BP), including the Holocene transgression maximum occurred during 8,400-7,400 cal a BP; (4) The marine-terrestrial transitional environment marked by littoral facies (after 6,200 cal a BP). A comparative analysis on the Holocene transgression intensity, as reconstructed by Sr/Ba in the WCP, and archaeological sites in the Ningshao Plain indicates that the ancestors gradually migrated to the eastern low-elevation plains and developed Neolithic rice cultivation after the transgression maximum. Our results sheds light on the correlation between the Holocene transgression, sedimentary evolution, and ancient human activities in Zhejiang Coastal Plain, providing valuable insights into Quaternary environmental changes and human adaptations in the eastern China.

This study investigates viscoelastic guided wave properties (e.g., complex–wavenumber–, phase–velocity–, and attenuation–frequency relations) for multiple modes, including different orders of antisymmetric, symmetric, and shear horizontal modes in viscoelastic anisotropic laminated composites. To obtain those frequency–dependent relations, a guided wave characteristic equation is formulated based on a Legendre orthogonal polynomials expansion (LOPE)–assisted viscoelastodynamic model, which fuses the hysteretic viscoelastic model–based wave dynamics and the LOPE–based mode shape approximation. Then, the complex–wavenumber–frequency solutions are obtained by solving the characteristic equation using an improved root–finding algorithm, which leverages coefficient matrix determinant ratios and our proposed local tracking windows. To trace the solutions on the dispersion curves of different wave modes and avoid curve–tracing misalignment in regions with phase–velocity curve crossing, we presented a curve–tracing strategy considering wave attenuation. With the LOPE–assisted viscoelastodynamic model, the effects of material viscosity and fiber orientation on different guided wave modes are investigated for unidirectional carbon–fiber–reinforced composites. The results show that the viscosity in the hysteresis model mainly affects the frequency–dependent attenuation of viscoelastic guided waves, while the fiber orientation influences both the phase–velocity and attenuation curves. We expect the theoretical work in this study to facilitate the development of guided wave–based techniques for the NDT and SHM of viscoelastic anisotropic laminated composites.

Pipes are widely used in various industries but are subject to plastic deformation and corrosion, during which microcracks may appear. Ultrasonic guided wave mixing has gained attention due to its high sensitivity. This study employs phase inversion and two-dimensional Fourier transform to investigate the nonlinear interaction between counter-propagating guided waves and microcracks. The generated sum-frequency components and difference-frequency components contain multiple flexural modes and propagate toward both ends of the pipeline. The generated sum-frequency components and difference-frequency components are used to locate the microcracks. The circumferential location of the microcracks is determined by polar diagrams (i.e., the amplitudes of difference-frequency or sum-frequency components and angles), while the axial location is determined by the relationship between the amplitudes of difference-frequency components or sum-frequency components and distance.

Dispersion characterization is crucial for nondestructive testing (NDT) and structural health monitoring (SHM). To understand the propagation of dispersive Lamb waves in isotropic plates, this paper presents physics-informed neural networks (PINNs) to calculate the frequency-wave number domain dispersion curves of Lamb waves propagating in aluminum plates. Considering the physical properties, boundary conditions, and wave equations of isotropic metal plates, the dispersion equation for the propagation of Lamb waves in an aluminum plate is derived. Then a deep neural network is constructed using PINNs to obtain the solution of the wave equation, which enables the network to satisfy both data fitting and physical constraints by fusing the priori information of the dispersion equation. To verify the accuracy of the PINNs algorithm, the solutions are compared with those of the Legendre orthogonal polynomial expansion method. The results of this study reveal that the PINNs-based approach has the ability to solve the dispersion relations of Lamb waves in isotropic plates. In our future research, we will extend the PINNs-based algorithm to the solving of wave equations of guided waves in complex structures such as anisotropic composites and arbitrary cross-sectioned waveguides.

Defects or damages on the surface or subsurface of composite rolls directly affect the quality of the rolled products, and their periodic inspection and accurate identification can provide a reference for the repair or replacement of composite rolls. Ultrasonic Rayleigh waves can non-destructively assess the surface or subsurface of composite rolls, during which similar original signals are perhaps generated for the defects or damages with different types or sizes, making it difficult to distinguish their types. Machine learning is proposed to solve these problems, and feature selection based on the ultrasonic Rayleigh waves mainly utilizes traditional methods such as ReliefF. However, these unsupervised methods have not been combined with specific classification algorithms. In this study, swarm intelligence optimization algorithms, including snake optimizer (SO), dung beetle optimizer (DBO), and grasshopper optimization algorithm (GOA), are investigated based on the support vector machine (SVM). Note that the utilized original signals are received on the left and right sides of defects or damages, and they are processed by segmentation, fast Fourier transform (FFT), and wavelet packet decomposition to build original feature sets. It is illustrated that Rayleigh waves passing through the defects or damages carry more valuable information about the types. In contrast, the ultrasonic waves reflected from the defects or damages can provide information about the types that the former does not contain. Furthermore, for the intelligent classification of defects or damages in composite rolls using ultrasonic Rayleigh waves, SO is more suitable for SVM and has certain advantages.

Estimating elastic constants in materials is markedly important in engineering and technology. Ultrasonic guided wave non-destructive testing provides an effective means for accurately assessing material properties. This paper presents a method for inverting the elastic constants of hollow pipes using the longitudinal mode of ultrasonic guided waves combined with a genetic algorithm (GA). The Legendre orthogonal polynomial expansion (LOPE) method serves as the forward model for analyzing the dispersion curves of axisymmetric guided wave modes, while the GA performs the inversion. A carefully designed finite element (FE) model generates pseudo-experimental data, which is transformed into the frequency-wave number domain for input into the GA. The comparison between simulation results and theoretical analysis confirms the validity of the FE model and the accuracy of the detected modes. The results demonstrate that the proposed method effectively inverts the elastic constants of isotropic hollow cylindrical structures, with an inversion error of less than 2% based on pseudo-experimental data.

Wafer-level Fan-out packaging (FOWLP) with multi-layer redistribution layers (RDL) emerges as a pivotal technology in 3D integration. Polyimide (PI) as an insulation layer in the construction of RDL is essential for FOWLP. The adhesion of PI has become a focal point of multi-layer RDL. This study focuses on solving the adhesion technologies for PI photoresist lithography to achieve four layer RDL. The adhesion of PI to both the complex substrate and varying RDL layouts is investigated as a significant determinant of package reliability, characterized predominantly by surface free energy (SFE). It reveals that improving the substrate morphology by flattening can significantly enhance the PI adhesion, thereby addressing fluctuations caused by temporary bonding defects. Techniques such as CF4 dry etching and optimization of the temporary bonding process were found effective in mitigating substrate imperfections. Furthermore, various surface treatments applied to the RDL layers were investigated to boost the interface adhesion between the RDL and PI. Notably, after subjecting the plated copper to a 180W, 3-minute Argon plasma atmosphere, we observed an increase in roughness to 12 nm and an elevation in SFE to 80.82 mN/m, markedly improving copper surface adhesion. Additionally, employing Plasma-Enhanced Chemical Vapor Deposition (PECVD) to deposit SiO2 on the surface of the RDL layer substantially increased the SFE to 83.1±0.7 mN/m, demonstrating the most significant enhancement in PI adhesion. These advancements propose promising pathways to improve the structural integrity and reliability of FOWLP.