Search

In this paper, a new Stroh formalism for gradient electro-mechanics is derived for the first time, which is both mathematically concise and numerically powerful, applicable to generally coupled anisotropic material systems. Based on this new formalism, the complicated Lamb wave in flexoelectric and piezoelectric plates is investigated. The dispersion equation is obtained by solving the eigenvalue problem along with the unconditionally stable dual-variable and position method. From the obtained dispersion equation, the dispersion curves and mode shapes of the Lamb wave are calculated by the 1D form of the multidimensional moduli ratio convergence method. Two important and interesting features are observed from our analysis: One is the difference in the mode shape symmetry between the piezoelectric and flexoelectric cases, and the other is the size-dependent property of the flexoelectric effect as observed by nondimensionalization. These features are further illustrated by comparing the dispersion curves and wave-mode shapes among the three different material models (purely piezoelectric, purely flexoelectric, and flexoelectric and piezoelectric coupled). The newly derived Stroh formalism offers a robust, concise, and unified approach for dealing with strain gradient electro-mechanic materials with crystal systems of general anisotropy. The present work also explains the physical mechanism of symmetry breaking observed, as induced by flexoelectric coupling in piezoelectric materials. [ABSTRACT FROM AUTHOR]

This work explores the infrared (IR) detection capabilities of 750 nm thick Z-cut lithium niobate (LN) thin film resonator at asymmetric modes of various orders: the first, third, fifth, and seventh order asymmetric (A1, A3, A5, and A7), with resonant frequencies of 2.35, 6.68, 11.09, and 15.49 GHz. Under the infrared radiation of 0.575 mW, the responses about admittance minima and frequency drift corresponding to these modes have been experimentally validated. Notably, the A1 mode exhibits the most significant admittance dip response with 2.62 dB, while the A7 mode demonstrates a maximum frequency drift response of 670 kHz. The optimal parameter for noise equivalent power reaches 15.41 pW/Hz1/2, and the optimal detectivity achieves 7.40 × 106 m Hz1/2/W. These findings indicate the immense potential of LN thin-film resonators for infrared sensing applications. [ABSTRACT FROM AUTHOR]

Multi-layer complex structures are widely used in large-scale engineering structures because of their diverse combinations of properties and excellent overall performance. However, multi-layer complex structures are prone to interlaminar debonding damage during use. Therefore, it is necessary to monitor debonding damage in engineering applications to determine structural integrity. In this paper, a damage information extraction method with ladder feature mining for Lamb waves is proposed. The method is able to optimize and screen effective damage information through ladder-type damage extraction. It is suitable for evaluating the severity of debonding damage in aluminum-foamed silicone rubber, a novel multi-layer complex structure. The proposed method contains ladder feature mining stages of damage information selection and damage feature fusion, realizing a multi-level damage information extraction process from coarse to fine. The results show that the accuracy of damage severity assessment by the damage information extraction method with ladder feature mining is improved by more than 5% compared to other methods. The effectiveness and accuracy of the method in assessing the damage severity of multi-layer complex structures are demonstrated, providing a new perspective and solution for damage monitoring of multi-layer complex structures. [ABSTRACT FROM AUTHOR]

A general expression for the magnetostatic field generated by mechanical deformations to a ferromagnetic material in the continuum description is derived. Linearization with respect to the displacement vector is shown to be well defined. To demonstrate the use of the formulation, two examples are discussed. First, a complete derivation of the magneto‐rotation coupling for a uniformly magnetized film is given. Second, the lowest asymmetric mode of Lamb waves propagating through a magnetic vortex is shown to induce an in‐plane magnetostatic field localized around the vortex core. [ABSTRACT FROM AUTHOR]

Manipulating terahertz (THz) polarization in an efficient and broadband manner is of great significance to facilitating THz applications, including communications, imaging, defense, and homeland security. In this work, a dispersion compensation scheme is proposed for high‐efficiency and ultra‐broadband THz polarization manipulation using an anisotropic dielectric‐metal hybrid metadevice. The operating bandwidth is broadened by dispersion compensation, where the dielectric grating provides an artificial birefringence with a phase dispersion of positive slope and the metallic grating provides a phase dispersion of negative slope. Experimental results show that the device achieves two ultra‐broadband dispersion compensation, corresponding to the achromatic quarter‐wave plate in the lower frequency band (QWP: 0.5–2.0 THz, PCR >0.95) and the achromatic half‐wave plate in the higher frequency band (HWP: 1.0–2.1 THz, PCR >0.9), respectively. Theoretically, the bandwidth of QWP can be further improved to 2.6 THz by optimizing the grating dispersion, which brings huge application space to cover most of the THz radiation. This hybrid metadevice configuration offers a versatile platform for engineering electromagnetic waves, and the strategy of phase compensation can be generalized to extend the bandwidth of the metadevice in imaging and communications. [ABSTRACT FROM AUTHOR]

Multimodal is the prominent characteristic of Lamb waves, which means a variety of Lamb wave modes propagate in the structure and each of them has unique propagation behaviour. For a wideband multimodal Lamb wave signal, it is possible that many different modes share the same group velocity at some frequency points, while their dispersion behaviours change differently to thickness variation. In this study, the diversity and difference of the interaction between the corrosion and Lamb wave modes are investigated. On this basis, a corrosion index (CI) is established to evaluate the time gap between two modes at their identical group velocity points. The simulation results show that the CI value of a corroded path is obviously larger than that of a healthy path, indicating the presence of the damage, which is independent of any base-line signal. Furthermore, the new reconstruction algorithm for the probabilistic inspection of damage (RAPID) was proposed, where the signal difference coefficient was replaced by the CI to visualise damage location. The experimental results demonstrate the effectiveness of the proposed multimodal Lamb wave baseline-free damage detection method. [ABSTRACT FROM AUTHOR]

The aim of this paper is to discuss the effect of the sensor on the acoustic emission (AE) signature and to develop a methodology to reduce the sensor effect. Pencil leads are broken on PMMA plates at different source–sensor distances, and the resulting waves are detected with different sensors. Several transducers, commonly used for acoustic emission measurements, are compared with regard to their ability to reproduce the characteristic shapes of plate waves. Their consequences for AE descriptors are discussed. Their different responses show why similar test specimens and test conditions can yield disparate results. This sensor effect will furthermore make the classification of different AE sources more difficult. In this context, a specific procedure is proposed to reduce the sensor effect and to propose an efficient selection of descriptors for data merging. Principal Component Analysis has demonstrated that using the Z-score normalized descriptor data in conjunction with the Krustal–Wallis test and identifying the outliers can help reduce the sensor effect. This procedure leads to the selection of a common descriptor set with the same distribution for all sensors. These descriptors can be merged to create a library. This result opens up new outlooks for the generalization of acoustic emission signature libraries. This aspect is a key point for the development of a database for machine learning. [ABSTRACT FROM AUTHOR]

Ice shelves are assumed to flow steadily from their grounding lines to the ice front. We report the detection of ice‐propagating extensional Lamb (plate) waves accompanied by pulses of permanent ice shelf displacement observed by co‐located Global Navigation Satellite System receivers and seismographs on the Ross Ice Shelf. The extensional waves and associated ice shelf displacement are produced by tidally triggered basal slip events of the Whillans Ice Stream, which flows into the ice shelf. The propagation velocity of 2,800 m/s is intermediate between shear and compressional ice velocities, with velocity and particle motions consistent with predictions for extensional Lamb waves. During the passage of the Lamb waves the entire ice shelf is displaced about 60 mm with a velocity more than an order of magnitude above its long‐term flow rate. Observed displacements indicate a peak dynamic strain of 10−7, comparable to that of earthquake surface waves that trigger ice quakes. Plain Language Summary: Ice shelves normally flow steadily toward their boundaries with the open ocean at the ice front. However, seismographs and Global Navigation Satellite System receivers deployed on the Ross Ice Shelf record guided elastic plate waves traveling in the ice as well as permanent displacement of the ice shelf. The elastic waves and ice shelf displacement originate from basal slip events of the Whillans Ice Stream, which flows into the Ross Ice Shelf. The velocity of the elastic waves is about 2,800 m/s, as expected for guided plate waves propagating in an ice shelf. During the passage of the elastic waves, the entire ice shelf with an area of 500,000 square kilometers is displaced about 60 mm in a direction away from the Whillans Ice Stream. These observations show that the strain imparted to the ice shelf by the once or twice daily Whillans Ice Stream basal slip events is sufficient to trigger ice quakes and perhaps enhance the deformation of the ice shelf. Key Points: Extensional Lamb waves propagate across the Ross Ice Shelf, radiated from slip events at the base of the Whillans Ice StreamDuring the passage of the Lamb waves, the entire ice shelf is displaced about 60 mm, with a velocity an order of magnitude above its long‐term flow rateThe displacement pulses produce a peak dynamic strain of 10−7, suggesting that they could trigger icequakes in the ice shelf [ABSTRACT FROM AUTHOR]

With the wide application of carbon fibre reinforced plastic (CFRP) structure, a structural health monitoring (SHM) system that can easily detect damages in CFRP structures is urgently needed. Since it is possible to detect damages effectively in a large area in CFRP by using the scattering of Lamb waves, in this research, we investigated the scattering of Lamb waves at an impact damaged area in quasi-isotropic (QI) CFRP laminate. By modelling the impact damage as a cylinder area with a uniform stiffness degradation, the scattering waves are calculated based on Mindlin plate theory, which is more precise than Kirchhoff plate theory. It is shown that in the low-frequency region, the calculation results based on Kirchhoff and Mindlin plate theory was similar, but in a higher frequency range, the results differed. The calculation results were compared with the simulation results, suggesting the validity of Mindlin plate theory within a practical frequency range. Moreover, we validated the analytical and simulation results experimentally using a QI CFRP laminate with a hole. We also conducted some parameter study based on the analytical calculation to clarify influential stiffness components. Since scattering behaviour of Lamb waves can be calculated in a fast and easy way using this method, this work is useful for the successful development of a scattering-based SHM system. [ABSTRACT FROM AUTHOR]

The Hunga Tonga–Hunga Ha'apai volcanic eruption on January 15, 2022 generated a tsunami that affected the entire Pacific Ocean. Tsunami waves from the event have been generated both by incoming waves from the source area with a long-wave speed in the ocean of ~200–220 m/s, and by an atmospheric wave propagating at a sound speed of ~315 m/s. Such a dual source mechanism created a serious problem and was a real challenge for the Pacific tsunami warning services. The work of the Russian Tsunami Warning Service (Yuzhno-Sakhalinsk) during this event is considered in detail. The tsunami was clearly recorded on the coasts of the Northwest Pacific and in the adjacent marginal seas, including the Sea of Japan, the Sea of Okhotsk, and the Bering Sea. We examined high-resolution records (1-min sampling) of 20 tide gauges and 8 air pressure stations in this region for the period of January 14–17, 2022. On the Russian coast, the highest waves, with a trough-to-crest wave height of 1.3 m, were recorded at Malokurilskoe (Shikotan Island) and Vodopadnaya (southeastern coast of Kamchatka). Using numerical simulation and data analysis methods, we were able to separate oceanic "gravity" tsunami waves from propagating atmospheric pressure waves. In general, we found that on the outer (oceanic) coasts and southern coast of the Sea of Okhotsk, oceanic tsunami waves prevailed, while on the coast of the Sea of Japan, oceanic and atmospheric tsunami waves had similar heights. [ABSTRACT FROM AUTHOR]

This paper presents an air-coupled impact echo (IE) technique that relies on the phase spectrum of the collected data to find the frequencies corresponding to the reflections from delaminations. The proposed technique takes advantage of the fact that the IE compression wave is not a propagating wave, but it is the 1st order symmetrical (S1) mode Lamb wave at zero group velocity (S1-ZGV). Therefore, it searches the phase spectra of the data collected by multiple sensors to locate the frequency corresponding to the lowest phase difference. As a result, the technique reduces the effect of propagating waves, including the direct acoustic wave and ambient noise. It is named the Constant Phase IE (CPIE). The performance of the CPIE is experimentally compared with the regular amplitude spectrum-based IE technique and two other multisensor IE techniques. The CPIE shows a performance advantage, especially in a noisy environment. [ABSTRACT FROM AUTHOR]

Background: The elastic modulus of polyethylene terephthalate (PET) sheets is typically measured through destructive tests that require specific sample preparation and time-consuming testing procedures. Objective: To improve the efficiency of measuring the elastic modulus of PET sheets, research on a non-destructive measurement approach using guided Lamb waves was conducted. Methods: In this approach, the group velocity of the zero-order symmetric Lamb wave mode (S0 mode) at a single frequency is first measured from PET sheets. The semi-analytical finite element method (SAFEM) is used as the forward model to calculate the corresponding numerical group velocity. Particle swarm optimisation (PSO) is used to update the elastic modulus in the SAFEM model until the numerical group velocity from the model matches the experimental results. Results: The results show that measuring the group velocity data at a single frequency is sufficient for elastic modulus measurement while the material thickness can be assumed as a constant, which improves the efficiency of the measurement. The identified modulus differs from the tensile modulus of the material due to the frequency dependence of the elastic modulus. However, this discrepancy could be eliminated by using a linear regression model. Conclusions: The method mentioned above can achieve non-destructive and efficient measurement of the elastic modulus of PET sheets, which can potentially be applied for in-line quality inspection in PET bottle production processes. [ABSTRACT FROM AUTHOR]

In this paper, Lamb mode identification method based on small-sample dictionary algorithm is proposed and applied for the separation of specific Lamb modes, the reconstruction of Lamb waves upon propagating a certain distance and damage identification. This approach includes the creation of small-sample dictionary and querying procession in a dictionary. Firstly, Lamb wave signals upon propagating at a series of distances are simulated, and signal features, {mode, distance, time of flight (Tof), wavelet energy}, are extracted to create a dictionary; secondly, Tof of the received signal is extracted, and then Lamb modes are identified by searching the dictionary; finally, energy parameters are estimated to reconstruct wavepackets. The feasibility of this algorithm is validated in AAA laminate, and the results are presented. In a 2D-simulation model of a pitch-catch configuration, A0 and S0 modes can be identified and reconstructed effectively when the direct waves and the reflected waves are synchronously received, with the propagation distance of 0.3 m and 0.5 m, respectively. In addition, a Lamb-wave-based delamination location is conducted in three-dimensional AAA laminate. The experimental results show that the delamination can be located relatively by combining the identified damage-scattered S0 waves and the probability-based diagnostic imaging. [ABSTRACT FROM AUTHOR]

The propagation characteristics of Lamb waves in a functionally graded material (FGM) plate with periodic gratings have been studied. The power series technique is employed to solve the governing differential equations with variable coefficients. In the propagation direction, the displacements of Lamb waves are expanded in the Fourier series due to the periodicity of the structure. The convergences of the power series and Fourier series are proved and the method presented in the article is verified by the finite element method (FEM). The band gaps are obtained by the couplings between the different modes of Lamb waves induced by FGM. The effects of the structural parameters (such as the periodicity, mass, and length of the gratings) and gradient coefficient on band gaps are investigated. Numerical results show that the band gaps shift up as the gradient coefficient increases and the second band gap (SBG) is closed when the gradient coefficient is large enough. The conclusions are of practical significance for designing elastic wave filters with high-performance. [ABSTRACT FROM AUTHOR]

Lamb wave resonators (LWRs) exhibiting high-quality factors and clean spectra demonstrate promising applications in RF communication and sensing. This paper discusses the relationship between the spurious mode, the quality factor, and the effective electromechanical coupling factor of resonators. When the resonant frequency of the spurious mode is slightly below the parallel resonant frequency (fp), the quality factor at fp (Qp) decreases dramatically. To enhance Qp and suppress the spurious mode, the LWRs with busbars including only the top electrode (non-overlap busbars) and the LWRs with busbars incorporating both top and bottom electrodes (overlap busbars) are designed and fabricated. The LWR with 12 μm-wide overlap busbars exhibits a notable enhancement in Qp, elevating it from 553.76 to 1488.17 and suppresses the spurious mode simultaneously. This research introduces a promising approach to suppress the spurious mode and enhance the quality factor of Lamb wave resonators, thereby holding great potential for applications in sensors and mobile communication. [ABSTRACT FROM AUTHOR]

The objective of the study was to analyze the influence of coating treatments on sound propagation speeds in thin boards, along the longitudinal and radial directions of resonance wood. The samples studied were thin boards made of spruce and maple wood with dimensions of 240 mm × 80 mm × 4 mm (length × width × thickness) subjected to different coating treatments (oil-based varnish and alcohol varnish) as well as unvarnished samples, exposed to radiation UV, and specimens treated in the saline fog. The test method consisted of evaluating the propagation speeds of Lamb waves applied to thin plates, according to a semicircular test model, so that the results highlighted both the acoustic response in the longitudinal and radial directions as well as the variation in the anisotropy of the samples with the change in the sound propagation direction relative to wood fibers. Based on the statistical analysis, sound propagation speed profiles were obtained in each of the 38 directions analyzed for all wood samples. The results highlighted that the oil-based varnish led to a decrease in the speed of propagation in the radial direction, compared to the alcoholic varnish, whose major effect was in the longitudinal direction, on the spruce wood. On maple wood, increasing the number of varnish layers, regardless of the type of varnish, led to a decrease in the anisotropy ratio between the longitudinal and radial directions. [ABSTRACT FROM AUTHOR]

This paper introduces a novel design for a solar photovoltaic/thermal (PV/T) air collector that utilizes staggered fins. The collector features double-layer flow channels in the same direction, with the upper channel equipped with transparent wave plates, and the lower channel fitted with staggered fins. The paper includes a calculation scheme for wave plate heat balance. The numerical model of the collector is established and verified by experimental results. A numerical model is used to analyze the height combination of the upper and lower runner and the fin arrangement of the lower runner. The results indicate that, under the given environmental parameters, as the PV panel moves down, the overall air heat transfer capacity decreases. When the height combination of the upper/lower runner is 23 mm/105 mm, the maximum value is 53.741%. With the increase of fin spacing, the heat transfer capacity of the lower runner decreases. With the increase of the number of fin rows, the heat transfer capacity of the lower runner increases. When the equivalent diameter of the rectangular channel and the number of fin rows were 70 mm and 3 rows, respectively, the maximum solar energy comprehensive utilization efficiency was 56.261%. [ABSTRACT FROM AUTHOR]

The analytical and geometrical conditions for the possible appearance of the infinite group velocity (IGV) points belonging to the dispersion curves of Lamb waves propagating in traction-free plates are studied by a combined method comprising Cauchy sextic formalism and the exponential fundamental matrix method. According to the obtained geometrical condition, the IGV corresponds to the coincidence of a tangent line to any of the dispersion curves with a straight line passing through the origin. The developed technique is demonstrated by applying to the analysis of Lamb wave dispersion in three-layered plates with a soft inner core. [ABSTRACT FROM AUTHOR]

Welded lap joints play a vital role in a wide range of engineering structures such as pipelines, storage tanks, pressure vessels, and ship hulls. This study aims to investigate the propagation of ultrasonic guided waves in steel welded lap joints for the baseline-free inspection of joint defects using the mode conversion of Lamb waves. The finite element method was used to simulate a single lap joint with common defects such as corrosion and disbonding. To identify the propagating wave modes, a wavenumber–frequency analysis was conducted using the 2D fast Fourier transform. The power loss of the transmitted modes was also determined to identify damage in the lap joints. The results indicate that the A0 incident in pristine conditions experienced significant transmission losses of about 9.5 dB compared to an attenuation of 2.8 dB for the S0 incident. The presence of corrosion was found to reduce these transmission losses by more than 28%. In contrast, introducing disbonding in the lap joint increased the transmission loss of the S0 incident, while a negligible loss was observed for the A0 incident. The mode-converted S0 (MC-S) and mode-converted A0 (MC-A0) incidents were found to exhibit a unique sensitivity to the presence of corrosion and disbonding. The results indicate that MC-S0 and MC-A0 as well as Lamb mode incidents interact differently in terms of corrosion and disbonding, providing a means to identify damage without relying on baseline signals. [ABSTRACT FROM AUTHOR]

Compact circularly‐polarized (CP) light sources are important for chirality‐based applications at the chip level. The CP light is conventionally generated by passing the linearly‐polarized (LP) one through quarter wave plates which are too thick for packed integrations. In this work, the in‐plane submicron phase shifter substitutes the quarter‐wave plate in the creation of CP light. After the lasing field of a holed microdisk is coupled into the nearby waveguide and phase shifter, it is guided into two grating couplers that output orthogonally LP waves vertically. The two LP waves are phase‐shifted by π/2$\pi /2$ and combine into the coherent CP radiation in the far‐field zone. Experimentally, the fabricated devices exhibit a degree of circular polarization as high as 74%. This device scheme is simple and effective in that it relies on no extrinsic materials, large‐area auxiliary structures, or specialized operation conditions critical for CP radiation. The compatibility issues for integrated photonic systems are of less concern in such schemes. [ABSTRACT FROM AUTHOR]

A theoretical approach was applied to study the vibration of simple-supported submerged horizontal plate. The derived analytical solution was used to determine natural frequencies for a horizontal plate vibrating in fluid. The investigations were conducted for a very wide range of material density and elasticity modulus covering all materials used in engineering practice. Analysis shows that plate vibration frequency decreases with increasing plate width and draft, and decreases with decreasing plate thickness. Moreover, the results show that a substantial effect on vibration of submerged plate has mass of water above plate. The results also show that plate vibration frequency decreases with increasing plate material density and decreases with decreasing elasticity modulus. The dominant factors affecting the vibration of the submerged plate are the plate width, the plate thickness, and elasticity modulus. For moderate and low values of elasticity modulus, vibration frequency is becoming lower than frequency of water waves. This is very important because wave frequencies overlap with the natural plate vibration frequencies, which may lead to resonance and failure of a structure. The problem is that the overlap of plate vibration frequencies and wave frequencies occurs for very wide range of wave and plate parameters. Laboratory experiments confirm theoretical results. [ABSTRACT FROM AUTHOR]

The ice formation over the aerofoil structure of the aircraft wing has been an obstruction as they abrupt the airflow, acting as drag. The investigation will intend to determine ice accumulation on carbon fiber-reinforced polymer (CFRP), approximated as ice build-up on aircraft wings. The observation is carried out over quasi-isotropic composite laminates using ultrasonic-guided waves with a central working frequency regime of 100 kHz. The three-dimensional (3D) finite element (FE) simulations are performed to observe the scattering effect to explore the reflection site in the far field. This effect was quite prominent for different thicknesses of Glaze ice (G-Ice) and was found to be strongly linked with the wave propagation and dispersion effect. The scattering results for the reflection of Lamb mode, when it interacted with the G-Ice interface, were quite noteworthy along the angular region rather than on the center line, indicating that the scattering was more prominent due to the presence of a 45° or (− 45)-degree fiber orientation in that laminate. A similar but complex scattering phenomenon was observed for different stacking sequences where the wave propagation angle and its amplitude at the receiver nodes are found to be closely bound with the exponential decay in group/phase velocity for the ice thicknesses studied. The FE approach is verified, and the results are validated analytically. Analytically, we have investigated a much-closed approximation with the detectability obtained from three-dimensional studies. Where the dispersion study performed has also contributed to verifying the present investigation in the long wavelength limits. This study can reveal the various optimized locations for placing the sensor for ice detection and quantification, which can be further helpful for practical guided wave inspection in ice detection and its removal. [ABSTRACT FROM AUTHOR]

Damage diagnosis of thin-walled structures has been successfully performed through methods based on tomography and machine learning-driven methods. According to traditional approaches, diagnostic signals are excited and sensed on the structure through a permanently installed network of sensors and are processed to obtain information about the damage. Good performance characterizes methods that process Lamb waves, which are described by long propagation distances and high sensitivity to anomalies. Most of the methods require extracting damage-sensitive features from the diagnostic signals to drive the damage diagnosis task. However, this process can lead to loss of information, and the choice of the specific feature to extract may introduce biases that hamper damage diagnosis. Furthermore, traditional approaches do not perform well when composites are considered, due to the anisotropy, inhomogeneity, and complex damage mechanisms shown by this type of material. To boost the performance of methods for damage diagnosis of composite plates, this work proposes a convolutional neural network (CNN)-based algorithm that localizes damage by processing Lamb waves. Different from other methods, the proposed method does not require extracting features from the acquired signals and allows localizing damage through the regression approach. The method was tested against experimental observations of Lamb waves propagating in two composite panels and in a hybrid panel, and the performance of two different sensor arrays was investigated. The pseudo-damage approach was used to generate large enough datasets for training the CNNs, and the performance of the framework was evaluated by localizing pseudo-damage and real damage determined by low-velocity impacts. The CNN-driven method accurately localized damage in all the considered scenarios, and it also outperformed traditional damage indices-based approaches, such as the reconstruction algorithm for probabilistic inspection of defects. [ABSTRACT FROM AUTHOR]

Composite materials are widely used in most industries due to their high specific strength, specific stiffness, and their relatively lighter weight compared to other traditional materials. However, the presence of defects arising from manufacturing processes or during service loads can make these structures more susceptible to a diminished performance. Furthermore, the former defects are inevitable in composite structures, but they can be reduced. Each type of defect requires specific inspection techniques and configurations. In this work, a review of the different types of composites manufacturing processes and their corresponding resultant defects is presented with the various nondestructive evaluation techniques employed for these defects' characterization. The emphasis of this paper is on ultrasonic inspection and detection techniques for they present high sensitivity to surface/subsurface discontinuities, superior depth of ultrasonic penetration for flaw detection, feasibility on large scales, and instantaneous and detailed images production. Notably, noncontact ultrasonic testing techniques are also reviewed, air-coupled techniques in specific, and highlighted as a fine alternative to conventional contact inspection systems as they reduce the restrictions that coexist with the use of couplants. Moreover, these ultrasonic testing techniques are summarized to show the latest research progress achieved in the field of air-coupled ultrasonic inspection systems for manufacturing defects' monitoring in composite structures including delamination, porosity, dryness, waviness, and resin lack/excess. Finally, we highlight the type and central frequency of the transducers and experimental results present in literature and obtained in terms of both detection and size of the defects. [ABSTRACT FROM AUTHOR]

Magnetostriction-based electromagnetic acoustic transducer (M-EMAT) is a promising tool for generating fundamental shear-horizontal (SH0) mode guided waves in plate. Though the M-EMAT possesses high-order harmonics excitation ability in nature, its conventional way can only generate a fundamental component of SH0 mode. The analytical modeling was performed in this study to releasing the ability of M-EMAT in generating odd harmonics of SH0 mode. First, the inaccurate conditions of magnetic fields for relative permeability calculation in the existing model are corrected in the proposed model. Second, the error of the existing model in predicting the spectrum of the SH0 mode generated in Nickel plate is estimated. Third, numerical solutions are provided by the improved model to examine the key factors governing the ability of M-EMAT in generating odd harmonics of SH0 mode. The conclusions demonstrated that the intensity ratio (HS/HD) of static and dynamic magnetic fields is adjusted below 1 and the ability of M-EMAT in generating odd harmonics of SH0 mode can be activated. The normalized amplitude of 3rd harmonics decays exponentially with the increase of HS/HD, which is independent of geometrical parameters of M-EMAT. The improved model can effectively optimize excitation parameters of M-EMAT and generate odd harmonics of SH0 mode in plate. [ABSTRACT FROM AUTHOR]

The Hunga Tonga–Hunga Ha′apai volcano erupted on 15 January 2022, launching Lamb waves and gravity waves into the atmosphere. In this study, we present results using 13 globally distributed meteor radars and identify the volcanogenic gravity waves in the mesospheric/lower thermospheric winds. Leveraging the High-Altitude Mechanistic general Circulation Model (HIAMCM), we compare the global propagation of these gravity waves. We observed an eastward-propagating gravity wave packet with an observed phase speed of 240 ± 5.7 m s -1 and a westward-propagating gravity wave with an observed phase speed of 166.5 ± 6.4 m s -1. We identified these waves in HIAMCM and obtained very good agreement of the observed phase speeds of 239.5 ± 4.3 and 162.2 ± 6.1 m s -1 for the eastward the westward waves, respectively. Considering that HIAMCM perturbations in the mesosphere/lower thermosphere were the result of the secondary waves generated by the dissipation of the primary gravity waves from the volcanic eruption, this affirms the importance of higher-order wave generation. Furthermore, based on meteor radar observations of the gravity wave propagation around the globe, we estimate the eruption time to be within 6 min of the nominal value of 15 January 2022 04:15 UTC, and we localized the volcanic eruption to be within 78 km relative to the World Geodetic System 84 coordinates of the volcano, confirming our estimates to be realistic. [ABSTRACT FROM AUTHOR]

Accurate computation of hydroelastic waves in shallow water is critical because many hydroelastic wave applications are nearshores, such as sea-ice and floating infrastructures. In this paper, Boussinesq assumptions for shallow water are employed to derive nonlinear Boussinesq-type equations of hydroelastic waves, in which non-uniform distribution of structural stiffness and varying water depth are considered rigorously. Application of Boussinesq assumptions enables complicated three-dimensional problems to be reduced and formulated on the two-dimensional horizontal plane, therefore the proposed Boussinesq-type models are straightforward and versatile for a wide range of hydroelastic wave applications. Two configurations, a floating plate and a submerged plate, are studied. The first-order linear governing equations are solved analytically with periodic conditions assuming constant depth and uniform stiffness, and the linear dispersion relations are subsequently derived for both configurations. For flexural-gravity waves of a floating plate, unique behaviours of flexural-gravity waves different from shallow-water waves are discussed, and a generalized solitary wave solution is investigated. A nonlinear numerical solver is developed, and nonlinear flexural-gravity waves are found to have smaller wavelength and celerity than their linear counterparts. For hydroelastic waves of a submerged plate, dual-mode analytical solutions are discovered for the first time. Numerical computation has demonstrated that a plate with decreasing submerged depth is able to transfer wave energy from the deeper water to the surface layer. [ABSTRACT FROM AUTHOR]

In this paper, the ability of a metasurface made of resonant elliptical pillars to focus flexural Lamb waves in the sub-wavelength regime is investigated. We report on the influence of the ellipticity parameter on the local resonances of the pillars, in particular the monopolar compressional and dipolar bending modes that are responsible for the desired focusing effect. We also discuss how the transmission through a line of pillars reveals these modes when the orientation of the pillars is changed with respect to the incident wave. Both the resonances can be superimposed for a particular choice of the ellipticity parameter, allowing a phase shift of 2π in the transmission coefficient for an incident antisymmetric Lamb wave, which is a necessary condition for the design of the metasurface. Finally, a gradient design for the pillar ellipticity is investigated, and its capacity to choose the focusing directionality of the transmitted wave at different targeted points is demonstrated. [ABSTRACT FROM AUTHOR]

Lamb-wave-based structural health monitoring is widely acknowledged as a reliable method for damage identification, classification, localization and quantification. However, due to the complexity of Lamb wave signals, especially after interacting with structural components and defects, interpreting these waves and extracting useful information about the structure's health is still a major challenge. Deep-learning-based strategy offers a great opportunity to address such challenges as the algorithm can operate directly on raw discrete time-domain signals. Unlike traditional methods, which often require careful feature engineering and preprocessing, deep learning can automatically extract relevant features from the raw data. This paper proposes an autoencoder based on a bidirectional long short-term memory network (Bi-LSTM) with maximal overlap discrete wavelet transform (MODWT). layer to detect the signal anomaly and determine the location of the damage in the composite structure. MODWT decomposes the signal into multiple levels of detail with different frequency resolution, capturing both temporal and spectral features simultaneously. Comparing with vanilla Bi-LSTM, this approach enables the model to greatly enhance its ability to detect and locate structural damage in structures, thereby increasing safety and efficiency. [ABSTRACT FROM AUTHOR]

In view of the lack of high-precision optical simulation equipment for dim space targets at present, in this study, a simulation method for dim space targets based on polarization stray light suppression is proposed, the overall optical system architecture of the optical engine for depolarization stray light suppression is constructed, the mechanism of stray light generation is explored, and the dark state light leakage suppression method is presented by compensating the phase of LCOS reflected light with wave plate; a high-image quality collimating optical system with large field of view and flat aberration is designed based on the illumination system optimization method of the critical angle matching of the spectroscopic film; and the polarization stray light suppression effect and star position simulation error of the dim target simulator are tested. The test results show that the illumination of the simulated dim target is ≮10−10 lx, the contrast is 6.96, the non-uniformity of the bright state is only 5.88%, and the simulation error of the star position is 9.9″. This research can make some contributions to enhancing the observability of detecting dim targets, breaking through the detection technology of extremely dark targets in space, developing advanced deep space detection capabilities, and improving the engineering technology system of deep space exploration. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southeast University (English Edition) is the property of Journal of Southeast University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The dual frequency Global Navigation Satellite System (GNSS) observations could determine the total electron content (TEC) in the ionosphere. In this study, GNSS TEC was applied to detect traveling ionospheric disturbances (TIDs) after the eruption of Hunga Tonga–Hunga Ha'apai (HTHH) on 15 January 2022. The eruption caused two types of tsunamis, first is tsunami generated by atmospheric wave (meteo‐tsunami) and second is caused by eruption induces water displacement or tsunami classic. At the same time with former tsunami, the atmospheric wave (shock and lamb waves) also caused TIDs at a speed of approximately ∼0.3 km/s. We found moderate correlation between this TIDs amplitude and the tsunami wave height model from tide gauge stations in New Zealand (0.64) and Australia (0.65). Further we attempted to reveal 3D structure of the TIDs in New Zealand, South Australia, and Philippines using 3D tomography. The tomography was set up > 1,170 blocks, as large as 1.0° (east–west) × 1.0° (north–south) × 100 km (vertical), up to 600 km altitude over selected regions. Tomogram shows beautiful concentric directivity of the first TIDs generated by atmospheric wave (AW). Key Points: 3D ionospheric disturbances during the 2022 Tonga eruption was investigated with spatial and temporal directionThe highest concentration of the electron disturbances was observed at an altitude of 200–300 km, which decreased at 500–600 kmA correlation between ionospheric disturbances and the height of tsunami associated with eruption was observed [ABSTRACT FROM AUTHOR]

Lamb wave-based damage quantification in large-scale composites has always been one of the concerning and intractable problems in aircraft structural health monitoring. In recent years, machine learning (ML) algorithms have been utilized to deeply explore the damage feature of Lamb wave signals, which aims to enhance the precision and accuracy of damage quantification. However, multi-damage quantification becomes one of the bottleneck problems because ML algorithms critically depend on the dataset. In this paper, a prioritizing selection and orderly permutation method is proposed to construct multi-damage dataset based on Born approximation principle, which shows the interaction between wave signals under multi- and single-damage conditions. Based on the multi-damage dataset, a multi-task deep learning algorithm is introduced to identify multiple damage, including the damage number, location, and size, in composite laminates. In the algorithm, a multi-branch 1D-convolution neural network framework, which includes a trunk network and branch networks is established to explore the damage features in Lamb wave scattering signals. Compared with single-task models, it has the ability to learn shared features for multiple tasks, effectively boosting the task results. The results show that the proposed multi-task learning (MTL) method saves 23.03% training time compared with the single-task learning method. In the task of quantifying multiple damage of composite laminate, the results of MTL are good for both the constructed test set and the measured test set, especially in the quantification of damage size, which shows the feasibility and reliability of this method. [ABSTRACT FROM AUTHOR]

This paper presents research on the application of ultrasonic-guided wave technology in corrosion defect identification, expounds the relevant ultrasonic-guided wave theories and the principle of ultrasonic-guided wave non-destructive testing of pipelines, and discusses the Lamb wave and shear horizontal wave mode selection that is commonly used in ultrasonic-guided wave corrosion detection. Furthermore, research progress in the field of ultrasonic-guided wave non-destructive testing (NDT) technology, i.e., regarding transducers, structural health monitoring, convolutional neural networks, machine learning, and other fields, is reviewed. Finally, the future prospects of ultrasonic-guided wave NDT technology are discussed. [ABSTRACT FROM AUTHOR]

The mode manipulation of Lamb waves plays an important role in damage detection and identification of damage types, location, and size. In this paper, we propose a composite phononic crystal (PC) plate with antisymmetric and symmetric PCs for realizing mode conversion from A0 to S0 mode of Lamb waves. The theoretical analysis, numerical simulations, and experimental validation are introduced and the mode conversion mechanism of the composite PC plate is systematically investigated. The effect of geometrical parameters on band structures of antisymmetric and symmetric PCs is first discussed. Then multi-physics field simulation models are developed and in-plane displacement fields are obtained in numerical simulations, which shows that the mode conversion is enhanced when the period number of the antisymmetric PC decreases and that of symmetric the PC increases. The composite PC plate specimens are fabricated with precision wire cutting technology for experimental measurements and the self-designed polyvinylidene fluoride (PVDF) comb transducer is used to stimulate the Lamb waves. The experimental results are consistent with the numerical simulations, which demonstrate that the proposed composite PC plate can achieve the mode conversion from A0 to S0 mode of Lamb waves. Our proposed structures have applicable values for the mode manipulation of Lamb waves in damage detection. [ABSTRACT FROM AUTHOR]

The lowest-order shear horizontal (SH0) guided wave in a plate is crucial for nondestructive testing and structural health monitoring due to its nondispersive nature. However, mode conversion at the interface for the SH0 wave complicates the received information and increases the difficulty of signal analysis. In this work, an elastic metasurface is proposed to suppress mode conversion at the interface and to reflect the SH0 wave directionally. The metasurface comprises a series of rectangular elements with a specific phase gradient covering the 2 π phase range. The effectiveness of the proposed metasurface is confirmed through finite element simulations and experimental validation. The results indicate that the metasurface can significantly reduce the amplitude of the reflected lowest-order symmetric Lamb wave when compared to the reflection without the metasurface, while simultaneously allowing the reflected SH0 wave to propagate at the designed angle. Furthermore, the metasurface maintains its functionality for SH0 wave with incident angles varying from 0° to 25°. This study provides a viable approach for suppressing mode conversion and modulating the reflection behavior of SH0 wave, which is expected to find applications in nondestructive testing and structural health monitoring. [ABSTRACT FROM AUTHOR]

The first asymmetric mode (A1 mode) lamb wave resonator (LWR) with a resonant frequency of 6 GHz based on Z-cut lithium niobate (LN) films is presented. An asymmetric electrode structure with different-sized electrode pads in the center and edged regions has been proposed, which can be used to optimize the distribution of the electric field and decrease acoustic impedance mismatch to improve the target mode. Experiment results reveal that LWRs with an asymmetric electrode structure can successfully enhance the A1 mode, achieving a high effective electromechanical coefficient ( k eff 2 ) of 26%, a quality factor (Q) of 1123, and an excellent figure-of-merit (FOM = k eff 2 ∙ Q) of 262. It demonstrates that asymmetric electrode structure provides a new way to suppress the spurious modes for LWRs and shows a great application prospect in wide-bandwidth and low-loss filters used in the sub-6 G frequency range. [ABSTRACT FROM AUTHOR]

This article proposes a framework for the damage assessment of and effect of temperature variations in laminated composites using Lamb waves and unsupervised autonomous features. A network of piezoelectric transducers is employed to generate data for 18 health states of a laminated composite plate. The data is processed with sparse autoencoder (SAE) for unsupervised autonomous features. The discriminative capabilities of the extracted features are confirmed by processing the feature space in the supervised and unsupervised frameworks of machine learning. The confusion matrices of supervised learning provided physical insights into the problem. The feature space was also visualized in two dimensions in an unsupervised manner through principal component analysis (PCA), which revealed physically consistent results for the effect of temperature variations, damage of different severity levels, and the undamaged paths between the actuator and sensors. The healthy state data and information on the paths between the actuator and sensors was processed via SAE for damage localization. The proposed approach can be employed for the autonomous assessment of composite structures for the presence of damage and variations of operating temperatures while using both supervised and unsupervised machine learning algorithms. [ABSTRACT FROM AUTHOR]

Surface gravity wave interaction with a novel composite pile-rock breakwater having a stack of porous plates fixed on its top is investigated in the present study. A numerical code based on the dual boundary element method (DBEM) is developed to understand the wave scattering and force coefficients within the framework of linearized potential flow theory. Out of the four different proposed configurations (pile-rock alone, vertical, horizontal, and H-shaped porous plate assembly with pile-rock), it is found that novel H-shaped porous plates with submerged pile-rock are effective in attenuating the wave energy. The parametric study for the H-shaped configuration with several key aspects like permeable plate porosity, horizontal plate's submergence depth, pile-rock relative height, and width of the pile-rock barriers are investigated. It is appropriate to use plate porosity in the range of 10-20% to secure wave transmission of less than 0.5 for a wide range of incident wave periods. By changing the relative submergence of the horizontal porous plate from (h2/h = 0.375-0.125), it is possible to reduce the wave transmission by about 10% but at the expense of increasing the vertical wave force by almost 50-75%. Increasing the pile-rock height (h1/h from 0.75 to 0.25) helps to reduce the wave transmission but significantly increases the horizontal wave force and moment on the perforated H-shaped barrier. The results of the parametric study can be used for optimizing the dimensions of the pile-rock cum porous plate wave barrier for a wide range of field conditions. [ABSTRACT FROM AUTHOR]

This study focuses on investigating hard-magnetic soft materials, characterized by magnetoactive polymers containing magnetically polarized particles as fillers. The research utilizes the Gent model of hyperelasticity to analyze the propagation of Lamb waves in a magnetically induced deformed compressible plate. In this investigation, we explore both finite deformations and incremental wave propagation in nonlinear hard-magnetic soft materials. The main objective is to formulate the elastic tensor and relevant wave equations within the framework of Lagrangian space. To assess the dispersion characteristics of the guided wave, the study introduces and discusses an extension of the semi-analytical finite element (SAFE) method. Using this numerical approach, the research further examines the effects of magnetic flux densities and its orientation with respect to wave propagation direction on the dispersion characteristics of the fundamental Lamb modes. The study starts by examining the limiting case of the neo-Hookean material model to explain such inherent dependencies. These dependencies are then further emphasized by including the strain-stiffening effect that the Gent material model describes. The research findings reveal the presence of a threshold applied magnetic flux, beyond which the Gent-type material may undergo a snap-through instability, resulting in changes in the dispersion characteristics of the fundamental symmetric Lamb mode. [ABSTRACT FROM AUTHOR]

Nonlinear waves have shown higher sensitivity to closed cracks in fatigue, corrosion, and thermal damage than linear waves. Using the frequency information, the existence of a closed crack can be detected along a 1D wave path. However, the extraction of nonlinear waves in the time domain is rarely reported. In this study, nonlinear Lamb waves at a closed crack formed by a thermal pulse are extracted in the time domain. Combining with the sensor array technique, an image is reconstructed to show the location of the closed crack on a 2D plate. The recognized crack is 1 mm wide, 2 cm long, and 1 mm deep. The distance between the transmitter and the crack is set to 100, 150, and 200 mm to demonstrate the reliability of the proposed method. The method reported facilitates the damage identification and predictive maintenance of plate-like structures. [ABSTRACT FROM AUTHOR]

Composite plates are susceptible to various damages in complex conditions and working environments, which may reduce the reliability of the structure and threaten equipment and personal safety. Thus, the implementation of a robust online Structural health monitoring (SHM) system for these composite structures becomes imperative. To enhance reliability and safety, we introduce a robust online SHM system anchored by our newly developed damage detection Bayesian neural network (DD-BNN). The main contribution of this study lies in the DD-BNN to perform precise and reliable damage detection and localization in composite plates using only one actuator-receiver pair without any signal/feature pre-processing and human intervention. The proposed DD-BNN model innovatively combines probabilistic modeling with deep learning to address uncertainty in Lamb wave-based damage detection and model performance for composite plates, featuring a specialized probabilistic layer trained through Bayesian inference to efficiently encapsulate and manage uncertainty in model weights and activation. Notably, our method significantly simplifies the SHM system design and manual operation requirements. In addition, this approach not only reduces overfitting but also enhances robustness to noise, as confirmed by experiments on perturbation analysis of Gaussian and Poisson noise. [ABSTRACT FROM AUTHOR]

It is well known that acoustic emission (AE) signals, generated by external impacts or damages such as crack initiation, mainly propagate in the form of Lamb waves in plate-like structures. In this work, MEMS-based resonant capacitive micro-machined ultrasonic transducers (CMUTs), which are designed for sensing out-of-plane displacements, have been verified by finite element method (FEM) modeling and theoretical analysis for their feasibility of detecting low-order Lamb waves (A0 and S0). First, combining the propagation theory of Lamb waves and the "spring-mass-damper" model of CMUTs, the out-of-plane sensing mechanism has been explained, together with the analytical expression of sensitivity. Then, simulations based on FEM have been carried out to show that the designed CMUTs are sensitive to out-of-plane displacements, while extremely insensitive to in-plane displacements. Meanwhile, a transient analysis has found the potential abilities of CMUTs for sensing A0 and S0 lamb waves. Besides, the sensing characteristics of CMUTs have also been investigated, including the influence of squeezed-film damping, the amplitude of the input signal, the cell number, and cell space. Finally, the ball drop impact is simulated to show the potential of identifying the location of the AE source by CMUTs. Our studies reveal the out-of-plane sensing behaviors of CMUTs for Lamb waves and may have the potential in promoting the miniaturization and integration of AE sensors. [ABSTRACT FROM AUTHOR]

A new type of stepwise radial metamaterial (SRM) with ultralow-frequency and broadband characteristics is proposed in this study. In contrast to the traditional radial metamaterial (TRM), the proposed structure is periodically arranged in a stepwise shape along the radial direction. The propagation characteristics of Lamb waves in the SRM were investigated using the finite element method. For the numerical analysis, the degeneracy between the bands of the SRM was separated, resulting in the opening of the bandgaps in the ultralow-frequency range. The total bandwidth was 75 times that of the TRM, and the wave attenuation ability was increased by more than 70%. The introduction of a stepwise array in the SRM opened up the local resonance and Bragg scattering bandgaps, and as a result, the SRM exhibited ultralow-frequency broadband characteristics. Furthermore, the influences of the structural parameters of the SRM on the bandgap characteristics were discussed. With the increase in the stepped angle, the coupling relationship between the Lamb wave mode and the local resonance was enhanced, which caused the band structure to shift to a lower frequency. In addition, the hole rotation and shape played important roles in the bandgap tuning. Finally, the experimental sample was processed based on the model, and the vibration propagation characteristics were tested to prove its ultralow-frequency broadband characteristics. The proposed shielding approach could provide a better alternative in the field of ultralow-frequency noise reduction and vibration reduction. [ABSTRACT FROM AUTHOR]

Detection and evaluation of micro-damages in the early stages of engineering failure are crucial for various industrial structures to ensure their safety and prevent further catastrophic accidents. The nonlinear ultrasonic technique (NUT) has gained increasing popularity and recognition for breaking through the detection sensitivity limit upon micro-damages that usually are invisible to conventional linear techniques. However, it remains an ongoing challenge to quantitatively characterize micro-damages using NUT due to great difficulties in fully modeling the complicated interaction mechanism between the nonlinear ultrasonic waves and micro-damages. This work presents a data-driven perspective for solving multiparameter underdetermined inverse problems that are at the core of NUT, while allowing by-passing the creation of high-fidelity physics-based models. Nonlinear Lamb wave measurements with group-velocity mismatching are conducted to introduce both size and localization information of damages to the assembled dataset. A nonlinearity-aware discrete wavelet transform-bidirectional long short-term memory network is proposed to directly process nonlinear ultrasonic responses to automatically model latent nonlinear dynamics, thus establishing the complex mapping between the nonlinear ultrasonic signals and the multi-dimensional damage features. In particular, an attempt is made to augment the physical explainability of the proposed deep learning approach through a frequency component importance analysis. The trained network enables accurate and explainable predictions of length and localization of closed cracks and robustness against varying degrees of noise. Our work paves a promising and practical way to promote the transformation of NUT from the qualitative analysis for accurate and efficient quantitative prediction. [ABSTRACT FROM AUTHOR]

Acoustoelasticity, a characteristic of material anharmonicity, gives rise to a link between wave propagation velocity and the stress state in materials. Ultrasonic techniques to monitor this coupling, particularly with high sensitivity and in a noncontact manner, can have widespread application both in the quantification of applied and residual stress and in the characterization of nonlinear material behavior through measurement of higher order elastic constants. Here, we use a laser ultrasonic technique to excite and detect zero group velocity (ZGV) Lamb wave resonances in aluminum plates under uniaxial loading. A laser line source is used to excite these resonances at different orientations with respect to the applied load, and the signals are detected using an interferometer. The effects of stress and source orientation on ZGV resonance frequencies are validated using the theory of acoustoelastic Lamb wave propagation. In addition, a model-based inversion technique is used to extract Murnaghan's third-order elastic constants from measurements of the stress dependence of the first two ZGV modes generated parallel and perpendicular to the applied load. Laser generation and detection of ZGV resonances is shown to be an effective and powerful approach for the noncontact and nondestructive acoustoelastic characterization of elastic waveguides. [ABSTRACT FROM AUTHOR]

We present the requirements, design, and evaluation of the cryogenic continuously rotating half-wave plate (CHWP) for the Simons Observatory (SO). SO is a cosmic microwave background polarization experiment at Parque Astronómico de Atacama in northern Chile that covers a wide range of angular scales using both small (⌀ 0.42 m) and large (⌀ 6 m) aperture telescopes. In particular, the small aperture telescopes (SATs) focus on large angular scales for primordial B-mode polarization. To this end, the SATs employ a CHWP to modulate the polarization of the incident light at 8 Hz, suppressing atmospheric 1/f noise and mitigating systematic uncertainties that would otherwise arise due to the differential response of detectors sensitive to orthogonal polarizations. The CHWP consists of a 505 mm diameter achromatic sapphire HWP and a cryogenic rotation mechanism, both of which are cooled down to ∼50 K to reduce detector thermal loading. Under normal operation, the HWP is suspended by a superconducting magnetic bearing and rotates with a constant 2 Hz frequency, controlled by an electromagnetic synchronous motor. We find that the number of superconductors and the number of magnets that make up the superconducting magnetic bearing are important design parameters, especially for the rotation mechanism's vibration performance. The rotation angle is detected through an angular encoder with a noise level of 0.07 μrad s . During a cooldown process, the rotor is held in place by a grip-and-release mechanism that serves as both an alignment device and a thermal path. In this paper, we provide an overview of the SO SAT CHWP: its requirements, hardware design, and laboratory performance. [ABSTRACT FROM AUTHOR]

During production or service life, lightweight components made of fibre-reinforced polymers (FRP) may suffer from different types of defects such as cracks or delamination, which may be detected, amongst others, with the help of ultrasonic lamb waves (LW). The study intends to illustrate the potentials of numerical models to assist the design of LW-based non-destructive testing (NDT) processes. For that, the complete NDT chain of an LW driven inspection system was supported by a Finite Element Analysis (FEA) using stringer-stiffened C FRP panels as an exemplary component. The study was divided in two publications: The first part focused on the description of the numerical model, illustration of its functionalities and – most importantly – the determination of LW related effects that were needed to design the inspection system (dispersion characteristics, excitation frequency, propagating modes etc.). In this part, the FEA driven design approach was first validated with self measured experimental data as well as experiments provided in literature. In the second step, the numerical model was applied for the performance of parameter studies in order to identify component specific aspects that proved important for the NDT process. Finally, general advices and FEA related working steps were derived from all findings to assist practitioners in the implementation of the technique. [ABSTRACT FROM AUTHOR]