Aluminum Plate Research Articles

Application of coded excitation in the Rayleigh wave detection of aluminum plates with narrow-magnet EMAT

Abstract The poor generation efficiency causes the low signal-to-noise ratio (SNR) of the electromagnetic acoustic transducers (EMATs). The magnetic fields at the edges of the magnet are fully utilized in the narrow-magnet EMAT to generate Rayleigh waves of higher amplitudes than the conventional EMAT. This paper applies the coded excitation technology to narrow-magnet EMAT to further improve the SNR and the lift-off performance in aluminum plate detection. The main phase encoding methods are Barker code and Golay code. Compared with the conventional tone-burst excitation method, both coded excitation technologies can effectively improve the SNR of the Rayleigh wave. Theoretically, the received Rayleigh waves using the Golay-coded excitation method have no sidelobe, which is different from the case using the Barker code. Hence the Golay-coded excitation achieves higher SNR in the received ultrasonic waves. In addition, the application of the Golay-coded excitation can also effectively improve the lift-off performance of the narrow-magnet EMAT.

Aluminum panel vibration reduction using single lead zirconate titanate and resonant circuit

This study aimed to reduce the vibration of an aluminum plate using a single lead zirconate titanate (PZT) electrical circuit. First, the natural frequencies and modes of the aluminum plate were analyzed using an analytical method to determine the dynamic characteristics of the plate. The frequency domain was used to derive the vibration characteristics of the acoustically excited aluminum plate. It was noted that the resonance region where the vibration of the panel increased rapidly was at 390 Hz, which was then set as the reduction target. Thereafter, the vibration reduction performances of the circuit that connects only the resistance element to the PZT panel and the resonant circuit that uses an inductor were compared. Through actual acoustic excitation, the vibration reduction of the aluminum panel using the PZT panel based on resistance and resonance circuits was validated. The results demonstrated that the vibration in the resonant frequency region of 384 Hz was reduced by 20% through the implementation of a resonant circuit, comprising an inductor and a resistor, added to a single PZT, whose weight was 0.08% of the weight of the aluminum panel. Therefore, this study confirmed that the vibration of aluminum plates can be effectively reduced using a low-weight PZT patch.

STABILITY INDICATING HIGH-PERFORMANCE THIN LAYER LIQUID CHROMATOGRAPHIC METHOD FOR EVEROLIMUS

Objective: Developing and validating a stability-indicating method for everolimus by HPTLC and depiction of degradation product of in alkaline conditions by LC-MS. Methods: The chromatographic separation was performed on aluminium plates pre-coated with silica gel 60 F254 as the stationary phase using Toluene: Methanol: Ethyl Acetate (6:2:2v/v/v) as the mobile phase. The evaluation was carried out at 277 nm. For the developed stability indicating method, the ICH Q2 (R1) guidelines were used for validation. Stress degradation studies like hydrolysis under different pH conditions, photolytic degradation, thermal degradation and oxidative degradation as per ICH Q1A (R2) and Q1B guidelines were performed. LC-MS analysis was carried out for the standard everolimus and its alkaline degradation sample using TOF analyser and the degradation pathway was proposed for each degradation product. Results: The Rf value of everolimus was found to be 0.63±0.03. The response was quite linear over the concentration range of 100-500 ng/band, with the regression coefficient value of 0.9921. Under alkaline hydrolytic conditions, everolimus was analyzed using Liquid Chromatography-Mass Spectrometry (LC-MS). The Retention Time (RT) and prominent mass fragmentation (m/z) for the everolimus standard were observed at 9.46 min with m/z values of 980.56 and 908.54. For the degradation products, DP-1 showed an RT of 8.88 min with m/z values of 349.23, 403.24, 574.33, and 646.35, while DP-2 exhibited an RT of 9.10 min with m/z values of 926.55, 614.32, and 542.30. These data were used to propose the structures of the degradation products. Conclusion: The proposed method can conveniently be applied for quantitative analysis of everolimus on routine basis and for stability testing under different stress environments.

Atypical second harmonic A0 mode Lamb waves in non-uniform plates for local incipient damage monitoring

Plates with non-uniform thickness, such as stiffened and notched plates, are commonly seen in engineering applications. Monitoring incipient damage in these structures is crucial to ensure their safety during service. Second harmonic Lamb waves hold great promise for structural health monitoring applications. However, the mechanisms underpinning the generation of the second harmonic Lamb waves in non-uniform plates are still not well understood due to the complex wave field. To tackle this issue, a theoretical analysis is first conducted to highlight the so-called atypical second harmonic A0 mode waves (2nd A0 waves) generated at the structural non-uniform section. Their existence, as well as their potential for local incipient damage monitoring applications, is then confirmed by finite element simulations. Experiments are carried out on a notched aluminum plate to monitor the incipient plastic damage induced by bending. Three mechanisms contributing to the generation of the atypical 2nd A0 waves in the non-uniform plate are identified: mode conversion from the second harmonic S0 mode waves, asymmetric nonlinear driving forces at the non-uniform section, and the mutual interaction between the mode-converted fundamental A0 and S0 waves. This study shows that the reported atypical 2nd A0 waves provide an effective means for monitoring local incipient damage in non-uniform structures.

Development of Quality Standard and a Comprehensive Quality Control Study of Bharngyadi Kvatha Churna: An Ayurvedic Formulation

Background: Bharngyadi Kvatha Churna (BKC) is an important polyherbal formulation mentioned in the Ayurvedic Formulary of India (AFI) for the treatment of intermittent fever and chronic fever but lacks the presence of standardised quality control parameters. Aims: The aim of the present study was to develop a quality standard of BKC and to carry out a comprehensive quality control study, including the evaluation of physicochemical parameters, safety parameters, elemental content, secondary metabolites, and selected phytochemical analysis. Methods: In HPTLC analysis, piperlongumine was quantified in BKC using a silica gel-coated aluminium plate and developing solvent of toluene: acetone (6:4 v/v). In HPLC analysis, piperine was quantified using acetonitrile: water (80: 20 v/v) mobile phase, and ellagic acid was quantified using water (0.05% KH2PO4): acetonitrile (70: 30 v/v) mobile phase. ICP-OES was used to determine elemental content. The estimation of secondary metabolites like total sugars, tannins, flavonoids, alkaloids, and saponins was also carried out using a UV-Vis spectrophotometer. The volatiles present in the volatile oil of BKC were analysed using the gas chromatography-mass spectrometry technique. Results: The physicochemical parameters namely, loss on drying, total ash, acid-insoluble ash, alcohol- soluble extractive, water-soluble extractive, pH (10% aq. susp.), and volatile oil ranged from 10.56% to 11.06%, 4.67% to 5.76%, 0.73% to 1.78%, 7.56% to 8.2%, 12.04% to 13.06%, 5.87% to 5.96%, and 0.091% to 0.097%, respectively. The amount of piperlongumine in BKC ranged from 0.7688 mg/g to 0.9902 mg/g. The amount of piperine and ellagic acid ranged from 0.1180% to 0.1362% and 0.0016% to 0.0034%, respectively. Oleyl alcohol is the major volatile phytochemical present in BKC. Conclusions: The developed standardised quality control parameters of BKC would aid the herbal industry in developing BKC with requisite quality.

On the cutoff, reappearance, and persistence of subsonic leaky A0 Lamb waves

Abstract Subsonic leaky A0 Lamb waves, whose phase speeds are lower than the fluid’s sound speed, exhibit several peculiar behaviours. In this work, we investigate three such behaviours: Cutoff, where the A0 branch cuts off at some point in the subsonic domain, reappearance, where the cut-off A0 branch reappears at lower frequencies, and persistence, where the A0 branch is never cut off at all. From the literature, we take the case of a 1 mm thick aluminium plate immersed in air of varying density. We then analyse its exact leaky A0 wave solutions by means of a sound radiation model that takes energy conservation into account. This analysis explains these peculiar behaviours by connecting them with the conditions that allow sound-radiating subsonic leaky A0 Lamb waves.

HPTLC – densitometric method of analysis for estimation of efonidipine hydrochloride and telmisartan used in treatment of hypertension

Precise, accurate, and sensitive high performance thin layer chromatographic method has been developed and validated for simultaneous determination of efonidipine hydrochloride (EFD) and telmisartan (TEL) in a tablet dosage form which is used in treatment of hypertension. The proposed method used aluminum plates pre-coated with silica gel 60 F254 as a stationary phase and n-butanol: toluene: acetic acid (3:7:0.2, v/v/v) as a mobile phase for separation purpose. Compact spots of TEL and EFD were obtained at Rf 0.73 and 0.37, respectively. Densitometric detection was carried out at 299 nm in UV. Linear responses were shown by the detector over the range of 200–1200 ng/band for both drugs. The proposed method was validated as per ICH guidelines. The method was successfully applied for estimation of both drugs in tablet formulations. Forced degradation study was carried and efonidipine was found to be susceptible to base hydrolysis and oxidative stress degradation while TEL was stable in acid-base hydrolysis, oxidative stress, dry heat and photo stability testing conditions. The developed method can be used for the analysis of stability samples. Greenness assessment of developed method was performed using AGREE software. The method was found to be greener having greenness score of 0.69.

Best reconstruction frequency for time-reversal process of Lamb waves and its determination from a single measurement

This article presents a theoretical framework for the concept of the best reconstruction frequency (BRF) of Lamb waves in elastic plates and its significance in the context of structural health monitoring (SHM). The time-reversal process (TRP) of Lamb waves has been widely explored for baseline-free damage detection in thin-walled structures. Previous studies have indicated that the accuracy of damage detection can be significantly improved by exciting Lamb waves at a frequency where the time-reversibility in the undamaged state is maximum within a desired frequency range. This frequency, termed the BRF, has been determined phenomenologically in prior research but lacked a rigorous theoretical foundation. In this study, the BRF is derived as the frequency at which the amplitude dispersion of the main mode of the reconstructed signal after the TRP is minimized. Accordingly, a method is put forth to determine this frequency from a single measurement using a broadband excitation eliminating the need to compute the similarity between the reconstructed and input waveforms at different excitation frequencies. The developed theory is validated with experiments conducted on an aluminium plate with Lamb waves generated and sensed by surface-bonded piezoelectric patch transducers. Notably, the study establishes that the BRF is a system property specific to a given transducer-plate-adhesive system and is independent of the distance between transducers. This characteristic makes it suitable for identifying damage locations when employing multiple sensing paths. The findings constitute an important milestone in understanding the TRP of Lamb waves and developing robust SHM technologies based on it.

Longitudinal Wave Defect Detection Technology Based on Ablation Mechanism

For laser ultrasound in the thermoelastic mechanism, excitation of ultrasonic body wave signal is weak, it is not easy to realize the detection of deep defects inside the workpiece. While the ablation mechanism produces a high and practical ultrasonic signal-to-noise ratio, this paper is based on the generation mechanism of laser ablation excitation of ultrasonic waves, the establishment of laser ultrasound in the ablation mechanism in the aluminum plate excitation and propagation of ultrasonic numerical model, through the solution, obtained the ultrasonic acoustic field map, discussed the ablation mechanism of the laser ultrasonic body wave acoustic field directionality. Additionally, the preliminary verification of the validity of the model is presented. Then, in order to explore the application potential of high signal-to-noise ratio longitudinal waves in defect detection, defects of different depths are preset in the model for simulation calculations, and waveform and acoustic field analyses are performed on the simulation results to study the ultrasonic propagation paths inside the member and the interaction with the defects, and the transverse position and depth of the internal defects are judged by using B-scan imaging. Finally, experimental validation is carried out. The experimental results are highly consistent with the simulation model, and the defect experiments can qualitatively determine the location of internal defects and verify the practicality and accuracy of the model.

The improvement of heat transfer using Co/SiO2 spiral structured catalyst for green diesel production by Fischer–Tropsch synthesis

In this study, the improvement of heat transfer was applied to eliminate hotspots of a highly exothermic reaction, Fischer–Tropsch synthesis (FTS), by means of two facile methods: (I) adding high thermal conductive materials media diluted in catalysts (SiC and Al chips), and (II) using structured reactors equipped with well-designed structured catalysts with advantages of heat dissipation/removal. The 20%Co/SiO2 catalyst powder prepared by simple impregnation was employed for constructing structured catalysts and granular packed bed catalysts. The structured catalyst was prepared by coating method of Co/SiO2 slurry on an aluminum spiral and plate substrate. The catalytic performance of as-prepared catalysts was then tested for FTS in a fixed-bed reactor at 210–230 °C, 20 bar. Both gaseous and liquid products were collected and analyzed. The heat transfer improvement of packed bed catalytic system and structured catalytic system were compared and discussed. As a result, the structured catalytic system with spiral structured catalyst can provide the best improvement of heat/mass transfer, resulting in enhanced diesel selectivity, though the oil production rate was unsatisfactory. Meanwhile, among the packed bed catalytic systems, SiC media possessed the best heat removal material, producing the highest oil yield. In addition, the fresh and spent catalysts were analyzed by several techniques including TEM, SEM, XRD, BET, ICP-OES, H2–TPR, and TGA to relate the physicochemical properties of the prepared catalysts and its FTS performance.

Design of an injera baking system using parabolic trough solar collectors at Mekelle University cafeteria

Injera baking poses a significant energy demand and strain on the national grid, requiring temperatures of 180–220 °C with traditional clay Mitads. This study aimed to design a solar thermal system to replace electrical baking energy at the Mekelle University student cafeteria. The system, designed for baking 11,000 Injera within a 6-h daily operation, comprises 92 Anodized aluminum plate Mitads heated by hot oil from an oil gallery, stored in a hot oil storage unit, and recharged via a parabolic trough solar collector. A heat exchanger and thermal storage system ensure efficient heat transfer and storage. Computational Fluid Dynamics (CFD) and Soltrace analyses were conducted to assess temperature distribution on the baking pan and oil gallery surfaces, as well as solar thermal heat flux. Results revealed a heating capacity of 2.11 kW per Mitad, meeting the required capacity, and a system energy consumption of 1216.5 MJ per hour, achieving a thermal efficiency of 57.4 %. Baking Injera at higher temperatures, enabled by a uniform temperature distribution, yielded uniformly textured Injera with an optimal number of eye bubbles and prevented sticking to the Mitad. Consequently, this design offers a viable alternative for the energy-intensive application at the Mekelle University student cafeteria, providing valuable insights for future solar thermal Injera baking system designers.

Heat transfer experimental and numerical study of a three-sided serpentine with the operating fluid directly contacting the PV cell back

The cooling methodologies of photovoltaic/thermal equipment are crucial not only to maintain optimal operating temperatures but also to improve the performance of the photovoltaic systems and prolong their lifespan. Traditional heat exchangers often require physical contact with the material to be cooled, posing challenges for specific projects. Therefore, this study introduces an innovative heat exchanger made of aluminum plate, allowing direct contact of the cooling liquid with the surface to be cooled. The thermal performance of the serpentine, coupled to a steel plate simulating a photovoltaic-thermal panel, was evaluated experimentally. CFD numerical simulations were conducted to analyze the thermal performance of the heat exchanger, providing valuable temperature profiles for single-phase flows. The outcomes showed that the simulated and experimental data agreed well. Particularly, when considering the outlet fluid temperature the mean absolute error between the simulated and experimental results was around 0.5 °C, with a relative error of aproximatelly 1.8 %. To evaluate the influence of the type of material that forms the serpentine, heat exchangers with two different polydimethylsiloxane (PDMS) serpentines were numerically investigated. The PDMS serpentine provided a more heterogeneous steel plate temperature profile compared to the aluminum one; however, such an issue can be corrected with geometry modifications, such as a greater width and cross-sectional area. For all flow rates, the steel plate temperature using aluminum serpentine presented a lower average temperature than that with PDMS serpentine (an average of 6.3 % lower). The wide PDMS serpentine exhibited a better cooling performance than the narrow PDMS serpentine (an average of 92 %) since the heat transfer surface area was enhanced in the former case.

Evaluation of two constitutive modeling approaches for finite element simulation of ballistic impact of varying thickness monolithic aluminum plates by steel spheres

Evaluation of two constitutive modeling approaches for finite element simulation of ballistic impact of varying thickness monolithic aluminum plates by steel spheres

Enhancing the performance of PVT-TEG power generation systems by heat pipes and Fe3O4 nanofluids

In recent years, enhancing the cooling of photovoltaic (PV) panels to improve overall energy efficiency has become a significant focus. In this study, we propose an improved power generation system integrating semiconductor thermoelectric generators (TEGs). The integration involves the installation of several heat pipes and serpentine copper tubes on the back of PV panels, with nanofluids flowing through the copper tubes as the working fluid, effectively cooling the PV panels. The copper tube is connected to the heat exchanger on the high-temperature side of the TEGs, forming a closed-loop circulation system. Consequently, the cooling fluid transfers heat to the hot surface of the TEGs, utilizing waste heat generated by the PV panels for electricity generation. The TEGs consist of 10 thermoelectric modules, with the low-temperature end in contact with the finned aluminum plate (TEGs radiator) and actively cooled by natural air cooling. Additionally, to validate the design rationale, multiple sets of comparative experiments were arranged. The experiments utilized nanofluids with volume fractions of 0.5 %, 1 %, 2 %, and 3 %, and water, as the cooling fluid. The experimental results demonstrated that the maximum operating temperature of the reference PV panel can reach 81.9 °C, and the average and maximum exergy efficiencies throughout a day are recorded at 16.91 % and 31.84 %, respectively. It’s noteworthy that the most significant cooling effect occurs when the nanofluid volume fraction is 2 %, reducing the maximum temperature of the PVT panel to 61.5 °C. Simultaneously, the average daily exergy efficiency and exergy efficiency of the PVT-TEG power generation system reached peak values of 21.06 % and 39.87 %, respectively. Compared to the reference PV panels, the output power of the PVT-TEG system increases by up to 30.51 %.

An Efficient Computational System For Defect Prediction through Neural Network And Bio-inspired Algorithms

Detecting and locating damage is essential in maintaining structural integrity. While Artificial Neural Networks (ANNs) are effective for this purpose, their performance can be significantly improved through advanced optimization techniques. This study introduces a novel approach using the Grasshopper Optimization Algorithm (GOA) to enhance ANN capabilities for predicting defect aluminum plates. The methodology begins by deriving input parameters from natural frequencies, with defect locations as the output. A Finite Element Model (FEM) is used to simulate data by varying defect locations, creating a comprehensive dataset. To validate this approach, experimental data from vibration analyses of plates with different defect locations is collected. We then compare the performance of our GOA-optimized ANN against other metaheuristic algorithms, such as Cuckoo Search Algorithm (CSA), Bat Algorithm (BA), and Firefly Algorithm (FA). Notably, CSA's performance is slightly close to GOA. The results show that our GOA-based method outperforms these traditional algorithms, demonstrating superior accuracy in damage prediction. This advancement holds significant potential for applications in structural integrity monitoring and maintenance.

Thermal management characteristics of a novel cylindrical lithium-ion battery module using liquid cooling, phase change materials, and heat pipes

To improve the thermal performance of large cylindrical lithium-ion batteries at high discharge rates while considering economy, a novel battery thermal management system (BTMS) combining a cooling plate, U-shaped heat pipes, and phase-change material (PCM) is proposed for 21700-type batteries. The effects of variables such as the contact angle between a corrugated aluminum plate (CAP) and the battery, the coolant flow direction in the cooling plate, the type of PCM, and the coolant flow velocity on the thermal characteristics of the batteries in the BTMS are investigated, and the advantages of this coupling cooling strategy relative to a single active cooling or a single active and passive cooling combination strategy are discussed. The results indicate that a corrugated aluminum plate is beneficial for significantly improving the temperature uniformity of the batteries. A staggered flow-direction scheme of adjacent channels significantly improves the temperature uniformity relative to the other inlet flow modes. The thermal performance of the batteries in the BTMS using paraffin and expanded graphite (PA/ EG) is superior to that with pure paraffin or paraffin and copper foam (PCF), with temperature uniformity improved by 44.6 % and 16.0 %, respectively. Increasing the coolant flow velocity can decrease the maximum temperature of the batteries and significantly reduce the heat dissipation share of PCM, resulting in a decrease in the temperature uniformity of the batteries in the BTMS. Meanwhile, compared with pure liquid cooling or a combination of liquid cooling and heat pipe or PCM, the proposed coupling BTMS not only reduces the maximum temperature of the batteries and further improves the temperature uniformity, but also significantly reduces the operating energy consumption of the BTMS.

Bolt looseness detection in lap joint based on phase change of Lamb waves

Bolts are widely applied to lap joints in many industrial fields. Due to harsh environment and low quality of operation, bolt looseness may appear during service. For lack of an understanding of the Lamb wave propagation process across bolted joints, most of the existing methods exploit some basic characteristics such as the transmitted energy as the looseness index, which is insensitive to bolt looseness at the early stage. To take full advantage of the information in the Lamb wave propagation and improve the detection performance, this study proposes a method for bolt looseness detection based on the phase change of Lamb waves during the propagation process. Firstly, the contact status is investigated based on the distribution of contact press, and the change of contact area along with bolt torque is analyzed. Subsequently, the propagation process of Lamb waves across bolted joints is revealed, based on which the monotonic relationship between the phase delay of Lamb waves and the extent of bolt looseness is derived. Thus, a looseness index based on phase change can be established to detect bolt looseness. Finally, the experiment is carried out in a bolted joint composed of two aluminum plates. The phase change in received signals conforms to the analyzed propagation mechanism of Lamb waves in bolted joints and verifies the effectiveness of the established bolt looseness index. Compared to the traditional methods based on the transmitted energy of Lamb waves, the proposed method is more sensitive to the change of bolt torque, especially at the early stage of bolt looseness.

The development of multiplexing capability for reflective matched fiber bragg gratings interrogation technique and its application in real-time micro cracks detection

Abstract Cracks detection in engineering structures is pivotal for ensuring structural reliability and preventing catastrophic failures. In this article we developed multiplexing capability of reflective matched fiber Bragg Gratings (RM-FBGs) interrogation technique and utilized it for crack detection in an assembly aluminum plates. Firstly, the proposed multiplexing capability is analyzed by applying axial strain on an array of five FBGs pasted on five separate aluminum assemblies. The strain in any FBG due to localized micro-crack resulted in variation its output itself by ascertaining no effect in the outputs of other FBGs, certifying the multiplexing capability of RM-FBGs scheme. The developed RM-FBGs scheme is practically applied micro-cracks detection in a V-shape crack produced in assembly of aluminum plates. The crack is monitored by an array of three multiplexed FBGs epoxied to the plate’s junction at three different positions P1, P2 and P3. Where P1 is at beginning, P2 is at middle and P3 is at end of the crack. Sensitivities of the FBGs at points P1, P2 and P3 were found to be 0.09 ± 0.0001 V μm−1, 0.10 ± 0.007 V μm−1 and 1.08 ± 0.09 V μm−1, respectively and resolutions were found to be 0.22 μm, 0.20 μm and 0.02 μm, respectively. Variation in gauge length of the optical fiber from 100 mm to 200 mm resulted in 76.36% increase in crack width sensing range but at the cost of compromise in sensitivity and resolution. The proposed multiplexed RM-FBG can be deployed for early micro-cracks detection in metallic and non-metallic structures with sub-micrometers resolution.

Numerical investigation on drying characteristics between hot wind and wet coating of battery electrode

In this paper, a three-dimensional dynamic drying model is established between hot wind and wet coating based on dynamic mesh method and multi-field coupling theory of porous media. This model considers the combined influences of hot wind and aluminum plate on drying characteristics of wet coating comprehensively based on meshless parallel method. It is proved to be reliable because its simulation data within the error range of plus/minus 15 %. Through this model, the influences and distribution of different operating parameters on drying characteristics are analyzed for surface and interior of wet coating, and the velocity, temperature and relative humidity of hot wind are selected as 8 m/s-10 m s-1, 353.15K-373.15 K and 35 %-55 %, respectively. The results show that the drying processes of surface and interior can be accelerated effectively for wet coating by increasing velocity and temperature of hot wind, while the relative humidity has little effect on its drying characteristics. Meanwhile, the variation trends of wet coating with the drying time as 0–20 s, 20s-30 s and 30s-50 s are consistent with the acceleration, uniform and deceleration drying processes of porous media, respectively. Finally, the drying uniformity is compared for different partitions of wet coating. The results show that the growth gradient of drying non-uniformity with the increase of velocity is smaller than that with the increase of temperature. The change gradient of drying non-uniformity for wet coating with the change of temperature is larger than that with the change of velocity. For drying model in this paper, the optimal operating strategy when the velocity of hot wind is 8 m/s-10 m s-1, temperature is 363.15 K and relative humidity is 45 % can be adopted to improve the drying uniformity of wet coating while reducing its total drying time in engineering. The research results provide an important theoretical basis for control parameters regulation of lithium-ion battery coating oven.

Modelling Low-Frequency Vibration and Defect Detection in Homogeneous Plate-Like Solids

The inspection of thick-section sandwich structures with skins around core materials such as honeycomb, balsa, and foam relies on low-frequency vibration techniques to identify defects through changes in amplitude or phase response. However, current industrial methods are often limited to detecting specific types of defects, potentially overlooking others. Moreover, these methods do not gather detailed information about the defect type or depth, as they only analyse a small portion of the available data instead of the full relevant response spectrum. This paper explores the scientific basis of using low-frequency vibration in the pitch-catch variant for defect detection in homogeneous solids, through analysis of the full relevant frequency spectrum (5–50 kHz). Defects in structures lead to reduced local stiffness and mass in the affected area, causing resonance in the layer above, resulting in amplified vibrations known as local defect resonance (LDR). In this work, an aluminium plate with a 40 mm diameter circular flat-bottomed hole (FBH) at a depth of 1 mm (representing a skin defect) is excited with a chirp signal of 5–50 kHz, and the response is monitored 17 mm away from the excitation point. Finite-element analysis (FEA) is used for the numerical model, addressing challenges in creating an accurate model. The process to optimise the numerical model and the reduce model-experiment error is outlined, including challenges such as the lack of knowledge of material damping. The study emphasizes the importance of modelling the probe’s stiffness and damping effects for achieving agreement between the model and experiment. After incorporating these effects, the maximum LDR frequency error decreased from approximately 3 kHz to less than 1 kHz. In addition, this study presents a method with the potential for defect classification through comparison to modelled responses. The minimum difference error was used to quantify the resonance frequencies’ error between the model and the experiment. Since the resonant frequencies are a function of the defect’s shape, size, and depth, a relatively low root mean squared (RMS) error across the resonance frequency error spectrum indicates the defect’s characteristics. Finally, defect detection and sizing using the pitch-catch probe are explored with a wide-band excitation signal and a line scan through the mid-plane of the defect. A method for defect sizing using a pitch-catch probe is presented and experimentally validated. Accurate defect sizing is achieved with the pitch-catch probe when the defect width is at least ≥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ge $$\\end{document} twice the 17 mm pin-spacing of the probe.