Maximum Impedance Research Articles

Interface Characterization of Fusion Bonded Composites Made from Laser-Pretreated Steel and Glass Fiber-Reinforced Thermoplastics Using Electrochemical Impedance Spectroscopy

Material-hybrid designs made of metal and plastic are becoming increasingly important in the automotive and aerospace industries. They place new demands on joining technology in particular. One promising process is the fusion bonding of metals and fiber-reinforced thermoplastics. In this process, the thermoplastic matrix material of the fiber-reinforced composite component is melted and a direct adhesive bond is created with the metallic joining partner. This joining technology has already been extensively studied in the past. In particular, the interface between the joining partners has been identified as a critical factor for the long-term quality of the joint. The interface can be altered by influences during production, such as e-coat process or the effects of harsh environmental conditions during operation like corrosion and thermomechanical loads. Determining the extent of these influences on the interface condition and thus the quality of the joint is difficult, but it is essential to support the use of the joining method in safety-critical areas. Previous investigations of this joining method have mostly been carried out destructively using tensile shear tests and non-destructively using fiber optic and piezo ceramic sensors, but all approaches have only shown limited significance with regard to the metal-plastic interface in detail. Electrochemical impedance spectroscopy (EIS) as a very sensitive measurement method could represent an almost non-destructive and at the same time very sensitive alternative which is currently not reported for this use case in the literature. In previous internal investigations, we found that EIS can be used to measure layer thicknesses of up to 3.5 mm, contrary to the usual use of this test method for characterizing the properties of thin coatings, corrosion behavior and battery performance. In fusion bonding applications, typical material thicknesses of thermoplastics above the interface are around 1.5 mm and are thus well above the usual layer thicknesses of approx. 20 µm to 100 µm for typical EIS applications. This study aims to examine how EIS can be used advantageously for the interface characterization of fusion bonded specimens and up to which extent the EIS can provide a statement about the metal-plastic interface. In this study, a joint of a laser-pretreated steel and a glass fiber-reinforced PA6 is investigated. We measured specimens directly after production, after a treatment similar to an automotive e-coat process and after certain intervals of a salt spray test. Using the Kramers-Kronig transformation, the EIS data was validated and qualitatively analyzed with Nyquist and Bode diagrams, the impedance at 0.1 Hz, the maximum impedance and equivalent circuits. Tensile shear and edge shear test serve as destructive reference tests to determine strength parameters of the joints and evaluate the respective fracture patterns. This opens up the possibility to correlate the results of EIS and destructive measurements. In summary, EIS is suitable for characterizing the metal-plastic interface, even with polymer thicknesses of 1.5 mm, which are comparatively high for EIS. Due to the very low phase angle and the resulting low dielectricity of the glass fiber-reinforced thermoplastic, changes in the impedance data are directly related to the interface condition. The measured impedance spectra could be differentiated with Nyquist and Bode diagrams, the impedance at 0.1 Hz and the maximum impedance.

Investigation of the Effects of Cu and Fe/Cu Doping on ZnO Nanoparticles for Application as a Solid Electrolyte Battery

In this work, investigation is done on the effect of doping with copper (Cu) and iron/copper (Fe/Cu) on zinc oxide (ZnO) nanomaterials synthesized through a cost‐effective wet chemical precipitation method for application as a solid‐state electrolyte battery. The scanning electron microscope with energy dispersive X‐ray spectroscopy is used to investigate the morphology and elements presence in Cu and Fe/Cu‐doped ZnO nanoparticles. The X‐ray diffraction data illustrates that the crystallite sizes of pure ZnO, Cu–ZnO, and Fe/Cu–ZnO nanoparticles are 14.86, 13.35, and 10.66 nm, respectively, at the (101) plan calculated by Debye Scherrer's formula. The UV‐Vis absorption spectrum shows that the band gap energies of ZnO, Cu–ZnO, Fe–ZnO, and Fe/Cu–ZnO nanoparticles are identified as 3.382, 3.690, 3.5, and 3.465 eV, respectively. The electrical characterization revealed maximum impedance in Fe/Cu–ZnO nanoparticles with 400 Ω at 1 KHz frequency in comparison to other samples. The current–voltage (I–V) measurement shows that the current sensitivity and electrical conductivity are both enhanced for Fe/Cu–ZnO nanoparticles. Fe and Cu co‐doping improved the electrical characteristics of ZnO, and the Fe/Cu–ZnO nanoparticles are employed as a solid electrolyte in a battery, which achieved a high specific charge capacity of 657.85 mAh g−1.

Role of impedance drop and lesion size index (LSI) to guide catheter ablation for atrial fibrillation.

When using lesion size index (LSI) to guide catheter ablation, it is unclear what combination of power, contact force and time would be preferable to use and what LSI target value to aim for. This study aimed at identifying desirable ablation settings and LSI targets by using tissue impedance drop as indicator of lesion formation. Consecutive patients, undergoing their first left atrial (LA) catheter ablation for atrial fibrillation, with radiofrequency energy (RF) powers of 20, 30 and 40W were enrolled. Tissue impedance, contact force (CF), Force Time Integral (FTI) and LSI values were continuously recorded during ablation and sampled at 100Hz. Mean CF and Contact Force Variability (CFV) were calculated for every lesion. The effect of RF power, ablation time, CF and CFV on impedance drop and LSI were assessed. A total of 3258 lesions were included in the analysis. For any target LSI value, use of higher RF powers translated into progressively higher impedance drops. The impact of lower CF and higher CFV on impedance drop was more relevant when using lower powers. Target LSI values corresponding to maximum impedance drop were identified depending on RF power, mean CF and CFV used. Even in the context of an LSI-guided ablation strategy, use of lower or higher powers might lead to different lesion sizes. Different LSI targets might be needed depending on the combination of RF power, CF and CFV used for ablation. Incorporating indicators of catheter stability, like CFV, in the LSI formula could improve the predictive value of LSI for lesion size. Studies with clinical outcomes are required to confirm the clinical relevance of these findings.

Effect of chromic acid anodization on the corrosion resistance of laser cladding austenitic stainless steel coatings based on orthogonal tests

In this paper, Ni transition layer and Fe-based alloy coatings were prepared on HT250 by laser cladding technology, and the corrosion resistance of the coatings was further enhanced by the chromic acid anodization (CAA) surface treatment process. The effects of time (t), current intensity (I), and temperature (T) on the microstructure and corrosion resistance of the coating after CAA were explored based on the three-factor and three-level orthogonal test method. The results show that after CAA, the intergranular morphology of the coating is corroded, the intragranular organization is exposed and protrudes, and the micro-morphology shows a multi-layer "skeleton" overlapping structure. The main phases were transformed from γ-Fe (FCC) to CrNi (FCC) and FeNi (BCC). The corrosion residue of the original coating is a lamellar metal-carbide weave, whereas the CAA coating is fibrous. The order of influence of CAA process parameters on corrosion depth and maximum impedance value is I >t >T. I on the degree of densification of the passivated film is 1.03 and 1.81 times higher than T and t, respectively. The best corrosion resistance of the sample was obtained at t = 30 min, I = 0.1 A, and T = 40 ℃, and its corrosion rate (2.83 × 10−3 g/m2·h) was 29.88 % lower than the original coating (4.03 × 10–3 g/m2·h).

Facile design of PTFE-kaolin-based ternary nanocomposite as a hydrophobic and high corrosion-barrier coating

Abstract Superhydrophobic nanostructured coatings are a promising technology in construction engineering. This study developed a hydrophobic film through a simple mixing method, utilizing kaolin and polytetrafluoroethylene as additive particles, 1H,1H,2H,2H-perfluoro-decyl triethoxysilane as a modifier, and epoxide resin and polyamide curing agent as adhesives. By controlling variables, it was determined that the C1P0.2EP coating immersed in a 3.5 wt% NaCl solution for 1, 3, and 7 days exhibited the maximum impedance radii of 47,373, 20,334, and 1,982 Ω·cm2, respectively. It also demonstrated the highest Bode modulus values, the largest E corr, and the smallest I corr. Furthermore, after 300 h in a salt spray chamber with a 3.5 wt% NaCl solution, the C1P0.2EP coating showed no rust spots or bubbles, demonstrating its excellent corrosion resistance. Moreover, wear resistance tests and self-cleaning experiments were conducted on the C1P0.2EP coating. The results showed that after 100 friction cycles, the surface exhibited no visible scratches, and the contact angle of the coating decreased by only 4°. Additionally, neither soil particles nor dirty water adhered to the coating, indicating that the C1P0.2EP hydrophobic coating possesses not only excellent corrosion resistance but also superior wear resistance and self-cleaning capabilities.

Electroacoustic evaluation of the bone conduction transducer B250 for vestibular and hearing diagnostics in comparison with Radioear B71 and B81

Objective The objective is to evaluate the electroacoustic performance of the B250 transducer and to compare it with the two most widely used audiometric transducers B71 and B81. Design The electroacoustic performance was evaluated in terms of sensitivity level, distortion, maximum hearing level and electrical impedance. Study sample Six B250 prototype transducers were evaluated and compared with published data of B71 and B81 together with complementary measurements of maximum hearing level at 125 Hz and phase of electrical impedance. Differences in reference equivalent threshold vibratory force levels were estimated by comparing hearing threshold measurements of 60 healthy ears using B81 and B250. Results B250 has approximately 27 dB higher sensitivity levels than both B71 and B81 at 250 Hz and can generate higher maximum hearing level at low frequencies: 11.8 to 35.8 dB (125–1000 Hz) higher than B71, and 1.4 to 18.6 dB (125–750 Hz) higher than B81. The maximum average difference in reference threshold force levels was 13.5 ± 8.7 dB higher for B250 at 250 Hz compared to B81. Conclusions B250 can produce higher output force with less distortion than B71 and B81, especially at 125 and 250 Hz, which could possibly improve low frequency investigations of the audio-vestibular system.

Super-wideband fractal antenna of two-arm structure with broadband balun

ABSTRACT A balanced two-arm antenna has been proposed for super-wideband (SWB) operation to work efficiently over the frequency range (2.95 − 34 GHz ). The antenna proposed for SWB operation can be considered as composed of two main parts. The first part is the radiating surface of the antenna and is composed of two-arms leading to a balanced antenna structure. For wideband operation, each arm has a double-fractal (angular/radial) structure. The second part of the antenna structure is the wideband feeding balun that is responsible for realising maximum power transfer and impedance matching while feeding the balanced radiating two-arm structure from the conventional unbalanced coaxial line. A prototype has been fabricated for experimental characterisation of the proposed antenna. Both the simulation results and the experimental measurements come in good agreement with each other showing that the proposed antenna can be good candidate for many super-wideband applications of future generations of mobile communications. The proposed antenna has overall dimensions of 40.0 mm × 21.0 mm × 1.5 mm . It is shown by simulation and measurement that the proposed antenna has %BW of 168 % , RBW of 11.5 : 1 , and BDR of 2015 . The maximum gain ranges between 2.3 and 6.2 dBi. The radiation efficiency is greater than 98% over the frequency range ( 2 − 24 GHz ) and is greater than 85% over the frequency range ( 24 − 34 GHz ).

Preparation and Corrosion Resistance of OMMT/EP Composite Coatings in Sulfur-Containing Sodium Aluminate Solution

Organic montmorillonite (OMMT) was prepared from Na-montmorillonite (MMT) by Hexadecylamine (HDA) modification. The composite material has good smoothness, acidity, and salt resistance. OMMT was characterized using small-angle X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and a video optical contact angle measuring instrument. The results showed that the layer spacing was enlarged from 1.44 nm to 2.87 nm after the modification, and the hydrophobicity performance was greatly improved. The organic modification of MMT was successful. The surface morphology, roughness, and anticorrosion properties of the organic montmorillonite/epoxy (OMMT/EP) composite coating were investigated and compared with those of the epoxy (EP) coating. The OMMT/EP composite coating had a flatter surface than the EP coating. The roughness was reduced from 65.5 nm to 10.3 nm. The electrochemical impedance spectroscopy showed that the composite coating’s thickness positively affected its anticorrosion performance, the corrosion current density (Icorr) decreased with the increase in thickness, and its maximum impedance was much larger than that of EP coating. The protection efficiency of the OMMT/EP composite coating was 77.90%, which is a significant improvement over the EP’s 31.27%. In addition, the corrosion resistance of the composite coating gradually decreased with increasing immersion time, but the change was insignificant.

A novel noise-reducing and anti-corrosion polyurethane elastomer coating material modified by MXene / porous TiO2

The present study reports on a composite coating exhibiting noise reduction and anti-corrosion properties. We successfully synthesized a Ti3C2Tx@TiO2-PDA composite filler that involves growing porous TiO2 onto lamellar MXene (Ti3C2Tx) material and further coating both surfaces with a layer of polydopamine (PDA) material, providing the coating material with a micro-cavity structure to enhance its ability to dissipate acoustic energy and resist corrosion. And we incorporated it into the prepared disulfide bond-modified polyurethane coating matrix. Experimental tests and finite element analysis demonstrate that the coating can reduce environmental noise by approximately 33% while maintaining a maximum impedance modulus |Z| of 5.51 × 107 Ω·cm2 after immersion in a 3.5 wt% NaCl solution for 25 days. The porous structure of the composite filler provides micro-cavities within the coating, while its lamellar structure acts as a physical barrier against corrosive media. Furthermore, introducing disulfide bonds enhances acoustic energy dissipation within the coating. Consequently, this coating exhibits exceptional corrosion resistance and noise reduction performance, presenting significant potential for applications in marine equipment's noise reduction and corrosion prevention.

Repair feasibility and performance enhancement analysis of Fe-based alloy coating on ductile iron surface by high-speed laser cladding

In this paper, high-speed laser cladding technology with a scanning speed of 40 mm/s was used to clad the ductile iron surface with the Fe-based alloy coating. The coatings' microstructure, element distribution, crystallographic structure, wear resistance, and corrosion resistance were investigated by using an optical microscope, SEM, XRD, friction and wear testing machine, super depth-of-field microscope, and electrochemical workstation. The results show that the microstructure of the coating is mainly γ-Fe solid solution and carbide eutectic structure. The phases of the coating are FCC phase (γ-Fe dominated), BCC phase, and carbide. The elemental distribution of the coating cross-section elements is uniform, and no quality obvious defects such as large gas pores and cracks are found. The coating mass loss was 60.0% and 47.1% of the substrate for different friction parameters and the more significant coating oxide build-up phenomenon with increased loading force. The self-corrosion rate of the coating was 0.006 g/m2·h, and the substrate was 0.042 g/m2·h; the maximum impedance value of the coating (1.34×104 Ω·cm2) was increased 20 times based on the substrate (619.2 Ω·cm2). In summary, Fe-based coatings with these process parameters can repair failed ductile iron parts and significantly extend their service life.

Dissolution dynamics of poly(4-hydroxystyrene) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions investigated by quartz crystal microbalance (QCM) method

Abstract The molecular size of alkaline cation has been reported to affect the dissolution of resist film in alkaline aqueous solution. However, the details are still unclear. In this study, the dissolution dynamics of poly(4-hydroxystyrene) (PHS) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions was investigated to clarify the effects of small alkaline cations on the dissolution dynamics of typical backbone polymer for chemically amplified resists by a quartz crystal microbalance (QCM) method. The temporal changes in the frequency and impedance of QCM substrates during development were measured. The maximum impedance reachable during development significantly exceeded that of the developer saturated with PHS unlike the case of tetramethylammonium and tetraethylammonium cations. This means that the PHS matrix near surface was swollen by decreasing the size of alkaline cation. By either increasing or decreasing the size of alkaline cation from tetramethylammonium and tetraethylammonium cations, the transient swelling layer became thick.

Determining Maximum Impedance Limits At A Point of Connection For Different Current Capacity Installations

Modern customers use many power electronics based devices that are often sensitive to power quality (PQ) related disturbances. Those devices produce current harmonics that in combination with the network’s impedance at a customer’s point of connection (POC) influence the network’s voltage quality. With a distorted supply voltage, many devices produce more current pollutions. Therefore, the network’s impedance at a POC is quite important and can have significant impact on the network’s power quality. At present some standards specify requirements of the voltage and/or current quality at a POC. However, only few requirements are given for the network’s impedance (short circuit power) which can highly influence the PQ performance at a POC. In this paper, estimation is made to determine the maximum impedance limits at the medium voltage (MV) and the low voltage (LV) customer’s POC. The network operators should be responsible to limit the maximum impedance value at a POC while approving a specific capacity connection to a customer.

Mechanical properties and oxidation corrosion resistance of phosphate ceramic coating enhanced by SiO2‐BNNSs material

AbstractA method of preparing SiO2‐BNNSs hybrid material by surface modification of boron nitride nanosheets (BNNSs) with SiO2 was proposed to improve the dispersion of BNNSs in the coatings. Then, phosphate ceramic coatings with BNNSs and SiO2‐BNNSs were prepared on stainless steel (304) by spraying. Characterization of BNNSs and SiO2‐BNNSs by X‐ray diffraction, Fourier transform‐infrared, Raman, and scanning electron microscopy proved the success of hybridization. The surface morphology and mechanical properties were conducted to characterize the protective performance of the coating. Simultaneously, the phase composition and electrochemical properties of the coatings after high‐temperature oxidation were studied. The results showed that ceramic coatings had low surface energy with a contact angle of 102.41° when .4 wt.% SiO2‐BNNSs was added. Compared with BNNSs coating, the mechanical properties of SiO2‐BNNSs coating were significantly enhanced, the hardness of .4 wt.%SiO2‐BNNSs coating was as high as 170 HV, and the interface bonding strength was 12.24 MPa. For the oxidation corrosion resistance, .4 wt.% SiO2‐BNNSs coating under oxidation at 400°C for 50 h had the minimum corrosion current density and maximum impedance, which were .864 μA/cm2 and 177 kΩ/cm2, respectively, this indicated that SiO2‐BNNSs coating could still maintain excellent oxidation corrosion resistance under high‐temperature conditions for a long time.

Pulse electrodeposition of a duplex-layer structured composite nickel-based coating with improved corrosion and abrasion resistance

In this study, a dual amorphous/crystalline nanocomposite coating of Ni–P/Ni–Mo–ZrO2 was designed and successfully deposited on pure copper substrates by pulse electrodeposition. The design of the Ni–P/Ni–Mo–ZrO2 dual coating takes advantage of the properties of the different structures and incorporates second phase reinforcing particles resulting in more comprehensive protective coatings. The surface morphology and microstructure were evaluated by SEM, EDS, WLI, XRD and TEM. The mechanical properties and electrochemical behaviors of the coating in a 3.5 wt% NaCl solution were investigated by wear tests, Tafel and EIS. The results show that the Ni–P/Ni–Mo and Ni–P/Ni–Mo–ZrO2 dual coatings are uniform, dense and crack-free, and the duplex interface is homogeneous. Compared with the Ni–Mo coating, the average friction coefficient and wear rate of the Ni–P/Ni–Mo duplex coating decreased to 0.18 and 5.433 × 10−4 mm3/N·m, respectively. The corrosion potential is positively shifted to −0.43 with a maximum impedance of 308 kΩ cm2. The mismatch of the interlayer defects causes a deviation in the corrosion path, resulting in a transformation from longitudinal pinhole corrosion into extended transverse corrosion, which effectively strengthens the capacity of the coating for corrosion resistance while maintaining the high hardness of its outer coating. Furthermore, the hardness of the dual Ni–P/Ni–Mo coating can be obviously reinforced by nanoparticles from 730 HV to 810 HV, the corrosion potential is shifted to −0.41 V, and the corrosion current density decrease to 7.7803 × 10−7 A/cm2. The improvement in the mechanical properties can be attributed to the ZrO2 nanoparticles, which could carry stress and transfer loads during the wear process. Meanwhile, the ZrO2 nanoparticles can reduce the nodule size by filling the binding boundary which is the main corrosion path, and reduce the number of surface defects, such as pinholes, which leads to a lower corrosion rate. In addition, the corrosion inhibition and nanoparticle codeposition mechanisms of the duplex coatings were further discussed.

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Pavement damage monitoring using electromechanical impedance of embedded piezoelectric plate

Piezoelectric transducers have seen widespread usage in the monitoring of structural health. It has tremendous potential for monitoring the health of infrastructure, especially pavement monitoring. In the present study, the impedance characteristics of a piezoelectric plate embedded in the pavement is utilized to monitor the health status of the pavement. Based on the piezoelectricity principle, a model of an electromechanical piezoelectric plate embedded in pavement is established. The damage of the pavement is considered as the thickness decreasing of the pavement layer. The present proposed model is verified by comparing its degeneration with the exact solution of a single layer model. Numerical results demonstrated that with the deceasing of the thickness of the pavement, which is considered as the deterioration of the pavement, the achievable maximum electromechanical impedance characterization including impedance, admittance and conductance decreased. This demonstrated that the achievable maximum impedance, admittance and conductance of an embedded piezoelectric plate could be used as the indicator of pavement health monitoring. This study primarily presents theoretical underpinnings for pavement monitoring using electromechanical impedance of piezoelectric plates.

The binding pattern of the docked two-segment-aptamer to penicillin G and its impedance sensing performance

A penicillin G (PEN-G) aptamer-docking-based impedance sensor was purposely designed and fabricated. The molecular dynamics simulation (MDS) method was used to decipher the binding pattern of the aptamer to PEN-G. Three electrochemistry techniques were involved in optimizing the key sensing parameters, characterizing the sensing process effectiveness, and systematically investigating the basic analytical performances. A comparative analysis of the binding pattern clarified the theoretical reason for the high impedance response produced by the optimized docked aptamer sequence. The research results indicated that the cis-D-5 T-PEN probe performed best among the four docked aptamers with the maximum impedance response when binding to the target. Compared with the parent single-sequence aptamer, the docked aptamers contain more active binding sites, which is conducive to generating larger impedance values to improve the method’s sensitivity. The sensor derived from the cis-D-5 T-PEN probe showed excellent analytical performance for detecting PEN-G residues in tap water. The detection limit and the linear range were confirmed to be ∼0.3 pM and 0.001–100.0 nM, respectively. The method’s average spiked recoveries were 79.8–92.1 %, with a relative standard deviation (RSD) of less than 20 %. The entire testing process could be completed within 1 h. The proposed sensor exhibits the advantages of simple operation, high sensitivity, and fast detection speed. Theoretical simulation effectively supports the experimental results, providing a new example and reference for introducing the MDS method into studying aptamer sensing systems.

Design of Domino-Resonators for Enhanced Power and Data Transmission of 13.56 MHz RFID Sensors

This paper presents a straightforward design algorithm to enhance power and data transmission for 13.56 MHz Radio Frequency Identification (RFID) sensor applications by using domino-resonators. In this algorithm, the transformed transponder impedance and modulation depth seen at the reader antenna are formulated and modeled under the presence of domino-resonators. To improve the accuracy, voltage-clamped mode of the tag Integrated Circuit (IC) is considered, which enables accurate calculation of the maximum readable distance, transferred power and equivalent tag IC impedance. For the sake of simplicity, a type-A ultralight tag IC is used and modeled, while all resonators and tag antenna dimensions are based on standard smart-card sized coils. The design algorithm is coded in MATLAB for a 5-coil RFID system, i.e. with three identical domino-resonators, and verified using LT-Spice simulations. For experimental validation, the designed 5-coil RFID system is implemented for enhancing the distance between a commercial 13.56 MHz RFID reader and ISO/IEC 14443A standard RFID tag IC.

Linear site-response characteristics at central and eastern U.S. seismic stations

Earthquake S waves can become trapped, or resonate, between the free surface and high-impedance basal layers, strongly contributing to site response at specific frequencies. Strong S-wave resonances have been observed in the central and eastern U.S., where many sites sit on unlithified sediments underlain by stiff bedrock. To evaluate S-wave resonances in this region, we calculated 1D linear site-responses at 89 seismic stations with developed S-wave velocity profiles into bedrock. We found that S-wave resonances at the fundamental and strongest (peak) modes occur across large ranges of frequencies, each spanning more than two orders of magnitude — 0.21–54.0 Hz and 0.29–71.5 Hz, respectively. Amplifications of ∼5 and ∼6 are common at the fundamental frequency and peak modes, respectively; the largest amplification calculated was 13.2. Using simple regression analyses, we evaluated the skills of six proxies derived from the S-wave velocity profiles to predict the frequencies and corresponding amplifications of the fundamental and peak modes. We found that the depths to the 1.0 km/s and 2.5 km/s horizons, consistent with other studies, and to the maximum impedance contrasts strongly correlate with the resonance frequencies and that the fundamental-mode and peak amplifications correlate with the maximum impedance ratios. Correlations improved for data subsets based on the number and magnitude of impedance ratios underlying the sites and are the strongest at sites underlain by a single impedance ratio of 3.0 or greater. Finally, we calculated the S-wave horizontal-to-vertical spectral ratios (HVSR) at each possible seismic station and found, consistent with other studies, that the first peak can be used to estimate fundamental-mode frequencies and the corresponding amplifications. Thus, S-wave HVSR, can provide useful estimates of the fundamental-mode linear site response parameters at sites lacking S-wave velocity profiles. Furthermore, S-wave HVSR curves appear to be useful to broadly categorize impedance-ratio profiles.

Machine learning based inversion for earth rock dam compaction density

In water resources and hydropower engineering and highway engineering, the compactness test of earth-rock mixed materials of the earth-rock dam and embankment plays an important role for construction quality assessment. The key is how to accurately and quickly evaluate the compaction density, which requires advanced methods. Meanwhile, machine learning has become an important and powerful tool for parameter prediction. In this work, a method to obtain the compactness of an earth-rock dam using machine learning algorithms is developed and verified. In so doing, first, by analyzing and processing the measured time history signal from a new fast Portable Falling Weight Deflectometer (PFWD), including time domain, frequency domain and mechanical impedance analyses, six optimized characteristic parameters are obtained to invert for the compactness, including the stiffness coefficient, the maximum time difference, the maximum amplitude ratio, the central frequency difference, the maximum stiffness impedance and the resonance frequency. Pearson coefficient was used to analyze the correlation among the six parameters and Gini index was used to analyze the influence degree of the parameters on the relative wet density. Then, the Decision Tree (DT) model, Random Forest (RF) model and Gradient Boosting Decision Tree (GBDT) model were used to predict the wet density and dry density of materials, respectively, and compared. PFWD was applied on a dam to acquire the time history signal, which was then preprocessed following a series of procedures including integrity check, outlier handling and normalization etc, and machine learning algorithms were used for training the data and parameter prediction. Examples show that, considering the generalization and optimization ability, for the GBDT model, the root-mean-square error (RMSE) of the predicted wet density of the earth-rock material is within 0.041 g/cm3 and that of the predicted dry density is within 0.032 g/cm3, which meet the requirements for construction detection and quality control. The proposed method based on PFWD signal analysis and machine learning algorithm models help better solve the nonlinear mapping problem between the PFWD signal and material density, and can accurately invert for the wet density and dry density of materials. It is an effective way for rapid detection and control of earth-rock dam construction quality.