Impedance Ratio Research Articles

Hetero Acoustic Layer Surface Acoustic Wave Resonator Composed of LiNbO3 and Quartz.

In this work, a shear-horizontal (SH) mode surface acoustic wave (SAW) resonator based on LiNbO3 (LN)/Quartz (Qz) hetero acoustic layer (HAL) structure was studied by simulation and experiment. By this HAL structure, the displacement and electric displacement are well confined in the piezoelectric layer. A lower mechanical loss of Qz than that of lossy amorphous SiO2 further enhances the quality ( Q ) factor. In addition, a negative temperature coefficient of frequency (TCF) of LN is compensated by selecting the crystalline orientation of Qz with a positive TCF. According to simulation results, the Euler angles of (0°, 101°, and 0°) and the normalized thickness of 0.2-0.3 λ (wavelength) for LN are selected to obtain a higher impedance ratio ( Z -ratio) and bandwidth (BW). The Euler angles of (0°, 160°, and 90°) for Qz are selected to obtain the positive maximum TCF. The fabricated resonator exhibits a Z -ratio of 95 dB and a BW of 15.9% in the 700 MHz range. The fit figure of merit (FoM) reaches 410, which is the best level ever reported for an LN-based resonator. The TCF of the resonator is -77 ppm/°C at anti-resonance frequency. A group of resonators composed of LN and LN/Qz with thin and thick electrodes were fabricated to further illustrate the good performance of LN/Qz. The LN/Qz HAL SAW resonator demonstrated in this work exhibits a high Z -ratio, low TCF, and wideband, which has the potential for high-performance wideband filters with steep passband and good temperature characteristics.

Optimizing stress impedance and medium-range ordered structure in Fe46.6Mo8.6Cr24.5B9.5C10Si6 amorphous alloy through tailored annealing treatment

Amorphous alloys are emerging as a highly promising category of materials for mechanical sensing, attributed to their favorable stress impedance performance. However, the practical achievement of the stress impedance ratio still falls considerably short of its theoretical potential, and the atomic-scale mechanisms underlying this phenomenon remain largely unexplored. Here, we report that the stress impedance ratio of Fe46.6Mo8.6Cr24.5B9.5C10Si6 amorphous alloy can be significantly enhanced by a tailored annealing treatment around the glass transition temperature (Tg), giving rise to the highest stress impedance ratio reaching up to 124%. Utilizing the high-energy synchrotron X-ray total scattering technique, the strong correlation between the stress impedance performance and the medium-range ordered structure of amorphous alloys is elucidated. Our findings revealed that an increase in edge-sharing atomic connection mode plays a pivotal role in enhancing the stress impedance performance. Furthermore, a composite film combining the amorphous alloy with silicone rubber was fabricated under the same annealing treatment, demonstrating a significantly improved sensitivity compared to the ribbon (706.10 MPa-1 vs. 32.93 MPa-1). This work not only contributes valuable insights into the atomic-scale mechanisms governing stress impedance in amorphous alloys but also proposes a general annealing strategy that holds the potential for unlocking new avenues in advanced sensing applications.

An Analytical Seismic Response for Rigid Underground Rectangular Tunnel Subjected to Incident P Waves

A diffraction model based on the diffraction theory of elastic waves for the dynamic response of underground rectangular tunnel subjected to incident P waves is established. The rectangular structure is assumed to be a movable rigid body embedded in a homogenous, isotropic, and linear elastic medium. One particular advantage of the model is that the effects of vital factors such as the rigid scattering, radiation scattering, as well as the two‐dimensional scattering effect, and the wedge diffraction during movement are fully considered. The numerical method is verified by comparing with experimental data and other solutions in the literature. In addition, a parametric analysis of the effects of the incident angle, surrounding rock medium, and aspect ratio on the tunnel is also presented. The results show that with the increase of the incident angle, different parts of the tunnel exhibit obvious nonuniform distribution characteristics, and the bending moment of the sidewall is greater than that of the top slab. When the impedance ratio exceeds 0.26, the influence of surrounding rock characteristics on the dynamics of structure is more obvious; with the increase of the aspect ratio, the peak values of axial force at the top slab increases, whereas it decreases at the sidewall.

Designing Parameters to Reshape the Inverter Output Impedance Based on the D-Split Method under Weak Grid Conditions

Novel energy generation technologies, such as high-permeability wind power and photovoltaic systems, exhibit inherent intermittency, randomness, and volatility. During periods of energy production from these sources, the impedance of the electrical grid frequently experiences significant fluctuations. Consequently, the grid manifests characteristics akin to a weak grid, highlighting the challenges associated with integrating renewable energy sources with variable output profiles. These fluctuations lead to a shift in resonance spikes of the LCL-type filter towards the lower frequency band, consequently impacting the stability of inverter grid connections. To mitigate this issue, the present study introduces a novel approach integrating the D-split method and a proportional–differential feedforward strategy. This combination aims to reshape the inverter’s output impedance, ensuring its consistent stability even amidst significant fluctuations in grid impedance. In this research, the optimal controller parameters for systems operating under robust grid conditions are initially determined. This selection process involves the application of the D-split method, supported by graphical visualization. Additionally, the amplitude and phase angle margin tester is employed while considering the system bandwidth as a limiting constraint. Moreover, accounting for the influence of grid impedance, the D-split method is reapplied to ascertain the most suitable values for the proportional–differential feedforward parameters. This adjustment aims to enhance the adaptability of the grid-connected inverter specifically in scenarios characterized by a weak grid. The hardware-in-the-loop (HIL) simulation results demonstrate that despite the presence of harmonics within the grid and a short circuit impedance ratio (SCR) of 3, the inverter maintains grid stability and effectively suppresses harmonics. Moreover, the total harmonic distortion factor (THD) of the grid-connected current remains below 5%.

The effects of joint spacing on transmission characteristics of stress waves through layered composite rock masses

AbstractThe effects of joint spacing on the transmission characteristics of stress waves through layered composite rock masses were investigated. First, a model of layered composite rock masses containing multiple parallel joints with different media in front of and behind the joints was introduced to study multiple reflections between joints. Second, wave transmission through layered composite rock masses was investigated and compared with wave transmission through traditional layered homogeneous rock masses. Finally, the effects of joint spacing and wave impedance ratio on particle velocity transmission coefficient were discussed. The results indicate that for wave propagation through rock masses with the same joint spacing, the onset time and amplitude of the transmitted wave in layered composite rock masses are smaller than those in layered homogeneous rock masses. For wave transmission through rock masses with the same nondimensional joint spacing, the onset time of the transmitted wave in the layered composite rock masses is similar to that in the layered homogeneous rock masses, while the amplitude of the transmitted wave in the layered composite rock masses is smaller than that in the layered homogeneous rock masses. In addition, the particle velocity transmission coefficient first increases and then decreases to be constant as the joint spacing increases, while it continues to increase as the wave impedance ratio increases for wave transmission through both layered composite rock masses and layered homogeneous rock masses.

Performance assessment of an iterative ensemble smoother with local analysis to assimilate big 4D seismic datasets applied to a complex pre-salt-like benchmark case

Abstract The use of 4D seismic (4DS) (or time-lapse seismic, TLS) in data assimilation (DA) makes the process more complex due to the higher amount of data to be assimilated, requiring more robust methods and better computational resources (processing capacity and memory). The development and application of permanent seismic monitoring technologies have increased in recent years, improving the overall 4D seismic quality in terms of signal resolution and repeatability. However, a massive amount of data is generated from the multiple monitors, making the incorporation of 4DS data in the DA process more complex. Therefore, robust DA methods capable of dealing with huge amount of data effectively and efficiently are essential. This paper aims to assess the performance of an iterative ensemble smoother method, named subspace ensemble randomized maximum likelihood with a local analysis, to assimilate a big dataset. The method was applied in a challenging pre-salt-like benchmark case with eight seismic surveys, one base, and seven monitors. The 4DS data are the impedance ratios (between two consecutive monitors) in 15 seismic horizons, totaling 105 maps to be assimilated. To our best knowledge, this is state of the art in terms of practical applications in DA. It was possible to assimilate all the data simultaneously: the 105 horizons for the 4DS data and the wells’ production and pressure data. The DA was successful in terms of results quality and method performance. We also ran a case assimilating only well data for comparison purposes.

Atlantic salmon adulteration authentication by machine learning using bioimpedance non-destructive flexible sensing

Temperature fluctuations at different stages of the supply chain increase the frozen-thawed cycle of perishable foods, potentially leading to quality and safety issues. For raw edible salmon in particular, it is not possible to ignore the issue of adulteration when frozen-thawed flesh is sold as fresh flesh. It is a challenge to achieve real-time detection of frozen-thawed salmon adulteration in fresh salmon. Existing impedance change ratio (Q-value) and PCA models cannot accurately authenticate frozen-thawed cycle adulterated salmon. In this paper, a flexible bioimpedance based non-destructive detection system was designed to authenticate adulterated salmon by online monitoring of changes in bioimpedance signals, ambient temperature, and relative humidity. The system provided a high level of monitoring accuracy and stability. Furthermore, an improved machine learning classification model based on principal component analysis - Bayesian optimization algorithm - support vector machine (PCA-BOA-SVM) was developed to effectively identify frozen-thawed adulterated salmon. The optimised model performance enhanced with prediction accuracy, precision, recall and F1 score of 0.9683, 0.9708, 0.9683 and 0.9679, respectively. This work could provide an effective solution to improve the authentication of food adulteration in the perishable food supply chain by improving traceability at all stages of the supply chain and sustainability of food industry development.

Abstract 14746: Association of Left Atrial Late Gadolinium Enhancement With Electrogram Abnormalities, Tissue Impedance, and Proximity to the Aorta

Introduction: Left atrial (LA) late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) predominates near the aorta(AO); however, LGE does not equate fibrosis and may be artifactual or indicate expanded interstituim. Hypothesis: We sought to examine the association of LA LGE with proximity to the descending and ascending AO and use regional impedance and voltage measurements to dissect the mechanism of LGE . Methods: The retrospective cohort included consecutive patients who underwent pre-procedural CMR and atrial fibrillation (AF) ablation between January 2016 - 2021. The association of voltage amplitude, impedance, and image intensity ratio (IIR) at each electroanatomic map point with distance from the nearest AO point was examined after adjustment for age, sex, AF type, AO stenosis, LA volume, and AO diameter. Results: Included 63 patients (age 65.5±8.8 years, 33% female). Among 42 ablation naive patients, distance from AO was unassociated with bipolar and unipolar voltage amplitudes, but associated with impedance (+0.04 ohm/mm, P=0.011) and IIR (-0.03 /mm, P<0.001). Among 21 patients with prior ablation, distance from AO was unassociated with IIR, but associated with bipolar (+0.01 mV/mm, P<0.001) and unipolar (+0.01 mV/mm, P=0.001) voltage amplitudes and impedance (+0.03 ohm/mm, P=0.025). Conclusions: Given lower impedance but normal voltage, de novo peri-AO LA-LGE likely signifies expanded interstitium, rather than fibrosis or fat infiltration. Following ablation, peri-AO voltage and impedance are both decreased compared to other LA regions, suggesting that peri-AO lesion delivery is more effective, likely due to lower impedance at baseline.

Impact of stress and magnetic field in annealing process on GMI and GSI effect of CoFeSiB amorphous material

This study focuses on investigating the impact of various annealing methods on the giant magneto-impedance (GMI) and giant stress induced GMI (GSI) effects of Co68Fe4.5Si12.5B15 ribbons. The GMI and GSI effect of the ribbons were characterized by impedance ratio under different annealing methods. The results indicate that the ribbon annealed with appropriate current density and additive 100 MPa tensile stress in Joule annealing exhibits the significant GMI ratio enhancing by 19.43 %. The study also demonstrates the significant influence of magnetic field in annealing, with magnetic field annealing showing great potential to improve both the GMI and GSI effects, increasing them to 75.76 % and 25.8 %, respectively. These findings provide insights into the development of materials with high sensitivity and thermal stability for modern sophisticated sensors.

Multi-target fault ride-through strategy for transformerless MMCs under asymmetric grounding faults in AC/DC hybrid distribution networks

In AC/DC hybrid distribution networks (HDNs), when asymmetric grounding faults occur, transformerless multiterminal modular multilevel converters (MMCs) should achieve three key targets of fault ride-through (FRT): 1) limiting the unbalanced fault currents; 2) injecting currents to support grid voltages in case of disconnection from grids; and 3) eliminating the zero-sequence circulating currents (ZSCCs) from fault networks through MMCs to nonfaulted networks. However, in medium voltage-level HDNs, the line impedances are mainly resistive-inductive, and traditional current injection methods are no longer effective. Moreover, in neutral nondirect grounding networks with multiple AC voltage levels, the voltages of nonfaulted phases rise, and it is difficult for MMCs to achieve fault current control. To solve the above issues, this manuscript proposes a multi-target FRT strategy. First, negative-sequence current controllers are used to eliminate the negative-sequence fault currents. Then, to support the positive-sequence voltages of grids, optimal and suboptimal active-reactive current references based on the line impedance ratios are proposed. To help transformerless MMCs with low modulation indices eliminate zero-sequence circulating currents, two zero-sequence voltage compensation modes and an improved zero-sequence current eliminator are proposed. Finally, the proposed fault current control is verified in MATLAB/Simulink.

Conflicting Associations among Bioelectrical Impedance and Cardiometabolic Health Parameters in Young White and Black Adults.

The purpose of this cross-sectional evaluation was to determine the associations between raw bioelectrical impedance and cardiometabolic health parameters in a sample of young non-Hispanic White and African American adults. A total of 96 (female: 52, male: 44) non-Hispanic White ( n = 45) and African American adults ( n = 51) between the ages of 19 and 37 yr (22.7 ± 3.83 yr) completed several fasted assessments including resting systolic blood pressure (rSBP), blood glucose (FBG), blood lipids, and bioelectrical impedance spectroscopy. Bioelectrical impedance spectroscopy-derived measurements included phase angle, bioimpedance index (BI), impedance ratio (IR), reactance index (XCi), fat-free mass (FFM), FFM index (FFMi), and absolute (a) and relative (%) total body water (TBW) and extracellular (ECF) and intracellular fluid (ICF). All bioelectric variables were collected at 50 kHz other than IR (250 kHz/5 kHz). Multiple regressions were conducted and adjusted for sex, age, and body mass index. rSBP was positively, and HDL was inversely, associated with all bioelectrical impedance and absolute hydration variables (all P ≤ 0.050) other than XCi for rSBP and XCi and FFMi for HDL. rSBP ( P < 0.001) was inversely, and HDL ( P = 0.034) was positively, associated with IR. FBG was positively associated with BI, XCi, FFM, TBWa, and ECFa (all P < 0.050). Metabolic syndrome severity was positively associated with BI, FFM, TBWa, and ECFa for women (all P ≤ 0.050) and with ICFa for African American women ( P = 0.016). Given the rapid increase in the prevalence of cardiometabolic health risks among young adults and the broad use of bioelectrical impedance in practice, the conflicting associations we observed in this age group suggest that bioelectrical impedance parameters should be used with caution in the context of cardiometabolic health risks and age.

Designed Structures of Interdigital Electrodes for Thin Film SAW Devices.

This paper studied the impact of the microstructure of interdigital electrodes on the performance of surface acoustic wave (SAW) resonators and proposed an innovative piston, dummy finger and tilt (PDT) structure, which was then applied to the GLONASS L3 band filters. Through the adoption of 3D finite element simulation (FEM), photolithography, and testing on an incredible high-performance surface acoustic wave (I.H.P. SAW) substrate, it is concluded that the total aperture length is 20T (T is period), resulting in a more optimal resonator performance; changing the width and length of the piston can suppress transverse modes spurious, but it does not enhance impedance ratio; to further improve the quality of the SAW resonator, the proposed PDT structure has been experimentally proven to not only effectively suppress transverse modes spurious but also possess a high impedance ratio. By utilizing a PDT structure within a "T + π" topology circuit, we successfully designed and manufactured a GLONASS L3 band filter with a bandwidth of 8 MHz and an insertion loss of 3.73 dB. The design of these resonators and filters can be applied to the construction of SAW filters in similar frequency bands such as BeiDou B2 band or GPS L2/L5 band.

Artificial neural network-aided decoupled prediction of earthquake-induced shallow and deep sliding displacements of slopes

The Newmark-type predictive models are extensively used to estimate earthquake-induced sliding displacements (D) of slopes. Most existing models are designed for shallow slope failure using polynomial regression. Based on a large amount of decoupled sliding-block analyses, this paper proposes an artificial neural network (ANN)-aided model to predict D for both shallow and deep slope failures using peak ground acceleration and spectral acceleration at the 2 s period (SA(2 s)). Three sub-models are included for estimating shallow sliding displacement, representing dynamic response of sliding mass, and modifying the displacement for deep failure, respectively. The key features achieved are as follows: (1) the inputted SA is more easily accessible than the mean period (Tm) required by the existing models; (2) impedance ratio (IR) is utilized to account for stiffness conditions of geo-materials underlying slip surfaces; (3) powerful ANN is introduced for the first time as a surrogate of the decoupled analysis. The SA-based model generally yields lower biases and uncertainty than the existing models. Since larger D is produced for smaller IR, the existing models with a single IR value would be unconservative for relatively stiff underlying soils and/or soft overlying soils. Coefficients of the proposed model are provided for practical applications.

Evaluation backscattering coefficients of heterogeneous media containing multispecies scatterers and lipids

Many attempts have been reported to evaluate tissue characterization from echo signals using the backscatter coefficient (BSC) as an indicator. In the evaluation of the BSC of the biological tissues, it is known that the effects of attenuation properties such as scattering attenuation and absorption attenuation, as well as interference between different scatterers, are significant. In this study, the effects of attenuations and interference were verified by evaluating a phantom with high absorption attenuation and a phantom with a mixture of two types of scatterers. Both the reflector method and the reference phantom method were applied to BSC evaluation for these phantoms, and the accuracy of the evaluation was verified. The results suggest that the effect of the acoustic impedance ratio between the scatterer and the surrounding medium tends to be reflected in the accuracy of the evaluation in media with large absorption attenuation. On the other hand, the difference between the mathematical theory and the actual evaluation results was observed due to interference effects. In terms of the accuracy of the evaluation method, the reflector method is effective in the vicinity of the focus, while the reference phantom method is effective in terms of application.

Adaptive Smith Predictor for Enhanced Stability of Power Hardware-in-the-Loop Setups

The stability and accuracy of power hardware-in-the-loop (PHIL) setups are sensitive to and deteriorated by the dynamics and non-ideal characteristics of their power interfaces, such as time delay, noise perturbation, and signal distortion. In this paper, a compensation scheme comprising a Smith predictor compensator is proposed to mitigate the impact of time delay on PHIL stability. Furthermore, an online system impedance identification technique is leveraged to enhance the robustness of the compensator and facilitate the compensation scheme with adaptivity to system impedance variation. Analytical assessment, simulation results, and PHIL experimental results are presented to verify the proposed compensation scheme. This scheme enables robust and stable testing of novel power technologies under varying impedance ratios representative of the complex scenarios emerging within the power sector.

Double-gradient seismic metamaterials with zero-frequency bandgap characteristic in a layered soil medium

Seismic metamaterials (SMs) are an artificially composite material designed within the sub-wavelength range. To attenuate low-frequency seismic surface waves, a metamaterial structural unit composed of a lead core and an auxetic foam coating layer was proposed; the higher impedance ratio results in the creation of a zero-frequency bandgap under layered soil conditions. To broaden the attenuation zone (AZ), double-gradient seismic metamaterials (DGSMs) were designed. The frequency domain analysis indicates that the attenuation area covering the range of 0–10 Hz is 89.8%. Through displacement-field analysis, the attenuation mechanism of DGSM on specific frequency surface waves can be fully explained. Finally, Taft seismic wave excitation is input for time history analysis, and the acceleration amplitude within 0–2 Hz decreases by 58.6%, which verifies the effectiveness of DGSMs in attenuation of low-frequency seismic waves.

Effects of changes in trunk inclination on ventilatory efficiency in ARDS patients: quasi-experimental study

BackgroundTrunk inclination from semirecumbent head-upright to supine-flat positioning reduces driving pressure and increases respiratory system compliance in patients with acute respiratory distress syndrome (ARDS). These effects are associated with an improved ventilatory ratio and reduction in the partial pressure of carbon dioxide (PaCO2). However, these physiological effects have not been completely studied, and their mechanisms have not yet been elucidated. Therefore, this study aimed to evaluate the effects of a change in trunk inclination from semirecumbent (45°) to supine-flat (10°) on physiological dead space and ventilation distribution in different lung regions.ResultsTwenty-two ARDS patients on pressure-controlled ventilation underwent three 60-min steps in which trunk inclination was changed from 45° (baseline) to 10° (intervention) and back to 45° (control) in the last step. Tunk inclination from a semirecumbent (45°) to a supine-flat (10°) position resulted in a higher tidal volume [371 (± 76) vs. 433 (± 84) mL (P < 0.001)] and respiratory system compliance [34 (± 10) to 41 (± 12) mL/cmH2O (P < 0.001)]. The CO2 exhaled per minute improved from 191 mL/min (± 34) to 227 mL/min (± 38) (P < 0.001). Accordingly, Bohr’s dead space ratio decreased from 0.49 (± 0.07) to 0.41 (± 0.06) (p < 0.001), and PaCO2 decreased from 43 (± 5) to 36 (± 4) mmHg (p < 0.001). In addition, the impedance ratio, which divides the ventilation activity of the ventral region by the dorsal region ventilation activity in tidal images, dropped from 1.27 (0.83–1.78) to 0.86 (0.51–1.33) (p < 0.001). These results, calculated from functional EIT images, indicated further ventilation activity in the dorsal lung regions. These effects rapidly reversed once the patient was repositioned at 45°.ConclusionsA change in trunk inclination from a semirecumbent (45 degrees) to a supine-flat position (10 degrees) improved Bohr’s dead space ratio and reduced PaCO2 in patients with ARDS. This effect is associated with an increase in tidal volume and respiratory system compliance, along with further favourable impedance ventilation distribution toward the dorsal lung regions. This study highlights the importance of considering trunk inclination as a modifiable determinant of physiological parameters. The angle of trunk inclination is essential information that must be reported in ARDS patients.

Power-frequency admittance model of multi-VSGs grid-connected system considering power coupling

The high penetration of renewable energy decreases the inertia of power systems. The virtual synchronous generator (VSG) control technology has good inertia compensation effect and has attracted considerable attention because of the similar external characteristics of synchronous generators. However, the power and frequency oscillation of multi-VSG grid-connected systems seriously threatens the stability of power system. Existing multi-VSG power frequency admittance (PFA) models ignore the power coupling caused by the large line impedance ratio in medium- and low-voltage microgrids, and the accuracy of these models needs improvement. Thus, this study aims to establish a multi-VSG grid-connected PFA model considering power coupling. The influence of power coupling on model accuracy is analyzed, and the impacts of line impedance and reactive loop coefficient on the power-frequency response characteristics are investigated. Simulation results verify that the proposed model has higher accuracy over existing models.

Analysis of the band structure of transient in-plane elastic waves based on the localized radial basis function collocation method

In this paper, the localized radial basis function collocation method is applied to investigate the in-plane elastic wave propagation of 2D phononic crystals. The direct method with local support domain in one line is used to enhance the stability of the localized radial basis function collocation method when dealing with the derivative calculations in the boundary and interface conditions. The Houbolt method is employed to discretize the time, and then the Fast Fourier Transform is adopted to obtain the band structure according to the wave vectors in the first Brillouin Zone. Different acoustic impedance ratios, filling rates, and lattice forms are studied. The numerical results can be used to validate the band structures obtained directly from the frequency domain.

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.