Impedance Variation Research Articles

Robust Controller Design for a Grid-Connected VSI via an LCL Filter in the Presence of Unknown Grid Impedance

Inverters connected to the grid can become unstable under specific grid impedance conditions. In order to find a solution to this problem, it is possible to ensure system stability and their robustness to R-L type grid impedances by satisfying two conditions. The first condition is to ensure that the closed-loop poles of the system are in stable positions to variations in the grid impedance. The second condition is reliant on the admittance model of the equivalent circuit. Specifically, the product of this admittance and the grid impedance must adhere to the Nyquist stability criterion. In this work, the stability of the converter connected to the grid through an LCL filter is analysed. For this purpose, the output admittance is modelled in the Laplace domain taking into account the behaviour of the discrete controller. In addition, to ensure that the closed-loop poles are in stable positions, the system open-loop response is analysed. These two conditions are examined across scenarios where system states are partially or completely fed back, for different system parameter values. Consequently, a robust controller is designed for variations of the R-L type grid impedance.

High flow nasal cannula and low level continuous positive airway pressure have different physiological effects during de novo acute hypoxemic respiratory failure

BackgroundLarge tidal volumes during de novo acute hypoxemic respiratory failure (AHRF) may promote patient self-inflicted lung injury. Tidal volume assessment under high flow nasal cannula (HFNC) is not routinely feasible at the bedside. Our objective was to determine whether tidal volume during low-level continuous positive airway pressure (CPAP) could predict tidal volume during HFNC and to compare the physiological effects of HFNC and low-level CPAP.MethodsProspective, single-center study including 29 de novo AHRF patients treated with HFNC (50 to 60 L.min− 1). Patients were monitored using electrical impedance tomography during HFNC then CPAP at 4 cmH2O. Tidal volume during HFNC was calculated based on tidal impedance variation. The ability of tidal volume under low-level CPAP to predict tidal volume under HFNC was explored using Bland-Altman analysis. CPAP and HFNC were compared in terms of tidal volume, minute ventilation, respiratory comfort, dyspnea, oxygenation, ventilation distribution, end-expiratory lung volume, thoraco-abdominal asynchrony and recruitment.ResultsUnder HFNC, patients had a tidal volume of 6.6 (5.9–8.7) mL.kg− 1 PBW. 20 (69%) patients exhibited a tidal volume between 4 and 8 mL.kg− 1 PBW, while in 5 (17%) patients it exceeded 9 mL.kg− 1 PBW. Tidal volume under CPAP was higher (9.4 (8.3–11) mL.kg− 1 PBW, p < 0.001). Tidal volumes under CPAP and under HFNC were modestly correlated (Spearman r = 0.50, p = 0.005). Bland-Altman analysis showed a bias of 2.4 mL.kg− 1, with limits of agreement ranging from − 1.1 mL.kg− 1to 5.9 mL.kg− 1. Nevertheless, a larger (> 11.5 mL.kg− 1 PBW ) tidal volume under low-level CPAP predicted a larger (> 9 mL.kg− 1 PBW ) tidal volume under HFNC with 80% sensitivity and 96% specificity. Low-level CPAP was associated with increased minute ventilation, end-expiratory lung volume, and oxygenation as compared to HFNC. It decreased signs of respiratory distress in the most severe patients but was associated with lower comfort compared to HFNC.ConclusionAmong ICU patients with de novo AHRF, tidal volume under HFNC was mostly protective. Tidal volume during CPAP at 4 cmH2O did not predict tidal volume during HFNC. Such low-level CPAP was associated with increased tidal volume, minute ventilation, end-expiratory volume, and oxygenation.Trial registrationClinicalTrials.gov ID NCT03919331. Registration date: 2019-03-26.

Dynamic Impedance Model of Low-Voltage Electric Shock in Animals Considering the Influence of Water Electrolysis

This study aims to tackle the challenge of explaining the underlying mechanisms behind the time-varying impedance phenomenon in animals experiencing low-voltage electric shocks. A dynamic impedance model that considers the effect of water electrolysis (WEDI) has been developed. First, we conducted root cause analyses through progressive validation experiments, identifying water within the shocked body as the key factor influencing impedance variation. Monitoring hydrogen concentration above the electrodes and measuring mass changes in the shocked body revealed that the time-varying impedance is closely related to internal water electrolysis. Second, we quantitatively analyzed the impact of water molecule decomposition during electrolysis on the salt concentration and conductivity within the electrically shocked body. A mathematical relationship between the variable resistance within the body and time was derived. A dynamic impedance model for animal electric shock that considered the effects of water electrolysis was subsequently established, explaining the underlying mechanism behind the time-varying impedance phenomenon. Finally, the Mean Absolute Percentage Error (MAPE), Mean Absolute Error (MAE), and Root Mean Square Error (RMSE) between the electric shock current predicted by the WEDI model and actual measurements were 0.00357, 0.00350, and 0.00446. Compared to existing models, the WEDI model demonstrates superior accuracy and interpretability.

Effect of Dielectric Properties of Cochlea on Electrode Insertion Guidance Based on Impedance Variation

The cochlear neuromodulator provides substantial auditory perception to those with impaired hearing. The accurate insertion of electrodes into the cochlea is an important factor, as misplaced may lead to further damage. The impedance measurement may be used as a marker of the electrode insertion guidance. It is feasible to investigate the impact of the dielectric properties of the cochlea tissue layers on the electrode insertion guidance using sophisticated bio-computational methods that are impractical or impossible to perform in cochlear implant (CI) patients. Although previous modeling approaches of the cochlea argued that the capacitive impact of the tissue layer can be neglected using the quasi-static (QS) approximation method, it is widely accepted that tissue acts as a frequency filter. Thus, the QS method may not always be appropriate due to short-duration pulses. This study aimed to investigate the impact of the frequency-dependent dielectric properties of the cochlea tissue layers on the impedance variation by following a systematic approach. The volume conductor model of the cochlea layers was developed, the dielectric properties of each tissue layer were attained, and the cochlea neuromodulator settings were applied to obtain the results based on both QS and transient solution (TS) methods. The results based on the QS and TS methods were compared to define to what extent these parameters affect the outcome. It was suggested that the capacitive impact of the cochlea layers should be considered after a certain frequency level.

Microfluidic and impedance analysis of rosemary essential oil: implications for dental health

BackgroundOral health is closely linked to systemic conditions, particularly non-communicable diseases (NCDs), which can exacerbate oral issues. Essential oils (EOs) have emerged as potential alternatives for oral health due to their antibacterial, anti-inflammatory, and antioxidant properties. Among these, rosemary essential oil (REO) shows promise due to its various biological activities. This study investigates the potential of REO in dental applications using microfluidic devices and electrochemical impedance spectroscopy (EIS) to analyze the electrical properties of REO in artificial saliva (AS) mixtures.ResultsThe study demonstrated significant variations in impedance across different REO concentrations and their mixtures with AS. Higher impedance was observed in REO mixtures, particularly at lower frequencies, indicating distinct electrical properties compared to pure AS. The impedance of REO was influenced by its concentration, with a 1% REO solution showing higher impedance than a 4% solution, possibly due to micelle formation and changes in dielectric properties. Additionally, microfluidic devices enabled precise control over fluid interactions and real-time monitoring, offering valuable insights into REO's behavior in a simulated oral environment. The impedance data demonstrated significant differences in REO–AS mixtures, highlighting potential interactions critical for oral care applications.ConclusionsRosemary essential oil exhibits unique electrical properties, making it a promising candidate for dental applications, particularly in preventing and treating oral diseases. Microfluidic devices enhance the accuracy and reliability of studying REO's interactions with AS, providing a robust platform for future dental research. The findings suggest that REO could be effectively incorporated into oral care products, offering a natural alternative for combating oral pathogens, reducing inflammation, and protecting against oxidative stress. Future research should focus on clinical trials to validate these findings and explore the synergistic effects of REO with other essential oils.

Biocompatible dipeptide coated on Pt/PEDOT:PSS modified silicon probes for tissues rejection alleviation

The implantable neural probe is an indispensable tool to record the high-quality spike signals. However, the high interface impedance of electrode-tissue and severe tissue rejection degrade the signal quality and shorten the service life of neural probes in-vivo. Here, a Pt/PEDOT:PSS modified silicon probes with biocompatible dipeptide layer is proposed to avoid these issues. First, a bilayer Pt/PEDOT:PSS was electrochemically deposited on gold microelectrodes to reduce the impedance. Then, a layer of dipeptide was deposited on the modified probe by physical vapor deposition (PVD) to mitigate tissue rejection. The electrochemical results show that the electrode-tissue interface impedance can be reduced by two orders of magnitude by the Pt/PEDOT:PSS modification, with negligible impedance variation by the following dipeptide layer. From the in-vitro accelerated aging, it can be inferred that the Pt/PEDOT:PSS/dipeptide modified microelectrodes can survive for more than 10 weeks. In-vitro cytotoxicity experiments show that the dipeptide can help improve the biocompatibility. Lastly, in-vivo implantation further proves that dipeptide may contribute to the realization of lower tissues rejection and higher signal-to-noise ratio within 8 weeks of implantation. The widely used silicon neural probes with the Pt/PEDOT:PSS modification and overall dipeptide coating provide as a new solution for long-term biocompatibility and high-quality neural signals.

Analysis of Low-Frequency Sound Absorption Performance and Optimization of Structural Parameters for Acoustic Metamaterials for Spatial Double Helix Resonators

Low-frequency noise absorbers often require large structural dimensions, constraining their development in practical applications. In order to improve space utilization, an acoustic metamaterial with a spatial double helix, called a spatial double helix resonator (SDHR), is proposed in this paper. An analytical model of the spatial double-helix resonator is established and verified by numerical simulations and impedance tube experiments. By comparing the acoustic absorption coefficients of the spatial double-helix resonator, it is shown that the results of the analytical model, the numerical model, and the experiments are in good agreement, proving the accuracy of the theoretical model. The effects of different structural parameters on the peak sound absorption coefficient and resonance frequency are quantitatively revealed. The impedance variation law of the model is obtained, and the resistance and reactance distributions at the resonance frequency are analyzed. In the optimization model, the Back Propagation (BP) network is used to construct the mapping between the structural parameters and the resonance frequency and sound absorption coefficient, and this is used as the constraints of the equation, which is combined with Wild Horse Optimization (WHO) to establish the BP-WHO optimization model to minimize the volume of the spatial double helix resonator. The results show that, for a given noise frequency, the optimized structural parameters enhance the space utilization without affecting the performance of the space double helix resonator.

Investigating electrochemical impedance and performance variation in nanostructured Mn3O4/activated carbon/reduced graphene oxide asymmetric supercapacitors with different electrolytes

Investigating electrochemical impedance and performance variation in nanostructured Mn3O4/activated carbon/reduced graphene oxide asymmetric supercapacitors with different electrolytes

A mollifier approach to seismic data representation

AbstractThe extension of the seismic bandwidth to lower frequencies enhances impedance contrasts that can be poorly represented by the broadband acquisition wavelet. Furthermore, long filters that are used to shape the wavelet of processed data can cause issues with noise, phase and interference between seismic events. In this paper, we use a mathematical technique known as mollification to resolve impedance variations with the highest detail allowed by the bandwidth of the data. The mollifier is integrated and windowed to match the low‐frequency content of the data to yield a convenient conversion to relative impedance. Synthetic data created from wedge models show that the windowed mollifier provides an improved representation of the impedance profile. This is replicated by application to an acoustic well log and a regular seismic dataset recorded in the Southern North Sea as well as a broadband dataset recorded in the North Sea.

Physiological definition for region of interest selection in electrical impedance tomography data: description and validation of a novel method

Objective. Geometrical region of interest (ROI) selection in electrical impedance tomography (EIT) monitoring may lack sensitivity to subtle changes in ventilation distribution. Therefore, we demonstrate a new physiological method for ROI definition. This is relevant when using ROIs to compute subsequent EIT-parameters, such as the ventral-to-dorsal ratio during a positive end-expiratory pressure (PEEP) trial.Approach.Our physiological approach divides an EIT image to ensure exactly 50% tidal impedance variation in the ventral and dorsal region. To demonstrate the effects of our new method, EIT measurements during a decremental PEEP trial in 49 mechanically ventilated ICU-patients were used. We compared the center of ventilation (CoV), a robust parameter for changes in ventro-dorsal ventilation distribution, to our physiological ROI selection method and different commonly used ROI selection methods. Moreover, we determined the impact of different ROI selection methods on the PEEP level corresponding to a ventral-to-dorsal ratio closest to 1.Main results.The division line separating the ventral and dorsal ROI was closer to the CoV for our new physiological method for ROI selection compared to geometrical ROI definition. Moreover, the PEEP level corresponding to a ventral-to-dorsal ratio of 1 is strongly influenced by the chosen ROI selection method, which could have a profound clinical impact; the within-subject range of PEEP level was 6.2 cmH2O depending on the chosen ROI selection method.Significance.Our novel physiological method for ROI definition is sensitive to subtle ventilation-induced changes in regional impedance (i.e. due to (de)recruitment) during mechanical ventilation, similar to the CoV.

Non-Invasive Bio-Impedance Imaging and Sensing for Medical Diagnostics and Industrial Applications

Bio-impedance-based imaging technique stands at the intersection of medical/industrial imaging techniques and is also known as electrical impedance tomography (EIT), imparting a non-invasive, value-powerful approach for imaging biological tissues and procedures. We begin by elucidating the essential standards underlying EIT, focusing on the size of impedance variations inside an object (plastic pipe) to reconstruct its inner conductivity distribution. Subsequently, we delve into the numerous programs of EIT across numerous fields and discuss recent experimental strategies and advancements aimed at mitigating these boundaries, such as novel electrode configurations, advanced reconstruction algorithms, and incorporation of complementary imaging modalities. Finally, we underscore the importance of experimental research in advancing the capabilities and packages of EIT as a valuable device in industrial monitoring, specifically in bedside tracking, process pipelines, tank monitoring and also used for other medical or industrial detection, even as additionally exploring its rising roles in commercial and environmental applications.

Iterative Numerical Approximation Technique for 3D Eddy Current Models in Harmonic Regime Based on the Electromagnetic T-Formulation and the Finite Element Method

In this paper, an iterative numerical approximation technique is used for analyzing the distribution of eddy currents density in conductive materials plates by using the electromagnetic T-formulation and the Biot-Savart law, solved by the finite element method. The proposed approach allows for the meshing of the different parts of the studied system separately, including the sensor and the conductive plate, without the need for an air region. Firstly, this approach reduces the number of unknown variables by avoiding the air region of the system's mesh. Secondly, it simplifies the consideration of the sensor's motion without the need to remesh the system. For this purpose, a calculation code has been developed for solving an electromagnetic three-dimensional non-destructive testing model. This latter permits the resolution of JSEAM # 6 Benchmark problem to validate the proposed method. The impedance variation due to the presence of a defect are evaluated. The obtained results are compared with the experimental ones found in the literature. These results reveal a good agreement, which proves the validity of the proposed method.

Comparative Characteristics of Electrolyte Solutions Using Electrical Impedance Spectroscopy Method

Electrolyte solutions can conduct electric current and help maintain balance in the human body. This study compares the electrical impedance characteristics of various electrolyte solutions using the Electrical Impedance Spectroscopy (EIS) method. Three types of electrolyte solutions were tested: NaCl solution, Ringer’s Lactate (RL) solution, and Simulated Body Fluid (SBF) solution with concentration variations of 20%, 40%, 60%, 80%, and 100%. Measurements were conducted over a frequency range from 1 Hz to 1 MHz to compare electrolyte solutions using a frequency of 10 kHz with an electric current of 50 μA. At a frequency of 10 kHz, a comparison of the three types of electrolyte solutions with concentration variations from 20% to 100% was made. The measurement result showed that the NaCl solution had an impedance value of 200Ω to 900Ω at high frequencies. The Ringer’s Lactate (RL) solution exhibited impedance variations with impedance values ranging from 800Ω to 300Ω, which is more complex due to the other hand, the Simulated Body Fluid (SBF) solution demonstrated impedance stability at high frequencies with impedance values ranging from 400Ω to 200Ω, indicating its electrical properties suitability with human body conditions. Each electrolyte solution has its characteristics in impedance values at a frequency of 10 kHz, which allows for comparing the three types of electrolyte solutions. For further research, additional studies could include impedance characteristics of electrolyte solutions to broaden understanding of their electrical properties, considering variations in frequency and current conditions to optimise impedance characteristic measurements for various electrolyte solutions.

A Joint Active Damping Strategy Based on LCL-Type Grid-Connected Inverters for Grid Current Feedback and PCC Voltage Unit Feedforward.

The negative high-pass filter feedback of the grid current (NFGCF) can offer active damping for the LCL-type grid-connected inverter. Due to the control delay in digital control systems, this damping can cause the system to exhibit non-minimum phase behavior within specific frequency ranges. This study proposes a joint active damping approach that combines grid current feedback and the point of common coupling (PCC) voltage unit feedforward. The proposed method introduces a dynamic damping region that varies with grid impedance. By developing suitable damping loop control parameters, this region can span the entire frequency range, even exceeding the Nyquist frequency fs/2. The research results demonstrate that the proposed approach enhances robustness against variations in grid impedance and eliminates non-minimum phase behavior. Simulation and experimental outcomes validate the effectiveness of this joint active damping method.

Influence of compression effect on the MEA structure and performance based on M−N–C electrocatalysts for PEMFC

The single-atom dispersed active sites and the thicker catalytic layer of metal-nitrogen-carbon (M-N-C) electrocatalysts based membrane electrode assembly (MEA) exhibit notable distinctions from Pt-based MEA, necessitating targeted optimization. This study systematically investigates the influence of compression on both structure and performance of the M-N-C electrocatalysts based MEA. Four compression ratios, ranging from 11.5% to 39.3%, were examined across diverse operational conditions. The variations in impedance across different electrochemical regions are observed, resulting from the superposition of distinct impedance components. It is found that the insufficient compression leads to higher porosity and the formation of cracks between catalytic layer and membrane, adversely impacting internal resistance and proton transport. Increasing compression first acts the catalytic layer, and then gradually acts on the interface, membrane and gas diffusion layer, thereby reducing internal resistance, charge transfer resistances, albeit at the expense of heightened mass transfer resistance. Among these factors, the influence of internal resistance affects significance to total performance. Furthermore, compression influenced mass transfer differently in various layers. For the catalyst layer, the effect was uniform and sustained, while for the gas diffusion layer, it initially remained constant and then experienced a sudden deterioration over a certain extent. Optimal MEA performance is achieved when the compression ratio attains 40 %, which 2.1 times higher than the low compression MEA. This finding emphasizes the necessity for higher compression on M-N-C electrocatalysts based MEA compared to Pt-based MEA.

Synthesis and Characterization of CdS and Sr-Doped CdS Quantum Dots: Impedance Analysis for Nano-Tuned Electronic Applications

This study reports the synthesis and comprehensive characterization of cadmium sulfide (CdS) and strontium-doped CdS quantum dots (QDs) using a straightforward chemical precipitation method. N, N-Dimethylformamide served as the stabilizing agent, while specific metal precursors facilitated the formation of the nanostructures. The incorporation of strontium into the CdS matrix aimed to enhance the electronic properties of the quantum dots. Energy Dispersive X-ray Analysis (EDAX) confirmed the successful doping of Sr into the CdS QDs. X-ray Diffraction (XRD) analysis verified the high-crystallinity of the synthesized quantum dots, with the mean crystal sizes determined to be 3.18 nm for pure CdS and 3.99 nm for Sr-doped CdS (2mM and 4mM concentrations). Impedance spectroscopy was utilized to study the frequency-dependent electrical properties of the QDs at room temperature, revealing significant variations in impedance with frequency. The results demonstrated that both pure and Sr-doped CdS QDs exhibit capacitive admittance, which is indicative of their potential application in nano-tuned electronic devices. The ability to fine-tune the resonant frequency by controlling the size and doping level of the quantum dots presents a significant advantage for their use in advanced electronic applications. The study highlights the promising application of CdS and Sr-doped CdS quantum dots in the development of high-performance, frequency-tunable nanoscale electronic devices.

A Power Circulating Suppression Method for Parallel Transient Inverters with Instantaneous Phase Angle Compensation

A unidirectional link is typically incorporated into the DC input side of an inverter to ensure the reliability and stability of the microgrid power supply. Due to impedance and control variations among inverters, circulating currents may rapidly arise during the operation of parallel transient inverters. Nonetheless, the unidirectional power circulating in a DC unidirectional link results in energy accumulation on the DC side, causing DC bus voltage pumping and affecting MGs’ operation safety and stability. This paper proposes a non-communication-based circulation suppression strategy to suppress power circulation in parallel transients based on the local information of inverters. First, a parallel transient is modeled, and the power circulation phenomenon and its influencing factors are analyzed. Then, the instantaneous power and absorbed active energy are calculated to adjust the phase of the inverter output voltage and suppress power circulation. Moreover, the output frequency is adjusted to balance the DC-side voltage of each inverter. Then, the stability of the parallel system after adding the circulation suppression control strategy is verified using the Lyapunov function method. Finally, simulation and experimental results verify the effectiveness of the proposed power circulation suppression strategy.

Lateral kinematic properties of offshore pipe piles embedded in saturated soil considering soil plug effect

AbstractThis study establishes a theoretical framework for analyzing the lateral oscillation of marine pipe piles. The additional mass model is introduced herein to consider the inertial fluctuation effect of the soil plug. Analytical mathematical methods are used to determine the complex impedance variation of the pile over a range of frequency effects. An investigation is performed to determine how the presence of soil plugs changes the lateral complex stiffness and natural frequency of pipe piles. Additionally, comparisons of the applicability of the plane strain model and continuous medium model have been conducted to enable the easy use of the theoretical model. The main conclusions can be drawn as (1) if the fluctuation inertia effect of the soil plug is not taken into consideration, the dynamic active length and the dynamic stiffness of the pipe pile will be underestimated; (2) for the soft soil, the plane strain model may give rise to substantial calculation errors attributed to them regardless of the vertical continuity of the soil, nevertheless, the calculation error decreases rapidly with the increase of soil shear modulus and vibration frequency.

A new hybrid fixed and adaptive gains control algorithm to reduce power losses on LLCL filter-based renewable energy conversion systems with systematic parametrization using Grey Wolf optimizer

Currently, there is a transition in the energy matrix around the world, where traditional sources of energy generation are continually being replaced by energy generation systems based on renewable sources to mitigate the climate crisis. In this bias, this work presents the mathematical modeling of an LLCL filter, used to connect power generation systems based on renewable energy sources to the electrical grid, and presents a novel hybrid fixed-and adaptive gains control strategy for current injection into the grid using this system. The developed hybrid controller is composed of a proportional–integral controller and a direct robust adaptive controller. The first term of the controller guarantees the reference current, while the second term of the controller is used for disturbance rejection. Furthermore, a systematic procedure for the controller’s parametrization based on Grey Wolf Optimizer is also provided. The control of the current injected into the grid is carried out considering the LLCL filter without passive damping resistors in the filter structure to avoid power losses due to the passive filter elements. Additionally, the LLCL filter model considers minimal parasitic resistances to evaluate the controller’s performance and optimize it for the application of interest, aiming to maximize the system performance by ensuring a short transient regime due to the fast closed-loop system response. Simulation results indicate high performance of this optimized control strategy with small tracking error even considering grid impedance variations.

Evaluation of sensor-enabled piezoelectric geoelectric cable in cyclic shear tests of subgrade soil under vertical cyclic loads

Of late, deformation of subgrade soil has led to an increasing number of road subsidence diseases. Real-time monitoring of subgrade deformation is critical to ensure the safety of subgrade operations. In this paper, a sensor-enabled piezoelectric geoelectric cable (SPGC) with impedance strain effect and piezoelectric effect is tested. The SPGC impedance and voltage signals obtained by cyclic shear test under vertical static load and cyclic shear test under vertical cyclic load are used to evaluate the monitoring effect. The results showed that normal stress had the greatest effect on the shear strength of the soil, whereas the normal stress and horizontal shear displacement amplitude significantly influenced the strain in the soil. Varying the normal and horizontal shear frequencies had little effect on the shear strength and strain of the soil. The normalized impedance and voltage of the SPGC, respectively, decreased and increased rapidly during the initial stage of the shear cycle; these changes were relatively small during the middle and late stages of the shear cycle. The SPGC voltage waveform revealed the changes in the shear stress and vertical displacement under different normal and horizontal shear frequencies, from which the stability of the subgrade soil under the aforementioned conditions could be evaluated. The variations in the SPGC impedance and effective voltage from the cyclic shear tests under both vertical static and vertical cyclic loads remained essentially consistent with the number of cycles. However, there was a difference in that the trough of the SPGC impedance under the vertical cyclic load was larger than that under the vertical static load; likewise, the effective SPGC voltage under the cyclic load was larger than that under the static load. Through an analysis of the SPGC impedance and voltage signals in the subgrade soil, the consistency of the SPGC-normalized impedance and effective voltage with shear stress was clarified; this helped us evaluate the health of the subgrade and monitor the characteristics of the precursor signals before a slide were to occur, thereby affording us an opportunity to issue timely warnings.