Frequency-independent Parameters Research Articles

Derivation and Application of Analytical Coupling Loss Coefficient by Transfer Function in Soil–Building Vibration

Vibrations generated by railways may undergo amplification or reduction while traversing the foundations, floors, and spans of adjacent structures. This fluctuation in the vibration intensity, identified as a building’s coupling loss, is commonly considered in vibration forecasts through the utilization of universal frequency-independent adjustment parameters. This article employs a theoretical analytical approach to investigate the propagation characteristics of Rayleigh waves in elastic foundation soil, as well as the variations at the contact surface of buildings’ foundations. Analytical expressions for the coupling loss coefficient are derived to explore the displacement transfer relationship in the soil–structure interaction. To accurately and efficiently analyze the proposed buildings and site, the entire vibration propagation system is decoupled into substructure systems for independent analytical calculations. Theoretical analytical methods are utilized to obtain the displacement transfer functions between the soil and the structures through the refraction and transmission of waves. From a theoretical perspective, a thorough understanding of the interaction between soil and buildings is achieved. The influence of various variables related to railways and foundations on the building responses is analyzed. By comparing with measured data, the correctness of the analytical form of the coupling loss coefficient is validated, filling a gap in the literature due to the lack of analytical research on displacement transfer losses in soil–structure interactions.

Ex vivo magnetic resonance elastography of the small bowel in Crohn's disease.

Conventional magnetic resonance enterography is limited in differentiating active inflammation and fibrosis in lesions of Crohn's disease (CD), thus providing a restricted basis for therapeutic decision making. Magnetic resonance elastography (MRE) is an emerging imaging tool that differentiates soft tissues on the basis of their viscoelastic properties. The aim of this study was to demonstrate the feasibility of MRE in assessing the viscoelastic properties of small bowel samples and quantifying differences in viscoelastic properties between healthy ileum and ileum affected by CD. Twelve patients (median age: 48 years) were prospectively enrolled in this study between September 2019 and January 2021. Patients of the study group (n=7) underwent surgery for terminal ileal CD, while patients of the control group (n=5) underwent segmental resection of healthy ileum. MRE of ileal tissue samples of surgical specimens from both groups was performed in a compact tabletop MRI scanner. Penetration rate (a in m/s) and shear wave speed (c in m/s) were determined as markers of viscosity and stiffness for vibration frequencies f of 1,000, 1,500, 2,000, 2,500, and 3,000 Hz. Additionally, damping ratio γ was deduced, and frequency-independent viscoelastic parameters were calculated using the viscoelastic spring-pot model. Penetration rate a was significantly lower in CD-affected ileum compared to healthy ileum for all vibration frequencies (P<0.05). Consistently, damping ratio γ was higher in CD-affected ileum, averaged over all frequencies (healthy: 0.58±0.12, CD: 1.04±0.55, P=0.03), as well as at 1,000 and 1,500 Hz individually (P<0.05). Spring-pot-derived viscosity parameter η was also significantly reduced in CD-affected tissue (2.62±1.37 versus 10.60±12.60 Pa·s, P=0.02). No significant difference was found for shear wave speed c between healthy and diseased tissue at any frequency (P>0.05). MRE of surgical small bowel specimens is feasible, allowing determination of viscoelastic properties and reliable quantification of differences in viscoelastic properties between healthy and CD-affected ileum. Thus, the results presented here are an important prerequisite for future studies investigating comprehensive MRE mapping and exact histopathological correlation including characterization and quantification of inflammation and fibrosis in CD.

Tutorial on broadband transmissive metasurfaces for wavefront and polarization control of terahertz waves

In order to harness the capabilities of terahertz waves, various metasurface-based functional devices have been developed recently. However, due to the limited usage of systematic optimization methodologies, many existing designs leave room for further bandwidth and efficiency improvement. This article provides an overview on the bandwidth limiting factors associated with metasurfaces and gives a tutorial on a semi-analytical approach to broadband design. The broadband approach incorporates network analysis and genetic algorithm to determine the frequency-independent optimal circuit parameters for multi-layer transmissive metasurfaces, so that targeted complex transmission coefficients can be achieved over a wide bandwidth. The broadband design approach is enabling the configuration and optimization of diverse metasurfaces for wavefront and polarization control of terahertz waves, including quarter- and half-waveplates.

Self-Referencing TDR Dielectric Spectroscopy Using Reflection-Decoupled Analysis With a Mismatched Section

An innovative self-referencing time-domain reflectometry (TDR) dielectric spectroscopy method is introduced. The method extracts the first reflection from a mismatched section (MS) immediately before the sensing section (SS) to capture the source characteristics and effect of leading sections. A reflection-decoupled analysis (RDA) is derived to characterize the complex dielectric permittivity (CDP) in the ss. Conventional time-domain spectroscopy (TDS) offers a more cost-effective alternative to frequency-domain methods, but its accuracy may suffer from input function variation, system mismatches, and probe design restrictions. RDA with MS approach provides an efficient, robust, and flexible dielectric spectroscopy technique including its calibration, which inherits all advantages of conventional TDS while using more economic TDR device and more flexible probe design. It adopts a nonconductive and nondispersive MS to serve as a reflector for reliable reference source directly embedded in a single TDR signal. Spectral ratios between the reflection from MS and all other reflections from the SS are experimentally determined and matched to the RDA-derived values as a function of CDP. RDA is inherently independent of source function, instrument mismatch, and cable resistance. There are only four frequency-independent system parameters that can be easily calibrated once and for all using a measurement of well-known material. The method is presented in a general framework without major restrictive assumptions, which explicitly expresses all probe parameters, allowing greater flexibility in probe design (e.g., geometric impedance, probe length, and end condition). Robustness of RDA was verified by numerical and experimental investigations using eight materials of different dielectric characteristics.

Efficient Multiband Channel Reconstruction and Tracking for Hybrid mmWave MIMO Systems

Multiband operation in millimeter wave (mmWave) will obtain lots of performance gain by offering larger bandwidth. However, the prerequisite is the acquisition of accurate channel state information (CSI), which is a knotty task with hybrid analog/digital architecture. This study devotes to efficiently reconstruct and track the time drifting multiband channel to keep CSI precise in time division duplex (TDD) mmWave multiple-input-multiple-output system with hybrid analog/digital architecture. Utilizing spatial reciprocity, an efficient multiband channel reconstruction scheme is introduced, which elaborately estimates the central sub-band channel and then reconstructs side sub-band channels from the central one. To this end, a beam training-based Newtonized orthogonal matching pursuit (BT-NOMP) algorithm is proposed to estimate the central sub-band channel. With the help of frequency-independent parameters extracted from BT-NOMP, side sub-bands channel can be well reconstructed with additional low-complexity path gains estimation process. Furthermore, to avoid frequent channel reconstruction in a slightly drifting channel meanwhile keep the CSI accurate, a rotated beam-based channel tracking algorithm is developed using historical observations of channel parameters. Numerical results prove the efficiency of the proposed multiband channel reconstruction scheme and the accuracy of the channel tracking algorithm.

Simulation study of 6–10 kV cable lines for transient processes calculation during earth faults

As a rule, researchers do not consider the dependence of the inductance of cable lines on frequency in their scientific papers devoted to the calculation of transient processes during single phase-to-ground fault in 6–10 cable networks. In some cases, it can lead to significant errors in evaluation of current and voltage transient components parameters. Therefore, it is an urgent task to estimate defined errors and the scope of application of frequency-independent equivalent circuits and models of 6–10 kV cable lines during calculation and simulation of transient processes in case of single phase-to-ground fault. The authors applied PSCAD / EMTDC software to study the effect of the frequency dependence of the inductances of 6–10 kV cable lines on the calculation accuracy of transient processes during single phase-to-ground fault. It allows to simulate electric power systems models with the usage of both frequency-dependent and frequency-independent cable line models with round conductors only. To check the adequacy of the frequency-dependent three phase cable model developed in PSCAD software, the authors have used a frequency-dependent model of 6–10 kV three-phase cable with sector-shaped conductors designed in COMSOL Multiphysics software. The authors have developed an approach to develop of 610 kV cable lines models with frequency-dependent and frequency-independent parameters. The authors have obtained error estimation in transient current and voltage parameters during single phase-to-ground fault in cable networks models that do not consider the frequency dependence on inductance (for discharge components the error is 1520 %, for charging components the error is equal to 510 %). It is shown that models with cable line parameters defined according to spreading speed of electromagnetic wave, can be used for approximate calculation of transient current and voltage to solve most of tasks of investigation of transient processes during single phase-to-ground faults. Application of the developed recommendations to determine three phase medium voltage cable lines parameters will increase the calculation accuracy of transient processes during single phase-to-ground faults in 6–10 kV cable networks. Only application of frequency-dependent models of cable lines allows us to provide required accuracy to develop methods of distant earth fault localization in 6–10 kV networks.

Transdimensional Bayesian inversion of magnetotelluric data in anisotropic layered media with galvanic distortion correction

SUMMARYPresence of electrical anisotropy in the lithosphere can provide useful constraints on regional structure patterns and dynamics of tectonic processes, and they can be imaged by magnetotelluric (MT) data. However, Inversion of MT data for anisotropic structures using standard gradient-based approaches requires subjective choices of model regularization for constraining structure and anisotropy complexity. Furthermore, the ubiquitous presence of galvanic distortion due to small-scale near-surface conductivity inhomogeneities prevents accurate imaging of subsurface structures if ignored or not properly removed. Here, we present a transdimensional Bayesian approach for inverting MT data in layered anisotropic media. The algorithm allows flexible model parametrization, in which both the number of layers and model parameters of each layer are treated as unknowns. In this manner, the presence or absence of anisotropy within the layers, as well as the level of model complexity, is determined adaptively by the data. In addition, to account for the effects of galvanic distortion, three frequency-independent distortion parameters resulting from the distortion decomposition are treated as additional variables during the inversion. We demonstrate the efficiency of the algorithm to resolve both isotropic and anisotropic structures with synthetic and field MT data sets affected by galvanic distortion effects. The transdimensional inversion results for the field data are compatible with results from previous studies, and our results improve the constraints on the magnitude and the azimuth (i.e. most conductive direction) of electrically anisotropic structures. For practical applications, the validity of 1-D anisotropic approximation should be first tested prior to the use of our approach. Otherwise it may produce spurious anisotropic structures due to the inapplicability of the anisotropic 1-D inversion for MT data affected by 2-D or 3-D electrical resistivity structures.

Terahertz transmissive half-wave metasurface with enhanced bandwidth.

Polarization conversion is useful for studies of chiral structures in biology and chemistry, and for polarization diversity in communications. It is conventionally realized with wave plates, which, however, present challenges due to limited material availability, as well as narrow bandwidth and low efficiency at terahertz frequencies. To enhance bandwidth and efficiency, the concept of the Huygens' metasurface is adopted here for a transmissive half-wave plate. The half-wave metasurface is designed following the optimal frequency-independent circuit parameters provided by a broadband semi-analytical approach. Simulation results of an optimal design suggest that a 15-dB extinction ratio can be sustained from 219 GHz to 334 GHz, corresponding to a fractional bandwidth of 41.6%. The measured results indicate that the fabricated structure enables a 15-dB extinction ratio from 220 GHz to 303 GHz, with a cross-polarization transmission efficiency above 76.7% for both linear and circular polarizations. This half-wave metasurface design can be readily integrated into compact terahertz systems for diverse applications.

Core Loss Model for Arbitrary Excitations With DC Bias Covering a Wide Frequency Range

Core loss prediction is quite complex as the excitation of magnetic materials varies depending on the topology and the operating mode of switched-mode power supplies. In particular, the waveform of the magnetic flux density, including its dc bias, affects core losses. This article presents the results of an extensive core loss study performed on Mn-Zn ferrites. The investigation comprises core excitations with, among others, sinusoidal and triangular shapes of the magnetic flux density with and without dc bias. Based on the obtained core loss data, an empirical core loss model has been derived for the prediction of specific core losses in Mn-Zn ferrites that is valid for arbitrary excitations, including dc bias of the magnetic flux density. Multiplying the quasi-static energy losses depending on the swing and the dc bias of the magnetic flux density by an effective frequency yields the core losses. The proposed model covers a wide frequency range and only requires the quasi-static energy losses at low frequencies and two frequency-independent parameters. These parameters can be easily extracted from a limited number of measurements or from the data provided by manufacturers. The verification of the proposed approach demonstrates an adequate accuracy of 15% for all investigated Mn-Zn ferrites and for the broad range of studied waveforms and parameters.

Краевые эффекты в бистатических измерениях характеристик рассеяния образцов материалов.

This work is devoted to studying errors emerging by the edge effects when measuring the reflection coefficient (R) and when finding Brewster angle. The impact of edge effects on the scattering characteristics of planar material samples with different geometries was considered. The method of moments in the FEKO program and analytical calculations using Fresnel formulas are used to study a model material with frequency-independent parameters of the medium. A plane linearly polarized wave falling on the object was studied. For each incidence angle of the wave, the electromagnetic field reflected from the object in the mirror direction was calculated. To calibrate the received signal a reference metal plate of the same size as the size of sample under study was used. To estimate the contribution of the finite-size of the sample in the of reflection coefficient, the simulation results were compared with analytical calculations using Fresnel formulas. The results of the electrodynamic simulation of the characteristics of the model material showed that the position of the sample relative to the polarization of the incident wave does not affect the R value; an increase in Brewster angle depending on the frequency was observed. The reflection coefficient of a square sample with a radar absorbent material (RAM) on a metal substrate was investigated. Measurements of the sample scattering characteristics were carried out in an indoor electromagnetic test bistatic facility (anechoic chamber) in ITAE RAS. The experimental results are in accordance with the calculated data obtained by the method of moments and analytical data. For the sample under study, the value of Brewster angle was not determined due to the fact that this value is outside the measurement range. A significant influence of edge effects on the reflection coefficient of the material sample was revealed, especially for angles closed to Brewster angle.

MR elastography frequency-dependent and independent parameters demonstrate accelerated decrease of brain stiffness in elder subjects.

To analyze the mechanical properties in different regions of the brain in healthy adults in a wide age range: 26 to 76years old. We used a multifrequency magnetic resonance elastography (MRE) protocol to analyze the effect of age on frequency-dependent (storage and loss moduli, G' and G″, respectively) and frequency-independent parameters (μ1, μ2, and η, as determined by a standard linear solid model) of the cerebral parenchyma, cortical gray matter (GM), white matter (WM), and subcortical GM structures of 46 healthy male and female subjects. The multifrequency behavior of the brain and frequency-independent parameters were analyzed across different age groups. The annual change rate ranged from - 0.32 to - 0.36% for G' and - 0.43 to - 0.55% for G″ for the cerebral parenchyma, cortical GM, and WM. For the subcortical GM, changes in G' ranged from - 0.18 to - 0.23%, and G″ changed - 0.43%. Interestingly, males exhibited decreased elasticity, while females exhibited decreased viscosity with respect to age in some regions of subcortical GM. Significantly decreased values were also found in subjects over 60years old. Values of G' and G″ at 60Hz and the frequency-independent μ2 of the caudate, putamen, and thalamus may serve as parameters that characterize the aging effect on the brain. The decrease in brain stiffness accelerates in elderly subjects. • We used a multifrequency MRE protocol to assess changes in the mechanical properties of the brain with age. • Frequency-dependent (storage moduli G' and loss moduli G″) and frequency-independent (μ1, μ2, and η) parameters can bequantitatively measured by our protocol. • The decreased value of viscoelastic properties due to aging varies in different regions of subcortical GM in males and females, and the decrease in brain stiffness is accelerated in elderly subjects over 60 years old.

Tuned mass dampers in wind response control of wind turbine with soil-structure interaction

The efficiency of tuned mass dampers (TMDs) in along-wind response mitigation of a wind turbine with consideration of blade coupling and soil-structure interaction (SSI) is investigated. The wind turbine tower is modeled as a multi-degree of freedom (MDOF) with three blades are connected as a MDOF system to the tower. The along-wind drag forces are generated using Shinozuka method. The effect of SSI is considered using frequency independent parameters. The equation of motion for the coupled system is numerically solved in time domain using the Newmark Beta method. In order to observe the changes in response of the system, the blades are subjected to rotating wind field to include the effects of the blade-tower interaction and rotor movement. The peak displacement, peak acceleration, root mean square (RMS) displacement, RMS acceleration, and power spectral density (PSD) of the wind turbine are the response quantities considered for comparative studies. Single TMD (STMD) and distributed multiple TMDs (d-MTMDs) are used to mitigate the wind response of the tower. Parametric studies are conducted to find the most suitable parameters (such as mass ratio, frequency bandwidth, and damping ratios) of the TMD schemes to increase the effectiveness of the strategy in the mitigation of the wind response of wind turbine with/without consideration of SSI. It is concluded that wind response of the wind turbine is amplified with inclusion of the SSI, blade-tower interaction, and rotor movement. In addition, it is concluded that the d-MTMDs are more effective and robust in wind response control of the wind turbine as compared to the STMD.

Tracking FDD Massive MIMO Downlink Channels by Exploiting Delay and Angular Reciprocity

The massive multiple-input multiple-output (MIMO) technology considerably enhances the spectral efficiency of a wireless communication system. However, it suffers from substantial performance degradation caused by the movement of users and the difficulty in acquiring downlink channel state information when combined with frequency division duplexing (FDD). This paper addresses these two fundamental problems by proposing a downlink channel tracking scheme that traces the multiuser downlink time-varying channel of an FDD massive MIMO system. By leveraging the delay and angular reciprocity between the uplink and downlink, a low-complexity module initially traces the frequency-independent parameters in each user's channel in the uplink. With the tracing results in previous instances, the module can efficiently trace the parameters of the existing paths, find paths that disappeared, and detect new paths from sparse uplink sounding reference signals. Then, in the downlink, a low-overhead module estimates the downlink gains for each user from a limited amount of cell-common sparse pilots. The K-means clustering algorithm is utilized to design these pilots and restrict them within a predefined amount. Accurate downlink channel tracking results can be obtained by using the frequently updated frequency-independent parameters and downlink gains, thereby compensating the performance degradation caused by movement. The numerical results validate the effectiveness and robustness of the proposed tracking scheme and suggest that we should frequently apply this scheme to ensure a high multiuser sum spectral efficiency performance.

FDD Massive MIMO Based on Efficient Downlink Channel Reconstruction

Massive multiple-input multiple-output systems deploying a large number of antennas at the base station considerably increase the spectrum efficiency by serving multiple users simultaneously without causing severe interference. However, the advantage relies on the availability of the downlink channel state information (CSI) of multiple users, which is still a challenge in frequency-division-duplex transmission systems. This paper aims to solve this problem by developing a full transceiver framework that includes downlink channel training (or estimation), CSI feedback, and channel reconstruction schemes. Our framework provides accurate reconstruction results for multiple users with small amounts of training and feedback overhead. Specifically, we first develop an enhanced Newtonized orthogonal matching pursuit (eNOMP) algorithm to extract the frequency-independent parameters (i.e., downtilts, azimuths, and delays) from the uplink. Then, by leveraging the information from these frequency-independent parameters, we develop an efficient downlink training scheme to estimate the downlink channel gains for multiple users. This training scheme offers an acceptable estimation error rate of the gains with a limited pilot amount. Numerical results verify the precision of the eNOMP algorithm and demonstrate that the sum-rate performance of the system using the reconstructed downlink channel can approach that of the system using perfect CSI.

Efficient Downlink Channel Reconstruction for FDD Multi-Antenna Systems

In this paper, we propose an efficient downlink channel reconstruction scheme for a frequency-division-duplex multi-antenna system by utilizing uplink channel state information combined with limited feedback. Based on the spatial reciprocity in a wireless channel, the downlink channel is reconstructed by using frequency-independent parameters. First, we estimate the gains, delays, and angles during uplink sounding. The gains are then refined through downlink training and sent back to the base station (BS). With limited overhead, the refinement can substantially improve the accuracy of the downlink channel reconstruction. The BS can then reconstruct the downlink channel with the uplink-estimated delays and angles and the downlink-refined gains. We also introduce and extend the Newtonized orthogonal matching pursuit (NOMP) algorithm to detect the delays and gains in a multi-antenna multi-subcarrier condition. The results of our analysis show that the extended NOMP algorithm achieves high-estimation accuracy. The simulations and over-the-air tests are performed to assess the performance of the efficient downlink channel reconstruction scheme. The results show that the reconstructed channel is close to the practical channel and that the accuracy is enhanced when the number of BS antennas increases, thereby highlighting the promising application of the proposed scheme in large-scale antenna array systems.

Full Parametric Impedance Analysis of Photoelectrochemical Cells: Case of a TiO2 Photoanode

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a TiO2 photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured TiO2 electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations. Key words: Photoanodes, Impedance, TiO2, Havriliak-Negami equation, Bisquert TL model

Model based prediction of sound pressure at the ear drum for an open earpiece equipped with two receivers and three microphones

In future hearing systems, one or more microphones and one or more receivers located within the earmold or ear canal are feasible. In order to predict the sound pressure at the ear drum in such a scenario, a one-dimensional electro-acoustic model of a prototype open earpiece with two integrated receivers and three integrated microphones was developed. The transducers were experimentally characterized by their (frequency-dependent) sensitivity (microphones) and Norton equivalents (receivers). The remaining acoustical system was modeled by 12 frequency-independent parameters which were fitted using a training set-up with well-defined loads at both sides of the ear piece. Put on an individual subject, the model could then be used to determine the acoustic impedance at the medial end of the earpiece, based on measured transfer functions between the integrated components. Subsequently, a model of the ear canal and its termination was estimated from the measured ear canal impedance, which could eventually be used to predict the drum pressure in the individual subject. Comparison to probe tube measurements of the drum pressure in 12 human subjects showed good agreement (less than ±3 dB up to 3 kHz, less than ±5 dB up to 6…8 kHz).

Solid viscosity of fluid-saturated porous rock with squirt flows at seismic frequencies

We have developed a macroscopic model for a two-phase medium (solid porous rock frame plus saturating pore fluid) with squirt flows based on Lagrangian continuum mechanics. The model focuses on improved physics of rock deformation, including explicit differential equations in time domain, causality, linearity, frequency-independent parameters with clear physical meanings, and an absence of mathematical internal or memory variables. The approach shows that all existing squirt-flow models can be viewed as microscopic models of viscosity for solid rock. As in existing models, the pore space is differentiated into compliant and relatively stiff pores. At lower frequencies, the effects of fluid flows within compliant pores are described by bulk and shear solid viscosities of the effective porous frame. Squirt-flow effects are “Biot consistent,” which means that there exists a viscous coupling between the rock frame and the fluid in stiff pores. Biot’s poroelastic effects associated with stiff porosity and global flows are also fully included in the model. Comparisons with several squirt-flow models show good agreement in predicting wave attenuation to approximately 1 kHz frequencies. The squirt-flow viscosity for sandstone is estimated in the range of [Formula: see text], which is close to field observations. Because of its origins in rigorous mechanics, the model can be used to describe any wavelike and transient deformations of heterogeneous porous media or finite bodies encountered in many field and laboratory experiments. The model also leads to new numerical algorithms for wavefield modeling, which are illustrated by 1D finite-difference waveform modeling.

Relaxation time distribution obtained from a Debye decomposition of spectral induced polarization data

We have developed an alternative formulation for Debye decomposition of complex electric conductivity spectra, by recasting it into a new set of parameters with a close relationship to the continuous formulation for the complex conductivity method. The procedure determines a relaxation time distribution (RTD) and two frequency-independent parameters that modulate the complex conductivity spectra. These two parameters represent (1) the direct current contribution and (2) the conductivity range spanned by the low- and high-frequency limits. The distribution of relaxation times quantifies the contribution of each distinct relaxation process. Assuming that characteristic times with insignificant contributions can be ignored, a minimum set of characteristic relaxation times is determined. Each contribution can then be associated with specific polarization processes that can be interpreted in terms of electrochemical or interfacial parameters of mechanistic models derived from inverted parameters obtained from the proposed approach. Synthetic tests show that the procedure can fit spectral induced polarization (SIP) data and successfully retrieve the RTD. We have applied the procedure to laboratory SIP data from experiments with sand and oil mixtures undergoing microbial degradation of hydrocarbons. The RTD reveals evidence of a length scale at which a new polarization process takes place as a result of the biodegradation process.

ID 219 – Characteristics of intracerebrally recorded high frequency oscillations and epileptogenic networks

Objective The purpose of present study is to identify if there are frequency-independent HFO parameters (amplitude and duration) which potentially differ in epileptic and non-epileptic region. Methods We studied 31 consecutive patients with medically intractable focal (temporal and extratemporal) epilepsies. Automated detection was used to detect HFO. The characteristics (amplitude and duration) of HFO within three groups/the seizure onset zone (SOZ), the irritative zone (IZ) and areas outside the irritative zone/seizure onset zone (nonSOZ/nonIZ)/ were statistically compared. Results The rate of fast ripples (FR) in SOZ was significantly higher than in nonSOZ/nonIZ region. The relative amplitude of HFO (both ripples and fast ripples) was higher in SOZ in comparison with IZ and nonIZ/nonSOZ region. Statistical analysis showed significantly shorter duration of ripples in SOZ in comparison with duration of HFO in either nonSOZ/nonIZ or IZ (in FR range the result was significant only between SOZ and nonSOZ/nonIZ). Conclusions In SOZ fast ripples are significantly more frequent and shorter with higher relative amplitude than in nonSOZ/nonIZ region. SOZ can be differentiate from IZ through the duration of R. Key message HFO parameters (rate, amplitude and duration) differ in epileptic and non-epileptic region.