Induced Polarization Effects Research Articles

Unsaturated cryptophanes: Toward dual PHIP/hyperpolarised xenon sensors.

Cryptophanes, cage-molecules constituted of aromatic bowls, are now well recognised as powerful xenon hosts in 129 Xe NMR-based biosensing. In the quest of a dual probe that can be addressed only by NMR, we have studied three cryptophanes bearing a tether with an unsaturated bond. The idea behind this is to build probes that can be detected both via hyperpolarised 129 Xe NMR and para-hydrogen induced polarisation 1 H NMR. Only two of the three cryptophanes experience a sufficiently fast hydrogenation enabling the para-hydrogen induced polarisation effect. Although the in-out xenon exchange properties are maintained after hydrogenation, the chemical shift of xenon encaged in these two cryptophanes is not strikingly modified, which impedes safe discrimination of the native and hydrogenated states via 129 Xe NMR. However, a thorough examination of the hyperpolarised 1 H spectra reveals some interesting features for the catalytic process and gives us clues for the design of doubly smart 1 H/129 Xe NMR-based biosensors.

Relationship between bulk mineralogy and induced polarisation responses in iron oxide-copper-gold and porphyry copper mineralisation, northern Chile

We have studied the correlation between bulk mineralogy and induced polarisation (IP) responses in iron oxide-copper-gold (IOCG) and porphyry copper mineralised systems in northern Chile. Twelve drillholes (> 5000 m) that intersect IP sections were mapped and sampled to obtain geological characteristics and to quantify metallic minerals concentration in ore bodies. Geological parameters and modelled geophysical responses (electrical chargeability and resistivity) were compared using qualitative and quantitative criteria.Data analyses show that bulk sulphide concentration is the major factor that explains variations in the IP effect, even for IOCG ore bodies associated with magnetite mineralisation (up to 5 vol. %). Electrical chargeability exhibits a direct, but non-linear proportionality with sulphides content, while no clear trend is observed when chargeability is compared to magnetite concentration. In drillhole segments where macroscopic sulphides were not mapped, but IP results suggested high chargeabilities, petrographic studies revealed at least 1 vol. % of pyrite occurring as micro crystals (< 0.125 mm). The apparent resistivity data do not show any direct relationship with chargeability or sulphide contents.

Electric Field Induced Polarization Effects Measured by in Situ Neutron Spectroscopy

Despite the success of electrical stimulation in many areas, including clay or sludge dewatering, extraction of juices from fruit pulp, fracture healing and targeted drug delivery, the induced transport mechanisms are controlled by unknown factors. While electroosmotic dewatering of clays particles <10 μm is well known, understanding of how tightly bound water molecules are removed from within the clay interlayers is still incomplete. By performing quasielastic neutron scattering experiments with in-situ electric field stimuli on calcium montmorillonite (Ca-Mt) pre-hydrated at relative humidity (RH) of 58 and 85%, we observed an increase in the water mean residence time, suggesting that hydrogen bonding lifetimes are prolonged under electric field. Assuming that at these RH most all water present resides within the interlayer space of the Ca-Mt, this result indicates strong polarization of the water by the interlayer cation. This electroosmotic induced reorganization has important implications in terms of...

Features research of ideal ahead-detecting method used in mining roadway and exploitation of a new technology --DFIP

In order to study the new high efficiency advanced detection technology of coal roadway, the characteristics of ideal advance detection are analyzed. Dual- frequency IP method advanced detection technology is based on the Induced polarization effect of coal (rock). The detection range of the angle and length scanning are achieved by simulation comply with the character of electric field superposition. So, the dual frequency IP method can meet the requirement of high efficiency advance detection of coal roadway. The research results provide theoretical support for the development of new advanced detection equipment.

Analysis and manipulation of the induced changes in the state of polarization by mirror scanners.

The induced polarization effects of metal-coated mirrors were studied in the configurations of one- and two-mirror lidar scanners as a function of azimuth and elevation angles. The theoretical results were verified experimentally for three types of mirrors (custom enhanced gold, off-the-shelf protected gold, and protected aluminum). A method was devised and tested to maintain a desired polarization state (linear or circular) of the transmit beam for all pointing directions by means of rotating wave plates in the transmit and detection paths. Alternatively, the mirror coating can be optimized to preserve the linear polarization state of the transmitted beam. The compensation methods will enable ground-based scanning lidars to produce absolutely calibrated depolarization measurements.

Inductive induced polarization effect in heliborne time-domain electromagnetic data for uranium exploration, northern part of Cuddapah Basin, India

The Peddagattu, Lambapur, Chitrial and Koppunuru uranium deposits along the northern margins of the Cuddapah Basin are confined to the middle Proterozoic unconformity interface between Archean basement granites and the overlying resistive quartzites. Negative transients observed in the coincident loop heliborne time-domain electromagnetic (HTEM) data over these deposits (occurring in outliers) are believed to be due to thick polarizable conductive zones occurring along the unconformity. Similar negative HTEM responses are recorded over the Gorukunta Tanda outlier. A ground spectral induced polarization (SIP) survey conducted over the outlier and ground geologic observations indicated an altered basement/regolith with thickness up to 5 m below 20–30 m thick quartzite. Interpretation of Cole-Cole parameters computed from the SIP data indicated a change in the dispersion. These Cole-Cole parameters were used in modeling negative HTEM data assuming a polarizable plate placed in a layered earth at a depth of approximately 50 m using the CSIRO LeroiAir program. A negative [Formula: see text] response in the late channels indicated that the negatives can be explained in terms of inductive induced polarization effects. Modeling of HTEM [Formula: see text] data for the profile through the Lambapur uranium deposit and the Gorukunta Tanda reveals the presence of a polarizable lithologic unit at a depth of approximately 40 m. This unit is interpreted as an argillic alteration of basement, with the presence of clay and/or disseminated sulfides as evidenced from the core extracted from the boreholes at depths below the highly resistive quartzite. Uranium mineralization is closely associated with altered basement and sulfides along the unconformity where the distinct negative electromagnetic (EM) signature is recorded. Furthermore, there exists a good correlation between the uranium mineralization grade and the thickness versus the averaged late-channel negative HTEM response over the known deposits. The negative EM response helped in locating the new target areas for uranium exploration.

Modeling induced polarization effects in helicopter time-domain electromagnetic data: Field case studies

Induced polarization (IP) effects are becoming more evident in time-domain helicopter airborne electromagnetic (AEM) data thanks to advances in instrumentation, mainly due to improvements in the signal-to-noise ratio and hence better data quality. Although the IP effects are often manifested as negative receiver voltage values, which are easy to detect, in some cases, IP effects can distort recovered transients in other ways so they may be less obvious and require careful data analysis and processing. These effects represent a challenge for modeling and inversion of the AEM data. For proper modeling of electromagnetic transients, the chargeability of the subsurface and other parameters describing the dispersion also need to be taken into consideration. We use the Cole-Cole model to characterize the dispersion and for modeling of the IP effects in field AEM data, collected by different airborne systems over different geologies and exploration targets, including examples from diamond, gold, and base metal exploration. We determined how multiparametric inversion techniques can simultaneously recover all four Cole-Cole parameters, including resistivity [Formula: see text], chargeability [Formula: see text], relaxation time [Formula: see text], and frequency parameter [Formula: see text]. The results obtained are in good agreement with the ancillary information available. Interpretation of the IP effects in AEM data is therefore seen by the authors as providing corrected electrical resistivity distributions, as well as additional information that could assist in mineral exploration.

Modeling induced polarization effects in helicopter time domain electromagnetic data: Synthetic case studies

We have developed a synthetic multiparametric modeling and inversion exercise undertaken to study the robustness of inverting airborne time-domain electromagnetic (TDEM) data to extract Cole-Cole parameters. The following issues were addressed: nonuniqueness, ill posedness, dependency on manual processing and the effect of constraints, and a priori information. We have used a 1D layered earth model approximation and lateral constraints. Synthetic simulations were performed for several models and the corresponding Cole-Cole parameters. The possibility to recover these models by means of laterally constrained multiparametric inversion was evaluated, including recovery of chargeability distributions from shallow and deep targets based on analysis of induced polarization (IP) effects, simulated in airborne TDEM data. Different scenarios were studied, including chargeable targets associated with the conductive and resistive environments. In particular, four generic models were considered for the exercise: a sulfide model, a kimberlite model, and two generic models focusing on the depth of investigation. Our study indicated that, in cases when relaxation time ([Formula: see text]) values are in the range to which the airborne electromagnetic is most sensitive (e.g., approximately 1 ms), it is possible to recover deep chargeable targets (to depths more than 130 m) in association with high electrical conductivity and in resistive environments. Furthermore, it was found that the recovery of a deep conductor, masked by a shallower chargeable target, became possible only when full Cole-Cole modeling was used in the inversion. Lateral constraints improved the recoverability of model parameters. Finally, modeling IP effects increased the accuracy of recovered electrical resistivity models.

FDTD modeling of induced polarization phenomena in transient electromagnetics

The finite-difference time-domain scheme is augmented in order to treat the modelling of transient electromagnetic signals containing induced polarization effects from 3-D distributions of polarizable media. Compared to the non-dispersive problem, the discrete dispersive Maxwell system contains costly convolution operators. Key components to our solution for highly digitized model meshes are Debye decomposition and composite memory variables. We revert to the popular Cole–Cole model of dispersion to describe the frequency-dependent behaviour of electrical conductivity. Its inversely Laplace-transformed Debye decomposition results in a series of time convolutions between electric field and exponential decay functions, with the latter reflecting each Debye constituents’ individual relaxation time. These function types in the discrete-time convolution allow for their substitution by memory variables, annihilating the otherwise prohibitive computing demands. Numerical examples demonstrate the efficiency and practicality of our algorithm.

1D Cole-Cole inversion of TEM transients influenced by induced polarization

Effects of induced polarization (IP) can have an impact on time-domain electromagnetic measurements (TEM) and may lead to sign reversals in the recorded transients. To study these IP effects on TEM data, a new 1D inversion algorithm was developed for both, the central-loop and the separate-loop TEM configurations using the Cole-Cole relaxation model. 1D forward calculations for a homogeneous half-space were conducted with the aim of analyzing the impacts of the Cole-Cole parameters on TEM transients with respect to possible sign reversals. The forward modelings showed that the variation of different parameters have comparable effects on the TEM transients. This leads to an increasing number of equivalent models as a result of inversion calculations. Subsequently, 1D inversions of synthetic data were performed to study the potentials and limitations of the algorithm regarding the resolution of the Cole-Cole parameters. In order to achieve optimal inversion results, it was essential to error-weight the data points in the direct vicinity of sign reversals. The obtained findings were eventually adopted on the inversion of real field data which contained considerable IP signatures such as sign reversals. One field data set was recorded at the Nakyn kimberlite field in Western Yakutiya, Russia, in the central-loop configuration. Another field data set originates from a waste site in Cologne, Germany, and was measured utilizing the separate-loop configuration.

In-Loop Transient Electromagnetic Responses With Induced Polarization Effects of Deep-Sea Hydrothermal Deposits

A transient electromagnetic (TEM) system using a small loop source is advantageous to the development of compact autonomous instruments, which are well suited to a submersible-based survey. Since the electrical conductivity of subseafloor materials can be frequency dependent, these induced polarization (IP) effects may affect the reliability of TEM data interpretation. In this paper, we investigate the IP effects on the TEM responses of deep-sea hydrothermal mineral deposits with a thin sediment cover. Time-domain target signals are larger and appear earlier in horizontal magnetic fields than in vertical magnetic fields. The IP effects cause transient magnetic fields to enhance initially, to decay rapidly, and then to reverse the polarity. The dc conductivity and chargeability in Cole–Cole parameters influence the time of sign reversals and the enhancement of target responses, simultaneously. A damped least squares inversion scheme is applied to reconstruct a polarizable hydrothermal deposit model using synthetic TEM sounding data sampled from a time interval before the sign reversal. The test example demonstrates that the Cole–Cole parameters of a highly conductive layer can be resolved more effectively from vertical magnetic fields than from horizontal magnetic fields.

Airborne IP: examples from the Mount Milligan deposit, Canada, and the Amakinskaya kimberlite pipe, Russia

There have been multiple occurrences in the literature in the past several years of what has been referred to as the induced polarisation (IP) effect in airborne time domain electromagnetic (TDEM) data. This phenomenon is known to be responsible for incorrect inversion modelling of electrical resistivity, lower interpreted depth of investigation (DOI) and lost information about chargeability of the subsurface and other valuable parameters. Historically, there have been many suggestions to account for the IP effect using the Cole-Cole model. It has been previously demonstrated that the Cole-Cole model can be effective in modelling synthetic TDEM transients. In the current paper we show the possibility of extracting IP information from airborne TDEM data using this same concept, including inverse modelling of chargeability from TDEM data collected by VTEM, with field examples from Canada (Mt Milligan deposit) and Russia (Amakinskaya kimberlite pipe).

Fitting superparamagnetic and distributed Cole-Cole parameters to airborne electromagnetic data: A case history from Quebec

Our aim was to confirm the ability of polarizable and superparamagnetic (SPM) thin sheets in the near surface to improve the model fit of airborne electromagnetic data. Our method was to fit induced polarization (IP) effects with Cole-Cole complex conductivity and fit SPM effects with Chikazumi complex permeability. Surficial conductors were assumed to be the source of the conductivity and IP effects. In this case history from Lac Brûlé, Quebec over an anorthosite intrusion, small to large IP effects were found to be essential to fit most of the observed data. In some areas, it was also possible to separate SPM effects from IP effects in the data. Most IP effects in this unusually polarizable area were adequately fit with a distributed decay characterized with a frequency dependence of [Formula: see text], but some required a sharper response characterized by [Formula: see text]. In general, fitted IP time constants were anticorrelated with fitted frequency dependence, with short time constants fitted to the larger [Formula: see text] values and vice versa. SPM effects were detected in a small but significant fraction of the data, and appear to be spatially related to static magnetic anomalies. The SPM in this case is presumably related to fine-grained rock magnetism, rather than the more common case of weathering products.

Comparing induced polarization responses from airborne inductive and galvanic ground systems: Lewis Ponds, New South Wales

We have evaluated the mapping of polarizable material using a Cole-Cole model to fit second-order effects in concentric-loop airborne electromagnetic system responses. At Lewis Ponds in New South Wales, an inverted ground dipole-dipole array data has accurately imaged in 3D disseminated sulfide extending above and around ore grade massive sulfides. The polarizable zone is present in the near-surface, where, from modeling, airborne systems may have sensitivity to the small inductive induced polarization effects. Although the inverted chargeability measured from galvanic current injection into the ground was spatially coincident with the mineralized target, the estimated chargeabilities from induced polarization effects in an airborne versatile time-domain electromagnetic survey were substantially displaced to the east. The airborne induced polarization response may be associated with finer grained mineralization in the hanging wall of the sulfide deposits, or have a quite different source, such as clays associated with faulting.

A discussion on the performance of seven existing models proposed to describe induced polarization

Many types of classical models of the induced polarization (IP) effects of rock ore have been introduced in previous studies. Our focus is on determining the most effective model for describing the rock ore IP effects based on a numerical simulation calculation and a rock mineral spectrum experiment. We have constructed a Delphi 7 program for seven models to calculate the complex resistivity spectrum of phase. We have also evaluated the influences of the parameters on the spectrum and the spectral scope. More than 50 pieces of various natural rock ore samples from 16 regions were selected, and the frequency sweep measurements were completed using an SI-1260 Solartron spectrometer. Another program of seven models was developed using a differential evolution algorithm and least-squares for fitting the experimental spectral data. The purpose was to evaluate the ability of these models for fitting the IP effects. The results found that the influence laws on the spectrum of the different parameters, as well as the spectral scope of the models, were different. The natural samples measured revealed unimodal and bimodal phase spectra. Dias and multi-Cole-Cole models were optimal for characterizing the unimodal and bimodal phase spectra of the selected metal minerals, with the highest fitting precision root-mean-square (rms) error of 2.5% and 1.16%, respectively. Warburg, Cole-Cole, and generalized Cole-Cole models were suitable for the unimodal phase spectra, with the highest fitting precision of 3.67%, 3.01%, and 3.27%, respectively. Madden and Cantwell model was suitable for characterizing the silver-ore- and gold-bearing pyrite, but the rms was [Formula: see text] for other samples. The Debye model had an rms [Formula: see text] for characterizing all our experimental samples.

Comparing induced polarization responses from airborne inductive and galvanic ground systems: Tasmania

We have first analyzed the ability of polarizable and superparamagnetic thin sheets in the near surface to fit airborne electromagnetic (AEM) data using data from western Tasmania. Then we analyzed the results of such fitting in the context of geologic mapping and available ground induced polarization (IP) data. Small to large IP effects were found to considerably improve the fit to the observed AEM data, and the overall fitted IP parameters were spatially consistent. However, the locations of anomalous IP parameters were quite distinct from anomalies in other geophysical data. The airborne chargeability highs were adjacent to or surrounded the ground chargeability highs in the five cases analyzed from Tasmanian data. Modeling using the established Cole-Cole physical property values for sulfides predicts that an inductive airborne system is insensitive to many conventional IP targets, unless the mineral grain size is substantially less than 1 mm. In the cases in which airborne IP responses were adjacent to ground IP targets, we hypothesized that the airborne IP may be finer grained minerals in an alteration halo surrounding the sulfide sources of the large ground IP anomalies. Surficial clays encountered in drillholes did not have significant ground or airborne IP responses. A companion paper comes to a similar conclusion using ground and airborne data from a copper deposit in New South Wales.

Phase-induced polarization method based on processing noise signals of the natural electromagnetic field of the Earth

The paper deals with the physical fundamentals of the phase geoelectric method of induced polarization (IP) based on the extraction of information from the natural electromagnetic field of the Earth (NEMFE) in the frequency range 0.1-20.0 Hz. Scientific and technical justification is provided for the differential measurement circuit parameters of the NEMFE and the algorithm of processing of the received signals with the calculation of the IP coefficient, assuming the identity of the field characteristics in two receiving lines. The method consists in recording random noise signals from two adjacent receiving electrical dipoles with simultaneous memorizing of the amplitudes and their automatic equalization. Then the difference between the signals is calculated, with subsequent energy normalization. The presented theoretical fundamentals for the calculation of the IP coefficient of the NEMFE and the processing algorithm were tested in laboratory experiments. Under the assumption of the complete identity of the medium beneath the receiving dipoles, the IP coefficient was 0.01-0.03, due to the error in the elemental base of the analog input path. The paper also presents the results of field experiments on the Samson iron deposit in the Republic of Khakassia. The experimental work confirmed the effect of IP on the NEMFE in the anomalous area and showed that the results are consistent with theoretical and laboratory predictions and the data obtained using a KEP-M pulse system. It is concluded that this method can be used to detect productive anomalies and has an advantage of eliminating artificial sources of excitation of geologic sections.

A non-linear induced polarization effect on transient electromagnetic soundings

In a TEM survey conducted for characterizing the subsurface for geothermal purposes, a strong induced polarization effect was recorded in all collected data. Surprisingly, anomalous decay curves were obtained in part of the sites, whose shape depended on the repetition frequency of the exciting square waveform, i.e. on current pulse length.The Cole–Cole model, besides being not directly related to physical parameters of rocks, was found inappropriate to model the observed distortion, due to induced polarization, because this model is linear, i.e. it cannot fit any dependence on current pulse. This phenomenon was investigated and explained as due to the presence of membrane polarization linked to constrictivity of (fresh) water-saturated pores. An algorithm for mathematical modeling of TEM data was then developed to fit this behavior.The case history is then discussed: 1D inversion, which accommodates non-linear effects, produced models that agree quite satisfactorily with resistivity and chargeability models obtained by an electrical resistivity tomography carried out for comparison.

Influence of electrostatic interactions on the properties of cyanobiphenyl liquid crystals predicted from atomistic molecular dynamics simulations

ABSTRACTThe influence of force field details in all-atom molecular dynamics (MD) simulations on the predicted thermodynamic, structural, and dynamic properties of bulk 4-cyano-4ʹ-pentylbiphenyl (5CB) systems have been investigated in the 292–368 K temperature range. The effect of the molecular dipole moment and the details of dihedral potential for biphenyl unit were investigated using both polarisable (POL) and non-polarisable (NP) versions of the quantum chemistry-based force field. The predicted densities for the nematic and isotropic phases of bulk 5CB were found to be in excellent agreement with available experimental data. The nematic-isotropic transition temperature (TNI) showed strong sensitivity to the force field details, MD simulations with partial atomic charge distributions and molecular dipole moment corresponding to high-level quantum chemistry calculations predicted an overestimation of the TNI by about 30 K. Rescaling the charges to allow the molecular dipole to be closer to experimentally reported values of 5CB dipole in condensed phases, significantly improved the prediction of TNI as well as other thermodynamic and dynamic properties of 5CB. We also discuss how the structural, thermodynamic, and dynamic properties of bulk 5CB are affected by the flexibility of the central biphenyl dihedral and the inclusion of induced polarisation effects.

Two-dimensional inversion of spectral induced polarization data using MPI parallel algorithm in data space

Traditional two-dimensional (2D) complex resistivity forward modeling is based on Poisson’s equation but spectral induced polarization (SIP) data are the coproducts of the induced polarization (IP) and the electromagnetic induction (EMI) effects. This is especially true under high frequencies, where the EMI effect can exceed the IP effect. 2D inversion that only considers the IP effect reduces the reliability of the inversion data. In this paper, we derive differential equations using Maxwell’s equations. With the introduction of the Cole–Cole model, we use the finite-element method to conduct 2D SIP forward modeling that considers the EMI and IP effects simultaneously. The data-space Occam method, in which different constraints to the model smoothness and parametric boundaries are introduced, is then used to simultaneously obtain the four parameters of the Cole—Cole model using multi-array electric field data. This approach not only improves the stability of the inversion but also significantly reduces the solution ambiguity. To improve the computational efficiency, message passing interface programming was used to accelerate the 2D SIP forward modeling and inversion. Synthetic datasets were tested using both serial and parallel algorithms, and the tests suggest that the proposed parallel algorithm is robust and efficient.