Horizontal Coil Research Articles

An Integration of Self Potential, Electromagnetic and Resistivity Profiling Methods in the Search for Sulfide Deposits in Gwoza, Borno State, Nigeria

The combination of Self Potential (SP), Electromagnetic (EM) and Resistivity profiling methods in Gwoza has resulted in the delineation of conductive zones suspected to be sulfide mineralization in the area. Mineralization potentials of –201 mV on the profile AA’, –250.2 mV on the profile BB’ and –203 mV on the profile CC’ respectively have been observed. Correspondingly, both the vertical coil and the horizontal coil readings of the EM anomalies on the profiles AA’, BB’ and CC’ also show significant negative anomalies across the delineated conductive zones. Three resistivity profiles DD’, EE’ and KK’ have also shown very low resistivity values across the said conductive zones. These conductive zones have been established as sulfide mineralization within faults in this work. The recovery of chalcopyrite samples from a hand-dug well close to the delineated conductive zone of the profile BB’ tends to lend credence to the interpretation in this study.

S102021 ひし形リンク構造を用いた免振設計に関する研究

This paper deals a seismic isolation system with nonlinear characteristics mechanism for a vertical seismic oscillation. The seismic isolation system consists of a rhombus shape link, horizontal coil springs and vertical coil springs. Restoring force of the system can be calculated by the geometric calculation. The authors propose a design principle of the system, using that natural period of the seismic isolation system can be calculated from its restoring force characteristics. A Seismic isolator using the nonlinear characteristics was actually made, and its restoring force characteristics were measured by static loading test From this experiment results, it revealed that the characteristics of the device can be accurately predicted from the design principle.

Effects of instrument orientation on small-loop electromagnetic induction surveys of localized 2D conductive targets

Frequency-domain electromagnetic induction (EMI) systems, composed of two coplanar small coils separated by a fixed distance (EMI or SLEM), enable the rapid detection of a great variety of near-surface structures. One coil generates a controlled, primary magnetic field and the other records the variations of the induced field while the instrument is moved over the studied area. The most usual acquisition configuration corresponds to horizontal coils, with the instrument axis parallel to the prospection lines. Usually, the interpretation is based on the direct visualization of the plan-views of the data measured at each frequency. In addition, to characterize the subsoil structure in-depth, 1D inversion methods are generally applied. The aim of this work is to analyse how the system orientation affects the ability of the method to detect localized, 2D conductive structures, buried at shallow depths, and the possibility of adequately characterizing these targets through 1D inversions. We performed a survey at a test site that contains two known structures of this type, buried in almost perpendicular directions. We performed parallel prospection lines in the direction of each structure, employing, aside from the usual configuration described before, other configurations that included horizontal and vertical coils, with the instrument axis parallel and perpendicular to the lines. For comparison, we also performed a geoelectric dipole–dipole line crossing one of the targets. The features of the anomalies observed in the graphs of the EMI apparent conductivity data strongly depend on the instrument orientation. In the horizontal coil configurations, a decrease of the apparent conductivity is observed just over the targets. Besides, each vertical configuration practically detects only the target aligned with the plane of the coils, as an important positive anomaly. Through numerical simulations, performed using a 2D forward modelling method, we demonstrate that these features are indeed 2D effects associated with the localized character of the studied conductive objects. Then, we applied to the data a 1D inversion method and drawing together the results generated pseudo 3D models of the subsoil. We found that the models obtained for the vertical coil configurations provide better results. They detect the targets as conductive structures and provide a rather good estimation of their depths. Finally, we compare the EMI results with the image obtained from the 2D inversion of the geoelectrical data and analyse the causes of the observed differences.

Remote field eddy current testing for steam generator inspection of fast reactor

We confirmed the defect detection performances of the remote field eddy current testing (RFECT) in order to inspect the helical-coil-type double wall tube steam generator (DWTSG) with the wire mesh layer for the new small fast reactor 4S (Super-Safe, Small and Simple). As the high sensitivity techniques, we tried to increase the direct magnetic field intensity in the vicinity of the inner wall of the tube and decrease the direct magnetic field around the central axis of the tube using the exciter coil with the flux guide made of the iron–nickel alloy. We adopted the horizontal type multiple detector coils with the flux guides arrayed circumferentially to enhance the sensitivity of the radial component. According to the experimental results, the output voltage of the detector coil in the region of indirect magnetic field increased more than 100 times by the application of the exciter and detector coils with the flux guides. Finally, we were able to detect the small hole defect of 1 mm in diameter and 20% of the outer tube thickness in depth over the wire mesh layer by the adoption of the exciter coil and horizontal type multiple detector coils with the flux guides. We also confirmed that the RFECT probe is useful for detecting thinning defects. These experimental results indicated that there is the possibility that we can inspect the double wall tube with the wire mesh layer using the RFECT.

The 2D coastal effect on marine time domain electromagnetic measurements using broadside dBz/dt of an electrical transmitter dipole

Galvanic transmitter-receiver arrays commonly are used in marine controlled-source electromagnetic (CSEM) exploration of electrically resistive targets such as hydrocarbons, gas hydrates, etc. These arrays utilize vertical electric currents and, as a result, are expected to provide better resolving capability for exploring subhorizontal resistive structures than arrays including horizontal coils. If, however, a subseafloor resistive target is located within a transition zone at distances of up to a few kilometers from the shoreline, the 2D sea-coast resistivity contrast significantly affects the resolving capability of the measurements. An extensive multidimensional modeling supported by numerous offshore measurements showed that the inductive array consisting of a horizontal electric dipole transmitter and a broadside vertical magnetic dipole (horizontal coil) receiver exhibits much better resolving power in time domain compared to all other arrays but those with a vertical electric dipole. This effect takes place only if a short offset receiver coil is located between the transmitter dipole and the coast. If the coil is located at the seaside of the transmitter dipole, the signal lacks the resolving capability almost entirely. At large offsets, the resolving capability of the measurements is relatively low at both sides of the transmitter dipole. Although actual field measurements were conducted only to explore a shallow target (fresh subseafloor groundwater body), calculations show that the same phenomenon exists in case of deep targets (e.g., hydrocarbons).

4C12 A Seesaw Swivel Type Actuator with New Magnetic Array Design

We present a new type actuator though the swing type arm was as a reference of small form factor optical pickup heads that had already utilized the material of piezoelectricity or slim plate of metal to perform focusing action. The seesaw type actuator is a new driving mechanism used for swiveling the small form devices. The configuration of the seesaw swivel actuator has unique features including a rotary supporting base for coarse and fine tracking, and a seesaw arm swivels along a pivot without a hinge to permit a tilted focus movement. Moreover, to achieve precision positioning of the seesaw actuator, a lateral focusing voice coil motor, which attached the middle seesaw arm, is proposed. In order to adjust the broad air gap between the tracking coil and the base magnet, a horizontal voice coil motor combined a ring type magnet provides uniform and uninterrupted magnetic output and the magnetic component is unlike multi-segmented magnet arrays form. The seesaw actuator was designed on the basis of finite element structural analyses for focus/tracking actuations and the dynamic characteristics were verified by this simulation. An original seesaw actuator with particular magnetic circuit was specifically manufactured and assembled for a micro ODD. Natural frequencies of seesaw swing arm are measured to confirm the results of finite element analyses. Furthermore, the parameters optimization procedure uses as design variables to optimize the initial model and improve the system response. The vital discussion is the New magnets array design

Horizontal stent-assisted coil embolisation of wide-necked intracranial aneurysms with the Enterprise stent—a case series with early angiographic follow-up

The purpose of the study is to describe our experience in eight cases of horizontal stenting across the circle of Willis in patients with terminal aneurysms. Eight patients were treated with horizontal stent placement and aneurysm coiling. All aneurysms had highly unfavourable dome to neck ratios. All patients were followed up with digital subtraction angiography at 3-12 months following treatment. The Enterprise stent was successfully deployed horizontally in vessels of less than 2-mm diameter with no stent occlusion. Neurological complications occurred in one patient. Immediate and follow-up angiographic results were encouraging with six stable occlusions at 6 months. There was one asymptomatic case of in-stent stenosis and one case of late organised in-stent thrombus. Horizontal deployment of the Enterprise stent to assist coil embolisation of wide-necked terminal aneurysms is feasible. This device can be navigated via relatively small communicating arteries, in cases with favourable anatomy. Early angiographic results were favourable; however, longer-term follow-up will be required.

2-Dimensional soil and vadose-zone representation using an EM38 and EM34 and a laterally constrained inversion model

The network of prior streams and palaeochannels common across the Riverine Plains of the Murray–Darling Basin act as conduits for the redistribution of water and soluble salts beneath the root-zone. To improve scientific understanding of these hydrological processes there is the need to better represent and map the connectivity and spatial extent of these physiographic and stratigraphic features. Groundbased electromagnetic (EM) instruments, which measure bulk soil electrical conductivity (σa), have been used widely to map their areal distribution across the landscape. However, methods to resolve their location with depth have rarely been attempted. In this paper we employ a 1-D inversion algorithm with 2-D smoothness constraints to predict the true electrical conductivity (σ) at discrete depth increments using EM data. The EM data we use include the root-zone measuring EM38 and the deeper sensing EM34. We collected EM38 data in the vertical (EM38v) and horizontal (EM38h) dipole modes and EM34 data in the horizontal mode and coil spacing of 10, 20, and 40 m (respectively, EM34-10, EM34-20, and EM34-40). In order to compare and contrast the value of the various EM data we carried out multiple inversions using different combinations, which include: independent inversions of (i) EM38 (root-zone) and (ii) EM34 data (vadose-zone), and in combination using (iii) EM38v, EM38h, and EM34-10 (near-surface), and (iv) all 5 EM datasets (regolith) available. The general patterns of σ are shown to compare favourably with the known pedoderms, physiographic, and stratigraphic features and soil particle size fractions collected from calibration cores drilled across the lower Macquarie Valley study area. In general we find that the EM38 assists in resolving root-zone variability, specifically duplex soil profiles and physiographic features such as prior streams, while the use of the EM34 assists in resolving the stratigraphic nature of the vadose-zone and specifically the likely location of palaeochannels and subsurface anomalies that may indicate the location of good quality groundwater and/or clay aquitards. In this case, our potential to use σ to predict clay content is limited by the non-linearity of the cumulative functions. In order to improve on the non-linearity of our inversion we need to develop a full solution of the forward problem.

Utilizing airborne electromagnetic (EM) data, high resolution DEM and hydrogeological information to derive customised products for natural resource management along the River Murray corridor

To improve on earlier hydrogeological models and to better manage the River Murray floodplain environment and water resources from salinity and irrigation impacts, stakeholders in the New South Wales and Victorian Mallee worked with project scientists to identify hydrogeological parameters that might be collected from existing data sets to help resolve land and water management issues (Lawrie at al., 2008). Several areas where improved information were identified, including the extent and thickness of the river flush zone, salt stores in both the unsaturated and saturated zones, and the thickness, extent and depth to the top of the Blanchetown Clay and other clay units across the floodplain and its adjacent uplands. Previous AEM-based studies have demonstrated the potential for these data to provide high geospatial resolution of key elements of the hydrogeological system (Walker et al., 2004). An airborne electromagnetic (AEM) survey was flown in early 2007 along a 450 km stretch of the Murray River and its floodplains in Victoria from the South Australian-Victorian border to Gunbower. The data were acquired under the auspices of the Australian Government?s Community Stream Sampling and Salinity Mapping Project, and were managed by the Bureau of Rural Sciences. This survey utilised a Fugro RESOLVE frequency domain system, with flight lines at 200m line spacing, and oriented at a high angle to the river corridor. RESOLVE is a six frequency EM system mounted in a bird towed beneath a helicopter at a nominal altitude of 30 m. The bird contains horizontal coplanar coils and measure EM responses at 390 Hz, 1798 Hz, 8177 Hz, 39470 Hz and 132700 Hz. It also has one coaxial coil pair which measured a response at 3242 Hz. This paper presents methods for mapping the thickness of Blanchetown Clay in the highlands of the areas surveyed during the course of this work, and the distribution of near surface clay across the floodplains, specifically at Lindsay-Wallpolla, Lake Victoria, Darling River and its anabranch.

Heat transfer in a horizontal coiled pipe in a transient regime and at a near-critical pressure of a fluid

It has been established that in the region of pressures close to a critical one, heat transfer in a transient regime of motion of a single-phase flow in a horizontal coil pipe changes nonuniformly over the cross section of the perimeter. The main factors here are the influence of inertia forces and of free convection. Equations to calculate the heat-transfer coefficient are suggested.

Conductivity-depth imaging of helicopter-borne TEM data based on a pseudolayer half-space model

Helicopter-borne time-domain electromagnetic (HTEM) systems with a concentric horizontal coil configuration have been used increasingly in mineral exploration. Conductivity-depth imaging (CDI) is a useful tool for mapping the distribution of geologic conductivity and for identifying conductive targets. A CDI algorithm for HTEM systems with a concentric coil configuration is developed based on the pseudolayer half-space model. Primary advantages of this model are immunity to altimeter errors and better resolution of conductive layers than other half-space models. Effective depth is derived empirically from the diffusion depth and apparent thickness of the pseudolayer. A table lookup procedure is established based on the analytic solution of a half-space model to speed up processing. This efficiency makes generation of real-time conductivity-depth images possible. Tests on synthetic data demonstrate that the pseudolayer conductivity-depth-imaging algorithm maps a wider range of conduc-tivities and does a better job of resolving highly conductive layers, compared with that of the homogeneous half-space model. Effective depths are close to true depths in many circumstances. Field examples show stable and geologically meaningful conductivity-depth images.

비이온계 계면활성제 첨가수에 대한 관내 유동저항 감소 및 열전달 촉진에 관한 연구

This paper has dealt with the effect of non ionized surfactant and water mixture on drag reduction and heat transfer enhancement in a circular pipe flow with experimentally. The test section was consisted of stainless steel pipe with inside diameter of 16mm. The wire coil was used to increase heat transfer in a pipe and the non ionized surfactant(Oleyl Dihydroxyethyl Amine Oxide, ODEAO) was used to reduce the drag force of water mixture with surfactant. The main parameters of this experiment were diameter and pitch of wire coil and the ratio of test section length and horizontal wire coil length. In this experiment, the acquired results were 1) Drag reduction effect existed in this ODEAO-water mixture, 2) Friction factor and heat transfer were increased with insertion the heat transfer enhancement coil, 3) With increasing of pitch ratio, heat transfer was decreased, and 4) Heat transfer was decreased by the decreasing of inserting coil diameter.

Induction-response functions for frequency-domain electromagnetic mapping system for airborne and ground configurations

A helicopter-towed electromagnetic (EM) sensor of the type typically flown in frequency-domain surveys may be towed over the ground on a trailer. The in-phase and quadrature components measured by a trailer-towed sensor will be dramatically different from those determined when the sensor is flown. For the airborne case, the in-phase and quadrature curves of the induction-response function are governed by the superposed-dipole behavior, in which flying height substantially exceeds the transmitting-receiving coil separation. In contrast, for a ground-based sensor, the coil separation substantially exceeds the sensor height, yielding the infinitely separated dipole case in which the sensor height is negligible compared to the coil separation. These two end cases — the superposed dipole and the infinitely separated dipole —yield EM amplitudes and phase angles that are very different from each other. For the superposed-dipole case of the airborne sensor, the in-phase component reaches a high positive value as the EM response approaches the inductive limit, whereas for the infinitely separated dipole case of the ground sensor, the in-phase component reaches a large negative value. Consequently, there must be a sensor height where the in-phase becomes zero at the inductive limit. This critical height is approximately 35% of the coil separation for the maximum coupled horizontal coplanar coils of the helicopter-towed EM system. The resolution of the ground sensor is superior to that of the airborne sensor, whereas the depth of exploration for the airborne sensor is superior to that of the ground sensor. This finding is to be expected from a consideration of the size of the footprint of the sensor.

Diurnal variations of ELF transients and background noise in the Schumann resonance band

Schumann resonances (SR) are resonant electromagnetic waves in the Earth‐ionosphere cavity, induced primarily by lightning discharges, with a fundamental frequency of about 8 Hz and higher‐order modes separated by approximately 6 Hz. The SR are made up of the background signal resulting from global lightning activity and extremely low frequency (ELF) transients resulting from particularly intense lightning discharges somewhere on the planet. Since transients within the Earth‐ionosphere cavity due to lightning propagate globally in the ELF range, we can monitor and study global ELF transients from a single station. Data from our Negev Desert (Israel) ELF site are collected using two horizontal magnetic induction coils and a vertical electric field ball antenna, monitored in the 5–40 Hz range with a sampling frequency of 250 Hz. In this paper we present statistics related to the probability distribution of ELF transients and background noise in the time domain and its temporal variations during the day. Our results show that the ELF signal in the time domain follows the normal distribution very well. The σ parameter exhibits three peaks at 0800, 1400, and 2000 UT, which are related to the three main global lightning activity centers in Asia, Africa, and America, respectively. Furthermore, the occurrence of intense ELF events obeys the Poisson distribution, with such intense events occurring every ∼10 s, depending on the time of the day. We found that the diurnal changes of the σ parameter are several percent of the mean, while for the number of intense events per minute, the diurnal changes are tens of percent about the mean. We also present the diurnal changes of the SR intensities in the frequency domain as observed at our station. To better understand the diurnal variability of the observations, we simulated the measured ELF background noise using space observations as input, as detected by the Optical Transient Detector (OTD). The most active center which is reflected from both ELF measurements and OTD observations is in Africa. However, the second most active center on the basis of ELF measurements appears to be Asia, while OTD observations show that the American center is more active than the Asian center. These differences are discussed. This paper contributes to our understanding of the origin of the SR by comparing different lightning data sets: background electromagnetic radiation and optical emission observed from space.

Vertical Spatial Sensitivity and Exploration Depth of Low‐Induction‐Number Electromagnetic‐Induction Instruments

Vertical spatial sensitivity and effective depth of exploration (de) of low‐induction‐number (LIN) instruments over a layered soil were evaluated using a complete numerical solution to Maxwell's equations. Previous studies using approximate mathematical solutions predicted a vertical spatial sensitivity for instruments operating under LIN conditions that, for a given transmitter–receiver coil separation (s), coil orientation, and transmitter frequency, should depend solely on depth below the land surface. When not operating under LIN conditions, vertical spatial sensitivity and de also depend on apparent soil electrical conductivity (σa) and therefore the induction number (β). In this new evaluation, we determined the range of σa and β values for which the LIN conditions hold and how de changes when they do not. Two‐layer soil models were simulated with both horizontal (HCP) and vertical (VCP) coplanar coil orientations. Soil layers were given electrical conductivity values ranging from 0.1 to 200 mS m−1 As expected, de decreased as σa increased. Only the least electrically conductive soil produced the de expected when operating under LIN conditions. For the VCP orientation, this was 1.6s, decreasing to 0.8s in the most electrically conductive soil. For the HCP orientation, de decreased from 0.76s to 0.51s Differences between this and previous studies are attributed to inadequate representation of skin‐depth effect and scattering at interfaces between layers. When using LIN instruments to identify depth to water tables, interfaces between soil layers, and variations in salt or moisture content, it is important to consider the dependence of de on σa

Vertical and Three-Dimensional Seismic Isolation Tables with Bilinear Spring Force Characteristics (For Which a .LAMBDA.-Shaped Link Mechanism Is Used)

In this paper, the authors propose a nonlinear spring mechanism for a vertical seismic isolation table. The nonlinear spring mechanism consists of a A-shaped link, horizontal coil springs, vertical coil springs and a linear guide, and has an approximate bilinear-type spring force characteristic. A vertical seismic isolation table using the nonlinear spring mechanism and magnetic damping was made, and the seismic responses of a mass installed on the table board were measured using a permanent magnet type vibration machine. Next, the vertical isolation table was attached to a horizontal seismic isolation table which was developed in our previous study, and the three-dimensional seismic responses of a mass installed on the table board were measured using the vibration machine. These experimental results were compared with the calculated results, and the effects of vibration isolation in three-dimensional directions and the validity of the calculations were substantiated.

Airborne electromagnetics in Europe: recent activities and future goals

Annika Steuer and Uwe Meyer of the Federal Institute for Geosciences and Natural Resources, report on a recent gathering of organizations in Europe using airborne electromagnetics. In numbers, European systems are dominated by frequency domain instruments. The Geological Surveys of Norway, Germany, and Austria, as well as the AWI, use helicopter electromagnetic (HEM) systems, which differ in the number of frequencies and configuration of the coil systems. NGU and GBA use the Geotech Hummingbird, NGU with three horizontal coplanar and two horizontal coaxial coils whereas GBA uses four horizontal coplanar coils. BGR operates a DIGHEM bird from Fugro with five horizontal coplanar coils. AWI developed a dual-frequency HEM system, specially designed for the sounding of seaice thicknesses in Polar Regions. The Geological surveys of the United Kingdom (BGS) and Finland (GTK) established a 'Joint Airborne-geoscience Capability' (JAC) based on a system originally developed by GTK. They operate a fixed wing aircraft carrying a four-frequency system using vertical coplanar coils. The Swedish Geological Survey and the University of Uppsala also use a fixed-wing. Both developed a new VLF instrument working in the wide frequency band of 1-350 kHz. At present, the only time-domain system in Europe is operated by the University of Aarhus. The Aarhus Sky TEM system is a transient electromagnetic technique in a 'central loop'-like configuration, towed by a helicopter.

Analysis of Tilted-Coil Eccentric Borehole Antennas in Cylindrical Multilayered Formations for Well-Logging Applications

Well-logging tools employing tilted coil antennas have been proposed to provide directional (azimuth) information and improved estimates of anisotropy when compared to conventional tools that use horizontal coils. In this paper, we analyze the response of logging tools with tilted coil antennas in eccentric boreholes crossing cylindrical multilayered formations (earth formations with invasion zones) by two approaches. The first approach is based on a pseudoanalytic formulation, previously applied for concentric boreholes and extended here to include eccentric boreholes. The second approach is based on three-dimensional (3-D) numerical simulations using the finite-difference time-domain (FDTD) algorithm extended to cylindrical coordinates and incorporating cylindrical perfectly matched layers (PML). The results from the two formulations are compared for different formations, showing very good agreement.

Comparison of Theoretical and Physical Model Studies of the Responses of Moving Source and Fixed Loop Electromagnetic Exploration Systems

Theoretical and physical scale model responses for moving source and fixed loop electromagnetic exploration systems are presented for the case of a vertical, thin, plate conductor located first in free-space and then in a conductive host. The results are presented in the form of anomaly index diagrams plotted in complex space. The two modeling approaches show general agreement on the behavior of the current gathering effect that operates when the conductive host is present. Both approaches show an onset of a strong positive effect at higher frequencies in the responses provided by both horizontal coplanar coil systems and by fixed loop systems. Agreement is also shown on an unanticipated negative effect that a conductive host causes in the responses provided by the vertical coplanar coincident coil system. Both modeling approaches demonstrate that the responses provided by fixed loop systems are predominantly caused by the current gathering effect. The extent of this effect for fixed loop systems depends on the size of the transmitter loop with respect to the target and on the depth of the target. The theoretical modeling demonstrates that both moving source and fixed loop systems operated over a target located in a conductive host, provide responses that become almost identical and independent of the conductance of the target at high frequency.

Investigation of Characteristic Features of Critical Heat Transfer under Conditions of Boiling of Subcooled Hydrocarbons in a Close-to-Critical Pressure Range

Results are given of an investigation of heat transfer under conditions of boiling of subcooled benzene and toluene at close-to-critical pressures in a vertical straight and horizontal coil pipes. A nonuniform distribution of the wall temperature along the perimeter of the horizontal coil pipe is revealed, as well as a smooth rise of this temperature under conditions of critical heat transfer. Equations are suggested for the calculation of critical heat flux in the pressure range identified above with the vertical position of the straight pipe.