Electromagnetic Ground Research Articles

Reconfigurable Metamaterial Antenna based an Electromagnetic Ground Plane Defects for Modern Wireless Communication Devices

In this paper, a design of a microstrip antenna based on metamaterial (MTM) and electromagnetic band gap (EBG) arrays. The patch is structured from 5×3 MTM array to enhance the antenna bandwidth gain product. The individual unit cell is structured as a split ring (SRR) with a T-resonator. The ground plane is defected with an EBG to suppress the surface waves diffraction from the substrate edges. The antenna is printed on a Roger substrate with permittivity of 10.2 and 1 mm thickness. It is found that the proposed antenna provides a frequency resonance around 2.45 GHz and 3.5 GHz with another band between 4.6 GHz to 5.6 GHz which are very suitable for Wi-Fi and 5G networks. Nevertheless, the antenna gain is found to vary from 3.5 dBi to less than 6 dBi. The antenna size is reduced enough to λ/5 of the guided wavelength to fit an area of 12 mm×20 mm. The proposed antenna performance is controlled with two PIN diodes for reconfiguration process. The antenna frequency resonance bands are found to be well controlled by stopping the current motion at the particular band. The antenna is fabricated and tested experimentally. Finally, the simulated results are compared to those obtained from measurements to provide an excellent agreement to each other with error of less than 3%.

3D Constrained Gravity Inversion and TEM, Seismic Reflection and Drill-Hole Analysis for New Target Generation in the Neves–Corvo VMS Mine Region, Iberian Pyrite Belt

Located in the Iberian pyrite belt, the Neves–Corvo mine is a world-class massive sulfide deposit and the largest operating mine in Portugal with underground mining down to 1000 m depth focused on massive and stockwork Cu, Zn, Pb rich ores. Gravimetric data have had a leading role in the discovery of the seven known deposits, together with time-domain electromagnetic (TEM) ground data. In this work, we present the results of a 3D constrained gravity inversion carried out with legacy ground gravity data. The 3D gravity inversions were carried out using an updated density database containing approximately 142,000 measurements. A recently constructed 3D geological model based on reprocessed 2D seismic reflection, 3D seismic, TEM and updated geology from detailed surface mapping and drill-hole data, was used to constrain the inversions. The results show multiple high-density anomalies that may indicate the presence of mineralization at depth. These anomalies were therefore cross-checked with holes previously drilled. Approximately 97% of more than 1000 available surface drill-holes located on or at a distance of less than 200 m from the high-density anomalies intersected mineralization. However, gravity anomalies have been drilled in the past and particularly dense black shales or rhyolitic/gabbroic rocks have been intersected. To increase the success of future drilling, gravimetric anomalies have been correlated spatially with high-conductivity TEM zones and strong-amplitude seismic reflections, because igneous rocks usually present weak-to-moderate conductivity and a massive column of black shales presents a seismic signature quite different from that of mineralization. We concluded that some of these locations represent high-quality targets to consider following up with drilling and further exploration.

Groundwater Quality Assessment of Abandoned Dumpsite in Osogbo Suburb, Nigeria: Hydrogeological and Geophysical Condition Six Years after Initial Study


 
 
 In this paper, we describe the result of a recent hydrogeological and geophysical investigation carried out within and around Aduramigba - Onibu-Eja Estate dumpsite with the aim of detecting evidence of contamination as well as depths to contamination of the groundwater after a previous study six years ago. Twenty water samples from shallow water wells and boreholes were analyzed for their physico-chemical constituents while five vertical electrical soundings and five electromagnetic ground penetrating radar surveys were conducted. The result shows high concentrations of anions of nitrates (NO3-), bicarbonates (HCO3-), chloride (Cl-) and sulphate (SO42-) with values of 73.97 mg/l, 91.5 mg/l, 331.2 mg/l, 222.4 mg/l respectively, cations values of Mg2+, Fe2+, Na+, and K+ having value of 25.44 mg/l, 6.23 mg/l, 37.31 mg/l and 35.41 mg/l, respectively, which were far above the World Health Organization (WHO) and Nigeria Drinking Water Quality Standard (NDWS). Heavy metal components such as Lead, Zinc, Copper and Nickel were also observed to be on the high side, having been contributed from effluents from rust metallic materials cum chemicals dumped within the dumpsite. Detailed geophysical study reveal the depth to contamination at between 4.1 meters in VES 3 to 5.9 meters in VES 2 with resistivity as low as 5.12 Ωm in VES 2 to 7.12 Ωm in VES 3 while ground penetrating radar (GPR) revealed that the leachate has permeated to a depth of 3.5 – 5.25 meters in traverse 4 and 4.0 – 6.0 meters in traverse 3 which correspond to the depth to unconfined aquifer within the dumpsite. The study conclude that this would pose a greater threat to residents living in this vicinity and as such, this might have contributed to the closure of the dumpsite.
 
 

Epitaxial Stabilization of Metastable 3C BaRuO3 Thin Film with Ferromagnetic Non‐Fermi Liquid Phase

AbstractThin films of perovskite ruthenates of the general formula ARuO3 (A = Ca and Sr) are versatile electrical conductors for viable oxide electronics. They are also scientifically intriguing, as they exhibit nontrivial electromagnetic ground states depending on the A‐site element. Among them, realization of the cubic perovskite (3C) BaRuO3 in thin film form has been a challenge so far, because the 3C phase is metastable with the largest formation energy among the various polymorph phases of BaRuO3. In this study, 3C BaRuO3 thin films are successfully prepared employing epitaxial stabilization. The 3C BaRuO3 thin films show itinerant ferromagnetism with a transition temperature of ≈48 K and a non‐Fermi liquid phase. The epitaxial stabilization of the 3C BaRuO3 further enables to make a standard comparison of perovskite ruthenates, thereby establishing the importance of the RuO orbital hybridization in understanding the itinerant magnetic system.

Geophysical investigation of the down-dip extension of the Lombador massive sulphide deposit, Neves-Corvo, Portugal

The 150 Mt Lombador massive sulphide deposit is one of the seven known deposits of the Neves-Corvo mine. The deposit dips approximately 30o–35o to the NE and is open down dip, with current exploitation reaching down at 1 km depth. To investigate the possible downwards continuation of the deposit, a 1D constrained inversion of time-domain electromagnetic (TEM) ground loop data was conducted, followed by 3D electromagnetic (EM) forward modeling and a constrained 3D gravimetric inversion over the same area. To perform the EM and gravity modeling/inversion, a 3D geologic model was built using a density database comprising of approximately 300 drill-holes, and an electrical conductivity database with measurements from resistivity surveys and 1D inversion of the TEM data. The EM modeling shows that the Neves Formation shales are a regional conductive layer extending down to approximately 1.6 km depth in the Lombador area. This layer, often topped by massive sulphides, has an average density of 2.83 g/cm3, whereas stockwork and massive sulphide reach on average 3.1 g/cm3 and 4.5 g/cm3, respectively. The 3D constrained gravity inversion results do not support the hypothesis of the presence of massive sulphides located in the down-dip direction of the Lombador deposit in the immediate vicinity of the known deposit. The lack of spatial resolution of the gravity grid, the study area limited size and the lack of information from within the basement suggest further studies are required to confirm the presence and amount of stockwork mineralization down-dip the Lombador deposit inside the Neves-Formation or the Phyllite-Quartzite basement.

Natural granular pile as electromagnetic ground cloak

Rendering an object invisible through a cloaking device is an ongoing dream of human beings and material scientists. Recently, intensive theories and experiments have predicted and demonstrated that such a cloaking device can be realized based on transformation optics and metamaterials, in fields of electromagnetics, optics acoustics, or even heat transfer. Metamaterials enable precise control over the propagation of waves due to their delicate micro-structures and spatially tailorable properties. However, a simple and natural way to achieve cloaking without a delicate micro-structure remains unattainable. Here, we report that an electromagnetic quasi-cloaking device can be readily achieved by a granular pile, formed by the falling-off and cumulation of particles on the object to be cloaked. We show that natural particle size segregation during the formation of the granular pile imparts the pile with a spatially variable filling ratio and resultant gradient-distributed permittivity, which enables the realization of the electromagnetic cloaking device. This work may open the possibility that a complicated electromagnetic device may be alternately achieved from manipulation of particle movement or arrangement.

Theory of polaritonic quantum-vacuum detection

Recent progress in electro-optic sampling has allowed direct access to the fluctuations of the electromagnetic ground state. Here, we present a theoretical formalism that allows for an in-depth characterisation and interpretation of such quantum-vacuum detection experiments by relating their output statistics to the quantum statistics of the electromagnetic vacuum probed. In particular, we include the effects of absorption, dispersion and reflections from general environments. Our results agree with available experimental data while leading to significant corrections to previous theoretical predictions and generalises them to new parameter regimes. Our formalism opens the door for a detailed experimental analysis of the different characteristics of the polaritonic ground state, e.g. we show that transverse (free-field) as well as longitudinal (matter or near-field) fluctuations can be accessed individually by tuning the experimental parameters.

Seepage investigations of heterogeneous soils beneath some buildings using geophysical approaches: example from southwestern Nigeria

Buildings along the flood plain of River Osun, southwest Nigeria, are usually thought of as been a safe haven for residence over the years. But in recent times with vast (increasing) population and growing urbanization, some of the buildings currently experience structural damages not related to constructional designs but rather ground conditions around building foundations. The ground conditions (seepages in this case) and how it influences properties of soils (water moisture, permeability etc.) to support the foundation of buildings. This paper attempts to map out seepages in heterogeneous soils around buildings in Erinle, southwest Nigeria where building cracks probably as a result of water seepages from subsurface through fissures and fractures where noticed. These cracks are a probable manifestation of a weakened foundation that could overtime result to a collapse, hence the need to investigate seepage prone zones. To achieve this, electrical resistivity (ER) and Electromagnetic Ground Penetrating Radar (EM-GPR) surveys were made along affected buildings to map out possible causes of deterioration. Geo-sections (analyzed ER data) shows high resistivity layer (topsoil) underlain by low resistivity layer (weathered basement) confirmed by planer reflections (topsoil) and fairly smooth to smooth reflections (weathered basement) in Radargrams (analyzed GPR data). An integration of the geo-section and radargram produced from ER and GPR data shows that buildings along traverses 1, 2, 3 and 5 is most prone to seepages especially as it exhibits very low anomalously resistivity values (< 25 Ωm) but this is not the case for buildings along traverses 4, 6, 7 and 8.

A new far‐field low‐frequency electromagnetic method for measurement of temporal variations in subsurface electrical conductivity averaged over a transect

ABSTRACTThe new far‐field low‐frequency electromagnetic method used the electromagnetic ground wave from distant radio transmitters at low frequencies to estimate temporal variations of factors affecting subsurface electrical conductivity averaged along the propagation path between either a transmitter and a receiver or two receivers that are in line with a transmitter. Phase and phase difference between two receivers depend on three factors that influence the changes in electrical conductivity: soil moisture, depth to the groundwater table and soil temperature. This dependence was investigated by simulations and evaluated by an experiment. The measurement layout was based on simulating ground wave propagation over a layered subsurface using the surface impedance method and the Sommerfeld ground wave attenuation function. A three‐layer model for the subsurface was used, which includes a soil layer, an unsaturated vadose zone and a saturated groundwater zone. The results of simulations at a frequency of 77.5 kHz showed that the phase of the ground wave is strongly influenced by natural variation of the above‐mentioned three factors; 77.5 kHz is the carrier frequency of the Normal Time Service Germany (DCF77) in Mainflingen/Germany, that was chosen as a source of the low‐frequency radio waves used in the experiment. Over a 2‐year measurement period, the amplitude and phase of the ground wave were recorded with two receivers, one 70 km and the other 110 km away from the transmitter. Additionally, phase difference between the two receivers was calculated. In situ observations of soil moisture, depth to the groundwater table, and soil temperature along the transects under investigation were used to estimate phase and phase difference dependencies. Multiple regression analysis of the measured phase and phase difference revealed a strong dependence on the depth to the groundwater table and on soil temperature, whereas the impact of soil moisture on the phase and phase difference was found to be very low. Conversely, the relations obtained can be used to estimate the variation of the depth to the groundwater table, if the phase at a given frequency and the soil temperature information are available.

An Unconditionally Stable Cylindrical FDTD Method to Analyze the EM Ground Wave Propagation

We extended the unconditionally stable associated Hermite (AH) FDTD method to the cylindrical coordinate system for analyzing the electromagnetic (EM) ground wave propagation. With AH domain differentiate operator technology and paralleling-in-order solution scheme, the cylindrical time-domain Maxwell equations with complex frequency shifted perfectly matched layer (CFS-PML) are transformed to AH domain generating a five-point banded equation, which also unified the formula from the central axis of cylinder. The numerical results represent the accuracy and efficiency of the proposed method when comparing for the conventional FDTD method.

A New Methodology for Assessment of Railway Infrastructure Condition

The majority of the railway infrastructure in Croatia is over one hundred years old. In common with many other EU member states, a lack of investment in maintenance and renewal projects in over the last 30 years has resulted in generally poor track conditions. As a result traffic speeds are often restricted with some important operating with speeds limited up to only 20km/h.This work describes a joint initiative between researchers and infrastructure managers (IM's) to revitalize risk assessment associated on ageing infrastructure, with the aim of increasing safety and reducing the costs of remediation. In order to achieve this, a new methodology for assessment of railway condition is developed. In this paper the use of phased investigation involving electromagnetic ground penetrating radar (GPR), seismic refraction, drones and in-situ geotechnical investigation to determine parameters affecting the track performance are presented. The features considered include ballast fouling, anomalies in railway embankments (including burrows), boundaries between layers, substructure condition, the water content of the soil, the slope geometry and drainage condition. The work constitutes the first step in a Decision Support Framework for IM's, being developed through the Horizon 2020 Project Destination Rail which will help to identify potential hot-spots on the rail network. By early identification of these locations low-cost remediation can be applied and thus costs can be reduced and failures avoided.In this paper the use of custom-made cart which allows acquisition of data along the three axes of railway rail cross-section and an innovative interpretation methodology is described. Based on GPR data, visual assessment and on photogrammetry images made using an unmanned aerial vehicle (UAV), a categorization of critical infrastructure data is collected to a quantitative risk assessment procedure. This provides a basis for preliminary design solutions as well as for establishment of detailed programme of investigation works and monitoring on sections where it was shown as necessary. A next step is implementation of this methodology into geographic information system (GIS) which would additionally fulfil the needs of decision-makers in railway sector.

Urban soil exploration through multi-receiver electromagnetic induction and stepped-frequency ground penetrating radar.

In environmental assessments, the characterization of urban soils relies heavily on invasive investigation, which is often insufficient to capture their full spatial heterogeneity. Non-invasive geophysical techniques enable rapid collection of high-resolution data and provide a cost-effective alternative to investigate soil in a spatially comprehensive way. This paper presents the results of combining multi-receiver electromagnetic induction and stepped-frequency ground penetrating radar to characterize a former garage site contaminated with petroleum hydrocarbons. The sensor combination showed the ability to identify and accurately locate building remains and a high-density soil layer, thus demonstrating the high potential to investigate anthropogenic disturbances of physical nature. In addition, a correspondence was found between an area of lower electrical conductivity and elevated concentrations of petroleum hydrocarbons, suggesting the potential to detect specific chemical disturbances. We conclude that the sensor combination provides valuable information for preliminary assessment of urban soils.

High Frequency Ground Wave Propagation

Electromagnetic ground wave propagation has been a topic of practical interest for broadcasting and underground prospection in the medium and lower radio frequencies for more than a century. A brief review of ground wave propagation and its development since the work of Zenneck and Sommerfeld a century ago is presented. Recently interest has been revived in using ground waves for wireless communication with remote under-populated areas using the high frequency (HF) range which extends from 3-30 MHz. We present numerical results for the fields excited by a vertical electric dipole (VED) on the earth' surface in this range of frequencies and study the effect of ground conductivity on the received fields. In addition, we explore the possibility of using horizontal electric dipoles (HED) as transmitting and receiving dipoles. In this case, it is necessary to elevate both dipoles above the earth's surface by a distance comparable to a wavelength in order to enhance the received signal level. This is practically feasible in the HF regime where the wavelengths are sufficiently short We conclude that elevated HED's can perform as well as the VED, or even better, when the operating frequency lies in the upper end of the HF range.

Appliance of Geophysical Methods to Detect the Ancient Remains at “Tell Defenneh” Area, Ismailia, Egypt

The main target of this study is to detect the ancient archaeological remains by using Helicopter Electromagnetic Method (HEM) and Ground Penetrating Radar (GPR) survey at “Tell Defenneh” Area, which is located in the west bank of Suez Canal at the northeastern Desert of Egypt. It is far about 15 Km to the northeast of “Qantara Gharb” town which is a part of “Ismailia” governorate. This area is full of different archaeological features, because it is located in the ancient international trade-military road (Horus Road). This road connected ancient Egypt with its neighboring eastern countries. In additional to that, this area used to protect ancient Egypt from invaders, who came from the East. HEM has been used to detect the conductivity anomalies over the study area. These anomalies are useful to show the different and distinctive places which can be focused, on small scalar, by GPR to identify it more clearly in the study area. According to the HEM data, it was noticed that there are distinctive geometric shape with very low resistivity or very high conductivity values in the northeastern part of the study area. These data have been supported by GPR survey focused on this part. It was suggested that these anomalies may be due to old man-made mud bricks that was customary used in the building in ancient times. The subsequently archaeological excavations, which are based on these interpreted data as a guide and proof, revealed that the remains belong to the citadel of pharaoh “Psamtik I” (664-610 BC). This result confirms that the incorporated geophysical methods can be efficiently supplied in the archaeological prospection in Egypt.

Technique to determine the electromagnetic properties of soil using moisture content

Accurate electromagnetic ground constants are required for applications such as modelling of ground wave propagation of radio signals and antennas above a real, imperfect earth and for use in geological surveys and agricultural applications. A simple method to determine the ground parameters (conductivity and relative dielectric constant) for any radio frequency is outlined here. The method has been verified over the 2–30-MHz frequency range but should be applicable up to several GHz. First, a low cost, commercial soil moisture meter using time domain reflectometry techniques is used to determine the soil moisture percentage. Then previously published universal soil models implemented on a programmable calculator or a PC are used to calculate the required constants at the frequency of interest according to the measured moisture percentage. The results obtained by this method compare favourably with those obtained by the input impedance of a low horizontal dipole technique. The received signal strength of a ground wave, HF transmission also compares favourably with that predicted by GRWave using ground constants calculated by the soil moisture technique. This method offers significant advantages in terms of simplicity, speed and cost when compared with current techniques.

On the Sensitivity of Practical Electromagnetic Ground Plane Cloaks

A numerical study of the sensitivity of the two dimensional electromagnetic ground plane cloak in the visible spectrum is performed using the finite difference time domain method. Transverse magnetic plane waves are launched at an angle towards an object placed on a ground plane and the scattering signature is suppressed by surrounding it by an all-dielectric cloak. In particular, we study the performance of the system as a function of the number of distinct components the cloak is divided into, the effects of lossy elements, the angle of incidence, as well as typical random variations of the permittivity of the building materials. Finally, we evaluate impedance matching layers that can surround the cloak and improve its effectiveness. The results provide useful information for the fabrication of practical cloaking devices.

Geophysical characterization of two circular structures at Bajada del Diablo (Patagonia, Argentina): Indication of impact origin

An impact origin has been proposed for the circular structures found in Bajada del Diablo, Patagonia, Argentina. Taking into account its extension and the number of impact structures, Bajada del Diablo would be the largest meteoritic impact areas known on Earth, being an extremely interesting area for the research of impact events and processes. Moreover, the global distribution of known impact structures shows a surprising asymmetry. Particularly, South America has only seven described areas. It is evident that this situation is an artifact, highlighting the importance of intensifying the research in the least studied areas such as Argentina. Circular structures in Bajada del Diablo have been identified on two rock types: the Quiñelaf eruptive complex and Pampa Sastre Formation. In the first case, circular structures are placed in olivine basalts. On the other hand, Pampa Sastre Formation (late Pliocene/early Pleistocene) corresponds to conglomerate layers with basalt clasts boulder and block in size in a coarse sandy matrix. With the aim of further the investigation of the proposed impact origin for these circular structures, we carried out detailed topographic, magnetic and electromagnetic ground surveys in two circular structures (“8” and “A”) found in Pampa Sastre conglomerates. Both circular structures are simple, bowl-shaped with rim diameters of 300m and maximum depths of 10m. They have been partially filled in by debris flows from the rims and wind-blown sands. Two preliminary magnetic profiles have also been carried out in circular structure “G” found in Quiñelaf basalts. The magnetic anomalies show a circular pattern with a slightly negative and relatively flat signal in the circular structures’ bases. Furthermore in the circular structures’ rims, high-amplitude, conspicuous and localized (short wavelength) anomalies are observed. Such large amplitude and short wavelength anomalies are not detected outside the circular structures. For all used frequencies, the electromagnetic profiles show lower apparent electrical conductivities in the circular structures’ base, while the rims present notably higher values. Curvature attributes, analytic signal, horizontal gradient and Euler solutions were calculated for the magnetic data. 2.5D magnetic models were developed across the studied circular structures. Our results suggest that in the circular structures’ bases up to 12m of Pampa Sastre conglomerate would have been removed. On the contrary, the circular structures’ rims exhibit high-amplitude, localized magnetic anomalies and higher apparent electrical conductivities, which would be related to the anomalous accumulation of basalt boulders and blocks remanently magnetized. Such high-amplitude anomalies are not present outside the surveyed circular structures. The geomorphological, geological and geophysical features of the studied circular structures can only be explained by means of an extra-terrestrial projectile impact. We conclude that, considering the results obtained to date, Bajada del Diablo should be envisaged as a focus of further research, which could provide novel information about impact events, associated processes and their evidences. Particularly, the data produced in this study could represent one of the first documented geophysical signatures of the impact of a comet nucleus on Earth.

High resistivities associated with a newly formed LNAPL plume imaged by geoelectric techniques ‐ a case study

In April 10, 1997, a rice field in Nankan county, northwestern Taiwan was flooded by sixty to seventy kilolitres of fuel oil as a result of an accidental underground pipeline leakage. Immediate action to excavate contaminated soil and remove it to a landfill were done. However, it was believed that a significant quantity of light non‐aqueous phase liquid (LNAPL) contaminant might have remained in the soil and infiltrated into the groundwater. This paper emphasizes the use of multiple geoelectric techniques to detect and map the LNAPL plume in this uncontrolled real‐world site, and help monitor the effectiveness of the clean‐up operation. A significant change in resistivity values was detected between polluted (> 140 ohm‐m) and non‐polluted areas (< 140 ohm‐m). Repeated measurements were conducted at 1, 4 and 10 month intervals after the first measurements. These data were used to monitor variation and a possible spreading of the LNAPL plume over time. The total LNAPL masses were concentrated or diluted in the soil matching the variations of the water table. Two additional resistivity profiles were conducted to investigate the spatial distribution of the LNAPL contaminant plume within the study area. Electromagnetic induction and ground penetrating radar were also used to outline the resistivity zone defined by the plumes. The results of the survey serve to provide insight into the sensitivity of geoelectrical methods for detecting a shallow subsurface LNAPL plume, and help to provide valuable information related to monitoring the movement of an LNAPL plume over time in a study area.

The performance properties and limitations of antenna elements spaced closely to PEC, PMC and electromagnetic bandgap ground planes

The performance properties and limitations of antenna elements spaced closely to PEC, PMC and electromagnetic bandgap ground planes

Symmetries and symmetry breaking

Several new proton-proton parity violation experiments are presently either being performed or are being prepared for execution in the near future. Similarly, a new measurement of the parity-violating gamma-ray asymmetry in polarized neutron capture on the proton is being developed with a ten-fold improvement over previous measurements. These experiments are intended to provide stringent constraints on the set of seven effective weak meson-nucleon coupling constants. Time-reversal-invariance non-conservation has now been unequivocally demonstrated in a direct measurement at CPLEAR. Tests may also be made of time-reversal-invariance non-conservation in systems other than the kaon system. There exist two classes of time-reversal invariance breaking interactions: P-odd/T-odd and P-even/T-odd interactions. Constraints on the first ones stem from measurements of the electric dipole moment of the neutron, while constraints on the second ones stem from the same and measurements of charge symmetry breaking in neutron-proton elastic scattering and from $K$ semi-leptonic decays. A series of precision experiments, either ongoing or being prepared, will determine the neutral weak current of the proton by measuring the parity-violating normalized asymmetry in electron-proton elastic scattering. A direct comparison between the electromagnetic and neutral weak ground state currents of the nucleon will allow a delineation of the contributions to these currents of the various quark flavours, including quarks which belong exclusively to the nucleon sea. An extension of these precision experiments to very low momentum transfer would permit stringent limits to be placed on physics beyond the standard model.