Induction Sensors Research Articles

A theoretical performance analysis and simulation of time-domain EMI sensor data for land mine detection

The physical phenomenology of electromagnetic induction (EMI) sensors' is reviewed for application to land mine detection and remediation. The response from time-domain EMI sensors is modeled as an exponential damping as a function of time, characterized by the initial magnitude and decay rate. Currently deployed EMI sensors that are used for the land mine detection process the recorded signal in a variety of ways in order to provide an audio output for the operator to judge whether or not the signal is from a mine. Sensors may sample the decay curve, sum it, or calculate its energy. Based on exponential decay model and the assumption that the sensor response is subject to additive white Gaussian noise, the performance of these, as well as optimal, detectors are derived and compared. Theoretical performance predictions derived using simplifying assumptions are shown to agree closely with simulated performance. It will also be shown that the generalized likelihood ratio test (GLRT) is equivalent to the likelihood ratio test (LRT) for multichannel time-domain EMI sensor data under the additive white Gaussian noise assumption and specific assumptions regarding the statistics of the decay rates of targets and clutter.

Three-dimensional inverse scattering applied to cross-well induction sensors

Cross-well induction logging as known in the oil industry is a method for determining the electrical conductivity distribution between boreholes from the low-frequency electromagnetic field measurements in the boreholes. The authors discuss the reconstructions of the three-dimensional (3D) conductivity distribution using the contrast source inversion (CSI) method. In order to improve the reconstruction results, the concept of the extended Born approximation has been used to arrive at a preconditioning operator. Results of a number of numerical examples show that by using this preconditioning operator, a large conductivity contrast of the unknown objects (factor of 100) can be reconstructed up to an acceptable degree of accuracy. Moreover, in each iteration, the computational effort to generate the preconditioning operator is negligible.

Evaluation of Calibration Methods for Interpreting Soil Salinity from Electromagnetic Induction Measurements

AbstractThe EM‐38 electromagnetic induction sensor of Geonics Ltd. (Canada) is a most useful instrument for rapid field identification and mapping of soil salinity. Interpretation of instrument measurements in terms of meaningful parameters of soil salinity is difficult, however, due largely to the non‐uniform response distribution with depth. Various models have been proposed that allow the conversion of measurements made on this instrument to the electrical conductivity of the bulk soil (ECa, as measured with the four‐electrode probe) or EC of the saturation extract (ECe). Seven of these models were evaluated in this study by comparing predicted with measured values. Four allow the estimation of ECa at 0.30‐m depth intervals down to 0.90 m, two allow the estimation of a single valued ECe, weighted for instrument response with depth, and one estimates ECe for 0.30‐m intervals down to 0.90 m. The performance of the models varied greatly, and likely reasons for poor prediction are discussed. For the model that produced the most accurate estimate of ECa, the estimated values were, based on 95% confidence limits, within 0.8 dS m‐1 of the values predicted using the regression equations. For the models that predict weighted ECe, the corresponding value was typically about 2.2 dS m‐1. While salinity measurements made with the EM‐38 are not highly accurate, the strength of the technique is that measurements of reasonable accuracy can be made very rapidly. Categories of soil salinity for large areas can be readily established, which represents useful information for salinity management and certain research applications.

UAV Sensor Platform

The Sikorsky Cypher unmanned aerial vehicle (UAV) was selected as the initial aircraft to be tested as a platform for the geophysical sensors that will be used to detect underground structures as part of the U.S. Department of Energy's Underground Facilities Program. Site inspections will require rapid coverage of areas that may be several square kilometers in size and may be hazardous or difficult to traverse in ground vehicles. The Cypher is a small donut‐shaped helicopter that can transport an 11‐kg sensor payload at hover or at speeds up to 80 km/hr. Several modifications and upgrades have been made in the avionics and flight‐control software of the aircraft, including high‐accuracy differential GPS and software for autonomous surveys. To date, the aircraft has been tested as a platform for cesium total‐field magnetometers and an electromagnetic induction sensor. In several field tests, including surveys of two underground structures at the Nevada test Site, magnetometer arrays have been effective in ...

Spectrum of synchrotron radiation from an extended source

Induction sensors with cores in the shape of hollow cylinder are widely used because of such advantages as decrease of mass and simplicity of manufacturing cores with defined geometry. Replacement of a real tubular cylindrical core by the model in the shape of hollow ellipsoid of rotation with equal values of relative lengths, ferromagnetic volumes and fluxes, that is proposed in the article, allows to find the calculation algorithms for determination of electromagnetic parameters of cylindrical rod with solid and tubular cores. The obtained algorithms take into account the influence of both the geometry and magnetic properties of core material on the electromagnetic parameters and are suitable for engineering calculations.

Induction sensors for boundary detection of metal foreign bodies

Induction sensors for boundary detection of metal foreign bodies

Comparison of airborne electromagnetic ice thickness data with NOAA/AVHRR and ERS‐1/SAR images

Abstract Snow‐plus‐ice thickness and surface‐ice roughness data collected by a helicopter‐towed sensor package was used to identify surface‐ice properties in March 1992 AVHRR and SAR images for the land‐fast and mobile pack ice off the northern coast of Newfoundland. The sensor package consisted of an electromagnetic induction sensor and laser profilometer. Observed snow depths and ice thicknesses verified that snow‐plus‐ice thickness over undeformed ice can be obtained to an accuracy of ±10 cm. Snow‐plus‐ice thickness and surface roughness data for flight sections covering several hundred kilometres indicated the change in pack ice properties seen in images from thin, smooth coastal ice and open water conditions to thick, rough consolidated offshore pack ice. Ice charts covering the same area showed similar variations in ice conditions based on AVHRR and fixed‐wing reconnaissance data. In the ERS‐1 SAR image, low backscattering coefficients were associated with large, smooth coastal floes interspersed with areas of high backscatter indicating the presence of waves in open water areas. Backscattering coefficients were higher in the rubble areas near the inshore edge of the pack ice than in the interior of the pack ice itself. Distinguishing ice types on the basis of tone alone in SAR imagery was found to be problematic; however in combination with other remotely sensed data such as AVHRR data, SAR data will become more useful in distinguishing ice types.

Three component magnetic field measurements using cubic anisotropy in (111) YIG films (abstract)

A magnetization behavior in YIG films with (111) orientation for a saturation in-plane magnetic field, taking into account the fourth (K1) and the sixth (K2) cubic anisotropy constants, is investigated theoretically and experimentally. Dependencies of a magnitude of the saturation field on material parameters were found. Different situations of a static and a rotating saturation magnetic field were considered. Analytical expressions for an induction signal caused by interference of in-plane magnetization homogeneous rotation with an ambient quasistatic magnetic field were obtained. It was shown that there exists a linear harmonic response to the ambient field both tangentially and perpendicularly to the film plane field orientations. Experimental results obtained for different kinds of YIG films were in good agreement with theory. Measured sensitivity was of the order of 10−7 Oe with a dynamic range of 80 dB. This, thereby, enables the design of a three component induction sensor with a high sensitivity and a large dynamic range.

Vertical eigenstate method for simulation of induction and MWD resistivity sensors

A method for computing responses of induction or MWD (measurement-while-drilling) resistivity sensors in layered formations with invasion zones is presented. The geometry is assumed to have an axial symmetry resulting in a two-dimensional problem. The solution of the wave equation is expressed by a summation of eigenstates in the vertical direction in each cylindrical region. The eigenmodes in each region are found numerically, and the variation of fields in the horizontal direction is expressed in terms of analytical functions. Computed results are used to simulate logging tool responses in invaded formations. It is found that the apparent resistivity reading is a complicated function of the resistivities of the invaded zone, that of the uninvaded zone, bed thickness, and invasion diameter. Since no simple rule can be used to describe the characteristics of the investigation depth of the tool, the use of a computer simulation software, such as the one developed in this work, would be very useful to a log analyst in log interpretation. >

An induction gradiometer for conductivity contrast detection: Experimental development

A gradiometric induction sensor has been developed as a sensitive indicator of spatial electrical conductivity gradients. Utilizing a configuration of three antennas in a single, monolithic metal slot, its design is simple and compact. Its feasibility as a geometry indicator for use in oil wells drilled with oil base mud has been demonstrated by a series of laboratory experiments which simulated many borehole and logging conditions. Response to real and synthetic rock arrays, resolution, standoff sensitivity, and response to dipping geologic beds are among the issues quantified by the experiments. In addition, some useful models are presented as an aid in conceptualizing the principles behind the operation of the sensor.

Analysis of an electromagnetic induction detector for real-time location of buried objects

Spatial response characteristics of an electromagnetic induction sensor as it passes over a metallic object are investigated using a simple analytical technique. In this low-frequency technique, one replaces a metallic object with equivalent electric and magnetic dipoles and then applies the principles of reciprocity to obtain the induced EMF in a sensor coil. Analysis is carried out for a sensor employing rectangular coils, and the object set is confined to a sphere and a prolate spheroid. The simple approach, which is illustrated with both numerical and experimental data, is found to be adequate to understand the effect on the response characteristics of parameters such as object depth, orientation, aspect ratio, and material properties. >

A high-bandwidth induction sensor coil

A description is given of an induction sensor coil, the main application of which is in low-level transient electromagnetic detection. The coil is a compact air-cored spiral design of high bandwidth with low distributed winding capacitance. The optimum signal-to-noise ratio is determined by the size of the coil and the noise voltage source of the field effect transistor (FET) used in the input preamplifier.

A system of remote measurement of forces and deformations in cyclic tests of irradiated materials in the elastoplastic region

In cyclic tests of design materials the forces and deformations must be measured continuously and recorded in the form of cyclic deformation curves and also curves of the change in the test parameters with time. As a result, the measuring system must be sufficiently rapid-acting. However, this requirement is not filled by the frequency-impuls e method of measuring displacements [4] or by the method of resonant hollows [61. In addition, it should be mentioned that the high sensitivity of the latter is possible only at a constant temperature and with location of the resonant cavity close to the sample, which makes the tests significantly more complex and expensive since the chamber together with the adjacent portions of the waveguides becomes a single-usage element. The simplest and most practical are measuring systems using resistance strain gauges and induction sensors. For the purpose of eliminating the effect of radiation the sensors are removed from the active zone and their connection with the sample is either by special extensions [7] or using design elements of the test machine itself. We should mention that despite the rigidity of test machines within the channel, tests made on the basis of design elements of the machine at a large distance from the sample satisfy the requirements of low-cycle tests since they make it possible to obtain data necessary for treating cyclic elastoplastic deformation curves under conditions of ideal elasticity of the design elements of the loading equipment. At the same time, despite some distortion of the mechanical hysteresis loop introduced by elastic deformation of the machine, the measured parameters of the curves (width of the elastoplastic hysteresis loop, its area, the torsional moment, the one-sided accumulated deformation) maintain their true values. In cyclic loading of a sample by a torsional moment, in contrast to tension-compress ion loading, the measurement of deformations is substantially easier since oscillations in temperature do not have an effect on the transmission of the angular displacements from the sample to the sensor. The use of resistance strain

Magnetic measurements in shock waves

In [5] a method was proposed in which the measurement winding was located directly in the specimen to be studied. The change in induction was determined by the decrease in area of the specimen cross section and, consequently, the decrease in winding area, as well as by the change in magnetization. Since in this method the cross-sectional area always decreases to some degree, a signal always exists, even when a change in specimen magnetization does not occur. In such a configuration, where the magnetic field is directed perpendicular to the direction of shock-front propagation, it is experimentally impossible to separate the effect of shock-induced magnetic anisotropy, produced by stress anisotropy in the shock-wave front, from the demagnetization connected with shock heating and the dependence of the Curie point on pressure. In the method proposed presently the magnetic field is parallel to the direction of shock-wave front propagation and thus it is possible in experiment to distinguish the effect of demagnetization produced by change of the Curie point with increase in pressure and shock heating from the induced magnetic anisotropy, while in the configuration used there is no signal connected with deformation of the induction sensor cross section. 2. We will analyze the situation in which a shock-wave front propagates parallel to a magnetic field. Let the specimen to be studied, surrounded by turns of the measurement winding, be located in a constant homogeneous magnetic field H e . The initial magnetic flux passing through the measurement winding will be