Electromagnetic Induction Techniques for Target Detection and Characterization

Electromagnetic induction methods exploit the interaction between time‐varying magnetic fields and conductive or permeable objects to detect and characterise hidden targets. A primary coil generates a magnetic field that induces eddy currents within a subsurface or concealed object; the resulting secondary field perturbations are measured by receiving coils or sensors. Analysis of these perturbations—across time, frequency or spatially distributed sensors—yields information on object presence, location, geometry and material properties. Techniques range from frequency‐domain metal detectors using coil arrays to transient electromagnetic (TEM) systems that record decay curves following a pulsed excitation. Advances in sensor design, signal processing and mathematical modelling have improved sensitivity to small or deeply buried items, enhanced discrimination between benign clutter and threats, and enabled parameter estimation such as conductivity, permeability and shape descriptors. Applications span security screening, unexploded ordnance (UXO) clearance, archaeological prospection, industrial quality control and recycling. Recent trends include integration of machine learning classifiers with spectral or temporal signatures, deployment of mobile or robotic platforms for in situ surveys, and the use of reduced‐order and asymptotic models to accelerate real‐time inversion. Together, these developments are forging new paths for rapid, accurate and non‐invasive subsurface sensing worldwide.

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Innovations in coil geometry and sensor arrays are extending the reach and resolution of induction‐based detection. A walking “crab” robot equipped with leg‐embedded Hall‐effect magnetometers has demonstrated precise discrimination between unexploded ordnance and innocuous metallic objects in sandy environments by correlating three‐axis field disturbances with dynamic leg movements. This mobile platform underscores the value of distributed sensing and data‐driven classification for field operations. Complementary work on the magnetic polarizability tensor (MPT) has employed projection‐based reduced‐order models and neural‐network‐enhanced schemes to predict tensor coefficients across multiple object shapes, sizes and material parameters, slashing computational cost while retaining accuracy in library generation for object identification. In parallel, a towed transient electromagnetic sensor array using an improved magnetic gradient tensor approach has achieved sub-10 cm localisation accuracy for multiple underground targets. By adaptively selecting subsets of coil responses for shallow and deep depths and combining early‐ and late‐time signals, this system overcomes signal‐to‐noise and overlapping‐response challenges, illustrating how sensor configuration and tensor‐based inversion synergise to refine target characterisation in complex terrains.

Electromagnetic Induction Techniques for Target Detection and Characterization publication trend

The graph below shows the total number of articles in electromagnetic induction techniques for target detection and characterization across all publications each year (not limited to Nature Index journals).

Technical terms

Electromagnetic induction: Generation of electric currents or fields in a conductor by a changing magnetic field.

Eddy current: Circular electrical currents induced within conductors exposed to time‐varying magnetic fields, producing secondary magnetic fields.

Magnetic polarizability tensor (MPT): A rank-2 tensor that encapsulates the linear response of an object’s induced magnetic dipole moment to an applied magnetic field over frequency.

Transient electromagnetic (TEM) system: A method that applies pulsed magnetic excitation and records the decay of induced secondary fields to infer subsurface properties.

Magnetic gradient tensor: A spatial derivative tensor of the magnetic field used to enhance localisation accuracy by exploiting gradient information from multiple receivers.

Hall‐effect sensor: A magnetic field sensor that measures the Hall voltage generated across a conductor carrying current in the presence of a perpendicular magnetic field, enabling compact field detection.

References

1. Probing with Each Step: How a Walking Crab-like Robot Classifies Buried Cylinders in Sand with Hall-Effect Sensors. Sensors (2024).
2. Reduced order model approaches for predicting the magnetic polarizability tensor for multiple parameters of interest. Engineering with Computers (2023).
3. Underground Target Localization Based on Improved Magnetic Gradient Tensor With Towed Transient Electromagnetic Sensor Array. IEEE Access (2022).