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Eddy Current Responses of Canonical Metallic Targets
Published in Carl E. Baum, Detection and Identification of Visually Obscured Targets, 2019
A metal detector is a device which induces eddy currents into metallic objects and then detects the magnetic fields produced by these eddy currents. A magnetic field is generated by a coil, or set of coils, through which a time-varying electrical current is driven. The frequency regime of interest is sufficiently low, a few Hertz to a few hundred kilohertz, so that the targets of interest are within the near field of the illuminator. Eddy currents are induced in the conducting targets by the incident magnetic field. These currents then decay with characteristic time constants related to the resistive and inductive elements of the paths through which the induced currents flow. These impedance parameters are related to the conductivity and permeability of the metal, as well as to its geometrical shape, size, and orientation, resulting in different decay patterns for different target objects. The eddy current loops then generate a secondary, scattered magnetic field which is detected by means of some magnetic field probe, usually a receiver coil which is set at a null with respect to the incident field generated by the transmitter coil.
Field Investigation Techniques for Potentially Contaminated Sites
Published in Kofi Asante-Duah, Management of Contaminated Site Problems, 2019
In its application, a transmitter creates an alternating magnetic field around the transmitter coil. A balance condition is achieved to cancel the effect of this primary field at a receiver coil; typically, the balance (or “null”) is accomplished by orienting the planes of the two coils perpendicular to one another. The primary field will induce eddy currents in a metal target within the instrument range. These eddy currents produce a secondary field that interacts with the primary field to upset the existing balance condition. This results in an audible signal. The most important factors influencing the detector response include the properties of the target, properties of the soil, target size (response is proportional to the area cubed), and depth. In general, the larger the target surface area, the greater the induced eddy currents, and therefore, the greater depth at which the target may be detected. Metal detector depth range decreases at a rate of the reciprocal of the target depth to the sixth power (i.e., signal intensity ∝ 1/[depth]6). Therefore, most metal detectors are limited to depths near the surface. In any case, metal detectors with coils of small diameter (less than 0.3 m), like those used by treasure hunters, are better than conventional “pipe locators” for locating small targets but have limited depth capabilities.
Input/Output Bank Programming and Interfacing
Published in A. Arockia Bazil Raj, FPGA-Based Embedded System Developer's Guide, 2018
A security system can be developed by using a metal detector. The metal detector is used to identify/avoid any illegal or unauthorized entry of metallic objects such as bombs, knives and guns, especially in public places like theaters, shopping malls, parks, airports, hotels, military/defense areas, and railway stations. Metal detectors are also used to sense weapons, identify steel reinforcement in concrete structures and detect the condition of pipes/wires buried in walls/floors. A metal detector is an electronic device that comprises an oscillator, which generates an AC current that passes via a coil generating an alternating magnetic field, as shown in Figure 5.18. When a part of the metal is near the coil, an eddy current will be induced in the metal object, and it generates a magnetic field of its own. This magnetic field can be sensed and measured using the coil to detect the metal object [59].
Peak scatter-based buried object identification using GPR-EMI dual sensor system
Published in Nondestructive Testing and Evaluation, 2019
In this section, identification results of the proposed method are presented. An illustration of our experimental setup is given in Figure 6. GPR antenna and metal detector coil have been integrated into a single case. Therefore, both GPR and MD data are collected simultaneously. Scanning velocity of the wooden-constructed robotic system is 20 cm/sec. Tests are performed at three different controlled terrains with different soil types and burial depths. Dielectric constants and conductivity values of the soil types are summarised in Table 1. Actually, dielectric constant of a material varies with frequency. For simplicity, an average value is provided for each soil type. Averaging is performed between 600 MHz and 2.2 GHz. More details are available in [36].
Detection and classification of landmines using machine learning applied to metal detector data
Published in Journal of Experimental & Theoretical Artificial Intelligence, 2021
L. Safatly, M. Baydoun, M. Alipour, A. Al-Takach, K. Atab, M. Al-Husseini, A. El-Hajj, H. Ghaziri
The data collection is a critical part in this work. We relied on the data acquisition setup discussed in the methods section. The addressed data in this work was obtained from a metal detector manufactured by Ceia. Since Ceia is not the only manufacturer of metal detectors, it is expected that other detectors will output different data. This was observed previously in literature as in (Pinar et al., 2015) and (Bruschini et al., 1998) where the metal detector data is clearly different. Thus, it is expected that a different detector would lead to another database, which would require to repeat the training phase of the model. In this case, the classification algorithms should be also revisited to select the most accurate model.