A novel pulse-induction (PI) metal detector (MD) is proposed to decrease the saturation time of the output voltage and increase the detection depth. The proposed MD utilises a receiver with a timedomain bucking circuit. The bucking circuit decreases the output voltage significantly without a target, so that the output voltage can be amplified more before becoming saturated. To demonstrate the performance of the proposed MD, it has been fabricated and measured. The measured output voltage shows that the saturation time is reduced and that the detection depth increases in comparison with a conventional PI MD.Introduction: Pulse-induction (PI) metal detector (MD) systems have been studied recently for detecting buried landmines or unexploded ordnance [1]. These systems are based on the principle of electromagnetic induction, with short current pulses fed into a search coil to excite the magnetic field. At the end of each pulse, the current in the search coil rapidly decreases to zero and a large counter-electromotive force (EMF) that induces an eddy current in nearby metallic objects is generated. The large voltage in the search coil due to the counter-EMF decays rapidly to zero within a few microseconds if there is no metallic object near the coil. If there is a metallic object near the search coil, the eddy current decay in the object causes a slowly decaying voltage in the search coil [2].The voltage across the coil output may be modelled approximately in the time domain as the sum of the exponential functions; i.e.

Magnetic sheet backing of the search coil is proposed to improve the detection range of a pulsed-induction (PI) metal detector (MD) system. A planar square spiral mono coil is printed on an FR-4 substrate, and layers of magnetic sheets are attached to the substrate. The coil geometry is modelled using the finite-element method, and the static magnetic field distributions are compared. With the magnetic sheet backing, the magnetic field is shown to increase in the target direction and to decrease in the opposite direction. The coils are fabricated and applied to a PI MD system. It is demonstrated that the proposed magnetic sheet-backed search coils have longer detection ranges than the coil without magnetic sheet backing.

Automatic landmine detection system using ground penetrating radar has been widely researched. For the automatic mine detection system, system speed is an important factor. Many techniques for mine detection have been developed based on statistical background. Among them, a detection technique employing the Principal Component Analysis(PCA) has been used for clutter reduction and anomaly detection. However, the PCA technique can retard the entire process, because of large basis dimension and a numerous number of inner product operations. In order to overcome this problem, we propose a fast anomaly detection system using 2D DCT and PCA. Our experiments use a set of data obtained from a test site where the anti-tank and antipersonnel mines are buried. We evaluate the proposed system in terms of the ROC curve. The result shows that the proposed system performs much better than the conventional PCA systems from the viewpoint of speed and false alarm rate.