Pulse Induction Metal Detector: A Performance Application

Abstract

Currently, metal detectors are actively used in the detection of treasures, underground cavities, historical artifacts, lost manhole covers and land mines, as well as firearms and other weapons for public security purposes. Metal detectors are categorized into four groups, based on their operating principles. Beat-frequency oscillation and resonant frequency oscillation are the two early techniques used in metal detectors. Detectors based on the said principles are not preferred due to frequency stability issues. Induction balance (IB) and pulse induction (PI) detectors are more widely used. Recent studies in the literature are mostly focused on the improvement of detection depth, sensitivity, discrimination capability, and soil balancing characteristics of metal detectors. There are many variables affecting detection depth, including detector operating frequency; search coil size; minerals in the soil; and target size, shape, type, and orientation. Among the aforesaid variables, various studies exist in the literature on search coil size and shape. These studies were conducted in vacuum or in nonmetallic media such as sand, not covering parameters such as target size, shape, type, and orientation. A novel PI metal detector was developed in this article, for the purpose of determining the effects of changes in the aforesaid target-related parameters on detection depth in a medium consisting of soil with metallic properties. First, a 3-D mechanical scanner system and the detector’s microcontroller electronics were manufactured in order to ensure position-controlled and parallel-to-the-surface mobility for the detector’s search coil. Subsequently, a data collection module was designed to process the detector’s electronic output data at 24-bit resolution and send data to a computer, as well as a software program to assess and record the data received by the computer. Then, aluminum, brass, iron, and copper objects with known geometric properties were buried in a soil with 28.5% magnetic particle content and 4.1% natural humidity, and detector data collected at various positions of the search coil, with the help of the 2-D motion of the mechanical system to which it is connected, were transferred to the digital medium. Such field scans, conducted for each object at a height of 5 cm above surface, enabled detection of the ( $x$ , $y$ ) position where the detector produced maximum output. The search coil was then fixed at such ( $x$ , $y$ ) positions and the depth of the object to the soil surface was increased in increments of 1 cm along the $z$ -axis. The procedure was repeated until the detector produced zero output, and the data were recorded into the computer. The study discusses the effects of parameters such as object size, shape, and type on maximum detection height for the detector developed.