The Johns Hopkins University Applied Physics Laboratory (APL) has developed a prototype metal detection survey system that will increase the search speed of conventional technology while maintaining high sensitivity. Higher search speeds will reduce the time to clear roads of landmines and improvised explosive devices (IED) and to locate unexploded ordnance (UXO) at Base Realignment and Closure (BRAC) sites, thus reducing remediation costs. The new survey sensor system is called the moving belt metal detector (MBMD) and operates by both increasing sensor speed over the ground while maintaining adequate sensor dwell time over the target for good signal-to-noise ratio (SNR) and reducing motion-induced sensor noise. The MBMD uses an array of metal detection sensors mounted on a flexible belt similar to a tank track. The belt motion is synchronized with the forward survey speed so individual sensor elements remain stationary relative to the ground. A single pulsed transmitter coil is configured to provide a uniform magnetic field along the length of the receivers in ground contact. Individual time-domain electromagnetic induction (EMI) receivers are designed to sense a single time-gate measurement of the total metal content. Each sensor module consists of a receiver coil, amplifier, digitizing electronics and a low power UHF wireless transmitter. This paper presents the survey system design concepts and metal detection data from various targets at several survey speeds. Although the laboratory prototype is designed to demonstrate metal detection survey speeds up to 10 m/s, higher speeds are achievable with a larger sensor array. In addition, the concept can be adapted to work with other sensor technologies not previously considered for moving platforms.
This paper describes a prototype three-dimensional electromagnetic induction (EMI) sensor system that has the potential to measure directly the multiple components of buried metal targets' magnetic polarizability tensor without the need to invert spatial data from single-axis EMI sensors. This novel sensor is called a three-dimensional steerable magnetic field (3DSMF) sensor system. The 3DSMF sensor is a high-time resolution, wide-bandwidth time-domain EMI system combined with a 3-axis magnetic field generator (3AMFG) and magnetic field receivers. The 3AMFG differs from previous 3-axis magnetic field generators in a number of ways: the projected magnetic field is relatively uniform in space and is steerable. These two features offer the potential to greatly improve target classification. This paper discusses the 3DSMF sensor system design philosophy and modeling results.