Technology Description

Photos of (a) 4.2” mortar, and (b) a half-round.

Drawing on the experience gained through completion of the Strategic Environmental Research and Development Program (SERDP) project MR-1225, investigators are building an optimally designed field prototype system. Using the numerical simulators, it was determined that a device based on three orthogonal transmitters and eight pairs of differenced receivers is optimal for the purpose. The transmitter-receiver assembly together with the drive electronics and signal detection hardware, as well as the battery power and global positioning system (GPS) receiver, will be mounted on a small cart to assure system mobility. An important feature of the design is that the parameters of a metallic target can be determined from a single position of the platform. The field prototype system is based on a triaxial transmitter. A well-proven switch was incorporated to produce alternating half-sine waveform with an optimal period and duty cycle. Eight receiver coils are placed horizontally along the two diagonals of the upper and lower planes of the two horizontal transmitter loops. The pairs are the coils that are symmetric through the center point of the transmitter coil configuration. Critically damped flat air core coils are used to sense the target signal. Each sensor is linked to an analog-to-digital converter (ADC) and a computer interface. The heart of the computer interface is a field programmable gate array (FPGA). This device will process the data and control the on-board memory to allow either direct transfer of the raw data into the computer or, for faster processing and display of results, direct average of 10 to 100 frames before transfer. Currently, all data are transferred to the computer for full interpretation.