부산대학교 도서관

Airborne Geophysical surveys include the exploration of mineral reserves by sub-surface conductivity measurement using Time Domain Electromagnetic Methods (TDEM). Transmitter-receiver coil assembly is suspended from the helicopter and the power required for energizing the transmitter and other paraphernalia is driven from the Helicopter. The pulsating high ramp rate currents in the Transmitter coils generate Electric fields in the sub-surface. These electric fields cause eddy current which depends on the electrical conductivity of the sub-surface. These eddy currents generate a secondary magnetic field that decays as a function of the electrical conductivity of the medium. The decay of the secondary magnetic field is measured by the secondary coil and processed by front-end electronics. The inverse problem is solved to estimate the nature of mineral reserves. The depth of penetration of magnetic fields generated by the transmitter coil is proportional to the cube of magnetic dipole moment of transmitter coil. The peak current in the coil thus becomes an important performance parameter. The electrical parameters of the optimized coil design require a minimum 48 Volts DC supply at the input. The power available from the Helicopter is limited to 28 V, 100 A which does not suffice the requirements of peak current. The up-conversion from 28 V to 48 V/96 V is carried out using a DC-DC converter. For meeting the statutory requirements of the airworthy clearance agency, the DC-DC converter is required to be MIL-STD-461E compliant. This paper describes the design of EMI compliant system which qualified conducted emissions (CE) and radiated emissions (RE) tests. Filter design, partition box design, and time-staggering of switching of resonant-type chopper concepts are detailed along with results of EMC qualifications.