100% Duty Cycle TEM: Faster Acquisition and Less Noise

Abstract

In a typical impulse TEM system, such as SIROTEM, the loop current is periodically switched between on and off with the direction of current flow alternating after every off period. Measurements are performed in the off period, thus, measurements are conducted in the absence of any primary field. In Australia almost all TEM systems are operated at 50% duty cycle, that is for half of the transmitter cycle the transmitter is not connected to the loop. With the introduction of relatively high-voltage, battery powered transmitters, such as the Zonge ZT-30 and full waveform recording, clean data from 100% duty cycle TEM is a matter of pushing a button. With current swing now doubled and changing at twice the normal rate we can expect a an improvement in signal-to-noise by almost a factor of three. However, is it TEM as we know it?