Patent ID: 6720771
Filing Date: 2004-04-13
Classification: G01V

Abstract:
A moving dipole source electromagnetic induction device for carrying out geophysical surveys, to locate deeper sub-surface bodies under poorer electrical conducting surfaces and for mapping sub-surfacial conductivity changes due to salinity or pollution, the device comprising:(a) an oscillator configured to generate a variable desired operating frequency sinusoidal signal; (b) power amplifier coupled to the oscillator, with the desired variable frequency sinusoidal signal from the oscillator as input and an amplified signal as output; (c) a transmitter coil coupled to the power amplifier, with the amplified signal from the power amplifier as input, the transmitter coil configured to generate a primary electromagnetic field as output; (d) tuning capacitors coupled to the transmitter coil to form a series resonant circuit, with the primary electromagnetic field from the transmitter coil as input and an in-phase sinusoidal signal as output; (e) a capacitor network coupled to the tuning capacitor, with the in-phase sinusoidal signal from the tuning capacitor as input and an out-of-phase sinusoidal signal as output; (f) a first amplifier coupled to the tuning capacitor, with the in-phase sinusoidal signal from the tuning capacitor as input and an amplified in-phase sinusoidal signal as output; (g) a second amplifier coupled to the capacitor network with the out-of-phase sinusoidal signal from the capacitor network as input and with an amplified out-of-phase sinusoidal signal as output; (h) a pair of potentiometers for producing a pair of dc voltages; (i) a dual comparator coupled to the first and second amplifiers and potentiometers, with the in-phase and out-of-phase sinusoidal signals from the first and second amplifiers along with dc voltages from the potentiometers as input and a rectangular waveforms as output; (j) a sampling pulse generator having two monostable multivibrators, coupled to the dual comparator, with the rectangular waveforms from the dual comparator as input and short duration time pulses as output; (k) a selector switch, coupled to the sampling pulse generator, with short duration time pulses from the sampling pulse generator as input, the selectors switch being configured to output the short duration time pulses from the sampling pulse generator one at a time; (l) a receiver coil configured to pick up a time varying secondary electromagnetic field from a conducting target which is a subsurface body and produce a received signal in response thereto; (m) a preamplifier, coupled to the receiver coil, with the received signal as input and with an amplified received signal as output; (n) a filter, coupled to the preamplifier, with the amplified received signal from the preamplifier as input, the filter being configured to provide a flat response leading to phase stability in a desired operating frequency range; (o) a variable gain amplifier, coupled to the filter; (p) a sample and hold amplifier, coupled to the selector switch and the variable gain amplifier, with short duration time pulses from the selector switch and a filtered amplified received signal from the variable gain amplifier as inputs; (q) an analog to digital converter, coupled to the sample and hold amplifier, the analog to digital converter being configured to output digital data representative of an output of the sample and hold amplifier; (r) an input/output device, coupled to the analog to digital converter, the input/output device being configured to generate an output for an LCD display; (s) an LCD display, coupled to the input/output device; and (t) a microcomputer unit for data computation coupled to the input/output device via a data bus.