RESONANT COIL FOR MEASURING SPECIMEN CONDITION

摘要

An oscillator provides a reference signal having a phase. A tunable reactive circuit, including an induction coil, is driven by the fixed frequency reference signal of the oscillator with coil adapted to be positioned adjacent the specimen to generate an oscillating signal corresponding to the condition of the specimen. The tunable reactive circuit provides an output signal having a parameter indicative of the condition of the specimen. A resonant control circuit compares the reference signal to the oscillating signal and provides to the tunable reactive circuit a resonance control signal representative of the comparison. The resonance control signal tunes the tunable reactive circuit, which may be a series RLC circuit, so that the frequency of the oscillating signal is substantially constant.