A resonant circuit consists of a precisely shaped coil and a capacitor. It is tuned to resonate at the frequency of excitation coil drive.
Advantages:
- The resonant coil signals are 90 degrees out of phase, so they are in quadrature with the direct breakdown signals.
- Higher resolution and accuracy compared to metal targets.
- Target does not need to be moved for sensor self-calibration.
Disadvantages:
- Greater installation height
- Commercial ASICs are not available; the analogue design is implemented in discrete, commercially available components.