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Calculations have been performed of normalized eddy current signal responses due to changes in test frequency and lift-off distance between a transmit-receive (also called "driver-pickup") eddy current probe with laterally spaced transmit and receive coils as shown below:
The transmit coil is excited with a time-harmonic (sinusoidal) electrical current and a voltage is induced in the receive coil which is equal to the time rate of change of magnetic flux through its windings.
Input parameters of the probe and test plate used in this study are summarized as follows:
The resulting normalized voltage diagram showing the transmit-receive ET probe signal changes due to test frequency and lift-off distance variations is shown below:
Some interesting observations are the "hook" shaped lift-off curves and the non-intuitive behaviors of the curves near the top of the diagram at lower test frequencies (below 100 kHz).
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