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As part of this effort, NASA Langley Research Center has developed several instruments based on a novel electromagnetic probe. One of these instruments, the flux-focusing eddy current sensor and rotating probe offers significant advancement in the detection of fatigue cracks under rivet heads. The device's unique driver-pickup coil configuration produces a zero output voltage when unflawed material is inspected. In the presence of a flaw or crack, a large output voltage is recorded. The signal offers the instrument operator an easy method for detecting and locating a flaw.