The edge-delaminated AFC from the host structure are characterized through impedance measurement and the resonant properties. The edge delaminations are categorized into three groups according to their orientations, including end delamination with its front perpendicular to the active fibers, side delamination with the front parallel to the fibers, and corner delamination. Since interdigital electrodes are symmetrically aligned on the opposite surfaces of AFC, the delaminated patch extensionally vibrates along the fibers when an alternating voltage is applied on the electrodes. The resonant frequencies of extensional vibration for the delaminated AFC are in reverse proportion to the characteristic length of debond in accordance with the measured impedances and simulated spectra. The decrease of resonant frequency for end delamination is smaller than that for side delamination. The ratio of the second lowest resonant frequency to the fundamental one remains a specific constant, 1.7, for the growing isosceles corner delamination. If the ratio becomes less than 1.7, it indicates that the delaminated region expands along the fiber direction. In contrast, the delamination spreading along the other direction perpendicular to the fibers results in an increasing ratio of the lowest two resonant frequencies beyond 1.7.