  We report the first unambiguous quasi-periodic large-scale
extreme-ultraviolet (EUV) wave or shock that was detected by the Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory. During the whip-like
unwinding eruption of a small filament on 2012 April 24, multiple consecutive
large-scale wavefronts emanating from AR11467 were observed simultaneously
along the solar surface and a closed transequatorial loop system. In the
meantime, an upward propagating dome-shaped wavefront was also observed, whose
initial speed and deceleration are about 1392 km/s and 1.78 km/s^2,
respectively. Along the solar surface, the quasi-peridoic wavefronts had a
period of about 163 +/- 21 seconds and propagated at a nearly constant speed of
747 +/- 26 km/s; they interacted with active region AR11469 and launched a
sympathetic upward propagating secondary EUV wave. The wavefronts along the
loop system propagated at a speed of 897 km/s, and they were reflected back at
the southern end of the loop system at a similar speed. In addition to the
propagating waves, a standing kink wave was also present in the loop system
simultaneously. Periodicity analysis reveals that the period of the wavefronts
was consistent with that of the unwinding helical structures of the erupting
filament. Based on these observational facts, we propose that the observed
quasi-periodic EUV wavefronts were most likely excited by the periodic
unwinding motion of the filament helical structures. In addition, two different
seismological methods are applied to derive the magnetic field strength of the
loop system, and for the first time the reliability of these inversion
techniques are tested with the same magnetic structure.
