  We investigate the detectability of gravitational waves (GWs) lensed by a
system that consists of binary black holes as lenses using time-domain
numerical simulations. The gravitational lensing potential of this system is no
longer static but evolves with time. When GWs from the source pass through the
binary lens, their amplitudes can be modulated, which is similar to the
phenomenon of amplitude modulation (AM) in radio communication. We find that
even the frequency of the binary lens itself is too low to be detected by the
LISA detection band, the sidebands in the spectrum of the lensed GWs due to AM
can still be within the sensitive range of the detection band. Moreover, we
also calculate the relative differences of SNR (mismatch) between the lensed
and unlensed GWs. We find that the {\it mismatch} can be as significant as
9.18%. Since mismatch does not depend on the amplitude of wavefrom, the
differences between the binary lensed and unlensed waveforms are substantial.
This provides a robust way to identify the lensing event for the LISA project
in the future.
