  The conformal mapping method is used to study the problem of flux line
interaction with surface cavities having cylindrical profile and characteristic
size much less than the penetration length, i.e, within mesoscopic scale. It is
shown that the metastable states are achieved when the dimensions of the
surface irregularities do not exceed the coherence length. Our study shows that
the surface barrier may vanished at some weak point at which the surface
irregularities have mesoscopic scales. On the other hand, the surface barrier
is completely disappeared when the surface defects size is more greater than
penetration length. Our results are compared with the available experimental
data and theoretical results.
