  We study superconducting microtraps with rectangular shapes for cold atomic
gases. We present a general argument why microtraps open, if brought close to
the surface of the superconductor. We show that for a given width of the strips
there exists an optimal thickness under which the closest distance of the
microtrap from the superconductor can be achieved. The distance can be
significantly improved, if the edge enhancement of the supercurrent near edges
and corners is exploited. We compare numerical calculations with results from
conformal mapping and show that conformal mapping can often give useful
approximate results.
