  AC losses of granular superconducting MgB2 were measured using non-resonant
rf power absorption techniques. The presence of two band-gaps makes the
temperature dependent ac loss pattern of MgB2 different from other high Tc
superconductors like YBa2Cu3O and BSCCO-2223. Josephson junction decoupling
plays a major role in MgB2 polycrystalline samples, both in the presence and
absence of magnetic field. We studied the ac loss of MgB2 samples with
different crystalline properties, grain sizes and pressures and sintered under
different physical and chemical conditions. The effects of frequency and
amplitude of ac current on the ac loss are discussed in detail.
