Resonant-mass detectors: status and perspectives

We review the main features and the perspectives of the resonant-mass gravitational wave detectors. Bar detectors have been taking data for the last few years with burst sensitivity h 4 ? 10?19 at SNR = 1, or, in spectral units, 3 ? 10?22 Hz ?1/2 over a bandwidth of about 1 Hz, with a duty cycle mainly limited by cryogenic operations. In addition to the systematic search for impulsive events, the data collected are being used to detect periodic waves over long time periods, to give new upper limits for the stochastic background of cosmological origin, and to study possible correlation with gamma ray bursts. The recent developments of readout electronics have allowed us to increase the detection bandwidth to a few tens of Hz, and even larger bandwidths are expected in the near future. Resonant-mass detectors of spherical shape have been investigated and many different solutions have been proposed. Two small (about 60 cm in diameter) spheres are under construction in Holland and Brazil. Recently, a new scheme has been proposed, the 'dual' detector, which can provide a wideband performance. We briefly describe the status of traditional resonant-mass detectors and the main features and the state of the art of the advanced acoustic detectors.