We report on a complete analysis of the noise sources in a ultracryogenic bar working at T ? 100 mK, equipped with GHz bias liquid helium cooled preamplifier r.f. SQUID. Optimal values for parameters, as transducer mass, the coupling inductance, etc. are numerically determined in order to get maximum sensitivity to impulsive gravitational wave signals. The sensitivity is improved by selectively cooling the fundamental resonance. The Standard Quantum Limit is found to be within reach of current cryogenic technology.
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