  The interaction of a gravitational wave with a system made of an RLC circuit
forming one end of a mechanical harmonic oscillator is investigated. We show
that, in some configurations, the coherent interaction of the wave with both
the mechanical oscillator and the RLC circuit gives rise to a mechanical
quality factor increase of the electromagnetic signal. When this system is used
as an amplifier of gravitational periodic signals in the frequency range
50-1000 Hz, at ultracryogenic temperatures and for sufficiently long
integration times (up to 4 months), a sensitivity of 10^(-24)-10^(-27) on the
amplitude of the metric could be achieved when thermal noise, shot noise and
amplifier back--action are considered.
