Wide bandwidth dual acoustic gravitational wave detectors

In a 'dual' detector a wideband sensitivity is obtained by measuring the differential displacement, driven by the gravitational wave, of the facing surfaces of two nested massive bodies mechanically resonating at different frequencies. By using the recently proposed 'selective readout' scheme, capable of specifically selecting the signal contributed by the vibrational modes sensitive to the gravitational waves, a flat spectral strain sensitivity can be obtained. In the case of a 1 m diameter molybdenum dual cylinder, the sensitivity expected at the standard quantum limit is about 10−23 Hz−1/2, in the wide frequency interval of 2–6 kHz. We discuss here the requirements imposed by the 'dual' design on the differential displacement readouts. A possible readout scheme is presented and its current limits analysed. The feasibility of a mechanical amplification stage (compliant mechanism) to increase the expected displacement at the readout input is also discussed.