Design of wideband acoustic detectors of gravitational waves equipped with displacement concentrators

We present the concept design of a new class of acoustic detectors of gravitational waves (GWs), which feature a wideband sensitivity. The main novelty relies in the geometry of the test mass, which is equipped with integrated whips. This tapering provides more resonant modes with favorable cross-section to GWs to achieve a large bandwidth. Moreover, the whips act as displacement concentrators and ensure a high mechanical gain at the sensing surfaces. The resulting decrease in mechanical stiffness allows us to achieve the noise matching condition with reasonable operating parameters of the displacement transducer. The performances of the detector are modeled taking into account the quantum and thermal noise sources in the case of a capacitive transducer with a SQUID amplifier. This class of detectors can be designed to target GWs in the frequency range above 1 kHz at a sensitivity comparable to that predicted for future long baseline interferometric detectors. After showing how to scale the design for different constructing materials and target frequencies, we discuss the predicted sensitivity to specific astrophysical signal waveforms.