Measurements of mechanical dissipation in high sound velocity materials: implications for resonant-mass gravitational radiation detectors

Abstract

The sensitivity of resonant-mass gravitational radiation detectors depends on both the antenna cross-section and the detector noise. The cross-section is determined by the sound velocity v s and density ϱ of the antenna material, while the principal detector noise sources are thermal Nyquist noise and noise due to the readout electromechanical amplifier. The thermal noise is proportional to T/Q, where T is the temperature and Q is the antenna's mechanical quality factor. For a given frequency and antenna geometry, the cross-section is proportional to ϱ v 5 s. Thus the speed of sound and Q are important figures-of-merit in selecting the antenna material. Materials with high v s are available that in principle could provide about a hundred-fold increase in the cross-section of resonant-mass gravity wave detectors as compared to current generation detectors. In this Letter we report the results of measurements of the temperature-dependent mechanical losses associated with excitation of the fundamental longitudinal acoustic mode in several potentially suitable materials. We also discuss the impact that these materials could have on the sensitivity of resonant-mass detectors.