Gravitational Shielding Revisited in the Hz Regime

With many recent advances in multi-messenger astronomy, fully controlled transmitter receiver laboratory experiments on dynamic gravitational fields (DGFs) have become more important. This implies measuring their phase and amplitude and assessing any non-gravitational crosstalk. To the authors’ knowledge, shielding effects for dynamic gravitational fields have not been experimentally investigated. Theoretically, the absorption cross-section is expected to be proportional to frequency squared.

Usually, dynamic experiments consist of a periodically moving mass distribution (here two rotating tungsten bars). The detector system consists of a high Q (10⁴), 42 Hz resonant titanium bending beam. Its gravitationally induced motion is analyzed using three laser Doppler vibrometers and multichannel lock-in amplifiers. Here, we present experimental results on shielding of DGFs using different metal shields with dimensions of about 1.4 × 0.3 × 0.1 m and mass of up to ~500 kg placed in between transmitter and detector. The signals for the two shield positions (with/without shield) are best analyzed by fitting a single degree of freedom response function in a ceteris paribus mode. At a frequency of more than four orders of magnitude higher than previous quasistatic shielding investigations, the relative change of the amplitude of the response signal is smaller than 10^-2 for both a 9 cm thick brass shield and a 10 cm thick lead shield. The phase at resonance for the two shield positions is unchanged for brass, but seems to show a small change for lead.