Halbach Magnetic Weber Bars

Abstract

Magnetic Weber Bars have been proposed to search for gravitational waves in the kHz to GHz regime by exploiting the mechanical deformation of a large magnet induced by a gravitational wave. Here we propose to increase the effectiveness of such devices by considering magnetic field configurations with strong gradients, albeit lower field strengths, such as Halbach arrays. We focus on one of the most challenging but most realistic signals, with short duration and low coherence, exploiting the ring-down period of the mechanical resonator. We show that with demonstrated technology this setup can reach sensitivities of $S_h^{1/2} \simeq 10^{-21}/\sqrt{\text{Hz}}$ at a broad set of frequencies around several resonance peaks at $\sim 10$ kHz, and $S_h^{1/2} \simeq 5 \cdot 10^{-20}/\sqrt{\text{Hz}}$ in a broadband search at higher frequencies. We discuss plausible upgrades to reach $S_h^{1/2} \simeq (10^{-23} - 10^{-21})/\sqrt{\text{Hz}}$ in a broadband search covering 10 kHz - MHz.