Lowhyphen;frequency noise spectra of a superconducting magnetic gradiometer

摘要

We present the first measurements of spectra that characterize noise in the frequency range 5times;10minus;4to 20 Hz of a superconducting magnetic gradiometer operating in a magnetically quiet environment. Spectra are effectively white at frequencies above about 0.1 Hz with a spectral power density of 0.03 (pT/m)2thinsp;Hzminus;1(1 pT/m=10minus;12T/m=10minus;10G/cm =10minus;3ggr;/m) and are of the formS(f) =S(fo)(fo/f)ggr;at frequencies below 0.1 Hz. A value of 1.3 for ggr; withS(fo) =0.002 (pT/m)2thinsp;Hzminus;1atfo=1Hz is representative of values observed during the quietest observational periods. Intrinsic noise of the superconducting quantum interference device (SQUID) then dominates observed spectra at frequencies below 0.1 Hz.