Question

Is it possible to do absolute magnetic field (flux) measurements using a SQUID?

Answer 1

In DC squid operation, the SQUID is usually flux-locked into a position on the flux-voltage curve, and the change in supercurrent required to maintain that lock point is used to determine changes in magnetic flux through the loop. Because the flux-voltage curve is periodic with period equal to the magnetic flux quantum, however, it does not seem to me to be possible to measure absolutely the flux coupled into the SQUID loop - rather, it seems only possible to measure changes in flux from some initial value.

Is there a way to use a DC SQUID to measure magnetic flux absolutely, or are only differential measurements possible?

EDIT in response to one of the comments below by @FraSchelle, a slight amendment to the question: Is it ever possible, using a SQUID with a known geometry, to say that the magnetic field B=0B=0? Or is it only possible to say that is has changed by ΔBΔB from the initial value when you first turned the SQUID on?

Answer 2

The energy flux in a magnetic field is given by the Poynting vector: Poynting vector S = E X B The direction of the Poynting vector gives you the direction of the energy flux.