Recently, it was observed that the low frequency noise of slotted SQUIDs is
not affected when cooling them down in magnetic fields up to 0.05 mT. This
behavior is ascribed to the Bet that magnetic vortices are expelled out of
the narrow strips into the slots. Thus 1/f noise by hopping of vortices in
the superconducting structure is eliminated. Here we present a systematic
investigation on a series of slotted high-T-c de SQUIDs. The number of slot
s varies from zero to eight. A model is developed that provides values for
the effective area and inductance of the slotted washers and the current di
stribution within the slotted SQUIDs. The model can explain the experimenta
lly observed maximum in the effective area for four slots very fell. The ob
served agreement with respect to the modulation depth supports the theoreti
cal values for the inductance. The white noise of the slotted SQUIDs is hig
her than expected, while the expected rise of low frequency noise for field
cooled solid washer SQUIDs was not observed.