The properties of Josephson devices are strongly affected by geometrical
effects. A loop-shaped superconducting electrode tightly couples a long
Josephson tunnel junction with the surrounding electromagnetic field. Due to
the fluxoid conservation, any change of the magnetic flux linked to the loop
results in a variation of the shielding current circulating around the loop,
which, in turn, affects the critical current of the Josephson junction. This
method allows the realization of a novel family of robust superconducting
devices (not based on the quantum interference) which can function as a
general-purpose magnetic sensors. The best performance is accomplished without
compromising the noise performance by employing an in-line-type junction few
times longer than its Josephson penetration length. The linear (rather than
periodic) response to magnetic flux changes over a wide range is just one of
its several advantages compared to the most sensitive magnetic detectors
currently available, namely the Superconducting Quantum Interference Devices
(SQUID). We will also comment on the drawbacks of the proposed system and
speculate on its noise properties.Comment: 13 pages, 4 figure