
14-1
Superconducting quantum interference devices (SQUIDs) have been a key factor in the development
an
d
co
mmercialization
of ul
trasensitive
ma
gnetic
me
asurement
sy
stems
[1
]
. In ma
ny
ca
ses,
SQ
UID
ma
gnetometers
o
er
t
he
a
bility
to m
ake
m
easurements
w
here
n
o
o
ther
m
ethodology
i
s
p
ossible
.
Be
cause
of th
eir
su
perconducting
na
ture,
SQ
UID
se
nsors
op
erate
at cr
yogenic
te
mperatures
.
Al
though
SQ
UID
el
ectronics
ha
ve
th
e
ca
pability
to op
erate
we
ll
ab
ove
1 MH
z,
mo
st
ap
plications
tend to be at lower frequencies. The ability of a SQUID sensor to measure changes in magnetic
fields and currents is based on four effects: superconductivity, the Meissner effe