Low-noise, single-layer YBa/sub 2/Cu/sub 3/O/sub 7-x/ DC SQUID magnetometers at 77 K

Squid Fundamentals

“…A typical performance is 40ITHz-I/2 at 1kHz and 6SITHz-l/2 at 1Hz. An even lower noise was achieved by Cantor et al [126] with the aid of a 20x2Omm 2 bicrystal and a larger pickup loop: 14ITHz-I/2 at 1kHz and 26ITHz-I/2 at 1Hz.…”

Epitaxial Oxide Heterostructures for Ultimate High-Tc Quantum Interferometers

“…The effective area A eff of a direct-coupled magnetometers is proportional to A pu L S /L pu ∝ a, where a is the size of the pickup coil; A pu ∝ a 2 is its area; and L pu ∝ a is its inductance. For the single-layer directly coupled magnetometers with a pickup loop 20 mm x 20 mm, inductance of the SQUID loop ≈ 50 pH, and flux sensitivity S ≈ 4.6 nT/Φ 0 , the best magnetic field resolution ≈ 24 fT/√Hz at 1 Hz and ≈ 14 fT/√Hz at 1 kHz was obtained at 77 K (Cantor et al, 1995). Much better coupling can be achieved with a multiturn input coil, which is connected in series to the pick-up coil and inductively coupled to the SQUID loop.…”

High transition-temperature SQUID magnetometers and practical applications

“…As far as sensitive magnetometers are concerned, in the case of a single-layer directly coupled SQUID magnetometer it is straightforward to make the SQUID with narrow linewidths (shown in Figure 5.6); the l / f noise in the pickup loop is expected to be negligible as was shown in the previous section'. The best directly coupled magnetometers on a 10 x 10 mm2 substrate have a field resolution of about 50 ff down to 1 Hz [53], adequate for most geophysical applications. For higher field sensitivity one would need to use a multilayer flux transformer but the limited coupling efficiency of the narrow linewidth SQUID would make this approach impractical.…”