# Can a SQUID perform real time measurements of a slow varying magnetic flux?

It is well known that a SQUID can detect an extremely small magnetic flux.

What if the flux is time-dependent? E.g. a slow varying sinusoidal magnetic flux

$$\Phi=\Phi_0\sin(\omega t).$$

Can I still perform a real time measurement of the slow varying flux considering the induced EMF?

By "slow" I mean $\omega$ is smaller than Josephson frequency (AC Josephson effect due to the EMF).

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## 1 Answer

I did something similar to that in a labs course once, where the flux was temperature-dependent and the temperature was time-dependent. However, ‘my’ rate of change was very slow (a few hours for a temperature change from 2 K to 300 K with an associated flux change of maybe 500%), so I don’t know how well this applies to your experiment.

Once I get home I can have a look at the data we collected back then to tell the exact times and rates of flux change.

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I just had a look at the data - the time frame was 50k seconds (approx. 14 hours) during which the flux changed by 250%. So if your $\omega$ is very very small, it should work - otherwise, I would love to hear your experimental results :) –  Claudius Oct 8 '12 at 18:55
Thank you very much! –  ChenChao Oct 10 '12 at 14:18
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