Abstract
The dc Superconducting Quantum Interference Device (dc-SQUID) is one of the most sensitive magnetic
field sensors available. In this thesis we concentrate on its application as an amplifier. In this configuration,
an input circuit of interest can be connected by means of a coupling coil. The intended application of
our developed low-Tc SQUID amplifiers is the readout of the first spherical gravitational wave antenna
MiniGRAIL.
Using small-signal analysis as well as numerical simulations, we study the achievable signal-to-noise
ratio of such sensors in practical measurements. Published theories and studies could be extended. Some
interesting points treated are the influence of the often used negative feedback (flux-locked loop), an altered
input impedance of the SQUID amplifier and the influence of back-action noise, which directly affects the
object of interest. The altered operation of the SQUID due to the presence of the input circuit is studied in
numerical experiments.
Another important issue, the influence of integrated input coils on the dynamics of SQUIDs, is
investigated theoretically and experimentally. The performance of our developed sensors is compared to
numerical simulations on detailed models. The results give insights into the behavior, design and usage
of dc-SQUIDs with integrated coils. For a SQUID with input inductances of 1.5 μH we reached a good
coupled energy sensitivity of about 170 ¯h in a dilution refrigerator.
Furthermore, we investigated the hot-electron effect. This effect typically limits the sensitivity of
superconducting electronics at sub-Kelvin bath temperatures due to a weakened electron-phonon coupling.
We performed heating experiments on thin-film resistors which are similar to the shunt resistors of the
Josephson junctions used in our sensors. The suppression of the hot-electron effect via electronic thermal
transport to attached cooling fins is investigated both experimentally, theoretically and numerically. The
numerical technique turns out to be a useful tool for the thermal design of superconducting electronics.
Original language | English |
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Awarding Institution |
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Supervisors/Advisors |
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Award date | 10 Jun 2009 |
Place of Publication | Enschede |
Publisher | |
Print ISBNs | 978-90-365-2832-0 |
DOIs | |
Publication status | Published - 10 Jun 2009 |
Keywords
- IR-61412