GravitationalRadiation Antenna In Leiden

Kamerlingh Onnes Laboratory, Leiden University, The Netherlands

Projects for students



Development of a high-Q impedance matching transformer based on superconducting Nb planar coil.

The mechanical oscillations can be converted into an electrical signal in different ways by means of a transducer. We are developing a capacitive and an inductive transducer. A schematic view of the capacitive transducer is given in the picture below.

An electrically isolated plate is mounted in front of the resonator and charged. The plate is charged with typically a few hundred volts, while the surface of the antenna is grounded. Vibrations of the resonator with respect to the antenna will change the width of the gap and thus the capacity. The output voltage of the parallel plate capacitor is read by a SQUID amplifier. Since the large difference of impedance between the capacitor output and the input of the SQUID, an impedance matching transformer is placed in between. The inductances of the primary and secondary coils of the transformer are denoted by Lp and Ls respectively. The SQUID amplifier is schematically presented by an input inductance Lin and a voltage and current noise Va and Ia.

Student project

This project comprises the development of a new transformer coil. Since the impedance mismatch between the capacitor output and the SQUID input is so large (about 6 orders of magnitude), the traditional transformer coil consists of about 30 000 windings and is very large. Eventually we want to put 6 or 7 transducers on the sphere, so it is important to minimize the size of the transformer.
This can be done by depositing a coil on a silicon wafer where the thickness of the "wire" and the distance between them can be reduced significantly. Moreover, once the coil is optimized, the fabrication can be done much faster. The project consists in testing new Nb planar coils fabricated by IPHT in Jena (Germany) in a high-Q electrical circuit and in an impedance matching transformer for the read-out of a mechanical resonator using a SQUID amplifier.