A SCANNING SQUID MICROSCOPE FOR IMAGING HIGH-FREQUENCY MAGNETIC FIELDS

Simple item page
dc.contributor.advisorWellstood, Frederick C.en_US
dc.contributor.authorVlahacos, Constantine Peteren_US
dc.contributor.departmentElectrical Engineeringen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2010-07-02T05:32:37Z
dc.date.available2010-07-02T05:32:37Z
dc.date.issued2009en_US
dc.description.abstractThis thesis examines the design and operation of a large-bandwidth scanning SQUID microscope for spatially imaging high frequency magnetic fields. Towards this end, I present results on a cryo-cooled 4.2 K scanning SQUID microscope with a bandwidth of dc to 2 GHz and a sensitivity of about 52.4 nT per sample. By using a thin-film hysteretic Nb dc-SQUID and a pulsed sampling technique, rather than a non-hysteretic SQUID and a flux-locked loop, the bandwidth limitation of existing scanning SQUID microscopes is overcome. The microscope allows for non-contact images of time-varying magnetic field to be taken of room-temperature samples with time steps down to 50 ps and spatial resolution ultimately limited by the size of the SQUID to about 10 micrometers. The new readout scheme involves repeatedly pulsing the bias current to the dc SQUID while the voltage across the SQUID is monitored. Using a fixed pulse amplitude and applying a fixed dc magnetic flux allows the SQUID to measure the applied magnetic flux with a sampling time set by the pulse length of about 400 ps. To demonstrate the capabilities of the microscope, I imaged magnetic fields from 0 Hz (static fields) up to 4 GHz. Samples included a magnetic loop, microstrip transmission lines, and microstrip lines with a break in order to identify and isolate electrical opens in circuits. Finally, I discuss the operation and modeling of the SQUID and how to further increase the bandwidth of the microscope to allow bandwidth of upwards of 10 GHz.en_US
dc.identifier.urihttp://hdl.handle.net/1903/10223
dc.subject.pqcontrolledEngineering, Electronics and Electricalen_US
dc.subject.pqcontrolledPhysics, Condensed Matteren_US
dc.subject.pquncontrolledcryo-cooleden_US
dc.subject.pquncontrolledhigh-frequency magnetic fieldsen_US
dc.subject.pquncontrolledimagingen_US
dc.subject.pquncontrolledMicroscopyen_US
dc.subject.pquncontrolledScanning SQUID microscopeen_US
dc.subject.pquncontrolledSQUIDen_US
dc.titleA SCANNING SQUID MICROSCOPE FOR IMAGING HIGH-FREQUENCY MAGNETIC FIELDSen_US
dc.typeDissertationen_US

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
Vlahacos_umd_0117E_11035.pdf
Size:
18.13 MB
Format:
Adobe Portable Document Format
Download

Collections

UMD Theses and Dissertations
Electrical & Computer Engineering Theses and Dissertations