Group 1: ‘SQUIDS’

Progress Report

[Introduction] [Details of the subsections] [Other work]

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This group has been set the task of researching the subject of Superconducting Quantum Interference Devices or SQUIDs. Work began in week 13 by choosing an Editor (Chris King) and Deputy Editor (Ben Powell). We also set ourselves a timetable to work to.


13Initial conference.
14Individual work following a brief meeting.
15Individual progress reports to be handed the Deputy Editor.
16Progress report to be handed in.
17Group members to hand in their completed contributions to the technical report to the Editor and the popular account to the Deputy Editor.
18Individual work following a brief meeting.
19All written work due in.

We split the subject into smaller more manageable subsections and decided who would research each of these. The other tasks that we would need to perform were divided amongst the group.

Division of Labour

  1. Superconductivity

  2. The Josephson junction

  3. SQUIDs

  4. Applications

  5. High Temperature SQUIDs

  6. Computing

  7. Presentation

  8. Written Documents

Each of the main sections has been allocated a target number of words in the technical report (see below) with the popular account to be approximately 20 to 25% as long.

Superconductivity1000 words.
The Josephson junction1000 words.
SQUIDs3000 words.
Applications3000 words.

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Details of the subsections

History of superconductors:

This section is designed to give a basic background to the subject of superconductivity. It will be particularly important for the popular account. The aim is to give the reader some idea of the history of superconductivity. This will be achieved, in part, through working very closely with the theory of superconductivity and Josephson junction groups. Information collated should include when superconductors were discovered, what their first uses were, how the temperature range of superconductors has changed with time, when high temperature and type II superconductors were discovered, and when Cooper and Josephson did their work. This section should also include a phenomenological survey of superconductors.

Theory of superconductors:

This section should explain how superconductors work. This will include explaining what a superconductor is, how superconductors are classified, what the physical properties of superconductors are (including a comparison with perfect conductors, the Messiner effect and perfect diamagnetism), the significance of London equation, penetration of magnetic fields, quantisation of magnetic flux, B.C.S. theory and Cooper pairs.

The Josephson junction:

This section underpins the whole of the research by explaining the basic theory about which SQUIDs function. This section must explain the Josephson effect, many body Cooper pair wavefunctions, coherence and the use of quantum interference devices to detect magnetic fields. Careful co-operation with the superconductivity and SQUIDs groups will be required.

The construction of SQUIDs:

This section is designed to explain the way in which SQUIDs are built starting from where the Josephson junction group leaves off. This group will have to work closely with both the Josephson junction group and the materials group. The group should seek to explain sandwich-type junctions, single crystal silicon membrane junctions, co-planar electrode junctions, DC and AC SQUIDs, the use of Josephson junctions in SQUIDs, Non-hysteric Josephson junctions, resistive shunting and how the electronics of a SQUID work.

Materials used in the construction of SQUIDs

This group must work closely with the construction group to explain the particular difficulties of constructing SQUIDs. To begin this group should consider which qualities are desirable in materials from which SQUIDs are to be made. They will also have to consider which compromises have to be made (such as between a high Tc and the brittleness of the material). This group will also be responsible for researching methods of fabrication and purification, films of superconducting materials and growth mechanisms.

Commercial availability of SQUIDs:

This group has obtained various manufacturers catalogues and much information from Dr. Meeson on the SQUIDs used at Bristol University. This group will be required to report on the different types of SQUIDs, which include Normal DC, RF and high temperature DC SQUIDs. The group will have to report on what the differences, advantages and disadvantages of these types of SQUIDs are and what each type is used for.

Medical Applications:

This is one of the most famous and eye-catching uses of SQUIDs. The main method of research will be searching in Journals and on the World-Wide Web. SQUIDs are used for Brain scanning and heart monitoring. This group will report on the techniques and helmets used for brain scans (including construction) and the computations performed on the images created by this process. This group will also consider why one should wish to measure brain activity.

Physical Applications:

SQUIDs are widely used in physical research, the low-temperature laboratory in Bristol University being a convenient example. With the aid of Dr Meeson (from the low-temperature group) this group will investigate how SQUIDs are used in this context. This will include the use of SQUIDs to measure local magnetic field strength and potential difference and a description of the scanning SQUID microscope and how it is used to measure local magnetic field strength.

Geophysical Applications:

Geophysics has found many uses for SQUIDs, particularly in searching for oil and rare earth elements, which create tiny differences in the Earth’s magnetic fields. This group will have to consider the problems of using SQUIDs in the environments in which geophysicists work. This group will also consider the advantages of High Temperature Superconductor SQUIDs (HTS-SQUIDs) for electromagnetic methods in exploration in geophysics. This will require close co-operation with the high temperature SQUIDs group.

High Temperature SQUIDs:

The new development of high temperature (that is above the boiling point of nitrogen) superconductors has inevitably lead to the development of SQUIDs which can work at these high temperatures. This leads to some further uses for SQUIDs, as they are not as difficult to cool as previously. This group will have to look into the mechanisms explaining high temperature superconductivity. They will also examine the benefits and disadvantages (particularly the difficulties in making SQUIDs from high temperature superconductors and the subsequent brittleness of HTS-SQUIDs) of HTS-SQUIDs.

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Other work.

We have also set up a web-site on the Internet ( and created our own file space on the Physics Teaching Lab server, which includes a list of everyone in the group’s e-mail address, to allow easy communication within the group and to simplify the editing process.

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This document was saved as HTML from a Word 97 document and then converted from its nasty output. This document was last updated on Wednesday 28th October 1998.