SQUID (superconducting quantum interference device)

In summary, a SQUID measures magnetic fields by changing the flux through a superconductor, which in turn causes a voltage to be produced across the Josephson junctions. This voltage is proportional to the magnetic field and can be used to extract information about the magnetic sample.
  • #1
VenaCava
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Hi all,
I am looking to do some magnetic measurements for some research (chemistry...) but I'm hoping to get an understanding of how a SQUID instrument works. I was wonder if anyone could give me a qualitative overview or if anyone know any resources without math-heavy explanations.
Thanks!
 
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  • #2
Wikipedia has a good, basic one-page description. Here's another site with good information
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/squid.html
Since SQUID operation involves quantum mechanical concepts (electron wavefunctions, Cooper pairs and tunneling, e.g.), you can't get too deep without math.
 
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  • #3
Thanks. I've actually already taken a look at those.
I guess I just wanted some clarification on a few points since I don't have too strong of a physics background.
I understand that the squid detector has a superconducting ring with 2 Josephson junctions. The sample that the magnetic measurements are being taken for produces a magnetic field... which causes a change in magnetic flux through the superconducting ring. In response, the superconductor produces a screening current.
This (somehow??) results in the formation of a voltage across the Josephson junctions which can then be measured. What is the simplest explanation for how this happens?
Also is this voltage proportional to the magnetic field?? How exactly is information about the magnetic sample obtained from this voltage measurement.

Thanks
 
  • #4
This is where you need to backtrack and see if you have understood the Josephson effect, because that is something that's used in SQUIDs. It's difficult to explain this right in the middle because one needs to understand a lot of concepts that LEADS to the physics of SQUIDs.

You may want to read this article to start with:

http://www.haverford.edu/physics/Amador/documents/01SQUID.doc

It teaches from, in elementary form, the physics of superconductivity (especially phase coherence which is central to SQUIDs) leading to why you need Josephson junctions.

Zz.
 
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1. What is a SQUID?

A SQUID, or superconducting quantum interference device, is a highly sensitive magnetometer that measures extremely small magnetic fields. It is made up of two superconducting loops connected by two Josephson junctions, which allows it to detect changes in magnetic flux with incredible precision.

2. How does a SQUID work?

A SQUID works by exploiting the quantum mechanical phenomenon of superconductivity, which allows electricity to flow without resistance in certain materials at very low temperatures. The two superconducting loops in a SQUID are made of a superconducting material, and the Josephson junctions are made of a non-superconducting material. When a magnetic field is applied, it causes a change in the current flowing through the SQUID, which can be measured and used to determine the strength and direction of the magnetic field.

3. What are the applications of SQUIDs?

SQUIDs have a wide range of applications in scientific research and technology. They are commonly used in medical imaging, such as in magnetoencephalography (MEG) to measure brain activity, and in magnetic resonance imaging (MRI) to create detailed images of the body's internal structures. They are also used in geological and environmental studies to measure magnetic fields from the Earth and other planets, and in materials science to study the magnetic properties of materials.

4. What are the advantages of using a SQUID?

SQUIDs have several advantages over other types of magnetometers. They are extremely sensitive, able to detect magnetic fields as small as 10^-18 tesla. They also have a wide dynamic range, meaning they can measure both very weak and very strong magnetic fields. Additionally, SQUIDs have a fast response time and can be easily integrated into complex systems for data collection and analysis.

5. What are the limitations of SQUIDs?

While SQUIDs have many benefits, they also have some limitations. They require very low temperatures to function, typically around 4 Kelvin (-269°C), which can be expensive and difficult to maintain. They are also sensitive to external magnetic fields, which can interfere with their measurements. Additionally, SQUIDs are complex devices that require specialized knowledge and equipment to operate, making them less accessible for general use.

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