What is so special about SQUID (Superconducting Quantum Interference Device)?

SQUID was an accidental discovery in the Ford Motor Company’s research lab in Dearborn, Michigan. Five Researchers John Lambe, James Zimmerman, Arnold Silver, Robert Jaklevic, and James Mercereau made this vital discovery in superconductivity. They found, when cooling the SQUID a few degrees above absolute zero, it can detect a magnetic field that is less than 5 quintillionths of a tesla.

Superconductivity research was performed for gaining knowledge rather than for Ford’s commercial requirements. In 1963, the group discovered the Josephson Effect in a sample of super-cooled phosphorous-doped silicon. There are two main types of SQUIDS – Direct Current (DC) and Radio Frequency (RF).

SQUID is otherwise known as Superconducting Interferometers and they come in all sizes and shapes. With the growing technological advancement, these devices have considerably shrunk in size. Now there are nano squids which are compact unlike the earlier version which stretched across many kilometers. Nano Squid are a type of SQUID made out of carbon nanotubes which is just one nanometer in diameter. This SQUID is powerful enough to detect magnetic changes even in a molecule.  

Interferometers or SQUIDS work by splitting a wave into two components and sending them along different paths. These waves are recombined to find out if any of the waves has encountered any strange obstruction or interference. The phase of the two waves are checked. If both of them have travelled the same distance then the phase remains the same for both the waves. But if one of the waves encountered an obstruction then the phase changes.  The details about the obstruction can be found out by measuring the phase difference between the two waves.

Applications of SQUID:

Since the SQUID is able to detect such small levels of magnetic field it is used in a variety of ways such as:

• Making analog-to-digital convertors
• Traditional and quantum computing
• Detection of the cosmic microwave background
• Geophysical and archaeological surveys
• Imaging the brain, heart, and other body parts
• Non-destructive testing of materials and devices

These devices are effective in places where machinery cannot be taken apart to find out its wear and tear. In such instances, these SQUID devices help to detect the depreciation value of the working equipment. Moreover, the information gathered from these devices helps service engineers to take the corrective steps for ensuring the machines working condition, within the safety rules. 

In the medical field, these devices have proven to be helpful in an exemplary way for the physicians. The usage of SQUID in Magneto Encephalography field is a good example of that. An array of squids are used to study neural activity inside the brain. Likewise, Magnetogastrography measures functions of the stomach.  Drugs maybe orally applied and the instrument will trace the path of the drug to find out the function of the stomach. In such scenarios the Magnetic Marker Monitoring method is used.

SQUIDS are very commonly used in Magnetic Property Measuring Systems. The magnetic property of any material can be measured when the temperature range of 300 K - 400 K is maintained for these operations.

SQUID has innumerable uses and recent innovative research has proven these priceless devices to be a powerful help in various fields. SQUID falls under the electromagnetic interference topic which is a deeper look at the Electromagnetics section on the Electrical FE Exam.