Some of the most sensitive magnetic-field detectors ever built have always had a strange blind spot: pinpointing exactly when a magnetic field is zero. Engineers at the University of Adelaide say they've just fixed that, without the costly complexity older solutions required.

  • 0: the exact magnetic-field reading these sensors have always struggled to confirm
  • Hundreds to thousands of loops needed in older competing circuit designs
  • Research published in the journal Physical Review Applied
  • Work led by Adelaide's Quantum and Nano Technology Group (QuaNTeG)

The problem with the world's best sensors

The devices in question are called SQUIDs — superconducting quantum interference devices — and they're already among the most sensitive magnetic sensors in existence, used in brain-imaging systems, advanced radio-frequency receivers and precision scientific instruments. Despite that sensitivity, SQUIDs have historically struggled to reliably identify an absolute zero magnetic field.

Engineers had worked around the problem before by building circuits packed with hundreds or even thousands of differently sized superconducting loops. That approach worked, but it came at a real cost: cramming in all those different loop sizes reduced the overall sensitivity that made SQUIDs valuable in the first place.

A simpler fix: loops that do less, together

The Adelaide team, including PhD students Ross Monaghan and Jonathan Marenkovic, found a different way in. Instead of varying loop sizes, they kept every loop the same size and swapped some of them for "bare loops" — loops missing a key SQUID component called a Josephson junction.

Those bare loops change how magnetic signals travel through the circuit, creating what the team calls a "synthetic area spread." The effect tricks the sensor into behaving as though it contained many differently sized loops, without the engineering complexity — or sensitivity loss — of actually building it that way.

"For decades, scientists have known how to make these devices identify an absolute magnetic field, but doing so required design compromises that reduced their performance," said Associate Professor Giuseppe Tettamanzi, the study's lead researcher. "Our work shows there is another way."

Why a tiny circuit trick could matter widely

The team confirmed the effect experimentally using fabricated superconducting circuits cooled to extremely low temperatures, and the results matched what their theory predicted. Beyond being an elegant trick, the researchers say the method could make future SQUID-based sensors both cheaper and easier to manufacture, since it removes the need to fabricate large arrays of differently sized loops.

Potential applications include more detailed brain-monitoring systems, more sensitive radio-frequency receivers for communications technology, and improved electromagnetic sensing for industrial and scientific use. The concept is already the subject of an international patent application, and the Adelaide group says further studies are underway to push device performance even further.

It's a reminder that not every breakthrough needs bigger, more complicated hardware. Sometimes the fix is removing a few components rather than adding more — and getting a cleaner answer to a question as simple as "is this field exactly zero?"

The full study, published in Physical Review Applied, was led out of the University of Adelaide's School of Chemical Engineering, with further testing already underway to bring quantum-limited sensors closer to real-world, commercial use.