China’s gravity-detecting SQUID gets closer to spotting US nuclear submarines

Caption: The superconducting weak force measurement system (left) and a test device built with two 10 kg spheres.

Photo: CAS Chinese researchers unveiled a gravity detector with world-leading precision last month, potentially expanding the military applications of the technology.

It uses a superconducting quantum interference device (SQUID) to detect objects by measuring tiny changes in gravity.

The team that developed the instrument says it can be used for scientific research and finding underground resources.

It also brings the country one step closer to being able to spot patrolling nuclear submarines.

According to a report on the Chinese Academy of Sciences (CAS) website, the instrument reduces gravity gradient measurement noise – outside effects that can disrupt a gravity detector’s accuracy, such as vibrations from seismic activity – to a level that is second only to gravitational wave detectors built on the kilometre scale.

One such detector is the Laser Interferometer Gravitational-Wave Observatory in the United States which uses mirrors spaced 4km (2.5 miles) apart to study the cosmos.

Meanwhile, the instrument built by the CAS team is about the size of an office cubicle.

Existing submarine detection methods – sonar, magnetic anomaly detection, and radar – can be evaded.

However, gravity cannot be masked.

Previous research suggests that gravity-based detection of the US Navy’s Ohio-class nuclear submarines is feasible.

While CAS’ new instrument does not yet reach the sensitivity level that the research estimated would be necessary for finding submarines, it is a step towards that capability.

However, images released with the report show the instrument was not placed in a highly controlled laboratory setting, suggesting its practical use in what the researchers describe as “normal environments”.

The project, known as superconducting weak force measurement, cleverly uses the Meissner effect: when cooled below a critical temperature, a superconductor expels magnetic fields and therefore repels nearby magnets.

Using this, the scientists suspend an object with a known mass within a magnetic field, eliminating all friction.

The system also relies on the SQUID, the world’s most sensitive kind of magnetic sensor.

When an external force, like gravity, moves the suspended object, the SQUID accurately measures the resulting electrical signal.

In simple terms, the superconducting suspension makes the suspended object highly sensitive to any e

原文链接: 南华早报