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Military Program Produces Gadget That Detects Machinery from Behind a Concrete Wall

The device from U.K. researchers picks up the changing magnetic fields caused by electric motors, combustion engines, and fans—including the kind found inside computers.

The U.K.’s Defence Science and Technology Laboratory is based at a restricted military base in Porton Down, not far from the ancient monument of Stonehenge in southwest England. The DSTL is the research and development arm of the U.K.’s Ministry of Defence, and its job is to find innovative ways to use science and technology in the defense and security of the country.

Like many military R&D organizations, its job has changed in recent years as the threats facing developed nations have evolved. That’s why, in 2015, it launched an unusual research project called: “What’s inside that building?”

The goal of this project was to develop “novel techniques to remotely provide information about the layout and situation inside a building.” For example, revealing the internal structure of a building in preparation for entry (including walls, furniture, and electrical equipment), working out the number of people inside and what they are doing, detecting concealed manufacturing activity, and so on.

Now, two years on, what kind of novel technologies has this project produced?

Today we get an answer of sorts thanks to the work of Luca Marmugi and a few pals at University College London. Funded by the “What’s inside that building?” project, these guys have developed a portable gadget that can detect electric motors, combustion engines, turbines, air conditioning units, fans (including those inside computers), and so on. And do it all discreetly from behind a concrete wall. Indeed, the device can detect any piece of rotating machinery from a distance.

The principle behind the new gadget is simple. Any rotating metal generates a periodically changing magnetic field, albeit a small one. So all that’s needed is a device that can detect this changing field.

Marmugi and co show that an atomic magnetometer does the job exactly. The device consists of a cloud of rubidium atoms zapped by a laser to align their atomic spins with a constant magnetic field generated by the device.

Any external magnetic field that is changing will then cause the atomic spins to “nutate,” or nod like a spinning top. And this can be detected by the light the atoms emit.

The entire setup works at room temperature, requires no shielding, and is suitcase-sized, with the potential to be made significantly smaller.

Marmugi and co have put it through its paces by using it to detect rotating steel discs of various sizes, some as small as coins, and also to detect small AC and DC electric motors, like those that turn computer fans. They’ve done it at a range of frequencies and say their device is particularly good at low frequencies below 15 Hz that other approaches cannot reach. And they’ve shown they can do all this from behind a thick concrete wall containing pipes, wires, and so on.

The team is clearly impressed with this performance and say significant improvements will be easy to make. “Given the proof-of-principle nature of the present work and taking into consideration data reported in literature on atomic magnetometers, one can anticipate a great potential for a further increase in detection capability and range,” they say.

That’s interesting work with numerous applications. “The approach [is] suitable for harmless, noninvasive and nondisrupting remote sensing for security and surveillance, but also for continuous control of civil industrial processes and health and usage monitoring,” say Marmugi and co.

So the “What’s inside that building?” project has begun to produce results. We’ll keep an eye on future developments—if they are ever made public.

Ref: Remote Detection of Rotating Machinery with a Portable Atomic Magnetometer


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