Novel landmine detectors based on nuclear magnetic resonance (NMR) have passed their first field-trial tests. Built by the Sydney-based company mRead, the devices could speed up the removal of explosives in former war zones. The company tested its prototype detectors in Angola late last year, finding that they could reliably sense explosives buried up to 15 cm underground — the typical depth of a deployed landmine.
Landmines are a problem in many countries recovering from armed conflict. According to NATO, some 110 million landmines are located in 70 countries worldwide including Cambodia and Bosnia despite conflict ending in both nations decades ago. Ukraine is currently the world’s most mine-infested country, making vast swathes of Ukraine’s agricultural land potentially unusable for decades.
Such landmines also continue to kill innocent civilians. According to the Landmine and Cluster Munition Monitor, nearly 2000 people died from landmine incidents in 2023 – double the number compared to 2022 – and a further 3660 were injured. Over 80% of the casualties were civilians, with children accounting for 37% of deaths.
Humanitarian “deminers”, who are trying to remove these explosives, currently inspect suspected minefields with hand-held metal detectors. These devices use magnetic induction coils that respond to the metal components present in landmines. Unfortunately, they react to every random piece of metal and shrapnel in the soil, leading to high rates of false positives.
“It’s not unreasonable with a metal detector to see 100 false alarms for every mine that you clear,” says Matthew Abercrombie, research and development officer at the HALO Trust, a de-mining charity. “Each of these false alarms, you still have to investigate as if it were a mine.” But for every mine excavated, about 50 hours is wasted on excavating false positives, meaning that clearing a single minefield could take months or years.
“Landmines make time stand still,” adds HALO Trust research officer Ronan Shenhav. “They can lie silent and invisible in the ground for decades. Once disturbed they kill and maim civilians, as well as valuable livestock, preventing access to schools, roads, and prime agricultural land.”
Hope for the future
One alternative landmine-detecting technology option is NMR, which is already widely used to look for underground mineral resources and scan for drugs at airports. NMR results in nuclei inside atoms emitting a weak electromagnetic signal in the presence of a strong constant magnetic field and a weak oscillating field. As the frequency of the signal depends on the molecule’s structure, every chemical compound has a specific electromagnetic fingerprint.
The problem with using it to sniff out landmines is pervasive environmental radio noise, with the electromagnetic signal emitted by the excited molecules being 16 orders of magnitude weaker than that used to trigger the effect. Digital radio transmission, electricity generators and industrial infrastructure all produce noise of the same frequency as the one the detectors are listening for. Even thunderstorms trigger such a radio hum that can spread across vast distances.
“It’s easier to listen to the Big Bang at the edge of the Universe,” says Nick Cutmore, chief technology officer at mRead. “Because the signal is so small, every interference stops you. That stopped a lot of practical applications of this technique in the past.” Cutmore is part of a team that has been trying to cut the effects of noise since the early 2000s, eventually finding a way to filter out this persistent crackle through a proprietary sensor design.
MRead’s handheld detectors emit radio pulses at frequencies between 0.5 and 5 MHz, which are much higher than the kilohertz-range frequencies used by conventional metal detectors. The signal elicits the magnetic resonance response in atoms of sodium, potassium and chlorine, which are commonly found in explosives. A sensor inside the detector “listens out” for the particular fingerprint signal, locating a forgotten mine more precisely than is possible with conventional metal detectors.
With over two million landmines laid in Ukraine since 2022, landmine clearance needs to be faster, safer, and smarter
James Cowan
Given that the detected signal is so small, it has be amplified, but this resulted in adding noise. The company says it has found a way to make sure the electronics in the detector do not exacerbate the problem. “Our current handheld system only consumes 40 to 50 W when operating,” says Cutmore. “Previous systems have sometimes operated at a few kilowatts, making them power-hungry and bulky.”
Having tested the prototype detectors in a simulated minefield in Australia in August 2024, mRead engineers have now deployed them in minefields in Angola in cooperation with the HALO Trust. As the detectors respond directly to the explosive substance, they almost eliminated false positives completely, allowing deminers to double-check locations flagged by metal detectors before time-consuming digging took place.
During the three-week trial, the researchers also detected mines that had a low content of metal, which is difficult to spot with metal detectors.“Instead of doing 1000 metal detections and finding one mine, we can isolate those detections and very quickly before people start digging,” says Cutmore.
Researchers at mRead plan to return to Angola later this year for further tests. They also want to finetune their prototypes and begin working on devices that could be produced commercially. “I am tremendously excited by the results of these trials,” says James Cowan, chief executive officer of the HALO Trust. “With over two million landmines laid in Ukraine since 2022, landmine clearance needs to be faster, safer, and smarter.”
