Innovative technology allows for navigation in areas where GPS can’t reach.
In a reported global first, researchers from the University of Tokyo have used superfast, subatomic particles known as muons to wirelessly navigate underground. The team utilized ground stations that detect muons, coordinating them with a subterranean muon-detecting receiver to pinpoint the receiver’s location in the basement of a six-story building.
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GPS, the global positioning system, is a well-established navigation tool and offers an extensive list of positive applications, from safer air travel to real-time location mapping. However, it has some limitations. GPS signals are weaker at higher latitudes and can be jammed or spoofed (where a counterfeit signal replaces an authentic one). Signals can also be reflected off surfaces like walls, interfered with by trees, and can’t pass through buildings, rocks, or water.
Muons exist for only 2.2 microseconds (one microsecond is just one-millionth of a second), but because they travel at the speed of light in a vacuum (300,000 kilometers per second), they have enough time to reach Earth from the atmosphere and penetrate deep into the ground. Credit: 2015 Hiroyuki K.M. Tanaka
By comparison, muons have been making headlines in recent years for their ability to help us look deep inside volcanoes, peek through pyramids, and see inside cyclones. Muons fall constantly and frequently around the world (about 10,000 per square meter per minute) and can’t be tampered with.
“Cosmic-ray muons fall equally across the Earth and always travel at the same speed regardless of what matter they traverse, penetrating even kilometers of rock,” explained Professor Hiroyuki Tanaka from Muographix at the University of Tokyo. “Now, by using muons, we have developed a new kind of GPS, which we have called the muometric positioning system (muPS), which works underground, indoors, and underwater.”
MuPS was initially created to help detect seafloor changes caused by underwater volcanoes or tectonic movement. It uses four muon-detecting reference stations aboveground to provide coordinates for a muon-detecting receiver underground. Early iterations of this technology required the receiver to be connected to a ground station by a wire, greatly restricting movement. However, this latest research uses high-precision quartz clocks to synchronize the ground stations with the receiver. The four parameters provided by the reference stations plus the synchronized clocks used to measure the muons’ “time-of-flight” enables the receiver’s coordinates to be determined. This new system is called the muometric wireless navigation system (MuWNS).
To test the navigation ability of MuWNS, reference detectors were placed on the sixth floor of a building while a “navigatee” took a receiver detector to the basement floor. They slowly walked up and down the corridors of the basement while holding the receiver. Rather than navigating in real time, measurements were taken and used to calculate their route and confirm the path they had taken.
“The current DOI: 10.1016/j.isci.2023.107000