The sensors respond as soon as someone attempts to climb or breach the fence, providing information on the precise location of the security gap. They can even detect a low-flying drone passing overhead. The thin cable containing the magnetic field sensors can be easily installed on perimeter fences of all types.
The research team is currently working on developing a system that can recognize the cause of a disturbance and automatically identify false alarms triggered by wind or animals. The team is collaborating with industry partners to produce a cable suitable for mass production.
If someone tries to tamper with a fence, or attempts to climb over it or cut it with bolt cutters, they will inevitably cause a vibrational disturbance. The back-and-forth movement of the metal fence, the movement of the metal cutters, or even the intruder's belt will all influence the Earth's magnetic field. These changes are being exploited by a team of experimental physicists at Saarland University for a new type of surveillance technology. "Our magnetometers (magnetic field sensors) are very sensitive and can reliably measure even the smallest changes in the ambient magnetic field," explained Professor Uwe Hartmann. The sensors are even capable of detecting when a drone flies low overhead—provided, of course, that the drone contains metal. "The sensors can detect alterations in the surrounding magnetic field, including the magnetic field directly above them, with a range extending several meters," adds research assistant Haibin Gao, who is working on the sensor technology as part of Hartmann's team.
The cable, which contains the linearly arranged sensors, has a diameter comparable to a standard electrical cable and allows for remote monitoring of kilometers of perimeter fencing. The cable can be attached to the fence, embedded in it, or even buried beneath it. “We are currently working with several companies to reduce the size of the system and, most importantly, to reduce the production cost of the sensors to a level where large-scale production is feasible,” says Uwe Hartmann. The contactless sensors are not subject to wear and tear and have low power consumption. They are unaffected by rain or fog. “The sensors operate regardless of the weather, and this gives them a significant advantage over other surveillance techniques, such as cameras, where humidity is often an issue. And the measurements are not problematic from a privacy standpoint. The sensors simply report that a vibration disturbance was caused by a human agent in a specific location. No other information is collected,” explains Professor Hartmann. Different types of sensor systems developed by his research group have already been deployed in traffic management systems, for example, at airports.
The miniature sensors on the cable are networked, and any changes they detect are immediately transmitted to the analysis unit. The location of the disturbance can be specified with high precision, which is invaluable, particularly when monitoring very large areas. The scientists on Hartmann's team are working on refining the technology so that the sensors can unambiguously assign a particular type of vibration or a specific change in the measured magnetic field to a particular type of disturbance. "The goal is to develop a system that can automatically identify false alarms triggered by wind, animals, or some other harmless cause," explains Hartmann. To this end, the researchers are simulating different types of disturbances. A series of fences on the Saarbrücken campus are currently undergoing long-term monitoring to determine how the system is affected by factors such as wind. This field data is used by physicists to model typical disturbance scenarios and to train the system using complex mathematical methods. The results are used to program the sensors and the analyzer unit. The new information allows the analyzer to automatically attribute a disturbance to a particular cause. If the cause is identified as human, an alarm is triggered; if the disturbance was due to animals rubbing against the fence, the alarm is not triggered.
