Military forces conducting urban operations are in need of non-line-of-sight sensor technologies for enhanced situational awareness. Disposable sensors ought to be able to detect and track targets through walls and within rooms in a building and relay that information in real-time to the soldier. We have recently developed magnetic sensor nodes aimed towards low cost, small size, low power consumption, and wireless communication. The current design uses a three-axis thin-film magnetoresistive sensor for low bandwidth B-field monitoring of magnetic targets such as vehicles and weapons carried by personnel. These sensor nodes are battery operated and use IEEE 802.15.4 communication link for control and data transmission. Power consumption during signal acquisition and communication is approximately 300 mW per channel. We will present and discuss node array performance, future node development and sensor fusion concepts.
Magnetic sensors configured as a tensor magnetic gradiometer not only detect magnetic targets, but also determine their location and their magnetic moment. Magnetic moment information can be used to characterize and classify objects. Unexploded ordnance (UXO) and thus many types of improvised explosive device (IED) contain steel, and thus can be detected magnetically. Suitable unmanned aerial vehicle (UAV) platforms, both gliders and powered craft, can enable coverage of a search area much more rapidly than surveys using, for instance, total-field magnetometers. We present data from gradiometer passes over different shells using a gradiometer mounted on a moving cart. We also provide detection range and speed estimates for aerial detection by a UAV.
KEYWORDS: Magnetism, Sensors, Magnetic sensors, Signal detection, Sensor networks, Target detection, Digital signal processing, Prototyping, Logic devices, Telecommunications
Quantum Magnetics has developed an autonomous battery-powered magnetic sensor node for distributed wireless sensor networks. The device digitizes the sensor output signals and transmits data over an RF link using a ZigBee 802.15.4 protocol. The prototype node incorporates Magneto-Resistive (MR) chips configured to measure all three components of the magnetic field, a logic device, analog-to-digital converters, a two-axis tilt sensor, a wireless transceiver, and a set of batteries. For use in outdoor environments, the sensor node is also GPS-ready. At present, the unit measures approximately 4 inches on a side, with about 40% of the volume occupied by the batteries. Using battery power, the node can operate for about 10 hours in a continuous mode and up to 40 hours with a 10% duty cycle. Efforts are underway to develop the next-generation magnetic node with significant reduction in size and part count.
Extensive studies of in-air testing of various metal detectors have been previously performed for a wide variety of targets and operating conditions. Using similar targets, we conducted a preliminary evaluation of a laboratory prototype wideband metal detector operating in the frequency domain (FD) under development at Quantum Magnetics. The wideband metal detector uses a small magnetoresistive (MR) sensor instead of an induction coil in the receive chain and can collect frequency response signatures of targets in the frequency band 100 Hz-150 kHz, thereby providing a more complete picture of a low metal mine response. These results suggest that wideband metal detection can play an important role in improving the false alarm rate (FAR) in a common detector platform by improving the amount of information provided to the fused algorithm process.
Using broadband magnetoresistive sensors, Quantum Magnetics is developing a metal detector for landmine/UXO detection and discrimination. When completed, this active system will be incorporated into a passive manportable gradiometer system being developed under funding from the Strategic Environmental Research and
Development Program. The resulting system will be a handheld passive/active magnetic tensor gradiometer detector capable of detecting, locating, and discrimination buried targets. In this paper, we discuss these developments and recent results.
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