KEYWORDS: Sensors, Target detection, Electromagnetic coupling, Metals, Land mines, Data acquisition, Mining, Calibration, Prototyping, Signal to noise ratio
Last year, we reported on a preliminary evaluation of GE’s frequency-domain EMI prototype sensor capable of measuring the wideband response of simulant and inert low metal mines at shallow depths over a frequency range from 100 Hz to 150 kHz. Since then, the prototype sensor has undergone further power and sensitivity improvements and has been taken to the field to collect signature data on targets in a calibration grid located at an Army facility in Virginia. The frequency-domain EMI responses have been analyzed by Duke University utilizing matched subspace detector (MSD) processing. The limited amount of data collected, so far, suggests that MSD processing of the frequency-domain data is a robust technique for target detection and identification. However, more data need to be collected for robust testing.
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.
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.
KEYWORDS: Sensors, Magnetic sensors, Detection and tracking algorithms, Magnetic tracking, Magnetism, Target detection, Data communications, Calibration, Weapons, Data conversion
Magnetic sensors are unaffected by rolling terrain, by vegetation and
by weather phenomena, so provide a consistent and predictable performance. Most magnetic tracking algorithms work best for a limited span of closest approach distances between the target and any sensor array node and have specific requirements in terms of the relative node placement. Unlike demonstration fields, where the nodes are carefully manually placed, proposed field deployment methods cannot reliably achieve specific spacings. We propose a novel algorithm that is insensitive to variations in spacing, thereby eliminating the limit on closest approach distances, so that the
sensor array can locally adapt the algorithm to the array configuration. This local adaptation also enables scalability for whole-array tracking.
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.
Magnetic sensors are able to detect, track and characterize
targets without line of sight, vegetation or weather constraints.
This paper discusses performance models, experimental data
and the capabilities of a specific magnetic sensor design.
These factors are combined to infer the operational parameters
of an effective future magnetic sensor array.
Blades, knives, handguns and vehicles are similar targets for magnetic tracking purposes, and their differences can be described parametrically. These parameters can be used for classification, and to model the performance of a sensor node being used for a proposed application. The scaling laws that relate these parameters to actual performance will be reviewed and applied to a real world example. This computed noise limit will be contrasted with the practical limit observed in those measurements.
KEYWORDS: Sensors, Magnetic sensors, Magnetism, Magnetic tracking, Target detection, Surveillance, Digital electronics, Acoustics, Infrared technology, Algorithm development
The development of magnetic sensors for the detection, localization, and classification of time-critical targets is of great importance in monitoring, surveillance, intelligence, and security applications. This is particularly true for the military where precision targeting of armed enemy troops, tracked and wheeled vehicles requires timely updates of their movements. To address this need, Quantum Magnetics (QM) is developing small, low power, low cost magnetic sensor modules, and high performance digital electronics that can be used to passively detect magnetic anomalies in the battlefield generated by the presence and movement of armed troops and military vehicles. The focus is on Magneto-Resistive (MR) sensors that can be fabricated by microelectronics techniques. These sensors represent a mature technology and are widely available commercially. They operate at room temperature with high sensitivity and have a broad bandwidth. The long-term vision is to integrate these modules into a network of battlefield microsensors that include a variety of other sensing technologies (acoustic, seismic, IR, etc.). We will discuss MR system design considerations and results obtained in recent field tests. A highly sensitive magnetic sensor module would also find numerous applications in security operations and surveillance of perimeters and borders, landmine/UXO detection, and detection of concealed weapons.
Quantum Magnetics (QM) has developed a sensing array using small and lightweight magnetoresistive (MR) sensors. These sensors, which operate at room temperature with high sensitivity and wide bandwidth, provide new operational performance capabilities. The wide bandwidth makes them ideal for both passive and active detection techniques. Using a DSP-based electronics developed by QM, we have been able to operate these sensors with an unprecedented noise performance at low frequencies. Recent tests using an MR room temperature gradiometer show that its resolution equals that of a fluxgate room-temperature gradiometer we have previously developed. These results represent an important development for both attended and unattended ground sensor applications since MR sensors cost about ten times less than fluxgate sensors.
KEYWORDS: Sensors, Magnetism, Magnetic sensors, Digital signal processing, Signal detection, Unattended ground sensors, Target detection, Calibration, Unmanned aerial vehicles, Analog electronics
Under funding from the Air Force Research Laboratory at Hanscom Air Force Base, Quantum Magnetics has been developing a room temperature, multi-axis magnetic gradiometer for the detection and characterization of underground structures. The gradiometer uses small, inexpensive, but highly sensitive magnetoresistive sensors operating with a flat frequency response from DC to several MHz and employs an innovative sensor configuration; called the three-sensor gradiometer (TSG) invented at IBM. The TSG affords unprecedented dynamic range that enables detection of signals near the sensor noise floor even when the system is in motion in the earth's field. The wideband response and high sensitivity of these sensors make them ideal for both passive and active detection techniques. A single sensor can detect perturbations in the earth's magnetic field from ferrous materials used in the construction of the structure, emissions at power and mechanical frequencies from equipment within the structure, and eddy currents in metallic materials within the structure induced by externally applied probe signals. These complimentary data sets can be combined in a sensor fusion scheme to minimize sensor clutter and discriminate against false targets. The sensing technology under development supports deployment by way of unattended ground sensors as well low-flying unmanned aerial vehicles.
We have developed a low frequency electromagnetic technique using sensitive room temperature magnetoresistive (MR) sensors for a variety of nondestructive evaluation (NDE) applications. These applications include the NDE of medical implants and aircraft structures, the detection of cracks and corrosion in metals, the detection of ferromagnetic foreign objects in the eye and the brain, and the noninvasive determination of iron content in the liver. Our technique consists of applying a low frequency ac magnetic field to the sample and detecting the sample response. The low excitation frequency enables us to probe deep into metal structures; the sensitivity of the MR sensor allows us to detect weak responses from the sample without applying too large an excitation field, particularly in the case of human tissue. The MR sensors are small and relatively inexpensive compared to other sensitive magnetic field sensors such as fluxgates and superconducting quantum interference devices or SQUIDs; hence the resulting NDE instrument will be compact and cost-efficient, enabling its commercialization for practical applications. In this paper, we focus primarily on NDE of orthopedic implants.
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