We have designed and constructed a magnetic gradiometer for underwater mine detection, location and tracking. The United States Naval Surface Warfare Center (NSWC PC) in Panama City, FL has conducted sea tests of the system using an unmanned underwater vehicle (UUV). The Real-Time Tracking Gradiometer (RTG) measures the magnetic field gradients caused by the presence of a mine in the Earth's magnetic field. These magnetic gradients can then be used to detect and locate a target with the UUV in motion. Such a platform can also be used for other applications, including the detection and tracking of vessels and divers for homeland (e.g., port) security and the detection of underwater pipelines. Data acquired by the RTG in sea tests is presented in this paper.
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.
Conventional concealed weapons detection portals, deployed worlwide at airports, governent buildings, courthouses, and other security critical facilities, are challenged by today's need for stringent and effective entry point screening. Modern threats, like exotic lightweight handguns, are becoming increasingly difficult to detect. Conventional portals do little, if anything, to assist security personnel in resolving the true nature of a potential threat. Systems that rely on blind operator intervention for alarm resolution invite too much human error so security is ultimately compromised. These systems do not instill confidence in the operator or the general public and thus do not present the necessary deterrent to those with sinister intent. Increased detection and improved discrimination do not adequately advance the utility of these security tools. High precision alarm object location information presented to the operator will result in the rapid resolution of the potential threat. Providing this information to the person under scrutiny via a static or streaming video image can enable self-divesting of the offending item without the need for security personnel intervention. Robust detection, effective discrimination, and precise object location information will result in superior entry point screening operations.
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.
KEYWORDS: Sensors, Target detection, Magnetism, Magnetic tracking, Magnetic sensors, Electromagnetism, Signal detection, Signal processing, Inspection, Submerged target detection
Passive magnetic measurements may be used to determine the azimuth, bearing and range to the target in real time using suitable signal processing without illuminating the target. Collision and even close approach must be avoided for classes of targets such as proximity fuzed mines. This paper describes a simple safety algorithm that monitors data from such a tensor magnetometer system and overrides the normal autopilot to ensure a minimum radius is always maintained
from all magnetic targets encountered.
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.
KEYWORDS: Magnetism, Sensors, Magnetic sensors, Unmanned aerial vehicles, Transducers, Interference (communication), Signal detection, Magnetic tracking, Data modeling, Computer simulations
Tensor magnetic gradiometry reports accurate direction and approximate range to an UXO using a single point measurement. Instead of using a sparse grid of points, a UAV can fly a series of adjacent tracks and acquire the data needed to locate all items. Some recent modeling suggests that normal UAV flight speeds can achieve an area coverage rate of 15 acres/minute. This contrasts sharply with total field magnetic techniques that require a much denser grid of sensor tracks. Synthetic data from equivalent surface-based measurements and simulations of real time processing substantiate the models.
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.
An increasingly important need today is to guard against terrorist attacks at key locations such as airports and public buildings. Liquid explosives can avoid detection at security checkpoints by being concealed as beverages or other benign liquids. Magnetic resonance (MR) offers a safe, non-invasive technology for probing and classifying the liquid contents inside sealed non-metallic containers or packages. Quantum Magnetics has developed a Liquid Explosives Screening System or `Bottle Scanner' to screen for liquid explosives and flammables, described at an earlier SPIE conference in 1996. Since then, the Bottle Scanner's performance has been significantly improved by the incorporation of neural network-based liquid classification. Recently we have shown that the incorporation of additional discrimination parameters can further enhance liquid classification. In addition to screening for explosives and flammables, the Bottle Scanner can be effective against chemical agents, many of which contain fluorine or phosphorous, both of which have MR signatures. Finally, we have evidence that the Bottle Scanner may also be able to detect narcotics dissolved in beverages, one of the methods used to smuggle narcotics across international borders. The development of the Bottle Scanner has been funded by the Federal Aviation Administration.
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.
KEYWORDS: Magnetism, Sensors, Magnetic sensors, Computing systems, Magnetometers, Electronics, Signal processing, Digital signal processing, Head, Signal detection
In Phase II of a Small Business Innovation Research contract funded through the Office of Secretary of Defense, Quantum Magnetics has developed a fieldable room-temperature gradiometer (RTG). The RTG affords unprecedented dynamic range that enables detection of signals near fluxgate sensor noise (approximately 5 pT/Hz1/2 at 1 Hz while the system is in motion in the earth's field (approximately 5 X 107 pT). To achieve this sensitivity when the RTG is integrated with an autonomous underwater vehicle (AUV), the magnetic interference generated by magnetic sources onboard the AUV must be removed. Direct magnetic feedback or signal processing using both ancillary sensors and a priori information about the interfering sources can be used to recover the baseline sensitivity of the RTG.
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.
Nuclear Quadrupole Resonance (NQR) combines the compound specific detection capability offered by chemical offered by chemical detection techniques with the spatial coating capability and convenience of an induction coil metal detector. In this paper we present the first results of the detection of TNT by NQR with sufficient for detection of many antipersonnel mines and essentially all antitank mines. In addition, we review the result of a blind in-field demonstration of the system in detecting RDX in which 28 out of 31 RDX-only targets were found with 1 false alarm in a 110 m test lane, and a second test in which 21 out of 21 RDX mines were found with zero false alarms at a clearance rate of 1.1 m2 per minute.
KEYWORDS: Magnetism, Sensors, Electronics, Navigation systems, Magnetic sensors, Prototyping, Global Positioning System, Naval mines, Data acquisition, Algorithm development
In Phase II of a Small Business Innovation Research (SBIR) contract funded through the Office of Secretary of Defense (OSD), Quantum Magnetics is developing a fieldable room- temperature gradiometer (RTG). The RTG uses 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 fluxgate sensor noise while the system is in motion int eh earth's field. Sensor enhancements undertaken in this Phase II program include: incorporation of ancillary sensors to enable gradiometer balancing in the presence of ambient field gradients; improved feedback linearity and use of a wideband reference fluxgate sensor to reduce motion noise; and improved filter matching between channels. Operational developments in progress include reduction of the sensor electronics package for man-portability and implementation of real-time operating and target localizing software. The Phase II system will be used for land-based operations to locate unexploded ordnance, and the sensor is being integrated with differential global position satellite navigation to locate targets in geographical coordinates. Separately funded programs will adapt the RTG for use by divers or AUVs in finding naval mines and obstacles.
KEYWORDS: Sensors, Magnetism, Prototyping, Magnetic sensors, Global Positioning System, Antennas, Algorithm development, Magnetometers, Signal detection, Navigation systems
The SBIR Phase I room temperature gradiometer localizer produced by Quantum Magnetics was received and evaluated in late summer of 1997. While still based on IBM's innovative three-sensor gradiometer (TSG), its performance was greatly improved over the original IBM prototype that was evaluated and reported several years prior. This system shows great promise both as a land based ordnance localizer as well as an underwater mine locator for diver or Autonomous Underwater Vehicle applications. The locating software induced both Frahm-Wynn and the newer 'Magnetic and Acoustic Detection of Mines' algorithms, both of which were evaluated against a variety of ordnance type targets. The TSG configuration affords unprecedented dynamic range that enables detection of signals at the fluxgate sensor noise while the system is in motion in the earth's field. Evaluation of the prototype revealed the need for additional positional sensor to enable more precise balancing and localization. Auxiliary sensors investigated were differential Global Positioning System and accelerometers. Localization software incorporating these sensors is reported elsewhere.
Ultrasonic inspection methods are often used to detect defects in ferrous and non-ferrous metal casting processes. The finite sensor recovery time following emission of the ultrasonic pulse leads to a 'shadow zone', from the surface to a depth of about 1 cm, that cannot be probed by ultrasonics. Conventional eddy current methods, operating at frequencies of several kHz or higher, can only detect surface-breaking flaws. Giant Magneto-REsistive and Anisotropic Magneto-Resistive sensors offer their full performance independently of frequency from 100kHz down to DC. This allows eddy current-based technique to prove ferrous materials deeper than heretofore, and thus to provide coverage through the shadow zone. The work presented here demonstrate the performance and sensitivity that can be achieved. The separation of eddy current and ferromagnetic signals allows the structure to be probed and the material properties to be imaged. We have detected artificial defects in ferrous steel samples to a depth of 1 cm as well as surface flaws smaller than those found by conventional eddy current methods. We also show results of probing a cast and rolled steel sample with real defects, where a band of presumed subsurface ferromagnetic inclusions masks the signal from tight surface cracks.
Nuclear Quadrupole Resonance (NQR) combines the compound specific detection capability offered by chemical detection techniques with the spatial localization capability and convenience of an induction coil metal detector. In the 16 years since NQR was last applied to mine detection in the U.S., there has been considerable improvement in the basic techniques. This paper reviews the progress achieved under a recent initiative to detect landmines by NQR. Two basic technical developments are summarized: the design of a detection coil suitable for probing the ground for landmines buried at typical depths, and an increase in the NQR signal obtained from the explosive TNT. In addition, we report the sensitivity of an NQR detection system to detect the electromagnetic response of metal-cased landmines.
A metallic mine detector is one of the most effective pieces of equipment for detection of mines. Their main drawback is their extremely rate of up to 100 percent, but it can also produce a high false alarm rate in many environments. The high false alarm rate reduces the usefulness of the metal detector in the field. In order to keep a high detection rate with fewer false alarms, object/mine characterization or identification must be used. Several techniques have been implemented to reduce the false alarm rate of metal detectors. They are size discrimination, target imaging, and target signatures such as dipole moment characterization. These techniques are applied for large metallic objects/mines. P.V. Czipott and D.A. Waldron each used separate techniques to characterize smaller metallic objects and some anti-personnel mines, in work supported by US Army CECOM, Night Vision and Electronic Sensors Directorate. Dr. Czipott characterized objects/mines by measuring the frequency dependence of magnetic fields caused by electric currents induced in the target. The frequency responses were measured by using a fixture incorporating a solenoid excitation coil, a receiving coil wound as a gradiometer, and a HP 4195A network/spectrum analyzer. Ms. Waldron characterized small objects with different conductivities and orientations by measuring their phase differences using a search head with one transmitter and four receiver coils and a phase-lock analyzer. We believe that target discrimination and identification are the keys to reduce false alarm rates of metallic mine detectors. Thus, we continue to analyze and characterize small metallic targets/mines using a variety of methods.
Sankaran Kumar, W. Casey McMichael, Y.-W. Kim, Alan Sheldon, Erik Magnuson, L. Ficke, T. Chhoa, C. Moeller, Geoffrey Barrall, Lowell Burnett, Peter Czipott, J. Pence, David Skvoretz
A particularly disturbing development affecting transportation safety and security is the increasing use of terrorist devices which avoid detection by conventional means through the use of liquid explosives and flammables. The hazardous materials are generally hidden in wine or liquor bottles that cannot be opened routinely for inspection. This problem was highlighted by the liquid explosives threat which disrupted air traffic between the US an the Far East for an extended period in 1995. Quantum Magnetics has developed a Liquid Explosives Screening systems capable of scanning unopened bottles for liquid explosives. The system can be operated to detect specific explosives directly or to verify the labeled or bar-coded contents of the container. In this system, magnetic resonance (MR) is used to interrogate the liquid. MR produces an extremely rich data set and many characteristics of the MR response can be determined simultaneously. As a result, multiple MR signatures can be defined for any given set of liquids, and the signature complexity then selected according to the level of threat. The Quantum Magnetics Liquid Explosives Screening System is currently operational. Following extensive laboratory testing, a field trial of the system was carried out at the Los Angeles International Airport.
Magnetic sensors have been the sensor of choice in the detection and classification of buried mines and unexploded ordnance (UXO), both on land and underwater, Quantum Magnetics (QM), together with its research partner IBM, have developed a variety of advanced, very high sensitivity superconducting and room temperature magnetic sensors to meet military needs. This work has led to the development and utilization of a three-sensor gradiometer (TSG) patented by IBM, which cannot only detect, but also localize mines and ordnance. QM is also working with IBM and the U.S. Navy to develop an advanced superconducting gradiometer for buried underwater mine detection. The ability to both detect and classify buried non-metallic mines is virtually impossible with existing magnetic sensors. To solve this problem, Quantum Magnetics, building on work of the Naval Research Laboratory (NRL), is pioneering work in the development of quadrupole resonance (QR) methods which can be used to detect the explosive material directly. Based on recent laboratory work done at QM and previous work done in the U.S., Russia and the United Kingdom, we are confident that QR can be effectively applied to the non-metallic mine identification problem.
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