Carl V. Nelson

Wide bandwidth time-domain electromagnetic sensor for metal target classification

A portable, wide bandwidth, time-domain electromagnetic sensor system has been developed and used extensively to measure the eddy current time-decay response of a wide variety of metal targets. The sensor has demonstrated the ability to measure metal target decay times starting approximately 3 to 5 /spl mu/s after the transmitter current is turned off and target decay time constants as short as 1.4 /spl mu/s. The sensor has demonstrated the potential for detecting very low-metal content mines due to the void they create in some types of electrically lossy soils. The development of the sensor is described in detail, and time-decay data are shown for a variety of metal targets, including low metal antitank and antipersonnel mines.

Wide-area metal detection system for crowd screening

Conventional metal detectors require people to walk through a door-like opening that houses the detection system. Typically, each person must be scanned individually. This creates a “choke point,” and long lines form at the screening point. This paper describes a metal detection sensor system that could screen large crowds of people more efficiently. The new system is called the Wide-Area Metal Detection (WAMD) sensor system. This sensor system is composed of a spatially distributed metal detector and a video surveillance system. The sensor system is designed to continually screen an area and reduce the need for each person to be examined separately.

A low-cost, expendable, helicopter-deployed buoy for ocean surface meteorological measurements

A low-cost, expendable, helicopter-deployed, wave-riding buoy is described that has been developed to measure meteorological properties at sea. The buoy weighs 8.2 kg and is 1.3-m long and 8.9 cm in diameter in its stored configuration. After deployment, the buoy extends a 2.5-m sensor mast above the water and a 3.8-m ballasted keel below the water. Buoyancy is provided by an inflated air bladder. An airsonde electronics package that measures relative humidity, barometric pressure, and air temperature transmits the data via a UHF transmitter to a receiver on a helicopter. The received data are displayed and recorded in the helicopter. The buoy is considered simple to construct, uses off-the-shelf hardware, and requires very few, easily machined components. >

Spatial scanning time-domain electromagnetic sensor: high spatial and time resolution signatures from metal targets and low-metal content land mines

This paper describes a spatial scanning time-domain electromagnetic induction (EMI) sensor and presents results from recent field experiments with buried metal and low-metal content (LMC) anti-personnel (AP) and anti-tank (AT) plastic-cased land mines. The EMI sensor is an modified version of the Electromagnetic Target Discriminator (ETD) sensor developed for the US Army CECOM/NVSED by the Johns Hopkins University Applied Physics Laboratory. The spatial scanning ETD sensor has demonstrated the ability to measure metal target decay times starting approximately 6 ms after the transmitter current is turned off and with metal target decay time constants as short as 1 ms. The sensor antenna sweeps 80 cm over a target area and makes time-decay measurements at 14.5 mm intervals. In addition to metal target signatures, the paper describes coincident void and metal signatures from LMC land mines. The detection of coincident void and metal signatures is shown to be an important classification technique for LMC land mines.

Low-cost backpack-portable robot system for mine and UXO detection and identification

The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has developed a prototype backpack-portable robot system for mine and unexploded ordnance (UXO) detection and identification. The robot system is compact, lightweight and is estimated to be inexpensive to construct. The robot has been designed with an inexpensive, highly accurate, wide bandwidth time-domain electromagnetic induction (EMI) sensor for the detection and identification of metal components in mines and UXO. The robot can be configured for autonomous or person-in-the-loop control. The robot system can be configured with additional light-weight and low-cost mine and UXO sensors such as ground penetrating radar (GPR) and chemical explosive detectors.

Wide-bandwidth time decay responses from low-metal mines and ground voids

This paper presents wide bandwidth, time decay responses from low metal content (LMC) mines, LMC mine simulates, and ground voids. Measurements were collected both in the laboratory and in the field. The target time decay responses were measured with the Johns Hopkins University Applied Physics Laboratory developed Electromagnetic Target Discriminator (ETD) sensor developed for the US Army CECOM/NVSED. The ETD sensor has demonstrated the ability to measure metal target decay times starting approximately 3 to 5)mus after the transmitter current is turned off and metal target decay time constants as short as 1.4)mus.

Development and testing of a magnetic position sensor system for automotive and avionics applications

A magnetic sensor system has been developed to measure the 3-D location and orientation of a rigid body relative to an array of magnetic dipole transmitters. A generalized solution to the measurement problem has been formulated, allowing the transmitter and receiver parameters (position, orientation, number, etc.) to be optimized for various applications. Additionally, the method of images has been used to mitigate the impact of metallic materials in close proximity to the sensor. The resulting system allows precise tracking of high-speed motion in confined metal environments. The sensor system was recently configured and tested as an abdomen displacement sensor for an automobile crash-test dummy. The test results indicate a positional accuracy of approximately 1 mm rms during 20 m/s motions. The dynamic test results also confirmed earlier covariance model predictions, which were used to optimize the sensor geometry. A covariance analysis was performed to evaluate the applicability of this magnetic position system for tracking a pilots head motion inside an aircraft cockpit. Realistic design parameters indicate that a robust tracking system, consisting of lightweight pickup coils mounted on a pilots helmet, and an array of transmitter coils distributed throughout a cockpit, is feasible. Recent test and covariance results are presented.

Horizontal electromagnetic field sensor for detection and classification of metal targets

This paper describes a prototype electromagnetic induction (EMI) sensor system designed specifically to measure the horizontal component of a metal targets eddy current time decay signature. Instead of creating a vertical magnetic field from a horizontal loop transmitter configuration used by most EMI metal detectors, the prototype transmitter geometry has been designed especially for creating a horizontal magneti field (HMF). One of the potential advantages of the HMF sensor is the relatively uniform magnetic field that is created over a large volume. A second potential advantage is that, compared to a conventional loop antenna, the magnetic field intensity falls off slowly with distance from the plane of the sensor. These two advantages potentially make the HMF sensor well suited for detection and classification of metal targets buried deeply in the ground (e.b., unexploded ordnance, UXO) or from a vehicle-mounted mine detector sensor. Preliminary modeling of the antenna and laboratory data from a time-domain version of the HMF sensor are presented.

Investigation of the electromagnetic induction spatial response of two closely spaced targets

Current state-of-the-art electromagnetic induction (EMI) metal detector research systems have shown the potential to detect low metal content buried targets as well as discriminate the type of target as a mine or clutter. However, further research is needed to investigate metal target discrimination potential for closely spaced metal targets. A series of experiments designed to investigate the spatial and time decay responses of multiple metal targets were conducted using a spatial scanning, time-domain EMI metal detector. Time decay signatures were taken of two calibration targets placed over varying distances with the objective of analyzing target identification and spatial resolution. This paper presents results of these experiments.

Eyesafe laser-illuminated tripwire (ELIT) detector

The technical issues of a standoff electro-optic tripwire detector are discussed. Significant advances in short-wave infrared (SWIR) laser diodes and InGaAs detector technologies have made it possible for the demonstration of a passive and active eyesafe (1.5 micron) laser illuminated tripwire (ELIT) detector. The demonstrated system utilizes COTS laser diodes and cameras. The Hough Transform was used for the detection of tripwires in images. System trade-offs are discussed and images are shown.