Dual mode detectors combining metal detection and ground-penetrating radar are increasingly being used during humanitarian demining operations because of their ability to discriminate metal clutter. There are many reports in the academic literature studying metal detector and ground-penetrating radar systems individually. However, the combination of these techniques has received much less attention. This paper describes the development of a novel dual modality landmine detector, which integrates spectroscopic metal detection with ground-penetrating radar. This paper presents a feature-level sensor fusion strategy based on three features extracted from the two sensors. This paper shows how the data from the two components can be fused together to enrich the feedback to the operator. The algorithms presented in this paper are targeted at automating the location of buried, visibly obscured objects; however, the system described is also capable of collecting information which could also be used for the potential classification of such items.

The performance of very short-range radar systems, such as ground penetrating radar for antipersonnel landmine detection, is critically dependent on the impulse characteristics of the antennas that are used. Typically, a pair of individual antennas is used in the radar, one for transmit and one for receive. These antennas are usually closely spaced for reasons of both portability and close in detectability. A variety of design techniques are used to achieve their wideband performance in terms of return loss, isolation, radiation patterns, polarization, and impulse formation. Not only the antenna elements but also their surrounds form the overall antenna structure and this ensemble becomes integral to the antenna performance and design process. Both the antenna and the surrounding structure can create late time signals or time sidelobes, which are in effect a form of self-generated clutter. Minimizing the duration of the antenna impulse response assists in reducing self-generated clutter and achieving optimum radar performance. This article considers the impact of the antenna on the system performance of the radar and shows that the clutter performance of the antenna can be the prime metric of system detection rather than the noise figure, given that the self-clutter often exceeds the latter.

The detection of small metallic objects buried in mineralized soil poses a challenge for metal detectors, especially when the response from the metallic objects is orders of magnitude below the response from the soil. This article describes a new, handheld, detector system based on magnetic induction spectroscopy (MIS), which can be used to detect buried metallic objects, even in challenging soil conditions. Experimental results consisting of 1669 passes across either buried objects or empty soil are presented. Fourteen objects were buried at three different depths in three types of soil including nonmineralized and mineralized soils. A novel processing algorithm is proposed to demonstrate how spectroscopy can be used to detect metallic objects in mineralized soils. The algorithm is robust across all types of soil, objects, and depths used in this experiment and achieves a true positive rate over 99% at a false-positive rate of less than 5%, based on just a single pass over the object. It has also been shown that the algorithm does not have to be trained separately for each soil type. The data gathered in the experiment are also published to enable more research on the processing algorithms for MIS-based detectors.

The Magnetic Polarizability Tensor (MPT) is a representative property of an electrically conducting or magnetic object that includes information about the object’s characteristics such as, shape, size and material. The MPT is especially relevant to metal detection (MD) and can be used to improve MD performance by helping to distinguish between objects. This paper describes an instrument intended to measure the MPT of objects such as anti-personnel landmines and metallic clutter, up to 130 mm in diameter. The instrument uses a novel multi-coil geometry to generate a uniform electromagnetic field over the volume containing the test object to accurately determine the MPT. Performance tests of the system shows peak variance in the MPT is approximately 15 mm ³ . Typical experimental repeatability is better than one percent for tests involving copper disks. Additionally, simulated data as well as previously published simulated and experimental data are used as a validation method of the experimental results. Good agreement between these and the measured MPTs of example targets are seen, proving the system’s capability of characterizing metallic objects.

Antennas are an important component in ground penetrating radar (GPR) systems. Although there has been much research reported on the design of individual antennas, there is less research reported on the design of the geometry of bi-static antennas. This paper considers the effects of key parameters in the setup of a GPR head consisting of a bi-static bow-tie pair to show the effect of these parameters on the GPR performance. The parameters investigated are the antenna separation, antenna height above the soil, and antenna input impedance. The investigation of the parameters was performed by simulation and measurements. It was found when the bi-static antennas were separated by 7 cm to 9 cm and were operated close to the soil (2 cm to 4 cm), the reflected signal from a near-surface object is relatively unaffected by height variation and object depth. An antenna input impedance of 250 Ω was chosen to feed the antennas to reduce the late-time ringing. Using these results, a new GPR system was designed and then evaluated at a test site near Benkovac, Croatia.

Microwave ultra-wideband technology has been widely adopted in instrumentation and measurement systems, including ground-penetrating radar (GPR) sensors. Baluns are essential components in these systems to feed balanced antennas from unbalanced feed cables. Baluns are typically introduced to avoid issues with return signals, asymmetrical radiation patterns and radiation from cables. In GPR systems, these issues can cause poor sensitivity due to a reduction in radiated power, blind spots due to changes in the radiation pattern and additional clutter from common mode radiation. The different balun technologies currently available exhibit a wide variation in performance characteristics such as insertion loss, reflection coefficient and phase balance, as well as physical properties such as size and manufacturability. In this study, the performance of two magnetic transformer baluns, two tapered microstrip baluns and an active balun based on high-speed amplifiers were investigated, all up to frequencies of 6 GHz. A radio frequency current probe was used to measure the common mode currents on the feed cables that occur with poor performing baluns. It was found that commercially available magnetic transformer baluns have the best phase linearity, while also having the highest insertion losses. The active balun design has the best reflection coefficient at low frequencies, while, at high frequencies, its performance is similar to the other baluns tested. It was found that the active balun had the lowest common mode current on the feed cables.