Abstract
Tripwire-operated landmines form a major hazard to deminers, especially where the wire is concealed invegetation which the deminer has to clear. It may be possible to detect the landmine by sensing the tripwire.Several sensing technologies such as acoustic, thermal imaging, and electromagnetic sensors, are considered aspossible candidates for tripwire detection. Strengths and weaknesses of the various sensing technologies areidentified in order to provide options for developing a reliable, small, inexpensive and long range detector whichcan find tripwires completely concealed in vegetation. Two possible tripwire detection methods have beenidentified for further investigation.
Keywords: bounding fragmentation mine, tripwire detection, electromagnetic induction, radar, acoustic
1 Introduction
Landmines are concealed explosive devices whichremain dangerous even after fighting has ended. Theycause injuries to civilians, and economic hardship toaffected communities by denying access to land.More than 70 countries have a landmine problem, andperhaps more than 70 million mines remain in theground. More than 15,000 casualties are reported eachyear [1]. Minefields are gradually being cleared byteams of deminers. A major hazard to such teams isthe bounding fragmentation mine, which is normallytripwire-operated and typically explodes at waistheight, sending out metal fragments at ballisticspeeds. A typical device will have a killing radius ofmore than 20 metres. The deminer is most at riskwhen clearing vegetation, within which a tripwiremay be concealed. A portable tripwire-sensing devicewould be an invaluable tool for the deminer. Thispaper considers some sensing technologies as possiblecandidates for such a device, and identifies two whichappear to be worthy of further investigation
2 Possible Detection Methods
A method used for tripwire detection is a tripwirefeeler, which is a thin stick that is held lightly at thefingers to sense the bouncing caused by the tripwire.However this method is often found to be impracticalwhen tripwires are concealed in vegetation, and thedeminer may be reduced to visual inspection. Thissection discusses and evaluates some possiblealternative sensing technologies for tripwire detection,including radar, thermal imaging, electromagneticinduction, and acoustic and vibration sensors.
2.1 Radar
Potentially, radar can detect tripwires by sensing echoreturns from a tripwire target. By analysing thereflected signal, the position of the tripwire can bedetermined. The different types of radar includecontinuous wave radar (CW), pulse radar, frequency -modulated continuous wave radar (FMCW), ultrawideband radar (UWB) and millimetre wave radar(MMW).
2.1.1 FMCW Radar
This is an extension of continuous wave radar, whichtransmits a continuous wave at fixed frequency.FMCW radar broadens the transmitted spectrum forbetter resolution by frequency-modulating the carrier[2]. A continuous signal is transmitted, and thisvaries with frequency over time. This allows thesystem to sweep a particular range of frequency,which may be an advantage over the single frequencyoperation in continuous wave radar. By measuring thedifference of frequency between the instantaneoustransmitted signal and the received signal from thetarget, a beat frequency is obtained which gives anindication of the range of the target. Li (1999) hasevaluated FMCW radar for landmine detection [3]. Ingeneral the bandwidth and hence resolution arelimited by the antenna [6].
2.1.2 UWB Radar
UWB radar systems have also been evaluated forlandmine detection [4]. Typically a very short pulse isused, which occupies a wide bandwidth. This cancombine good ground-penetrating ability with goodtarget resolution. However, UWB radar facilitiestypically use large, wideband antennas and do notcurrently lend themselves easily to tripwire detectionin minefields.


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