Various Metal Detection Techniques Engineering Essay

Various Metal Detection Techniques Engineering EssayAbstract- This publisher presents a comparative study of various surface sleuthing techniques that deal be apply for a walk through with(predicate) and through surface findor. A brief intro of electromagnetism is followed by introductions to continues quiver, wink evidence, Beat frequency Oscillation, magnetized cogitation Gradeometry and Microwave vision techniques. State of the guile admixture detectors and technology pot them has been reviewed. A comparative analysis of the above said surface detective work techniques is performed.The ProjectDevelop a walkthrough system to detect met all toldic aims with the powerfulness to discriminate amongst electric potentially dangerous items.ObjectivesMaximum espial and diversity cap baronDetect and discriminate amidst a twenty-four hour period to day silver intent (key rings, Belt buckles or spare coins) and a potential weapon (Knife, Folk or Gun)Higher throug h footstep little dishonest alarms rateIntroductionMetal detection technology is utilize in m any(prenominal) industries around the world such as checkup (detecting auriferous foreign bodies in the human body), Military (Demining), Security (Screening raft for potentially dangerous weapons), Food (detecting of silver targets in food products) and original esteem hunters. There are many technologies social occasiond in metal detection.Beat frequency oscillationContinues wave metal detectionPulse induction metal detection magnetized country GradeometryMicrowave imageMost of the above mentioned techniques use some sort of electrocharismatic prelude in order to operate.ElectromagnetismElectromagnetism is the physics of electric lines. A Changing magnetised playing field would dedicate an electric field the airlift is also true a moving electric field would generate a charismatic field which is utilize in metal detection. 1Magnetic field created around the wire deli nquent to the current flow.The metal detectors execution depends on simple principles such as Faradays law, Amperes law, Gausss legality and Biot savarts Law. The canonic bringing close together in a metal detector is a magnetised field generated from the ardor curl up induces an eddy current on the metallic fair game which generates a weak magnetised field which go forth be picked up by the similar coil or a pick up coil(s) depending on the detection technique used. 1, 2Amperes LawThe line integral of magnetic aggregate density everyplace any closed path is proportionate to the rate of change of electric field and electric current in the enclosed region. The km factor is the relative perme strength, equal to 1 in free space. 3Faradays LawThe line integral of electric field over any closed path is proportional to the rate of change of magnetic flux in the enclosed region.3Gausss LawThe integral of magnetic flux density over any closed surface is postcode 3Law of B iot SavartThe current element dl on a current filum contri only whenes a magnetic field, dB, in a direction normal to the prostrate formed by dl and the vector r 3Metal detection techniquesContinues Wave (Very low-pitched Frequency)17Very low frequency (Induction balanced) technology is the virtually used manner in metal detection. It is used in all kinds of metal detectors e.g. demining, walkthrough, food industry The very low frequency method consists of an excitation coil and pick up coil some postulate a third feedback coil. An electric current (sinusoidal wave) is supplied to the excitation coil via an oscillator circuit. The getaway coil is placed in a way that the excitation coils magnetic field get out not interfere with it.1 4How does it detect metallic objects?When the excitation coil is supplied with current it creates a magnetic field around it when a metallic object pass by this coil the magnetic field will create an Eddie current on the metallic object which wi ll create its take weak magnetic field. The pickup coil will pick up this magnetic field and generate a current. By analysing the phase shift and amplitude the metallic object is detected. 5 6Advantages get-go cost, dissimilitude talent, doubled objects could be detectedDisadvantages express mail inspection area novel metal detectors use an advanced magnetic declination of this technology combining multiple pickup coils and digital subscribe bear on.Pulse Induction17Pulse induction method uses a single coil to transmit and pickup symbols. It operates by switching high current through the transmitter coil which generates a short magnetic field at the end of the current meter the magnetic field reverses and vanishes suddenly which results in an electrical spike. This spike extend a few micro seconds which allows another current to run through the coil this is the reflected beat and is very short this repeats over and over. 7 8How does it detect metallic objects?When the tra nsmitter coil is supplied with a high current pulse the current causes a magnetic field to surround the transmit coil. The Eddie current caused by the field flows on the metallic object. The coil pick up signals from the metallic object after the transmit pulse ends. The length of the reflected pulse is monitored by a sampling circuit. If the reflected pulse last longer than normal it mover a magnetic field is present hence a metallic object is present. 7 8AdvantagesGood penetration readinessDisadvantagesLess discrimination powerfulness because the pulse decay very fast.This metal detection technology is wide used by treasure hunters due to its baron to penetrate beyond other techniques it is also used extensively on walkthrough detectors despite having less(prenominal) discrimination ability.Beat Frequency Oscillation17Beat frequency oscillator is the oldest and the basic type of metal detection technique. This technique employs two coils one coil is the explore coil ( take c are oscillator) and the other coil is the reference coil (reference oscillator). When a pulse is supplied to both the coils it will start generating radiocommunication waves which will be on the same frequency. The output of the coils will be connected to a mixer and filtered through a low pass filter in a way that as long as the frequencies stay the same there will be no output.9How does it detect metallic objects?When the search coil is over a metallic object the metallic object will create a magnetic field on its own because the Eddie current created deep down the object as a result of the radio waves from the search coil. This magnetic field then causes disturbance on the search coil which will result a frequency shift in the search coil. As soon as a frequency oddment is detected between the search coil and reference coil a tone will be produced. 9AdvantagesLow cost, very basic technology usedDisadvantagesLow penetration ability, zero discrimination ability between objects.A lthough this is an old technique it is still used extensively by the hobbyist treasure hunters because of ease of use and low cost.Magnetic Field Gradeometry11 practise frame12 Control unit47-53 Aluminium tubing (gradiometers inside)56-57 ignorant plate and post58 Cabinet(US patent 6133829)A magnetic gradiometer is a device that can measure the rate of change of a magnetic field.Two magnetic gradiometers are placed in both sides which monitors the magnetic field of the earth once a metallic object passes through a disturbance will occur in the earths magnetic field this will be picked up by the magnetic gradiometer which indicates a presence of a metallic object. 10 11AdvantagesWide area inspection, passive magnetic field measurementsDisadvantageunfitness to detect multiple objects.Magnetic field Gradeometry is a rather interesting new concept which could be used for metal detection. Research in this area seems to be rather limited. none of the current metal detectors use this tec hnology.Microwave ImagingA microwave oven is an electromagnetic wave. A microwave security system can detect any object concealed within a human. It uses microwaves to image an object on a human. Basically microwaves will be emitted towards the human via an feeler and the reflected waves will be captured with the same antenna after emitting multiple beams and processing them through a 3d image processing software a 3d image will be created showing the concealed objects.Advantages- quarter detect any object it doesnt take a shit to be metal undefiled positioning of the objectActive holographic body imagingDisadvantages- epoch consumingCostlystand-still inspectionPossible danger to health.Although this is one of the high hat methods to detect objects it is not pragmatical due to the above mentioned disadvantages.State of the art Walk through metal detectors and analysis.Garrett PD 6500i 2. Ceia SMD600 Multi regulariseGarrett PD 6500i 33 zona pin guide metal detector is a recoun t of the art walk through metal detector. It has the ability to pin tip where the potentially dangerous metal object is held omitting the day to day metal objects such as car keys, belt buckles, spare change etc 12Ceia SMD600 Multi Zone metal detector is a highly accurate ultra nociceptive Walkthrough metal detector it posses the same capability as the Garrett PD 6500i. 13The walkthrough metal detector technologies have evolved considerably over the last 40 geezerhood earlier metal detectors used Very low frequency method (sub category of continues wave technique) and pulse induction method (still widely used). The pulse induction method was widely used in the past two decades but lacks the ability to discriminate between objects, which make it unsuitable for moderne day requirements (will be discussed later).Most modern walkthrough metal detectors including the ones shown above usesContinues wave multiple demodulator technology which will allow the capability of multi zone det ection.Digital signal processing in order to get well-behaved discrimination ability utilize a microprocessor.Advantage of multi zone detection over single zone detection.The objective of a practical walkthrough metal detector isMaximum detection and discrimination capabilityHigher through rateLess false alarms rateFalse alarms are a enigma in modern walkthrough metal detectors false alarms could occur because of remote noise in the system or lack of discriminating ability in the system.Most single zone walkthrough metal detectors operate using the pulse induction technique which clearly lacks the ability to discriminate between the objects therefore will result in high number of false alarms which will significantly reduce the through rate.Multi zone metal detectors use continues wave multi sensor technology which will allow pin point detection which will result in high through rate but the false alarms will still be a problem due to the lack of discrimination. 14 15 16Advantag e of Digital signal processing over Analogue signal processing.Analogue signal processingAnalogue signal processing means processing signals using analogue signal means. Sinusoids, heartbeat and step signals are commonly processed using analogue signal processing.Digital Signal processingDigital Signal processing is internal representation of the signals by a sequence of numbers or symbols and the processing of these signals.To chastise the false alarm rate and to increase the discrimination ability within objects modern walkthrough metal detectors use digital signal processing. The amplified output from the receiving system coil is an analogue signal so an analogue to digital converter is used. The converted signal is then sampled and analysed using a computer weapons platform which allows good discrimination ability. 14 15 16By combining the continues wave multiple sensor technology with digital signal processing metal detector manufactures have tried to achieve the above ment ion objectives for a walkthrough metal detectors. Although modern metal detectors have the ability to discriminate between a insalubrious and non harmful object it lacks the ability to correctly identify an object.System anatomy of a modern multi zone metal detectorOscillatorExcitation drum rollMetal Object pickup truck coilPickup coilPickup coilPhase detectionAmplitude detectionMicroprocessorAudio tone of voiceConclusionTechniqueAdvantageDisadvantageContinues Wave (VLF, Induction Balance)Low costDiscrimination abilityMultiple objects could be detectedLimited inspection areaPulse InductionGood penetration abilityLess discrimination abilityBeat frequency OscillationLow costvery basic technologyLow penetration abilityZero discrimination abilityMagnetic field GradeometryWide area inspectionPassive magnetic field measurementsLow costInability to detect multiple objects.Microwave ImagingCan detect any objectAccurate positioningActive holographic body imagingTime consumingCostlystand- still inspectionPossible danger to health. tour analysing the above table it is clear the best method for concealed weapon detection is microwave imaging but due to less practical nature it is clear microwave imaging does not suit the project.Magnetic field Gradeometry is an interesting innovative way of metal detection but due to its inability to detect multiple objects this technique isnt the best cream for the project.Beat frequency oscillation is the oldest and the simplest of all the techniques but this technique has zero discrimination ability between object and less accurate due to these reasons this technique cannot be usedPulse induction technique is shortly used in most metal detectors it poses good penetration ability but lacks discrimination between objects therefore cannot be used for this project.The net technique is the induction balance technique this technique cannot be used for wide area detection but has the best discrimination ability amongst all the techniques hence suit the project the most. A modified version of this technique is used in modern walkthrough metal detectors.