DESIGN AND CONSTRUCTION OF A METAL DETECTOR

1.1 Introduction

A metal detector is described as an electronic instrument which detects the presence of metal nearby. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects. If the sensor comes near a piece of metal this is indicated by a changing tone in earphones, or a needle moving on an indicator. Usually the device gives some indication of distance; the closer the metal is, the higher the tone in the earphone or the higher the needle goes. Another common type are stationary "walk through" metal detectors used for security screening at access points in prisons, courthouses, and airports to detect concealed metal weapons on a person's body.

As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.

1.2 Background of Study

Nowadays, the metal detector is used to identify metallic devices such as bombs, guns for security purpose. To avoid any illegal or unauthorized entry of metallic objects, bombs, knives, guns within the luggage bags of the person carrying them in public places like theatres, shopping malls, parks, airports, hotels, railway stations. A security system is developed by using proximity sensor which is named as a metal detector. So, a metal detector is used in many robotic or electronics projects to detect any present metals which are nearby or the existence of hidden items within objects. This article gives an overview of metal detector working principle and applications.

Metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a magnetometer), the change in the magnetic field due to the metallic object can be detected.

It has been observed that the rapid growth in the technological knowledge across the world has been accompanied by a rapid rise in crime rate. These criminal acts takes the form of breaking of private and official homes and making away with a huge sum of money, valuable and in most cases hosts of lives. The background of this project work comes into play for the removal or minimization of the above criminal act by a way of a METAL DETECTOR, which will be handily or connected to a strategic position in our homes and offices.

Detection and clearance are still very often carried out in humanitarian demining ways using manual methods or computer as primary procedure. When operating in this way, detection phase still relies heavily on metal detectors, whereby, each alarm needs to be carefully checked until it has been fully understood or its source removed. This is normally done visually and prodding or excavating the ground. Metal detectors are probably going to remain in use for some time.

Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the design and construct a metal detector.

1.3 Statement of Problems

Going by the sophisticated means armed robbers adopt these days in breaking into banks, super markets and highly secured areas or the activities of assassins in conference hall, airport, hospital e.g. there are every indication that they are out for the worst and a better way of lessening the harshness of these menace is to get highly alerted security wise. No security system will be optimized or complete without the installation of metal detector. This will stop or reduce barest minimum, the cases of men of the underworld breaking into banks, hotels, conference hall, homes, hospital e.t.c. systematically undetected.

The exigency of Metal detector involvement in security outfits whether national, sub-national and domestic level cannot be over emphasized.

The researcher was motivated to design a project which will demonstrate the undisputable wide use of transistors in field of electronics to produce the kind of sound that should be able to alert people for special attention, and serves as a danger signal in a nutshell.

1.4 Aim and Objectives of Study

The aim of the study is to design and construct a metal detector. In achieving this aim, the following specific objectives were laid out as follows:

1. To construct a walk through metal detector that is capable of detecting the presence of a metallic device.
2. To walk through metal detector world also incorporate the functionality of metallic object.
3. The walk through metal detector will be capable of producing an alarm on reception of a metallic object.

1.5 Significance of Study

The significant of this project is to construct a functional electronic detector security system, which will be beneficial technology to human beings. This project will also bring technology nearer home especially to the student, and to me as the designer, and the contribution in the advancement of technology, thus helping them to assemble, design and construct projects based on simple component and material locally or foreign.

Again, this project will encourage indigenous technology and discourage the large expense being made on foreign security systems. All these were born in mind during the assembling, designing construction and casing of this project.

This study will be of immense benefit to other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.

1.6 Methodology

This system is developed using several electrical and electronic principles. The principle of electromagnetism is a major principle applied. When the coil which serves as the sensor is placed over a metal and the system is switched ON, the electric current passing through the coil makes it magnetic and being placed over a metal, the metal generates a very small voltage (in micro volts) in form of eddy currents. This generated eddy current is received by the sensors and thus it causes a disturbance to the main current flow. The difference is harnessed by electronics and connected to an amplifier from where it is fed into the audio output which serves as the transducer to the system.

1.7 Scope of the Study

The metal detector designed in this project will make use of technology called Beat Frequency Oscillator (B.F.O). this technology employs two oscillators at resonance and a variation of the frequency of oscillation of one of the oscillators due to the presence of a metallic object would be picked up by a tiny receiver within the control box which creates an audible series of tones (beats) based on the difference between the frequencies.

1.8 Limitations of the Study

During the course of this study, many things militated against its completion, some of which are:

1. Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
2. Research material: availability of research material is a major setback to the scope of the study.
3. Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
4. Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).

1.9 Project Outline

The first chapter of this project write-up gives an introduction to the work intended. It discusses a short background of the project work. The specific objectives of the project are also clearly stated. The problem the system is to solve and its significance is also highlighted. The scope of the work is stated here in terms of the parameters to be achieved in the design.

The second chapter of this write-up reviews the related literature of the work. It gives basic insight as to principle of operation of the system. It also reviews past design in this field and the results obtained.

The third chapter show cases the design methodology and on the explanation of each method employed.

The fourth discusses the actual design of the work. The analysis, assumptions an mathematical models involved in achieving a complete system design is discussed.

The chapter five deals on the procedures observed in the coupling of the different designs and modules of the work. Also the result of the finished project after test and evaluation and conclusion made are stated.

The last chapter contains the conclusion and recommendations made. It also contains the Bill of Engineering Measurement and Evaluation (BEME).