بسم هللا الرحمن الرحيم METAL DETECTOR A THESIS SUBMITTED TO University of Khartoum In partial fulfillment of the requirement for the Degree of B.Sc. (HONS) Electrical and Electronic Engineering (POWER SYSTEMS ENGINEERING) Faculty of engineering Department of Electrical and Electronic Engineering By MOHAMMED TAJ ELSSIR MOHAMED OSMAN Supervisor: Dr. Kamal Ramadan Daoud July 2011 Declaration of originality I declare that this report entitled ''Metal Detector'' is my own work except as cited in the references. The report has not been accepted for any degree and is not being submitted concurrently in candidature for any degree or other award. Signature: _________________________ Name: ____________________________ Date: _____________________________ ii Acknowledgement During the development of my graduation project in the University of Khartoum several persons collaborated directly and indirectly with my project. Without their support it would be impossible for me to finish my work. That is why I wish to dedicate this section to recognize their support. I want to start expressing a sincere acknowledgement to my advisor, Dr. kamal Ramadan because he gave me the opportunity to research under his guidance and supervision. I received motivation; encouragement and support from him during all my studies. I also want to thank my family for their unconditional support, motivation, inspiration and love. Also great thanks to all teaching staff of electrical and electronics engineering department for their great support among my study period. iii Dedication TO MY Father To my mother To all those who teach me TO MY COLLEAGUES TO ALL COMRADES iv Abstract This project aims to design, simulate, and construct a simple and cheap metal detector. This metal detector was implemented using LC colpitts oscillator. The background information of the history and uses of metal detectors, basic elements of metal detectors and the theory behind how a basic colpitts oscillator metal detector works are presented as well as the design criteria for the constructed metal detector. The simulation was done using workbench simulation software and the simulation results are presented in this thesis. The metal detector circuit was successfully constructed. This detector was capable of detecting metal near to its region. The performance and limitations of this metal detector are discussed in this thesis. المستخلص يهذف هذا الوشزوع الي تصوين وهذاكاة وبٌاء جهاس كاشف هعادى بسيط التزكيب ورخيص التكلفه . وقذ تن استخذام هذبذات كىلبت في تصوين هذا الجهاس. الوعلىهات التاريخيه عي جهاس كاشف الوعاى , وكذلك الوكىًات اﻻساسيه للجهاس وطزيقه عوله وكذلك ًظزيه عول هذبذات الكىلبت تن تقذيوها في التقزيز العام عي الوشزوع. وقذ توت هذاكاة الجهاس باستخذام بزًاهج الوذاكاة )Electronic workbench( كوا هىضخ في التقزيز . تن تٌفيذ الجهاس بٌجاح . وقذ توكي الجهاس هي الكشف عي الوعادى في الوٌطقه الوذيطه بولف الكاشف, وكذلك توت هٌاقشه خصائص التصوين واداء الجهاس وهساده عوله ودقه وضىح ًتائجه في هذا التقزيز. v Table of contents Declaration of originality.............................................................................................. II Acknowledgement....................................................................................................... III Dedication.................................................................................................................... IV Abstract................................................................................................................................... V V .........................................................................................................................المستخلص Table of contents.......................................................................................................... VI List of figures............................................................................................................ VIII Chapter 1: Introduction..................................................................................................…... 1 1.1 Background......................................................................................................…... 2 1.2 Importance of the project........................................................................................ 2 1.3 Project aim........................................................................................................….. 2 1.4 metal detectors technologies.............................................................................….. 3 1.4.1 Very low frequency (VLF)...................................................................... 3 1.4.2 Pulse induction (PI).................................................................................. 3 1.4.3 Beat-frequency oscillation (BFO)............................................................ 3 1.4.4 RF oscillators........................................................................................... 3 1.5 Thesis Structure....................................................................................................... 4 Chapter 2: literature Review...........................................................................................….. 5 2.1 Introduction.......................................................................................................….. 6 2.2 History ..............................................................................................................….. 6 2.2.1 The Pioneer.............................................................................................. 6 2.2.2 The induction balance........................................................................….. 7 2.2.3 Discrimination.......................................................................................... 8 2.3 The wireless age.................................................................................................... 10 2.4 Further refinements............................................................................................... 10 2.5 principles of operation of metal detectors............................................................. 11 Chapter 3: Elements of metal detector............................................................................... 12 3.1 Introduction.......................................................................................................…. 13 3.2 Search coil............................................................................................................. 13 3.2.1 Search coil basics................................................................................... 13 3.2.2 Principles of operation of search coil................................................…. 14 3.2.3 Search coil depth.................................................................................... 14 3.3 Types of search coil.............................................................................................. 14 3.3.1 Concentric search coil............................................................................ 15 3.3.2 Mono search coil.................................................................................... 15 3.3.3 Imaging search coil................................................................................ 16 3.3.4 Double-D search coil............................................................................. 16 3.3.5 Two-box search coil............................................................................... 17 3.4 Sizes and shapes of search coil............................................................................. 17 3.4.1 Smallest search coils.............................................................................. 18 3.4.2 Small search coils................................................................................... 18 3.4.3 Medium search coils.............................................................................. 18 3.4.4 Large search coils................................................................................... 19 vi 3.5 Factors that affect the choosing of metal detectors............................................... 19 3.5.1 Depth...................................................................................................... 20 3.5.2 Sensitivity............................................................................................... 20 3.5.3 Discrimination........................................................................................ 20 3.5.4 Ground balance. .................................................................................... 21 3.5.5 Coil types............................................................................................... 21 Chapter 4: Design & Construction of the metal detector.................................................. 22 4.1 Construction of the circuit..................................................................................... 23 4.2 Design................................................................................................................... 23 4.2.1 Main circuit (Colpitts Oscillator circuit)................................................ 23 4.2.2 Indicator circuit...................................................................................... 25 4.3 Block diagram....................................................................................................... 26 4.4 Simulation............................................................................................................. 26 4.4.1 When there is no other field near to the metal detector........................