Student Attendance free essay sample

This project focuses on the development of a web based attendance register system, called mobile student attendance monitor. This project is motivated due to the fact that the students attendance record is the most important element which can reflect their academic achievement in the institutions. Mostly, the attendance register is circulated in the lecture rooms by the lecturers. This is a very time consuming method and not ideal for a large number of students in a big lecture hall. The aim of the project is to develop a user friendly, efficient and effective mobile attendance system that provides an alternative solution to manual attendance in the educational institutions. The development of this prototype system has been built using the web-based applications such as PHP, My SQL and VB. NET to deal the students attendances by using RFID reader. As, most of the academic institutions provide their students and staffs, ID cards with RFID tags on them. These cards are also known as Contactless smart cards. This project is designed to collect and manage student attendance through this technology which works on the verification basis of the students and recording their time of entrance and exit in the lecture hall. Keyword: web based prototype, PHP, MySQL, VB. NET, RFID, readers, tag, and contactless smart cards. INTRODUCTION OF THE PROJECT AND THE SYSTEM Introduction Management in organizations is a very important aspect in every field as economy is growing at a very fast speed in this busy world. One of the most important factors of the management of nearly all the organizations is to keep the records of the attendance of the individuals. Many researches and the evidences in them have shown that there is an important relationship between the attendances and the performances of the individuals. If the individuals do not attend the places, their performances will link to poor retentions and results. The development of this system is provoked due to the fact that the students attendance record is one of the important elements that may reflect their academic achievements in the institutions. For the sake of good results, it is also very important for the institutions to keep the records of the students at all times. As having the accurate and more powerful attendance systems, it helps in the monitoring of the students activities and their interest in the course. With the help this kind of systems, it would be very easy to handle the record management. Importance of Attendance Empirical evidences have shown that there is a significant correlation between students attendances and their performances [1]. This aspect is agreed by both Mazza and Dimitrova where they claimed that this factor is the most important aspect which indicates the behavior of the student for the course. With the help of this analysis, the judgment can be made about their tendency and dedication of the students toward the courses. [2]. Results taken from the study done by Newman-Ford, Lloyd and Thomas have shown that attendance was a significantly better predictor of grade than any other factors such as age, prior education background or even gender [3]. From the study, it had also revealed that retention rates were substantially better for students who were consistently attending classes than those more frequently absent. All of these findings have showed that attendance records have primarily become the proxy to determine the success of the students in most of the higher academic institutions. [4] Manual Attendance System Traditionally, in most of the higher academic institutions, the recording of the students attendances are mainly done by paper and pen. On the other hand, this practice will also lead to human errors that could be happening during or after the process of attendance taking. For this process, the attendance sheets are to be distributed in the classes for the students to sign in and this whole process consumes a lot of time. Sometimes this list requires the registrant to write his/her time of entry to the classroom as well. In most cases, there is not any list available and students have to write their names on a plain piece of paper plus their signatures and possibly ID (Identification data) numbers which are assigned to them by their institutions. By using the manual system, the process of attendance becomes more difficult for the management to update the record regularly and manually calculate the percentage of classes attended [5]. All of these limitations regarding the manual system indicate the needs to improve the process of attendance recording and reporting. Using papers are not just inefficient but it will require the management of the academic institution to provide a well-managed filing system to cater the attendance records. Therefore, it is crucial to reinforce the use of attendance register system in order to improve the process of recording and reporting students attendances in the higher academic institutions. [4] By proper analysis of this method, we can observe a lot of problems in the process which are unsuitable for the system. If we start the whole procedure from the beginning, we can notice that each student has to look his/her name up on the list which takes some time, some fellow students can sign for their friends and colleagues who are absent and the lecturer could not identify the signatory, any mistake can occur like list do not have proper names, times for entering in the lecture hall and their registration numbers on the list, the list would be difficult and time consuming to circulate in large lecture rooms consisting of high number of students, some students may forget to sign their attendance on the register. For the lecturer, it might be a big hassle to pass this to the department of administration because of their busy schedule and timings. Especially for the administration; its always a tough task to keep the records over a long period of time which may confuse them when searching for the record of a specific student in particular dates. Web Based Applications Web-based applications have now become one of the preferable technologies that are used to ease the process of managing data and records. Some of the motivations that contribute to the development of any web-based systems nowadays are because of its efficiency in handling rapid access of documents and its ability in supporting multi-users simultaneously, thus saving a lot of time and hassle free [6], [7]. Web based applications have many advantages over software that you have to download. You dont need to install or update anything on your PC. You can use the application from any PC or mobile device. Web applications are easy to use and make working with other people much simpler. You dont need to worry about backups because your data is safely stored on a server. [7] Furthermore, web-based applications are designed with the same principles as a regular website. So, it is as simple to use a website as to use a web-based application. [8] Use of RFID in the System Recording the students attendances has also become the prospective process to be automated by using the web-based system. Many researches are involved in more advanced technologies that are integrated with the online systems such as the use of bar code technology, biometric technology and Radio Frequency Identification. These days, mostly all the institutes and organizations do provide their students with ID cards which have been integrated with RFID transponders which contains the basic details of the card holder. These cards may have different details like the student registration number, roll number, name, batch number and department ID and the department name etc This ID card which is also known as Contactless smart card is provided to the students for the access to different premises in the university like laboratories, libraries, buildings, seminar rooms, parking lots and class rooms. To access different areas, students have to present their ID cards to different machines which are mostly called scanners or readers, located in campus in the university and these machines are capable of reading ID cards even they are not touched with them. For this project, in order to design a system, first we need record the attendance of the students using their ID cards. This system is equipped with an RFID reader which reads student ID cards and records their time of attendance at each lecture, into its memory. In order to take the attendance, lecturers can connect this machine to an external host station to print a full list of students attending lecture and the list can be easily viewed by them. Project Outline * Chapter 2 provides the basic idea about the automatic identification system and its general types * Chapter 3 focuses on the technology overview of RFID system * Chapter 4 focuses on the system design and implementation. * Chapter 5 discusses the evaluation and testing of the different scenarios of the system * Chapter 6 concludes the project and recommendations for the future work AUTOMATIC IDENTIFICATION SYSTEMS In recent years, the automatic identification systems have become very popular as they are providing services in many fields like industries, purchasing and distribution logistics, industry, manufacturers and material flow systems. These are the systems which exist so they can provide information about humans, products, animals and goods in transport. Barcode Procedure Bar codes have successfully held their own against other systems over the past few years, as the turnover of the bar codes in the decade of 90s. The bar code system consists of bars and gaps arranged in parallel configuration which is a physical representation of a binary code. They can be either narrow or wide which also have associated numerical readings. For this reason they are arranged in a pattern which is decided and they are representing data that refer to an associate symbol. All bar codes represent data in a machine readable form. Different bars and spaces in a bar code represent different numbers and letters which can be decoded with the help of a bar code scanner. When they are scanned by optical lasers, the white gaps and black bars produce dissimilar reflections from the laser beam which provide for different sets of codes. This scanned data is then sent to a computer where it is recorded and then processed. [10] In addition, there are many barcodes which are popular in the industry, they are as follows: * Code Coda bar * Code 2/5 interleaved * Code 39 * Code 128 * UPC Optical Character Recognition This type of identification system was developed in the 1960s. Optical character recognition is usually abbreviated to OCR. OCR is a field of research in pattern recognition, and artificial intelligence. It is the mechanical or electronic translation of written images, typed or printed text into machine-editable text. It is used to convert paper books and documents into electronic files. When a paper is scanned, it produces just an image file, or a photo of the page. As the computer cannot understand the letters on the page, so OCR software is used to convert it into a text or word processor file.. The result is much more flexible and compact than the original one. All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. Most OCR systems use a combination of hardware and software to recognize characters. OCR systems have completely failed to be deployed in the different fields in the world as the scanners are highly expensive and the readers are complicated in comparison to the other readers of the automatic identification systems. Biometric Procedures This is a unique method for recognizing humans which is based on one or more intrinsic physical or behavioral characteristics and qualities. The main purpose of this system is to identifying human beings by detecting and comparing the physical characteristics of each person such as hands and finger prints and with the help of their voice and iris. Finger Identification Systems Finger print is one of the most important procedures in this field and its applications are used to identify criminals. It is most developed of all the biometric technologies and its price is low enough to see it beginning to make inroads in to the mass market. When this procedure is run to identify personal identification, the finger is placed on the specified reader. The system calculates it pattern and this analysis of fingerprints for matching, generally requires the comparison of several features of the print pattern. These include patterns, which are aggregate characteristics of ridges, and minutia points, which are unique features found within the patterns. It is also necessary to know the structure and properties of human skin in order to successfully employ some of the imaging technologies. Voice Identification Voice identification technology was initiated in the early 1960s. Since then, voice ID has undergone aggressive research and development to bring it into the mainstream. Voice ID is sometimes called voice authentication, which is a type of user authentication that uses voiceprints and pattern recognition software to verify an individual. [13] Voice identification is possible because every person has a unique set of voice characteristics and speech patterns. Voice identification extracts specific and unique features from a persons speech, such as pitch, tone, cadence, harmonic level and vibrations in the larynx, and stores and uses them to differentiate that persons voice from the other voices. This system requires speech samples from the subject. The input is compared with a stored sample of the subjects speech. This stored sample is called a voiceprint. A voice print is a plot of frequency density vs. time. [14] Early voice identification systems made matches between sets of such plots. If these samples match, then the person can be identified or a reaction can be initiated (e. g. open door). Smart Cards A smart card, a type of chip card is a plastic card embedded with a computer chip that stores and transacts data between users. This data is associated with either value or information or both and is stored and processed within the cards chip, either a memory or microprocessor. The card data is transacted via a reader that is part of a computing system. Smart card-enhanced systems are in use today throughout several key applications, including healthcare, banking, entertainment and transportation. [15] The microprocessor on the smart card is there for security. The host computer and card reader actually talk to the microprocessor. The microprocessor enforces access to the data on the card. If the host computer read and wrote the smart cards random access memory (RAM), it would be no different than a diskette. Smarts cards may have up to 8 KB of RAM, 346 KB of read only memory (ROM), 256 KB of programmable ROM, and a 16-bit microprocessor. The smart card uses a serial interface and receives its power from external sources like a card reader. The processor uses a limited instruction set for applications such as cryptography. Smart cards can be used with a smart-card reader attachment to a personal computer to authenticate a user. Web browsers also can use smart card technology to supplement Secure Sockets Layer (SSL) for improved security of Internet transactions. [16] The most common smart card applications are: Credit cards * Electronic cash * Computer security systems * Wireless communication * Banking * Government identification Smart cards are much more popular in Europe than in the United States. In Europe, the health insurance and banking industries use smart cards extensively. Every German citizen has a smart card for health insurance. Even though smart cards have been around in the ir modern form for at least a decade, they are just starting to take off in the United States. [16] Therefore, this market represents one of the fastest growing subsectors of the microelectronics industry. They have two types, either a memory card or one with computer capacity known as a microprocessor card. The memory cards operate using a sequential logic state machine which accesses the memory (EEPROM) of the card. Security can be increased by adding stream ciphering algorithms. The functionality of the memory card in question is usually optimized for a specific application. Flexibility of application is highly limited but the advantage is the cards are very cost effective. Therefore they are used in price sensitive, large scale applications. The microprocessor cards, contains a microprocessor which is connected to a segmented memory (ROM, RAM and EEPROM segments). The mask ROM incorporated an operating system for the microprocessor and is inserted during the chip manufacture. The contents of the ROM are determined during the manufacturing are identical for all the chips from the same batch and cannot be overwritten. The chips EPROM contains application data and application related program code. Reading from or writing to this memory area is controlled by the operating system. The RAM is the microprocessor temporary working memory. Data stored in it is lost whenever supply voltage is disconnected. Microprocessor cards are very flexible as it is possible to integrate different applications in one card. The application specific parts of the program are not loaded in to the EPROM until manufacture and can be initiated via the OS. [19] THE BASICS OF RFID TECHNOLOGY What is RFID? In twelfth night, Shakespeare wrote Some are born great, some achieve greatness, and some have greatness thrust upon them. RFID is one of the more recent four letter abbreviations to have greatness thrust upon it in a flurry of industry mandates, government legislation, and hyperbole. 20] RFID is basically the abbreviation of four letters which are combined together which stands for Radio Frequency Identification. This describes a system which can identify wherein an electronic device that uses radio frequency and magnetic field attached to an electronic device. The object of any RFID system is to carry out any form of data to suitable tran sponders which are called tags and to retrieve data with the help of machine at a suitable time and place to satisfy particular needs. These are the two most important components of this system, one is tag and the other one is called the reader, which recognizes the presence of RFID tags and reads the information which is manually stored on them. This information is then passed to another system confirming the presence of tags. The software with which the system is communicated with the reader is called RFID middleware and it stands between reader and the applications. Case for RFID Much of the recent interest surrounding RFID has arisen from mandates and recommendations by the government agencies such as the U. S Department of Defense (DoD) and the Food and Drug Administration (FDA) and from a few private sector mega corporations. For instance, Wal-Mart called for its top 100 suppliers to begin providing RFID tags by early 2005 on pallets shipped to its stores. This mandate caused the companies in Wal-Marts supply chain to focus in implementing RFID solutions. Companies worked to decide which tags and readers to use and how to attach them with tags or embed them with the products and how to test the read rates for RF tags on pallets as they moved through doors or trucks. Several companies have announced their support for what are commonly known as tags and ship applications. [20] Applications of RFID RFIDs can have many applications depending on their type of functionality. They can be appropriate for different industries and commercial markets. Certain type of RFID applications characterize the whole approach of technology which can be differentiated on the basis of the considerations and implementations. The term autoid, short for automatic ID, describes any automated system for attaching an identity to an item. Real-Time Location Systems (RTLSs) are automated systems for tracking the location of an item. [21] The tree below shows the relationship between different identifications systems and the different types of RFID types. These five categories of RFID are the basic applications which can demonstrate some sense and issues in the physical implementation of this technology. Access Control Most organizations today require a performing and efficient access control system. There are many reasons for having such a system which are: 1. Enhanced security to limit access to restricted areas. 2. Tracking employee activity and . Improve loss prevention Some primary considerations for this type are counterfeiting which means that tags must be recognized and any kind of violation must be discouraged. The other consideration which is very important is tailgating, which occurs when an unauthorized object enters behind an authorized object before or after its entrance. To deal with tailgating and issues like emergency access, this can be implemented with the help of barriers which can be done by singulation, keeping a check which entity is entering through the sensors, either to allow them access or restrict them at a time. But the factor of counterfeiting is a hard process to be address and explained as many systems are been reversed and they proved vulnerable to the attacks. Therefore, strong encryption is necessary on both ends of messages and the digital signatures. An RFID access control system can provide an easy and efficient solution. RFID badges can be read from much further distances than other traditional technologies and the embedded electronic information for each badge can be over-written repeatedly. Furthermore, multiple RFID badges can be read all at the same time. Information about employee access, attendance, and duties performed, can be easily and efficiently monitored and stored in a database. [24] Tag and Ship Tag and ship applications are minimal RFID systems that allows a user to associate an RFID tag with an item, apply the physical tag to the item and then verify that tags operate properly to the attached item or not. Logistics and transportation are major areas of implementation for RFID technology. For example, yard management, shipping and freight and distribution centers are some areas where RFID tracking technology is used. Some considerations of this application are cost, isolation, tag failure and their impact on the processes. For this process, it is very important to purchase tags and device with low cost that the owner has to bear for its implementation. Therefore, a simple equipment best fits for its implementation. Furthermore, to buy some extra tags and devices lower down the cost of the maintenance of the system. It can be implemented by using simple labels that are encoded by the appliances rather than coded by tag vendors. Smart Shelf Keeping an accurate inventory of shelved items in real time constitutes is one of the most desired attributes in any retail business, resource collection, or library system. A Radio Frequency Identification (RFID) system offers an ideal way to track how often an item gets removed from or looked at and returned to a shelf. RFID uses radio-frequency communication to identify, track, and manage objects or living things via a reader and- tag system. An item fitted with RFID tag couples radio signals that a RFID reader receives to obtain the details. 26] Some important considerations for this applications are item-level inventory, hardware used and to handle the spurious tag reading. Track and Trace One of the most important and earliest of the RFID applications was to track dairy cattle. Therefore, the animals were tagged with glass capsules or ear tags which were used to identify lost animals. But now, this application is used far more like to sort information from live stock, and pharm aceutical tracking. The primary considerations of this application are information sharing and instant based control. In case of information sharing, the repetition of identification cannot be ignored therefore, unique numbers are assigned to the products so that they can be easily sorted and traced by the vendors. RFID System Categories RFID systems can be grouped into four different categories which are as follows: EAS Systems Electronic article surveillance (EAS) is a technological method for preventing shoplifting from retail stores. These systems are basically the one bit which can sense the presence or absence of an item. EAS is a technology used to identify articles as they pass through a gated area in a store. This identification is also used to alert someone if any unauthorized removal of items is being attempted. Portable Data Capture Systems Portable data capture systems are characterized by the use of portable data terminals with integral RFID readers and are used in applications where a high degree of variability in sourcing required data from tagged items may be exhibited. The readers capture data that is transmitted directly to a host information management system via a radio frequency data communication (RDFC) link or held for delivery by line linkage to the host on a batch processing basis. 29] Networked Systems Networked systems applications can generally be characterized by fixed position readers deployed within a given site and connected directly to a networked information management system. The transponders are positioned on moving or immoveable items, or people, depending on the application. [29] Positioning Systems Positioning systems use transponders to facilitate automated location and navigation support for guided vehicles. Readers are positioned in the vehicles and linked to onboard computer and RDFC link to the host information management system. The transponders are embedded in the floor of the operating environment and programmed with appropriate identification and location data. The reader antenna is usually located beneath the vehicle to allow close proximity to the embedded transponders. [29] Advantages of RFID There are many different ways to identify different objects, people and animals. For identifying small number of items of any kind object, the policy to count and write them on a paper is fine but when the number grow more than hundreds, some kind of automation is required, in a limited number of hours. To summarize, some of the benefits of RFID are the following: Alignment is not necessary: A scan does not require line of sight which saves time in processing that would otherwise be spent lining up items. Item level tracking: Different types of tags are used which have the capability to track the number of items. Re-writ ability: Some RFID tags are written and re-written many times which is a big advantage. For an item on a store shelf, this type of tag might be a security liability, so write once tags are also available in the market. So, tags can be reused and therefore extremely low maintenance cost occurs. Variety of form factors: Tags are available in a great range of types, sizes and materials. RFID tags range in size from a lunch box to a tiny passive tags smaller than the grain of the rice. Different tags are used for different purposes in wide variety of environments. High speed inventory: Multiple items can be scanned at multiple times. Therefore, it results in extreme low error rate when tracking bulk of items. Labor saving technology RFID technology is a labor-saving technology. This translates to cost savings. System Components of RFID RFID uses wireless communication technology and the basic purpose of the system is to identify objects and people which are tagged, there are three basic components as below: * A tag: Tags are also known as transponders. A tag is an identification device attached to the object we want to track or identify. * An Interrogator: This device is also referred as reader. A device that can recognize the data stored in the RFID tags. A reader is composed of an antenna, an RF electronics module, and a control electronics module. A controller: Interrogator reads the information/ data on RFID tags and passes this data to a workstation. The workstation usually runs software or middleware are to control and manage the required actions associated with the tags. The tag and the interrogator communicate information between one another via radio waves. When a tagged object enters the read zone of an interrogator, the interrogator signals the t ag to transmit its stored data. Tags can hold many kinds of information about the objects they are attached to, including serial numbers, time stamps, configuration instructions, and much more. Once the interrogator has received the tags data, that information is relayed back to the controller via standard network interface such as an Ethernet LAN or event the internet. The controller can then use that information for a variety of purposes. For instance, the controller could use the data to simply inventory the object in a database, or it could use the information to redirect the object on a conveyor belt system. [30] Tag RFID tags are the object tracking devices that are used to store and transmit data to the interrogator. These tags are made up of an electronic chip and an antenna. The electronic chip contains memory (for data read/write purpose) and other usable circuitry. Batteries may also be encapsulated with chips and antennas to provide on board power source for RFID tags RFID Tag Shapes and Sizes RFID tags can be manufactured in several different shapes and sizes depending on the type of application in which they will be used. Some are the size of a pencil lead or are less than a half-inch in length and can be inserted under the skin of animals and livestock. Screw-shaped tags are used to identify specific trees. * Rectangular RFID tags found in some products are used as an anti-theft device. * Large, heavy duty tags that are several inches in length, width, and depth are used to track large containers or large vehicles such as trucks or rail cars. [31] Basic Types of RFID Tags There are two types of RFID tags: * Active tags ( self –powered ) * Passive tags ( no battery ) * semi-passive tags ( Combination of Passive and Active ) On board power source is the main differentiating factor between these tag types. Active Tags Active tags have their own power source to broadcast signal to RFID reader (interrogator) and power electronic chips. These tags have comparatively larger memories and are much complex than passive counterparts. Usually a battery is used as the power source. By using a battery as power source, active tags are able to transmit data and communicate with low-powered RFID readers. Another advantage of using active tags is that it can transmit signals over relatively longer distances. The complexity, power source, and larger memories make these tags more expansive. Passive Tags Passive tags have no power source and rely on RFID readers. These tags derive power from the signal sent by RFID readers. Due to this fact, these tags require high powered RFID interrogators and have short effective range (usually less than 2 feet). Passive tags have smaller memory capacities as compared to active tags due to power source absence. As a result, these tags are much less complex and are less expansive to manufacture. Semi-Passive Tags Some passive tags have built-in power source but do not use this source for signal transmission. In fact, they use power source for on-board circuitry. Such types of tags are called battery-assisted passive tags or semi-passive tags. Basic Tag Capabilities Many basic operations can be performed with an RFID tag: * Attaching the tag: Any RFID tag must be attached to an item through some way. * Reading the tag: tag must be able to communicate with the reader through radio frequency. * Write once: Some tags are manufactured with their values at the factory, but some are left as the user can write once on them and after that the tag values cannot be changed and manipulated. Write many: some tags are manufactured for a reason that the data can be written again and again on them. * Anti-collision: these are some intelligent form of tags which can wait for their turn incase, when many tags are in close proximity. * Security and encryption: some tags are more intelligent as they are able to participate in encrypted communication and they can respond to those readers only, which can prov ide a secret password. * Disable: once tag is disables, it never responds to the reader again. Selection of Tags Many considerations are important in the selection of the tags which are as follows: * Read range: Active tags provide a longer range than the passive tags. For the purpose of the retail, the read range is fulfilled by the passive tags. * Material: In order to deploy the RFID tags in different materials, it is very important to keep in mind where they will be used. For example, in case water or metal, radio frequency or their waves may be obstructed and hamper down. * Cost: This is the most important of the selection criteria as many applications use many kinds of tags. So, to make an affordable system, it plays an important role. Form: As tags are of different sizes, shapes and materials, therefore it is obvious that the tags which will be used for the specific purpose depends on the packaging used in the product and goods. * Standards: EPC global and the International Standards Organizations (ISO) provide standards for the communications between RFID tags and the readers. Character istics in RFID To understand and appreciate the capabilities of RFID systems, it is important to understand the basic parts, data flow that influences the choice of the systems and practicalities of communicating across the air interface. By taking into consideration the components of RFID systems and the different types of functions within the chain, it is possible to take hold of the important issues that influence the effective application of RFID. Thus, it is important to make a start from the method of communication as how it is achieved and the special techniques involved in the design of this system. The Air Interface and Wireless Communication The air interface describes the way in which a tag communicates with the reader. Having knowledge about the tags air interface, we can determine tags read and identity readers compatible with the tag. Communication of data between tags and a reader is done by the wireless communication. For this purpose, there are two methods which can be distinguished from each other, the first one is based on proximity and electromagnetic which is also known as inductive coupling and the other is based on the propagation of electromagnetic waves. Coupling is done via antenna structures that form an integral feature in both tags and readers. The term antenna is basically used for the propagation systems and is applied to the inductive systems. Carrier Frequencies In wired communication systems, the physical wiring constraints allow ommunication links and networks to be effectively isolated from each other and this approach is adopted for radio frequency communication channels. This requires and is generally covered by the government legislations with different parts of electromagnetic spectrums being assigned for different purposes. Not all the countries in the world have access to all the freque ncies which are listed in the table below as some countries have assigned these bands to other users. Within each country and frequency, these are some specific regulations that govern the use of these frequencies. Range and Power Levels The range that can be achieved in RFID system is determined by: * The power which is available at the reader to communicate with the tag * The power available within the tag to respond * The environmental conditions and structures, including signal to noise ratio. Although the level of power is the first determinant of the range, the manner and the efficiency in which the power is deployed also influence the range. The field from the antenna extends into space which surrounds its place and its strength diminishes with respect to its distance. Therefore, strength of the field always reduced to the square of its distance. The power within the tag is generally a lot less than in the reader. In some systems, the reader comprises of the receiver and is separate from the transmitter. As it is possible to choose power levels for different applications, there are some restrictions on its frequencies and constraints on power levels. Although 100 – 500 m W are values which are often quoted in many countries but these values can be confirmed from the authorities for its use. Types of Keying The term keying comes from the days of telegraphy when an operator pressed a manual key to make short and long tones. Keying is described which attributes of an analog carrier, the analog carrier can be a wave or a field, may be modulated to represent the 1s and 0s of a digital message. There are 3 main types of the keying which are: Amplitude shift keying (ASK): A type of keying that sends digital data over analog carriers by changing the amplitude of a wave in time with the data stream. Frequency shift keying (FSK): A type of keying that sends changes through the frequency of the wave. Phase shift keying (PSK): A type of keying that sends changes through the distance by which the waves lead or follow a reference point in time. Coupling A tags coupling mechanism determines the way a circuit on the tag and a circuit on the reader influences each other to send and receive information on power. The type of coupling a tag uses directly affects the range between the tag and the reader. Along with the range, the choice of coupling mechanism strongly affects the frequency which is used by the tag. Some of the coupling techniques are describes which are described below: Backscatter coupling This technique provides an elegant solution to the puzzle of how to make an RFID tag without the battery. This describes that the RF waves transmitted by the reader are spread out by the tag, so waves are bounced back to the source to send a signal. As the term describes, it means that the tags are reflect at the same frequency emitted by the readers, but some of the qualities of the reflection are changed during all this process. But this is the distinguishing feature of this method that both the tags and the readers use the same frequency. Therefore, this is a half duplex communication mode. The reader powers the tag even when the reader is waiting for the signal or sending from itself. Some components of the tag used in this kind of coupling are shown below: Inductive coupling Inductive coupling is a common type of remote coupling. In technical terms, inductive coupling is the transfer of energy from one circuit to another by virtue of the mutual inductance between the circuits. In an RFID system that uses inductive coupling, the reader antenna and the tag antenna each have a coil, which together form a magnetic field. The tag draws energy from the field. The microchip uses this energy to change the electrical load on the tag antenna. These changes are picked up by the reader antenna and converted into a unique serial number. [40] For this reason, it is sometime called transformer coupling. Magnetic coupling It is close to inductive coupling because the reader and tag form a pair of transformer coils. In this coupling, the reader coil is round or u shaped ferrite core with windings on it. Tag must be within 1 cm when operational and placed over the gaps in the core. As the distance is so small, therefore ASK modulation is used due to strong strength of magnetic coupling to make it simple. Tags are inserted in the reader as they can power up the chips which are complex. This is the reason they are ideal to be used in smart cards. Capacitive coupling It is another form of close coupling that works best for the systems in which tags are inserted in the reader. It is also used for the smart cards. Capacitive coupling dispense with antennas and replace them with electrodes. The reader and tag have conductive patches and they work together with a capacitor when held exactly parallel to each other without touching. It uses simple ASK with load modulation to transfer data. Storage and Processing Capacity Information storage and processing capacity is the final and major consideration when choosing a tag. There are many ranges of tags which can store information according to their capability. The simplest one is the tag that can store 1 bit only. On this basis, the presence and absence of an object or an individual is identified. On the other hand, some tags can store KB of data. Larger capacities usually require active tags and even among passive tags. Larger memory capacity directly increases the cost of the tag. 43] Some of the types of tags are as follows: One -bit EAS tags Electronic article surveillance (EAS) tags are typically used to prevent thefts in libraries and mostly markets. EAS tags are called 1 bit tag as they are capable to store 1 bit of the information whether tag is present or not. This is the reason they are mostly used as they are inexpensive and simple. They do not have microchips are always passive using a specific modulation whi ch is appropriate to the coupling that may be recognized by the reader. Surface acoustic wave tags (SAW) In between the 1 bit tag and other, more advanced tags are SAW tags, which operate in microwave range as the backscatter tags and have no processors. They can be encoded at the time of manufacture to contain a number. A saw tag is shown in the figure given below: The antenna at left receives microwaves pulses from the reader and feeds them back to the transducer, which contains a piezoelectric crystal that vibrates when it receives the pulses and this vibration creates an acoustic waves that travels through the tag, encountering reflecting strips. The strips reflect back part of the waves, causing the crystal to vibrate again and creating a reflection. The number of the strips and the distance between them determines the timing and number of the pulses sent back to the reader. Since the number is set at the manufacture time, SAW tags are read only as they have no logic circuits. These tags respond to the pulses at the same time causing the problems to the readers, in sorting out where one tag response starts and another stop. At the time of the writing, practical size also limits these tags to a 32- bit capacity. [45] State machines and microprocessors Some tags are more complex as they have logic circuits in them. Many others tags like 1bit tags and SAW tags have no circuits. The state machines allow these tags to participate in a complex process of anti-collision with the reader. [45] More complicated processors can provide security through encryption or through the control sensors built in the chips. Advanced smart cards even have powerful processors that can be programmed and reprogrammed. As with the memory capacity, more capacity gain means higher will be the cost. The best principle is Dont buy more than you need. Fortunately, even the most advanced tags are dropping in prices as production volume increases. [45] Interrogators RFID interrogators are essentially small computers. They are also composed of roughly three parts: an antenna, an RF electronics module, which is responsible for communicating with the RFID tag, and a controller electronics module, which is responsible for communicating with the controller. An RFID interrogator acts as a bridge between the RFID tag and the controller and has just a few basic functions which are: * Read the data contents of an RFID tag * Write data to the tag (smart cards only) Relay data to and from the controller * Power the tag (passive tags only) In addition to performing the four basic functions above, more complex RFID interrogators are able to perform three more critical functions: * implementing anti-collision measures to ensure simultaneous RW communication with many tags, * authenticating tags to prevent fraud or unauthorized access to the syste m, * Data encryption to protect the integrity of data. [47] Types of Interrogators Different readers are for different purposes as they fit for different occasions. They differ in size and shapes, support various protocols and requirements. Some readers are half an inch across to the the size of a computer desk. Some readers conform to the same standards as the tags read, but some can support multiple protocols or the tags protocols made by the vendors only. The most important of all is the power levels, frequency variations and requirements vary from region to region. Interrogators Placement RFID systems do not require line of sight between tags and readers the way that bar code systems do. As a result of this, system designers have much more freedom when deciding where to place interrogators Readers and antennas can be placed in variety of places for different purposes. These categories are as follows: Portals The word portal means doorways or the entrance. In this category, they are placed where they can recognize tagged items entering or leaving the place. It is common setup for the warehouses. Tunnels It can be useful for the assembly lines as the readers may identify the station when an item is currently passing through. Handhelds These readers work in a place where the items are heavy enough and they cannot be moved near the readers. They can communicate with the help of wireless Ethernet or RF modem. Forklift readers In some workplaces these readers are now placed on the forklifts as a person might carry a handheld reader. Smart shelves It is potentially made for the real time inventory of the stocks in the workplaces. Smart shelves are the units where antennas are incorporated in a way that readers can acknowledge whether item is coming or departing from the shelves. RFID Controllers RFID controllers are the brains of any RFID system. They are used to network multiple RFID interrogators together and to centrally process information.