Design Of Rfid Reader Computer Science Essay

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Radio Frequency Identification (RFID) is an automatic identification method, using handheld reader or another device that can read and store remotely and retrieving data. RFID use devices called RFID tags or transponders. The RFID technology is not a recent technology, rather it has been used for decades by different organizations. However, initially, the cost of implementing RFID technology was very high. This is the reason, not many people knew about RFID technology. The RFID technology is advancing day by day and researches are on to help reduce the cost that can lead to easy availability of the RFID services. Research and study is carried out on RFID reader design. The approach of the work starts by designing the RF antenna then proceed with designing the gain stage for the reader.

Radio Frequency Identification (RFID) systems use radio frequency to identify, locate and track people, assets, and animals. Passive RFID systems are composed of three components: a reader, a passive tag, and a host computer. A tag has an identification number (ID) and a reader recognizes the information from the tag. The reader sends out a signal which supplies power to a tag. The tag transmits its ID to the reader and the reader consults an external database with received ID to recognize the information.

The tag is composed of an antenna coil and a silicon chip that includes basic modulation circuitry and non-volatile memory. The tag is energized by a time-varying electromagnetic radio frequency (RF) wave that is transmitted by the reader. This RF signal is called a carrier signal. When the RF field passes through an antenna coil, there is an AC voltage generated across the coil. This voltage is rectified to supply power to the tag. The information stored in the tag is transmitted back to the reader. This is often called backscattering. By detecting the backscattering signal, the information stored in the tag can be fully identified.

Data decoding for the received signal is accomplished using a microcontroller. The microcontroller is written in such a way to transmit the RF signal, decode the incoming data and communicate with the host computer. Typical, reader is a read only device. RFID reader is a device that activates the tag and retrieves the information stored in its IC and then passes the data to a computer for processing.

The focus of this project is to design a hardware part of a RFID reader which consists of designing the antenna, filters and programming a microcontroller. The reader can detect data from a passive tag and then later send the data received from the tag to the host system.

Problem Statement

Normally, UTP will buy the RFID reader that is costly for any project or applications. University usually bought the reader that might cost around RM350 and above. This project will design RFID reader that can retrieve data from the passive tag and send the data to the host computer.

Objective

The main objectives of this project are:

To design a resonant antenna circuit using a coil that can receive the ID from RFID tag.

To design an active low pass filter and active bandpass filter for the RFID reader

To design and develop a low cost RFID reader using a microcontroller (PIC16F628A) that capable of reading a 125 kHz RFID tag.

To design a reader that can read the RFID tag numbers and transmit them to a host computer for data collection and storage

Scope of Study

The main scope of this project is the study of RFID focusing on designing the RFID reader part. The project includes the design a coil antenna, low pass filter, bandpass filter and programming a microcontroller for the reader.

CHAPTER 2

LITERATURE REVIEW AND THEORY

2.1 RFID Components

The purpose of an RFID system is to enable data to be transmitted by a portable device, called a tag, which is read by an RFID reader and processed according to the needs of a particular application. A reader sends an electromagnetic signal to the tag. Upon receiving the reader's signal, the tag transmits its code to the reader. The data transmitted by the tag may provide identification or location information, or specifics about the product tagged, such as price, color or date of purchase.

A basic RFID system consists of three hardware components which are RFID tag, reader and host system.

Figure 1: RFID basic components

Gain Stage

High Voltage Stage

Low Pass

Band Pass

Detector

125 kHz Signal Source

Microcontroller

To PC

Control

Coder/ Decoder

Modulator/ Demodulator

Figure 2: RFID reader block diagram

The job of the reader circuit is to sends out a signal which supplies power to a tag, retrieve the data stored in the tag and display the data to the host computer. In order to interpret the data, the carrier frequency must be removed, and the enveloping frequencies must be magnified into something measureable.

2.2 Resonant Antenna Circuit

Passive RFID tags work in such a way that they are actually powered by an external signal, which, in most cases is the carrier signal from the reader circuit. The reader and tag communicate using magnetic coupling since their respective antennas can sense changes in magnetic field, which is observed as a change in voltage in the reader circuit.

One of the limiting factors in low frequency passive RFID is reading distance. Maximum reading distance is determined by frequency, power and signal interference. Typical reading distance for RFID is only a few centimeters. Because increasing power and frequency is not always practical, a common solution to increase reading distance is modify antenna being used.

The magnetic induction type antenna used for low frequency RFID is constructed from multiple turns of magnetic wore in a loop. Generally, a bigger radius of a loop will result in a greater reading distance.

Generally, RF antenna is a series resonance circuit of resistance (R), inductance (L) and capacitor (C). The relation of component L and C is [1]:

f = resonate frequency (Hertz)

L = inductance (Henries)

C = Capacitance (Farad)

An oscilloscope can be used to examine how the LC circuit responds to the frequency produce by sine wave generator. The peak response will be at the frequency of natural resonance of the circuit.

Figure 3: Series Resonant Circuit

The inductance of antenna coil is dependent on shape, size and the number of turns in the antenna coil [1]. To construct an antenna with the necessary inductance, a coil of copper wire is used. Inductance of a rectangular coil is determined by the following equation:

L = inductance (µH)

x = width of the coil (cm)

y = length of the coil (cm)

h = height (cm)

b = width across the conducting part of the coil (cm)

N = number of turns

2.3 Gain Stage

Filters are essential components in any electrical systems. In the RFID reader, filters are required to remove undesired signals at different stages of the receiving process, such as noise from incoming signals the antenna receives, undesired signals at the image frequency, and harmonics after the mixing operation. All analogue filters fall in one of two categories: passive or active. In this low frequency RFID system, active filters are used because of the following advantages:

Active filter can generate gain larger than one.

Higher order filters can easily be cascaded since each Op-amp can be second order.

Filters are small in size as long as no inductors are used, which make it very useful as integrated circuit.

An active low pass filter will reject undesired carrier signal and remove bulk of carrier frequency. The active band pass filter is to extract the FSK signal and reject the signals outside 10-20 kHz signals. These are because the ID signals from the tag are 12.5 kHz and 15.65 kHz and signal power is very low [2].

2.3.1 Low Pass Filter

A Low-Pass Filter is a frequency selective device which passes low frequencies and blocks high frequencies. It has a single passband and a single stopband. fC is defined as the frequency that separates the two bands. This is also known as the cutoff frequency and is the point at which the amplitude is 3 dB below its maximum value.

Figure 4: Active low pass filter

Cutoff frequency:

Gain:

The negative sign indicates that the inverting amplifier generates a 180° phase shift from the filter input to the output.

2.3.2 Active Band Pass Filter

The simplest design of a band-pass filter is the connection of a high-pass filter and a low pass filter in series, which is commonly done in wide-band filter applications.

Figure 5: Active band pass filter

Centre frequency is the frequency at the center of the band which typically the peaks of the frequency response curve.

Gain:

The filter bandwidth (BW) is the difference between the upper and lower passband frequencies. A formula relating the bandwidth is:

The quality factor, or Q of the filter is a measure of the distance between the upper and lower frequency points and is defined as (Center Frequency / BW) so that as the passband gets narrower around the same center frequency, the Q factor becomes higher. The quality factor represents the sharpness of the filter,

For a single op-amp bandpass filter with both capacitors the same value, the Q factor must be greater than the square root of half the gain.

Resistors value:

Capacitor values:

CHAPTER 3

METHODOLOGY

3.1 Flow of Work

The development of the project adopts the methodology flow as figure below:

Project Initialization

Start

Problem Identification

Literature Review

Feasibilities Studies

Study on RFID Reader Design

Antenna Design

Design Analysis and Circuit Diagram

Low Pass and Bandpass Filter

No

Simulation and Experiment

Successful

Microcontroller Programming

Yes

Integrating hardware with the microcontroller (Generate Code)

No

Successful

Yes

Prototyping

Testing

Final Integration

Figure 6: Project Development Phase

CHAPTER 4

RESULT AND DISCUSSION

4.1 Resonant Antenna Design

In a RFID system, operating frequency is fixed, consequently the resonant frequency is fixed [3] which are 125 kHz. In order to be able to calculate roughly the capacitance C of the coil, it is necessary to estimate the inductance L of the circuit. The inductance is determined and the estimated value of the coil inductance is 220µH. As a result, capacitance C is:

C = 7.369µF = 7369pF

However, there is no capacitance value of 7369pF. The nearest capacitance values available are 6800pF and 8200pF.

The numbers of turns for the rectangular coil with the width, x and length, y of the coil are 6cm and the thickness, h is 0.3cm. The inductance value used is 220µH and below is the estimated number of turns for the rectangular coil antenna:

N = 40 turns

6cmThe number of turns out to be 40 turns and finished coil is extracted and secured with tape.

0.3cm

6cm

Figure 7: Rectangular coil antenna

To fine tune the resonant frequency of the entire system is simply by changing the capacitance value until the oscilloscope displayed the highest resonant voltage from the carrier frequency. Below are the result obtain form the oscilloscope for the resonant voltage after tuned the antenna. From the oscilloscope, observed that capacitance value of 6800pF gives the highest resonant voltage compared to 8200pF capacitor value.

we

Figure 8: Resonant voltage for 6800pF capacitance

Figure 9: Resonant voltage for 8200pF capacitance

4.2 Gain Stage

4.2.1 Active Low Pass Filter circuit design

The frequency involved in this project is quite low, so the low frequency performance of the TL062 Op-amp should not be an issue. The values for the low pass filter components are calculated, and the circuits are then simulated using Pspice. Take the value for R2 = 160kΩ and C = 100pF.

The cut-off frequency calculated:

fc = 9.947 kHz

Gain:

k = 16

Figure 10: Active low pass filter schematic

4.2.2 Active Low Pass Filter simulation

Figure 11: Active Low Pass Filter Response

From the simulation, it could be observed that the cut-off frequency for the active low pass filter is 9.880 kHz

4.2.3 Active Bandpass Filter circuit design

The circuits are composed of one Op-amps, three resistors, and two capacitors. The amplifiers are based on the TL062. Assume the capacitor value, C = C1= C2 = 1nF. The bandpass filter with a centre frequency of fc = 17 kHz, a quality factor of Q = 6, and a gain of A = -30. All value of capacitors are obtained:

BW = 3.183k

Figure 12: Active bandpass filter schematic

4.2.4 Active Bandpass Filter simulation

Figure 13: Bandpass Filter Response

As can be seen from figure 13, the bandpass filter mostly isolates the pass band (10-20 KHz), with roughly unity gain for all frequencies outside the pass band. The Centre frequency is 17.113 kHz which almost to the calculated value. The simulated results satisfy the system requirements, these circuit structures are suitable for the designed RFID application.

CHAPTER 5

CONCLUSION

A basic passive RFID system is composed of three main components which are reader, passive tag, and host computer. This project focus on designing an RFID reader which can sends out a signal to supplies power to a tag, retrieve the data stored in the tag and display the data to the host computer. The reader composed of an antenna, a low pass filter and bandpass filter as well as a microcontroller. The RF antenna is a series resonance circuit and was designed in a rectangular shape using a coil. The gain stage consists of an active low pass filter and an active band pass filter. An active low pass filter was designed to reject undesired carrier signal and remove bulk of carrier frequency. The active band pass filter is to extract the FSK signal and reject the signals outside 10-20 kHz signals. The active low pass and band pass filter components were calculated and simulated in Pspice. The project will proceed to programming the PIC16F628A microcontroller

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