The radio frequency recognition (RFID) technology is a kind of contactless automatic diagnosis technology, it uses the radio frequency signal space coupling and the transmission characteristic, realizes to the static or moves in the thing to be recognized to make the automatic machine recognition. The radio frequency recognition system generally consists of 2 parts, namely the electronic label and the reader.
The vast majority of RFID is according to the electromagnetic coupling principle work, the radio frequency coupling signal in the reader and the transponder (electronic label) between the transmission energy and the data, the type as shown in Fig.1.
Figure.1 RFID coupling type
Inductive coupling: transformer model, through the space of high-frequency alternating magnetic field to achieve coupling, based on the law of electromagnetic induction. Inductive coupling method is generally suitable for medium and low frequency work of the close range RFID system typical working frequency are: 125KHz, 225KHz and 13.56MHz. recognition action distance <1m, typical action distance 10-20cm. Electromagnetic backscattering coupling: radar principle model, transmit out electromagnetic wave, encounter the target after reflection, while carrying back the target information, based on the The spatial propagation law of electromagnetic waves. Electromagnetic backscatter coupling way is generally suitable for high frequency, microwave work of long-distance range radio frequency identification system. Typical working frequency has: 433MHz, 915MHz, 2.45GHz and 5.8GHz. recognition action distance >1m, typical action distance is 3-10m. low frequency near distance RFID system mainly concentrates in 125kHz, 13.56MHz system. High-frequency long-distance RFID is mainly concentrated in UHF band 915MHz, 2.45GHz and 5.8GHz system.
Research on deactivator technology
Table of Contents
RFID deactivator technology fundamentals
RFID response range with or without transponders, the information detected only 2 states, 1 or 0, that is, 1bit minimum unit signal. 1bit RFID function is simple, but the use of a wide range of applications, the main application areas are electronic theft deterrent (EAS) in shopping malls. EAS consists of a reader, detector antenna, security and confidentiality equipment or tags, and an optional after the payment to make the tag The deactivator is invalidated after payment. Each transponder (electronic label) oscillation circuit has a specific resonant frequency fH, when the reader detects that the alternating electromagnetic field frequencies fG and fH of the antenna coincide, the oscillation circuit is excited resonance, in the oscillation process transponder from the alternating electromagnetic field to obtain energy. Therefore, the resonance process can be detected according to the short-time voltage change or current change of the oscillation coil that generates the alternating electromagnetic field. This short-time rise in coil current (or drop in coil voltage) is intuitively called a drop (Dip). Transponder coils were earlier constructed with capacitors and coiled enameled wire inductors soldered in plastic cases (hard tags), and are now generally etched into transponder coils on thin film conductors behind commodity labels. the relative strength of Dip depends on the distance between coils, the speed of coil approach, and the quality factor of the excited oscillation loop. In order to reliably identify the lbit information of the transponder oscillation loop pasted on the product and to obtain a Dip that is as distinct as possible, we achieve this by a special sweeping technique: the oscillator frequency is continuously swept over the transponder Depending on the payment or not, the system may permanently damage the transponder’s film capacitance with an induced voltage to invalidate the tag or activate an alarm.
The induced voltage U2, in the transponder coil is used to power the passive transponder. In order to improve efficiency, the capacitor C is connected in parallel on the transponder coil to form a parallel resonant circuit, whose resonant frequency is consistent with the operating frequency of the RF identification system, and the resonant frequency is: (1), in fact, C is composed of the actual parallel capacitance C’ and the parasitic capacitance Cp of the circuit, that is: (2).
The resistance of Balise coil L2 is R2. If uq2 = UI is the voltage induced in coil L2, the voltage U2 generated on the load resistance RL in the equivalent circuit is:(3) as well as (4) So the voltage U2 is related to the electromagnetic coupling of the transmitter antenna and the transponder antenna as:(5), as well as (6).
The design requires a center frequency of 8.2 MHz, and the frequency domain of 8.2 (1±0.1) MHz is the scanning range of the reader.
RFID sweep technology solution discussion
There are three design circuits for general sweep technology. Each of these designs has its advantages and disadvantages, and the third design circuit is chosen in this design.
- (1) The sweep circuit composed of MC145151, MAX038, and MAX7541 is used. High-frequency waveform generator MAX038 can generate <1Hz> 20MHz low-distortion sine, triangle, ramp or momentary line (pulse) waveform, which consists of a sweep system with few external components, easy to adjust the frequency and duty cycle, but the higher chip cost is the biggest obstacle to the design application.
- (2) Using CPLD frequency division of the 74HC4046 sweep circuit. The use of crystal for the reference frequency with CPLD editor composed of JV frequency division circuit, the frequency division ratio can be controlled by a microcontroller. The application of CPLD and microcontroller enables the step control of sweeping circuit and the generation of accurate frequency. However, too high a crossover ratio will be difficult to enter the trivial (calculated and verified can not be greater than 100), and this design requires at least 576 crossover frequencies. As the crossover ratio increases, the stabilization time also becomes longer and does not reach the frequency of 85Hz.
- (3) Sweep circuit using the signal frequency modulation function of NE564. The maximum operating frequency of the high-frequency analog phase-locked loop NE564 can reach 50MHz, with better modulation and demodulation performance, and without the need for an external complex filter, the NE564 output sweep frequency is controlled by the input voltage modulation signal. Since no feedback control is used, the resulting sweep frequency control is not precise enough, but it can already meet the requirements of this design.
Figure 2 is the block diagram of the deactivator design, which is composed of five modules. The transmitting frequency of the deactivator is 8.2MHz as the center frequency, with 10% frequency deviation on the left and right, and the frequency is generated by sweeping the frequency (85Hz sweep) in 128 steps to complete 7. 389. 02MHz. Using the FM principle, the frequency is generated by voltage, i.e. V/F conversion. Figure 3 shows the frequency modulation circuit of NE564. The input NE564 step voltage (Vi-0) is used to generate the desired step frequency output (WAVE) by NE564. The input (Vi-0) is controlled by the microcontroller D/A to generate the required step output current, and then converted into the corresponding step voltage by LM324, with the reference voltage is added to get the output of the step voltage (Vi-0), the step voltage generation circuit is shown in Figure 4.
When the tag resonates, the antenna will appear a DIP point, the task of the detection circuit is to detect this special frequency in the antenna’s many frequencies, and generate the external interrupt level of the microcontroller. dip point detection is not easy to achieve, but detect the second harmonic generated by the electronic tag resonance is easier to achieve. Put a transponder into a frequency range of 8.2MHz that has the ability to make it resonate, and when the transponder resonates, the second harmonic it generates will be emitted in the opposite direction and can be detected by the receiver. The detection circuit is mainly composed of the receiver antenna, bandpass filter circuit, amplifier circuit, and level conversion road. The receiver antenna is used to receive the higher harmonics, the bandpass filter circuit is used to take out the second harmonic component, and the level conversion circuit is used to convert the AC component to DC component and send it to the microcontroller for interrupting the Shenqing signal. During system detection, the microcontroller generates a set of control signals to control the HC4066 (Figure 5) to turn on and off the transmitter circuit and detection circuit. The detection signal is passed by Fi0 and Fi1
The second harmonic component output bandwidth is 14-18MHz through the second-order bandpass filter composed of IN4148 limiter and OP37.
Figure.2 Block diagram of the deactivator
Figure.3 NE564 voltage-controlled phase-locked loop sweep wave generation circuit
Fig.4 MCU controlled D/A step voltage (vi-0) generation circuit
Figure.5 Acceptance and bandpass filter circuit
The detection signal fed back at resonance is weak, and the second harmonic signal output after band-pass filtering is even weaker. A resonant amplifier composed of inductor and capacitor is also required to amplify it to obtain the required harmonic component, and the DC level voltage output by shaping controls the generation of the microcontroller detection interrupt.
Electronic label deactivator technical indicators
To resonant frequency of 8.2 (1 ± 0.1) MHz electronic tag recognition, and its de-activation processing (high voltage breakdown).
Experimental parameters of deactivator technical index
- (1) Sweep frequency step: l2.8KHz.
- (2) Sweep frequency rate: 85Hz.
- (3) Maximum working distance: 45cm.
- (4) Maximum working speed: 30 pieces/s.
- (5) Rated power: P≤10W.
- (6) input power: a 220 (1 ± 0.2) V (50Hz).
RFID has a large amount of information, contactless read and write, can identify high-speed objects, and simultaneous identification of multiple objects, anti-interference ability and good confidentiality performance, these aspects are the bar code can not be compared. With China’s second-generation RFID ID card into use, will promote the rapid improvement of the level of information technology in various industries, RFID technology will have a broad application prospects and huge commercial interests.
Author: Zhao Yang, Lu Shunchang, Ren Yuanlin
Source: China Deactivator Manufacturer – Actility Technologies Company Limited (www.tractility.com)
Actility provides powerful security solutions for retail store management to prevent asset and property losses, improve transaction security, and provide intelligent analysis. We produce AM/EM/RFID systems, EAS tags, EAS soft labels, EAS safer, lanyards, detachers and all kinds EAS accessories products. Infrared people counter and camera people counter is available.
If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]