CN104331568A - Method for implementing RFID (radio frequency identification) field strength simulation model - Google Patents

Abstract

The invention discloses a method for implementing an RFID (radio frequency identification) field strength simulation model. The method comprises the following steps of equalizing an RFID sending end circuit to a signal source with internal resistance; equalizing the RFID sending end circuit to a circuit with a reader-writer antenna and a source impedance; equalizing an RFID label circuit to a circuit with a label antenna and label impedance; obtaining a coupling coefficient of current and voltage on a label through Kirchhoff voltage law. Through the embodiment, the model can provide accurate simulation to simulate a true working mode, so that the research and development progress and the success rate of products can be improved.

Description

A kind of method realizing RFID field intensity realistic model

Technical field

The present invention relates to technical field of RFID, be specifically related to a kind of method realizing RFID field intensity realistic model.

Background technology

Radio-frequency (RF) identification (RadfoFrequencyIdentification is called for short RFID) technology is a kind of contactless automatic identification technology, and it is by electromagnetic wave or inductance misfortune conjunction mode transmission of signal, to complete the automatic identification to destination object.Compared with other automatic identification technology such as bar code, magnetic card, Contact Type Ic Card, namely RFID technique have identifying need not manual intervention, can identify that multiple target, information storage are large, can work in the advantages such as various rugged surroundings simultaneously.Therefore, RFID technique has been widely used in the fields such as fixed capital management, production line automation, animal and vehicle identification, highway toll, gate control system, storage, commodity counterfeit prevention, airline baggage management, container management.Typical radio-frequency recognition system can be divided into label, reader and Back end data disposal system three parts.

Because the information transmission between reader and card is by radio-frequency antenna wireless transmission, design in, if want accurate simulation, just must set up one with the actual field intensity model conformed to.Otherwise the mode of operation that all emulated datas are real in being all divorced from reality, causes occurring various problem, greatly delay research and development progress and product success ratio.

Summary of the invention

For deficiency of the prior art, cannot accurate simulation be realized in prior art, the invention provides a kind of method realizing RFID field intensity realistic model, thus improve the success ratio of research and development progress and product.

The invention provides a kind of method realizing RFID field intensity realistic model, comprise the steps:

RFID transmitting terminal circuit equivalent is become to have the signal source of internal resistance;

RFID transmitting terminal circuit equivalent is become to have the circuit of reading and writing device antenna and source impedance;

RFID label tag circuit equivalent is become to have the circuit of label antenna and label impedance;

The coupling coefficient of the current/voltage on label is obtained by Kirchhoff's second law.

The described signal source becoming to have internal resistance by RFID transmitting terminal circuit equivalent comprises:

RFID transmitting terminal circuit is become a signal source with internal resistance with the equivalence of EMC wave filter.

The present invention is directed to actual RFID circuit, provide a kind of method of field intensity Building of Simulation Model, this model can provide accurate simulation, thus simulates real mode of operation, thus can strengthen the success ratio of research and development progress and product.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is RFID card reader in the embodiment of the present invention and tag circuit structural representation;

Fig. 2 is the method flow diagram realizing RFID field intensity realistic model in the embodiment of the present invention;

Fig. 3 is the RF circuit simulation model circuit theory diagrams in the embodiment of the present invention;

Fig. 4 is the RFID field intensity realistic model circuit theory diagrams in the embodiment of the present invention.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making other embodiments all obtained under creative work prerequisite, belong to the scope of protection of the invention.

Rfid interrogator in the embodiment of the present invention and tag circuit structural representation are as shown in fig. 1.Wherein, MP1, MN1 are the power MOS pipe of read write line transmitting terminal, MP1 and MN1 is managed by multiple P and N pipe composes in parallel, and the number of paralleling MOS pipe determines that transmitting terminal sends the depth of modulation of data.13.56M clock signal is received on the grid of power tube, produces the sinusoidal carrier signal of 13.56M after EMC filtering, impedance matching and antenna on antenna.Comprise abundant harmonic components in 13.56M clock signal, need low-pass filtering to be filtered, the EMC wave filter be made up of L_emc and C_emc plays the effect of filtering 13.56M harmonic components just; Cs_reader and Cp_reader forms impedance matching network, and on the one hand coupling antenna and the impedance from EMC wave filter and transmitting terminal, make antenna resonance on a carrier frequency on the other hand; R1, for adjusting the Q value of antenna, makes the bandwidth of antenna meet the requirement transmitting data.

For Fig. 1, Fig. 2 of the present invention shows the method flow diagram realizing RFID field intensity realistic model, comprises the steps:

S201, RFID transmitting terminal circuit equivalent is become to have the signal source of internal resistance;

When carrying out circuit simulation, be difficult to transmit by the number changing parallel power pipe the data-signal that depth of modulation is 10% at read write line transmitting terminal.RFID transmitting terminal circuit equivalent is become to have the signal source of internal resistance by the embodiment of the present invention, then change the internal resistance that parallel power pipe is equivalent to change signal source, thus change the output voltage of transmitting terminal.Further, RFID transtation mission circuit is become a signal source with internal resistance with the equivalence of EMC wave filter, the RF circuit simulation model shown in lower Fig. 3 can be obtained.

In simulation process, be considered as by Rin_reader constant, and change the amplitude of signal source, this and actual conditions are just contrary, but can make reading and writing device antenna produces identical waveform signal, and therefore the two is equivalent.

S202, RFID transmitting terminal circuit equivalent is become to have the circuit of reading and writing device antenna and source impedance;

S203, RFID label tag circuit equivalent is become to have the circuit of label antenna and label impedance;

Need to illustrate S202 and S203, according to Electromagnetic Fields & Magnetic Waves knowledge, to be the squaerial field strength distribution computing formula of a, b be (can be obtained in conjunction with infinitesimal analysis by Biot-Savart law) length of side:

$H=\frac{\mathrm{INab}}{4\mathrm{\π}\sqrt{{\left(\frac{a}{2}\right)}^2+{\left(\frac{b}{2}\right)}^2+x^2}}[\frac{1}{{\left(\frac{a}{2}\right)}^2+x^2}+\frac{1}{{\left(\frac{b}{2}\right)}^2+x^2}]=I*f\left(x\right)$

Wherein, N is the antenna number of turn, x be vertical rectangle coil plane central shaft to distance, to be the Distribution of Magnetic Field computing formula of the radius circular antenna of circular antenna be R:

$H=\frac{{\mathrm{INR}}^2}{2{(R^2+x^2)}^{\frac{3}{2}}}=I*f\left(x\right)$

Can be known by above formula, the magnetic field that antenna produces is determined by the size of antenna, the number of turn and the electric current that flows through antenna.Here can simulate the electric current I on the antenna producing this magnetic field according to the data of actual measurement field intensity, release the signal source amplitude Reader_vin in RF circuit simulation model thus.So far, RF realistic model can be utilized to simulate the magnetic field produced with the actual reading and writing device antenna conformed to.

Coupling coefficient corresponding under different distance can be obtained by the method for emulation matching test, and its principle can be illustrated by lower Fig. 4 and formula, and wherein: L1 is reading and writing device antenna, L2 is label antenna, and ZS is source impedance, and ZL is label impedance.

S204, obtained the coupling coefficient of the current/voltage on label by Kirchhoff's second law.

Can obtain according to Kirchhoff's second law:

-V _S+I ₁Z _S+jωL ₁I ₁+jωMI ₂＝0

jωMI ₁+jωL ₂I ₂+Z _LI ₂＝0

Can be drawn by upper two formulas:

$I_1=\frac{V_S}{Z_S+{\mathrm{j\ωL}}_1+\frac{{\mathrm{\ω}}^2{M}^2}{{\mathrm{j\ωL}}_2+Z_L}}$

$I_2=\frac{-{\mathrm{j\ωMI}}_1}{{\mathrm{j\ωL}}_2+Z_L}$

Can learn, when antenna circuit is determined, the current/voltage on label antenna is determined by coupling coefficient k completely, like this, we just can carry out the data of matching test by the coupling coefficient changing artificial circuit, thus the coupling coefficient under obtaining different distance.

After completing whole Building of Simulation Model, can carry out realistic model data test based on this realistic model, correlation step is as follows:

Step 1: the inductance value (label antenna is identical with boresight antenna) measuring read write line, label and boresight antenna

Utilizing MFJ269 electric impedance analyzer to measure the inductance value of associated antenna, in order to reduce the impact of antenna parallel parasitic capacitance on inductance measuring value, measuring the inductance in low-frequency range.

Step 2: estimate read write line signal source equiva lent impedance Rin_reader

Usually, the impedance of signal source is about 40 ~ 80 ohm (with reference to NXP reading and writing device antenna design datas), electric impedance analyzer can be utilized to measure the equiva lent impedance of output impedance as signal source of EMC level, adopt accepted value 50 ohm here.

Step 3: record impedance matching network capacitance, this step also can go out optimum matching network capacitance value by theory calculate

Step 4: measure the magnitude of voltage on read write line field strength distribution value and boresight antenna

Step 5: utilize curve-fitting method to draw reading and writing device antenna electric current I (use MATLAB Curve Fitting Toolbox to do linear fit, remove matching field intensity H with f (x), obtain fitting coefficient I), release signal source voltage value Reader_vin afterwards

Step 6: by changing the voltage that the coupling coefficient of artificial circuit comes fitted calibration antenna is responded to, obtains the coupling coefficient of read write line under different distance and label chip antenna.

To sum up, the embodiment of the present invention is for the RFID circuit of reality, and provide a kind of method of field intensity Building of Simulation Model, this model can provide accurate simulation, thus simulates real mode of operation, thus can strengthen the success ratio of research and development progress and product.

One of ordinary skill in the art will appreciate that all or part of step in the various methods of above-described embodiment is that the hardware that can carry out instruction relevant by program has come, this program can be stored in a computer-readable recording medium, storage medium can comprise: ROM (read-only memory) (ROM, Read Only Memory), random access memory (RAM, Random Access Memory), disk or CD etc.

Above the method realizing RFID field intensity realistic model that the embodiment of the present invention provides is described in detail, apply specific case herein to set forth principle of the present invention and embodiment, the explanation of above embodiment just understands method of the present invention and core concept thereof for helping; Meanwhile, for one of ordinary skill in the art, according to thought of the present invention, all will change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention.

Claims (2)

1. realize a method for RFID field intensity realistic model, it is characterized in that, comprise the steps:

RFID transmitting terminal circuit equivalent is become to have the signal source of internal resistance;

RFID transmitting terminal circuit equivalent is become to have the circuit of reading and writing device antenna and source impedance;

RFID label tag circuit equivalent is become to have the circuit of label antenna and label impedance;

The coupling coefficient of the current/voltage on label is obtained by Kirchhoff's second law.

2. realize the method for RFID field intensity simulation model testing as claimed in claim 1, it is characterized in that, the described signal source becoming to have internal resistance by RFID transmitting terminal circuit equivalent comprises:

RFID transmitting terminal circuit is become a signal source with internal resistance with the equivalence of EMC wave filter.