CN215644064U

CN215644064U - Electric field shielding structure for RFID electronic tag magnetic induction coil

Info

Publication number: CN215644064U
Application number: CN202122361517.1U
Authority: CN
Inventors: 蔡云枝; 邓小斌; 朱聪; 王海波
Original assignee: Taicang T&W Electronics Co Ltd
Current assignee: Taicang T&W Electronics Co Ltd
Priority date: 2021-09-28
Filing date: 2021-09-28
Publication date: 2022-01-25
Anticipated expiration: 2031-09-28

Abstract

The utility model discloses an electric field shielding structure for a magnetic induction coil of an RFID (radio frequency identification) electronic tag, which comprises the magnetic induction coil, wherein two side surfaces of the magnetic induction coil are provided with grounding metal shielding grids, each metal shielding grid consists of a square frame with an opening at one side and a plurality of grid strips which are connected with the square frame and are orthogonal to the track of the magnetic induction coil, and only one end of each grid strip is connected with the square frame. The magnetic induction coil is characterized in that the magnetic induction coil is provided with a non-closed shielding grid, the non-closed shielding grid is arranged on the magnetic induction coil, and the non-closed shielding grid is perpendicular to the track of the magnetic induction coil.

Description

Electric field shielding structure for RFID electronic tag magnetic induction coil

Technical Field

The utility model belongs to the technical field of RFID communication, and particularly relates to an electric field shielding structure for an RFID electronic tag magnetic induction coil.

Background

RFID (Radio Frequency Identification), also called RFID, is a communication technology that can identify a specific target and read and write related data through Radio signals without establishing mechanical or optical contact between the Identification system and the specific target. Radio frequency, generally microwave, 1-100GHz, is suitable for short-range identification communication. The RFID reader is also divided into mobile type and fixed type, and the current RFID technology is widely applied, for example: library, access control system, food safety traceability and the like.

Near Field Communication (NFC) is an emerging technology, devices (such as mobile phones) using the NFC technology can exchange data when they are close to each other, and is integrated and evolved from a non-contact Radio Frequency Identification (RFID) and an interconnection and interworking technology, and by integrating functions of an induction card reader, an induction card and point-to-point Communication on a single chip, applications such as mobile payment, electronic ticketing, door access, mobile identity recognition, anti-counterfeiting and the like are realized by using a mobile terminal.

The "near field" in the NFC chinese name refers to radio waves in the vicinity of an electromagnetic field. Since radio waves are actually electromagnetic waves, it follows maxwell's equations, and electric and magnetic fields alternately perform energy conversion all the time when propagating from a transmitting antenna to a receiving antenna and enhance each other when performing the conversion, for example, radio signals used by our mobile phone propagate by using this principle, which is called far-field communication. Within 10 wavelengths of electromagnetic waves, the electric field and the magnetic field are independent from each other, the electric field has little meaning, but the magnetic field can be used for short-distance communication, which is called near field communication.

A complete set of RFID system is composed of Reader, TAG (electronic TAG), Transponder and application software system, and features that the Reader transmits the energy of radio wave with a specific frequency to the Transponder for driving the Transponder circuit to send out internal data, and the Reader receives and decodes the data in turn and sends it to application program for relative processing.

Generally, the communication and energy sensing method between the RFID card reader and the electronic tag can be divided into Inductive Coupling (Inductive Coupling) and backscattering Coupling (Back scatter Coupling), and generally, the first method is used for the low frequency RFID, and the second method is used for the higher frequency RFID.

The reader can be a reading or reading/writing device according to different structures and technologies used, and is an RFID system information control and processing center. The reader is generally composed of a coupling module, a transceiver module, a control module and an interface unit. The reader and the transponder generally exchange information in a half-duplex communication mode, and the reader provides energy and time sequence for the passive transponder through coupling. In practical application, the management functions of collecting, processing and remotely transmitting the object identification information can be further realized through Ethernet or WLAN. Transponders are the information carriers of RFID systems, and nowadays most transponders are passive units consisting of a coupling element (coil, microstrip antenna, etc.) and a microchip.

The transponder typically comprises:

a. an antenna: for receiving signals transmitted by the reader and for transmitting the required data back to the reader.

AC/DC circuit: the radio frequency signal sent by the card reader is converted into a DC power supply, and the DC power supply stores energy through a large capacitor and provides a stable power supply through a voltage stabilizing circuit.

c. A demodulation circuit: the carrier is removed to extract the true modulated signal.

d. The logic control circuit: the signal sent by the reader is decoded and the data is sent back to the reader according to the requirement.

e. Memory: as a location for system operation and storing identification data.

f. A modulation circuit: and the data sent by the logic control circuit is loaded to the antenna through the modulation circuit and then sent to the reader.

The basic working principle of the RFID technology: after the Tag enters a magnetic field, the Tag receives a radio frequency signal sent by the reader, product information (a passive Tag or a passive Tag) stored in a chip is sent out by means of energy obtained by induced current, or a signal (an Active Tag or an Active Tag) with a certain frequency is actively sent out by the Tag, and the reader reads and decodes the information and sends the information to a central information system for related data processing.

The passive RFID product is the earliest and the most mature product with the widest market application. For example, bus cards, dining room cards, bank cards, hotel entrance guard cards, second-generation identification cards and the like are seen everywhere in our daily life and belong to the near-distance contact type identification class. The main working frequencies of the product comprise low frequency 125KHZ, high frequency 13.56MHZ, ultrahigh frequency 433MHZ and ultrahigh frequency 915 MHZ.

When an electronic system or device is in a harsh and noisy environment, electromagnetic interference (EMI) may occur, disrupting system-level functionality or causing a product electromagnetic compatibility (EMC) test to fail. Electromagnetic interference is essentially any harmful radiated or conducted electrical signal that negatively impacts the performance of a system or device. As more and more wireless radiating devices are used, it is crucial to ensure EMC and comply with its standards. As part of normal operation, RFID drives an inductive sensor, which deliberately radiates a magnetic field to sense nearby conductive objects. The induction coil itself may act as an antenna, producing far field radio frequency radiation or receiving radio frequency interference from the environment.

Shielding is a method of preventing unwanted signals from leaving or entering critical or sensitive areas of the system. Whenever there is a moving charge, a magnetic field (b-field) and an orthogonal electric field (e-field) are generated. If left unmanaged, these fundamental domains may be the source of potential EMl problems, each with its own coupling mechanism to the victim circuit. Thus, the direction of the aggressor and/or victim has a significant impact on the magnitude of the interference. The magnetic field is generated by the current in the closed loop and is very sensitive to large di/dt variations coupled to other loops. The electric field is generated by large voltage transients on high impedance lines that radiate or couple to other high impedance lines that receive incoming signals like an antenna.

Electromagnetic waves are classified into electric field waves, magnetic field waves, and plane waves according to their wave impedance.

The wave impedance ZW of an electromagnetic wave is defined as: the ratio of the electric field component E to the magnetic field component H in the electromagnetic wave, i.e., ZW ═ E/H, depends on the radiation source properties of the electromagnetic wave, the distance from the observation point to the radiation source, and the propagation medium in which the electromagnetic wave is located. The wave impedance depends on the radiation source characteristics when the radiation source is close. When the radiation source has a large current and a low voltage (the impedance of the radiation source is low), the wave impedance of the generated electromagnetic wave is less than 377, which is called a magnetic field wave. When the radiation source is at a high voltage and a small current (the impedance of the radiation source is high), the wave impedance of the generated electromagnetic wave is more than 377, which is called an electric field wave. When the distance from the radiation source is long, the wave impedance is only related to the electric field wave propagation medium, the value of the wave impedance is equal to the characteristic impedance of the medium, and the air is 377 omega. The wave impedance of the electric field wave decreases with increasing propagation distance, and the wave impedance of the magnetic field wave increases with increasing propagation distance.

Based on the relevant studies, the following conclusions are drawn regarding masking:

1) the better the conductivity and magnetic permeability of the material, the higher the shielding effectiveness, but the practical metal material cannot take into account both of these two aspects, for example, copper has good conductivity, but magnetic permeability is poor; iron has good magnetic permeability but poor electrical conductivity. What material should be used, whether it is predominantly conductive or permeable, depending on whether the particular shield relies primarily on reflection losses or absorption losses; for the electric field shielding of the magnetic induction coil, a copper conductor with good conductivity can be selected, and copper cladding of a PCB material can be selected.

2) When the frequency is lower, the absorption loss is very small, the reflection loss is a main mechanism of the shielding efficiency, and the reflection loss is improved as much as possible; while the passive RFID we are aiming at is low frequency.

3) The reflection loss is related to the characteristics of the radiation source, and for an electric field radiation source, the reflection loss is large; for a magnetic field radiation source, the reflection losses are small.

4) The reflection loss is related to the distance from the shielding body to the radiation source, and for the electric field radiation source, the closer the distance is, the larger the reflection loss is; for a magnetic field radiation source, the closer the distance, the smaller the reflection loss; it is an important matter of the design of the structure to correctly judge the nature of the radiation source and decide whether it should be close to the shield or far from the shield.

5) For low frequency radiation, the longer wavelength allows the shield to have a suitable gap (typically requiring a maximum dimension in one direction not exceeding 1/4 wavelengths) without affecting its shielding performance.

For inductive sensing products such as RFID, the inductive sensor itself is based on emitting a magnetic field to sense nearby conductive materials. Therefore, the goal of shielding the induction coil is to minimize electric field coupling by reducing the number of high impedance nodes, while still allowing the conductive targets needed for magnetic field sensing.

Eddy currents (Eddy currents) are currents circulating in conductors, like Eddy currents in water flows. They are caused by magnetic field variations and flow in a closed loop perpendicular to the magnetic field plane. They may be generated when a conductor passes through a magnetic field, or when the magnetic field around a stationary conductor changes, i.e. any thing that causes a change in the strength or direction of the magnetic field of the conductor may generate eddy currents. The magnitude of the eddy current is proportional to the magnitude of the magnetic field, the area of the coil, and the rate of change of the magnetic flux, and inversely proportional to the resistivity of the conductor.

Like any current flowing through a conductor, eddy currents also generate their own magnetic fields. Lenz's law states that the direction of a magnetically induced current, like an eddy current, causes a magnetic field to be generated that is opposite to the change in the magnetic field that generated it.

The Eddy Current (also known as foucault Current) phenomenon was discovered in 1851 by french physicist lyon foucault. Due to a moving magnetic field intersecting the metal conductor or due to the moving metal conductor intersecting the magnetic field perpendicularly. In short, it is caused by the electromagnetic induction effect. This action creates a current that circulates in the conductor. The faster the magnetic field changes, the larger the induced electromotive force and the stronger the eddy current; the eddy currents can cause the conductor to heat up. In devices where the magnetic field is varied, the conductor is often divided into a set of sheets or a bundle of thin strips insulated from each other to reduce the eddy current strength and thus the energy loss. When the current in a coil changes with time, an induced current is generated in another coil in the vicinity due to electromagnetic induction. Induced currents are generated in virtually any conductor in the vicinity of this coil.

For larger magnetic field sensors or magnetic field sensors that are directly exposed to large voltage transients (e.g., ESD), the shield shields the sensor coil from nearby high electric fields. However, the method of using a complete solid ground plane directly above the interference source or sensitive component, which is usually adopted in the PCB, is not suitable for the magnetic field sensor such as the induction coil, because it can block the radiation of the magnetic field and directly prevent the electronic tag from detecting the target, so that it cannot perform the required function.

SUMMERY OF THE UTILITY MODEL

The technical problem to be solved by the utility model is to provide an electric field shielding structure for a magnetic induction coil of an RFID electronic tag, which can shield strong electric field radiation interference without influencing the magnetic field induction function.

In order to solve the problems, the technical scheme adopted by the utility model is as follows:

the utility model provides an electric field shielding structure for RFID electronic tags magnetic induction coil, includes magnetic induction coil's both sides face sets up ground connection metal shield bars, metal shield bars comprises one side open-ended mouth word frame and a plurality of bars of being connected with this mouth word frame and magnetic field induction coil orbit quadrature, the bars only one end is connected with a mouthful word frame.

Preferably, the metal shielding grid is made of copper.

Furthermore, the metal shielding grid is grounded through the square frame, and the single-point grounding is conducted at the position, far away from the magnetic induction coil, of the square frame.

Further, the unidirectional maximum dimension of the metal shielding grid does not exceed 1/4 wavelengths of the working frequency.

Preferably, the grid bars are linear grid bars, the length of the grid bars is the same, one half of the grid bars are connected with the left side edge of the square frame, the other half of the grid bars are connected with the right side edge of the square frame, and the grid bars connected with the left side edge of the square frame and the grid bars connected with the right side edge of the square frame are symmetrically arranged; the spacing between the grid bars is the same.

Preferably, the grid bars are linear grid bars, the length of the grid bars is the same, one half of the grid bars are connected with the left side edge of the square frame, the other half of the grid bars are connected with the right side edge of the square frame, and the grid bars connected with the left side edge of the square frame and the grid bars connected with the right side edge of the square frame are arranged at intervals; the spacing between the grid bars is the same.

Preferably, the grid bars are L-shaped grid bars, one half of the grid bars are connected with the left side edge of the square frame and symmetrically arranged, the other half of the grid bars are connected with the right side edge of the square frame and symmetrically arranged, and the grid bars connected with the left side edge of the square frame and the grid bars connected with the right side edge of the square frame are symmetrically arranged; the spacing between the grid bars is the same.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

the magnetic induction coil is characterized in that the magnetic induction coil is provided with a non-closed shielding grid, the non-closed shielding grid is arranged on the magnetic induction coil, and the non-closed shielding grid is perpendicular to the track of the magnetic induction coil.

Drawings

FIG. 1 is a schematic structural view of example 1 of the present invention;

FIG. 2 is a schematic structural view of example 2 of the present invention;

FIG. 3 is a schematic structural diagram of example 3 of the present invention;

wherein: 1. magnetic induction coil, 2, grid bar, 3, square frame, 4, metal shielding grid.

Detailed Description

The utility model is described in further detail below with reference to the attached drawings:

the utility model relates to an electric field shielding structure for a magnetic induction coil of an RFID electronic tag, which is used for shielding the influence of electric field radiation on the magnetic induction coil.

Example 1

As shown in fig. 1, the magnetic induction coil comprises a magnetic induction coil 1, two side surfaces of the magnetic induction coil are provided with grounding metal shielding grids 4, each metal shielding grid is composed of a square frame 3 with an opening on one side and a plurality of grid bars 2 which are connected with the square frame and are orthogonal to the track of the magnetic induction coil, and only one end of each grid bar is connected with the square frame. In order to achieve a good shielding effect, the metal shielding grid in this embodiment is made of copper. The metal shielding grid is grounded through the square frame, and the square frame is grounded at a single point far away from the magnetic induction coil. In order to ensure the shielding effect, the maximum dimension of the metal shielding grid in a single direction in the embodiment does not exceed 1/4 wavelengths of the operating frequency. The grid bars are L-shaped grid bars, half of the grid bars are connected with the left side edge of the square frame and symmetrically arranged, the other half of the grid bars are connected with the right side edge of the square frame and symmetrically arranged, and the grid bars connected with the left side edge of the square frame and the grid bars connected with the right side edge of the square frame are symmetrically arranged; the spacing between the grid bars is the same.

In practical product application, if the RFID electronic tag is positioned in a multilayer PCB, the metal shielding grid is manufactured on the multilayer PCB, namely the metal shielding grid is manufactured on an upper PCB layer and a lower PCB layer of a corresponding area of a PCB layer where the magnetic induction coil is positioned, and the metal shielding grid is manufactured by copper-clad on the PCB layer. Such as: the magnetic induction coil is positioned on a third PCB of the 4 layers of PCBs, and copper shielding grids are arranged in corresponding areas of a second PCB layer and a fourth PCB layer of the PCBs.

If the RFID electronic tag is positioned on the bottom layer of the single-sided PCB, the metal shielding grids are adhered to two side faces of the PCB. Such as: the magnetic induction coil is positioned at the bottom layer of the single-sided PCB, the metal shielding grids are pasted in the corresponding areas of the top layer and the bottom layer of the PCB, and the metal shielding grids pasted at the bottom layer are insulated from the magnetic induction coil.

If the RFID electronic tag is positioned on the bottom layer or the top layer of the double-sided PCB, a metal shielding grid is manufactured by copper plating in the top layer or the corresponding area of the bottom layer of the PCB where the magnetic induction coil is positioned, and the metal shielding grid is adhered to the corresponding area of the bottom layer or the top layer of the PCB. Such as: and the magnetic induction coil is positioned on the top layer of the double-sided PCB, a metal shielding grid is manufactured on the bottom layer of the double-sided PCB by copper plating, and the metal shielding grid is adhered to the corresponding area of the top layer of the double-sided PCB.

Example 2

As shown in fig. 2, the present embodiment is different from embodiment 1 in that: the grid bars are linear grid bars, the length of the grid bars is the same, one half of the grid bars are connected with the left side edge of the square frame, the other half of the grid bars are connected with the right side edge of the square frame, and the grid bars connected with the left side edge of the square frame and the grid bars connected with the right side edge of the square frame are symmetrically arranged; the spacing between the grid bars is the same.

Example 3

As shown in fig. 3, the present embodiment is different from embodiment 1 in that: the grid bars are linear grid bars, the length of the grid bars is the same, one half of the grid bars are connected with the left side edge of the square frame, the other half of the grid bars are connected with the right side edge of the square frame, and the grid bars connected with the left side edge of the square frame and the grid bars connected with the right side edge of the square frame are arranged at intervals; the spacing between the grid bars is the same.

The above examples are only specific embodiments of the present invention, and are not intended to limit the present invention, and any variations based on the present invention are within the scope of the present invention.

Claims

1. The utility model provides an electric field shielding structure for RFID electronic tags magnetic induction coil which characterized in that: the magnetic induction coil is characterized by comprising magnetic induction coils, wherein two side faces of each magnetic induction coil are provided with grounding metal shielding grids, each metal shielding grid comprises a square frame with one open side and a plurality of grid bars which are connected with the square frame and are orthogonal to the track of the magnetic field induction coil, and only one end of each grid bar is connected with the square frame.

2. The electric field shielding structure for the magnetic induction coil of the RFID electronic tag according to claim 1, wherein: the metal shielding grid is made of copper.

3. The electric field shielding structure for the magnetic induction coil of the RFID electronic tag according to claim 2, wherein: the metal shielding grid is grounded through the square frame, and the square frame is grounded at a single point far away from the magnetic induction coil.

4. The electric field shielding structure for the magnetic induction coil of the RFID electronic tag according to claim 3, wherein: the unidirectional maximum dimension of the metal shielding grid does not exceed 1/4 wavelengths of the operating frequency.

5. An electric field shielding structure for magnetic induction coil of RFID electronic tag according to any of claims 1-4, characterized in that: the grid is the straight-line grid, and grid length is the same, and half grid is connected with the square frame left side, and second half grid is connected with the square frame right side, and the grid of being connected with the square frame left side and the grid symmetrical arrangement of being connected with the square frame right side.

6. The electric field shielding structure for the magnetic induction coil of the RFID electronic tag according to claim 5, wherein: the spacing between the grid bars is the same.

7. An electric field shielding structure for magnetic induction coil of RFID electronic tag according to any of claims 1-4, characterized in that: the grid is the straight line grid, and grid length is the same, and half grid is connected with the square frame left side, and second half grid is connected with the square frame right side, and the grid of being connected with the square frame left side and the grid interval arrangement of being connected with the square frame right side.

8. The electric field shielding structure for the magnetic induction coil of the RFID electronic tag according to claim 7, wherein: the spacing between the grid bars is the same.

9. An electric field shielding structure for magnetic induction coil of RFID electronic tag according to any of claims 1-4, characterized in that: the bars are L-shaped bars, half of the bars are connected with the left side edge of the square frame and symmetrically arranged, the other half of the bars are connected with the right side edge of the square frame and symmetrically arranged, and the bars connected with the left side edge of the square frame and the bars connected with the right side edge of the square frame are symmetrically arranged.

10. The electric field shielding structure for the magnetic induction coil of the RFID electronic tag according to claim 9, wherein: the spacing between the grid bars is the same.