RFID dumbbell-shaped magnetic core coil antenna design method based on voltage sensitivity

Abstract

The invention discloses an RFID dumbbell-shaped magnetic core coil antenna design method based on voltage sensitivity, and belongs to the field of RFID antennae, and the method comprises the following steps: S1, building an RFID dumbbell-shaped magnetic core coil antenna ferrite magnetic core equivalent model; s2, constructing a voltage sensitivity model according to the RFID antenna ferrite core equivalent model established in the step S1; s3, determining structural parameters of the ferrite core of the RFID dumbbell-shaped magnetic core coil antenna according to the voltage sensitivity model; and S4, preparing the RFID antenna based on the ferrite core structure parameters of the RFID dumbbell-shaped magnetic core coil antenna obtained in the step S3. According to the method, resource and time waste caused by repeated experimental design can be avoided, the development period of the dumbbell-shaped antenna can be shortened, and compared with a large-size cylindrical magnetic core, a prepared finished product is light in weight and good in coupling effect.

Description

Technical Field

[0001] The invention relates to the field of RFID antennas, and in particular to a design method of an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity. Background Art

[0002] RFID (Radio Frequency Identification) technology is a wireless communication technology that can identify specific targets and read and write related data through wireless signals or electromagnetic coupling. It has been widely used in various fields such as industry, civil, medical, and military. The performance of RFID antennas largely determines the performance of RFID tags in transmitting and receiving data. In the research of low-frequency RFID antennas, copper coils are usually wound to form simple coil antennas, and ferrite cores are inserted in the center of the coils to increase the read and write distance of the tags. How to determine the coil winding pattern and the size of the ferrite core is the focus of current research. Summary of the invention

[0003] In view of the above problems, the present invention provides a design method of an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity, which can effectively reduce the difficulty of designing a low-frequency RFID antenna and effectively improve its performance.

[0004] The technical solution of the present invention is:

[0005] A design method for an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity comprises the following steps:

[0006] S1. Establish an equivalent model of ferrite core of RFID dumbbell core coil antenna;

[0007] S2, constructing a voltage sensitivity model according to the RFID antenna ferrite core equivalent model established in step S1;

[0008] S3, determining the structural parameters of the ferrite core of the RFID dumbbell-shaped core coil antenna according to the voltage sensitivity model;

[0009] S4. Prepare an RFID antenna based on the ferrite core structure parameters of the RFID dumbbell-shaped core coil antenna obtained in step S3.

[0010] In step S2, the voltage sensitivity model is:

[0011]

[0012] Where S e is the voltage sensitivity, V; H is the magnetic field strength; f is the natural frequency of the antenna; N is the number of turns of the coil; A is the cross-sectional area of ​​the coil; Q is the quality factor of the coil; u0 is the effective magnetic permeability of the ferrite core; ur is the initial relative permeability of the ferrite core, l1 is the winding height of the coil, d1 is the diameter of the central part of the ferrite, and x is the length of the hypotenuse at the end of the ferrite.

[0013] For the step S3, the method for determining the structural parameters of the RFID antenna ferrite core is as follows:

[0014] 1) Determine the relationship between the cross-sectional area of the coil, the effective permeability of the ferrite core, the length of the ferrite core, and the diameter of the central part of the ferrite, and determine the optimal height-diameter ratio of the ferrite. The determination basis is as follows;

[0015] u0 increases with the increase of l e / d1, and A·u0 decreases with the increase of l e / d1. A is the cross-sectional area of the coil, u0 is the effective permeability of the ferrite core, d1 is the diameter of the central part of the ferrite, and l e is the equivalent length of the ferrite core;

[0016] 2) Determine the structural dimension parameters of the large end of the ferrite. The determination basis is as follows;

[0017] x increases with the increase of d2 and y dimensions. The increase of x leads to the increase of l e / d1, and further increases A·u;

[0018] 3) Determine the parameters of the wound coil. The determination algorithm is as follows;

[0019] N = ml1 / d coil

[0020] where d coil is the diameter of the wound coil, N is the number of turns of the coil, and m is the number of layers of the wound coil.

[0021] For the step S4, the method for manufacturing the RFID antenna is as follows:

[0022] a) Wind a copper coil at the central part of the ferrite core;

[0023] b) Install a chip and a memory in the copper coil, and install an antenna and a matching impedance at the end.

[0024] The copper coil is an insulated, capacitance-free and closed-loop copper coil.

[0025] The ferrite core is dumbbell-shaped.

[0026] The beneficial effects of the present invention are:

[0027] By designing the core structure size through the voltage sensitivity model, the development cycle of low-frequency RFID coil antenna can be shortened and the waste of large-scale experimental resources and time can be avoided. Compared with directly designing RFID tags with large-size cylindrical cores, the weight of the tag itself is greatly reduced, which can save production materials; at the same time, the applicability of buried RFID tags can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is an overall flow chart of a method for designing a RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity according to an embodiment of the present invention;

[0029] Figure 2 It is a schematic diagram of the structure of a voltage-sensitive RFID dumbbell-shaped ferrite core according to an embodiment of the present invention;

[0030] Figure 3 It is a schematic structural diagram of an equivalent cylindrical ferrite core of a low-frequency RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity according to an embodiment of the present invention; DETAILED DESCRIPTION

[0031] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0032] Example:

[0033] like Figure 1-Figure 3 As shown, a design method of a RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity, in which the ferrite core of the low-frequency RFID in this embodiment is dumbbell-shaped, comprises the following steps:

[0034] S1. Establish an equivalent model of ferrite core of RFID dumbbell core coil antenna;

[0035] The dumbbell-shaped ferrite core model consists of l1 coil winding height, l2 ferrite total height, d1 ferrite center part diameter, d2 ferrite end diameter, x ferrite end hypotenuse length, and the y ferrite end height indicates;

[0036] The equivalent cylindrical ferrite core model consists of l1 coil winding height, d1 ferrite center diameter, x ferrite end hypotenuse length and l e Ferrite core equivalent length, l e =l1+2x represents.

[0037] S2, constructing a voltage sensitivity model according to the RFID antenna ferrite core equivalent model established in step S1;

[0038] The voltage sensitivity model is:

[0039]

[0040] Where S e is the voltage sensitivity, V; H is the magnetic field strength; f is the natural frequency of the antenna; N is the number of turns of the coil; A is the cross-sectional area of ​​the coil; Q is the quality factor of the coil; u0 is the effective magnetic permeability of the ferrite core; u r is the initial relative magnetic permeability of the ferrite core, l1 is the coil winding height, d1 is the diameter of the central part of the ferrite, and x is the length of the hypotenuse at the end of the ferrite.

[0041] S3, determining the structural parameters of the RFID antenna ferrite core according to the voltage sensitivity model;

[0042] The method for determining the structural parameters of the RFID antenna ferrite core is as follows:

[0043] 1): Determine the relationship between the cross-sectional area of ​​the coil, the effective magnetic permeability of the ferrite core, the length of the ferrite core, and the diameter of the central part of the ferrite, and determine the optimal aspect ratio of the ferrite. The basis for determination is as follows:

[0044] Although ultra-high frequency and high frequency electromagnetic waves have long transmission distances, they have poor anti-interference ability and poor penetration. Therefore, the buried RFID antenna frequency selects a low frequency of 125kHz (which is also the common low frequency selection for buried tags that meet standards).

[0045] Determine the effect of A·u0 on l e / d1 dependence, the optimal height-to-diameter ratio of the RFID dumbbell-shaped ferrite core equivalent model is obtained. In the formula, l e The larger the value of / d1 is, the larger the value of u0 is (in direct proportion). e The increase of can greatly improve the voltage sensitivity of the dumbbell-shaped magnetic core antenna, but in the actual underground application, the size of the RFID tag has relevant requirements and should not be too large. In this embodiment, the size of l2 and d2 is limited to 150mm and 100mm respectively. e Increasing the / d1 value can increase the u0 value, but as d1 decreases, the voltage sensitivity or the value of A·u0 decreases instead of increasing. Therefore, it can be seen that the cross-sectional area A of the coil winding is the main factor affecting A·u0. Therefore, within the structural size constraints of the buried RFID system, d1 needs to be appropriately increased in size during design, or Se can be regarded as a linear function of d1 and its derivative to obtain the maximum value of d1 design (generally, the maximum size will exceed the restricted size range). In this embodiment, d1 is taken as 25mm within the restricted range for further design of the magnetic core.

[0046] 2): Determine the structural size parameters of the large end of the ferrite, and the basis for determination is as follows:

[0047] Determine the influence of d2, x, and y on the magnetic induction intensity, and obtain the optimal structural size parameters of the large end of the dumbbell-shaped ferrite; l e =l1+2x. By applying a constant magnetic field through electromagnetic simulation, changing the d2 size parameter under the same other conditions, it is found that the larger the d2 size, the higher the magnetic induction intensity value through the axis. Therefore, d2 needs to be designed to be larger under the limited size, so the design size of d2 takes the maximum value of 100mm. It is also found through electromagnetic simulation that the size of y has little effect on the peak value of the magnetic induction intensity through the axis, and the ferrite core with a longer l1 can maintain a long distance of high magnetic induction intensity on the axis, which is beneficial to the winding of the coil. Therefore, the size of y should be shortened under the condition that it can be used normally and is not easily fractured or damaged by buried soil and ground pressure. Here, it is to meet the requirements of the ground and soil for label 10. 4 Pa pressure, in this embodiment, in order to ensure the integrity of the label, y is designed to be 10 mm, thus x=26.93 mm, le=183.85 mm.

[0048] 3): In this embodiment, a copper coil with a diameter of 0.5 mm is selected to tightly wind the dumbbell-shaped ferrite core, and N=l1 / 0.5=260 for one layer. Generally, two layers are required to obtain a coil-type RFID tag with good coupling performance, so N=520.

[0049] S4. Prepare an RFID antenna based on the RFID antenna ferrite core structural parameters obtained in step S3.

[0050] The RFID antenna preparation method is as follows:

[0051] a) Wind a copper coil around the center of the ferrite core;

[0052] Winding high-performance insulated, non-conductive copper coils to form a closed loop.

[0053] b) Install the chip and storage inside the copper coil, and install the antenna and matching impedance at the end.

[0054] Select chips and storage devices with appropriate size and performance as needed and connect them to the closed loop of the coil. Design a corresponding matching network at the end of the antenna to adjust the matching impedance between the antenna and the chip to ensure maximum signal transmission efficiency.

[0055] The parameters selected for designing the dumbbell-shaped magnetic core RFID antenna in this embodiment are coil quality factor Q=10, relative magnetic permeability μ r =4000, f=125kHz, l2=150mm, d2=100mm, d1=50mm, y=10mm, n=560, the voltage sensitivity of the dumbbell core RFID antenna is S e=98331.5V·m / A;

[0056] The calculated voltage sensitivity value of the cylindrical magnetic core RFID antenna with the same size of height L=150mm, diameter d=50mm, number of winding turns, and the same magnetic core material coil quality factor is Se=80851.2V·m / A.

[0057] The voltage sensitivity of the dumbbell core RFID antenna is much greater than the voltage sensitivity of the cylindrical core RFID antenna of the same size, so the dumbbell core has better performance than the cylindrical core.

[0058] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A design method for RFID dumbbell core coil antenna based on voltage sensitivity, characterized in that: The steps include: S1. Establish an equivalent model of ferrite core of RFID dumbbell core coil antenna; S2, constructing a voltage sensitivity model according to the RFID antenna ferrite core equivalent model established in step S1; S3, determining the structural parameters of the ferrite core of the RFID dumbbell core coil antenna according to the voltage sensitivity model; S4. Prepare an RFID antenna based on the ferrite core structure parameters of the RFID dumbbell-shaped core coil antenna obtained in step S3.

2. The design method of a voltage-sensitive RFID dumbbell-shaped magnetic core coil antenna according to claim 1, characterized in that: In step S2, the voltage sensitivity model is: Where S e is the voltage sensitivity, V; H is the magnetic field strength; f is the natural frequency of the antenna; N is the number of turns of the coil; A is the cross-sectional area of ​​the coil; Q is the quality factor of the coil; u0 is the effective magnetic permeability of the ferrite core; u r is the initial relative magnetic permeability of the ferrite core, l1 is the coil winding height, d1 is the diameter of the central part of the ferrite, and x is the length of the hypotenuse at the end of the ferrite.

3. The design method of a RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity according to claim 1 is characterized in that: In step S3, the method for determining the structural parameters of the RFID antenna ferrite core is as follows: 1) Determine the relationship between the cross-sectional area of ​​the coil, the effective magnetic permeability of the ferrite core, the length of the ferrite core, and the diameter of the central part of the ferrite, and determine the optimal aspect ratio of the ferrite. The basis for determination is as follows; u0 increases with l e / d1 increases, and A·u0 decreases with l e / d1 increases, where A is the cross-sectional area of the coil, u0 is the effective permeability of the ferrite core, d1 is the diameter of the central part of the ferrite, and l e is the equivalent length of the ferrite core; 2) Determine the structural size parameters of the large end of the ferrite, and the basis for determination is as follows; As the size of d2 and y increases, x increases, which leads to l e / d1 increases, which in turn increases A·u; 3) Determine the coil winding parameters, the determination algorithm is as follows; N=ml1 / d coil where d coil is the diameter of the winding coil, N is the number of coil turns, and m is the number of coil layers.

4. The design method of a voltage-sensitive RFID dumbbell-shaped magnetic core coil antenna according to claim 1, characterized in that: In step S4, the RFID antenna preparation method is as follows: a) Wind a copper coil around the center of the ferrite core; b) Install the chip and storage inside the copper coil, and install the antenna and matching impedance at the end.

5. The design method of a voltage-sensitive RFID dumbbell-shaped magnetic core coil antenna according to claim 4, characterized in that: The copper coil is an insulated and non-conductive copper coil forming a closed loop.

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