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

Abstract

The present invention discloses a method for designing an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity, belonging to the field of RFID antennas. The method comprises the following steps: S1, establishing an equivalent model of a ferrite core of the RFID dumbbell-shaped magnetic core coil antenna; S2, constructing a voltage sensitivity model based on the equivalent model of the ferrite core of the RFID antenna established in step S1; S3, determining structural parameters of the ferrite core of the RFID dumbbell-shaped magnetic core coil antenna based on the voltage sensitivity model; and S4, preparing the RFID antenna based on the structural parameters of the ferrite core of the RFID dumbbell-shaped magnetic core coil antenna obtained in step S3. The method can avoid the waste of resources and time in repeated experimental design, shorten the development cycle of the dumbbell-shaped antenna, and the prepared finished product has a lighter weight and a better coupling effect than a large-sized cylindrical magnetic core.

Description

Technical Field

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

[0002] RFID (Radio Frequency Identification) is a wireless communication technology that can identify specific targets and read and write relevant data through wireless signals or electromagnetic coupling. It is currently widely used in various fields, including industrial, civil, medical, and military. The performance of the RFID antenna largely determines the ability of the RFID tag to transmit and receive data. In low-frequency RFID antenna research, a simple coil antenna is usually formed by winding a copper coil, and a ferrite core is inserted in the center of the coil to increase the tag's read and write distance. How to determine the coil winding pattern and ferrite core size is currently a key research focus. Summary of the Invention

[0003] To address the above problems, the present invention provides a design method for an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity, which can effectively reduce the difficulty of designing low-frequency RFID antennas while effectively improving their 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 includes the following steps:

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

[0007] S2. Construct a voltage sensitivity model based on the RFID antenna ferrite core equivalent model established in step S1;

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

[0009] S4. Prepare an RFID antenna based on the ferrite core structural parameters of the RFID dumbbell-shaped magnetic 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 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-to-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] [[ID=第十九]]2) Determine the structural size 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 winding coil. The determination algorithm is as follows;

[0019] N = ml1 / d coil

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

[0021] For 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] Designing the core structure size through the voltage sensitivity model can shorten the development cycle of low-frequency RFID coil antennas and avoid the waste of large-scale experimental resources and time. 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, it can improve the applicability of buried RFID tags. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 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 Schematic diagram of the structure 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 with reference to the accompanying drawings.

[0032] Example:

[0033] like Figure 1-Figure 3 As shown, a design method for an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity is provided. In this embodiment, the ferrite core of the low-frequency RFID is dumbbell-shaped, and the method includes the following steps:

[0034] S1. Establish an equivalent model of the ferrite core of the RFID dumbbell-shaped magnetic 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 height of the y-ferrite end;

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

[0037] S2. Construct a voltage sensitivity model based on 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 ferrite center part, and x is the length of the hypotenuse of the ferrite end.

[0041] S3. Determine 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 coil cross-sectional area, the effective magnetic permeability of the ferrite core, the length of the ferrite core, and the diameter of the ferrite center part, and determine the optimal aspect ratio of the ferrite. The basis for determination is as follows:

[0044] Since ultra-high frequency and high frequency electromagnetic waves have long transmission distances but poor anti-interference ability and penetration, 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 dumbbell core antenna, but in the actual buried application, the size of 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 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 set to 25 mm within the restricted range for further design of the magnetic core.

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

[0047] Determine the relationship between d2, x, and y on the magnetic induction intensity and obtain the optimal structural size parameters of the dumbbell-shaped ferrite large end; l e =l1+2x. By applying a constant magnetic field through electromagnetic simulation and changing the d2 dimension parameter while keeping other conditions the same, it was found that the larger the d2 dimension, the higher the magnetic induction intensity value through the axis. Therefore, within the limited size, d2 needs to be designed to be larger, so the design dimension of d2 takes the maximum value of 100mm. Similarly, through electromagnetic simulation, it was found that the size of y has little effect on the peak magnetic induction intensity through the axis, and the ferrite core with a longer l1 can maintain a high magnetic induction intensity over a long distance on the axis, which is beneficial for coil winding. 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. 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 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 calculated as S e=98331.5V·m / A;

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

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

[0058] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A design method for an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity, characterized in that: The steps include: S1. Establish an equivalent model of the ferrite core of the RFID dumbbell-shaped magnetic core coil antenna; S2. Construct a voltage sensitivity model based on the RFID antenna ferrite core equivalent model established in step S1. 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 permeability of the ferrite core, l1 is the coil winding height, d1 is the diameter of the ferrite center part, and x is the length of the hypotenuse at the end of the ferrite; S3. Determine the structural parameters of the ferrite core of the RFID dumbbell-shaped magnetic core coil antenna according to the voltage sensitivity model; S4. Prepare an RFID antenna based on the ferrite core structural parameters of the RFID dumbbell-shaped magnetic 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, wherein: In step S3, the method for determining the structural parameters of the ferrite core of the RFID dumbbell-shaped magnetic core coil antenna is as follows: 1) Determine the relationship between the coil cross-sectional area, the effective magnetic permeability of the ferrite core, the length of the ferrite core, and the diameter of the ferrite center part, 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. A is the cross-sectional area of the coil, u0 is the effective magnetic 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, where l e = l1 + 2x, x is the length of the hypotenuse of the end of the ferrite, and l1 is the winding height of the coil; 2) Determine the structural size parameters of the ferrite large end, 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, and then increases A·u, x is the length of the hypotenuse of the ferrite end, d2 is the diameter of the ferrite end, y is the height of the ferrite end, where, 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, m is the number of coil layers, and l1 is the coil winding height.

3. The design method of a voltage-sensitive RFID dumbbell-shaped magnetic core coil antenna according to claim 1, wherein: 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.

4. The method for designing an RFID dumbbell-shaped magnetic core coil antenna based on voltage sensitivity according to claim 3, wherein: The copper coil is insulated, non-conductive and forms a closed loop.

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