Transmitting device based on passive parasitic coil and magnetic induction communication system

Abstract

The application discloses a kind of transmitting device and magnetic induction communication system based on passive parasitic coil, belong to wireless communication field;In the present application, the receiving device of magnetic induction communication includes: receiving coil;Transmitting device includes: cross section mutually parallel, and coaxially placed transmitting coil and passive parasitic coil;By introducing passive parasitic coil, and design the distance between passive parasitic coil and transmitting coil, so that when transmitting device transmits signal, the power at each frequency point between the double-peak signal received by receiving coil is greater than or equal to half-power bandwidth threshold, the directional control of frequency splitting degree can be realized, the single resonance frequency point is expanded into double-peak continuous spectrum, and the device is simple, the complexity of the design of the existing multiple coupling coils is reduced, therefore, continuous bandwidth expansion can be realized with lower hardware cost.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication, and more specifically, relates to a transmitting device and a magnetic induction communication system for magnetic induction communication. Background Technology

[0002] Due to its unique magnetic field coupling mechanism, magnetic induction communication exhibits excellent anti-interference ability, signal penetration and multi-directional radiation characteristics in complex electromagnetic environments, and has been widely used in underground communication, mine rescue, underwater exploration and other scenarios in recent years.

[0003] The bandwidth limitation of traditional magnetic induction communication mainly stems from the physical resonance mechanism of the magnetic coil. Magnetic induction communication typically operates in the low or mid-frequency range, and its resonant frequency is determined by the coil inductance L and matching capacitance C. The bandwidth is limited by the coil quality factor Q. Although a high Q value can improve the transmission rate, it will further compress the bandwidth, thus severely restricting the data transmission rate and making it difficult to meet the requirements of high real-time communication.

[0004] To address these issues, some technical solutions involve constructing multi-resonant communication systems by introducing multiple magnetic induction coils. For example, existing research has shown that by arranging multiple coupled coils at the transmitting or receiving end, signals can be transmitted simultaneously at multiple frequency points using the mutual inductance effect between the coils, thus achieving multi-band parallel communication. While this approach increases the overall bandwidth, it achieves bandwidth expansion by segmenting the frequency points, resulting in discontinuous bandwidth across the entire frequency band and limited actual spectrum utilization. Furthermore, the construction of multi-coil systems requires precise spatial layout and impedance matching design, leading to a significant increase in hardware costs. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a transmitting device and a magnetic induction communication system for magnetic induction communication, the purpose of which is to achieve continuous bandwidth expansion with lower hardware cost.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a transmitting device for magnetic induction communication; wherein the receiving device for magnetic induction communication includes: a receiving coil;

[0007] The aforementioned transmitting device includes: a transmitting coil and a passive parasitic coil with parallel cross sections and placed coaxially; the distance between the transmitting coil and the passive parasitic coil satisfies the following condition: when the transmitting device transmits a signal, the power at each frequency point between the two peaks of the signal received by the receiving coil is greater than or equal to the half-power bandwidth threshold.

[0008] More preferably, the transmitting coil and the passive parasitic coil are placed coaxially with the receiving coil; the transmitting coil, the passive parasitic coil, and the receiving coil have the same number of turns;

[0009] Axial spacing x between the transmitting coil and the passive parasitic coil tp satisfy:

[0010]

[0011] Equivalent circuit model:

[0012]

[0013]

[0014] Among them, P r This represents the received power of the receiving coil at angular frequency ω. The half-power bandwidth threshold; I r I is the current of the receiving coil at angular frequency ω. r1 Let ω be the current in the receiving coil when ω = ω1; ω1 is the coefficient matrix of the equivalent circuit model described above. The first eigenvalue; R L U is the load resistance of the receiving device. t M represents the voltage amplitude of the transmitting device. tp M is the mutual inductance between the transmitting coil and the passive parasitic coil. pr M is the mutual inductance between the passive parasitic coil and the receiving coil. tr R is the mutual inductance between the transmitting and receiving coils; j is the imaginary unit; t R is the resistance of the transmitting coil. p R is the resistance of the passive parasitic coil. r C is the resistance of the receiving coil. t C is the capacitance of the transmitting coil. p The capacitance of the passive parasitic coil; C r L is the capacitance of the receiving coil. t L is the inductance of the transmitting coil. p The inductance of a passive parasitic coil; L r The inductance of the receiving coil is given by ; N is the number of turns of the transmitting coil, passive parasitic coil, or receiving coil; μ0 is the permeability of free space; a t a is the radius of the transmitting coil; p The radius of the passive parasitic coil; a r x is the radius of the receiving coil; tr x is the axial distance between the transmitting coil and the receiving coil. pr This is the axial distance between the passive parasitic coil and the receiving coil.

[0015] More preferably, the current I of the receiving coil r The solution obtained by solving the equivalent circuit model is as follows:

[0016]

[0017] Among them, Z t The impedance of the transmitting coil, Z p The impedance of the passive parasitic coil, Z r The impedance of the receiving coil,

[0018] More preferably, the resistance R of the transmitting coil t The resistance R of the passive parasitic coil p The resistance R of the receiving coil r The same, denoted as R; the inductance of the transmitting coil is L. t The inductance L of a passive parasitic coil p The inductance L of the receiving coil r The same, denoted as L; the capacitance C of the transmitting coil. t The capacitance C of the passive parasitic coil p The capacitance C of the receiving coil r If they are the same, denote them as C;

[0019] at this time,

[0020]

[0021] Where ω0 is the resonant angular frequency of the transmitting coil, passive parasitic coil, or receiving coil.

[0022] k tp Let be the coupling coefficient between the transmitting coil and the receiving coil. k pr The coupling coefficient between the passive parasitic coil and the transmitting coil.

[0023] More preferably, the peak power of the receiving coil in:

[0024]

[0025] More preferably, when the ratio of the axial distance between the transmitting coil and the receiving coil to the radius of the transmitting coil is greater than a preset ratio, the above equivalent circuit model simplifies to:

[0026]

[0027] At this time, the current I of the receiving coil r for:

[0028]

[0029] When ω = ω1, the current I of the receiving coil r1 for:

[0030]

[0031] in,

[0032] More preferably, the above-mentioned transmitting device further includes: an adjustment module for adjusting the distance between the transmitting coil and the passive parasitic coil, so that: when the transmitting device transmits a signal, the power at each frequency point between the two peaks of the signal received by the receiving coil is greater than or equal to the half-power bandwidth threshold.

[0033] More preferably, a passive parasitic coil is used to place between the transmitting coil and the receiving coil.

[0034] More preferably, the above-mentioned transmitting device further includes: a signal generator, a first LC tuning circuit, and a second LC tuning circuit; the signal generator is connected in series with the transmitting coil through the first LC tuning circuit; the second LC tuning circuit is connected in series with the passive parasitic coil.

[0035] The first LC tuning circuit is used to make the transmitting coil resonate;

[0036] The second LC tuning circuit is used to make the passive parasitic coil resonate.

[0037] In a second aspect, the present invention provides a magnetic induction communication system, comprising: a transmitting device and a receiving device; wherein the transmitting device is the transmitting device provided in the first aspect of the present invention; and the receiving device comprises: a receiving coil.

[0038] More preferably, the receiving device further includes: a third LC tuning circuit and a signal analyzer;

[0039] The signal analyzer is connected in series with the receiving coil via a third LC tuning circuit;

[0040] The third LC tuning circuit is used to make the receiving coil resonate.

[0041] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0042] 1. This invention provides a transmitting device for magnetic induction communication. By introducing a passive parasitic coil and designing the distance between the passive parasitic coil and the transmitting coil, the power at each frequency point between the two peaks of the signal received by the receiving coil after the transmitting device transmits a signal is greater than or equal to the half-power bandwidth threshold. This enables directional control of the frequency splitting degree, expanding a single resonant frequency point into a double-peak continuous spectrum. Moreover, the device is simple, reducing the complexity of existing designs that add multiple coupling coils. Therefore, continuous bandwidth expansion can be achieved at a lower hardware cost.

[0043] 2. The transmitting device for magnetic induction communication provided by the present invention, by introducing a passive parasitic coil and optimizing its spatial layout, realizes the adjustment of the coupling strength between the parasitic coil and the transmitting coil, and excites a controllable frequency splitting phenomenon. While significantly widening the system bandwidth, it can maintain a high energy transmission efficiency and realize the effective utilization of spectrum resources. It can break through the inherent narrow bandwidth limitation in magnetic induction communication without adding active components or complex circuits, and provides a new way for high data rate communication in complex environments.

[0044] 3. Furthermore, the transmitting device for magnetic induction communication provided by this invention starts from Kirchhoff's voltage equation for a three-coil system and constructs an equivalent circuit model, thereby establishing a complete theoretical framework covering parasitic effects, frequency splitting, and impedance changes. It reveals the intrinsic relationship between coupling strength and bandwidth characteristics, realizes the accurate design of the distance between the passive parasitic coil and the transmitting coil, and provides theoretical guidance for engineering practice.

[0045] 4. Furthermore, in the transmitting device for magnetic induction communication provided by the present invention, when the ratio of the axial distance between the transmitting coil and the receiving coil to the radius of the transmitting coil is greater than a preset ratio, the communication distance is longer. At this time, the mutual inductance between the transmitting coil and the receiving coil and the mutual inductance between the transmitting coil and the parasitic coil are approximately equal. Based on this, the equivalent circuit model is simplified, and the design of the distance between the passive parasitic coil and the transmitting coil can be realized with a lower computational load.

[0046] 5. Furthermore, in the transmitting device for magnetic induction communication provided by the present invention, a passive parasitic coil is placed between the transmitting coil and the receiving coil, which can further improve the communication bandwidth.

[0047] 6. This invention provides a magnetic induction communication system, wherein the transmitting device in the system is the transmitting device provided in the first aspect of this invention; the layout of the parasitic coil provides freedom of choice for the dynamic adjustment of system performance. By precisely adjusting the distance between the parasitic coil and the transmitting coil, directional control of the frequency splitting degree can be achieved, enabling continuous bandwidth expansion with low hardware cost and adapting to different transmission distances and scenario requirements. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of a three-coil magnetic induction communication system provided in an embodiment of the present invention;

[0049] Figure 2 The equivalent circuit diagram of the three-coil magnetic induction communication system provided in the embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the frequency splitting mode of a three-coil magnetic induction communication system provided in an embodiment of the present invention;

[0051] Figure 4 This is a schematic diagram illustrating the bandwidth expansion effect of a magnetic induction communication system at the optimal parasitic distance, as provided in an embodiment of the present invention.

[0052] Figure 5 This is an equivalent circuit model of a transmitting device based on parasitic coils for long-distance magnetic induction communication, provided in an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0054] To achieve the above objectives, in a first aspect, the present invention provides a transmitting device for magnetic induction communication; wherein the receiving device for magnetic induction communication includes: a receiving coil;

[0055] The aforementioned transmitting device includes: a transmitting coil and a passive parasitic coil with parallel cross-sections and placed coaxially; the distance between the transmitting coil and the passive parasitic coil (i.e., the parasitic distance) satisfies the following: when the transmitting device transmits a signal, the power at each frequency point between the two peaks of the signal received by the receiving coil is greater than or equal to the half-power bandwidth threshold (at this time, the peak power difference of the continuous spectrum of the two peaks of the signal received by the receiving coil is ≤3dB).

[0056] It should be noted that the principle of frequency splitting is based on the coupling effect between magnetic coils. When the relative distance between the two coils decreases, the coupling mode of the system changes, and the single peak of the received power gradually splits into two peaks. During this change, there exists a moment when the two peaks are close but do not overlap, and far apart but do not break. By accurately calculating and adjusting the distance between the parasitic coil and the transmitting coil, the frequency splitting can be made to an ideal degree, thereby expanding the bandwidth of magnetic induction communication. This invention uses half-power bandwidth as the standard for measuring bandwidth, which refers to the frequency range where the signal power drops to half of the maximum power.

[0057] In one alternative implementation, the transmitting coil and the passive parasitic coil are placed coaxially with the receiving coil to ensure maximum coupling of magnetic flux; the transmitting coil, the passive parasitic coil, and the receiving coil have the same number of turns.

[0058] Axial spacing x between the transmitting coil and the passive parasitic coil tp (i.e., parasitic distance) satisfies:

[0059]

[0060] Among them, P r This represents the received power of the receiving coil at angular frequency ω. The half-power bandwidth threshold; I r I is the current of the receiving coil at angular frequency ω. r1 R is the current in the receiving coil when ω = ω1; L ω represents the load resistance of the receiving device. ω represents the angular frequency (a positive real number), which has a linear relationship with the frequency f.

[0061] It should be noted that the current in the receiving coil can be obtained by solving the equivalent circuit model of the magnetic induction communication system, which includes the aforementioned transmitting and receiving devices. This equivalent circuit model is constructed based on Kirchhoff's Voltage Law (KVL) equations and Maxwell's equations, specifically as follows:

[0062]

[0063] Among them, U t M represents the voltage amplitude of the transmitting device. tp M is the mutual inductance between the transmitting coil and the passive parasitic coil. pr M is the mutual inductance between the passive parasitic coil and the receiving coil. tr R is the mutual inductance between the transmitting and receiving coils; j is the imaginary unit; t R is the resistance of the transmitting coil. p R is the resistance of the passive parasitic coil. r C is the resistance of the receiving coil. tC is the capacitance of the transmitting coil. p The capacitance of the passive parasitic coil; C r L is the capacitance of the receiving coil. t L is the inductance of the transmitting coil. p The inductance of a passive parasitic coil; L r The inductance of the receiving coil is given by ; N is the number of turns of the transmitting coil, passive parasitic coil, or receiving coil; μ0 is the permeability of free space; a t a is the radius of the transmitting coil; p The radius of the passive parasitic coil; a r x is the radius of the receiving coil; tr x is the axial distance between the transmitting coil and the receiving coil. pr This is the axial distance between the passive parasitic coil and the receiving coil.

[0064] In one alternative implementation, the equivalent circuit model described above is solved using the Cramer method to obtain the current I of the receiving coil. r for:

[0065]

[0066] Among them, Z t The impedance of the transmitting coil, Z p The impedance of the passive parasitic coil, Z r The impedance of the receiving coil,

[0067] It should be noted that ω1 is the odd-mode splitting frequency, specifically the coefficient matrix of the equivalent circuit model described above. The first eigenvalue.

[0068] In one alternative implementation, the resistance R of the transmitting coil t The resistance R of the passive parasitic coil p The resistance R of the receiving coil r The same, denoted as R; the inductance of the transmitting coil is L. t The inductance L of a passive parasitic coil p The inductance L of the receiving coil r The same, denoted as L; the capacitance C of the transmitting coil. t The capacitance C of the passive parasitic coil p The capacitance C of the receiving coil r The same, denoted as C; and the reciprocity theorem guarantees that M tp =M pt M pr =M rp M tr =M rtTherefore, the above equivalent circuit model can be rewritten in matrix equation form. Under conditions of strong coupling and low frequency, the reactance generated by the inductor and capacitor is much greater than the coil resistance, so the R / jωL term can be ignored. Thus, the above equivalent circuit model of the three-coil system simplifies to the following matrix equation:

[0069]

[0070] Where ω0 is the resonant angular frequency of the transmitting coil, passive parasitic coil, or receiving coil, and is related to the inductance and capacitance of the coil, satisfying the following condition: k tp is the coupling coefficient between the transmitting coil and the receiving coil; k tr is the coupling coefficient between the transmitting coil and the receiving coil; k pr This represents the coupling coefficient between the passive parasitic coil and the transmitting coil. The coupling coefficient reflects the ratio of mutual inductance to self-inductance; specifically,

[0071] If we consider the current values ​​in the three coils as a three-dimensional vector, then according to the definition of the eigenvalues ​​of a square matrix, These are the eigenvalues ​​of the coefficient matrix on the left. A third-order square matrix always has three eigenvalues, meaning a three-coil system will have three new resonant frequencies, namely:

[0072]

[0073] Among the three new resonant frequencies, one frequency value is the same as the original resonant frequency. The larger frequency value will increase rapidly as the coil spacing decreases. This frequency value is called the even-mode splitting frequency, while the smaller frequency value will decrease slowly as the coil spacing decreases. This frequency value is called the odd-mode splitting frequency.

[0074] The received power is always greatest at the odd-mode splitting frequency. Substituting ω = ω1 into the current I of the receiving coil described above... r In the expression, the half-power bandwidth threshold is calculated.

[0075] In the calculation process, the odd-mode splitting frequency is first simplified and expressed as a function of the mutual inductance between coils:

[0076]

[0077] Substituting the above equation into the current I of the receiving coil... r The expression for the received power and the expression for the received power The peak power of the received signal can be obtained from this. in:

[0078]

[0079] This is the half-power bandwidth threshold.

[0080] In one optional embodiment, when the axial distance between the transmitting coil and the receiving coil is much larger than the radius of the transmitting coil (i.e., when the ratio of the axial distance between the transmitting coil and the receiving coil to the radius of the transmitting coil is greater than a preset ratio, in one optional embodiment, the preset ratio is greater than or equal to 10, preferably 10), the mutual inductance between the receiving coil and the transmitting coil, and between the receiving coil and the parasitic coil, is approximately equal. The influence of the parasitic coil on the transmitting coil can be converted into an equivalent circuit, connected in parallel across the two ends of the transmitting coil. To simplify calculations, this invention proposes an equivalent circuit model of the parasitic structure at the transmitting end. The input resistance and reactance of the equivalent transmitting device are as follows:

[0081]

[0082] As can be seen from the above formula, the parasitic coil essentially affects the resistance and reactance of the transmitting device. The increase in resistance and the change in reactance not only alter the amplitude and spectrum of the transmitted signal but also significantly impact the resonant frequency and bandwidth of the magnetic induction communication system. Specifically, R is the resistance of the transmitting coil, which is always positive, representing the equivalent resistance of the transmitting device's equivalent circuit. The value has always increased. The first half of the equivalent reactance of the equivalent circuit of the transmitting device is the reactance of the transmitting coil, and the sign of the second half depends on whether the equivalent circuit is inductive or capacitive at the current frequency. This also shows that the frequency splitting phenomenon has already occurred in the transmitting device, and the received spectrum must have a double-peak characteristic.

[0083] The equivalent circuit of the magnetic induction communication system is analyzed using the above equivalent circuit model, which can be simplified as follows:

[0084]

[0085] Compared to a three-coil system, the dimension of the coefficient matrix decreases, and the computational load is greatly reduced. At this point, the current I of the receiving coil... r for:

[0086]

[0087] When ω = ω1, the current I of the receiving coil r1 for:

[0088]

[0089] By substituting the calculated current value in the receiving coil into the expression for the received power, the peak power can be recalculated and the bandwidth determined.

[0090] Preferably, in an optional embodiment, the transmitting device further includes an adjustment module for adjusting the distance between the transmitting coil and the passive parasitic coil, such that when the transmitting device transmits a signal, the power at each frequency point between the two peaks of the signal received by the receiving coil is greater than or equal to the half-power bandwidth threshold.

[0091] Preferably, in an alternative implementation, a passive parasitic coil is used to place between the transmitting coil and the receiving coil to further improve the communication bandwidth.

[0092] In one optional embodiment, the transmitting device further includes: a signal generator, a first LC tuning circuit, and a second LC tuning circuit; the signal generator is connected in series with the transmitting coil via the first LC tuning circuit; the second LC tuning circuit is connected in series with the passive parasitic coil.

[0093] The first LC tuning circuit is used to make the transmitting coil resonate;

[0094] The second LC tuning circuit is used to make the passive parasitic coil resonate.

[0095] In summary, this invention introduces a passive parasitic coil and utilizes the strong coupling effect between the coils to excite a controllable frequency splitting phenomenon, expanding the single-peak spectrum of traditional magnetic induction communication into a double-peak continuous spectrum, significantly improving system bandwidth while maintaining high receiving power. By optimizing the distance between the parasitic coil and the transmitter, precise control of the double-peak spectrum is achieved, overcoming the limitation of narrow bandwidth on data transmission rate. For long-distance communication scenarios, an equivalent circuit model for the transmitter is proposed, simplifying the complex three-coil coupled system into a two-coil analysis, significantly reducing computational complexity while preserving the double-peak characteristics, providing theoretical guidance for engineering applications. This solution, with its advantages of low cost and low hardware complexity, provides an efficient solution for high-reliability communication in complex environments such as underground and mines, promoting the development of magnetic induction communication technology.

[0096] In a second aspect, the present invention provides a magnetic induction communication system, comprising: a transmitting device and a receiving device; wherein the transmitting device is the transmitting device provided in the first aspect of the present invention; and the receiving device comprises: a receiving coil.

[0097] In one alternative implementation, the receiving device further includes: a third LC tuning circuit and a signal analyzer;

[0098] The signal analyzer is connected in series with the receiving coil via a third LC tuning circuit;

[0099] The third LC tuning circuit is used to make the receiving coil resonate.

[0100] The related technical solutions are the same as the launching device provided in the first aspect of this invention, and are not limited here.

[0101] To further illustrate the transmitting device and magnetic induction communication system for magnetic induction communication provided by the present invention, a detailed description is provided below with reference to a specific embodiment:

[0102] like Figure 1 As shown, the magnetic induction communication system of this embodiment includes a transmitting device (including a transmitting module and a parasitic structure module) and a receiving device, forming a complete hardware link. The corresponding equivalent circuit diagram is shown below. Figure 2 As shown, a controllable frequency splitting effect is achieved by matching the physical parameters and electrical characteristics of each part. The transmitting module includes: a signal generator, a transmitting coil, and a first series π-type LC tuning circuit; in this embodiment, the signal generator is a RIGOL DG1022 model, which outputs a swept frequency signal with a frequency range of 350kHz to 550kHz, with a peak-to-peak voltage set to 10V and a sweep time fixed at 1 second to ensure the stability of the spectrum analysis. The parasitic structure module includes: a parasitic coil and a second series π-type network LC tuning circuit. The receiving device includes: a receiving coil, a series π-type network matching circuit, and a signal analyzer. In this embodiment, the signal analyzer is a Keysight N9020A MAX model, which supports a 0.1Hz resolution bandwidth setting and can accurately capture the power distribution characteristics of the double-peak spectrum, displaying the bandwidth expansion effect of the double-peak continuous spectrum. In this embodiment, all three coils are wound with high-purity copper wire with a wire diameter of 1mm, a coil radius of 0.2m, and 30 turns. The operating center frequency is calibrated to 450kHz, and the resonant frequency deviation is controlled within 1%. The transmitting coil has a resistance of 17.7Ω, an inductance of 832.4μH, and a capacitance of 150pF; the parasitic coil has a resistance of 21.2Ω, an inductance of 834.7μH, and a capacitance of 150pF; and the receiving coil has a resistance of 18.6Ω, an inductance of 829.9μH, and a capacitance of 150pF. The signal generator and transmitting coil, as well as the receiving coil and signal analyzer, are connected via low-loss coaxial cables. The cable shielding uses a double-braided structure to suppress external electromagnetic interference. The parasitic structure module undergoes closed-loop processing and is an independent passive circuit.

[0103] To verify the theoretical application of bandwidth extension, an equivalent circuit model of the three-coil system needs to be established based on Maxwell's equations and Kirchhoff's voltage law. This model reflects the relationship between the internal currents of the transmitting coil, parasitic coil, and receiving coil. Only the transmitting coil is active, while the parasitic coil and receiving coil passively receive magnetic flux, thereby generating induced current.

[0104]

[0105] In this context, R, L, and C represent the resistance, inductance, and capacitance of the coil, respectively; subscript t represents the transmitting coil, subscript p represents the parasitic coil, and subscript r represents the receiving coil. ω is the angular frequency, which has a linear relationship with the frequency f. M ij This refers to the mutual inductance between coil i and coil j. The values ​​of i and j can be any two different values ​​from t, p, and r. The magnitude of the mutual inductance is influenced by the coil radius a, the number of turns N, and the axial distance x between the two coils. ij Impact:

[0106] M ij The mutual inductance between coil i and coil j can be calculated using the following formula:

[0107]

[0108] In the above formula, the number of coil turns N is 30, x ij Given the coil spacing, according to the definition of mutual inductance, M is always less than the coil's self-inductance L. Therefore, the coupling coefficient k is used to reflect the degree of influence of M on L.

[0109]

[0110] When the coupling coefficient k exceeds the critical coupling coefficient, the system is in an overcoupled state, at which point a significant frequency splitting phenomenon will occur. The splitting frequency mode of the three-coil system is as follows: Figure 3 As shown. By solving for the eigenvalues ​​of the coefficient matrix on the left side of the above equivalent circuit model, the three split frequency values ​​are obtained:

[0111]

[0112] The magnitude of ω2 is the same as the original resonant frequency of the transmitting coil:

[0113] In this embodiment, in order to meet the needs of long-distance magnetic induction communication in various applications, the three coils are placed coaxially, and the parasitic coil is placed between the transmitting coil and the receiving coil, and close to the transmitting coil.

[0114] like Figure 4 As shown, two of the three peaks of the split are close to each other. When the depression in the middle of the two peaks crosses the half-power bandwidth threshold, the maximum bandwidth expansion effect can be obtained.

[0115] Half-power bandwidth threshold It can be calculated using the following formula:

[0116]

[0117] in,

[0118] A magnetic induction communication system consisting of the same transmitting and receiving devices has a bandwidth of approximately 7.1 kHz and a peak received power of approximately -0.3 dB. In contrast, the magnetic induction communication system based on parasitic coils used in this invention has a bandwidth of 20.7 kHz and a peak received power of approximately -2.4 dB. While the system bandwidth is increased by three times, the peak power decreases by only 2.1 dB.

[0119] Furthermore, when the communication distance is long, much larger than the radius of the transmitting coil, the mutual inductance between the transmitting and receiving coils, and the mutual inductance between the transmitting coil and the parasitic coil are approximately equal. To simplify the calculation, this invention proposes an equivalent circuit model of the parasitic structure at the transmitting end. The equivalent process of this model is as follows: Figure 5 As shown. The resistance and reactance of the equivalent transmitter are as follows:

[0120]

[0121] R is the resistance of the transmitting coil, which is always positive, i.e., the equivalent resistance of the transmitting terminal's equivalent circuit. The value has always increased. The first half of the equivalent reactance of the transmitting end's equivalent circuit is the reactance of the transmitting coil, while the sign of the second half depends on whether the equivalent circuit exhibits inductive or capacitive behavior at the current frequency. This also indicates that frequency splitting has already occurred at the transmitting end.

[0122] Furthermore, the equivalent circuit model described above is used to analyze the equivalent circuit of the equivalent magnetic induction communication system:

[0123]

[0124] Compared to a three-coil system, the dimension of the coefficient matrix decreases, significantly reducing the computational load. The magnitude of the current in the receiving coil is then:

[0125]

[0126] When ω = ω1, the current I of the receiving coil r1 for:

[0127]

[0128] Based on the above calculations, in this embodiment, the adjustable range of the distance between the transmitting coil and the passive parasitic coil is 0.2m to 0.4m, and by adjusting this distance, the half-power bandwidth of the system's bi-peak spectrum covers the target frequency band. When the distance between the parasitic coil and the transmitting coil is 0.265m, the effective bandwidth of the system at the 450kHz center frequency is 26.5kHz, and the received power drop corresponding to the half-power bandwidth is ≤3dB.

[0129] In summary, to address the data transmission rate limitation problem caused by the inherent narrow bandwidth of magnetic induction communication systems, this embodiment proposes introducing a passive parasitic coil at the transmitting end of the system. By optimizing the distance between the parasitic coil and the transmitting coil, the frequency splitting effect of the three-coil coupling system is controlled, expanding the single resonant frequency point into a double-peak continuous spectrum, thereby significantly improving the system bandwidth. Specifically, based on Kirchhoff's voltage law, an equivalent circuit model of the three coils, including the transmitting end, the parasitic structure, and the receiving end, is established. The quantitative relationship between frequency splitting and coupling coefficient is derived, and the double-peak spectrum is continuously covered within the half-power bandwidth threshold by adjusting the parasitic distance. Experimental results show that when the parasitic distance is 0.265m, the system achieves an effective bandwidth of 26.5kHz at a center frequency of 450kHz, which is approximately three times higher than that of the traditional single-coil magnetic induction communication system, while the peak power at the receiving end decreases by only 2.1dB. This invention achieves bandwidth expansion by adding passive parasitic structure optimization, avoiding the complexity and high cost of multi-channel design. While maintaining high receiving power and anti-interference capability, it significantly improves spectrum utilization and is suitable for high-reliability wireless communication scenarios in complex environments such as underground and mines.

[0130] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A transmitting device for magnetic induction communication, characterized in that, The receiving device for the magnetic induction communication includes: a receiving coil; The transmitting device includes: a transmitting coil and a passive parasitic coil with parallel cross sections and placed coaxially; the distance between the transmitting coil and the passive parasitic coil satisfies the following condition: when the transmitting device transmits a signal, the power at each frequency point between the two peaks of the signal received by the receiving coil is greater than or equal to the half-power bandwidth threshold. The transmitting coil and the passive parasitic coil are placed coaxially with the receiving coil; the transmitting coil, the passive parasitic coil, and the receiving coil have the same number of turns; The axial distance between the transmitting coil and the passive parasitic coil satisfy: Equivalent circuit model: in, For the receiving coil at angular frequency The received power at the following levels; This is the half-power bandwidth threshold; For the receiving coil at angular frequency The current below; For when The current in the receiving coil at that time; The coefficient matrix of the equivalent circuit model The first eigenvalue; The load resistance of the receiving device; The voltage amplitude of the transmitting device; The mutual inductance between the transmitting coil and the passive parasitic coil; The mutual inductance between the passive parasitic coil and the receiving coil; The mutual inductance between the transmitting coil and the receiving coil; j The imaginary unit; The resistance of the transmitting coil; The resistance of the passive parasitic coil; The resistance of the receiving coil; The capacitance of the transmitting coil; The capacitance of the passive parasitic coil; The capacitance of the receiving coil; The inductance of the transmitting coil; The inductance of the passive parasitic coil; The inductance of the receiving coil; N The number of turns of the transmitting coil, the passive parasitic coil, or the receiving coil; The vacuum permeability; The radius of the transmitting coil; The radius of the passive parasitic coil; The radius of the receiving coil; The axial distance between the transmitting coil and the receiving coil; The axial distance between the passive parasitic coil and the receiving coil is denoted as .

2. The launching device according to claim 1, characterized in that, The receiving coil at angular frequency Current under The solution obtained by solving the equivalent circuit model is as follows: in, The impedance of the transmitting coil is... ; The impedance of the passive parasitic coil is... ; The impedance of the receiving coil is... .

3. The launching device according to claim 1, characterized in that, The resistance of the transmitting coil The resistance of the passive parasitic coil The resistance of the receiving coil Same, denoted as R The inductance of the transmitting coil The inductance of the passive parasitic coil The inductance of the receiving coil Same, denoted as L The capacitance of the transmitting coil The capacitance of the passive parasitic coil The capacitance of the receiving coil Same, denoted as C ; at this time, in, The resonant angular frequency of the transmitting coil, the passive parasitic coil, or the receiving coil. ; Let be the coupling coefficient between the transmitting coil and the receiving coil. ; The coupling coefficient between the passive parasitic coil and the transmitting coil is denoted as . .

4. The launching device according to claim 3, characterized in that, The peak power of the receiving coil ;in: 。 5. The launching device according to claim 1, characterized in that, When the ratio of the axial distance between the transmitting coil and the receiving coil to the radius of the transmitting coil is greater than a preset ratio, the equivalent circuit model simplifies to: At this time, the current of the receiving coil for: when The current of the receiving coil at that time for: in, ; .

6. The launching device according to any one of claims 1-5, characterized in that, The transmitting device further includes an adjustment module for adjusting the distance between the transmitting coil and the passive parasitic coil, such that when the transmitting device transmits a signal, the power at each frequency point between the two peaks of the signal received by the receiving coil is greater than or equal to the half-power bandwidth threshold.

7. The launching device according to any one of claims 1-5, characterized in that, The transmitting device further includes: the source parasitic coil is used to place between the transmitting coil and the receiving coil.

8. The launching device according to any one of claims 1-5, characterized in that, Also includes: A signal generator, a first LC tuning circuit, and a second LC tuning circuit; the signal generator is connected in series with the transmitting coil through the first LC tuning circuit. The second LC tuning circuit is connected in series with the passive parasitic coil; The first LC tuning circuit is used to make the transmitting coil resonate; The second LC tuning circuit is used to make the passive parasitic coil resonate; The receiving device further includes: a third LC tuning circuit and a signal analyzer; The signal analyzer is connected in series with the receiving coil via a third LC tuning circuit; The third LC tuning circuit is used to make the receiving coil resonate.

9. A magnetic induction communication system, characterized in that, include: A transmitting device and a receiving device; wherein the transmitting device is the transmitting device according to any one of claims 1-8; the receiving device includes: a receiving coil.

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