CN117811615A - Underground magnetic induction communication channel acquisition method and application facing metal environment - Google Patents
Underground magnetic induction communication channel acquisition method and application facing metal environment Download PDFInfo
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Abstract
The invention discloses a method for acquiring an underground magnetic induction communication channel facing a metal environment and application thereof, belonging to the technical field of magnetic induction line communication; the method comprises the steps of enabling a transmitting coil, a metal plate and a receiving coil to be equivalent to three mutually coupled circuits, listing a voltage equation of each circuit based on kirchhoff's law, obtaining a voltage equation set, calculating mutual inductance between the transmitting coil and the receiving coil, mutual inductance between the transmitting coil and the metal plate and mutual inductance between the metal plate and the receiving coil, substituting the mutual inductance into the voltage equation set to solve, and further obtaining channel information; the invention provides an analytical model of a magnetic induction communication channel in a metal environment, which can be used for describing the association among a plurality of variables affecting the channel, considers the influence of actual circuit parameters on a magnetic induction system by constructing an equivalent circuit, lists a voltage equation set according to the coupling relation among a transmitting coil, a metal plate and a receiving coil, and can accurately acquire the underground magnetic induction communication channel of the metal environment with lower calculated amount.
Description
Technical Field
The invention belongs to the technical field of magnetic induction line communication, and particularly relates to a method for acquiring an underground magnetic induction communication channel facing a metal environment and application thereof.
Background
The wireless underground sensor network (Wireless Underground SensorNetworks) is an emerging research field in the 21 st century, and is widely applied to the fields of intelligent agriculture, mine rescue, geological earthquake prediction, border patrol, security protection and the like. Because of the large attenuation of links of wireless subsurface sensor networks due to the need for signals to travel through soil, rock, and water in the subsurface, establishing reliable communication links in non-uniform and varying subsurface environments presents challenges. In order to solve these problems, magnetic induction communication (Magnetic Induction Communication) is proposed, which transmits data by quasi-static magnetic field coupling, the transmission characteristics of which depend mainly on the permeability of the medium. Thus, the magnetic induction signal can similarly penetrate most of the underground without high path loss, thereby ensuring the stability and robustness of the wireless underground sensor network link.
The acquisition of an underground magnetic induction communication channel is critical to the design and implementation of an underground communication system and the entire sensor network. However, in practical underground environments, metal objects are usually contained, and eddy currents are excited on the surface of the metal objects in a time-varying magnetic field, so that a secondary magnetic field is generated, and a magnetic induction channel has frequency selectivity, so that a traditional channel model is not applicable any more. For underground magnetic induction communication in a metal environment, most of the existing researches establish numerical models of magnetic induction transmission in the metal environment through finite element simulation, however, calculation of the models requires a large amount of running time and storage space, and correlation among a plurality of variables affecting channels cannot be described. In order to solve the problems, the method for acquiring the underground magnetic induction communication channel facing the metal environment derives the signal intensity of the receiving end by calculating the secondary magnetic field generated on the metal, and does not consider the influence of actual circuit parameters on a magnetic induction system in magnetic field analysis, so that the underground magnetic induction communication channel facing the metal environment cannot be accurately acquired.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides a method for acquiring an underground magnetic induction communication channel facing a metal environment and application thereof, and aims to accurately acquire the technical problem of the underground magnetic induction communication channel facing the metal environment with lower calculation amount.
To achieve the above object, in a first aspect, the present invention provides a method for obtaining an underground magnetic induction communication channel facing a metal environment, including:
calculating the mutual inductance between the transmitting coil and the receiving coil, the mutual inductance between the transmitting coil and the metal plate, and the mutual inductance between the metal plate and the receiving coil;
calculating the equivalent inductance and the equivalent resistance of the metal plate;
the transmitting coil, the metal plate and the receiving coil are equivalent to three mutually coupled circuits, and the voltage equation of each circuit is listed based on kirchhoff's law to obtain a voltage equation set;
and substituting the mutual inductance between the transmitting coil and the receiving coil, the mutual inductance between the transmitting coil and the metal plate, the mutual inductance between the metal plate and the receiving coil and the equivalent inductance and resistance of the metal plate into the voltage equation set to solve, so as to obtain the transmitting current of the transmitting coil and the receiving current of the receiving coil, and further solve to obtain channel information.
Further preferably, when the secondary inductive path is a reflective path, the mutual inductance M between the transmitting coil and the receiving coil t,r Comprising the following steps: mutual inductance between the transmitting coil and the receiving coil on the reflection path; mutual inductance M between the transmitting coil and the metal plate t,m Comprising the following steps: mutual inductance between the transmitting coil and the metal plate on the reflection path; mutual inductance M between the metal plate and the receiving coil m,r Comprising the following steps: mutual inductance between the metal plate and the receiving coil on the reflection path;
the reflection path is a path formed by the transmitting coil, the metal plate and the receiving coil; on the reflection path, the signal is transmitted to the metal plate through the transmitting coil, a secondary induction signal is generated on the surface of the metal plate, and the secondary induction signal directly reaches the receiving coil from the surface of the metal plate.
Further preferably, the mutual inductance M between the transmitting coil and the receiving coil on the reflection path, and the mutual inductance M between the transmitting coil and the metal plate on the reflection path t,m,f Reverse and reverse directionMutual inductance M between metal plate and receiving coil on radiation path m,r,f The method comprises the following steps of:
wherein μ is the permeability of the transmission medium; n (N) t Turns of the transmitting coil; n (N) r Turns for the receiving coil; a, a t Is the radius of the transmitting coil; a, a r Is the radius of the receiving coil; d is the distance between the transmitting coil and the receiving coil; w is the length of the metal plate; h is the width of the metal plate; taking the center of the transmitting coil as an origin, taking the plane of the transmitting coil as an xy plane, and taking the plane vertical to the transmitting coil as a z axis to establish a rectangular coordinate system, (x) 0 ,y 0 ,z 0 ) Is the coordinate of the center of the metal plate on a rectangular coordinate system; (x, y, z) is the coordinates of any position on the metal plate on a rectangular coordinate system.
Further preferably, when the secondary inductive path is a refractive path, the mutual inductance M between the transmitting coil and the receiving coil t,r Comprising the following steps: mutual inductance between the transmitting coil and the receiving coil on the refraction path; mutual inductance M between the transmitting coil and the metal plate t,m Comprising the following steps: mutual inductance between the transmitting coil and the metal plate on the refraction path; mutual inductance M between the metal plate and the receiving coil m,r Comprising the following steps: mutual inductance between the metal plate and the receiving coil on the refraction path;
the refraction path is a path formed by the transmitting coil, the metal plate and the receiving coil; on the refraction path, the signal is transmitted to the metal plate through the transmitting coil, and after the secondary induction signal is generated on the surface of the metal plate, the signal penetrates through the metal plate to reach the receiving coil.
Further preferably, a mutual inductance M' between the transmitting coil and the receiving coil on the refraction path, and a mutual inductance M between the transmitting coil and the metal plate on the refraction path t,m,z Mutual inductance M between metal plate and receiving coil on refraction path m,r,z The method comprises the following steps of:
M′＝αM 0 S+(1-α)M 0
wherein alpha is an attenuation coefficient, specifically: the ratio of the magnetic flux penetrating the metal plate to the total magnetic flux in the plane of the metal plate; m is M 0 For the mutual inductance of the transmitting coil directly sensed to the receiving coil, in particularS is an attenuation factor; mu is the magnetic permeability of the transmission medium; n (N) t Turns of the transmitting coil; n (N) r Turns for the receiving coil; a, a t Is the radius of the transmitting coil; a, a r Is the radius of the receiving coil; d is the distance between the transmitting coil and the receiving coil; w is the length of the metal plate; h is the width of the metal plate; taking the center of the transmitting coil as an origin, taking the plane of the transmitting coil as an xy plane, and taking the plane vertical to the transmitting coil as a z axis to establish a rectangular coordinate system, (x) 0 ,y 0 ,z 0 ) Is the coordinate of the center of the metal plate on a rectangular coordinate system; (x, y, z) is the coordinates of any position on the metal plate on a rectangular coordinate system.
Further preferably, the magnetic flux phi penetrating the metal plate, the total magnetic flux phi in the plane of the metal plate total The method comprises the following steps of:
wherein alpha is 0 Is the main radiation radius of the magnetic field; i is the current in the transmitting coil; b is the radius of a circle centered on the center point of the metal plate.
Further preferably, the transmitting coil, the metal plate and the receiving coil are equivalent to three mutually coupled circuits, so as to obtain a transmitting circuit, a metal circuit and a receiving circuit;
the transmission circuit includes: the voltage source, the power internal resistance, the transmitting coil inductance and the transmitting end resonance capacitance are connected in series;
the metal circuit includes: a metal plate equivalent resistor and a metal plate equivalent inductor connected in series;
the receiving circuit includes: the receiving coil resistor, the receiving coil inductor, the receiving end resonant capacitor and the load resistor are connected in series;
the above-mentioned voltage equation set is:
wherein Z is t The impedance of the transmitting circuit is specifically:R t the resistance value of the resistance of the transmitting coil; r is R s Is the resistance value of the internal resistance of the power supply; l (L) t The inductance value is the inductance of the transmitting coil; c (C) t The capacitance value of the resonant capacitor of the transmitting end; j is an imaginary symbol; omega is the working frequency of magnetic induction communication; m is M t,r Is the mutual inductance between the transmitting coil and the receiving coil; i t A current for the transmitting circuit; i r A current for the receiving circuit; m is M t,m Is the mutual inductance between the transmitting coil and the metal plate; i m A current that is a metal circuit; u (U) s Is the voltage of the voltage source; z is Z r For impedance of receiving circuitThe method specifically comprises the following steps: />R r The resistance value of the receiving coil resistor; l (L) r An inductance value that is the inductance of the receiving coil; c (C) r The capacitance value of the resonant capacitor of the receiving end; r is R L The resistance value of the load resistor; m is M m,r Is the mutual inductance between the metal plate and the receiving coil; z is Z m The impedance of the metal circuit is specifically: z is Z m ＝R m +jωL m ；R m The resistance value of the equivalent resistance of the metal plate; l (L) m The inductance value is the equivalent inductance of the metal plate.
Further preferably, the sheet metal equivalent resistance has a resistance R m Inductance value L equivalent to metal plate inductance m The method comprises the following steps of:
wherein ρ is the resistivity of the metal plate material; w is the length of the metal plate; h is the width of the metal plate; l is the thickness of the metal plate; mu is the permeability of the transmission medium.
In a second aspect, the present invention provides a method for underground magnetic induction communication in a metal environment, for a transmitting end, including:
coding information to be transmitted by adopting channel information of underground magnetic induction communication to obtain a coding sequence; modulating the coding sequence and then transmitting the coded sequence;
the method for acquiring the underground magnetic induction communication channel is characterized in that the channel information of the underground magnetic induction communication is acquired by adopting the method for acquiring the underground magnetic induction communication channel provided by the first aspect of the invention.
Further preferably, the above-mentioned underground magnetic induction communication method further comprises:
in the transmitting process, the channel capacity is calculated through the channel information so as to control the maximum data volume transmitted by the underground magnetic induction communication channel, thereby regulating and controlling the information volume carried by the transmitting signal.
In a third aspect, the present invention provides a transmitting apparatus comprising: the system comprises a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to execute the underground magnetic induction communication method provided by the second aspect of the invention.
In a fourth aspect, the present invention provides an underground magnetic induction communication system facing a metal environment, which comprises a receiving device and a transmitting device provided in a third aspect of the present invention.
In a fifth aspect, the present invention also provides a computer readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls an apparatus in which the storage medium is located to perform the method for obtaining an underground magnetic induction communication channel provided by the first aspect of the present invention and/or the method for underground magnetic induction communication provided by the second aspect of the present invention.
In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:
1. the invention provides a method for acquiring an underground magnetic induction communication channel facing a metal environment, which comprises the steps of enabling a transmitting coil, a metal plate and a receiving coil to be equivalent to three mutually coupled circuits, listing a voltage equation of each circuit based on kirchhoff's law, obtaining a voltage equation set, calculating mutual inductance between the transmitting coil and the receiving coil, mutual inductance between the transmitting coil and the metal plate and mutual inductance between the metal plate and the receiving coil, substituting the mutual inductance into the voltage equation set to solve, obtaining transmitting current of the transmitting coil and receiving current of the receiving coil, and further solving to obtain channel information; the invention provides an analytical model of a magnetic induction communication channel in a metal environment, which can be used for describing the association among a plurality of variables affecting the channel; the method has the advantages that the influence of actual circuit parameters on the magnetic induction system is considered, an equivalent circuit is constructed, circuit parameters such as a voltage source, a voltage internal resistance and a resonant capacitor in the actual magnetic induction communication system are contained in the model, the method is more suitable for actual application scenes and convenient to analyze, a voltage equation set is listed by combining the coupling relation among the transmitting coil, the metal plate and the receiving coil on the basis, the characteristics of a magnetic induction channel under the influence of metal can be more accurately depicted in a simple mode, meanwhile, the finite element and iterative calculation process is not needed to be divided, the calculated amount is greatly reduced, and meanwhile, the accuracy of acquiring the underground magnetic induction communication channel facing the metal environment is guaranteed.
2. Furthermore, according to the method for acquiring the underground magnetic induction communication channel, provided by the invention, the influence of the metal plate on the magnetic induction system is equivalent to reflection and refraction of a metal object, the conditions of a reflection path and a refraction path are respectively considered and processed, the channel model under various metal distribution conditions is established through an equivalent circuit, and the characteristics of the underground magnetic induction channel when the metal plates with different sizes and distribution exist can be accurately depicted.
3. Further, according to the underground magnetic induction communication channel acquisition method provided by the invention, when the reflection condition is considered, the mutual inductance between the receiving and transmitting coils is not influenced by the metal plate, so that the mutual inductance between the transmitting coil and the receiving coil on the reflection path is expressed as the mutual inductance which is directly sensed by the transmitting coil to the receiving coil; in the case of refraction, the mutual inductance between the receiving and transmitting coils is affected by the metal plate to generate attenuation, so that the transmitting coil directly senses the mutual inductance M of the receiving coil based on the attenuation coefficient alpha, the attenuation factor S and the mutual inductance M 0 The mutual inductance between the transmitting coil and the receiving coil on the refractive path is expressed as M' =αm 0 S+(1-α)M 0 Since only part of magnetic flux can pass through the metal plate to generate attenuation, the mutual inductance value under the refraction condition can be more accurately represented by adding the attenuation coefficient, so that the accuracy of the underground magnetic induction communication channel is further improved.
Drawings
FIG. 1 is a flow chart of a method for acquiring an underground magnetic induction communication channel facing a metal environment according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a reflection metal, a refraction metal and an established rectangular coordinate system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an equivalent circuit and mutual inductance in a metal environment according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of an overall underground magnetic induction communication channel acquisition process provided by an embodiment of the present invention;
FIG. 5 is a schematic diagram showing the variation of the received power with the distance between the receiving and transmitting coils in the simulation and the experiment of the present invention; wherein, (a) is a schematic diagram of the change of the receiving power along with the distance between the receiving and transmitting coils in the simulation; (b) The receiving power is shown as the change of the distance between the receiving coil and the transmitting coil in the experiment;
FIG. 6 is a schematic diagram of the variation of received power with operating frequency for simulation and inventive experiment; wherein, (a) is a schematic diagram of the change of the receiving power along with the working frequency in the simulation; (b) A schematic diagram showing the change of the receiving power along with the working frequency in the experiment of the invention;
FIG. 7 is a schematic diagram of the bandwidth of a received signal as a function of operating frequency for simulation and experiment of the present invention; wherein, (a) is a schematic diagram of the change of the bandwidth of the received signal along with the working frequency in the simulation; (b) The bandwidth of the received signal in the experiment of the invention is shown as the change of the working frequency.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
To achieve the above object, in a first aspect, the present invention provides a method for obtaining an underground magnetic induction communication channel facing a metal environment, as shown in fig. 1, including:
calculating the mutual inductance between the transmitting coil and the receiving coil, the mutual inductance between the transmitting coil and the metal plate, and the mutual inductance between the metal plate and the receiving coil;
calculating the equivalent inductance and the equivalent resistance of the metal plate;
the transmitting coil, the metal plate and the receiving coil are equivalent to three mutually coupled circuits, and the voltage equation of each circuit is listed based on kirchhoff's law to obtain a voltage equation set;
the mutual inductance between the transmitting coil and the receiving coil, the mutual inductance between the transmitting coil and the metal plate, the mutual inductance between the metal plate and the receiving coil, and the equivalent inductance and resistance of the metal plate are substituted into the voltage equation set to be solved, so that the transmitting current of the transmitting coil and the receiving current of the receiving coil are obtained, and further, channel information including the receiving power, the frequency characteristic, the bandwidth and the like of a channel is obtained.
According to the characteristics of secondary induction, the secondary induction of the metal plates at different positions is equivalent to a refraction path and a reflection path, and the primary induction between the receiving and transmitting coils is equivalent to a direct path. And respectively deducing mutual inductance between the receiving and transmitting coils, between the transmitting coil and the metal plate and between the receiving coil and the metal plate under the condition of reflection and refraction of the metal plate. Specifically, the secondary induction of the metal plate can be equivalent to reflection and refraction according to the placement position of the metal plate. In an alternative embodiment, the metal plate forms a metal refraction when placed in parallel with the transceiver coil on the line connecting the center axes of the transceiver coil; when the metal plate is perpendicular to the receiving and transmitting coil and is placed outside the connecting line range of the central axis of the transmitting coil, metal reflection is formed. As shown in fig. 2. Under the reflection condition, the metal plate is parallel to the main magnetic field, only the leakage magnetic flux passes through and induces current in the plate, the induced magnetic field mainly weakens the leakage magnetic flux, the main magnetic field is not weakened, and meanwhile, the generated induced current excites the secondary magnetic field to strengthen the transmission of the main magnetic field to a certain extent. In the case of refraction, the metal plate is perpendicular to the main magnetic field, which is attenuated by the metal plate when transmitted to the receiver coil.
When the secondary induction path is a reflection path, the mutual inductance M between the transmitting coil and the receiving coil t,r Comprising the following steps: mutual inductance between the transmitting coil and the receiving coil on the reflection path; mutual inductance M between the transmitting coil and the metal plate t,m Comprising the following steps: mutual inductance between the transmitting coil and the metal plate on the reflection path; between the metal plate and the receiving coilIs M m,r Comprising the following steps: mutual inductance between the metal plate and the receiving coil on the reflection path;
the reflection path is a path formed by the transmitting coil, the metal plate and the receiving coil; on the reflection path, the signal is transmitted to the metal plate through the transmitting coil, a secondary induction signal is generated on the surface of the metal plate, and the secondary induction signal directly reaches the receiving coil from the surface of the metal plate.
Under the reflection condition, the mutual inductance between the receiving and transmitting coils is not affected by the metal plate, and the mutual inductance M between the transmitting coil and the receiving coil on the reflection path can be expressed as:wherein μ is the permeability of the transmission medium; n (N) t Turns of the transmitting coil; n (N) r Turns for the receiving coil; a, a t Is the radius of the transmitting coil; a, a r Is the radius of the receiving coil; d is the distance between the transmitting coil and the receiving coil.
When the coil size is not enough to be far smaller than the distance, the coil antenna can no longer be regarded as a magnetic dipole, and the magnetic field strength of the transmitting coil can be expressed as
As shown in fig. 2, the center of the transmitting coil is taken as an origin, the plane in which the transmitting coil is located is an xy plane, and a rectangular coordinate system is established by taking the plane perpendicular to the transmitting coil as a z axis, wherein (x, y, z) is the coordinate of any position on the metal plate on the rectangular coordinate system. i. j and k are unit direction vectors in positive directions of x, y and z axes in fig. 2, respectively. In the case of reflection, only the magnetic field in the y direction is taken into account, and the mutual inductance M between the transmitting coil and the metal plate in the reflection path is obtained from m=Φ/I t,m,f Mutual inductance M between metal plate and receiving coil on reflection path m,r,f Expressed as:
wherein W is the length of the metal plate; h is the width of the metal plate; (x) 0 ,y 0 ,z 0 ) Is the coordinate of the center of the metal plate on a rectangular coordinate system; it should be noted that this is only one of the system establishment methods, and a polar coordinate system can be established, and is not limited, M under different system establishment methods t,m,f And M m,r,f The expression of (c) is only adapted accordingly.
When the secondary induction path is a refraction path, the mutual inductance M between the transmitting coil and the receiving coil t,r Comprising the following steps: mutual inductance between the transmitting coil and the receiving coil on the refraction path; mutual inductance M between the transmitting coil and the metal plate t,m Comprising the following steps: mutual inductance between the transmitting coil and the metal plate on the refraction path; mutual inductance M between the metal plate and the receiving coil m,r Comprising the following steps: mutual inductance between the metal plate and the receiving coil on the refraction path;
the refraction path is a path formed by the transmitting coil, the metal plate and the receiving coil; on the refraction path, the signal is transmitted to the metal plate through the transmitting coil, and after the secondary induction signal is generated on the surface of the metal plate, the signal penetrates through the metal plate to reach the receiving coil.
In the case of refraction, the mutual inductance between the transmitting and receiving coils is attenuated by the influence of the metal plate, so that the mutual inductance M' =αm between the transmitting coil and the receiving coil on the refraction path 0 S+(1-α)M 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein alpha is an attenuation coefficient, specifically: the ratio of the magnetic flux penetrating the metal plate to the total magnetic flux in the plane of the metal plate; m is M 0 For the mutual inductance of the transmitting coil directly sensed to the receiving coil, in particularS is an attenuation factor, and specifically: />μ m Sigma is the magnetic conductivity and the electric conductivity of the metal plate respectively, l is the thickness of the metal plate, and omega is the working frequency of magnetic induction communication. In an alternative embodiment: />Magnetic flux phi penetrating the metal plate and total magnetic flux phi in the plane of the metal plate total The method comprises the following steps of:
wherein alpha is 0 The primary radiation radius of the magnetic field is selected to be twice the radius of the transmitting coil in the embodiment; i is the current in the transmitting coil; b is the radius of a circle centered on the center point of the metal plate. As shown in fig. 2, the center of the transmitting coil is taken as the origin, the plane of the transmitting coil is xy-plane, and a rectangular coordinate system is established by taking the plane perpendicular to the transmitting coil as the z-axis, (x) 0 ,y 0 ,z 0 ) Is the coordinate of the center of the metal plate on a rectangular coordinate system; (x, y, z) is the coordinates of any position on the metal plate on a rectangular coordinate system.
Under refraction, only the magnetic field in the z direction is counted into the effective magnetic flux, and the mutual inductance M between the transmitting coil and the metal plate on the refraction path can be obtained t,m,z Mutual inductance M between metal plate and receiving coil on refraction path m,r,z The method comprises the following steps of:
wherein μ is the permeability of the transmission medium; n (N) t Turns of the transmitting coil; n (N) r Turns for the receiving coil; a, a t Is the radius of the transmitting coil; a, a r Is the radius of the receiving coil; d is the distance between the transmitting coil and the receiving coil; w is the length of the metal plate; h is the width of the metal plate.
It should be also noted that this is only one of the system establishment methods, and a polar coordinate system can be established, and M is not limited to the different system establishment methods t,m,z 、M m,r,z 、φ、φ total The expression of (c) is only adapted accordingly.
As shown in fig. 3, in an alternative embodiment, the transmitting coil, the metal plate and the receiving coil are equivalent to three mutually coupled circuits, so as to obtain a transmitting circuit, a metal circuit and a receiving circuit;
the transmission circuit includes: the voltage source, the power internal resistance, the transmitting coil inductance and the transmitting end resonance capacitance are connected in series;
the metal circuit includes: a metal plate equivalent resistor and a metal plate equivalent inductor connected in series;
the receiving circuit includes: the receiving coil resistor, the receiving coil inductor, the receiving end resonant capacitor and the load resistor are connected in series;
the above-mentioned voltage equation set is:
wherein Z is t The impedance of the transmitting circuit is specifically:R t the resistance value of the resistance of the transmitting coil; r is R s Is the resistance value of the internal resistance of the power supply; l (L) t The inductance value is the inductance of the transmitting coil; c (C) t The capacitance value of the resonant capacitor of the transmitting end; j is an imaginary symbol; omega is the working frequency of magnetic induction communication; m is M t,r Is a transmitting coil and a receiving coilMutual inductance between the two; i t A current for the transmitting circuit; i r A current for the receiving circuit; m is M t,m Is the mutual inductance between the transmitting coil and the metal plate; i m A current that is a metal circuit; u (U) s Is the voltage of the voltage source; z is Z r The impedance of the receiving circuit is specifically: />R r The resistance value of the receiving coil resistor; l (L) r An inductance value that is the inductance of the receiving coil; c (C) r The capacitance value of the resonant capacitor of the receiving end; r is R L The resistance value of the load resistor; m is M m,r Is the mutual inductance between the metal plate and the receiving coil; z is Z m The impedance of the metal circuit is specifically: z is Z m ＝R m +jωL m ；R m The resistance value of the equivalent resistance of the metal plate; l (L) m The inductance value is the equivalent inductance of the metal plate.
The mutual inductance between the circuits is also different, due to the difference in magnetic flux caused by reflection and refraction. Respectively M in reflection and refraction scenes t,r 、M t,m And M m,r Substituting the current into the voltage equation set to solve to obtain currents of a transmitting end and a receiving end in different scenes, and further obtaining a channel model.
Specifically, when the secondary sensing path is a reflection path, M is t,r ＝M、M t,m ＝M t,m,f 、M m,r ＝M m,r,f And carrying out the voltage equation set to obtain:
solving the voltage equation set to obtainWherein the method comprises the steps ofk 3 ＝-M m,r,f Z r Z t Z m ，k 5 ＝-MM m,r,f Z m 。
Specifically, when the secondary inductive path is a refractive path, M is t,r ＝M′、M t,m ＝M t,m,z 、M m,r ＝M m,r,z And carrying out the voltage equation set to obtain:
solving the voltage equation set to obtainWherein the method comprises the steps ofk 3 ＝-M m,r,z Z r Z t Z m ，k 5 ＝-M′M m,r,z Z m 。
The resistance R of the equivalent resistance of the metal plate is obtained m Inductance value L equivalent to metal plate inductance m There are various methods of (a) and (b). In an alternative embodiment, the equivalent inductance and equivalent resistance of the metal plate are calculated assuming that the eddy currents are uniformly distributed within the metal plate and circulate in a rectangular path. Specifically, the resistance value R of the metal plate equivalent resistor m Inductance value L equivalent to metal plate inductance m The method comprises the following steps of:
wherein ρ is the resistivity of the metal plate material; w is the length of the metal plate; h is the width of the metal plate; l is the thickness of the metal plate; mu is the permeability of the transmission medium.
In a second alternative embodiment, the sheet metal equivalent resistance has a resistance valueWherein h is the equivalent depth of the vortex ring, r 1 Is the outer radius of the vortex equivalent loop, r 2 σ is the metal sample conductivity, which is the inner radius of the equivalent loop. Inductance value L of metal plate equivalent inductance m ＝μ 0 S(r 1 ,r 2 ) Wherein S (r 1 ,r 2 ) Is the sum coil outer diameter r 1 And an inner diameter r 2 Related expressions.
The range and depth of the vortex in the second alternative embodiment are relatively difficult to obtain compared to the first alternative embodiment, and therefore the first alternative embodiment is preferably used.
A schematic diagram of the overall subsurface magnetic induction communication channel acquisition process is shown in fig. 4. In the magnetic field analysis stage, secondary induction generated by metal eddy current is equivalent to refraction and reflection of signals according to the placement position of a metal plate, and mutual inductance between receiving and transmitting coils and between metal and coils, and equivalent resistance and equivalent inductance of the metal are calculated according to different conditions; in the circuit analysis stage, the receiving and transmitting coil and the metal plate are equivalent to a transmitting circuit, a receiving circuit and a metal circuit, parameters calculated by magnetic field analysis are substituted, a voltage equation is listed for each loop, a transmitting current and a receiving current are obtained by solving a joint equation set, a channel model is further obtained, and communication indexes such as receiving power, frequency characteristics, bandwidth and the like are analyzed. The invention provides an analysis method of magnetic induction channel modeling facing to a metal environment by a method combining magnetic field and circuit analysis, which can accurately characterize the characteristics of a magnetic induction channel under the influence of metal and can characterize the influence of metal plates with different positions and different sizes on the magnetic induction communication channel.
When a plurality of metal blocks exist in the underground magnetic induction communication environment, the method for acquiring the underground magnetic induction communication channel is adopted for solving the metal blocks.
The invention provides a modeling method of an underground magnetic induction channel facing to a metal environment, which establishes a comprehensive and accurate analytic channel model for underground magnetic induction communication. The influence of the rectangular metal plate on the magnetic induction system is studied, the secondary induction of the metal object is equivalent to reflection and refraction, channel models under various metal distribution conditions are established through an equivalent circuit, and the mathematical expression of mutual inductance and parameters of the metal equivalent circuit are strictly deduced. The method can accurately characterize the underground magnetic induction channel when single metal plates and multiple metal plates with different sizes and distributions exist.
In order to further illustrate the performance of the method for obtaining an underground magnetic induction communication channel facing to a metal environment provided by the present invention, the following details are described in connection with specific experiments:
the experiment first researches the received power of magnetic induction communication under different distances. The distance between the transmitting coil and the receiving coil varies between 0.2m and 0.5 m. The position of the transmitter coil is kept unchanged, the receiver coil is gradually far away, the working frequency is 0.82MHz, the resonance capacitor is connected in series to enable the receiving-transmitting coil to generate resonance on the working frequency, the metal plate is a copper plate, and the length, the width and the thickness of the copper plate are respectively 10cm, 10cm and 1mm. In the case of reflection, the copper plate is located (10,5,0) parallel to the coil axis; in the case of refraction, the copper plate is located (10,0,0) perpendicular to the coil axis, all coordinates being in cm. Fig. 5 shows the received powers of the original channel, the single reflection channel, and the single refraction channel, and it can be seen that the variation trend of the experiment is similar to the simulation. The reflected channel enhances the received power, while the refracted channel cuts the received power. However, the experimental data received relatively little power, since the circuit loss and joule heating consumed by the metal plate are not accounted for and do not affect the accuracy of the channel model in the present invention.
Next, the experiment investigated magnetic induction communication channels containing metal plates at different frequencies. The operating frequency varies from 0.25MHz to 3.2MHz, each frequency having its corresponding resonant capacitance, so that both the transmitting coil and the receiving coil reach a resonant state. The distance between the receiving coil and the transmitting coil is fixed to be 20cm, the metal plate is also a copper plate, and the length, the width and the thickness of the copper plate are also respectively 10cm, 10cm and 1mm. The copper plate is centered (5,5,0) in the case of reflection and (5,0,0) in the case of refraction. As shown in fig. 6, the experimental variation trend of different frequencies is consistent with the simulation result. It can be seen that in all three cases the received power increases with increasing frequency and that reflection enhances the power of the magnetically induced signal and refraction attenuates the power. This shows that the magnetic induction channel has frequency selective characteristics, and the reflection channel of the high frequency band can better enhance the signal intensity.
Finally, the influence of the metal plate on the bandwidth of the magnetic induction communication is studied, and the bandwidth of the magnetic induction communication is represented by adopting a 3dB bandwidth. In the experiment, the distance between the receiving coil and the transmitting coil is fixed to be 20cm, a copper plate is also selected as the metal plate, and the length, the width and the thickness of the copper plate are respectively 20cm, 20cm and 1mm. A resonance capacitor is connected in series in the transmitting and receiving coils, and the resonance frequency is set to 1.88MHz. The experiment changes the working frequency of the signal, and obtains the 3dB bandwidth by measuring the frequency bandwidth of the received signal (the bandwidth refers to the frequency range in which the highest point of the received power is reduced by 3 dB); when the frequency deviates from the resonance frequency, the resonance state of the coil disappears, resulting in a decrease in the received power. The simulation and experimental results are shown in fig. 7, and the results have good consistency. In the simulation, the bandwidths of the original channel, the reflection channel, and the refraction channel are about 0.062MHz, 0.058MHz, and 0.058MHz, respectively. The channel bandwidth with the conductive object is reduced by 6.5% compared to the original channel.
In the experiment, the bandwidths of the original channel, the reflection channel and the refraction channel were 0.074MHz, 0.072MHz and 0.070MHz, respectively. The presence of the reflective metal plate reduces the communication bandwidth by 2.8%, but increases the signal power by 14.9%, and the bandwidth and power trade-off can be made in practical systems. Whereas in the case of refraction, the communication bandwidth is reduced by 5.4% and the signal power is reduced by 24.2%, which is a disadvantage for magnetic induction communication; it can be seen that accurate acquisition of an underground magnetic induction communication channel is critical for analyzing underground magnetic induction communication performance.
In summary, compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) The analytical channel model in the metal environment provided by the invention does not need to occupy a large amount of CPU resources or overlong calculation time, and a channel modeling method which is as simple as possible is provided while the accuracy is ensured.
(2) The multi-condition Jing Xindao model in the metal environment provided by the invention can analyze the path loss of the metal plate magnetic induction channels with different sizes and different positions, and can more comprehensively describe the characteristics of the underground magnetic induction channels under the influence of metal.
In a second aspect, the present invention provides a method for underground magnetic induction communication in a metal environment, for a transmitting end, including:
coding information to be transmitted by adopting channel information of underground magnetic induction communication to obtain a coding sequence; modulating the coding sequence and then transmitting the coded sequence;
the method for acquiring the underground magnetic induction communication channel is characterized in that the channel information of the underground magnetic induction communication is acquired by adopting the method for acquiring the underground magnetic induction communication channel provided by the first aspect of the invention.
The related technical solution is the same as the method for obtaining an underground magnetic induction communication channel provided in the first aspect of the present invention, and will not be described herein.
In an alternative embodiment, the above-mentioned underground magnetic induction communication method further includes: in the transmitting process, the channel capacity is calculated through the channel information so as to control the maximum data volume transmitted by the underground magnetic induction communication channel, thereby regulating and controlling the information volume carried by the transmitting signal.
In a third aspect, the present invention provides a transmitting apparatus comprising: the system comprises a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to execute the underground magnetic induction communication method provided by the second aspect of the invention.
The related technical solution is the same as the underground magnetic induction communication method provided in the second aspect of the present invention, and will not be described herein.
In a fourth aspect, the present invention provides an underground magnetic induction communication system facing a metal environment, which comprises a receiving device and a transmitting device provided in a third aspect of the present invention.
The related technical solution is the same as the transmitting device provided in the third aspect of the present invention, and will not be described herein.
In a fifth aspect, the present invention also provides a computer readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls an apparatus in which the storage medium is located to perform the method for obtaining an underground magnetic induction communication channel provided by the first aspect of the present invention and/or the method for underground magnetic induction communication provided by the second aspect of the present invention.
The related technical solutions are the same as the method for obtaining an underground magnetic induction communication channel provided in the first aspect of the present invention and the method for underground magnetic induction communication provided in the second aspect of the present invention, and are not described herein.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. A method for acquiring an underground magnetic induction communication channel oriented to a metal environment, comprising:
calculating the mutual inductance between the transmitting coil and the receiving coil, the mutual inductance between the transmitting coil and the metal plate, and the mutual inductance between the metal plate and the receiving coil;
calculating the equivalent inductance and the equivalent resistance of the metal plate;
the transmitting coil, the metal plate and the receiving coil are equivalent to three mutually coupled circuits, and voltage equations of each circuit are listed based on kirchhoff's law, so that a voltage equation set is obtained;
substituting the mutual inductance between the transmitting coil and the receiving coil, the mutual inductance between the transmitting coil and the metal plate, the mutual inductance between the metal plate and the receiving coil, and the equivalent inductance and the equivalent resistance of the metal plate into the voltage equation set to solve, so as to obtain the transmitting current of the transmitting coil and the receiving current of the receiving coil, and further solve to obtain channel information.
2. The method of claim 1, wherein,
when the secondary induction path is a reflection path, the mutual inductance between the transmitting coil and the receiving coil is the mutual inductance between the transmitting coil and the receiving coil on the reflection path; the mutual inductance between the transmitting coil and the metal plate is the mutual inductance between the transmitting coil and the metal plate on the reflection path; the mutual inductance between the metal plate and the receiving coil is the mutual inductance between the metal plate and the receiving coil on the reflection path;
when the secondary induction path is a refraction path, the mutual inductance between the transmitting coil and the receiving coil is the mutual inductance between the transmitting coil and the receiving coil on the refraction path; the mutual inductance between the transmitting coil and the metal plate is the mutual inductance between the transmitting coil and the metal plate on the refraction path; the mutual inductance between the metal plate and the receiving coil is the mutual inductance between the metal plate and the receiving coil on the refraction path;
the reflection path is a path formed by the transmitting coil, the metal plate and the receiving coil; on the reflection path, a signal is transmitted to the metal plate through the transmitting coil, a secondary induction signal is generated on the surface of the metal plate, and the secondary induction signal directly reaches the receiving coil from the surface of the metal plate;
the refraction path is a path formed by the transmitting coil, the metal plate and the receiving coil; on the refraction path, a signal is transmitted to the metal plate through the transmitting coil, and after a secondary induction signal is generated on the surface of the metal plate, the signal penetrates through the metal plate to reach the receiving coil.
3. The method of claim 2, wherein the mutual inductance between the transmitting coil and the receiving coil in the reflection path is:
M＝M 0
the mutual inductance between the transmitting coil and the receiving coil on the refraction path is as follows:
M′＝αM 0 S+(1-α)M 0
wherein M is 0 For the mutual inductance of the transmitting coil directly sensed to the receiving coil, in particularMu is the magnetic permeability of the transmission medium; n (N) t Turns of the transmitting coil; n (N) r Turns for the receiving coil; a, a t Is the radius of the transmitting coil; a, a r Is the radius of the receiving coil; d is the distance between the transmitting coil and the receiving coil; alpha is an attenuation coefficient, specifically: the ratio of the magnetic flux penetrating the metal plate to the total magnetic flux in the plane of the metal plate; s is an attenuation factor.
4. A method of obtaining an underground magnetic induction communication channel according to claim 3 wherein the magnetic flux phi penetrating the metal sheet, the total magnetic flux phi in the plane of the metal sheet total The method comprises the following steps of:
wherein W is the length of the metal plate; h is the width of the metal plate; alpha 0 Is the main radiation radius of the magnetic field; i is the current in the transmitting coil; b is the radius of a circle taking the center point of the metal plate as the center of the circle; taking the center of the transmitting coil as the origin, the plane of the transmitting coil is xy plane, and the plane is vertical to the transmitting coilThe plane establishes a rectangular coordinate system for the z axis, (x) 0 ,y 0 ,z 0 ) Is the coordinate of the center of the metal plate on a rectangular coordinate system; (x, y, z) is the coordinates of any position on the metal plate on a rectangular coordinate system.
5. The method of claim 2, wherein the mutual inductance between the transmitting coil and the metal plate in the reflection path is:
the mutual inductance between the metal plate and the receiving coil on the reflection path is as follows:
the mutual inductance between the transmitting coil and the metal plate on the refraction path is as follows:
the mutual inductance between the metal plate and the receiving coil on the refraction path is as follows:
wherein W is the length of the metal plate; h is the width of the metal plate; taking the center of the transmitting coil as an origin, taking the plane of the transmitting coil as an xy plane, and taking the plane vertical to the transmitting coil as a z axis to establish a rectangular coordinate system, (x) 0 ,y 0 ,z 0 ) Is the coordinate of the center of the metal plate on a rectangular coordinate system; (x, y, z) is the coordinates of any position on the metal plate on a rectangular coordinate system; mu is the magnetic permeability of the transmission medium; n (N) t Turns of transmitting coil；N r Turns for the receiving coil; a, a t Is the radius of the transmitting coil; a, a r Is the radius of the receiving coil; d is the distance between the transmitting coil and the receiving coil.
6. The method according to any one of claims 1 to 5, wherein the transmitting coil, the metal plate, and the receiving coil are equivalent to three mutually coupled circuits, to obtain a transmitting circuit, a metal circuit, and a receiving circuit;
the transmission circuit includes: the voltage source, the power internal resistance, the transmitting coil inductance and the transmitting end resonance capacitance are connected in series;
the metal circuit includes: a metal plate equivalent resistor and a metal plate equivalent inductor connected in series;
the receiving circuit includes: the receiving coil resistor, the receiving coil inductor, the receiving end resonant capacitor and the load resistor are connected in series;
the system of voltage equations is:
wherein Z is t The impedance of the transmitting circuit is specifically:R t the resistance value of the resistance of the transmitting coil; r is R s Is the resistance value of the internal resistance of the power supply; l (L) t The inductance value is the inductance of the transmitting coil; c (C) t The capacitance value of the resonant capacitor of the transmitting end; j is an imaginary symbol; omega is the working frequency of magnetic induction communication; m is M t,r Is the mutual inductance between the transmitting coil and the receiving coil; i t A current for the transmitting circuit; i r A current for the receiving circuit; m is M t,m Is the mutual inductance between the transmitting coil and the metal plate; i m A current that is a metal circuit; u (U) s Is the voltage of the voltage source; z is Z r The impedance of the receiving circuit is specifically: />R r The resistance value of the receiving coil resistor; l (L) r An inductance value that is the inductance of the receiving coil; c (C) r The capacitance value of the resonant capacitor of the receiving end; r is R L The resistance value of the load resistor; m is M m,r Is the mutual inductance between the metal plate and the receiving coil; z is Z m The impedance of the metal circuit is specifically: z is Z m ＝R m +jωL m ；R m The resistance value of the equivalent resistance of the metal plate; l (L) m The inductance value is the equivalent inductance of the metal plate.
7. A method of underground magnetic induction communication for a metallic environment, comprising:
coding information to be transmitted by adopting channel information of underground magnetic induction communication to obtain a coding sequence; modulating the coding sequence and then transmitting the coded sequence;
wherein, the channel information of the underground magnetic induction communication is obtained by adopting the underground magnetic induction communication channel obtaining method of any one of claims 1-6.
8. The method of claim 7, wherein during transmission, channel capacity is calculated from the channel information to control a maximum amount of data transmitted by the underground magnetic induction communication channel to regulate an amount of information carried by the transmitted signal.
9. A transmitting device, comprising: a memory storing a computer program and a processor which when executed performs the method of underground magnetic induction communication of claim 7 or 8.
10. A metal-environment-oriented underground magnetic induction communication system comprising a receiving device and the transmitting device of claim 9.
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