CN109543318B - Human body channel modeling method, terminal equipment and storage medium - Google Patents
Human body channel modeling method, terminal equipment and storage medium Download PDFInfo
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Abstract
The invention relates to the technical field of human body channel modeling, and provides a human body channel modeling method, terminal equipment and a storage medium. It can be used to calculate the electromagnetic field distribution in each medium and on each interface when any uniform plane wave is incident on multiple layers of conducting or non-conducting media at different angles. The method further enriches and supplements the incident propagation theory of the electromagnetic wave, and can provide a theoretical basis for the relevant practical application of the microwave radio frequency.
Description
Technical Field
The present invention relates to the field of human body channel modeling technologies, and in particular, to a human body channel modeling method, a terminal device, and a storage medium.
Background
At present, the existing human body channel modeling is mainly concentrated in wearable equipment adopting current coupling human body communication, can be widely applied to a body area network, especially the short-distance wireless communication fields of medical detection, motion monitoring, consumer electronics, soldier monitoring and the like, and has wide application prospect and market potential. For example, the invention patent with the application number of 201410281066.2 provides a human body communication channel modeling method and system based on a non-uniform medium, which divides a human body into a plurality of structure models according to structures, abstracts the structure models into regular geometric bodies, divides the medium layers in the structure models, sets the thickness of each medium layer, and calculates the equivalent electrical parameters of the models. The invention patent with the application number of 201510736412.6 provides a field-circuit combined wearable device multi-coupling type human body channel modeling method, wherein external factors such as parasitic capacitive impedance between electrodes and coupling capacitive impedance of an external environment are equivalent to an external circuit model, and then an electric field model of a human body is combined to form a field-circuit combined wearable device multi-coupling human body channel model. The invention patent with the application number of 201710129609.2 provides a wearable device human body channel modeling method based on a multilayer transmission line model, a human body equivalent geometric model is constructed firstly, then human body distributed impedance is decomposed into axial, annular and radial equivalent distributed impedance, a multilayer transmission line circuit model and a circuit equation based on skin, fat and muscle are established, a voltage and current mathematical expression capable of describing signal transmission along a human body channel is obtained, and therefore the transmission characteristics of the human body channel can be calculated and analyzed. These models are directed to low-frequency (below 20 MHz) body surface and body communication, and are not suitable for implantable devices using radio frequency communication (the implantable communication international standard requires a frequency above 400 MHz).
Most researches on the characteristics of the human body channel of the implanted communication under radio frequency adopt professional electromagnetic field software to simulate and calculate the loss of the whole human body channel between transceivers on a digital human body model or a multilayer plane model, and the researches can not visually reflect the internal mechanism of signal transmission through skin inside and outside a human body, particularly can not describe the transmission characteristics of the signal on different tissue interfaces of the human body. In the prior art, in the method for vertically incident the uniform plane electromagnetic wave to the layered human tissue plane model, the electromagnetic transmission characteristics such as reflection, refraction coefficient and the like of the electromagnetic wave on each human tissue interface are theoretically calculated, unfortunately, the vertical incidence is a special case of electromagnetic wave incident transmission and has no generality. In addition, the existing electromagnetic wave incidence theory mainly provides a method for calculating reflection, refractive index and the like when uniform plane electromagnetic waves obliquely enter a single non-conductive medium interface (two different non-conductive media and one interface) and vertically enter a plurality of layers of different non-conductive media (a plurality of different non-conductive media and a plurality of interfaces), does not relate to oblique incidence of the electromagnetic waves to the plurality of layers of media (a plurality of conductive or non-conductive media and a plurality of interfaces), and is not suitable for channel modeling of a multilayer conductive tissue such as a human body.
In summary, the existing human body channel model and the research method cannot correctly analyze the inherent mechanism of electromagnetic wave propagation in multilayer human body tissues, i.e. the transmission characteristics of the electromagnetic wave in the human body tissues and on different tissue interfaces under the conditions of different frequencies, different angles of incidence, different implantation positions, etc. are not clear, and the real situation of electromagnetic wave propagation in the human body cannot be reflected, so that the method is not suitable for human body channel modeling of implantable equipment.
Disclosure of Invention
In order to solve the above problems, the human body channel modeling method, the terminal device and the storage medium according to the present invention can reflect the actual situation of electromagnetic wave propagation inside the human body, and can be applied to human body channel modeling of an implanted device.
The specific scheme is as follows:
a human body channel modeling method comprises the following steps:
s1: constructing a layered plane geometric model of a specific part of a human body according to a plurality of layers of tissue media of the part;
s2: calculating the relative dielectric constant and the conductivity of each medium;
s3: defining electromagnetic wave expressions of incident waves and reflected waves of each medium;
s4: calculating the complex dielectric constant, wave impedance, wave number and transmission angle on the interface of each medium according to the dielectric constant, the conductivity and the magnetic conductivity of each medium;
s5: calculating the tangential equivalent wave impedance, reflection coefficient and transmission coefficient on each medium interface;
s6: calculating electromagnetic wave expressions in each medium area to obtain a mathematical model for describing human body channel electromagnetic waves based on oblique incidence;
s7: and calculating the propagation condition and path loss of the electromagnetic wave energy in the human body channel by using a human body channel electromagnetic wave mathematical model.
Further, the relative dielectric constant ε of each medium in step S2 r And conductivity σ was calculated using the following method of the 4 th-order Cole-Cole model:
wherein, the first and the second end of the pipe are connected with each other,
is complex relative dielectric constant, ε 'is real part of complex number, ε' is imaginary part of complex number, j is imaginary unit, ε 0 Is the vacuum dielectric constant ε ∞ Is the dielectric constant, Δ ε, at frequencies approaching infinity n Is the dielectric relaxation increase, τ n Is the relaxation time, alpha n Is a coefficient between 0 and 1, σ i Is the conductivity in the static state and ω is the angular frequency.
Further, the electromagnetic wave expression of step S3 is:
…
among them, in a medium n (n =1,2,3.): z = d n Is the interface of the nth medium,. Epsilon n 、σ n 、μ n Dielectric constant, conductivity, and permeability of medium n, respectively, e ni 、e nr Unit vectors of the propagation directions of the incident wave and the reflected wave, respectively, E ni 、E nr The electric field intensity H of the incident wave and the reflected wave respectively ni 、H nr Magnetic field strength of incident wave and reflected wave, respectively, E nim 、E nrm The intensity complex amplitude of the incident wave and the reflected wave, and the incident angle theta ni Angle of reflection theta nr Wave vector k of incident wave and reflected wave respectively ni 、k nr The included angle between the normal line of the interface; k is a radical of cn Is the wave number of the medium n, is a complex number, and the corresponding wave vector is k ni ＝k cni e ni ，k nr ＝k cnr e nr ；η cn Is the eigen wave impedance of medium n, also a complex number; r is a position vector, r = xe x +ye y +ze z ，e x 、e y 、e z Is a unit vector in the directions of x, y and z axes.
Further, the calculation method in step S4 is:
s41: dielectric constant epsilon according to medium n n Conductivity σ n And magnetic permeability mu n Calculating the complex dielectric constant ε of the medium n cn Wave impedance η cn Wave number k cn ：
S42: define with propagation constant: γ = α + j β = jk c Calculating the phase constant beta in the medium n n And attenuation constant alpha n Comprises the following steps:
β n ＝Re(k cn )，α n ＝-Im(k cn )
wherein, re () and Im () respectively represent the real part and the imaginary part of the complex number;
s43: calculating the transmission angle theta at the interface of each medium m Comprises the following steps:
setting up
Angle of incidence of time
Called critical angle of incidence theta c 。
Further, the calculation method in step S5 is:
s51: setting medium interface z = d n Upper reflection coefficient Γ n And a transmission coefficient T n Respectively as follows:
s52: setting a tangential equivalent wave impedance Z on the Z = d plane t Comprises the following steps:
wherein E is t (d) Is the tangential component of the electric field strength in the z = d plane, H t (d) Is the tangential component of the magnetic field strength in the z = d plane;
s53: calculating the tangential equivalent wave impedance Z of each medium interface t Reflection coefficient gamma m And transmissionCoefficient T m Respectively as follows:
(1) Vertically polarized wave
(2) Parallel polarized wave
Further, in step S6, the expression of the mathematical model of the body channel electromagnetic wave is:
(1) Vertically polarized wave
(2) Parallel polarized wave
Wherein H xm And H zm The ratio is expressed as the magnetic field strength in the x and z directions, E xm And E zm The division ratio is an electric field strength representing the x and z directions.
Further, the calculation method in step S7 is:
s71: calculating the average poynting vector S av ：
Wherein H * Is the conjugation of the magnetic field strength H
S72: pathloss PL at a point in the human body channel dB Comprises the following steps:
wherein S is av Is the value of the average poynting vector at that point, S 1av Is the value of the average poynting vector of the incident wave,
a human body channel modeling terminal device comprises a processor, a memory and a computer program stored in the memory and operable on the processor, wherein the processor implements the steps of the above method of the embodiment of the present invention when executing the computer program.
A computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the steps of the above-mentioned method according to an embodiment of the invention.
The invention adopts the technical scheme and has the beneficial effects that: the invention firstly constructs a human body equivalent geometric model, simplifies the human body into a multilayer tissue medium, obtains a mathematical expression capable of describing the spatial distribution of electromagnetic waves when signals are transmitted along a human body channel by deducing the impedance, the reflection coefficient and the transmission coefficient of the tangential equivalent wave on each interface when the electromagnetic waves are obliquely incident to the human body tissue, and can calculate and analyze the transmission characteristic of the human body channel. The invention fully considers the influence of multilayer human tissues on the signal transmission characteristics, is simpler than a modeling method based on electromagnetic field numerical calculation, has small calculation amount, perfects the integrity of human channel modeling, can comprehensively reflect the real situation of an actual measurement environment, has high goodness of coincidence with the channel characteristics of a real human body, can more intuitively and vividly describe the transmission mechanism of signals in a human channel and the transmission characteristics on each tissue interface, provides a more accurate modeling method for the research of the human channel characteristics, provides a basis for the enrichment and development of implantable human communication theories (carrier frequency, coding mode, transmission rate and the like), and lays a theoretical foundation for the development and application of implantable communication devices.
Drawings
Fig. 1 is a schematic diagram of a communication link of an implantable device according to an embodiment of the present invention.
Fig. 2 is a schematic view of a layered planar geometric model of the human abdomen according to the embodiment.
Fig. 3 (a) is a schematic diagram showing a vertically polarized wave in oblique incidence of an electromagnetic wave to an arbitrary n-layer medium in this embodiment.
Fig. 3 (b) is a schematic diagram showing parallel polarized waves in oblique incidence of electromagnetic waves to an arbitrary n-layer medium in this embodiment.
Fig. 4 shows a flow chart of this embodiment.
Detailed Description
To further illustrate the various embodiments, the invention provides the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the embodiments. Those skilled in the art will appreciate still other possible embodiments and advantages of the present invention with reference to these figures.
The invention will now be further described with reference to the accompanying drawings and detailed description.
In the practical application environment of the implantable device, a complete implantable human body communication system mainly comprises a station/base station 1, a transmitting and receiving antenna 2, a human body model 3 and a transceiver 4, as shown in fig. 1 (taking the implantable device located in the abdominal muscle of the human body as an example). When the communication is in 'external → internal', the electric signal generated by the base station signal source is transmitted to the free space through the transmitting antenna, then part of the electric signal is incident to the human body, then the electric signal is transmitted through the human body tissue, finally the signal is received by the implanted device, the electromagnetic wave is transmitted along the human body channel after being transmitted into the human body, because the human body channel is special, the human body channel is composed of a plurality of biological tissues, the dielectric property of each tissue is different, therefore, the signal has different phase coefficients and attenuation coefficients in different tissues when being transmitted along the channel direction, and the reflection phenomenon of the electromagnetic wave can occur on the interfaces of different tissues. The same phenomenon exists when the communication is reversed "in vivo → in vitro".
The first embodiment is as follows:
in order to more vividly and accurately describe the characteristics of the human body channel and the inherent propagation mechanism, and consider the particularity that the human body channel contains multilayer biological tissues, the embodiment provides a human body channel modeling method, which comprises the following steps:
s1: according to the multilayer tissue medium of a specific part of a human body, a layered plane geometric model of the part is constructed.
In this embodiment, taking the human abdomen as an example, the equivalent of the human abdomen is simplified to the layered planar geometric model of the human abdomen shown in fig. 2, which includes 4 layers of tissues including skin, fat, muscle and small intestine. Wherein d is s 、d f 、d m 、d i The thickness of each layer is the thickness of human skin, fat, muscle and intestinal wall.
The incident wave is incident on the interface of air and skin at any angle, and the device can be implanted in any position of muscle, fat and the like in a human body.
It should be noted that, in practical applications, the tissue type, the number of layers, and the thickness of the layered plane geometric model will be different according to the different parts (such as the head, the chest, the arm, etc.) of the human body where the device is implanted.
S2: obtaining the relative dielectric constant of human tissues by using a 4-order Cole-Cole model according to the following formula
ε r And the electrical conductivity σ.
Wherein the content of the first and second substances,
is complex relative dielectric constant, ε 'is real part of complex number, ε' is imaginary part of complex number, j is imaginary unit, ε 0 Is the vacuum dielectric constant ε ∞ Is the dielectric constant, Δ ε, at frequencies approaching infinity n Is the dielectric relaxation increase, τ n Is the relaxation time, alpha n Is a coefficient between 0 and 1, σ i Is the conductivity in the static state and ω is the angular frequency.
The model is a known model, and values of specific parameters corresponding to a specific tissue can be obtained in the model according to specific tissue results (such as skin, fat, muscle, small intestine and the like).
The human tissue is a non-magnetic conductive medium, the relative magnetic permeability is 1, but the dielectric constant and the electric conductivity of the human tissue are related to the frequency, so the relative dielectric constant and the electric conductivity of the human tissue such as skin, fat, muscle and the like under the frequency of 10Hz to 100GHz can be calculated by adopting a 4-order Cole-Cole model.
S3: according to the following formulaCalculating the electric field intensity E of the incident wave of each medium i Magnetic field intensity H i Electric field intensity E of the reflected wave r Magnetic field intensity H r 。
The oblique incidence of uniform planar electromagnetic waves to any n layers of different media is shown in fig. 3 and is divided into two cases: vertically polarized waves and parallel polarized waves. Uniform planar electromagnetic wave at an angle theta 1i Oblique incidence from medium 1 to n layers of medium, z = d 1 ，z＝d 2 ，…，z＝d n Each of the n medium interfaces, i.e., medium 1,2, …, n, has an incident wave and a reflected wave, and medium n +1 (the last layer) has only a transmitted wave.
Thereby, incident waves (E) in each medium region i 、H i ) And a reflected wave (E) r 、H r ) The electromagnetic wave expression of (a) is:
wherein, in medium n (n =1,2,3.): epsilon n 、σ n 、μ n Dielectric constant, conductivity, and permeability of medium n, respectively, e ni 、e nr Unit vectors of the propagation directions of the incident wave and the reflected wave, respectively, E ni 、E nr The electric field intensity of the incident wave and the reflected wave, H ni 、H nr Magnetic field strength of incident wave and reflected wave, respectively, E nim 、E nrm The intensity complex amplitude of the incident wave and the reflected wave, and the incident angle theta ni Angle of reflection theta nr Wave vector k of incident wave and reflected wave respectively ni 、k nr Angle to the interface normal; k is a radical of cn Is the wave number of medium n, is a complex number, and the corresponding wave vector is k ni ＝k cni e ni ，k nr ＝k cnr e nr ；η cn Is the eigenwave impedance of the medium n, also a complex number; r is a position vector, r = xe x +ye y +ze z ，e x 、e y 、e z Is a unit vector in the directions of x, y and z axes.
Due to the electromagnetic wave expressions of the incident wave and the reflected wave, except for E 1im Other numbers are unknown, and therefore, the respective parameters in the above expression are calculated according to the following steps S4 and S5.
S4: calculating the complex dielectric constant ε of each medium cn Wave impedance η cn Wave number k cn Reflection angle and transmission angle at the interface.
According to the electromagnetic characteristic parameter epsilon of medium n n 、σ n 、μ n Then the complex dielectric constant epsilon of each medium n can be calculated cn Wave impedance η cn Wave number k cn Respectively as follows:
define with propagation constant: γ = α + j β = jk c The phase constant beta in the medium n can be calculated n And attenuation constant alpha n Comprises the following steps:
β n ＝Re(k cn )，α n ＝-Im(k cn ) (4)
where Re (), im () respectively represent the real and imaginary parts of the complex numbers.
From Snell's law of reflection "angle of reflection equals angle of incidence", a medium boundary z = d can be defined n The upper incident angle and the reflection angle are:
θ ni ＝θ nr ＝θ n
as can be seen from FIG. 3, when the electromagnetic wave is incident on the medium 1 at the incident angle θ 1 At oblique incidence to the n-layer medium, the transmission angle at the boundary surface 1 is the incident angle θ at the boundary surface 2 2 The transmission angle at the dividing plane 2 is the angle of incidence θ at the dividing plane 3 3 By analogy, the transmission angle at the boundary surface n is the incident angle θ at the boundary surface n + 1 n+1 。
According to Snell transmission law, the method comprises the following steps: beta is a 1 sinθ 1 ＝β m sinθ m (m =2,3, …, n + 1). Further, the transmission at the interface of each medium can be calculatedThe angle is:
note that, according to the above formula, when
The electromagnetic wave will be at the interface z = d m Total reflection occurs when the light beam satisfies
Angle of incidence of time
Called critical angle of incidence theta c I.e. when the angle of incidence is greater than theta c The electromagnetic wave cannot be transmitted into the medium m + 1.
S5: calculating the tangential equivalent wave impedance Z on the interface of each medium t And a reflection coefficient gamma m With a transmission coefficient T m 。
Medium interface z = d n Upper reflection coefficient Γ n And a transmission coefficient T n Is defined as:
in order to calculate the reflection and transmission coefficients of each interface, the present embodiment proposes a tangential equivalent wave impedance concept according to the interface link conditions, and defines the tangential equivalent wave impedance on the z = d plane as:
wherein E is t (d) Is the tangential component of the electric field strength on the z = d plane, H t (d) Is the tangential component of the magnetic field strength in the z = d plane.
Derived tangential equivalent wave impedance Z of each medium interface t Reflection coefficient gamma m With a transmission coefficient T m Respectively as follows:
(1) Vertically polarized wave
(2) Parallel polarized wave
S6: through the values of the parameters in the expression of S3 calculated in the steps S4 and S5, the electromagnetic wave expressions of the incident wave and the reflected wave on the interface of each medium can be determined, and then the electromagnetic wave expressions in each medium region are deduced, so that a mathematical model for describing the human body channel electromagnetic wave based on oblique incidence is obtained.
As can be seen from fig. 3, the total electromagnetic wave in the media 1 to n is the sum of the incident wave and the reflected wave, and only the transmitted wave exists in the medium n +1, so after the reflection coefficient and the transmission coefficient on each interface are calculated, the electromagnetic wave expression in each medium is obtained as follows:
(1) Vertically polarized wave
(2) Parallel polarized wave
Wherein H xm And H zm The ratio is expressed as the magnetic field strength in the x and z directions, E xm And E zm The division ratio is an electric field strength representing the x and z directions.
S7: and calculating the propagation condition and path loss of the electromagnetic wave energy in the human body channel by using a human body channel electromagnetic wave mathematical model.
The propagation of electromagnetic energy along the body channel can be determined by using the average poynting vector S av And (3) calculating:
wherein H * Is the conjugate of the field strength H.
Further, the path loss at a certain point in the body channel can be calculated as follows:
wherein S is av Is the value of the average poynting vector at that point, S 1av Is the value of the average poynting vector of the incident wave, is
In conclusion, the implanted device human body channel modeling method based on oblique incidence of electromagnetic waves to multilayer tissues is completed according to the 7 steps. When the method is used specifically, software such as Mathematica and Matlab or a C language writing program can be used for calculation, for example, a specific flow for establishing a channel model applied in fig. 2 is shown in fig. 4.
In the embodiment, the characteristics of calculating channel loss and the like based on the electromagnetic wave oblique incidence layered tissue human body channel modeling are provided; a calculation method of the tangential equivalent wave impedance, the reflection coefficient and the transmission coefficient on each tissue interface during oblique incidence-based human body channel modeling is provided: formulae (6) to (11); and providing an electromagnetic wave calculation expression of each tissue region during oblique incidence-based human body channel modeling: formulas (12) and (13); the tangential equivalent wave impedance concept is proposed, which is different from the traditional equivalent wave impedance definition, which is:
where E (d) and H (d) are the electric field strength and the magnetic field strength, respectively, on the z = d plane. When the electromagnetic wave is obliquely incident, the electric field intensity and the magnetic field intensity on two sides of the interface are discontinuous, so that the equivalent wave impedance is discontinuous on the interface and cannot be used for calculating the reflection coefficient.
The present invention proposes that the tangential equivalent wave impedance is defined as:
wherein E is t (d) Is the tangential component of the electric field strength in the z = d plane, H t (z) is the tangential component of the magnetic field strength in the z = d plane. According to the linking condition of the interface, the electric field intensity on both sides of the interface is continuous with the tangential component of the magnetic field intensity, so that the impedance of the tangential equivalent wave is continuous everywhere on the interface, and the method is suitable for calculating the reflection coefficient.
The embodiment of the invention takes the human abdomen as an example, the human abdomen is equivalent to 4 layers of tissues of skin, fat, muscle and small intestine, when the implanted antenna is positioned in the muscle, the communication link contains 4 media of air, skin, fat and muscle, and the application scene is shown in figure 1. On the basis of the basic theory of electromagnetic wave propagation, a mathematical equation of propagation characteristics of the uniform plane electromagnetic waves obliquely incident to multilayer human tissues is deduced by combining interface link conditions (boundary conditions), and the mathematical equation mainly comprises tangential equivalent wave impedance, reflection coefficient and transmission coefficient on each tissue interface and mathematical calculation expressions of electromagnetic waves in each tissue region, so that a human channel mathematical model is constructed, and is used for calculating the distribution condition of the electromagnetic fields in human channels (human tissues) and the path loss of the human channels when any uniform plane waves are incident to the human tissues at different angles.
Example two:
the invention further provides a human body channel modeling terminal device, which comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, wherein the processor executes the computer program to realize the steps of the method embodiment of the first embodiment of the invention.
Further, as an executable scheme, the human body channel modeling terminal device may be a computing device such as a vehicle-mounted computer. The human body channel modeling terminal device may include, but is not limited to, a processor, a memory. It is understood by those skilled in the art that the above-mentioned constituent structure of the human body channel modeling terminal device is only an example of the human body channel modeling terminal device, and does not constitute a limitation on the human body channel modeling terminal device, and may include more or less components than the above, or combine some components, or different components, for example, the human body channel modeling terminal device may further include an input/output device, a network access device, a bus, etc., which is not limited by the embodiment of the present invention.
Further, as an executable solution, the Processor may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, a discrete Gate or transistor logic device, a discrete hardware component, and the like. The general processor may be a microprocessor or the processor may be any conventional processor, etc., and the processor is a control center of the human body channel modeling terminal device and connects various parts of the whole human body channel modeling terminal device by using various interfaces and lines.
The memory may be used to store the computer program and/or the module, and the processor may implement various functions of the human body channel modeling terminal device by operating or executing the computer program and/or the module stored in the memory and calling data stored in the memory. The memory can mainly comprise a program storage area and a data storage area, wherein the program storage area can store an operating system and an application program required by at least one function; the storage data area may store data created according to the use of the mobile phone, and the like. In addition, the memory may include high speed random access memory, and may also include non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), at least one magnetic disk storage device, a Flash memory device, or other volatile solid state storage device.
The invention also provides a computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the steps of the above-mentioned method of an embodiment of the invention.
The integrated module/unit of the human body channel modeling terminal device may be stored in a computer-readable storage medium if it is implemented in the form of a software functional unit and sold or used as a separate product. Based on such understanding, all or part of the flow of the method according to the embodiments of the present invention may also be implemented by a computer program, which may be stored in a computer-readable storage medium, and when the computer program is executed by a processor, the steps of the method embodiments may be implemented. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, usb disk, removable hard disk, magnetic disk, optical disk, computer Memory, read-Only Memory (ROM), random Access Memory (RAM), software distribution medium, and the like.
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (6)
1. A human body channel modeling method is characterized by comprising the following steps:
s1: constructing a layered plane geometric model of a specific part of a human body according to a plurality of layers of tissue media of the part;
s2: calculating the relative dielectric constant and the conductivity of each medium;
s3: defining electromagnetic wave expressions of incident waves and reflected waves of each medium;
s4: according to the electromagnetic characteristic parameters of each medium: calculating the complex dielectric constant, wave impedance, wave number and transmission angle on the interface of each medium; the calculation method comprises the following steps:
s41: dielectric constant epsilon according to medium n n Conductivity σ n And magnetic permeability mu n Calculating the complex dielectric constant ε of the medium n cn Wave impedance η cn Wave number k cn ：
Wherein j is an imaginary unit and ω is an angular frequency;
s42: define with propagation constant: γ = α + j β = jk c Calculating the phase constant beta in the medium n n And attenuation constant alpha n Comprises the following steps:
β n ＝Re(k cn )，α n ＝-Im(k cn )
wherein, re () and Im () respectively represent the real part and the imaginary part of the complex number;
s43: calculating the transmission angle theta at the interface of each medium m Comprises the following steps:
setting up
Angle of incidence of time
Called critical angle of incidence θ c ；
S5: calculating the tangential equivalent wave impedance, reflection coefficient and transmission coefficient on each medium interface; the calculation method comprises the following steps:
s51: setting media interface z = d n Of upper reflection coefficient r n And a transmission coefficient T n Respectively as follows:
s52: setting a tangential equivalent wave impedance Z on the Z = d plane t Comprises the following steps:
wherein E is t (d) Is the tangential component of the electric field strength in the z = d plane, H t (d) Is the tangential component of the magnetic field strength in the z = d plane;
s53: calculating the tangential equivalent wave impedance Z of each medium interface t And a reflection coefficient gamma m With a transmission coefficient T m Respectively as follows:
(1) Vertically polarized wave
(2) Parallel polarized wave
S6: calculating electromagnetic wave expressions in each medium region to obtain a mathematical model for describing human body channel electromagnetic waves based on oblique incidence; the expression of the human body channel electromagnetic wave mathematical model is as follows:
(1) Vertically polarized wave
(2) Parallel polarized wave
Wherein E is nim 、E nrm The electric field intensity complex amplitudes of the incident wave and the reflected wave, e x 、e y 、e z Is a unit vector in the directions of x, y and z axes, H xm And H zm Magnetic field strength in x and z directions, respectively, E xm And E zm Electric field strength in x and z directions, respectively;
s7: and calculating the propagation condition and path loss of the electromagnetic wave energy in the human body channel by using a human body channel electromagnetic wave mathematical model.
2. The human channel modeling method of claim 1, wherein: relative dielectric constant ε of each medium in step S2 r And conductivity σ was calculated using the following method of the 4 th-order Cole-Cole model:
wherein the content of the first and second substances,
for complex relative permittivity, ε 'is the real part of the complex number, ε' is the imaginary part of the complex number, ε 0 Is a vacuum mediumElectric constant epsilon ∞ Is the dielectric constant, Δ ε, at frequencies approaching infinity n Is the dielectric relaxation increase, τ n Is the relaxation time, σ i Is the conductivity in the static state.
3. The human channel modeling method of claim 2, wherein: the electromagnetic wave expression of step S3 is:
…
wherein, in medium n: z = d n Is the interface of the nth medium,. Epsilon n 、σ n 、μ n Respectively, the dielectric constant, conductivity, and permeability of the medium n, e ni 、e nr Unit vectors of the propagation directions of the incident wave and the reflected wave, respectively, E ni 、E nr The electric field intensity H of the incident wave and the reflected wave respectively ni 、H nr The magnetic field intensity of the incident wave and the reflected wave, and the incidence angle theta ni Angle of reflection theta nr Wave vector k of incident wave and reflected wave respectively ni 、k nr The included angle between the normal line of the interface; k is a radical of formula cn Is the wave number of the medium n, is a complex number, and the corresponding wave vector is k ni ＝k cni e ni ，k nr ＝k cnr e nr ；η cn Is the eigenwave impedance of the medium n, also a complex number; r is a position vector, r = xe x +ye y +ze z 。
4. The human channel modeling method of claim 1, wherein: the calculation method of the step S7 comprises the following steps:
s71: calculating the average poynting vector S av ：
Wherein H * Is the conjugation of the magnetic field strength H
S72: pathloss PL at a point in the body channel dB Comprises the following steps:
wherein S is av Is the value of the average poynting vector at that point, S 1av Is the value of the average poynting vector of the incident wave,
5. a human body channel modeling terminal device, characterized in that: comprising a processor, a memory and a computer program stored in the memory and running on the processor, the processor implementing the steps of the method according to any of claims 1-4 when executing the computer program.
6. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 4.
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