CN113040741A - Multi-frequency electrical impedance imaging method and system for crop root zone - Google Patents

Abstract

The invention provides a multi-frequency electrical impedance imaging method and a multi-frequency electrical impedance imaging system for a crop root zone, wherein the multi-frequency electrical impedance imaging method for the crop root zone comprises the following steps: exciting an electrode arranged on the boundary of the area to be tested by using a multi-frequency composite excitation signal to obtain a voltage waveform signal; wherein the crop root area is arranged in the area to be detected; the multi-frequency composite excitation signal is formed by superposing a plurality of sine waves with the same amplitude and different frequencies; decomposing the voltage waveform signal in a variation mode to obtain signal components with different frequencies; determining amplitude information and phase information of the signal component based on the signal component; and determining an electrical impedance image of the root zone of the crop based on the amplitude information and the phase information. The multi-frequency signals which can be superposed at one time in parallel are used as excitation signals for scanning, single-frequency signals are quickly separated from the multi-frequency signals, and accurate imaging is realized on the basis of ensuring accurate amplitude and phase and higher signal-to-noise ratio.

Description

Multi-frequency electrical impedance imaging method and system for crop root zone

technical field

The invention relates to the technical field of agricultural production, in particular to a multi-frequency electrical impedance imaging method and system in the root zone of crops.

Background technique

The root zone of a plant is often the "hidden" part of the plant, but its role is very large, and its main function in the traditional sense is to take in water and nutrients. The entire root zone of a plant includes the plant's root system and soil, and the soil provides the necessary water and nutrients for the growth of the root system. The root system of crops is an important organ to maintain the healthy growth of crops, and its growth, death and disease have a great impact on crop yield. Therefore, the root zone is an important part of research to improve crop yield, especially for crops grown in arid regions.

Electrical impedance imaging (Electrical Imedance Tomography, referred to as EIT) technology is a non-invasive, fast, low-cost, safe, and simple system structure imaging technology that utilizes the distribution and changes of electrical impedance in living organisms. The basic principle is to first apply a safe voltage/current excitation to the surface of the object according to the different electrical characteristics of the internal tissue of the object to be measured, and then measure the electrical signal at the boundary of the object to obtain the distribution and change of the internal electrical impedance of the object.

Since the single-frequency electrical impedance imaging technology only uses a fixed frequency as the excitation frequency, the electrical impedance imaging can only obtain the electrical impedance distribution at one frequency at a time, and the state of the organism will also change during the long measurement time. , resulting in a larger error. The multi-frequency electrical impedance imaging technology can quickly obtain the electrical impedance distribution at multiple frequencies, but the existing multi-frequency electrical impedance imaging technology scans frequency-by-frequency serially, and the imaging speed is slow.

Therefore, how to provide a multi-frequency electrical impedance imaging method and system in the root zone of crops, which can scan the superimposed multi-frequency signals as excitation signals at a time in parallel, and quickly separate the single-frequency signals from the multi-frequency signals. Correct imaging under the condition of accurate phase and high signal-to-noise ratio has become an urgent problem to be solved.

SUMMARY OF THE INVENTION

Aiming at the defects in the prior art, the present invention provides a multi-frequency electrical impedance imaging method and system for the root zone of crops.

The invention provides a multi-frequency electrical impedance imaging method of crop root zone, comprising: using multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured to obtain a voltage waveform signal; wherein, the crop root zone is placed on the Inside the area to be tested; the multi-frequency composite excitation signal is composed of a plurality of sine waves with the same amplitude and different frequencies superimposed;

Variational modal decomposition of the voltage waveform signal to obtain signal components of different frequencies;

Based on the signal components, determining amplitude information and phase information of the signal components;

Based on the magnitude information and phase information, an electrical impedance image of the crop root zone is determined.

According to the multi-frequency electrical impedance imaging method of the crop root region provided by the present invention, the multi-frequency composite excitation signal is used to excite the electrodes arranged on the boundary of the area to be measured, and the voltage waveform signal is obtained, which specifically includes:

Selecting adjacent electrode pairs in the electrodes as excitation electrode pairs;

Exciting the excitation electrode pair with the multi-frequency composite excitation signal;

Detecting the voltage between each pair of adjacent measurement electrodes to obtain a voltage waveform signal; wherein, the measurement electrodes are all electrodes except the excitation electrodes;

Repeat the above steps of selecting and exciting the excitation electrode pairs, detecting the voltage between each pair of adjacent measurement electrodes, and acquiring voltage waveform signals, until the voltage waveform signals when all excitation electrode pairs are excited are acquired.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the variational mode decomposes the voltage waveform signal to obtain signal components of different frequencies, which specifically includes:

Taking the number of sine waves constituting the multi-frequency composite excitation signal as the number of layers of variational mode decomposition;

Variational modal decomposition is performed on the voltage waveform signal, and after each layer is decomposed, a signal component of one frequency is obtained until signal components of different frequencies corresponding to the number of layers are obtained.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, determining the amplitude information and phase information of the signal component based on the signal component specifically includes:

The signal component is subjected to quadrature sequence demodulation based on the center frequency of the signal component, and amplitude information and phase information of the signal component are determined.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the quadrature sequence demodulation of the signal component based on the center frequency to determine the amplitude information and phase information of the signal component specifically includes:

According to the center frequency, generate a 0° reference signal and a 90° reference signal of the corresponding frequency;

The signal components are processed using the 0° reference signal and the 90° reference signal, and amplitude information and phase information of the signal components are determined.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the determination of the electrical impedance image of the crop root zone based on the amplitude information and the phase information specifically includes:

Setting the parameters of the area to be measured, electrode parameters, subdivision density, initial electrical impedance, excitation mode, measurement mode and the multi-frequency composite excitation signal;

Set up an electrical impedance imaging positive problem model and an electrical impedance imaging inverse problem model; the positive problem is the known electrical impedance to solve the potential distribution in the area to be measured; the inverse problem is to know the potential distribution in the to-be-measured area to solve the electrical impedance ; Based on the initial electrical impedance, the amplitude information and the phase information, solve the positive problem of electrical impedance imaging, and determine the potential distribution in the area to be measured;

The potential distribution in the area to be measured obtained from each positive problem solution is used as the known condition for solving the inverse problem, and the electrical impedance in the area to be measured obtained from the inverse problem is used as the known condition for the next positive problem solution, and iteratively solves the forward problem and the inverse problem, until the target electrical impedance in the area to be tested that makes the target function reach the minimum value is determined;

determining a target potential distribution in the to-be-measured area based on the target electrical impedance;

An electrical impedance image of the crop root zone is determined based on the target potential distribution.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the multi-frequency composite excitation signal is composed of superposition of multiple sine waves with the same amplitude and a frequency difference of 1 KHz within a frequency range of 100 Hz-5 MHz.

The present invention also provides a multi-frequency crop root zone electrical impedance imaging system, comprising:

a signal acquisition unit, used for using a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured to obtain a voltage waveform signal; wherein, the crop root area is placed inside the area to be measured; the multi-frequency composite excitation The signal consists of multiple sine waves with the same amplitude and different frequencies superimposed;

a signal decomposition unit, used for variational mode decomposition of the voltage waveform signal to obtain signal components of different frequencies;

a signal processing unit, configured to determine amplitude information and phase information of the signal component based on the signal component;

An image generation unit, configured to determine an electrical impedance image of the crop root zone based on the amplitude information and the phase information.

The present invention also provides an electronic device, comprising a memory and a processor, the processor and the memory communicate with each other through a bus; the memory stores program instructions that can be executed by the processor, and the process The computer can call the program instructions to execute the various steps of the above-mentioned multi-frequency electrical impedance imaging method of the crop root zone.

The present invention also provides a non-transitory computer-readable storage medium on which a computer program is stored, and when the computer program is executed by a processor, implements each step of the above-mentioned method for multi-frequency electrical impedance imaging of crop root zone.

The multi-frequency electrical impedance imaging method and system of the crop root zone provided by the present invention can scan the superimposed multi-frequency signals as excitation signals at a time in parallel, quickly separate the single-frequency signals from the multi-frequency signals, and obtain the multi-frequency signals at more frequencies. Imaging information, on the basis of ensuring the accuracy of amplitude, phase and high signal-to-noise ratio, optimizes the imaging effect of the root zone, realizes the function of simultaneous multi-frequency fast imaging, monitors the root health status in real time, and improves crop yield.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

Fig. 1 is the flow chart of the multi-frequency electrical impedance imaging method of crop root zone provided by the present invention;

2 is a schematic flowchart of the steps of a multi-frequency electrical impedance imaging method for crop root zones provided by the present invention;

3 is a multi-frequency signal separation effect diagram provided by the present invention;

4 is a schematic structural diagram of a multi-frequency crop root zone electrical impedance imaging system provided by the present invention;

FIG. 5 is a schematic diagram of the physical structure of the electronic device provided by the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Fig. 1 is a flow chart of a multi-frequency electrical impedance imaging method for crop root zone provided by the present invention. As shown in Fig. 1, the present invention provides a multi-frequency electrical impedance imaging method for crop root zone, comprising:

Step S1, use a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured, and obtain a voltage waveform signal; wherein, the crop root area is placed inside the area to be measured; the multi-frequency composite excitation signal is composed of multiple A superposition of sine waves with the same amplitude and different frequencies;

Step S2, decompose the voltage waveform signal in a variational mode to obtain signal components of different frequencies;

Step S3, based on the signal component, determine the amplitude information and phase information of the signal component;

Step S4, based on the amplitude information and the phase information, determine the electrical impedance image of the root region of the crop.

Specifically, FIG. 2 is a schematic flowchart of the steps of a multi-frequency electrical impedance imaging method for crop root regions provided by the present invention; as shown in FIG. 2 , an FPGA (Field Programmable Gate Array) is used as the control device used in the present invention. Taking a chip as an example, the solution of the present invention will be described. The use of FPGA can realize the rapid generation of multi-frequency load signals and the rapid decomposition of voltage waveform signals. Besides, the FPGA can also be replaced with other chips or microprocessors, which is not limited in the present invention.

The area to be measured is set in advance, multiple electrodes are set on the boundary of the area to be measured, and the root area of the crop to be measured is placed inside the area to be measured.

的关系为，其中N为相位累加器的位数：In the FPGA, n times of direct digital frequency synthesis (Direct Digital Synthesis, DDS) technology is called to generate n single-frequency sinusoidal signals, in which the change of phase increment (PINC) and phase offset (POFF) can realize the Control of frequency and phase of single frequency signal, PINC and POFF and output frequency f _out and initial phase

The relationship is, where N is the number of bits in the phase accumulator:

The multi-frequency composite excitation signal formed by the superposition of n single-frequency sinusoidal signals with the same amplitude and different frequencies obtained is used as the excitation signal. In step S1, the obtained multi-frequency composite excitation signal (that is, the multi-frequency hybrid excitation signal in FIG. 2) is used to excite the electrodes arranged on the boundary of the area to be measured, and the voltage waveform signal (that is, the multi-frequency hybrid measurement signal in FIG. 2) is obtained. .

It should be noted that the shape of the area to be measured is generally set as a circle. In addition, it can also be set to a regular polygon, or an irregular figure, and the number and arrangement of motors set on the boundary of the area to be measured. The method (generally set evenly with the same spacing on the interval of the area to be tested) and the number of layers can be adjusted according to actual needs. Secondly, the number, amplitude, frequency and phase of the sine waves constituting the multi-frequency composite excitation signal can be adjusted according to the actual situation. In addition, the excitation modes using the excitation signal include adjacent excitation, interphase excitation, relative excitation, and cross excitation, etc. The specific excitation mode used can be adjusted according to the actual situation. The above content of the present invention is not limited.

Based on the Variational Mode Decomposition (VMD) blind signal separation technology, in step S2, any voltage waveform signal (blind signal) is subjected to variational modal decomposition to obtain n signals of different frequencies weight.

If only one voltage waveform signal is obtained in step S1, after the variational mode decomposition, n signal components with different frequencies are obtained. If in step S1, M voltage waveform signals are obtained, after the variational modal decomposition, n groups of signal components with different frequencies are obtained, each group contains M signal components of the same frequency, and a total of n*M signal components are obtained signal component.

Taking n as 2 as an example, FIG. 3 is a multi-frequency signal separation effect diagram provided by the present invention. As shown in FIG. 3, 310 is a multi-frequency voltage waveform signal. a single frequency signal component.

In step S3, the signal components obtained in step S2 are demodulated, and amplitude information and phase information corresponding to the signal components one-to-one are determined. Among them, the amplitude information and phase information corresponding to each group of signal components of the same frequency can determine an electrical impedance image.

It should be noted that, in addition to using the quadrature sequence demodulation in the example of FIG. 2, the method of determining the amplitude information and phase information according to the signal components can also use switch demodulation, analog multiplier demodulation (digital quadrature demodulation) demodulation), sample-and-hold demodulation, and zero-crossing phase detection method demodulation, etc. The demodulation method can be adjusted according to the actual situation, which is not limited in the present invention.

In step S4, based on the amplitude information and phase information obtained in step S3, the potential distribution in the area to be measured can be determined, and the electrical impedance image of the crop root area is determined based on the potential distribution.

It should be noted that the method of applying the VMD algorithm to the measurement signal separation of the multi-frequency EIT system in the crop root zone provided by the present invention can not only be used for the electrical impedance imaging of the root zone of the crop to be measured, but also can detect the Other parts, or migrated, are used in fields such as the medical field and the manufacturing field.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, by applying the VMD algorithm to the measurement signal separation of the multi-frequency EIT system of the crop root zone, can scan the superimposed multi-frequency signals as the excitation signal at a time in parallel, and quickly The single-frequency signal is separated from the multi-frequency signal, and the imaging information at more frequencies is obtained. On the basis of ensuring the accuracy of amplitude, phase and high signal-to-noise ratio, the imaging effect of the root zone is optimized to achieve simultaneous multi-frequency fast imaging. Function. It overcomes the shortcoming that a single frequency cannot obtain imaging information at multiple frequencies at the same time, can acquire more imaging information, and make the imaging effect more accurate. It also realizes fast imaging of multiple frequencies at the same time, with fast speed and small error. The method provides a fast and accurate signal separation method for the multi-frequency electrical impedance imaging technology, and can provide help for the imaging of the root zone of the crops, thereby improving the crop yield.

According to the multi-frequency electrical impedance imaging method of the crop root region provided by the present invention, the multi-frequency composite excitation signal is used to excite the electrodes arranged on the boundary of the area to be measured, and the voltage waveform signal is obtained, which specifically includes:

Selecting adjacent electrode pairs in the electrodes as excitation electrode pairs;

Exciting the excitation electrode pair with the multi-frequency composite excitation signal;

Detecting the voltage between each pair of adjacent measurement electrodes to obtain a voltage waveform signal; wherein, the measurement electrodes are all electrodes except the excitation electrodes;

Repeat the above steps of selecting and exciting the excitation electrode pairs, detecting the voltage between each pair of adjacent measurement electrodes, and acquiring voltage waveform signals, until the voltage waveform signals when all excitation electrode pairs are excited are acquired.

Specifically, the present invention uses adjacent excitation and adjacent measurement modes for excitation to obtain voltage waveform signals. The multi-frequency composite excitation signal composed of n single-frequency sinusoidal signals with the same amplitude and different frequencies is denoted as S(t), and the number of electrodes on the boundary of the area to be measured is denoted as 2K (the electrode numbers are 1, 2, ..., 2K).

Correspondingly, the steps of using the multi-frequency composite excitation signal to excite the electrodes arranged on the boundary of the area to be measured to obtain the voltage waveform signal specifically include:

The i-th and i+1 adjacent electrode pairs in the electrodes are selected as excitation electrode pairs, and the remaining other electrodes are used as measurement electrodes.

The excitation electrode pair (electrodes i and i+1) is excited with a multi-frequency composite excitation signal S(t).

Measure the voltage between each pair of adjacent electrodes except the excitation electrodes (ie, each pair of adjacent electrodes in all measurement electrodes, 2N-3 pairs in total), and determine the voltage waveform signal Vjm(t).

Denote i=1 as the first round of stimulation, starting from i=1, repeat the above process in turn, after a total of 2K rounds of stimulation (the electrodes selected in the last round are electrodes numbered 2K and 1) stimulation, each round of stimulation obtains 2K- Three pairs of voltage waveform signals between adjacent electrodes can finally obtain 2K*(2K-3) voltage waveform signals containing n frequencies.

Wherein, in Vjm(t), j=1, 2, 3,..., 2K, m=1, 2,..., 2N-3. j represents the number of excitation rounds, and m represents the number of the voltage waveform signal collected in each round (the recording method of the number can be clockwise or counterclockwise recording of excitation electrodes, etc., which is not limited here).

The advantage of using the adjacent electrode excitation mode is that more independent data can be obtained with the same number of excitation electrodes. Because the detection range of the crop root zone is generally small, and the shortcomings of the adjacent electrode excitation mode, the excitation current is mainly distributed at the edge of the electrode, and the edge resolution of the imaging target is higher, but the imaging resolution in the middle is lower than that of the middle. The influence on the scheme of the present invention is small.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the invention can scan the superimposed multi-frequency signals as excitation signals at a time in parallel, separate the multi-frequency measurement signals into a plurality of single-frequency signals accurately and quickly, and ensure the amplitude and phase. It is accurate, and demodulates each single-frequency signal to obtain a large amount of data for electrical impedance imaging, which realizes fast simultaneous multi-frequency imaging of plant root zone, and can monitor crop growth status in real time, thereby improving crop yield.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the variational mode decomposes the voltage waveform signal to obtain signal components of different frequencies, which specifically includes:

Taking the number of sine waves constituting the multi-frequency composite excitation signal as the number of layers of variational mode decomposition;

Variational modal decomposition is performed on the voltage waveform signal, and after each layer is decomposed, a signal component of one frequency is obtained until signal components of different frequencies corresponding to the number of layers are obtained.

Specifically, n-layer variational modal decomposition is respectively performed on 2K*(2K-3) voltage waveform signals containing n frequencies, and n signal components can be obtained for each voltage waveform signal.

The core of the decomposition method uses the Hilbert function, including the Hilbert transform and the analytic function conversion. During the first decomposition, a voltage waveform signal is used as the basis function. After the first decomposition, a signal is separated. After the components, the remaining unseparated signals become the new basis functions, and the above separation process is repeated. Each iteration separates a signal component and recomposes a new basis function until the signal components of n different frequencies are separated.

梯度下降更新公式。The specific formulas include: the update formula of the basis function u _k , the update formula of the center frequency ω _k of each signal component and

Gradient descent update formula.

使用梯度下降更新。Among them, ω _k is the center frequency formula of each basis function uk, f is the multi-frequency signal to be separated, that is, the pure function form of the basis function, k is the number of separated basis functions,

Update using gradient descent.

Further, it can be understood that due to the signal components separated by the variational mode decomposition method, the order of separation is not regular, and the number of separated signals is large. In order to facilitate subsequent data processing, after determining the waveform of the signal components and After the center frequency is obtained, use the Fourier transform FFT to determine the center frequency of the signal components and sort them (for example, according to the frequency from small to large, all the signal components are divided into a group according to the same frequency).

The multi-frequency electrical impedance imaging method in the crop root zone provided by the present invention applies VMD to the multi-frequency signal separation process of the multi-frequency EIT system in the crop root zone. Scanning, based on variational modal decomposition, accurately and quickly separates the multi-frequency measurement signal into multiple single-frequency signal components, and ensures that the amplitude and phase of the signal components are accurate, and demodulates each single-frequency signal to obtain a large amount of data. Electrical impedance imaging realizes fast simultaneous multi-frequency imaging of plant root zone. The combination of VMD algorithm and agricultural production field has extremely high application value for electrical impedance imaging technology of crop root zone, which can accurately and quickly separate signals, and then It has a great promotion effect on crop yield.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, determining the amplitude information and phase information of the signal component based on the signal component specifically includes:

The signal component is subjected to quadrature sequence demodulation based on the center frequency of the signal component, and amplitude information and phase information of the signal component are determined.

Specifically, the orthogonal sequence demodulation constructs a pair of orthogonal sine sequences, calculates the inner product of the acquired sequence and the two sequences, thereby obtains the real and imaginary parts of the corresponding frequency components, and then determines the amplitude information and phase information.

In the present invention, after the signal components are determined, for each signal component, quadrature sequence demodulation is performed on the signal component based on the center frequency of the signal component, and the amplitude information and phase information of the signal component are determined.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the invention can scan the superimposed multi-frequency signals as excitation signals at a time in parallel, separate the multi-frequency measurement signals into a plurality of single-frequency signals accurately and quickly, and then carry out normalization respectively. Cross-sequence demodulation is used to obtain a large amount of data for electrical impedance imaging, which realizes fast simultaneous multi-frequency imaging of plant root zone, and can monitor crop growth status in real time, thereby improving crop yield.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the quadrature sequence demodulation of the signal component based on the center frequency to determine the amplitude information and phase information of the signal component specifically includes:

According to the center frequency, generate a 0° reference signal and a 90° reference signal of the corresponding frequency;

The signal components are processed using the 0° reference signal and the 90° reference signal, and amplitude information and phase information of the signal components are determined.

Specifically, after acquiring the signal components at n frequencies, according to the center frequency of each signal component, a 0° reference signal and a 90° reference signal of the corresponding frequency are generated.

Among them, ω is the center frequency of each signal component separated by VMD, B is the amplitude of the measurement signal, α is the phase angle of the measurement signal, y _ref0 represents the reference signal of 0°, y _ref90 represents the reference signal of 90°, y _meas represents the signal component.

First, multiply each signal component with the 0° reference signal and 90° reference signal of the corresponding frequency, y ₁ and y ₂ are the results of multiplying the signal component with the 0° reference signal and 90° reference signal of the corresponding frequency respectively:

Pass y ₁ and y ₂ through a low-pass filter and analog-to-digital conversion to get V ₁ and V ₂ :

Finally, the amplitude B (amplitude information) and phase angle α (phase information) of the measured signal can be obtained:

Based on the above method of generating 0° reference signals and 90° reference signals of corresponding frequencies based on the center frequency of the signal components, and determining the amplitude and phase angle, the n*2K*(2K-3) signal components are subjected to quadrature sequence demodulation , can quickly obtain n groups of amplitude and phase information, that is, obtain more data for imaging, and realize fast and accurate imaging of electrical impedance in the root zone of crops.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the invention can scan the superimposed multi-frequency signals as excitation signals at a time in parallel, separate the multi-frequency measurement signals into a plurality of single-frequency signals accurately and quickly, and then separately based on the signals The center frequency of the component generates a 0° reference signal and a 90° reference signal of the corresponding frequency, and performs orthogonal sequence demodulation to obtain a large amount of data for electrical impedance imaging, which realizes fast simultaneous multi-frequency imaging of the root zone of plants, and can monitor crops in real time. growth state, thereby increasing crop yields.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the determination of the electrical impedance image of the crop root zone based on the amplitude information and the phase information specifically includes:

Setting the parameters of the area to be measured, electrode parameters, subdivision density, initial electrical impedance, excitation mode, measurement mode and the multi-frequency composite excitation signal;

Set up an electrical impedance imaging positive problem model and an electrical impedance imaging inverse problem model; the positive problem is the known electrical impedance to solve the potential distribution in the area to be measured; the inverse problem is to know the potential distribution in the to-be-measured area to solve the electrical impedance ; Based on the initial electrical impedance, the amplitude information and the phase information, solve the positive problem of electrical impedance imaging, and determine the potential distribution in the area to be measured;

The potential distribution in the area to be measured obtained from each positive problem solution is used as the known condition for solving the inverse problem, and the electrical impedance in the area to be measured obtained from the inverse problem is used as the known condition for the next positive problem solution, and iteratively solves the forward problem and the inverse problem, until the target electrical impedance in the area to be tested that makes the target function reach the minimum value is determined;

determining a target potential distribution in the to-be-measured area based on the target electrical impedance;

An electrical impedance image of the crop root zone is determined based on the target potential distribution.

Specifically, after measuring the voltage waveform signal in the root zone of the crop, and decomposing it to obtain n groups of signal components at different frequencies, and obtaining the amplitude information and phase information corresponding to the signal components, electrical impedance imaging simulation software, such as EIDORS, is generally used. , to generate an electrical impedance image of the crop root zone.

The electrical impedance image technology is actually based on the acquired data, setting a forward problem and an inverse problem, combining the solution of the forward problem and the inverse problem, inverting the electrical impedance distribution of the root zone of the crop, and further reconstructing the obtained image. The specific steps are as follows:

(1) Set the parameters of the area to be measured (geometric size of the area to be measured), electrode parameters (the number of electrodes, number of layers, distribution position and distribution law), subdivision density (finite element subdivision density), Initial electrical impedance, excitation mode (eg, adjacent excitation, interphase excitation, etc.), measurement mode (eg, adjacent measurement, interphase measurement, etc.), and the multi-frequency composite excitation signal (ie, multi-frequency composite excitation signal).

It should be noted that, the adjustment of the position of the layers and the nucleus of the electrode can make the final image to be different images such as the transverse section, longitudinal section, and 3D image of the crop root zone. limited.

Further, it can be understood that the improved multi-frequency electrical impedance imaging method of the crop root zone of the present invention can also be used to construct a model, and realize data acquisition and electrical impedance imaging based on the model. When setting the model, in addition to the above-mentioned relevant parameters, it is also necessary to set the relevant parameters of the root zone to be tested, such as the size and position of the root zone of the crop to be tested.

(2) Set the positive problem model, and solve the positive problem based on the set electrode contact impedance, excitation mode, measurement mode, multi-frequency composite excitation signal and initial electrical impedance, as well as the determined amplitude and phase information.

The positive problem of EIT is to solve the potential distribution φ of the field with the known electrical impedance σ, which is actually the solution of the boundary value problem of the electromagnetic field, that is, the known data is the impedance distribution and excitation current information in the target domain, so as to calculate the boundary voltage distribution .

The electromagnetic field boundary value problem is usually composed of partial differential equations, basic boundary conditions and natural boundary conditions. According to the definite solution conditions of the boundary value problem, the solution of the field potential φ is related to the distribution of electrical impedance, the shape of the field and the position of the electrode, and the finite element method is used for the positive problem.

For example, for the circular EIT measurement field, the potential distribution function φ and the electrical impedance distribution function σ satisfy the partial differential Laplace equation, namely:

Its boundary conditions include:

Basic boundary conditions:

Natural boundary conditions:

表示场域Ω的边界；f表示已知边界电位；j表示流入场域Ω的电流密度；n表示场域Ω的外法向单位向量。in,

represents the boundary of the field Ω; f represents the known boundary potential; j represents the current density flowing into the field Ω; n represents the outer normal unit vector of the field Ω.

(3) Create an inverse problem model. The inverse problem of EIT is to calculate the internal point impedance distribution through the measured boundary surface voltage. First, the electrical impedance obtained by the inverse problem is obtained, and the electrical impedance obtained by the inverse problem is used as the input of the positive problem to calculate The potential distribution on the outbound boundary.

The objective function is used for continuous iterative comparison, and finally the comparison value is controlled within a certain threshold. At this time, the resistivity distribution that minimizes the above objective function has been found.

The objective function f(ρ) can be selected as:

Among them, ρ is the resistivity distribution vector, v ₀ is the vector of the measured potential value on the surface of the test object, and v(ρ) is the calculated potential vector of the test object surface with the resistivity distribution ρ.

In this scheme, the initial electrical impedance is used to solve the first positive problem. After solving the inverse problem, the electrical impedance solved by the inverse problem is used as a known quantity to solve the positive problem, and the inverse problem and the positive problem are solved iteratively to determine the target electrical impedance. , and then determine the electrical impedance image.

It should be noted that the above-mentioned method for building a model and a specific solution is only a specific example, and for a specific example in which the method provided by the present invention is applied to model building, it can be adjusted according to actual needs in the specific application process. Not limited. It should be noted that, in the improved multi-frequency electrical impedance imaging method of the crop root region of the present invention, after variational modal decomposition, a plurality of signal components at different frequencies can be obtained at one time. Electrical Impedance Image The number of electrical impedance images depends on the number of sine waves that make up the multi-frequency composite excitation signal. Specifically, it can be adjusted according to the actual situation, which is not limited in the present invention.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, by applying the VMD algorithm to the measurement signal separation of the multi-frequency EIT system of the crop root zone, can scan the superimposed multi-frequency signals as the excitation signal at a time in parallel, and quickly The single-frequency signal is separated from the multi-frequency signal, and the imaging information at more frequencies is obtained. On the basis of ensuring the amplitude, phase accuracy and high signal-to-noise ratio, the imaging effect of the root zone is optimized, and the simultaneous multi-frequency fast imaging is realized. Function. It overcomes the shortcoming that a single frequency cannot obtain imaging information at multiple frequencies at the same time, can acquire more imaging information, and make the imaging effect more accurate. It also realizes fast imaging of multiple frequencies at the same time, and can reconstruct multiple images at one time, with fast imaging speed and small error. The method provides a fast and accurate signal separation method for the multi-frequency electrical impedance imaging technology, and can provide help for the imaging of the root zone of crops, thereby improving the crop yield.

According to the multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, the multi-frequency composite excitation signal is composed of superposition of multiple sine waves with the same amplitude and a frequency difference of 1 KHz within a frequency range of 100 Hz-5 MHz.

Specifically, based on the characteristics of the system and EIT technology, when the frequency of the excitation signal is lower than 100Hz, the detection error is large, and when the frequency is higher than 5MHz, signal attenuation is common, so the frequency range of the multi-frequency signal used can be guaranteed within 100Hz-5MHz. All signal components obtained by decomposing the acquired voltage waveform signal can ensure the accurate amplitude, phase and high signal-to-noise ratio.

The selected frequency range is within 100Hz-5MHz, the frequency difference is 1KHz, and multiple sine waves with the same amplitude are superimposed to form a multi-frequency composite excitation signal, which can ensure that the difference in frequency of the decomposed signal components at different frequencies is stable and covers the range. It overcomes the disadvantage that a single frequency cannot obtain imaging information at multiple frequencies at the same time, and can obtain more imaging information and make the imaging effect more accurate.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention selects a frequency range of 100 Hz-5 MHz and a frequency difference of 1 KHz to superimpose a plurality of sine waves with the same amplitude to form a multi-frequency composite excitation signal. The superimposed multi-frequency signal is scanned as an excitation signal, and the multi-frequency measurement signal is accurately and quickly separated into multiple single-frequency signals, ensuring that all signal components obtained by decomposing the acquired voltage waveform signal can ensure accurate amplitude, phase and high. Signal-to-noise ratio. Then, the signal components are demodulated by orthogonal sequence respectively, and a large amount of data is obtained for electrical impedance imaging, which realizes fast simultaneous multi-frequency imaging of plant root zone, and can monitor the growth status of crops in real time, thereby improving crop yield.

The scheme of the present invention is explained below in conjunction with specific application examples:

Taking the transparent cylindrical experimental device as the area to be tested, 32 electrodes are set on the circular plane boundary of the transparent cylindrical experimental device, and the electrode numbers are i=1, 2, . . . , 32. The multi-frequency composite excitation signal S(t) is superimposed by three sine waves with the same amplitude and frequencies of 30 kHz, 50 kHz and 70 kHz respectively.

Add pure brine medium to the transparent cylindrical experimental device, put carrots in the medium as the root area of the crop to be tested, and set carrots on the connection line between No. 1 and No. 17 electrodes, and the center of the circle is away from the plexiglass barrel of the transparent cylindrical experimental device. Center 92.5mm.

The Direct Digital Synthesis (DDS) IP core is called in the FPGA to generate a multi-frequency signal and a multi-frequency composite excitation signal S(t), and the multi-frequency composite excitation signal S(t) is used to analyze the pure signal in the plexiglass barrel. Brine medium and carrots for stimulation. There are 32 electrodes in each layer of the system. The method of adjacent excitation and adjacent measurement is used for signal excitation and acquisition. S(t) is used as the excitation signal, and the voltage waveform signal Vjm(t) is excited and obtained in the circular area to be measured. .

Starting from i=1, i and i+1 are used as a pair of electrodes as excitation electrodes to apply a multi-frequency excitation composite signal S(t) to the detection domain, which is recorded as the first round of stimulation, j=1, and subsequent numbers j=2, 3, .

For the obtained j*m=928 voltage waveforms Vjm signals containing 3 frequencies, the obtained multi-frequency measurement signals are separated by the VMD method, and 3-layer variational modal decomposition (VMD) is performed respectively. Three signal components are obtained, the center frequency and bandwidth of each component are determined, and the mixed signal is effectively separated adaptively, and the center frequency determined by the decomposed signal is sorted and sorted by fast Fourier transform (FFT).

According to the center frequency of each signal component, generate a 0° reference signal and a 90° reference signal of the corresponding frequency, and perform quadrature sequence demodulation on 3*928=2784 signal components, where y _re0 and y _ref90 represent 0° and y ref90, respectively. 90° reference signal, ω is the center frequency of each signal component separated by VMD, B is the amplitude of the measurement signal, α is the phase angle of the measurement signal:

First, multiply each signal component with the 0° reference signal and 90° reference signal of the corresponding frequency, y ₁ and y ₂ are the results of multiplying the signal component with the 0° reference signal and 90° reference signal of the corresponding frequency respectively:

Pass y ₁ and y ₂ through a low-pass filter and analog-to-digital conversion to get V ₁ and V ₂ :

Finally, the amplitude B (amplitude information) and phase angle α (phase information) of the measured signal can be obtained:

Get 3 sets of amplitude and phase information.

The obtained 3 pairs of amplitude and phase information are uploaded to the host computer through USB to reconstruct the electrical impedance image, and 3 images of carrots in pure saline under 32 electrodes can be obtained.

It should be noted that, the above solution is only used as a specific example to explain the multi-frequency crop root zone electrical impedance imaging method provided by the present invention, and the present invention is not limited.

The beneficial effects of the scheme of the present invention are described below in conjunction with experimental data:

Input a multi-frequency signal superimposed by five single-frequency signals for decomposition. The five signals are respectively 1Hz, 10Hz, 100Hz, 500Hz and 1000Hz, and the corresponding amplitudes (units are V) are 0.4 and 0.6 respectively. , 0.8, 1.0, 1.2, the corresponding phases are 10, 20, 30, 40, 50 (unit is °), respectively, simulated in MATLAB, and the decomposition results are as follows:

Table 1 Comparison table of parameter information obtained by VMD and orthogonal decomposition methods

The orthogonal decomposition method has poor decomposition effect for the latter two frequencies. It can be seen that when there are many mixed frequencies, the effect of orthogonal decomposition is not good, but the decomposition result of VMD is still stable.

In order to verify the decomposition effect of these two methods on high-frequency multi-frequency signals, input a multi-frequency signal with a higher frequency superimposed by three single-frequency signals for decomposition. The five signals are 30KHz, 100KHz and 5MHz, the corresponding amplitudes are 0.4, 0.6, and 0.8, respectively, and the corresponding phases are 10, 20, and 30, respectively. Simulations are carried out in MATLAB, and the decomposition results are as follows:

Table 2 Comparison table of parameter information obtained by VMD and orthogonal decomposition method at high frequency

It can be seen that when the frequency is large, the phase of the quadrature decomposition will have a large error, and the effect is not as good as the VMD method. That is, compared with the digital quadrature decomposition technology widely used in multi-frequency signal decomposition, the amplitude and phase precision obtained by the VMD method are higher, and the decomposition is more accurate.

To sum up, the method of the present invention applies VMD to the multi-frequency signal separation process of the multi-frequency EIT system in the crop root zone, realizes the conversion of multi-frequency measurement signals into multiple single-frequency signals, and facilitates the separation of orthogonal sequences. Demodulation, to meet the fast and accurate multi-frequency EIT system. The experimental results show that the combination of the VMD algorithm and the field of agricultural production has a very high application value for the electrical impedance imaging technology of the crop root zone, which can accurately and quickly separate the signals, thereby greatly promoting the crop yield.

FIG. 4 is a schematic structural diagram of a multi-frequency crop root zone electrical impedance imaging system provided by the present invention. As shown in FIG. 4 , the present invention also provides a multi-frequency crop root zone electrical impedance imaging system, including:

The signal acquisition unit 410 is configured to use a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured, and obtain a voltage waveform signal; wherein, the crop root area is placed inside the area to be measured; the multi-frequency composite excitation signal The excitation signal is composed of multiple sine waves with the same amplitude and different frequencies.

a signal decomposition unit 420, configured to decompose the voltage waveform signal in a variational mode to obtain signal components of different frequencies;

a signal processing unit 430, configured to determine amplitude information and phase information of the signal component based on the signal component;

The image generation unit 440 is configured to determine an electrical impedance image of the crop root zone based on the amplitude information and the phase information.

Specifically, FIG. 2 is a schematic flowchart of the steps of a multi-frequency electrical impedance imaging method for crop root regions provided by the present invention; as shown in FIG. 2 , an FPGA (Field Programmable Gate Array) is used as the control device used in the present invention. Taking a chip as an example, the solution of the present invention will be described. The use of FPGA can realize the rapid generation of multi-frequency load signals and the rapid decomposition of voltage waveform signals. Besides, the FPGA can also be replaced with other chips or microprocessors, which is not limited in the present invention.

The area to be measured is set in advance, multiple electrodes are set on the boundary of the area to be measured, and the root area of the crop to be measured is placed inside the area to be measured.

的关系为，其中N为相位累加器的位数：In the FPGA, n times of direct digital frequency synthesis (Direct Digital Synthesis, DDS) technology is called to generate n single-frequency sinusoidal signals, in which the change of phase increment (PINC) and phase offset (POFF) can realize the Control of frequency and phase of single frequency signal, PINC and POFF and output frequency f _out and initial phase

The relationship is, where N is the number of bits in the phase accumulator:

The multi-frequency composite excitation signal formed by the superposition of n single-frequency sinusoidal signals with the same amplitude and different frequencies obtained is used as the excitation signal. The signal acquisition unit 410 is used for using the obtained multi-frequency composite excitation signal (i.e. the multi-frequency hybrid excitation signal in FIG. 2 ) to excite the electrodes arranged on the boundary of the area to be measured to obtain a voltage waveform signal (i.e. the multi-frequency hybrid measurement in FIG. 2 ). Signal).

It should be noted that the shape of the area to be measured is generally set as a circle. In addition, it can also be set as a regular polygon, or an irregular figure, and the number and arrangement of motors set on the boundary of the area to be measured. The method (generally set evenly with the same spacing on the interval of the area to be tested) and the number of layers can be adjusted according to actual needs. Secondly, the number, amplitude, frequency and phase of the sine waves constituting the multi-frequency composite excitation signal can be adjusted according to the actual situation. In addition, the excitation modes using the excitation signal include adjacent excitation, interphase excitation, relative excitation and cross excitation, etc. The specific excitation mode used can be adjusted according to the actual situation. The above content of the present invention is not limited.

Based on the Variational Mode Decomposition (VMD) blind signal separation technology, the signal decomposition unit 420 is configured to perform variational modal decomposition on any voltage waveform signal (blind signal), and can obtain n different frequencies the signal component.

If the signal acquisition unit 410 only obtains one voltage waveform signal, after the variational modal decomposition, n signal components with different frequencies are obtained. If the signal acquisition unit 410 obtains M voltage waveform signals, after the variational modal decomposition, n groups of signal components with different frequencies are obtained, each group contains M signal components of the same frequency, and a total of n*M signals are obtained weight.

Taking n as 2 as an example, FIG. 3 is a multi-frequency signal separation effect diagram provided by the present invention. As shown in FIG. 3, 310 is a multi-frequency voltage waveform signal. a single frequency signal component.

The signal processing unit 430 is configured to demodulate the signal components obtained by the signal decomposition unit 420, and determine amplitude information and phase information corresponding to the signal components one-to-one. Among them, the amplitude information and phase information corresponding to each group of signal components of the same frequency can determine an electrical impedance image.

It should be noted that, in addition to using the quadrature sequence demodulation in the example of FIG. 2, the method of determining the amplitude information and phase information according to the signal components can also use switch demodulation, analog multiplier demodulation (digital quadrature demodulation) demodulation), sample-and-hold demodulation, and zero-crossing phase detection method demodulation, etc. The demodulation method can be adjusted according to the actual situation, which is not limited in the present invention.

The image generation unit 440 is configured to determine the potential distribution in the area to be measured based on the amplitude information and phase information obtained by the signal processing unit 430, and determine the electrical impedance image of the crop root area based on the potential distribution.

It should be noted that the method of applying the VMD algorithm to the measurement signal separation of the multi-frequency EIT system in the crop root zone provided by the present invention can not only be used for the electrical impedance imaging of the root zone of the crop to be measured, but also can detect the Other parts, or migrated, are used in fields such as the medical field and the manufacturing field.

The multi-frequency electrical impedance imaging method of the crop root zone provided by the present invention, by applying the VMD algorithm to the measurement signal separation of the multi-frequency EIT system of the crop root zone, can scan the superimposed multi-frequency signals as the excitation signal at a time in parallel, and quickly The single-frequency signal is separated from the multi-frequency signal, and the imaging information at more frequencies is obtained. On the basis of ensuring the accuracy of amplitude, phase and high signal-to-noise ratio, the imaging effect of the root zone is optimized to achieve simultaneous multi-frequency fast imaging. Function. It overcomes the shortcoming that a single frequency cannot obtain imaging information at multiple frequencies at the same time, can acquire more imaging information, and make the imaging effect more accurate. It also realizes fast imaging of multiple frequencies at the same time, with fast speed and small error. The method provides a fast and accurate signal separation method for the multi-frequency electrical impedance imaging technology, and can provide help for the imaging of the root zone of the crops, thereby improving the crop yield.

It should be noted that the multi-frequency electrical impedance imaging system of the crop root zone provided by the embodiment of the present invention is used to execute the above-mentioned multi-frequency electrical impedance imaging method of the crop root zone, and its specific implementation is the same as that of the method, which will not be repeated here. .

FIG. 5 is a schematic diagram of the physical structure of the electronic device provided by the present invention. As shown in FIG. 5 , the electronic device may include: a processor (processor) 510, a communication interface (communication interface) 520, a memory (memory) 530 and a communication bus (bus) 540 , wherein the processor 510 , the communication interface 520 , and the memory 530 communicate with each other through the communication bus 540 . The processor 510 can call the logic instructions in the memory 530 to execute the above-mentioned method for multi-frequency electrical impedance imaging in the root zone of crops, including: using a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured, to obtain a voltage waveform signal; wherein , the crop root area is placed inside the area to be measured; the multi-frequency composite excitation signal is composed of a plurality of sine waves with the same amplitude and different frequencies superimposed; the variational mode decomposes the voltage waveform signal to obtain different frequency signal components; based on the signal components, determine amplitude information and phase information of the signal components; based on the amplitude information and phase information, determine the electrical impedance image of the crop root region.

In addition, the above-mentioned logic instructions in the memory 530 can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention can be embodied in the form of a software product in essence, or the part that contributes to the prior art or the part of the technical solution. The computer software product is stored in a storage medium, including Several instructions are used to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disk and other media that can store program codes .

On the other hand, an embodiment of the present invention also provides a computer program product, the computer program product includes a computer program stored on a non-transitory computer-readable storage medium, the computer program includes program instructions, when the program instructions When executed by a computer, the computer can execute the multi-frequency electrical impedance imaging method of the crop root zone provided by the above method embodiments, the method includes: using a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured, and obtain a voltage waveform wherein, the crop root area is placed inside the area to be tested; the multi-frequency composite excitation signal is composed of a plurality of sine waves with the same amplitude and different frequencies superimposed; the voltage waveform signal is decomposed by variational mode , to obtain signal components of different frequencies; based on the signal components, determine the amplitude information and phase information of the signal components; based on the amplitude information and phase information, determine the electrical impedance image of the crop root zone.

In yet another aspect, embodiments of the present invention further provide a non-transitory computer-readable storage medium on which a computer program is stored, and when the computer program is executed by a processor, it is implemented to execute the above embodiments to execute the crop root zone A multi-frequency electrical impedance imaging method, the method comprising: using a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of an area to be measured to obtain a voltage waveform signal; wherein the crop root area is placed inside the area to be measured; The multi-frequency composite excitation signal is composed of a plurality of sine waves with the same amplitude and different frequencies. based on the amplitude information and phase information; determine the electrical impedance image of the crop root zone based on the amplitude information and phase information.

The device embodiments described above are only illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in One place, or it can be distributed over multiple network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution in this embodiment. Those of ordinary skill in the art can understand and implement it without creative effort.

From the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and certainly can also be implemented by hardware. Based on this understanding, the above-mentioned technical solutions can be embodied in the form of software products in essence or the parts that make contributions to the prior art, and the computer software products can be stored in computer-readable storage media, such as ROM/RAM, magnetic A disc, an optical disc, etc., includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to perform the methods described in various embodiments or some parts of the embodiments.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. a crop root zone multi-frequency electrical impedance imaging method, is characterized in that, comprises: Using a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured, to obtain a voltage waveform signal; wherein, the crop root area is placed inside the area to be measured; the multi-frequency composite excitation signal is composed of multiple amplitudes The same sine waves with different frequencies are superimposed; Variational modal decomposition of the voltage waveform signal to obtain signal components of different frequencies; Based on the signal components, determining amplitude information and phase information of the signal components; Based on the magnitude information and phase information, an electrical impedance image of the crop root zone is determined. 2. The multi-frequency electrical impedance imaging method of the crop root zone according to claim 1, wherein the multi-frequency composite excitation signal is used to excite the electrodes arranged on the boundary of the area to be measured, and the voltage waveform signal is obtained, specifically comprising: Selecting adjacent electrode pairs in the electrodes as excitation electrode pairs; Exciting the excitation electrode pair with the multi-frequency composite excitation signal; Detecting the voltage between each pair of adjacent measurement electrodes to obtain a voltage waveform signal; wherein, the measurement electrodes are all electrodes except the excitation electrodes; Repeat the above steps of selecting and exciting the excitation electrode pairs, detecting the voltage between each pair of adjacent measurement electrodes, and acquiring voltage waveform signals, until the voltage waveform signals when all excitation electrode pairs are excited are acquired. 3. The multi-frequency electrical impedance imaging method of crop root zone according to claim 1, wherein the variational mode decomposes the voltage waveform signal to obtain signal components of different frequencies, and specifically comprises: Taking the number of sine waves constituting the multi-frequency composite excitation signal as the number of layers of variational mode decomposition; Variational modal decomposition is performed on the voltage waveform signal, and after each layer is decomposed, a signal component of one frequency is obtained until signal components of different frequencies corresponding to the number of layers are obtained. 4 . The multi-frequency electrical impedance imaging method of crop root zone according to claim 1 , wherein, determining the amplitude information and phase information of the signal component based on the signal component, specifically comprising: 5 . The signal component is subjected to quadrature sequence demodulation based on the center frequency of the signal component, and amplitude information and phase information of the signal component are determined. 5 . The multi-frequency electrical impedance imaging method of crop root zone according to claim 4 , wherein the signal component is demodulated in a quadrature sequence based on the center frequency, and the amplitude of the signal component is determined. 6 . information and phase information, including: According to the center frequency, generate a 0° reference signal and a 90° reference signal of the corresponding frequency; The signal components are processed using the 0° reference signal and the 90° reference signal, and amplitude information and phase information of the signal components are determined. 6. The multi-frequency electrical impedance imaging method of the crop root zone according to claim 5, wherein the determining the electrical impedance image of the crop root zone based on the amplitude information and the phase information specifically comprises: Setting the parameters of the area to be measured, electrode parameters, subdivision density, initial electrical impedance, excitation mode, measurement mode and the multi-frequency composite excitation signal; Set up an electrical impedance imaging positive problem model and an electrical impedance imaging inverse problem model; the positive problem is the known electrical impedance to solve the potential distribution in the area to be measured; the inverse problem is to know the potential distribution in the to-be-measured area to solve the electrical impedance ; Based on the initial electrical impedance, the amplitude information and the phase information, solve the positive problem of electrical impedance imaging, and determine the potential distribution in the area to be measured; The potential distribution in the area to be measured obtained from each positive problem solution is used as the known condition for solving the inverse problem, and the electrical impedance in the area to be measured obtained from the inverse problem is used as the known condition for the next positive problem solution, and iteratively solves the forward problem and the inverse problem, until the target electrical impedance in the area to be tested that makes the target function reach the minimum value is determined; determining a target potential distribution in the to-be-measured area based on the target electrical impedance; An electrical impedance image of the crop root zone is determined based on the target potential distribution. 7. The multi-frequency electrical impedance imaging method of crop root zone according to any one of claims 1-6, wherein the multi-frequency composite excitation signal has a frequency range of 100Hz-5MHz, and a frequency difference of 1KHz. Multiple sine waves with the same amplitude are superimposed. 8. A multi-frequency crop root zone electrical impedance imaging system, comprising: a signal acquisition unit, used for using a multi-frequency composite excitation signal to excite electrodes arranged on the boundary of the area to be measured to obtain a voltage waveform signal; wherein, the crop root area is placed inside the area to be measured; the multi-frequency composite excitation The signal consists of multiple sine waves with the same amplitude and different frequencies superimposed; a signal decomposition unit, used for variational mode decomposition of the voltage waveform signal to obtain signal components of different frequencies; a signal processing unit, configured to determine amplitude information and phase information of the signal component based on the signal component; An image generation unit, configured to determine an electrical impedance image of the crop root zone based on the amplitude information and the phase information. 9. An electronic device, characterized in that it comprises a memory and a processor, and the processor and the memory communicate with each other through a bus; the memory stores program instructions that can be executed by the processor, and the The processor can execute the multi-frequency electrical impedance imaging method of the crop root zone according to any one of claims 1 to 7 by invoking the program instructions. 10. A non-transitory computer-readable storage medium on which a computer program is stored, characterized in that, when the computer program is executed by a processor, the crop root zone multi-frequency resistance according to any one of claims 1 to 7 is realized Anti-imaging methods.

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