阅读说明：本技术 一种基于射频信号的粮食水分快速检测方法及系统 (Grain moisture rapid detection method and system based on radio frequency signals ) 是由 杨卫东 李世锋 徐振强 许德刚 李智 李滨 于 2021-08-13 设计创作，主要内容包括：本发明公开了一种基于射频信号的粮食水分快速检测方法及系统,涉及粮食水分检测技术领域,方法包括：确定已知水分含量的粮食,采集穿过所述粮食的射频信号中的相位数据；对所述相位数据进行数据预处理,得到真实相位值；依据所述真实相位值和电磁波原理,得到所述粮食的介电常数；将粮食的介电常数和对应的水分含量输入到学习模型中进行训练,得到水分检测模型；采集穿过待测粮食的射频信号的相位数据,得到待测粮食的介电常数,将所述待测粮食的介电常数输入到所述水分检测模型中,得到待测粮食的水分含量。本发明将介质函数的获取转换为相位的获取,通过简单的仪器设备,即可准确检测出粮食水分含量,具有装置简单、成本低、检测精度高等优点。(The invention discloses a method and a system for quickly detecting grain moisture based on radio frequency signals, which relate to the technical field of grain moisture detection, and the method comprises the following steps: determining grain with known moisture content, and collecting phase data in a radio frequency signal passing through the grain; carrying out data preprocessing on the phase data to obtain a real phase value; obtaining the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle; inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model; and acquiring phase data of a radio frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected. The invention converts the acquisition of the medium function into the acquisition of the phase, can accurately detect the moisture content of the grain by simple instruments and equipment, and has the advantages of simple device, low cost, high detection precision and the like.)

1. A grain moisture rapid detection method based on radio frequency signals is characterized by comprising the following steps:

determining grain with known moisture content, and collecting phase data in a radio frequency signal passing through the grain;

carrying out data preprocessing on the phase data to obtain a real phase value;

obtaining the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle;

inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model;

and acquiring phase data of a radio frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected.

2. The method as claimed in claim 1, wherein the RFID system is used to collect the phase data of the RF signal passing through the grain.

3. The method for rapidly detecting grain moisture based on the radio frequency signal according to claim 2, wherein an AIEN9640 passive tag is selected as the electronic tag of the RFID system;

the transmitting antenna of the reader in the RFID system is an E9208CR/L antenna, and the antenna gain is 9dBi c.

4. The method as claimed in claim 1, wherein the data preprocessing comprises outlier detection and replacement, and phase unwrapping.

5. The method as claimed in claim 4, wherein the method for rapidly detecting moisture in grain based on RF signal comprises detecting and replacing abnormal values by Lauda method.

6. The method as claimed in claim 4, wherein the phase unwrapping is performed by a path integration method.

7. The method as claimed in claim 4, wherein the data preprocessing further comprises data normalization.

8. The utility model provides a grain moisture short-term test system based on radio frequency signal which characterized in that includes:

the data acquisition module is used for determining the grain with known moisture content and acquiring phase data in the radio frequency signal passing through the grain;

the data preprocessing module is used for preprocessing the phase data to obtain a real phase value;

the dielectric constant acquisition module is used for acquiring the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle;

the moisture detection model training module is used for inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model;

and the grain moisture detection module to be detected is used for acquiring the phase data of the radio-frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected.

Technical Field

The invention relates to the technical field of grain moisture detection, in particular to a method and a system for quickly detecting grain moisture based on radio frequency signals.

Background

In the storage period of the grains, a series of indexes such as temperature, moisture, mildew, insect damage and the like of the grains need to be detected. The detection of the index of the water content of the grain is the important factor in the safe storage of the grain. Too high or too low moisture of the grain can affect the quality and safety of the grain. The moisture of the grain is too high, the grain can be mildewed, and the like, and the organic matters in the grain can be damaged if the moisture of the grain is too low, so that the processing quality of the grain is influenced. Therefore, the detection of the moisture content of the food is a great challenge for the different stages of the entire distribution chain of the food from storage to the table.

The existing wheat moisture measurement methods can be roughly divided into two types: direct detection methods and indirect detection methods.

At present, the direct detection method is commonly used by a hot drying method and a chemical method. Wherein the hot drying method is to use the existing method to dry the wheat in an oven at a specific temperature for a certain time to determine the moisture content of the wheat. However, this method is cumbersome and time consuming, and is not suitable for large scale use in wheat trading. The chemical method is to consume the moisture in the wheat sample by using chemical reaction so as to calculate the moisture content of the wheat. But has the disadvantages of high price of used chemical reagents, corrosive damage to instruments and high maintenance cost of the instruments. At present, the situation of detecting the moisture of the grain by a chemical method is rarely seen.

The other method is an indirect measurement method, and the principle of the method is to indirectly detect the moisture content of the grain by using a physical quantity closely related to the moisture content of the grain. The main methods currently well known in the art and academia are capacitive, resistive, neutron and microwave methods. The capacitive moisture detection method is also very popular, but its detection effect is limited by many factors, such as the measurement value being sensitive not only to temperature but also to the flow rate and density of the grain in the dryer, and furthermore the measurement result may be affected by other factors in the measurement process, for example the sensors used need to be recalibrated after a long period of use; the on-line resistance type grain moisture detector used by the resistance method is designed based on a nonlinear correction method between the measurement frequency and the grain moisture content, the detector consists of an upper computer and a lower computer, the lower computer mainly detects the wheat resistance value according to V/F conversion, and the upper computer is mainly used for carrying out nonlinear correction among the moisture content, the measurement frequency and the temperature; the microwave method and the neutron method have the advantages of high precision, high detection speed, no loss, non-invasive detection and the like, can very easily detect the moisture in the grains, but have more complex measuring devices and higher cost.

From the above summary, each method has its own advantages, but has certain limitations in the aspect of realizing grain moisture detection, cannot realize large-scale popularization and application, and is difficult to meet the practical application of grain depots.

With the widespread deployment of a large number of wireless devices, radio frequency technology (RFID) is widely used in our daily lives. The popularization of applications such as sensing, detection and identification based on RFID has received wide attention of researchers at home and abroad. At present, many research teams and research scholars at home and abroad are dedicated to applying the RFID technology to the field of research of the research thereof to research the related technology of the RFID.

In recent years, research and application around RFID technology have had a wide prospect in various industries of society. In academia, the RFID is used for researches such as fine-grained positioning, gesture recognition and material perception. Such as human motion tracking, gesture and activity recognition, elderly fall detection, indoor positioning, etc. These radio frequency based sensing technologies include hyperspectral cameras, infrared mass spectrometry, and high frequency X-ray, among others, are utilized by researchers. However, these hardware devices are often expensive to manufacture, costly to deploy in large-scale grain moisture detection, and inefficient. However, inexpensive passive RFID tags require only 5 cents or even less, and each tag can also be reused multiple times. While the cost of the reader can be amortized over the use of multiple tags at the same time. Therefore, sensing applications based on RFID are favored by many researchers, for example, TagScan uses the propagation characteristics of RFID signals in the target to identify materials. In the actual industry, books are searched for by using RFID robots in intelligent libraries, and each commodity, a bus card, a smart car key and the like are traced by using RFID tags in logistics. Compared with other wireless radio frequency signal devices such as radars, X-rays, CT, near infrared instruments and the like, the RFID tag is small in size and easy to deploy. The RFID signal can penetrate through nonmetal, can run in dark environment and has the advantage of low cost. Making it one of the key technologies in the internet of things (IOT).

Based on the above-mentioned defects of the prior art related to grain moisture detection, how to create a grain moisture detection technology that is fast, accurate, simple, and low-cost is a problem that needs to be solved by those skilled in the art.

Disclosure of Invention

In view of the defects of the grain moisture detection technology and the popularization of the RFID technology in the prior art, the invention provides a grain moisture rapid detection method and system based on radio frequency signals, which can rapidly and accurately detect the moisture content in grains with low cost.

In order to achieve the above purpose, meanwhile, when the radio frequency signal passes through grain media with different moisture contents, the strength loss of the radio frequency signal is a function of the dielectric constant of the material, and the dielectric constant mainly depends on the moisture content of the material, so the invention provides the following technical scheme:

a grain moisture rapid detection method based on radio frequency signals comprises the following steps:

firstly, determining grains with known moisture content, and acquiring phase data in a radio frequency signal passing through the grains;

step two, carrying out data preprocessing on the phase data to obtain a real phase value;

thirdly, obtaining the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle;

inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model;

and step five, acquiring phase data of the radio-frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected.

Preferably, the phase data of the radio frequency signal passing through the grain is collected using an RFID system. The RFID system is used for collecting the characteristic information, and has the advantages of small volume, low cost, capability of penetrating nonmetal, operation in dark environment and the like.

Preferably, the electronic tag of the RFID system is an AIEN9640 passive tag;

the transmitting antenna of the reader in the RFID system is an E9208CR/L antenna, and the antenna gain is 9dBi c.

The data preprocessing comprises abnormal value detection and replacement and phase unwrapping.

Preferably, the detection and replacement of the abnormal value are performed by using the law of Layda, specifically:

sample averaging of all phase data samples

Obtaining the ith phase sample data X according to the sample mean value_iAmplitude residual V of_iAnd the standard deviation σ;

if | V_iIf | is greater than 3 σ, then X_iFor abnormal values, X is further used_iReplacing the abnormal value X by the arithmetic mean of two normal values adjacent to each other_i。

By adopting the method, the influence of data length change caused by removing abnormal values can be avoided.

Phase unwrapping is performed using a path integration method.

The data preprocessing further comprises data normalization, specifically:

normalizing the phase data set after replacing the abnormal value, wherein the ith phase sample data after normalization is Y_i，

Wherein X_iExpressed as the ith original phase sample data, X_meanIs the average of the phases after the replacement of the outliers, X_meanAnd X_minAre the maximum and minimum values of the phase after the replacement of the outlier.

The above process performs data preprocessing on the phase data, and can obtain accurate and clear phase data. Abnormal data values can be removed through abnormal value detection and replacement, data accuracy is guaranteed, detection precision can be improved through data normalization, the requirements of subsequent machine learning and models are met, and true phase data can be guaranteed through phase unwrapping.

The invention also provides a radio frequency signal-based grain moisture rapid detection system, which specifically comprises:

the data acquisition module is used for determining the grain with known moisture content and acquiring phase data in the radio frequency signal passing through the grain;

the data preprocessing module is used for preprocessing the phase data to obtain a real phase value;

the dielectric constant acquisition module is used for acquiring the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle;

the moisture detection model training module is used for inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model;

and the grain moisture detection module to be detected is used for acquiring the phase data of the radio-frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected.

According to the technical scheme, the invention discloses and provides a method and a system for quickly detecting grain moisture based on radio frequency signals, and compared with the prior art, the method and the system have the following beneficial effects:

(1) the invention uses the relationship between the dielectric constant of the grain and the grain moisture to establish a model, and in the traditional method, the dielectric constant is generally acquired by using large-scale expensive equipment such as a vector network analyzer and the like, which is not beneficial to large-scale application.

(2) The invention uses the RFID system to collect the characteristic information (phase data), and has the advantages of small volume, low cost, capability of penetrating nonmetal, operation in dark environment, and the like.

(3) After the phase data information is obtained in the technical scheme of the invention, the data is preprocessed by further using technologies such as Lauda rule, path integration method and the like to obtain accurate phase data information, so that the requirement of subsequent model establishment is met, and an accurate grain moisture detection result is obtained.

(4) According to the method, the phase information of the grain is acquired by introducing the RFID system, the dielectric constant of the grain is acquired through the phase information, and then the relation between the dielectric constant and the grain moisture is established.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a schematic diagram of the process steps of the present invention;

FIG. 2 is a block diagram of a system of the present invention;

FIG. 3 is a phase diagram of the original RF signal of the wheat sample in the example;

FIG. 4 is a diagram showing the phase of the RF signal of the wheat sample after removing the abnormal value in the example;

FIG. 5 is a schematic diagram of wheat moisture content detection accuracy of a moisture detection model based on an SVM algorithm;

FIG. 6 is a schematic diagram of the moisture content detection precision of wheat based on a moisture detection model of a convolutional neural network;

FIG. 7 is a schematic diagram showing the moisture content detection accuracy of five different wheat varieties;

FIG. 8 is a schematic diagram of the moisture content detection accuracy of ten different wheat varieties.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention discloses a method for quickly detecting grain moisture based on radio frequency signals, which is shown in figure 1 and comprises the following steps:

firstly, determining grain with known moisture content, and acquiring phase data in a radio frequency signal passing through the grain.

For acquiring the phase data of the radio frequency signal, in the embodiment of the invention, the Impinj Speedway R420 RFID system is used for acquiring and storing the characteristic value data in the radio frequency signal penetrating through the grain medium, and the phase reading of the RFID system has a finer resolution (0.0015 radian). The universal RFID system comprises four parts, namely a tag, an antenna, a reader and a software system, for the selection of the electronic tag, through the comparison of different tags, the Alien 9640 passive tag is finally selected, in an experiment, the transmitting antenna of the reader adopts an E9208CR/L antenna, and the antenna gain is 9 dBic. In the RFID system, a reader is positioned below a container to transmit a radio frequency signal, an electronic tag positioned above the container receives the radio frequency signal transmitted by the reader, modulates the signal and transmits a return signal to the reader, and the reader receives data information of grain samples.

And collecting the phase data of the radio frequency signal of the grain by using an RFID system. The electronic tag of the RFID system is an AIEN9640 passive tag; the transmitting antenna of the reader in the RFID system is an E9208CR/L antenna, and the antenna gain is 9dBi c.

And secondly, performing data preprocessing on the phase data to obtain a real phase value, wherein the data preprocessing comprises abnormal value detection and replacement and phase unwrapping.

1. Outlier detection and replacement

In the process of radio frequency signal transmission, when the RFID hardware equipment acquires data of various moisture wheat samples, some abnormal data are inevitably acquired. In order to ensure the accuracy of the final result, stable and accurate experimental data need to be obtained. We checked the collected experimental data to remove outliers in the original data. As shown in fig. 3, the phase data corresponds to the collected wheat sample with 13% moisture content. It can be seen from fig. 3 that there are some abnormal high peaks in the data curve, and these abnormal high peaks are the data outliers that we need to remove. If the abnormal values are not processed, result analysis is influenced, and the difficulty of data analysis and verification experiments is increased; on the other hand, the interference and the influence on the final experimental result are also caused, and the accuracy of moisture detection and classification is finally influenced.

The embodiment of the invention uses Lauda rule (3 sigma criterion) to detect and replace abnormal values, specifically:

step (1), order X_i(i-1, 2, …, n) is the phase of the RFID data sample, and the sample mean is determined for all phase data samples

Step (2), the ith phase sample data X is obtained according to the sample mean value_iAmplitude residual V of_iAnd the standard deviation σ.

Step (3) if | V_iIf | is greater than 3 σ, then X_iFor abnormal values, X is further used_iReplacing the abnormal value X by the arithmetic mean of two normal values adjacent to each other_i。

Repeating the steps (1) - (3) until all abnormal values are detected and replaced. As shown in fig. 4, in order to obtain a data curve after performing an abnormal value processing on the phase data corresponding to the wheat sample with the moisture content of 13% by using the law of rayda, as can be seen from a comparison between the two graphs shown in fig. 3 and 4, fig. 4 is a method performed on the phase graph after removing the abnormal value, and the abnormal peak data in the phase data graph has been detected and replaced, that is, the abnormal value in the original data has been removed.

In the above embodiment, the replacement of the abnormal value is performed by taking an average value, and in another embodiment, a median replacement strategy may also be used, which is not limited in the present invention.

2. Data normalization

In one embodiment, in order to speed up the classification speed and the classification accuracy of the classification algorithm used in the subsequent verification experiment, the data preprocessing process further needs to perform a normalization operation on the data set after removing the outlier, i.e. limiting the input data within the range of (0, 1) when performing the algorithm classification, specifically:

normalizing the phase data set after replacing the abnormal value, wherein the ith phase sample data after normalization is Y_i，

Wherein X_iExpressed as the ith original phase sample data, X_meanIs the average of the phases after the replacement of the outliers, X_maxAnd X_minAre the maximum and minimum values of the phase after the replacement of the outlier.

3. Phase unwrapping

Due to the irregular shape of grains and the shape of stacked grains, the path of a phase during propagation is influenced, which causes problems of pi phase jump and phase loss, and in order to eliminate the influence, the phase data needs to be processed after being collected so as to obtain real phase data, which is a classical phase unwrapping problem. Phase unwrapping is further divided into one-dimensional phase unwrapping and two-dimensional phase unwrapping. The RFID phase information collected by the method is one-dimensional information, so the process of solving the real phase of measuring the grain moisture can be called one-dimensional phase unwrapping.

For the problem of one-dimensional phase unwrapping, the method solves the wrapping phase by using a path integration method. The specific process is as follows: the RFID phase measurements in the system can be expressed as:

then, a phase winding operator L is defined, and the periodic winding process in phase propagation can be expressed as:

-π＜L(φ(m))＜π (7)

wherein the measured phase values are obtained from the true phase values by means of a phase wrapping operator L. Then, carrying out differential operation on the two acquired adjacent real phase values to obtain:

Δφ(m)＝φ(m+1)-φ(m) (8)

-π＜Δφ(m)＜π (9)

when the condition of the Nyquist sampling theorem is met, the difference operation is also carried out on the two collected adjacent measurement phase values to obtain:

and then, performing phase winding operation on the measured phase difference through a phase winding operator L to obtain:

L(Δφ(m))＝(Δφ(m)+2Δk(m)π)+2k(m)π (11)

according to the definition of the phase winding operator L. It is possible to obtain:

the integral solving expression of the real phase can be obtained by combining the above formula:

from the definition of the phase winding operator, one can get:

in the embodiment of the invention, the real phase value of the grain sample can be calculated by using the formula.

And thirdly, obtaining the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle.

The real phase value phi of the grain can be obtained in the second step₀Based on the real phase value phi of the grain₀The method for calculating the dielectric constant epsilon of the grain comprises the following steps:

according to Maxwell's electromagnetic wave theory, the velocity v of an electromagnetic wave propagating in a medium is expressed by equation (17):

wherein mu is the relative magnetic permeability of the medium, epsilon is the dielectric constant of the medium, and c is the speed of the electromagnetic wave in the air, and is specifically the eighth power of 3 x 10. Here we define the medium as a grain medium, and from the above equation, the product of the permittivity ∈ and permeability μ of the grain medium is expressed by equation (18):

meanwhile, when the propagation distance and the frequency are unchanged, the phase before and after the target appears can be changed and the wavelength can be changed in the process of RF signal propagation, so that when the medium is converted into grain from air, the propagation speed c and the wavelength lambda of electromagnetic waves in the air and the propagation speed v and the wavelength lambda of electromagnetic waves in the grain medium are the same at the same frequency f₀The relationship can be expressed as in equation (19):

where λ is the wavelength of the electromagnetic wave in air, λ₀Is the wavelength of electromagnetic waves in grain media. Combining equations (19) and (18) to obtain equation (20):

however, it is known that the permeability of the medium is a factor affecting the propagation performance of the electromagnetic wave, and since grain is a non-magnetic medium and the relative permeability thereof is approximately 1, ∈ μ in formula (20) can be regarded as ∈, so that the permittivity ∈ of the grain can be expressed by formula (21):

from the above formula, we can only need to obtain the grain dielectric constant epsilon by only requiring the wavelength of the electromagnetic wave in the air and the wavelength of the electromagnetic wave in the grain medium, wherein the wavelength lambda in the air can be easily calculated from the speed c in the formula (19) and the frequency f of the RF signal, and then only need to obtain lambda₀And (4) finishing.

For lambda₀In the RFID communication system, the real phase phi of the grain medium can be measured₀Determining lambda₀. In the previous subsection, the real phase of the RFID measured grain medium is calculated by a path integration method. Can be expressed as equation (22):

where d is the thickness of the grain medium and C is the inherent system noise generated during RFID system transmission, which we cannot directly eliminate. But C can be eliminated by measuring the phase difference before and after the occurrence of the grain medium by the RFID system. In the experiment, the tag and the antenna can be fixed and fixed, and the grain medium to be detected can be movedMeasuring to obtain the air phase phi_airExpressed as equation (23).

Wherein the wavelength lambda of the air in the formula is obtained by the formula (19), and then the phase difference of the phase change before and after the grain medium appears is obtained by the formulas (22) and (23) to obtain the formula (24):

wherein phi is₀，φ_airλ, d are known, and λ can be obtained from the above equation₀Expressed by equation (25):

then will lambda₀The dielectric constant ε of the grain medium was calculated by substituting the equation (21).

And step four, inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model. The model comprises a Support Vector Machine (SVM) model and a convolutional neural network model.

And step five, acquiring phase data of the radio-frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected.

Another embodiment of the present invention further provides a system for rapidly detecting moisture in grain based on radio frequency signals, referring to fig. 2, including the following components:

the data acquisition module comprises an RFID system and is used for determining the grain with known moisture content and acquiring phase data in a radio frequency signal passing through the grain;

the data preprocessing module is used for preprocessing the phase data to obtain a real phase value;

the dielectric constant acquisition module is used for acquiring the dielectric constant of the grain according to the real phase value and the electromagnetic wave principle;

the moisture detection model training module is used for inputting the dielectric constant of the grain and the corresponding moisture content into a learning model for training to obtain a moisture detection model;

and the grain moisture detection module to be detected is used for acquiring the phase data of the radio-frequency signal penetrating through the grain to be detected to obtain the dielectric constant of the grain to be detected, and inputting the dielectric constant of the grain to be detected into the moisture detection model to obtain the moisture content of the grain to be detected.

Experiments are carried out by taking wheat as an example, and the technical scheme is implemented to prove the feasibility and the accuracy of the method.

1. Wheat production

In the example, wheat in grains was selected as an experimental material. Whilst ensuring the effectiveness and integrity of the system, 10 accurate samples (9% -18%) of different moisture contents of wheat are prepared, typically about 13% of normal moisture content of wheat, but varying in moisture content either high or low throughout the wheat from harvest to storage to processing. Specifically, summer wheat in the same area is selected as a raw material, all the wheat is directly solarized at high outdoor temperature before preparing each moisture sample to reduce the moisture of the wheat to a consistent level, and then the wheat samples with different moisture are prepared according to the same (100g of wheat: 1g of water) proportion standard. In order to make the wheat absorb water uniformly, a professional stirrer is required to be used for fully and uniformly stirring the sample after water is added. All wheat samples were then individually sealed in a fresh bag. And finally, putting 10 samples into a refrigeration house with the room temperature of 5 ℃ for standing for three months. After three months, taking out the wheat sample with sufficient water absorption from a refrigeration house, firstly calibrating the water content of the wheat sample by using an oven drying method, and calibrating the real water content of the wheat. The high-speed universal pulverizer and the electric heating constant-temperature air blowing drying box are used in the process.

2. Hardware structure

For the hardware part of RFID data collection, an Impinj Speedway R420 RFID system is used, and an Impinj Speedway R420 RFID reader is used for inquiring the passive tags of the commodities. In the selection of RFID electronic tags, different types of commodity passive tags (such as Alien 9640, Alien9652 and Impinj H47 tags) are evaluated, and the Alien 9640 passive tags are finally selected in experiments. The RFID system operates in the Ultra High Frequency (UHF) band, between 902MHz and 928MHz, while both the reader and the tag follow the standard EPC protocol that arbitrates collisions between the tag and the tag at the MAC layer. The present embodiment configures transmission power to 39 dBm. The reader can support 4 directional antennas at most, and in experimental design, an E9208CR/L antenna is adopted, and the antenna gain is 9 dBi. The reader transmits the low level data with the time stamp to the notebook computer by means of an ethernet cable. In the RFID system, the position of the tag is fixed at the middle position of the sample box, so that the best system performance is obtained, and meanwhile, the distance between the reader and the electronic tag is reduced as much as possible, and a better detection effect is obtained.

3. Experimental verification process and results

In general, the moisture of grains in a normal-temperature storage state in a granary cannot exceed 13%, and the storage period of the grains can reach more than one year, so that the moisture 13% is used as a critical value for abnormal classification in an abnormal detection and verification experiment of the moisture. And then comparing the phase value corresponding to the wheat sample with normal water content and the phase value corresponding to the wheat sample with abnormal water content with the phase value corresponding to the wheat sample with 13% of wheat moisture content, thereby realizing the two-classification detection of the wheat moisture. In the embodiment, 1000 data samples are collected from wheat samples with different water contents in an experimental scene, and training and testing are respectively carried out on the SVM model created by training. Fig. 5 shows a classification result of classifying and detecting normal wheat moisture and abnormal wheat moisture and a moisture critical value by using phase data in RFID data in a classification detection model based on an SVM algorithm. From fig. 5, it can be seen that the classification accuracy can reach 90% or more for the moisture contents of 11.2%, 14.5% and 16.3%, wherein the classification accuracy reaches up to 97% for the moisture content of 14.5%.

In the test and verification of the wheat moisture classification detection experiment, five wheat samples with different moisture contents are selected to acquire phase data. For a plurality of wheat samples, 1000 data samples are collected for the wheat samples with different water contents under the experimental scene, wherein 800 data samples are used for training the established CNN network model, and the other 200 data samples are used for testing. Fig. 6 shows the multi-classification detection result performed by using the phase data in the RFID data of five wheat samples with different moisture contents collected in the classification detection model based on the convolutional neural network algorithm in the experimental scene. From fig. 6, it can be seen that the precision of the classification detection of the wheat samples with different moisture contents reaches more than 90%, wherein when the moisture content level of the wheat is 14.6%, the highest classification accuracy of the classification detection of the moisture content of the wheat is 96.4%.

The above is an experiment for detecting moisture of wheat with different moisture contents, and the moisture content detection of wheat with different moisture contents is more complex and rigorous, so that the method of average accuracy is used for evaluating the experimental result, and the accuracy and the rigidness of the experimental result are further ensured.

First, a first five wheat samples were tested. As shown in fig. 7, which is the experimental result of the first batch of wheat samples, it can be seen from fig. 7 that the accuracy of the detection results of the five types of moisture all reach 90% or more, and the detection accuracy of the system is 97% at most. Furthermore, the average accuracy of the detection of the system for five samples was 95.2%.

We then performed a second test on 10 wheat samples, as shown in fig. 8 for the accuracy of the classification of the second wheat sample. We can note that the accuracy of the moisture detection of the wheat in this group was over 90%. The detection precision of the system is 96.6% at most, and when the moisture content of the wheat is 9.6% and 17.8%, the detection precision of the system is 92% and 91% at most. In addition, the average accuracy of the system for detecting ten wheat moisture samples is 94.6%.

According to the embodiment about wheat moisture detection, the feasibility of grain moisture detection can be realized by using the radio frequency identification technology, and the abnormal detection and the accurate detection of grain moisture are realized. Therefore, the method can accurately detect the moisture content of the grain, has simple device and low cost, and can realize the accurate measurement of the moisture of the grain without using expensive instruments.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.