A grain moisture content detection device based on microwave reflection quadrature mixing and a detection method thereof

Abstract

The application discloses a kind of microwave reflection quadrature mixing based grain moisture content detection device and its detection method, belong to microwave application technical field, including measured sample, sample container, front panel, device shell and microwave oscillator located in the inside of device shell, power divider, quadrature mixer, circulator, transceiver multiplexing antenna, sliding bracket, guide rail unit and control unit;The application adopts quadrature mixing technology, designs corresponding transceiver multiplexing antenna, realizes the continuous measurement of space standing wave signal by the movement of transceiver multiplexing antenna, and the reflected signal after the action of microwave transmitting signal and sample is quadrature mixed by quadrature mixer, and the function relationship formula is established to retrieve grain moisture content by processing and analyzing signal through control unit, to realize grain moisture content real-time measurement.The application improves the portability and measurement accuracy of microwave moisture content detection device, so that the measurement result is not affected by material thickness and bulk density, and rapid, non-destructive, high-precision detection of granular grain moisture content can be realized.

Description

Technical Field

[0001] This invention belongs to the field of microwave application technology, specifically relating to a grain moisture content detection device and its detection method based on microwave reflection orthogonal mixing. Background Technology

[0002] In grain production and management, accurate moisture content measurement is crucial for ensuring grain quality, safe storage, and control of processing techniques. Excessive moisture content leads to mold growth, while insufficient moisture content damages the organic matter and dry matter within the grain, affecting its quality and shelf life, resulting in waste and economic losses. Therefore, employing modern testing technologies for rapid and non-destructive moisture detection during the storage, transportation, and processing of grains and other agricultural products is of great significance.

[0003] Currently, methods for detecting grain moisture content are divided into two categories: direct methods and indirect methods. Direct methods include drying, toluene distillation, and Karl Fischer titration. These methods offer high accuracy but are cumbersome, time-consuming, labor-intensive, and destructive, making rapid, non-destructive testing difficult. They are mainly used for precise measurements in laboratories, with drying being the internationally accepted standard method for grain moisture content detection. Indirect methods mainly include capacitance, resistance, neutron, infrared, and microwave methods, each with different characteristics, applicable ranges, and measurement accuracies.

[0004] Microwave moisture detection is a relatively new technology that has emerged in recent years. Water has a very high complex dielectric constant and exhibits a maximum dielectric loss in the ultra-high frequency range. By detecting changes in electromagnetic parameters such as energy loss and phase shift after microwaves interact with the material, the moisture content of the material can be calculated. Microwave moisture detection is highly sensitive, fast, and non-contact, providing representative results of the total water content within a volume.

[0005] Microwave detection methods can currently be divided into space wave method, transmission line method, and resonant cavity method. The latter two methods are suitable for contact measurements but not for online measurements. The principle of the space wave method is to indirectly reflect the moisture content of the material by measuring the attenuation, phase magnitude, and changes of the transmitted or reflected portion of the microwave after it interacts with the material in space. Summary of the Invention

[0006] To address the shortcomings of existing technologies and improve the portability and measurement accuracy of microwave moisture content detection devices, this invention provides a grain moisture content detection device and method based on microwave reflection orthogonal mixing. This invention applies microwave transmitted and reflected wave mixing technology to grain moisture content detection, employing orthogonal mixing and designing corresponding transceiver multiplexed antennas and signal processing circuits to measure microwave spatial reflection signals and obtain the moisture content of the sample. The device has a simple structure, is easy to operate, offers high measurement accuracy and a wide range, strong anti-interference capabilities, and can achieve online non-destructive continuous measurement at a low cost, making it a promising candidate for application in industrial and agricultural production.

[0007] This invention is achieved through the following technical solution:

[0008] A grain moisture content detection device based on microwave reflection orthogonal mixing includes a sample 1, a sample container 2, a front panel 3, a display output unit 13, a device housing 4, and a microwave oscillator 5, a power divider 6, an orthogonal mixer 7, a circulator 8, a transceiver multiplexed antenna 9, a sliding bracket 10, a guide rail unit 11, and a control unit 12 located inside the device housing 4. The sample 1 is placed inside the sample container 2. The sample container 2 is fixed to the front end of the device housing 4, and the front panel 3 is located between the sample container 2 and the device housing 4. The oscillator 5 is connected to the power divider 6, which is connected to the quadrature mixer 7 and the circulator 8 respectively. The circulator 8 is connected to the transceiver multiplexed antenna 9, which is fixed on the sliding bracket 10 of the guide rail unit 11 and can move freely in the horizontal direction. A circulator 8 is also provided between the power divider 6 and the transceiver multiplexed antenna 9. The circulator 8 is used to isolate reflected signals and reduce the interference of reflected signals on the microwave oscillator 5. The quadrature mixer 7 is connected to the control unit 12, which is connected to the display output unit 13 for display output.

[0009] The microwave oscillator 5 generates a microwave transmission signal and sends it to the power divider 6. The power divider 6 distributes the power of the microwave transmission signal evenly and then transmits it to the quadrature mixer 7 and the circulator 8. The microwave transmission signal from the circulator 8 passes through the transceiver multiplexed antenna 9, then interacts with the sample under test 1 in space via the front panel 3 and the sample container 2. The resulting microwave reflection signal is received again by the transceiver multiplexed antenna 9 and transmitted to the quadrature mixer 7 via the circulator 8. The microwave transmission signal and the microwave reflection signal transmitted to the quadrature mixer 7 are quadraturely mixed and detected in the quadrature mixer 7, and then... The voltage signal containing the moisture information of the sample 1 is transmitted to the control unit 12 through the I and Q ports of the quadrature mixer 7. The control unit 12 controls the driver in the guide rail unit 11. After receiving the control signal, the driver controls the stepper motor to rotate, which drives the sliding bracket 10 to move, and then drives the transceiver multiplexed antenna 9 to move. At the same time, the control unit 12 collects the detected voltage signal output from the I and Q ports of the quadrature mixer 7, calculates the microwave attenuation and phase shift through the formula and extracts the data of the antinode, thereby calculating the moisture content information of the sample 1 and outputting the detection result to the display output unit 13 for display.

[0010] Furthermore, the sample 1 being tested is a granular grain sample with a uniform density distribution;

[0011] The thickness, mass, and volume of the sample container 2 remain constant, and the material is acrylic sheet or plastic.

[0012] The front panel 3 is made of ceramic or glass; during measurement, the front panel 3 is in close contact with the sample container 2 to achieve the best measurement accuracy.

[0013] The outer casing 4 of the device is made of metal, which has good conductivity and hardness, and can protect the internal circuits while shielding external electromagnetic interference.

[0014] Furthermore, the microwave oscillator 5 is used to generate microwave transmission signals with a frequency output range of 3GHz-12GHz;

[0015] The power divider 6 distributes the microwave transmission signal power generated by the microwave oscillator 5 equally to the quadrature mixer 7 and the circulator 8 respectively, with an effective operating frequency of 1.5-12GHz.

[0016] The quadrature mixer 7 performs quadrature mixing and detection of microwave transmitted signals and microwave reflected signals, with an effective frequency range of 400mHz-12GHz.

[0017] Furthermore, the circulator 8 is connected to the power divider 6, the quadrature mixer 7, and the transceiver multiplexed antenna 9 respectively. It transmits the microwave transmission signal output by the power divider 6 to the transceiver multiplexed antenna 9 and transmits the microwave reflection signal received by the transceiver multiplexed antenna 9 to the quadrature mixer 7. This is used to isolate the reflection signal and reduce the interference of the reflection signal to the microwave source. The effective operating frequency is 5-7.3GHz.

[0018] Furthermore, the operating frequency range of the transceiver multiplexed antenna 9 is not lower than 2-12 GHz, and the effective gain within the frequency band is greater than 10 dBi.

[0019] Furthermore, the sliding bracket 10 is slidably connected to the guide rail unit 11. The sliding bracket 10 is moved horizontally by the rotation of the motor, and the effective sliding distance is greater than one microwave wavelength, ensuring that the transmit / receive multiplexed antenna 9 can obtain a measurement signal of more than one complete cycle.

[0020] Furthermore, the transceiver multiplexed antenna 9 has a double-layer structure, consisting of a rectangular antenna patch, a dielectric substrate, and a metal backplate. The rectangular antenna patch is distributed at the four corners of the dielectric substrate and connected to the feed point at the center of the dielectric substrate through a microstrip line. The lower layer is the metal backplate. The operating frequency is 3-10GHz, the effective gain is greater than 10dBi, and the signal receiving range is greater than 30 degrees. The effective gain at the center frequency is 12dBi, and the effective radiation angle is 20 degrees.

[0021] Furthermore, the quadrature mixer 7 has four ports: an LO port, an RF port, an I port, and a Q port. The LO port is connected to the power divider 6, the RF port is connected to the circulator 8, and the I and Q ports are both connected to the control unit 12. The microwave transmission signal generated by the microwave oscillator 5 before passing through the sample is input to the LO port through the power divider 6 as a reference signal. The microwave reflection signal received by the transceiver multiplexed antenna 9 after interacting with the sample is input to the RF port through the circulator 8 as a radio frequency signal. The quadrature mixer 7 outputs an in-phase signal obtained by directly mixing the RF signal and the reference signal at the I port. It outputs a quadrature signal obtained by mixing the RF signal and the reference signal after a 90-degree phase shift at the Q port. The control unit 12 calculates the microwave attenuation and phase shift using the voltage signals output from the I and Q ports of the quadrature mixer 7.

[0022] Furthermore, the control unit 12 includes a power supply module, an A / D conversion module, a microcontroller operation control unit, and a serial port conversion unit; wherein, the power supply module is used to provide the required power and voltage conversion for each unit circuit, the A / D conversion module is used to convert the mixing voltage signal output by the quadrature mixer 7 into a digital signal for internal operation by the microcontroller, and the microcontroller operation control unit realizes the control functions of digital signal acquisition, internal operation processing, initialization alarm, and serial port conversion of the A / D conversion module and the serial port conversion unit.

[0023] The measurement principle of a grain moisture content detection device based on microwave reflection orthogonal mixing, according to the present invention, is explained as follows:

[0024] The complex permittivity can characterize the energy storage and loss changes of water molecules in grains. The complex permittivity can be calculated using microwave attenuation and phase shift.

[0025] ε=ε′-jε″ (1)

[0026]

[0027] In the formula: ε′ is the dielectric constant, which represents the material's ability to store energy; ε″ is the dielectric loss factor, which represents the material's ability to dissipate energy in the form of heat; c is the speed of light in a vacuum; f is the frequency; and d is the material thickness.

[0028] Attenuation ΔA and phase shift of microwave signals The signals output from the I and Q terminals of the IQ mixer can be used for calculation. Let the output voltages be VI (mV) and VQ (mV), and the following relationship exists:

[0029]

[0030] In the formula: V I0 and V Q0 It is the voltage value when no sample is present, V I1 and V Q1 It is the voltage value when a sample is present.

[0031] During the detection process, the microwave interacts with the material under test in space, generating a reflected wave with the same frequency as the incident wave but opposite to its propagation direction. The superposition of the two waves in space can be represented as:

[0032]

[0033] Equation (6) is a typical expression for a traveling standing wave, where The standing wave component, E, varies periodically with the change in the position x of the transmit / receive multiplexed antenna. When the standing wave component is at its maximum, the traveling-standing wave is at the antinode. cmax = (1 + |Γ|)E i ;

[0034] The device of this invention uses the antinode as a feature point to establish the grain moisture content M and the antinode attenuation ΔA. 波腹 Phase shift The functional relationship between them is as follows:

[0035]

[0036] To achieve rapid and non-destructive detection of grain moisture content.

[0037] On the other hand, the present invention provides a detection method for a grain moisture content detection device based on microwave reflection orthogonal mixing, the specific steps of which are as follows:

[0038] S1, No-load signal detection;

[0039] With the sample container 2 empty, the control unit 12 controls the driver in the guide rail unit 11 to drive the stepper motor to rotate, so that the transceiver multiplexed antenna 9 fixed on the sliding bracket 10 moves along the guide rail in a direction that gradually moves away from the sample 1 under test. The voltage values ​​output by the I port and Q port of the quadrature mixer 7 are detected and recorded simultaneously when the transceiver multiplexed antenna 9 is in different positions.

[0040] S2, Full load signal detection;

[0041] After the sample container 2 is filled with the sample, the measurement steps of step S1 are repeated to record the voltage values ​​output by the I port and Q port of the quadrature mixer 7 when the transmit and receive multiplexed antenna 9 is in different positions.

[0042] S3. Calculation of microwave attenuation and phase shift;

[0043] The microcontroller inside control unit 12 uses the voltage values ​​received at the I and Q ports of quadrature mixer 7 to calculate the microwave attenuation ΔA and phase shift according to the following formula. Perform calculations and extract the data ΔA of the antinodes. 波腹 and

[0044]

[0045] In the formula: V I0 and V Q0 It is the voltage value when no sample is present, V I1 and V Q1 It is the voltage value when a sample is present;

[0046] S4. Sample moisture content calculation:

[0047] The microcontroller inside control unit 12 calculates the moisture content M of the grain according to the following formula:

[0048]

[0049] In the formula: ΔA 波腹 For power attenuation at antinodes, The antinode phase shift is represented by a, b, c, and d, which are fitting coefficients. For a given sample 1, the fitting coefficients are constants, and the parameters are fitted in advance using samples with known moisture content.

[0050] S5. Real-time output of grain moisture content:

[0051] After being processed by the microcontroller inside the control unit 12, the moisture content information of the sample being tested is uploaded to the display output unit 13 via the serial port for real-time display output.

[0052] Compared with the prior art, the advantages of the present invention are as follows:

[0053] (1) The present invention provides a grain moisture content detection device based on microwave reflection orthogonal mixing. The device uses an orthogonal mixer to apply microwave transmitted wave and reflected wave mixing technology to grain moisture content detection. It also uses a single transmit and receive multiplexed antenna, which simplifies the device design and provides good portability and anti-interference capabilities.

[0054] (2) The detection method of the present invention adopts the microwave spatial reflection detection method, which only requires a single probe to detect one interface of the sample in real time. Microwaves have penetrability, and the detection results can characterize the overall moisture content of the sample without damaging the sample.

[0055] (3) The measuring device of the present invention has a simple circuit and is easy to acquire, analyze and process parameters. It can realize real-time, fast and high-precision non-destructive measurement of grain moisture content, effectively meeting the needs of industrial and agricultural production measurement and control. Attached Figure Description

[0056] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0057] Figure 1 This is a schematic diagram of the structure of a grain moisture content detection device based on microwave reflection orthogonal mixing according to the present invention;

[0058] Figure 2 This is a schematic diagram of the transceiver multiplexed antenna and sliding bracket of the device of the present invention;

[0059] Where a is the front view and b is the rear view;

[0060] Figure 3 This is a schematic diagram of the quadrature mixer structure of the device of the present invention;

[0061] Figure 4 This is a schematic diagram of the circulator structure of the device of the present invention;

[0062] Figure 5 The graph shows the relationship between microwave attenuation and antenna movement distance for rice samples with moisture contents of 10.04%, 13.26%, and 16.35% in Example 4 of this invention.

[0063] In the figure: 1. Sample under test; 2. Sample container; 3. Front panel; 4. Device housing; 5. Microwave oscillator; 6. Power divider; 7. Quadrature mixer; 8. Circulator; 9. Transceiver multiplexed antenna; 10. Sliding bracket; 11. Guide rail unit; 12. Control unit; 13. Display output unit. Detailed Implementation

[0064] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:

[0065] Example 1

[0066] like Figure 1 As shown, this embodiment provides a grain moisture content detection device based on microwave reflection orthogonal mixing, including a sample 1, a sample container 2, a front panel 3, a display output unit 13, a device housing 4, and a microwave oscillator 5, a power divider 6, an orthogonal mixer 7, a circulator 8, a transceiver multiplexed antenna 9, a sliding bracket 10, a guide rail unit 11, and a control unit 12 located inside the device housing 4; wherein, the sample 1 is placed inside the sample container 2; the sample container 2 is fixed to the front end of the device housing 4, and the front panel 3 is located between the sample container 2 and the device housing 4; the microwave oscillator 5 and the power divider 6 are located inside the device housing 4. A power divider 6 is connected to a quadrature mixer 7 and a circulator 8. The quadrature mixer 7 is connected to the circulator 8 and a control unit 12. The circulator 8 is connected to a transceiver multiplexed antenna 9, which is fixed on a sliding bracket 10 of the guide rail unit 11 and can move freely in the horizontal direction. A circulator 8 is also provided between the power divider 6 and the transceiver multiplexed antenna 9. The circulator 8 is used to isolate reflected signals and reduce the interference of reflected signals on the microwave oscillator 5. The quadrature mixer 7 is connected to the control unit 12, which is connected to the display output unit 13 for display output.

[0067] The microwave oscillator 5 generates a microwave transmission signal and sends it to the power divider 6. The power divider 6 distributes the power of the microwave transmission signal evenly and then transmits it to the quadrature mixer 7 and the circulator 8. The microwave transmission signal from the circulator 8 passes through the transceiver multiplexed antenna 9, then interacts with the sample under test 1 in space via the front panel 3 and the sample container 2. The resulting microwave reflection signal is received again by the transceiver multiplexed antenna 9 and transmitted to the quadrature mixer 7 via the circulator 8. The microwave transmission signal and the microwave reflection signal transmitted to the quadrature mixer 7 are quadraturely mixed and detected in the quadrature mixer 7, and then... The voltage signal containing the moisture information of the sample 1 is transmitted to the control unit 12 through the I and Q ports of the quadrature mixer 7. The control unit 12 controls the driver in the guide rail unit 11. After receiving the control signal, the driver controls the stepper motor to rotate, which drives the sliding bracket 10 to move, and then drives the transceiver multiplexed antenna 9 to move. At the same time, the control unit 12 collects the detected voltage signal output from the I and Q ports of the quadrature mixer 7, calculates the microwave attenuation and phase shift through the formula and extracts the data of the antinode, thereby calculating the moisture content information of the sample 1 and outputting the detection result to the display output unit 13 for display.

[0068] In this embodiment, the sample container 2 is a square acrylic sheet box with an acrylic sheet thickness of 3mm and internal dimensions of 20cm*20cm*5cm. The thickness, mass, and volume remain fixed.

[0069] In this embodiment, the front panel 3 is a ceramic sheet with a thickness of 4mm and a size of 13cm*11cm.

[0070] In this embodiment, the outer shell 4 of the device is made of stainless steel, with a wall thickness of 2cm and dimensions of 30cm*13cm*11cm.

[0071] In this embodiment, the microwave oscillator 5 is used to generate microwave transmission signals, with a center operating frequency of 6 GHz.

[0072] In this embodiment, the power divider 6 transmits the microwave transmission signal generated by the microwave oscillator 5 to the quadrature mixer 7 and the circulator 8 respectively, with an effective operating frequency of 1.5-12GHz.

[0073] In this embodiment, the effective operating frequency range of the quadrature mixer 7 is 400mHz-12GHz.

[0074] In this embodiment, the circulator 8 is as follows: Figure 4 As shown, port 1 is connected to the quadrature mixer 7, port 2 is connected to the power divider 6, and port 3 is connected to the transceiver multiplexed antenna 9, which is used to isolate reflected signals and reduce the interference of reflected signals to the microwave source. The effective operating frequency is 5-7.3GHz.

[0075] In this embodiment, the transceiver multiplexed antenna 9 is a planar antenna with dimensions of 10cm*8cm and a thickness of 2cm. It operates at a frequency of 3-10GHz, has an effective gain of 12dBi at the center frequency, and an effective radiation angle of approximately 20 degrees.

[0076] In this embodiment, the sliding bracket 10 is slidably connected to the guide rail unit 11. The sliding bracket 10 is driven to move horizontally by the rotation of the motor. The driver is a DM542 series motor driver, powered by 24V DC voltage, with a rated current of 4A. The stepper motor is a 42-type stepper motor with a maximum torque of 2.3N / m. The effective sliding distance of the sliding bracket 10 is greater than 5 cm.

[0077] In this embodiment, the control unit 12 includes a power module, an A / D conversion module, a microcontroller operation control unit, and a serial port conversion unit. The power module provides the necessary power and voltage conversion for each unit circuit of the system. The A / D conversion module converts the mixing voltage signal output from the quadrature mixer 7 into a digital quantity for internal microcontroller operation. The microcontroller operation control unit performs control functions for digital signal acquisition, internal processing, initialization alarm, and serial port conversion of the A / D conversion module and the serial port conversion unit. The microcontroller operation control unit uses a 32-bit ARM core STM32F103 series processor with an integrated analog-to-digital converter, 12-bit conversion accuracy, and a single conversion acquisition time of 1μs. The driver in the guide rail unit 11 is started by controlling the PWM pulse output of the STM32 processor. The serial port conversion unit uploads the current measured real-time moisture content to the display output unit 13, which is a PC that reads the measurement data via a 232 serial port.

[0078] Example 2

[0079] like Figure 2 As shown in the figure, this embodiment describes the specific structure of the transceiver multiplexed antenna and the sliding bracket; the transceiver multiplexed antenna 9 consists of a rectangular antenna patch, a dielectric substrate, and a metal backplate, and adopts a double-layer structure. The rectangular antenna patch is distributed at the four corners of the dielectric substrate and is connected to the feed point at the center of the dielectric substrate through a microstrip line. The lower layer is a metal baffle; the size is 10cm*8cm, the thickness is 2cm, the operating frequency is 3-10GHz, the effective gain is greater than 10dBi, and the signal receiving range is greater than 30 degrees; the effective gain at the center frequency is 12dBi, and the effective radiation angle is about 20 degrees.

[0080] The transceiver multiplexed antenna 9 is fixed together with the sliding bracket 10. The horizontal movement measurement is achieved by sliding the sliding bracket 10. When the microwave electric field intensity measured at a certain point is the maximum value of the traveling standing wave, that point is the antinode of the traveling standing wave.

[0081] Example 3

[0082] like Figure 3 As shown, this embodiment describes the specific structure of the quadrature mixer. The quadrature mixer 7 has four ports: the LO port connects to the power divider 6, the RF port connects to the circulator 8, and the I and Q ports connect to the control unit 12. The microwave transmission signal generated by the microwave oscillator 5, before passing through the sample, is input to the LO port through the power divider 6 as a reference signal. The microwave reflection signal received by the multiplexed antenna 9 after interacting with the sample is input to the RF port through the circulator 8 as a radio frequency signal. The quadrature mixer 7 outputs an in-phase signal obtained by directly mixing the RF signal and the reference signal at the I port; and an orthogonal signal obtained by mixing the RF signal and the reference signal after a 90-degree phase shift at the Q port. The control unit 12 calculates the microwave attenuation and phase shift using the voltage signals output from the two output ports, I and Q, of the quadrature mixer 7.

[0083] Example 4

[0084] This embodiment uses rice as the measurement object to illustrate the specific measurement method of the device. The initial moisture content of the naturally sun-dried rice was 10.04%. By adding water to the sample and continuously stirring it evenly, three rice samples with different moisture contents were finally obtained, with the moisture content ranging from 10.04% to 16.35%.

[0085] This embodiment provides a detection method for grain moisture content detection device based on microwave reflection orthogonal mixing, the specific steps of which are as follows:

[0086] S1. No-load signal detection:

[0087] With the sample container 2 empty, the control unit 12 controls the driver in the guide rail unit 11 to drive the stepper motor to rotate, so that the transceiver multiplexer antenna 9 fixed on the sliding bracket 10 moves along the guide rail in a direction that gradually moves away from the sample 1 under test. The voltage values ​​output by the I port and Q port of the quadrature mixer 7 are detected and recorded simultaneously when the transceiver multiplexer antenna 9 is in different positions.

[0088] S2, Full Load Signal Detection:

[0089] After the sample container 2 is filled with the sample, repeat the measurement step S1 and record the voltage values ​​output by the I port and Q port of the quadrature mixer 7 when the transmit and receive multiplexed antenna 9 is in different positions.

[0090] S3. Calculation of microwave attenuation and phase shift:

[0091] The microcontroller inside control unit 12 uses the voltage values ​​received at the I and Q ports of quadrature mixer 7 to calculate the microwave attenuation ΔA and phase shift according to the following formula. Perform calculations and extract the data ΔA of the antinodes.波腹 and

[0092]

[0093] In the formula: V I1 and V Q1 The voltage value, V, is present when the sample is present. I0 and V Q0 It is the voltage value when no sample is present.

[0094] Figure 5 The figure shows the relationship between microwave attenuation and antenna movement distance for rice samples with moisture contents of 10.04%, 13.26%, and 16.35%. The antinodes are marked with asterisks in the figure. The measured ΔA for rice with a moisture content of 10.04% was... 波腹 4.94459dB The ΔA value for rice is 5.62545 rad with a moisture content of 13.26%. 波腹 2.91076dB The ΔA value for rice is 5.81836 rad with a moisture content of 16.35%. 波腹 1.99275dB It is 6.01818 rad;

[0095] S4. Sample moisture content calculation:

[0096] The microcontroller inside control unit 12 calculates the moisture content M of the grain according to the following formula:

[0097]

[0098] In the formula: ΔA 波腹 For power attenuation at antinodes, Let a, b, c, and d be the phase shift at the antinodes, and a, b, c, and d be the fitting coefficients. For the determined sample 1, the fitting coefficients are constants. Substituting the detection results of power attenuation and phase shift at the antinodes of rice samples with different moisture contents in Table 1 into the data, and performing linear fitting using Origin data processing software, the fitting coefficients are obtained as follows: a = 0.74613, b = -7.61402, c = -2.07567, and d = 41.1922.

[0099] S5. Real-time output of grain moisture content:

[0100] After processing by the microcontroller inside the control unit 12, the moisture content information of the sample being tested is uploaded to the display output unit 13 via the serial port for real-time display output, as shown in Table 1.

[0101] Table 1: Measurement data of rice samples

[0102]

[0103] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0104] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0105] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A grain moisture content detection device based on microwave reflection orthogonal mixing, characterized in that, The device includes a test sample (1), a sample container (2), a front panel (3), a display output unit (13), a device housing (4), and a microwave oscillator (5), a power divider (6), an orthogonal mixer (7), a circulator (8), a transceiver multiplexed antenna (9), a sliding bracket (10), a guide rail unit (11), and a control unit (12) located inside the device housing (4). The test sample (1) is placed inside the sample container (2). The sample container (2) is fixed to the front end of the device housing (4), and the front panel (3) is located between the sample container (2) and the device housing (4). The microwave oscillator (5) and the power divider (6) are located inside the device housing (4). The power divider (6) is connected to the quadrature mixer (7) and the circulator (8) respectively. The circulator (8) is connected to the transceiver multiplexed antenna (9). The transceiver multiplexed antenna (9) is fixed on the sliding bracket (10) of the guide rail unit (11) and can move freely in the horizontal direction. A circulator (8) is also provided between the power divider (6) and the transceiver multiplexed antenna (9). The circulator (8) is used to isolate the reflected signal and reduce the interference of the reflected signal to the microwave oscillator (5). The quadrature mixer (7) is connected to the control unit (12). The control unit (12) is connected to the display output unit (13) for display output. The microwave oscillator (5) generates a microwave transmission signal and sends it to the power divider (6). The power divider (6) distributes the power of the microwave transmission signal evenly and then transmits it to the quadrature mixer (7) and the circulator (8). The microwave transmission signal transmitted through the circulator (8) passes through the transceiver multiplexing antenna (9), and then interacts with the sample under test (1) in space through the front panel (3) and the sample container (2). The resulting microwave reflection signal is received again by the transceiver multiplexing antenna (9) and transmitted to the quadrature mixer (7) through the circulator (8). The microwave transmission signal and the microwave reflection signal transmitted to the quadrature mixer (7) are quadraturely mixed and detected in the quadrature mixer (7). Then, the voltage signal containing the moisture information of the sample (1) is transmitted to the control unit (12) through the I port and Q port of the quadrature mixer (7); the control unit (12) controls the driver in the guide rail unit (11). After receiving the control signal, the driver controls the stepper motor to rotate, which drives the sliding bracket (10) to move, and then drives the transceiver multiplexed antenna (9) to move; at the same time, the control unit (12) collects the voltage signal after detection output from the I port and Q port of the quadrature mixer (7), calculates the microwave attenuation and phase shift through the formula and extracts the data of the antinode, thereby calculating the moisture content information of the sample (1) and outputting the detection result to the display output unit (13) for display; The quadrature mixer (7) has four ports: LO port, RF port, I port, and Q port. The LO port is connected to the power divider (6), the RF port is connected to the circulator (8), and the I and Q ports are connected to the control unit (12). The microwave transmission signal generated by the microwave oscillator (5) without passing through the sample is input to the LO port through the power divider (6) as a reference signal. The microwave reflection signal received by the transceiver multiplexed antenna (9) after interacting with the sample is input to the RF port through the circulator (8) as a radio frequency signal. The quadrature mixer (7) outputs an in-phase signal obtained by directly mixing the RF signal and the reference signal at the I port. It outputs a quadrature signal obtained by mixing the RF signal and the reference signal after a 90-degree phase shift at the Q port. The control unit (12) calculates the microwave attenuation and phase shift through the voltage signals output from the I and Q ports of the quadrature mixer (7). The detection method of the grain moisture content detection device specifically includes the following steps: S1, No-load signal detection; Keep the sample container (2) empty. The control unit (12) controls the driver in the guide rail unit (11) to drive the stepper motor to rotate, so that the transceiver multiplexer (9) fixed on the sliding bracket (10) moves along the guide rail in a direction that gradually moves away from the sample (1) under test. The voltage values ​​output by the I port and Q port of the quadrature mixer (7) are detected and recorded simultaneously when the transceiver multiplexer (9) is in different positions. S2, Full load signal detection; After the sample container (2) is filled with the sample, the measurement steps of step S1 are repeated to record the voltage values ​​output by the I port and Q port of the quadrature mixer (7) when the transmit and receive multiplexed antenna (9) is in different positions. S3. Calculation of microwave attenuation and phase shift; The microcontroller inside the control unit (12) attenuates the microwave based on the voltage values ​​received at the I and Q ports of the quadrature mixer (7) according to the following formula. and phase shift Perform calculations and extract the data of the antinodes. and : (4) (5) In the formula: and This is the voltage value when no sample is present. and It is the voltage value when a sample is present; S4. Sample moisture content calculation: The microcontroller inside the control unit (12) calculates the moisture content M of the grain according to the following formula: In the formula: For power attenuation at antinodes, The phase shift of the antinode is given by , and a, b, c, and d are fitting coefficients. For a given sample (1), the fitting coefficients are constants, and the parameters are fitted in advance using samples with known moisture content. S5. Real-time output of grain moisture content: After being processed by the microcontroller inside the control unit (12), the moisture content information of the sample being tested is uploaded to the display output unit (13) via the serial port for real-time display output.

2. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The sample (1) being tested is a grain sample with granular shape and uniform density distribution; The thickness, mass and volume of the sample container (2) remain constant, and the material is acrylic sheet or plastic. The front panel (3) is made of ceramic or glass; during measurement, the front panel (3) is in close contact with the sample container (2) to achieve the best measurement accuracy; The outer casing (4) of the device is made of metal, which has good conductivity and hardness, and can protect the internal circuit while shielding external electromagnetic interference.

3. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The microwave oscillator (5) is used to generate microwave transmission signals with a frequency output range of 3GHz-12GHz; The power divider (6) distributes the power of the microwave transmission signal generated by the microwave oscillator (5) equally and transmits it to the quadrature mixer (7) and the circulator (8) respectively. The effective operating frequency is 1.5-12GHz. The quadrature mixer (7) performs quadrature mixing and detection of microwave transmitted signals and microwave reflected signals, with an effective frequency range of 400mHz-12GHz.

4. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The circulator (8) is connected to the power divider (6), the quadrature mixer (7) and the transceiver multiplexed antenna (9) respectively. It transmits the microwave transmission signal output by the power divider (6) to the transceiver multiplexed antenna (9) and transmits the microwave reflection signal received by the transceiver multiplexed antenna (9) to the quadrature mixer (7) to isolate the reflection signal and reduce the interference of the reflection signal to the microwave source. The effective operating frequency is 5-7.3GHz.

5. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The operating frequency range of the transceiver multiplexed antenna (9) is 3-10 GHz, and the effective gain within the frequency band is greater than 10 dBi.

6. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The sliding bracket (10) is slidably connected to the guide rail unit (11). The sliding bracket (10) is moved horizontally by the rotation of the motor. The effective sliding distance is greater than one microwave wavelength, ensuring that the transmit / receive multiplexed antenna (9) can obtain a measurement signal of more than one complete cycle.

7. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The transceiver multiplexed antenna (9) has a double-layer structure, consisting of a rectangular antenna patch, a dielectric substrate, and a metal backplate. The rectangular antenna patch is distributed at the four corners of the dielectric substrate and is connected to the feed point at the center of the dielectric substrate through a microstrip line. The lower layer is a metal backplate. The operating frequency is 3-10GHz, the effective gain is greater than 10dBi, and the signal receiving range is greater than 30 degrees. The effective gain at the center frequency is 12dBi, and the effective radiation angle is 20 degrees.

8. The grain moisture content detection device based on microwave reflection orthogonal mixing as described in claim 1, characterized in that, The control unit (12) includes a power supply module, an A / D conversion module, a microcontroller operation control unit, and a serial port conversion unit. The power supply module is used to provide the required power and voltage conversion for each unit circuit. The A / D conversion module is used to convert the mixing voltage signal output by the quadrature mixer (7) into a digital signal for internal operation by the microcontroller. The microcontroller operation control unit realizes the control functions of digital signal acquisition, internal operation processing, initialization alarm, and serial port conversion of the A / D conversion module and the serial port conversion unit.

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