A microwave resonance detection device and detection method for synchronous measurement of material moisture content and bulk density

Abstract

The present invention discloses a microwave resonance detection device and method for synchronously measuring the moisture content and bulk density of a material. The device belongs to the field of microwave application technology and includes a sample chamber, a resonant chamber, a discharge device, a temperature sensor, a signal processing module, and a display unit. The device generates a microwave signal through a signal processing module, which is coupled to the resonant chamber via a transmitting probe. After interacting with the sample, the microwave signal is received by a receiving probe. A reference detector and a signal detector within the signal processing module detect the resonant frequency and power attenuation. A temperature sensor within the sample tank detects the sample temperature. The signal is analyzed by the signal processing module, and a functional relationship is established to achieve synchronous measurement of the moisture content and bulk density of the material being measured. The device improves the measurement accuracy of the microwave moisture content and bulk density detection device, ensuring that the measurement results are not affected by temperature, and enabling rapid and high-precision detection of materials such as particles and powders.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave applications, and in particular relates to a microwave resonance detection device and a detection method for synchronously measuring the moisture content and bulk density of a material. Background Art

[0002] For various materials in industry and agriculture, such as grains, soil, wood, tobacco, and medicines, moisture content and bulk density are important indicators of product quality and are key factors in ensuring product prices and the stability of production processes. Accurately, quickly, and stably detecting the moisture content and bulk density of materials is an issue that urgently needs to be overcome. Traditional methods for measuring moisture content and bulk density include drying and weighing methods and density bottle methods. These methods are cumbersome to operate and can easily introduce errors if not operated properly, and cannot achieve fast real-time measurement. Modern detection methods include nuclear magnetic resonance and X-ray methods. The nuclear magnetic resonance method requires expensive instruments, complex operations, high measurement costs, and relatively slow measurement speeds. The size and shape of the sample have a certain impact on the measurement results, requiring special sample preparation and processing. The X-ray method is harmful to the human body and requires strict protective measures. The instruments and equipment are complex and expensive.

[0003] Microwave analysis is a new technology developed in recent years. Polar molecules affect the dielectric constant. In the microwave frequency band, water has a strong polarization property, and its dielectric constant is much greater than that of general materials. Therefore, the amount and spatial distribution of water molecules in a material directly affect the dielectric properties. The amount of water molecules is expressed as the moisture content, and the spatial distribution is expressed as the bulk density. Therefore, by measuring changes in microwave parameters related to dielectric properties, it is possible to infer the moisture content and bulk density.

[0004] Microwave detection methods are primarily categorized into microwave reflection, microwave transmission, microwave scattering, and microwave resonant cavity methods. The microwave resonant cavity method offers extremely high measurement accuracy and sensitivity, capable of detecting even minute changes in the dielectric constant. Currently, most microwave resonant cavity-based material moisture content and bulk density tests rely on perturbation measurements, which are limited to small sample volumes and lack practicality. Given this current situation, the research and development of a cylindrical resonant cavity capable of simultaneously measuring the moisture content and bulk density of large numbers of samples is of great significance. Summary of the Invention

[0005] In response to the defects in the existing technology and to improve the measurement accuracy and simplicity of microwave moisture content and bulk density detection devices, the present invention provides a microwave resonance detection device and detection method for the synchronous measurement of material moisture content and bulk density. A circular resonant cavity is used in conjunction with a designed sweeping circuit and signal processing circuit to measure the resonant frequency and power attenuation, thereby obtaining the moisture content and bulk density of the measured sample.

[0006] The present invention is achieved through the following technical solutions:

[0007] A microwave resonance detection device for synchronous measurement of moisture content and bulk density of materials, comprising a sample cavity, a resonance cavity, a transmitting probe, a receiving probe, a discharge device, a temperature sensor, a signal processing module, a transmitting isolator, a receiving isolator and a display unit; wherein the sample cavity is arranged inside the resonance cavity, the discharge device is installed at the bottom of the sample cavity, the temperature sensor is arranged below the sample cavity and is used to measure the temperature of the sample in real time, the signal processing module is used to transmit the microwave signal generated by an internal voltage-controlled oscillator to the transmitting isolator; after the microwave signal is subjected to gyromagnetic isolation processing by the ferrite inside the transmitting isolator, the microwave signal is transmitted to the receiving isolator through the transmitting probe. The signal is coupled to the resonant cavity, and after interacting with the measured sample in the sample cavity, a microwave resonant signal is generated. The receiving probe transmits the microwave resonant signal to the receiving isolator. After the microwave signal is gyromagnetically isolated by the ferrite inside the receiving isolator, it is sent to the signal processing module. The signal detector inside the signal processing module converts the microwave resonant signal into a voltage value. The signal processing module is respectively connected to the unloading device, the temperature sensor and the display unit, and is used to control the unloading device to unload after the measurement is completed, obtain the temperature data of the measured sample measured in real time by the temperature sensor, calculate the moisture content and bulk density of the measured sample, and output the calculation results to the display unit.

[0008] Furthermore, the sample cavity is a cylindrical structure located in the central area inside the resonant cavity, the radius of the sample cavity ranges from 5 to 40 mm, and the height ranges from 5 to 30 cm; the sample to be tested is a non-metallic water-containing material such as food, fertilizer, powder, etc.

[0009] Furthermore, the resonant cavity is a cylindrical metal cavity with a cavity radius ranging from 5 to 20 cm and a cavity height ranging from 5 to 30 cm. The dimensions are adjusted according to the actual microwave frequency and the amount of the sample.

[0010] Furthermore, the transmitting probe and the receiving probe are inserted into the resonant cavity symmetrically at 180°. The transmitting probe is used to excite the resonant cavity to generate resonance, and the receiving probe is used to receive the microwave signal after interaction. The length range of the probe coupling inside the resonant cavity is 2-10 mm.

[0011] Furthermore, the unloading device includes a steering gear and a material partition, and the material partition can be rotated within a range of 0-180 degrees under the drive of the steering gear to achieve unloading control.

[0012] Furthermore, the signal processing module includes a voltage-controlled oscillator, a splitter, a reference detector, a signal detector and a single-chip microcomputer operation and control unit. The voltage-controlled oscillator is used to generate microwave signals and perform frequency sweeping, and the frequency sweeping range is 0.5GHz-6GHz; the splitter evenly distributes the microwave signals generated by the voltage-controlled oscillator and transmits them to the reference detector and the transmitting isolator respectively. The single-chip microcomputer operation and control unit converts the voltage signals output by the reference detector and the signal detector into digital quantities for internal calculations, thereby realizing digital signal acquisition, internal calculation processing, and frequency sweeping control functions.

[0013] On the other hand, the present invention also provides a detection method for a microwave resonance detection device for synchronously measuring the moisture content and bulk density of a material, the specific steps of which are as follows:

[0014] S1, no-load signal detection:

[0015] Keep the sample chamber empty, the discharge port of the discharge device closed, the signal processing module generates a microwave sweep signal, and the single chip operation control unit detects different frequencies The voltage value of the internal reference detector and the voltage value of the signal detector , calculate the attenuation value according to the following formula:

[0016]

[0017] Record the maximum no-load attenuation value and its corresponding microwave resonant frequency ;

[0018] S2, full load signal detection:

[0019] The sample cavity is filled with the sample to be tested, the signal processing module generates a microwave sweep signal, and the single chip computer operation control unit detects different frequencies Internal reference detector voltage value Sum signal detector voltage value , calculate the attenuation value according to the following formula:

[0020]

[0021] Record the maximum attenuation value of the sample fully loaded , and its corresponding full-load microwave resonant frequency , read the measurement data of the temperature sensor ;

[0022] The difference between the maximum attenuation values ​​under full load and no load is calculated using the following formula: The difference between the resonant frequency :

[0023]

[0024] ;

[0025] S3. Calculation of sample moisture content:

[0026] The moisture content is calculated according to the following formula and bulk density Perform the operation:

[0027]

[0028]

[0029] Where: a, b, c, d, e, h, j, Km, Kρ are fitting coefficients. For a given sample, the fitting coefficients are constants, and the parameters are fitted in advance using samples with known moisture content and bulk density.

[0030] S4. Real-time output of grain moisture content and bulk density:

[0031] The signal processing module uploads the moisture content information and bulk density information of the tested sample to the display unit through the serial port for real-time display output, and at the same time controls the discharge port of the discharge device to open to complete the discharge.

[0032] The measurement principle of the material moisture content and density detection device based on microwave cavity resonance of the present invention is described as follows:

[0033] A microwave resonant cavity is a relatively closed cavity composed of a metal conductor and is a resonator with distributed parameters. Within a microwave resonant cavity, electromagnetic waves can only oscillate back and forth and cannot propagate forward, forming an electromagnetic standing wave. If the sample being measured contains water, the water molecules will absorb some of the microwave energy, resulting in electromagnetic field energy loss. According to the perturbation theory of the resonant cavity, we can obtain:

[0034]

[0035]

[0036] in, 、 represents the resonant frequency of the resonant cavity before and after the sample is placed, , represents the quality factor of the resonant cavity before and after the sample is placed, is the real part of the dielectric constant, is the imaginary part of the dielectric constant, is the volume of the resonant cavity, is the sample chamber volume, is a shape factor related to the shape. For a fixed resonant cavity, the above formula shows that the resonant frequency and quality factor are directly related to the dielectric constant of the sample. In the microwave frequency band, water has a strong polarization characteristic, and the dielectric constant of water is much larger than that of general materials. After placing different samples in the cavity, the changes in the resonant frequency and quality factor can directly reflect the number and spatial distribution of water molecules. Temperature affects the energy state of water molecules in the sample. The increase in temperature will intensify the thermal motion of water molecules in the sample, affect its polarization characteristics and thus change the dielectric constant of the sample as a whole. The device of the present invention simultaneously measures the resonant frequency, power attenuation and temperature of the sample under test, and establishes a functional relationship with temperature compensation to invert the moisture content and bulk density of the sample.

[0037] Compared with the prior art, the advantages of the present invention are as follows:

[0038] (1) The present invention designs a cylindrical resonant cavity structure based on the working principle of the microwave resonant cavity, and the device structure is simple and easy to operate;

[0039] (2) The samples of the present invention do not require any treatment, and the materials can be subjected to non-destructive testing in their natural state; the test results are not affected by any surface characteristics of the tested materials;

[0040] (3) When the material being measured is changed, the device does not need to change the hardware, and is widely applicable to the measurement of moisture content and bulk density of various non-metallic granular or powdered materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0042] Figure 1 Schematic diagram of the structure of a microwave resonance detection device for synchronously measuring the moisture content and bulk density of a material according to the present invention;

[0043] Figure 2 A top view of the microwave resonant cavity of the present invention;

[0044] Figure 3 This is a structural diagram of the internal units of the signal processing module of the detection device of the present invention;

[0045] Figure 4 This is a comparison chart of the frequency sweep measurement results of corn samples by the detection device of the present invention;

[0046] In the figure: sample cavity 1, resonant cavity 2, transmitting probe 3, receiving probe 4, unloading device 5, temperature sensor 6, signal processing module 7, transmitting isolator 8, receiving isolator 9, display unit 10. DETAILED DESCRIPTION

[0047] In order to clearly and completely describe the technical solution and specific working process of the present invention, the specific implementation methods of the present invention are as follows in conjunction with the accompanying drawings:

[0048] Example 1

[0049] like Figure 1 As shown in the figure, a microwave resonance detection device for synchronous measurement of moisture content and bulk density of materials in this embodiment is provided. The detection device includes a sample cavity 1, a resonance cavity 2, a transmitting probe 3, a receiving probe 4, a discharge device 5, a temperature sensor 6, a signal processing module 7, a transmitting isolator 8, a receiving isolator 9 and a display unit 10; wherein, the sample cavity 1 is located inside the resonance cavity 2; the discharge device 5 is located at the bottom of the sample cavity 1; the temperature sensor 6 is located below the sample cavity 1 and is used to measure the temperature of the sample in real time; the signal processing module 7 transmits the microwave signal generated by the internal voltage-controlled oscillator to the transmitting isolator 8, the receiving isolator 9 and the display unit 10. 8; the microwave signal is coupled by the transmitting probe 3 and transmitted to the resonant cavity 2, interacting with the sample to be measured in the sample cavity 1, and the generated microwave resonance signal is transmitted to the receiving isolator 9 through the receiving probe 4, and the signal detector inside the signal processing module 7 completes the detection and converts the microwave signal into a voltage value; the signal processing module 7 is respectively connected to the unloading device 5, the temperature sensor 6, and the display unit 10, and is used to control the unloading device 5 to unload after the measurement is completed, obtain the temperature data of the sample to be measured in real time measured by the temperature sensor 6, calculate the moisture content and bulk density of the sample to be measured, and output the calculation results to the display unit 10.

[0050] In this embodiment, the sample cavity 1 is a cylindrical structure made of polypropylene and is located in the central area of ​​the resonant cavity 2. The inner radius of the sample cavity 1 is 15 mm, the height is 18 cm, and the thickness is 3 mm.

[0051] In this embodiment, the resonant cavity 2 is a cylindrical structure with an inner radius of 8 cm, a cavity height of 15 cm, and is made of aluminum with a wall thickness of 4 mm.

[0052] In this embodiment, the transmitting probe 3 and the receiving probe 4 are both made of metal and have a length of 10 mm. They are installed at the center of the resonant cavity 2 and penetrate into the cavity wall of the resonant cavity 2. The length of the coupling into the cavity is 6 mm. The two probes are 180 degrees in the cavity. Figure 2 shown.

[0053] In this embodiment, the unloading device 5 includes a steering gear and a material partition, with a maximum torque of 15KG and a maximum current of 2A. The steering gear controls the extension of the plastic partition at the unloading port, and the extension angle is 90°.

[0054] like Figure 3 As shown, in this embodiment, the signal processing module 7 includes a voltage-controlled oscillator, a splitter, a reference detector, a signal detector, and a single-chip microcomputer operation and control unit. The voltage-controlled oscillator is a swept-frequency signal source with a swept-frequency output range of 2055MHz-2095MHz. The splitter evenly distributes the microwave signal generated by the voltage-controlled oscillator and adopts a balanced resistor structure with an effective operating frequency of 0.1MHz-6GHz. The reference detector and signal detector have an effective detection frequency of 1MHz-4GHz and a dynamic range of 80dB. The single-chip microcomputer operation and control unit uses a 32-bit ARM core STM32F103 series processor, and the A / D converter uses the STM32 internal integrated analog-to-digital converter with 12-bit conversion accuracy and a single conversion acquisition time of 1μs.

[0055] Example 2

[0056] This example uses corn as the measurement object to illustrate the specific detection method of the detection device. The initial moisture content of the naturally air-dried corn is 14.25%. By adding water to the sample and continuously stirring it evenly, five rice samples with different moisture contents are finally obtained. The moisture content varies from 14.25% to 25.4%.

[0057] This embodiment provides a detection method for a microwave resonance detection device for synchronously measuring the moisture content and bulk density of a material. The specific steps are as follows:

[0058] S1, no-load signal detection:

[0059] Keep the sample chamber 1 empty, the discharge port of the discharge device 5 is closed, the signal processing module 7 generates a microwave sweep signal, and the single chip operation control unit detects different frequencies. Internal reference detector voltage value Sum signal detector voltage value , calculate the attenuation value according to the following formula:

[0060]

[0061] The measurement results are as follows Figure 4 As shown in the no-load curve on the right side, record the maximum no-load attenuation value is -7.3dB, and the corresponding no-load microwave resonant frequency It is 2089.16MHz.

[0062] S2, full load signal detection:

[0063] The sample chamber 1 is filled with the corn sample to be tested, and the signal processing module 7 generates a microwave sweep signal, and the single chip computer operation control unit detects different frequencies. Internal reference detector voltage value Sum signal detector voltage value , calculate the attenuation value according to the following formula:

[0064]

[0065] The measurement results are as follows Figure 4 As shown in the full load curve on the left, the maximum attenuation value of different samples is recorded. , and its corresponding full-load microwave resonant frequency , read the measurement data of temperature sensor 6 , calculate the difference between the maximum attenuation values ​​under full load and no load according to the following formula The difference between the resonant frequency :

[0066]

[0067]

[0068] The measurement results are shown in Table 1.

[0069] S3. Calculation of sample moisture content:

[0070] The single chip microcomputer inside the signal processing module 7 calculates the moisture content according to the following formula: and bulk density Perform the operation:

[0071]

[0072]

[0073] Where: a, b, c, d, e, h, j, Km, Kρ are fitting coefficients. For a certain sample, the fitting coefficient is a constant. The moisture content in Table 1 is , bulk density , the difference between the maximum attenuation values , the difference in resonant frequency and temperature The test results were substituted into the formula and fitted using the origin data processing software. The fitting coefficients were a, b, 160.426, c, 94.659, d, -0.00264, e, -0.174, h, 0.00717, j, 4.451, Km, -6.471, and Kρ, -0.0486.

[0074] S4. Real-time output of grain moisture content and density:

[0075] After being processed by the signal processing module 7, the moisture content information and bulk density information of the tested sample are uploaded to the display unit 10 through the serial port for real-time display output, and at the same time, the discharge port of the discharge device 5 is controlled to open to complete the discharge.

[0076] Table 1: Corn sample measurement data

[0077]

[0078] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within 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 scope of protection of the present invention.

[0079] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0080] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A detection method for a microwave resonance detection device for synchronous measurement of moisture content and bulk density of a material, characterized in that: The specific steps are as follows: S1, no-load signal detection: The sample chamber (1) is kept empty, the discharge port of the discharge device (5) is closed, and the signal processing module (7) generates a microwave frequency sweep signal. The single-chip computer operation control unit detects the voltage value Vc of the internal reference detector and the voltage value Vs of the signal detector at different frequencies f, and calculates the attenuation value according to the following formula: A=20log(Vs / Vc) Record the maximum no-load attenuation value A0 and its corresponding microwave resonant frequency f0; S2, full load signal detection: The sample cavity (1) is filled with the sample to be tested, and the signal processing module (7) generates a microwave frequency sweep signal. The single-chip computer operation control unit detects the internal reference detector voltage value Vc and the signal detector voltage value Vs at different frequencies f, and calculates the attenuation value according to the following formula: A=20log(Vs / Vc) Record the maximum attenuation value A1 of the sample under full load and its corresponding full load microwave resonant frequency f1, and read the measurement data T of the temperature sensor (6); The difference in maximum attenuation ΔA and resonant frequency Δf between full load and no load are calculated using the following formula: ΔA=A0-A1 Δf=f0-f1; S3. Calculation of sample moisture content: The moisture content M and bulk density ρ are calculated according to the following formula: M=a(Δf / ΔA) 2 +b(Δf / ΔA)+KmT+c ρ=dΔf 2 +eΔf+hM+KρT+j Where: a, b, c, d, e, h, j, Km, Kρ are fitting coefficients. For a certain sample, the fitting coefficients are constants, and the parameters are fitted in advance by samples with known moisture content and bulk density; S4. Real-time output of grain moisture content and bulk density: The signal processing module (7) uploads the moisture content information and bulk density information of the tested sample to the display unit (10) through the serial port for real-time display output, and simultaneously controls the discharge port of the discharge device (5) to open to complete the discharge; The method is implemented by using a microwave resonance detection device for synchronously measuring the moisture content and bulk density of a material, wherein the detection device comprises a sample cavity (1), a resonance cavity (2), a transmitting probe (3), a receiving probe (4), a discharge device (5), a temperature sensor (6), a signal processing module (7), a transmitting isolator (8), a receiving isolator (9) and a display unit (10); wherein the sample cavity (1) is arranged inside the resonance cavity (2), the discharge device (5) is installed at the bottom of the sample cavity (1), the temperature sensor (6) is arranged below the sample cavity (1) and is used to measure the temperature of the sample in real time, and the signal processing module (7) is used to transmit the microwave signal generated by the internal voltage-controlled oscillator to the transmitting isolator (8); the microwave signal is subjected to gyromagnetic isolation processing by the ferrite inside the transmitting isolator (8). Afterwards, the microwave signal is coupled to the resonant cavity (2) through the sending probe (3), and a microwave resonant signal is generated after interacting with the sample to be measured in the sample cavity (1). The receiving probe (4) transmits the microwave resonant signal to the receiving isolator (9), and after the microwave signal is subjected to gyromagnetic isolation processing by the ferrite inside the receiving isolator (9), it is sent to the signal processing module (7), and the signal detector inside the signal processing module (7) converts the microwave resonant signal into a voltage value; the signal processing module (7) is respectively connected to the unloading device (5), the temperature sensor (6) and the display unit (10), and is used to control the unloading device (5) to unload after the measurement is completed, obtain the temperature data of the sample to be measured in real time by the temperature sensor (6), calculate the moisture content and bulk density of the sample to be measured, and output the calculation results to the display unit (10).

2. The detection method of a microwave resonance detection device for synchronously measuring moisture content and bulk density of a material according to claim 1, characterized in that: The sample cavity (1) is a cylindrical structure and is located in the central area inside the resonant cavity (2). The radius of the sample cavity (1) is in the range of 5-40 mm and the height is in the range of 5-30 cm.

3. The detection method of a microwave resonance detection device for synchronously measuring moisture content and bulk density of a material according to claim 1, characterized in that: The resonant cavity (2) is a cylindrical cavity made of metal, with a cavity radius ranging from 5 to 20 cm and a cavity height ranging from 5 to 30 cm.

4. The detection method of a microwave resonance detection device for synchronously measuring moisture content and bulk density of a material according to claim 1, characterized in that: The transmitting probe (3) and the receiving probe (4) are inserted into the resonant cavity (2) symmetrically at 180 degrees. The transmitting probe (3) is used to excite the resonant cavity to generate resonance, and the receiving probe (4) is used to receive the microwave signal after the interaction. The length range of the probe coupling inside the cavity of the resonant cavity (2) is 2-10 mm.

5. The detection method of a microwave resonance detection device for synchronously measuring moisture content and bulk density of a material according to claim 1, characterized in that: The unloading device (5) comprises a steering gear and a material partition plate, and the material partition plate can be rotated within a range of 0-180 degrees under the drive of the steering gear to achieve unloading control.

6. The detection method of a microwave resonance detection device for synchronously measuring moisture content and bulk density of a material according to claim 1, characterized in that: The signal processing module (7) includes a voltage-controlled oscillator, a splitter, a reference detector, a signal detector and a single-chip computer operation control unit. The voltage-controlled oscillator is used to generate a microwave signal and perform frequency sweeping. The frequency sweeping range is 0.5 GHz-6 GHz. The splitter evenly distributes the microwave signal generated by the voltage-controlled oscillator and transmits it to the reference detector and the transmitting isolator (8) respectively. The single-chip microcomputer operation control unit converts the voltage signals output by the reference detector and the signal detector into digital quantities for internal operation, thereby realizing digital signal acquisition, internal operation processing, and frequency sweep control functions.

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