CN116626072A - Material moisture content detection device and method based on microwave cavity resonance - Google Patents
Material moisture content detection device and method based on microwave cavity resonance Download PDFInfo
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- 239000000523 sample Substances 0.000 claims abstract description 98
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 70
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- 238000004458 analytical method Methods 0.000 description 1
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N22/00—Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more
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Abstract
The invention discloses a device and a method for detecting the moisture content of a material based on microwave cavity resonance, which belong to the technical field of microwave application and comprise a detected sample, a microwave generating device, a weighing unit, a sample tank, a temperature sensor, a microwave resonant cavity, an excitation probe, a detection probe, a detector, a control unit and a display output unit; the invention controls the excitation voltage of the microwave generating device and generates a microwave signal, the microwave signal enters the microwave resonant cavity through the excitation probe and is received by the detection probe, the detection of the resonance frequency change is realized through the detection probe positioned in the microwave resonant cavity, the temperature of the detected sample is measured through the temperature sensor positioned below the sample groove, a functional relation is established, and the water content of the detected material is inverted; the invention improves the universality and the detection precision of the microwave water content detection device, and the result is not influenced by the material temperature and the accumulation condition, thereby realizing the rapid nondestructive high-precision detection of the water content of the particle, powder or liquid material.
Description
Technical Field
The invention belongs to the technical field of microwave application, and particularly relates to a device and a method for detecting the water content of a material based on microwave cavity resonance.
Background
In the processing and manufacturing industries of grains, soil, chemical fertilizers, petroleum and the like, the water content of raw materials is an important index of product quality and is closely related to the price of the product. The accurate, effective and convenient detection of the water content of materials has become a hot spot problem in the research of the detection technical field. The measurement of the water content comprises two modes of direct measurement and indirect measurement, wherein the direct measurement method mainly adopts a wet-based method, and the water content is calculated by measuring the specific gravity of the weight difference of the sample before and after drying, but the method has low measurement speed, and meanwhile, the material needs to be destroyed, so that the method is generally used for water calibration in a laboratory. The indirect measurement method of the water content mainly comprises a resistance method, a capacitance method, a neutron method, an infrared method, a microwave method and the like, and has the characteristics, application range and measurement accuracy different from each other. The microwave method utilizes the light speed propagation characteristic of high-frequency electromagnetic waves in space, and the measuring process does not damage the structure of a sample, so that the rapid nondestructive detection requirement of the water content of the material can be met, and the method has wide application scenes.
The complex dielectric constant of water is far higher than that of other dry matters under the microwave frequency, so that the water content of the material can be indirectly measured by measuring physical quantities related to dielectric constants such as power attenuation, phase change and the like after the interaction of microwaves and the material. The microwaves have penetrability, and the measurement result reflects the overall water content of the sample, so that the method is more representative.
The detection of the water content of the material based on the microwave technology is mainly divided into a space wave method, a transmission line method and a resonant cavity method, wherein the space wave method is generally suitable for continuous on-line detection of a large number of samples, after the interaction of microwaves and the detected samples, the space microwaves can generate reflection, transmission and scattering phenomena, and the multiple reflection of electromagnetic waves can reduce the measurement accuracy of the water content. The transmission line method sensor needs to be in direct contact with the measured material, and the uniformity of sampling the material in the measuring process is high. In the current measuring process of the water content of the material based on the resonant cavity method, samples need to be uniformly filled in the cavity and directly contacted with the microwave probe, and different samples cannot be rapidly and accurately detected in a short time. Based on the current situation, the research and development of the method and the device for detecting the microwave water content have important significance, and are economical and practical, high in universality and high in precision.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a device and a method for detecting the water content of a material based on the resonance of a microwave cavity, when the microwave frequency is matched with the natural frequency of the cavity, resonance is generated, the size of the resonance frequency is related to the water content of a measured sample in the cavity, and a functional relation is established by detecting the change of the resonance frequency to invert the water content of the measured material; the detection device can realize rapid nondestructive detection of the moisture content of particles, powder or liquid materials, and has the advantages of simple structure and high measurement accuracy.
The invention is realized by the following technical scheme:
the device for detecting the water content of the material based on the resonance of the microwave cavity comprises a detected sample 1, a microwave generating device 2, a weighing unit 3, a sample tank 4, a temperature sensor 5, a microwave resonant cavity 6, an excitation probe 7, a detection probe 8, a detector 9, a control unit 10 and a display output unit 11; the microwave generating device 2 is used for generating sweep frequency microwave signals, is connected with the excitation probe 7 through a coaxial line, transmits the microwave excitation signals into the microwave resonant cavity 6, receives the microwave signals transmitted in the cavity through the detection probe 8, and transmits the microwave signals to the detector 9 outside the microwave resonant cavity 6 through the coaxial line for power detection; the weighing unit 3 is positioned at the bottom of the microwave resonant cavity 6 and is used for recording the weight of the empty load and the weight of the full load; the sample tank 4 is positioned at the top of the microwave resonant cavity 6, and a temperature sensor 5 is arranged below the sample tank 4 and is used for measuring the temperature of the measured sample 1 in real time; the control unit 10 is respectively connected with the detector 9, the temperature sensor 5 and the weighing unit 3 through signal wires, and controls the excitation voltage of the microwave generating device 2, the control unit 10 calculates the water content information of the measured sample 1 through an internal function according to the read detection voltage, temperature and weight information, and the measurement result is output through the display output unit 11.
Further, the tested sample 1 is a nonmetallic water-containing material with uniform density distribution, such as grains, soil, fertilizer and the like.
Further, the microwave generating device 2 is a voltage-controlled sweep frequency signal source, the voltage control range is 0-5V, and the frequency output is in the range of 3GHz-12 GHz.
Further, the sample tank 4 is of a cylindrical structure with a cover, is made of metal, has a height range of 30-70mm, is positioned at the top of the resonant cavity, is provided with a non-metal partition plate at the bottom, can be made of low attenuation materials for microwaves such as ceramics, plastics or glass, and is connected with the resonant cavity 6 to form a part of the resonant cavity.
Further, the effective temperature measuring range of the temperature sensor 5 is not lower than 0-100 ℃ and the accuracy is not lower than +/-0.5 ℃.
Further, the microwave resonant cavity 6 is of a cylindrical structure and made of metal, the radius range of the inner part of the cavity is 10-40mm, and the length range of the cavity is 20-80mm.
Further, the excitation probe 7 and the detection probe 8 are both made of metal materials and are vertically inserted into the cavity wall of the microwave resonant cavity 6, the two probes form 90 degrees in the cavity of the microwave resonant cavity 6, and the length range of vertical cavity coupling is 5-20mm.
Further, the control unit 10 includes a power supply, an a/D converter, a D/a converter, and a single-chip microcomputer operation control unit, where the a/D converter is configured to convert a detection voltage signal output by the detector 9 into a digital value for internal operation of the single-chip microcomputer, and the effective bit number of the a/D converter is not less than 12 bits; the D/A converter is used for converting the control signal of the singlechip into a voltage value and controlling the microwave generating device 2 to generate a sweep frequency microwave signal, and the effective bit number of the D/A converter is not lower than 12 bits.
The measurement principle of the material moisture content detection device based on microwave cavity resonance is described as follows:
for the resonant cavity, resonance is generated when the microwave frequency is matched with the natural frequency of the cavity, and if the sample to be detected contains moisture, water molecules can absorb a part of microwave energy, so that the energy loss of an electromagnetic field is caused; these losses ultimately manifest themselves as a decrease in the Q-value of the quality factor of the microwave cavity, a broader peak of the cavity natural frequency, and a shift toward lower frequencies.
For a cylindrical cavity, the resonant frequency satisfies the following calculation relation:
wherein c is the speed of light, ε m And the dielectric constant is l, the length of the resonant cavity is l, and R is the radius.
For a resonant cavity of fixed size, the radius R and length l are fixed, and the above equation is transformed into:
wherein,,is constant.
The above equation illustrates that the resonant frequency is directly related to the dielectric constant. Under the microwave frequency, the water molecules have strong dipole moment, so that the dielectric constant of the water is far higher than that of other dry matters, and after different samples are placed in the cavity, the change of the resonance frequency can directly reflect the change of the water of the samples.
In addition, the dielectric properties of the material are affected by both temperature and sample stacking conditions, the temperature affects the energy state of water molecules in the material, and the stacking density affects the spatial distribution of water molecules in the material. For a fixed volume sample cell, the change in sample mass within it directly reflects the change in bulk density of the sample. The device of the invention simultaneously measures the resonance frequency, temperature and mass of the measured sample, and establishes a functional relation inversion sample water content with temperature and bulk density compensation.
On the other hand, the invention also provides a detection method of the device for detecting the water content of the material based on the resonance of the microwave cavity, which comprises the following steps:
s1, no-load signal detection;
holding a sampleThe tank 4 is empty, the control unit 10 controls the sweep voltage variation of the microwave generating device 2, synchronously detects and records the value of the detection voltage of the detector 9, records the value of the sweep voltage corresponding to the extreme point of the detection voltage, and correspondingly converts the value into the resonant frequency f 0 The method comprises the steps of carrying out a first treatment on the surface of the Synchronous measurement of the output weight m of the weighing cell 3 during idling 0 ；
S2, detecting a full-load signal;
the sample fills the sample tank 4, the control unit 10 controls the sweep frequency voltage change of the microwave generating device 2, synchronously detects and records the value of the detection voltage of the detector 9, records the value of the sweep frequency voltage corresponding to the extreme point of the detection voltage, and correspondingly converts the value into the resonance frequency f 1 The method comprises the steps of carrying out a first treatment on the surface of the Synchronously measuring the output weight m of the weighing unit 3 during full load 1 The temperature sensor 5 outputs a sample temperature value T;
s3, calculating the water content of the material;
the singlechip inside the control unit 10 adopts the following formula to calculate the water content:
W＝a(f1-f0)/(m1-m0)+bT+c
wherein W represents the water content of the measured material, f0 and f1 are respectively the resonance frequencies measured during no-load and full-load, and m0 and m1 are respectively the weights measured during no-load and full-load; a. b and c are coefficients obtained by measuring and fitting known water content data, and T is a temperature value of a measured sample;
s4, displaying and outputting the water content in real time;
after the single chip microcomputer in the control unit 10 completes the water content operation, the display output unit 11 outputs and displays the water content information of the tested sample 1.
Compared with the prior art, the invention has the following advantages:
(1) The invention designs a cylindrical resonant cavity structure based on the working principle of a microwave resonant cavity; the cavity integrity is realized, and meanwhile, the sealing performance is good, the electromagnetic interference resistance is realized, the structure is light, and the device is economical and practical;
(2) The detection device has simple circuit, easy parameter acquisition, analysis and processing, high water content detection precision and high speed, can compensate the temperature and the quality of a sample, and is suitable for detecting various materials in the processing and manufacturing industry.
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. Like elements or portions are generally identified by like reference numerals throughout the several figures. In the drawings, elements or portions thereof are not necessarily drawn to scale.
FIG. 1 is a schematic structural diagram of a device for detecting the moisture content of a material based on resonance of a microwave cavity;
FIG. 2 is a top view of a microwave cavity of the present invention;
FIG. 3 is a schematic diagram of a sample cell according to the present invention;
FIG. 4 is a flow chart of control of the measurement signal of the detection device of the present invention;
FIG. 5 is a diagram showing the change of the resonant frequency of the detection device before and after the sample is added;
in the figure: the device comprises a measured sample 1, a microwave generating device 2, a weighing unit 3, a sample tank 4, a temperature sensor 5 positioned below the sample tank 4, a microwave resonant cavity 6, an excitation probe 7, a detection probe 8, a detector 9, a control unit 10 and a display output unit 11.
Detailed Description
For a clear and complete description of the technical scheme and the specific working process thereof, the following specific embodiments of the invention are provided with reference to the accompanying drawings in the specification:
example 1
Referring to fig. 1, a schematic structural diagram of a device for detecting moisture content of a material based on resonance of a microwave cavity according to this embodiment is shown, where the device includes a sample 1 to be detected, a microwave generating device 2, a weighing unit 3, a sample tank 4, a temperature sensor 5, a microwave resonant cavity 6, an excitation probe 7, a detection probe 8, a detector 9, a control unit 10, and a display output unit 11; the microwave generating device 2 generates sweep frequency microwave signals, is connected with the excitation probe 7 through a coaxial line, transmits the microwave excitation signals into the microwave resonant cavity 6, and receives the microwave signals after propagation in the cavity through the detection probe 8; the weighing unit 3 is positioned at the bottom of the microwave resonant cavity 6; the sample tank 4 is positioned at the top of the microwave resonant cavity 6, and a temperature sensor 5 is arranged below the sample tank 4; the microwave generating device 2 and the detector 9 are connected with the microwave resonant cavity 6 through coaxial lines; the detector 9 is connected with the detection probe 8 through a coaxial line; the control unit 10 is respectively connected with the detector 9, the temperature sensor 5 and the weighing unit 3 through signal wires; the output display unit 11 is connected with the control unit 10;
in this embodiment, the microwave generating device 2 is a voltage-controlled frequency sweep signal source, the voltage control range is 0-4.5V, and the frequency sweep output range is 8-10GHz.
In this embodiment, the weighing sensor of the weighing unit 3 is in a bridge structure, and the maximum measuring range is 3KG, and the accuracy is 0.1g.
In this embodiment, the microwave resonant cavity 6 is of a cylindrical structure, made of stainless steel material, and has a radius of 11mm and a cavity length of 40mm.
In this embodiment, the temperature sensor 5 is a DS18B20 temperature sensor, and the measured temperature range is-55 to +125 ℃, with accuracy of ±0.5 ℃.
In this embodiment, the control unit 10 includes a power supply, an a/D converter, a D/a converter, and a single-chip microcomputer operation control unit, where the single-chip microcomputer operation control unit uses a 32-bit ARM core STM32F103 series processor, uses 3.3 v power supply, the chip operating frequency is set to 72mhz, the a/D converter uses an STM32 processor internal integrated analog-to-digital converter, and sets 12-bit conversion accuracy and 1 μs single conversion acquisition time.
In this embodiment, as shown in fig. 2, the excitation probe 7 and the detection probe 8 are both made of metal materials, have a length of 8mm, are installed in the middle position of the resonant cavity 6, are vertically inserted into the cavity wall of the microwave resonant cavity 6, have a coupling length into the cavity of 5mm, and have an angle of 90 ° in the cavity.
In this embodiment, as shown in fig. 3, the sample tank 4 is of a cylindrical structure with a cover, is made of metal, has a height of 10mm, is positioned at the top of the resonant cavity, has a ceramic partition plate at the bottom, has a thickness of 2mm, and has an inner radius of 11mm.
As shown in fig. 4, the signal control process of the material water content detection device of this embodiment is as follows:
the control unit 10 controls the excitation voltage of the microwave generating device 2 to gradually change from small to large through D/A digital-to-analog conversion in the interior, the generated sweep frequency microwave signal enters the interior of the microwave resonant cavity 6 through the excitation probe 7, and the microwave signal transmitted through the sample tank 4 is received through the detection probe 8; the detector 9 detects the power of the microwave signal voltage in the cavity through the detection probe 8; the weighing unit 3 collects the empty and full weight information; the temperature sensor 5 collects temperature information of the measured sample 1; the control unit 10 calculates the water content information of the measured sample 1 by an internal function based on the read detection voltage, temperature and weight information, and outputs the measurement result by the display output unit 11.
Example 2
In the embodiment, the specific measurement method of the detection device is described by taking corn as a measurement object, the initial water content of the naturally aired corn is 9.8%, 6 corn samples with different water contents are finally obtained by adding water into the samples and continuously and uniformly stirring, the water content change range is 9.8% -24.2%, and in order to ensure the uniformity of sample accumulation, the samples are ground into powder by a grinder and then measured.
The embodiment provides a detection method of a material moisture content detection device based on microwave cavity resonance, which comprises the following specific steps:
s1, no-load signal detection;
the sample tank 4 is kept empty, the control unit 10 controls the sweep frequency voltage change of the microwave generating device 2, synchronously detects and records the value of the detection voltage of the detector 9, records the value of the sweep frequency voltage corresponding to the extreme point of the detection voltage, and correspondingly converts the value into the resonance frequency f 0 . Synchronous measurement of the weight m output by the weighing unit 3 during no-load 0 。
S2, detecting a full-load signal;
the sample fills the sample tank 4, the control unit 10 controls the sweep frequency voltage change of the microwave generating device 2, synchronously detects and records the value of the detection voltage of the detector 9, and records the detectionThe value of sweep frequency voltage corresponding to the wave voltage extreme point is correspondingly converted into the resonant frequency f 1 . Synchronously measuring the output weight m of the weighing unit 3 during full load 1 The temperature sensor 5 outputs a sample temperature value T.
Fig. 5 shows the comparison of the change in resonance frequency between the empty load and the corn measurement of 9.8% moisture content, with 9.425GHz empty load resonance frequency and 9.270GHz resonance frequency after sample addition.
Table 1 shows the moisture content W, the empty resonance frequency f of 6 corn samples of different moisture contents in the test 0 Full load resonant frequency f 1 Weight of no load m 0 Full load weight m 1 And a measurement of the sample temperature T.
S3, calculating the water content of the material
The singlechip inside the control unit 10 performs the water content calculation using the following formula:
W＝a(f1-f0)/(m1-m0)+bT+c
wherein W represents the water content of the measured material, f0 and f1 are respectively the resonance frequencies measured in the no-load and full-load conditions, and m0 and m1 are respectively the weights measured in the no-load and full-load conditions. a. b and c are coefficients obtained by fitting the measurement of the known water content data, and T is the temperature value of the measured sample. For the determined measurement samples, the fitting coefficient is constant, and the water content W and the empty resonance frequency f in the table 1 are different 0 Full load resonant frequency f 1 Weight of no load m 0 Full load weight m 1 And taking the sample temperature T into the formula, and performing linear fitting by using origin data processing software to obtain fitting coefficients a of 632.52, b of 1.43 and c of 5.47.
Table 1: corn sample sensor measurement data
S4, displaying and outputting the water content in real time
After the single chip microcomputer in the control unit 10 completes the water content operation, the display output unit 11 outputs and displays the water content information of the tested sample 1.
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.
In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.
Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.
Claims (9)
1. The device for detecting the water content of the material based on the resonance of the microwave cavity is characterized by comprising a detected sample (1), a microwave generating device (2), a weighing unit (3), a sample tank (4), a temperature sensor (5), a microwave resonant cavity (6), an excitation probe (7), a detection probe (8), a detector (9), a control unit (10) and a display output unit (11); the microwave generating device (2) is used for generating sweep frequency microwave signals, is connected with the excitation probe (7) through a coaxial line, transmits the microwave excitation signals into the microwave resonant cavity (6), receives the microwave signals transmitted in the cavity through the detection probe (8), and transmits the microwave signals to the detector (9) outside the microwave resonant cavity (6) through the coaxial line for power detection; the weighing unit (3) is positioned at the bottom of the microwave resonant cavity (6) and is used for recording the weight of the empty load and the weight of the full load; the sample tank (4) is positioned at the top of the microwave resonant cavity (6), and a temperature sensor (5) is arranged below the sample tank (4) and is used for measuring the temperature of the measured sample (1) in real time; the control unit (10) is respectively connected with the detector (9), the temperature sensor (5) and the weighing unit (3) through signal wires, and controls the excitation voltage of the microwave generating device (2), and the control unit (10) calculates the water content information of the tested sample (1) through an internal function according to the read detection voltage, temperature and weight information and outputs the measurement result through the display output unit (11).
2. The device for detecting the water content of the material based on the resonance of the microwave cavity according to claim 1, wherein the detected sample (1) is a nonmetallic water-containing material with uniform density distribution such as grains, soil and fertilizer.
3. The device for detecting the water content of the material based on the resonance of the microwave cavity according to claim 1, wherein the microwave generating device (2) is a voltage-controlled sweep signal source, the voltage control range is 0-5V, and the frequency output is in the range of 3GHz-12 GHz.
4. The device for detecting the water content of the material based on the resonance of the microwave cavity as claimed in claim 1, wherein the sample tank (4) is of a cylindrical structure with a cover, is made of metal, has the height range of 30-70mm, is positioned at the top of the resonant cavity, is provided with a nonmetal baffle at the bottom, is made of ceramic, plastic or glass material with low attenuation to microwaves, is connected with the resonant cavity (6), and forms a part of the resonant cavity.
5. The device for detecting the water content of the material based on the resonance of the microwave cavity according to claim 1, wherein the effective temperature measurement range of the temperature sensor (5) is not lower than 0-100 ℃ and the accuracy is not lower than +/-0.5 ℃.
6. The device for detecting the water content of the material based on the resonance of the microwave cavity according to claim 1, wherein the microwave cavity (6) is of a cylindrical structure and is made of a metal material, the radius range of the cavity is 10-40mm, and the length range of the cavity is 20-80mm.
7. The device for detecting the water content of the material based on the resonance of the microwave cavity as claimed in claim 1, wherein the excitation probe (7) and the detection probe (8) are made of metal materials, are vertically inserted into the cavity wall of the microwave cavity (6), form 90 degrees in the cavity of the microwave cavity (6), and have the coupling length of 5-20mm.
8. The device for detecting the moisture content of the material based on the resonance of the microwave cavity according to claim 1, wherein the control unit (10) comprises a power supply, an A/D converter, a D/A converter and a single chip microcomputer operation control unit, wherein the A/D converter is used for converting a detection voltage signal output by the detector (9) into a digital quantity for the internal operation of the single chip microcomputer, and the effective bit number of the A/D converter is not lower than 12 bits; the D/A converter is used for converting the control signal of the singlechip into a voltage value and controlling the microwave generating device (2) to generate a sweep frequency microwave signal, and the effective bit number of the D/A converter is not lower than 12 bits.
9. The detection method of the material moisture content detection device based on microwave cavity resonance as claimed in claim 1, which is characterized by comprising the following steps:
s1, no-load signal detection;
the sample tank (4) is kept empty, the control unit (10) controls the sweep frequency voltage change of the microwave generating device (2), synchronously detects and records the value of the detection voltage of the detector (9), records the value of the sweep frequency voltage corresponding to the extreme point of the detection voltage, and correspondingly converts the value into the resonance frequency f 0 The method comprises the steps of carrying out a first treatment on the surface of the Synchronous measurement of the output weight m of the weighing cell (3) during no-load 0 ；
S2, detecting a full-load signal;
the sample is filled in the sample tank (4), the control unit (10) controls the sweep frequency voltage change of the microwave generating device (2), synchronously detects and records the value of the detection voltage of the detector (9), records the value of the sweep frequency voltage corresponding to the extreme point of the detection voltage, and correspondingly converts the value into the resonance frequency f 1 The method comprises the steps of carrying out a first treatment on the surface of the Synchronously measuring the output weight m of the weighing unit (3) during full load 1 The temperature sensor (5) outputs a sample temperature value T;
s3, calculating the water content of the material;
the singlechip inside the control unit (10) adopts the following formula to calculate the water content:
W＝a(f1-f0)/(m1-m0)+bT+c
wherein W represents the water content of the measured material, f0 and f1 are respectively the resonance frequencies measured during no-load and full-load, and m0 and m1 are respectively the weights measured during no-load and full-load; a. b and c are coefficients obtained by measuring and fitting known water content data, and T is a temperature value of a measured sample;
s4, displaying and outputting the water content in real time;
after the water content calculation is finished by the singlechip in the control unit (10), the display output unit (11) outputs and displays the water content information of the tested sample (1).
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| CN (1) | CN116626072A (en) |
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2023
- 2023-06-06 CN CN202310657606.1A patent/CN116626072A/en active Pending
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