Method and system for measuring liquid dielectric parameters based on coplanar waveguide

Abstract

The invention discloses a coplanar waveguide-based liquid dielectric parameter measurement method and system, and the method comprises the steps: transmitting an initial high-frequency electromagnetic signal generated by an electromagnetic field excitation source to a to-be-measured liquid medium through a coplanar waveguide; acquiring a reflected electromagnetic signal after the initial high-frequency electromagnetic signal penetrates through the to-be-detected liquid medium and is reflected, and reversely transmitting the reflected electromagnetic signal to the electromagnetic field excitation source; according to the reflected electromagnetic signal, determining a target dielectric parameter of the liquid medium to be measured through an inversion algorithm and an iterative algorithm; and recording a measurement result of the target dielectric parameter for a user to check and record measurement data. The electromagnetic field distribution can be effectively controlled, the external interference is reduced, the stability of the measurement result is ensured, and the method has the advantages of high stability, wide applicability, simplicity and convenience in operation, low cost and the like.

Description

Technical Field

[0001] The present invention relates to the field of microwave technology, and particularly to a method and system for measuring liquid dielectric parameters based on coplanar waveguide. Background Art

[0002] The dielectric parameters (dielectric constant and dielectric loss) of liquid materials are important parameters characterizing their electromagnetic properties and have important application values in fields such as biomedicine, food safety, and agriculture. At present, conventional measurement methods mainly include the parallel plate capacitor method, the resonant cavity method, and the coaxial probe method. However, these methods have many deficiencies when used to measure or invert the dielectric parameters of liquid materials:

[0003] Although the parallel plate capacitor method has simple equipment, due to factors such as the edge effect and parasitic inductance of the capacitor, it has obvious limitations in high-frequency measurement, high-precision requirements, and complex sample conditions, and cannot meet the demand for high-precision measurement of liquid dielectric parameters.

[0004] Although the resonant cavity method has high precision, it usually works in a single or narrow frequency band, and it is difficult to comprehensively reflect the dielectric properties of liquid substances at different frequencies, which limits its applicability in wide-frequency applications. The resonant cavity method has high requirements for the preparation of test materials. It is necessary to know the electromagnetic field distribution inside the cavity in advance, and the added material cannot significantly affect the field distribution inside the cavity, otherwise it will cause measurement errors. At the same time, the measurement equipment and operation of the resonant cavity method are complex, requiring professional personnel to operate and maintain, with high costs. In addition, the electrical measurement parameters of liquids are sensitive to temperature, and precise temperature control is also required, increasing the difficulty and cost of practical applications.

[0005] Although the coaxial probe method is simple to operate, non-destructive, and has a wide applicable frequency range, it has large errors when measuring materials with high dielectric constants because high-dielectric-constant materials have a large disturbance to the electromagnetic field. In addition, the coaxial probe method may also not be able to obtain accurate results when measuring some liquid materials with special properties.

[0006] Therefore, the current measurement methods cannot meet the requirements for high precision, wide frequency range, fast, non-destructive, portable, and real-time online monitoring in the measurement of liquid dielectric parameters; it is particularly urgent and important to develop a new liquid dielectric parameter measurement method that can overcome these limitations and has higher measurement accuracy and a wider applicable range. Summary of the Invention

[0007] Embodiments of the present invention provide a method and system for measuring liquid dielectric parameters based on coplanar waveguide to solve the technical problem in the prior art of how to provide a high-precision, high-efficiency, and low-cost measurement method applicable to the dielectric parameter measurement of various liquid materials to meet the measurement requirements of liquid dielectric parameters in multiple fields.

[0008] In view of the above technical problems, an embodiment of the present invention provides a method for measuring the liquid dielectric parameters based on a coplanar waveguide, including:

[0009] Conduct the initial high-frequency electromagnetic signal generated by the electromagnetic field excitation source to the liquid medium to be measured through the coplanar waveguide;

[0010] Obtain the reflected electromagnetic signal after the initial high-frequency electromagnetic signal penetrates and is reflected by the liquid medium to be measured, and transmit the reflected electromagnetic signal in the reverse direction to the electromagnetic field excitation source;

[0011] Determine the target dielectric parameters of the liquid medium to be measured through an inversion algorithm and an iterative algorithm according to the reflected electromagnetic signal;

[0012] Record the measurement result of the target dielectric parameters for the user to view and record the measurement data.

[0013] The present invention also provides a measurement system for liquid dielectric parameters based on a coplanar waveguide, including:

[0014] A signal generation and transmission module for conducting the initial high-frequency electromagnetic signal generated by the electromagnetic field excitation source to the liquid medium to be measured through the coplanar waveguide;

[0015] An acquisition module for obtaining the reflected electromagnetic signal after the initial high-frequency electromagnetic signal penetrates and is reflected by the liquid medium to be measured, and transmitting the reflected electromagnetic signal in the reverse direction to the electromagnetic field excitation source;

[0016] A calculation module for determining the target dielectric parameters of the liquid medium to be measured through an inversion algorithm and an iterative algorithm according to the reflected electromagnetic signal;

[0017] A display and query module for recording the measurement result of the target dielectric parameters for the user to view and record the measurement data.

[0018] In the present invention, the method for measuring the liquid dielectric parameters based on coplanar waveguide mainly aims at measuring the dielectric parameters of liquid materials and is widely applicable to fields such as biomedicine, food safety, and agriculture. The present invention fully considers the fluidity of the liquid and the contact stability with the waveguide, and uses the reflection characteristics of electromagnetic signals to invert the dielectric parameters of liquid materials. It performs excellently especially in the measurement of high-frequency bands and low-loss materials, and can quickly and non-destructively detect and evaluate the electromagnetic characteristics of liquid substances. Through the coplanar waveguide structure, the present invention can better control the electromagnetic field distribution, reduce external interference, and improve the measurement stability. In addition, this method realizes high-precision and wide-band measurement, covers the dielectric relaxation frequency band of liquid materials, and ensures the accuracy of the measurement results. The sample preparation process is simple, the operation is easy to master, and no complex professional training is required, which greatly reduces the operation difficulty and cost. The simplicity and high integration of the coplanar waveguide structure effectively control the overall equipment cost, and at the same time have high stability and anti-interference ability, further improving the reliability of the measurement results.

[0019] By adopting advanced inversion algorithms and data processing technologies, the present invention can generate intuitive data visualization results and support the export and sharing of data, further enhancing its application value. In summary, the method and system for measuring liquid dielectric parameters based on coplanar waveguide provide an efficient and reliable solution for measuring the electromagnetic characteristics of liquid materials with multiple advantages such as high precision, wide bandwidth, simple operation, low cost, high stability, and wide applicability, and have significant practicality and promotion value. Brief Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings without creative efforts based on these drawings.

[0021] Figure 1 is a flowchart of the method for measuring liquid dielectric parameters based on coplanar waveguide in an embodiment of the present invention;

[0022] Figure 2 is a structural diagram of the system for measuring liquid dielectric parameters based on coplanar waveguide in an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of the system for measuring liquid dielectric parameters based on coplanar waveguide in an embodiment of the present invention. Detailed Embodiments

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] The measurement method of liquid dielectric parameters based on coplanar waveguide provided by the embodiment of the present invention can be applied to the application environment as Figure 1 shown. Specifically, the measurement method of liquid dielectric parameters based on coplanar waveguide is applied in a measurement system of liquid dielectric parameters based on coplanar waveguide. The measurement system of liquid dielectric parameters based on coplanar waveguide includes a client and a server as Figure 2 shown. The client communicates with the server through a network. Among them, the client, also known as the user side, refers to a program that provides local services for the client corresponding to the server. The client can be installed on, but not limited to, various personal computers, laptop computers, smart phones, tablet computers, and portable wearable devices. The server can be implemented by an independent server or a server cluster composed of multiple servers.

[0026] As Figure 1 shown, an embodiment of the present invention provides a measurement of liquid dielectric parameters based on coplanar waveguide, including:

[0027] S10. Conduct the initial high-frequency electromagnetic signal generated by the electromagnetic field excitation source to the liquid medium to be measured through the coplanar waveguide; specifically, the step S10 further includes the following sub-steps:

[0028] S101. Determine the vector network analyzer as the electromagnetic field excitation source, connect the vector network analyzer to the coplanar waveguide, and extend the coplanar waveguide into the sample cell containing the liquid medium to be measured to a preset depth;

[0029] S102. Start the vector network analyzer, set the measurement frequency range, and the vector network analyzer emits an initial high-frequency electromagnetic signal to the coplanar waveguide;

[0030] S103. The coplanar waveguide conducts the initial high-frequency electromagnetic signal to the liquid medium to be measured in the sample cell.

[0031] It can be understood that the vector network analyzer, as the electromagnetic field excitation source, is used to generate the initial high-frequency electromagnetic signal and excite the electromagnetic field in the waveguide transmission line. The vector network analyzer is connected to the coplanar waveguide through a transmission cable. The coplanar waveguide includes a dielectric substrate and a center conductor strip. The dielectric parameter ε of the substrate ris 4.3, the substrate thickness is 3 mm, the thickness of the central conductive strip is 0.0035 mm, the width of the central conductive strip is 5.05 mm, and the length of the central conductive strip is 60 mm. During specific operations, the coplanar waveguide is installed on the fixing device, and the sample cell is installed on the lifting platform. The lifting platform can adjust the distance between the sample cell and the coplanar waveguide, ensuring that the contact depth between the end of the coplanar waveguide and the liquid surface reaches the preset depth l during measurement, and ensuring uniform contact between the liquid and the surface of the coplanar waveguide.

[0032] S20. Obtain the reflected electromagnetic signal after the initial high-frequency electromagnetic signal penetrates the liquid medium to be measured, and reversely transmit the reflected electromagnetic signal to the electromagnetic field excitation source. Specifically, the step S20 further includes the following sub-steps:

[0033] S201. The initial high-frequency electromagnetic signal is transmitted through the coplanar waveguide and penetrates the liquid medium to be measured;

[0034] S202. The coplanar waveguide receives the reflected electromagnetic signal after penetrating the medium;

[0035] S203. The reflected signal is reversely transmitted back to the vector network analyzer through the cable, and the data of the reflected electromagnetic signal is recorded.

[0036] Understandably, the vector network analyzer can also be used to detect the change of the initial high-frequency electromagnetic signal after passing through the liquid material, and the changed signal is the reflected electromagnetic signal.

[0037] S30. Determine the target dielectric parameters of the liquid medium to be measured according to the reflected electromagnetic signal through the inversion algorithm and the iterative algorithm; specifically, the step S30 further includes the following sub-steps:

[0038] S301. Receive the reflected electromagnetic signal, perform digital filtering processing on the reflected electromagnetic signal to eliminate noise and interference signals; normalize the amplitude of the reflected signal to a preset reference range to eliminate the influence of amplitude fluctuations; calibrate using the reflected signal of the known standard medium to correct the system error;

[0039] S302. Construct an inversion model, and inversely calculate the intermediate dielectric parameters according to the processed reflected electromagnetic signal. The mathematical calculation expression of the inversion model is:

[0040]

[0041] where S 11 represents the known reflected electromagnetic signal, γ0 represents the propagation constant of the electromagnetic wave in air, γ represents the propagation constant of the electromagnetic wave in the liquid medium, l represents the preset depth, δ represents the phase related to the preset depth, 1 / β represents the effective impedance, β represents the effective admittance, ω represents the angular frequency, c represents the speed of light, λ c represents the cut-off wavelength, μ rrepresents the relative magnetic permeability of the liquid medium, ε r represents the relative permittivity of the liquid medium; μ r and ε r are intermediate dielectric parameters;

[0042] S303. Based on the intermediate dielectric parameters, construct an iterative model to calculate the target dielectric parameter; the mathematical calculation expression of the iterative model is:

[0043] f(x) = S 11 *(-2β + [(δ + 1) - (δ - 1)β 2 tanhγ] + 2βδ - [(δ + 1) - (δ - 1)β 2 tanhγl]) (6)

[0044]

[0045] J = f'(x) (8)

[0046] wherein, x0 represents the given initial value, and x represents the target dielectric parameter.

[0047] Understandably, the present invention adopts the short - circuit line method to invert the electromagnetic parameters (complex permittivity and complex magnetic permeability) of materials. By measuring the reflection coefficient S of the short - circuit transmission line with a vector network analyzer 11 , and importing the reflection coefficient S 11 into the data processing center to invert the dielectric parameter, and then deduce the electromagnetic characteristics of the material through the inversion algorithm and the iterative algorithm; the dielectric parameter includes the permittivity and the dielectric loss. Since the conductivity of the liquid material is 1, at this time, only the permittivity needs to be obtained. The data processing center can be the software of a computer.

[0048] S40. Record the measurement results of the target dielectric parameter for the user to view and record the measurement data. Specifically, the step S40 further includes the following sub - steps:

[0049] S401. Identify and separate the noise components in the measurement result data, and suppress or separate the noise; Understandably, determine the first - type noise in the measurement result data: including high - frequency noise, DC noise, electrical noise, optical noise, temperature noise, vibration noise, mode noise, and electrophoresis noise; determine the second - type noise in the measurement result data: including spike noise (generated by echo resonance); adopt a filtering algorithm (such as wavelet transform, Kalman filter) to suppress or separate the noise.

[0050] S402. Combine the target dielectric parameter data at different frequencies, and use the weighted average or fitting algorithm to calculate the target dielectric parameter to ensure the consistency and complementarity of the data in different frequency bands, and verify the reliability of the target dielectric parameter.

[0051] S403. Convert the measurement results into a specified format, store the measurement data according to the timestamp and sample number; associate the original measurement waveform and the intermediate data during the processing.

[0052] S404. Generate a curve graph of the target dielectric parameter varying with frequency based on the intermediate data, mark the key feature points to form a report of the measurement results, transmit the report to the user device through the USB / network interface, and generate a shared link.

[0053] In the present invention, the measurement method of the liquid dielectric parameter based on the coplanar waveguide is mainly for measuring the dielectric parameter of liquid materials, and is widely applicable to fields such as biomedicine, food safety, and agriculture. The present invention fully considers the fluidity of the liquid and the contact stability with the waveguide, and uses the reflection characteristics of electromagnetic signals to invert the dielectric parameter of the liquid material, especially showing excellent performance in the measurement of high-frequency bands and low-loss materials, and can perform rapid and non-destructive detection and evaluation of the electromagnetic characteristics of liquid substances. The present invention can better control the electromagnetic field distribution through the coplanar waveguide structure, reduce external interference, and improve the measurement stability. In addition, this method realizes high-precision and wide-band measurement, covers the dielectric relaxation frequency band of liquid materials, and ensures the accuracy of the measurement results. The sample preparation process is simple, the operation is easy to master, and no complex professional training is required, which greatly reduces the operation difficulty and cost. The simplicity and high integration of the coplanar waveguide structure effectively control the overall equipment cost, and at the same time have high stability and anti-interference ability, further improving the reliability of the measurement results.

[0054] By adopting advanced inversion algorithms and data processing technologies, the present invention can generate intuitive data visualization results and support the export and sharing of data, further enhancing its application value. In summary, the measurement method and system of the liquid dielectric parameter based on the coplanar waveguide provide an efficient and reliable solution for measuring the electromagnetic characteristics of liquid materials with multiple advantages such as high precision, wide band, simple operation, low cost, high stability, and wide applicability, and have significant practicality and promotion value.

[0055] In an embodiment, as Figures 2 to 3 shown, the present invention also provides a measurement system for the liquid dielectric parameter based on the coplanar waveguide, and the measurement system for the liquid dielectric parameter based on the coplanar waveguide corresponds one-to-one to the measurement of the liquid dielectric parameter based on the coplanar waveguide in the above embodiment. As Figure 2 shown, the measurement system for the liquid dielectric parameter based on the coplanar waveguide includes:

[0056] A signal generation and transmission module, configured to conduct the initial high-frequency electromagnetic signal generated by the electromagnetic field excitation source to the liquid medium to be measured through the coplanar waveguide;

[0057] An acquisition module, configured to acquire the reflected electromagnetic signal after an initial high-frequency electromagnetic signal penetrates a liquid medium to be measured and is reflected, and reversely transmit the reflected electromagnetic signal to an electromagnetic field excitation source;

[0058] A calculation module, configured to determine the target dielectric parameter of the liquid medium to be measured according to the reflected electromagnetic signal through an inversion algorithm and an iterative algorithm;

[0059] A display and query module, configured to record the measurement result of the target dielectric parameter for a user to view and record measurement data.

[0060] In a specific embodiment of the system of the present invention, the working process of the measurement system for the liquid dielectric parameter based on a coplanar waveguide may be as follows:

[0061] Equipment and material preparation: Select glycerol with a purity ≥ 99.5% as the liquid medium to be measured. Preheat the vector network analyzer for 30 minutes. Adopt a single-port calibration method (open-circuit - short-circuit - load calibration kit), and extend the calibration reference plane to the coplanar waveguide feed point. The substrate of the coplanar waveguide uses a substrate with ε r = 4.3 and a thickness of 3 mm. The width of the center conductor strip is 5.05 mm, the length of the center conductor strip is 60 mm, and the surface gold plating thickness is 0.0035 mm, which can withstand glycerol corrosion.

[0062] Sample cell and coplanar waveguide installation: Inject glycerol into a cylindrical liquid sample cell with an inner diameter of 20 mm and a height of 30 mm. Place the liquid sample cell on a lifting table. Fix the coplanar waveguide through a clamp, and adjust the height of the lifting table so that its end is parallelly immersed in the liquid surface to a preset depth, and the preset depth is 2.5 ± 0.05 mm.

[0063] Network analyzer parameter setting and data acquisition: Set the scanning frequency of the vector network analyzer to 0.5 GHz - 5 GHz to cover the glycerol dielectric relaxation frequency band; the output power is -15 dBm to avoid nonlinear effects; enable the time-domain gating technology (gate width 1.5 ns, center position delay matching the waveguide length) to eliminate the residual reflection of the clamp and the cable. Adopt a frequency-domain weighted average algorithm, such as the window function Blackman–Harris, to perform 3 repeated scans on the S 11 data and take the weighted mean to reduce random noise.

[0064] Data processing and solution of the target dielectric parameter: In the data processing center, preset the initial parameters of glycerol based on the Debye model: ε' r = 10.5, ε” r = 2.1, μ r = 1.0; Design the maximum number of iterations to be 100, and the tolerance error to be 10 -10, based on the propagation constant γ0 of electromagnetic waves in air, the target dielectric constant is solved by an inversion algorithm and an iterative algorithm.

[0065] Verification of measurement results: Measured at 5 GHz: ε' = 9.85, ε'' = 2.05, the measurement error is within the predicted range, and the deviation compared with the international standard (IEC 61189-3) of the SCL method is <1.8%.

[0066] The above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for measuring liquid dielectric parameters based on a coplanar waveguide, characterized in that, Including: S10. Conduct the initial high-frequency electromagnetic signal generated by the electromagnetic field excitation source to the liquid medium to be measured through a coplanar waveguide; S20. Obtain the reflected electromagnetic signal after the initial high-frequency electromagnetic signal penetrates and reflects from the liquid medium to be measured, and transmit the reflected electromagnetic signal in the reverse direction to the electromagnetic field excitation source; S30. Determine the target dielectric parameter of the liquid medium to be measured according to the reflected electromagnetic signal through an inversion algorithm and an iterative algorithm; S40. Record the measurement result of the target dielectric parameter for the user to view and record the measurement data.

2. The measurement method of liquid dielectric parameters based on coplanar waveguide according to claim 1, characterized in that The step S10 includes: S101. Determine the vector network analyzer as the electromagnetic field excitation source, connect the vector network analyzer to the coplanar waveguide, and extend the coplanar waveguide into the sample cell containing the liquid medium to be measured to a preset depth; S102. Start the vector network analyzer, set the measurement frequency range, and the vector network analyzer emits an initial high-frequency electromagnetic signal to the coplanar waveguide; S103. The coplanar waveguide conducts the initial high-frequency electromagnetic signal to the liquid medium to be measured in the sample cell.

3. The measurement method of liquid dielectric parameters based on coplanar waveguide according to claim 2, characterized in that The step S20 includes: S201. The initial high-frequency electromagnetic signal is transmitted through the coplanar waveguide and penetrates the liquid medium to be measured; S202. The coplanar waveguide receives the reflected electromagnetic signal after penetrating the medium; S203. The reflected signal is transmitted back to the vector network analyzer through the cable in the reverse direction, and the data of the reflected electromagnetic signal is recorded.

4. The method for measuring liquid dielectric parameters based on a coplanar waveguide according to claim 1, characterized in that The step S30 includes: S301. Receive the reflected electromagnetic signal, perform digital filtering processing on the reflected electromagnetic signal to eliminate noise and interference signals; normalize the amplitude of the reflected signal to a preset reference range to eliminate the influence of amplitude fluctuations; use the reflected signal of the known standard medium for calibration to correct the system error; S302. Construct an inversion model, and invert the intermediate dielectric parameter according to the processed reflected electromagnetic signal. The mathematical calculation expression of the inversion model is: Among them, S 11 represents the known reflected electromagnetic signal, γ0 represents the propagation constant of electromagnetic waves in air, γ represents the propagation constant of electromagnetic waves in the liquid medium, l represents the preset depth, δ represents the phase related to the preset depth, 1 / β represents the effective impedance, β represents the effective admittance, ω represents the angular frequency, c represents the speed of light, λ c represents the cut-off wavelength, μ r represents the relative magnetic permeability of the liquid medium, ε r represents the relative dielectric constant of the liquid medium; μ r and ε r are intermediate dielectric parameters; S303. According to the intermediate dielectric parameter, construct an iterative model to calculate the target dielectric parameter; the mathematical calculation expression of the iterative model is: f(x) = S 11 *(-2β + [(δ + 1) - (δ - 1)β 2 tanhγ] + 2βδ - [(δ + 1) - (δ - 1)β 2 tanhγl]) (6) J=f'(x) (8) where x0 represents the given initial value, and x represents the target dielectric parameter.

5. The measurement method of liquid dielectric parameters based on coplanar waveguide according to claim 3, characterized in that, The step S40 includes: S401. Identify and separate the noise components in the measurement result data, and suppress or separate the noise; S402. Combine the target dielectric parameter data at different frequencies, and use a weighted average or fitting algorithm to calculate the target dielectric parameter to ensure the consistency and complementarity of the data in different frequency bands, and verify the reliability of the target dielectric parameter; S403. Convert the measurement result into a specified format, store the measurement data according to the time stamp and sample number; associate the original measurement waveform and the intermediate data in the processing process; S404. Generate a curve graph of the target dielectric parameter changing with frequency according to the intermediate data, mark the key feature points to form a report of the measurement result, and transmit the report to the user device through the USB / network interface to generate a shared link.

6. A measurement system for liquid dielectric parameters based on a coplanar waveguide, characterized in that, Including: A signal generation and transmission module for conducting the initial high-frequency electromagnetic signal generated by the electromagnetic field excitation source to the liquid medium to be measured through a coplanar waveguide; An acquisition module, configured to acquire a reflected electromagnetic signal after an initial high-frequency electromagnetic signal penetrates a liquid medium to be measured and is reflected, and reversely transmit the reflected electromagnetic signal to an electromagnetic field excitation source; A calculation module, configured to determine a target dielectric parameter of the liquid medium to be measured according to the reflected electromagnetic signal through an inversion algorithm and an iterative algorithm; A display and query module, configured to record the measurement result of the target dielectric parameter for the user to view and record measurement data.

Images