Method for detecting aqueous solutions with different electrical conductivities based on terahertz wave band

Abstract

The invention relates to a method for detecting aqueous solutions with different electrical conductivities based on a terahertz wave band. The method comprises the following steps: S1, building a detection system; comprising a terahertz wave source, a collimation system, a focusing device, a cuvette, an off-axis parabolic mirror, a light beam guiding system and a detector which are sequentially arranged in a straight line, and further comprises a data acquisition and control system connected with the detector and an optical platform for supporting the components, s2, calibrating a detection system; s3, preparing a sample; s4, data acquisition; s5, data processing and analysis; and S6, result interpretation and report writing. According to the invention, relative technical means of terahertz wave band spectrum are combined to detect and diagnose aqueous solutions with different conductivities, nondestructive analysis is carried out, the problem of poor electrode contact or contact resistance caused by bubbles in traditional electrical measurement is effectively avoided, and the measurement accuracy is improved. And the interference of rapid flow of bubbles on the measurement accuracy is reduced on the aspect of ultrafast time response capability.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz spectrum detection and analysis, and in particular to a method for detecting aqueous solutions with different electrical conductivities based on the terahertz band. Background Art

[0002] Conductivity is a common and important parameter in water quality testing. It's a crucial indicator of water's salt content, ion composition, and impurities. Water purity is inversely proportional to its conductivity: the purer the water, the lower its conductivity and the higher its resistivity. Conversely, increased conductivity often indicates water contamination. Different uses of water have different conductivity standards: drinking water should have a conductivity below 50 μs / cm; domestic water is permitted to have a conductivity no greater than 1000 μs / cm; and urine conductivity is generally maintained at around 10,000 μs / cm.

[0003] Conductivity is usually measured using the electrode method, the basic principle of which is to insert two parallel electrodes into the solution and calculate the conductivity of the solution by measuring the resistance between the electrodes. The existing traditional electrode method for measuring conductivity has the following defects:

[0004] Two electrodes are immersed in the solution, and the conductivity is calculated by measuring the current and voltage. The direct contact between the electrodes and the solution may not only introduce contamination, but is also limited by the corrosiveness of the electrode material and the measurement environment. A large sample volume is required for measurement, and high cleanliness requirements are placed on the sample. Traditional methods usually take a long time to obtain stable measurement results, and the accuracy may be affected by electrode surface contamination and changes in electrolyte solution conditions. Bubbles exist in the aqueous solution, forming a complex gas-liquid mixture system. These bubbles may form a dense layer on the electrode surface during the conductivity measurement process, while forming a dispersed layer in areas far away from the electrode, significantly affecting the accuracy of the conductivity measurement.

[0005] Terahertz waves, an electromagnetic wave between microwaves and infrared, show great potential in the field of material detection due to their unique penetrating properties, fingerprint spectral characteristics, and sensitivity to the internal structure of materials. However, the application of terahertz technology to the direct measurement of the conductivity of aqueous solutions is still a new field. Therefore, it is necessary to develop a more accurate and less susceptible to external interference method for detecting aqueous solutions of different conductivities based on terahertz waves. Summary of the Invention

[0006] The present invention aims to address the deficiencies of the prior art and provides a method for detecting aqueous solutions with different conductivities based on the terahertz band.

[0007] To achieve the above-mentioned object, the present invention adopts the following technical solution: a method for detecting aqueous solutions with different conductivities based on the terahertz band, comprising the following steps:

[0008] S1. Build a detection system;

[0009] The system includes a terahertz wave source, a collimation system, a focusing device, a cuvette, an off-axis parabolic mirror, a beam guiding system, and a detector arranged in a straight line, as well as a data acquisition and control system connected to the detector, and an optical platform supporting the above components;

[0010] S2, calibration detection system;

[0011] S3, preparing samples;

[0012] S4, data acquisition, testing samples and collecting data through the detection system;

[0013] S5, data processing and analysis;

[0014] S51, raw data preprocessing, including noise filtering and error correction;

[0015] S52, data conversion, converting the time domain data into frequency domain data through Fourier transform, and then extracting key parameters from the frequency domain data;

[0016] S53, correlating conductivity, establishing a mathematical model between the terahertz signal change and the sample conductivity, and achieving quantitative measurement of the sample conductivity;

[0017] S6. Interpretation of results and report writing.

[0018] In particular, the terahertz wave source uses a femtosecond laser to emit light.

[0019] In particular, the collimation system is composed of one or more pairs of lenses, and the lenses are zinc selenide lenses.

[0020] In particular, the beam steering system uses several mirrors to change the optical path.

[0021] In particular, S2 includes the following steps:

[0022] S21, background measurement, recording background signal in the absence of sample;

[0023] S22. Calibrate the system using standard substances to ensure the accuracy of the measurement results.

[0024] Specifically, S3 includes the following steps:

[0025] S31. Prepare a series of aqueous solution samples with different conductivity according to experimental requirements;

[0026] S32, placing the sample in a pre-prepared cuvette, and placing the cuvette in a designed light path;

[0027] The aqueous solution samples include pure water samples, aqueous solution samples with a conductivity of 12.778 mS / cm, aqueous solution samples with a conductivity of 111.03 mS / cm, and aqueous solution samples with a conductivity of 1413 μS / cm.

[0028] In particular, S4 includes the following steps:

[0029] S41, starting the terahertz wave source to generate a stable terahertz beam, and after being collimated by the collimation system, focusing the terahertz beam onto the aqueous solution sample in the cuvette through the focusing device;

[0030] S42, the terahertz beam after transmitting through the aqueous solution sample is collected by an off-axis parabolic mirror, and the transmitted beam is focused to a point and then guided to a detector through a beam guiding system;

[0031] S43. The detector records the intensity or phase change of the terahertz wave after passing through the sample, and transmits the recorded data to the data acquisition and control system.

[0032] In particular, S53 includes the following steps:

[0033] S531. Assuming that the sample is homogeneous and its conductivity is constant, the propagation of terahertz waves is described by formula 1:

[0034] Formula 1, E(z,t)=E0 exp[-α1(z)·z]exp[i(kz-ωt)];

[0035] Where E(z,t) is the terahertz electric field intensity, E0 is the intensity of the incident electric field, α1(z) is the propagation loss coefficient; k is the wave number, ω is the angular frequency of the terahertz wave, t is time, and z is the spatial coordinate along the propagation direction;

[0036] S532. When the terahertz wave propagates in the sample, the relationship between the attenuation coefficient α2 and the conductivity σ is described by formula 2:

[0037] Formula 2,

[0038] Where α2 is the attenuation coefficient, σ is the conductivity, ε0 ​​is the electric constant in vacuum, and ω is the angular frequency of the terahertz wave;

[0039] S533. In addition to attenuation, the phase of the terahertz wave is affected by the conductivity of the sample. The relationship between the phase change and the conductivity is described by formula 3:

[0040] Formula 3,

[0041] Where ∆φ is the phase change, d is the thickness of the sample, and c is the speed of light;

[0042] S534. From Formula 1 and Formula 2, it can be seen that the attenuation coefficient is proportional to the conductivity. The conductivity of the sample can be inferred by measuring the attenuation coefficient. From Formula 3, it can be seen that the conductivity can be further derived by measuring the phase change of the terahertz wave after passing through the sample.

[0043] Specifically, S6 includes the following steps:

[0044] S61. Compare and verify: compare the results of the current sample with other standards to verify the accuracy and reliability of the measurement;

[0045] S62, Error analysis, considers factors that affect measurement accuracy and assesses the uncertainty of the final result;

[0046] S63. Organize information, summarize all measurement data, processing steps and conclusions, and form a detailed report;

[0047] S64. Visual display: Use chart tools to draw spectra and three-dimensional surface maps to intuitively display the terahertz characteristics of aqueous solutions with different conductivity, and derive the relevant conductivity and other parameters of the aqueous solution samples.

[0048] The beneficial effects of the present invention are:

[0049] 1. Contactless measurement: Combined with terahertz spectroscopy-related technical means, it can detect and diagnose aqueous solutions with different electrical conductivities and perform non-destructive analysis. This effectively avoids the problems of poor electrode contact or contact resistance caused by bubbles in traditional electrical measurements, as well as electrode contamination, solution electrolysis, or the influence of electrodes on the solution.

[0050] 2. Fast response: Terahertz waves can quickly penetrate the solution and interact with solute ions and water molecules, so measurement results can be obtained in a shorter time. At the same time, the ultra-fast time response capability reduces the interference of rapid bubble flow on measurement accuracy.

[0051] 3. High Precision: By analyzing the absorption, scattering, and phase changes of terahertz waves, the conductivity of the solution can be more accurately reflected. The sensitivity of terahertz waves to ions and molecules in the solution enables this method to provide accurate measurement results even with small changes.

[0052] 4. Smaller sample requirements: Compared with traditional methods that require larger sample volumes, the method in this application can effectively measure with smaller sample amounts and is suitable for the detection of small volumes or diluted solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a block diagram of the detection system of the present invention;

[0054] Figure 2 is a flow chart of the method of the present invention;

[0055] Figure 3 This is a terahertz time-domain spectrum analysis diagram of aqueous solution samples with different conductivities of the present invention;

[0056] The following is a detailed description of the embodiments of the present invention with reference to the accompanying drawings. DETAILED DESCRIPTION

[0057] The present invention will be further described below in conjunction with embodiment:

[0058] like Figure 1-Figure 3 As shown, a method for detecting aqueous solutions with different conductivities based on the terahertz band includes the following steps:

[0059] S1. Build a detection system;

[0060] It includes a terahertz wave source, a collimation system, a focusing device, a cuvette, an off-axis parabolic mirror, a beam guiding system, and a detector arranged in a straight line. It also includes a data acquisition and control system connected to the detector, and an optical platform supporting the above components.

[0061] The terahertz wave source uses a femtosecond laser to emit a light source, generating a stable terahertz beam as the measurement light source. The collimation system is composed of one or more pairs of lenses, each of which is a zinc selenide lens. A focusing device, such as a lens or parabolic mirror, is used to focus the terahertz beam on the aqueous solution sample to be measured. The cuvette is used to place aqueous solution samples of different concentrations. The cuvette must be made of a material that is transparent to terahertz waves and does not affect the properties of the sample, such as quartz or glass, to ensure the transmittance of the terahertz wave. The off-axis parabolic mirror collects the terahertz signal after it passes through the sample. The beam guidance system uses several reflectors to change the optical path and guide the terahertz signal to the detector, which detects the intensity or phase changes of the transmitted signal. These changes are directly related to the conductivity of the solution. When connecting, ensure that the connection is stable and the signal transmission is lossless. It is used to output the processed signal to subsequent equipment or systems.

[0062] S2. Calibrate the detection system; comprising the following steps:

[0063] S21, background measurement, recording background signal in the absence of sample;

[0064] S22. Calibrate the system using standard substances to ensure the accuracy of the measurement results.

[0065] S3, preparing samples; comprising the following steps;

[0066] S31. Prepare a series of aqueous solution samples with different conductivity according to experimental requirements;

[0067] S32, placing the sample in a pre-prepared cuvette, and placing the cuvette in a designed light path;

[0068] The aqueous solution samples include pure water samples, aqueous solution samples with a conductivity of 12.778 mS / cm, aqueous solution samples with a conductivity of 111.03 mS / cm, and aqueous solution samples with a conductivity of 1413 μS / cm.

[0069] S4, data acquisition, testing samples and collecting data through the detection system; including the following steps:

[0070] S41. Start the terahertz wave source to generate a stable terahertz beam. After collimation by the collimation system, it propagates in the form of a parallel beam, ensuring the flatness of the wavefront and reducing distortion during transmission. The terahertz beam is focused onto the aqueous solution sample in the cuvette through a focusing device to improve the focusing accuracy of the light and the intensity of the signal. The conductivity of the aqueous solution affects its absorption, scattering, and phase change of terahertz waves. The higher the conductivity, the more significant the absorption or phase change of terahertz waves. The conductivity and other physical and chemical properties of the sample will affect its absorption, scattering, and phase change of terahertz waves. When terahertz waves interact with molecules in the sample, the conductivity of the aqueous solution will affect the absorption, scattering, and phase change of the terahertz waves. Samples with high conductivity generally absorb more terahertz waves and cause more significant phase changes.

[0071] S42, after transmitting through the aqueous solution sample, the terahertz beam is collected by an off-axis parabolic mirror, and the transmitted beam is focused to a point, thereby improving the detection efficiency, and then guided to the detector through a beam guiding system;

[0072] S43. The detector records the intensity or phase change of the terahertz wave after passing through the sample, and transmits the recorded data to the data acquisition and control system.

[0073] S5. Data processing and analysis: The data acquisition and control system receives the data transmitted by the detector and processes and analyzes it;

[0074] S51, raw data preprocessing, including noise filtering and error correction;

[0075] S52, data conversion, converting the time domain data into frequency domain data through Fourier transform, and then extracting key parameters from the frequency domain data;

[0076] S53, correlating conductivity, establishing a mathematical model between the terahertz signal change and the sample conductivity, and achieving quantitative measurement of the sample conductivity; comprising the following steps:

[0077] S531. The propagation characteristics of terahertz waves in materials (such as speed and attenuation) are affected by the material's conductivity. Assuming the sample is homogeneous and its conductivity is constant, the propagation of terahertz waves is described by Equation 1:

[0078] Formula 1, E(z,t)=E0 exp[-α1(z)·z]exp[i(kz-ωt)];

[0079] Where E(z,t) is the terahertz electric field intensity, E0 is the intensity of the incident electric field, α1(z) is the propagation loss coefficient; k is the wave number, ω is the angular frequency of the terahertz wave, t is time, and z is the spatial coordinate along the propagation direction;

[0080] S532. When terahertz waves propagate in a sample, they will attenuate due to the presence of electrical conductivity. The relationship between the attenuation coefficient α2 and the electrical conductivity σ is described by formula 2:

[0081] Formula 2,

[0082] Where α2 is the attenuation coefficient, σ is the conductivity, ε0 ​​is the electric constant in vacuum, and ω is the angular frequency of the terahertz wave;

[0083] S533. In addition to attenuation, the phase of the terahertz wave is affected by the conductivity of the sample. The relationship between phase change and conductivity is described by formula 3:

[0084] Formula 3,

[0085] Where ∆φ is the phase change, d is the thickness of the sample, and c is the speed of light;

[0086] S534. Equations 1 and 2 show that the attenuation coefficient is proportional to conductivity. By measuring the attenuation coefficient (by observing the attenuation of the terahertz wave's intensity), the conductivity of the sample can be inferred. Equation 3 shows that by measuring the phase change of the terahertz wave after it passes through the sample, the conductivity can be further derived. This method offers the advantages of being contactless, fast, and requiring no conductive path for the sample. It is particularly suitable for high-impedance or liquid samples that are difficult to measure using traditional methods.

[0087] S6. Interpretation of results and report writing;

[0088] S61. Compare and verify: compare the results of the current sample with other standards to verify the accuracy and reliability of the measurement;

[0089] S62, Error analysis, considers factors that affect measurement accuracy and assesses the uncertainty of the final result;

[0090] S63. Organize information, summarize all measurement data, processing steps and conclusions, and form a detailed report;

[0091] S64. Visual display: Use chart tools to draw spectra and three-dimensional surface maps to intuitively display the terahertz characteristics of aqueous solutions with different conductivities, and derive the relevant conductivity and other parameters of the aqueous solution samples.

[0092] The present invention proposes a method for detecting aqueous solutions with different conductivity based on the terahertz band, which is a new non-destructive testing technology, in which the irradiation area of ​​the terahertz spot can be less than 1mm 2 This means that accurate measurements can be obtained as long as there are no bubbles in the irradiated area and the density of the aqueous solution is uniform. Secondly, the non-contact measurement method effectively avoids the problems of poor electrode contact and contact resistance caused by bubbles in traditional electrical measurements. Furthermore, the spectral differences of aqueous solutions in the terahertz band can be inferred, resulting in a new, stable and accurate detection method.

[0093] The detection system of the present invention collects signals from solutions with different conductivities (pure water, 12.778 mS / cm, 111.03 mS / cm, and 1413 μS / cm), processes them through a data acquisition and control system, and generates terahertz (THz) spectral data related to the THz band. It can be seen that different conductivity solutions produce different THz time-domain spectra in the THz band, and different aqueous solution samples can be identified based on these spectral differences.

[0094] The present invention combines terahertz band spectroscopy-related technical means to detect and diagnose aqueous solutions with different electrical conductivities and perform non-destructive analysis, effectively avoiding the problems of poor electrode contact or contact resistance caused by bubbles in traditional electrical measurements, and also avoiding electrode contamination, solution electrolysis or the influence of electrodes on the solution. Terahertz waves can quickly penetrate the solution and interact with solute ions and water molecules, so measurement results can be obtained in a relatively short time. At the same time, the interference of rapid bubble flow on measurement accuracy is reduced in terms of ultra-fast time response capability. By analyzing the absorption, scattering and phase changes of terahertz waves, the conductivity of the solution can be more accurately reflected. The sensitivity of terahertz waves to ions and molecules in the solution enables this method to provide accurate measurement results under slight changes. Compared with traditional methods that require larger volumes of samples, the method of the present application can perform effective measurements with smaller sample amounts and is suitable for the detection of small volumes or dilute solutions.

[0095] The above is an exemplary description of the present invention. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as various improvements are made using the method concept and technical solution of the present invention, or they are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A method for detecting aqueous solutions with different conductivity based on the terahertz band, characterized in that: The following steps are involved: S1. Build a detection system; The system includes a terahertz wave source, a collimation system, a focusing device, a cuvette, an off-axis parabolic mirror, a beam guiding system, and a detector arranged in a straight line, as well as a data acquisition and control system connected to the detector, and an optical platform supporting the above components; S2, calibration detection system; S3, preparing samples; S4, data acquisition, testing samples and collecting data through the detection system; S5, data processing and analysis; S51, raw data preprocessing, including noise filtering and error correction; S52, data conversion, converting the time domain data into frequency domain data through Fourier transform, and then extracting key parameters from the frequency domain data; S53, correlating conductivity, establishing a mathematical model between the terahertz signal change and the sample conductivity, and achieving quantitative measurement of the sample conductivity; S6. Interpretation of results and report writing.

2. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: The terahertz wave source uses a femtosecond laser to emit light.

3. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: The collimation system is composed of one or more pairs of lenses, and the lenses are zinc selenide lenses.

4. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: The beam steering system uses several mirrors to change the light path.

5. The method for detecting aqueous solutions with different conductivity based on the terahertz band according to claim 1, characterized in that: S2 includes the following steps: S21, background measurement, recording background signal in the absence of sample; S22. Calibrate the system using standard substances to ensure the accuracy of the measurement results.

6. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: In S3, the following steps are included: S31. Prepare a series of aqueous solution samples with different conductivity according to experimental requirements; S32, placing the sample in a pre-prepared cuvette, and placing the cuvette in a designed light path; The aqueous solution samples include pure water samples, aqueous solution samples with a conductivity of 12.778 mS / cm, aqueous solution samples with a conductivity of 111.03 mS / cm, and aqueous solution samples with a conductivity of 1413 μS / cm.

7. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: S4 includes the following steps: S41, starting the terahertz wave source to generate a stable terahertz beam, and after being collimated by the collimation system, focusing the terahertz beam onto the aqueous solution sample in the cuvette through the focusing device; S42, the terahertz beam after transmitting through the aqueous solution sample is collected by an off-axis parabolic mirror, and the transmitted beam is focused to a point and then guided to a detector through a beam guiding system; S43. The detector records the intensity or phase change of the terahertz wave after passing through the sample, and transmits the recorded data to the data acquisition and control system.

8. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: S53 includes the following steps: S531. Assuming that the sample is homogeneous and its conductivity is constant, the propagation of terahertz waves is described by formula 1: Formula 1, E(z,t)=E0 exp[-α1(z)·z]exp[i(kz-ωt)]; Where E(z,t) is the terahertz electric field intensity, E0 is the intensity of the incident electric field, α1(z) is the propagation loss coefficient; k is the wave number, ω is the angular frequency of the terahertz wave, t is time, and z is the spatial coordinate along the propagation direction; S532. When the terahertz wave propagates in the sample, the relationship between the attenuation coefficient α2 and the conductivity σ is described by formula 2: Formula 2, Where α2 is the attenuation coefficient, σ is the conductivity, ε0 ​​is the electric constant in vacuum, and ω is the angular frequency of the terahertz wave; S533. In addition to attenuation, the phase of the terahertz wave is affected by the conductivity of the sample. The relationship between phase change and conductivity is described by formula 3: Formula 3, Where ∆φ is the phase change, d is the thickness of the sample, and c is the speed of light; S534. From Formula 1 and Formula 2, it can be seen that the attenuation coefficient is proportional to the conductivity. The conductivity of the sample can be inferred by measuring the attenuation coefficient. From Formula 3, it can be seen that the conductivity can be further derived by measuring the phase change of the terahertz wave after passing through the sample.

9. The method for detecting aqueous solutions with different conductivities based on the terahertz band according to claim 1, characterized in that: S6 includes the following steps: S61. Compare and verify: compare the results of the current sample with other standards to verify the accuracy and reliability of the measurement; S62, Error analysis, considers factors that affect measurement accuracy and assesses the uncertainty of the final result; S63. Organize information, summarize all measurement data, processing steps and conclusions, and form a detailed report; S64. Visual display: Use chart tools to draw spectra and three-dimensional surface maps to intuitively display the terahertz characteristics of aqueous solutions with different conductivity, and derive the relevant conductivity and other parameters of the aqueous solution samples.

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