CN1255688C - High sensitivity liquid dielectric constant measuring probe - Google Patents

Abstract

The present invention relates to a high sensitivity probe for measuring the dielectric constant of liquid. The probe comprises a coaxial line type outer conductor (1), a coaxial line type inner conductor (2), and fillers (3) between the inner conductor and the outer conductor, wherein the coaxial line type outer conductor (1) is partially cut thin and connected with an outer tunable conductor (4); and the coaxial line type inner conductor (2) is partially hollowed. The hollowed part is scarfed or sheathed with an inner tunable conductor (5), both the lengths of the outer tunable conductor (4) and the inner tunable conductor (5) are adjustable, and a plurality of grooves are arranged in the outer tunable conductor(4).

Description

A liquid dielectric constant measuring probe

technical field

The invention relates to a liquid equivalent dielectric constant measurement probe, in particular to an on-line measurement probe for the equivalent dielectric constant of a dilute solution chemical reaction with water as a solvent.

Background technique

As early as 1967, N.H.Williams reported the experimental results of using microwaves to speed up chemical reactions. Since then, people have paid great attention to using microwaves to speed up and control chemical reactions. Now microwave has been widely used in petrochemical, food chemical, pharmaceutical chemical and other fields and has produced huge economic benefits. The study of the interaction between electromagnetic fields and chemical reaction systems has become a new interdisciplinary subject developed in recent years, and has been highly valued and extensively studied by many scientific and technological workers at home and abroad.

Since the chemical reaction system is a non-equilibrium system, under the action of electromagnetic waves, the system absorbs electromagnetic energy and converts it into a temperature rise. The temperature rise changes the reaction rate, and the change of the reaction rate accelerates the change of the material composition in the reaction system, resulting in the equivalent medium parameter Changes occur, which in turn affect the absorption and reflection of electromagnetic waves, which is an unbalanced and nonlinear process. In the process of studying the interaction between electromagnetic field and chemical reaction system, the macroscopic equivalent dielectric constant of the reaction system is a very key research content. It is very difficult to deduce the equivalent dielectric constant strictly from the non-equilibrium system; using the experimental method, the dielectric constant of the reaction system can be obtained by measuring the reflection coefficient of the reaction process online.

"Journal of Shandong University" 1997, 032 (001), P.54-61 discloses a terminal open-circuit coaxial probe for mixed liquid medium measurement, which can measure the medium characteristics of liquid substances and low-water substances by using the resonance method . Although the above-mentioned probe is a high-sensitivity probe, when it is used to measure the chemical reaction system of a dilute solution using water as a solvent, bubbles generated by electrochemical effects and the like will adhere to the measuring probe. Because the dielectric constant of water is much larger than the change of the macroscopic equivalent dielectric constant of the entire reaction system caused by the change of reactants, the existence of air bubbles will directly affect the accuracy of the measurement results. Therefore, the above-mentioned probes cannot rule out the influence of air bubbles on the measurement results. Secondly, the above-mentioned probes can only be used for dielectric constant measurement at fixed frequency points.

The invention designs a novel probe which can be used for on-line measurement of the equivalent dielectric constant of the liquid-phase chemical reaction, can eliminate air bubbles during the measurement process, and has the characteristics of multi-frequency point on-line measurement and high sensitivity.

Contents of the invention

The present invention is formed by transforming common coaxial lines. It includes the coaxial outer conductor 1, the coaxial inner conductor 2 and the filler 3 between the coaxial outer conductor 1 and the coaxial inner conductor 2, and also includes the tunable outer conductor 4, the tunable inner conductor 5 and the adjustable The slot 6 on the tuning outer conductor 4 forms a hollow slotted coaxial line part, and the hollow slotted coaxial line part forms a coaxial resonant cavity with an open terminal. The length of the resonant cavity can be adjusted by adjusting the tunable outer conductor 4 and the tunable inner The conductor 5 is tuned; the outer conductor 1 of the coaxial line is partially thinned, and the thinned part is connected with the tunable outer conductor 4, and the inner conductor 2 of the coaxial line is partially hollow, and the hollow part is embedded or sleeved with the tunable inner conductor 5 One or several slots 6 are opened on the tunable outer conductor 4 .

Description of drawings

Fig. 1: structural representation of the present invention;

Fig. 2: appearance drawing of the present invention;

Fig. 3: A-A sectional structure schematic diagram of the present invention;

Fig. 4: The present invention is used in the frequency sweep measurement graph of different moments of chemical reaction, wherein, the horizontal axis is the measurement frequency (6Hz), and the vertical axis is the modulus value (dB) of the reflection coefficient

Figure 5: Comparison of frequency sweep measurement curves of the probe in pure water with and without bubbles. In the figure, the solid line indicates the modulus value (dB) of the reflection coefficient when there are bubbles, and the dotted line indicates the modulus of the reflection coefficient after the bubbles are excluded. value (dB).

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and in conjunction with an embodiment.

As shown in Figures 1 and 2, the probe consists of two parts: a conventional coaxial cable and a hollow slotted coaxial cable. Among them, the traditional coaxial cable is composed of a coaxial outer conductor 1 and a coaxial inner conductor 2, and the filler 3 between the coaxial outer conductor 1 and the coaxial inner conductor 2 is polytetrafluoroethylene; the hollow opening Slotted coaxial line is composed of tunable outer conductor 4, tunable inner conductor 5, one or several slots 6 on tunable outer conductor 4, and the space between tunable inner conductor 4 and tunable outer conductor 5 is filled with the measured medium . The part of the hollow slotted coaxial line constitutes a coaxial resonant cavity with an open terminal, and its length ΔL is tuned by adjusting the tunable inner conductor 4 and the tunable outer conductor 5 . ΔL varies within the range of 2 to 30 mm. In this embodiment, the threaded connection between the tunable outer conductor 4 and the coaxial outer conductor 1 is realized through the thread 7 , and the threaded connection between the tunable inner conductor 5 and the coaxial inner conductor 2 is realized through the thread 8 .

During measurement, some air cannot be removed when the probe is inserted into the liquid, and due to electrochemical effects and other effects during the measurement process, air bubbles will be generated inside the open-circuit coaxial resonant cavity of the probe. Studies have shown that the presence of air bubbles can have a huge impact on the accuracy of the measurement, as shown in Figure 5. The present invention has several grooves on the outer conductor of the open-circuit coaxial resonant cavity at the terminal, which is beneficial to remove air bubbles in time when the probe is inserted into the liquid. During measurement, the probe must be shaken constantly to discharge air bubbles due to electrochemical effects in time. This embodiment shows that two grooves are symmetrically opened at the terminal position of the cavity, but this does not exclude asymmetrical grooves. The width of this groove should be appropriate, too narrow is not conducive to the elimination of air bubbles, and too wide will make the reflection coefficient resonance curve not obvious due to too much energy leakage. The groove width selected in this embodiment is 1 mm.

Because many liquids, especially chemical reaction solutions, are often corrosive. In order to prevent the probe from being corroded during measurement, the whole probe is plated with gold in this embodiment.

The present invention has the following prominent substantive features and remarkable progress:

1. Realization of high sensitivity

The probe is very sensitive near the resonant frequency. As shown in Figure 4, at five moments in the liquid phase chemical reaction process, due to the continuous changes of reactants and products, the small changes in the equivalent dielectric constant of the entire reaction system, and the small changes in the reflection coefficient caused by it, can be used The probe detects, which is not possible with traditional coaxial probes.

2. Used for the measurement of multiple frequency points

Figure 4 shows the frequency sweep measurement results of the probe when the cavity length ΔL is 8mm and 6mm respectively. It can also be seen from Figure 4 that the resonant frequency varies with the length of the cavity. Therefore, by adjusting the length of the cavity, the resonant frequency can be changed to track the dielectric constant of the liquid at a certain frequency point. The probe is composed of coaxial line and hollow slotted coaxial line. The hollow slotted coaxial line part can be adjusted, so that the length of the resonant cavity can be adjusted, and accurate measurement can be performed in the range of 900MHz to 3GHz.

3. High accuracy

Bubbles have a great influence on the accuracy of measurement results (as shown in Figure 5). Moreover, different positions of the bubbles have different effects on the measurement results. The existence of the bubbles has randomness in the error of the measurement results, and the influence cannot be eliminated by calibration. Traditional probes cannot rule out the influence of air bubbles. However, the terminal of the resonant cavity of the probe of the present invention has a groove, and the air bubbles can be discharged by shaking the probe, thus avoiding the bad influence of the air bubbles on the measurement results.

4. Anti-corrosion

The outer surface of the probe of the invention is gold-plated, which prevents it from being corroded by chemical solutions.

Claims (7)

1. A liquid dielectric constant measuring probe, comprising a coaxial outer conductor (1), a coaxial inner conductor (2) and between the coaxial outer conductor (1) and the coaxial inner conductor (2) The filler (3) is also characterized in that it includes a hollow slotted coaxial line composed of an adjustable outer conductor (4), an adjustable inner conductor (5) and a slot (6) on the adjustable outer conductor (4) part, the hollow slotted coaxial line part constitutes a coaxial resonant cavity with an open terminal, and the length of the resonant cavity is tuned by adjusting the tunable outer conductor (4) and the tunable inner conductor (5); the coaxial outer conductor ( 1) Partially thinned, the thinned part is connected to the tunable outer conductor (4), the inner conductor (2) of the coaxial line is partially hollow, and the hollow part is embedded or socketed with the tunable inner conductor (5). 2. The liquid dielectric constant measuring probe according to claim 1, characterized in that one or several grooves (6) are opened on the tunable outer conductor (4). 3. The liquid dielectric constant measuring probe according to claim 1 or claim 2, characterized in that it is threadedly connected between the tunable outer conductor (4) and the coaxial line outer conductor (1), tunable The inner conductor (5) is threaded or socketed with the hollow part of the coaxial inner conductor (2). 4. The liquid dielectric constant measuring probe according to claim 1 or claim 2, characterized in that the slot (6) on the tunable outer conductor (4) is symmetrical at the end of the open-circuit coaxial resonant cavity distribution or asymmetric distribution. 5. The liquid dielectric constant measuring probe according to claim 1 or claim 2, characterized in that the width of the slot (6) on the tunable outer conductor (4) is 1 mm. 6. The liquid dielectric constant measuring probe as claimed in claim 1, characterized in that by tuning the tunable outer conductor (4) and the tunable inner conductor (5), the length ΔL of the open-circuit coaxial resonant cavity of the described terminal is The adjustable change range is within 2 ~ 30mm. 7. The liquid dielectric constant measuring probe as claimed in claim 1, characterized in that the entire probe is a gold-plated probe.

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